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Tailoring Hydrocarbon Polymers and All-Hydrocarbon Composites for Circular Economy
Abstract
The world population will rapidly grow from 7 to 9 billion by 2050 and this will parallel a surging annual plastics consumption from today’s 350 million tons to well beyond 1 billion tons. The switch from a linear economy with its throwaway culture to a circular economy with efficient reuse of waste plastics is therefore mandatory. Hydrocarbon polymers, accounting for more than half the world’s plastics production, enable closed‐loop recycling and effective product‐stewardship systems. High‐molar‐mass hydrocarbons serve as highly versatile, cost‐, resource‐, eco‐ and energy‐efficient, durable lightweight materials produced by solvent‐free, environmentally benign catalytic olefin polymerization. Nanophase separation and alignment of unentangled hydrocarbon polymers afford 100% recyclable self‐reinforcing all‐hydrocarbon composites without requiring the addition of either alien fibers or hazardous nanoparticles. Recycling of durable hydrocarbons is far superior to biodegradation. The facile thermal degradation enables liquefaction and quantitative recovery of low molar mass hydrocarbon oil and gas. Teamed up with biomass‐to‐liquid and carbon dioxide‐to‐fuel conversions, powered by renewable energy, waste hydrocarbons serve as renewable hydrocarbon feedstocks for the synthesis of high molar mass hydrocarbon materials. Herein, an overview is given on how innovations in catalyst and process technology enable tailoring of advanced recyclable hydrocarbon materials meeting the needs of sustainable development and a circular economy.
... Polyolefins, such as PE and PP, account for more than half of all worldwide plastics production and more than 90% of all packaging materials (Hees et al., 2019). Because of their superior chemical stability and tailorable mechanical qualities, they are widely used. ...
... Because of their superior chemical stability and tailorable mechanical qualities, they are widely used. Chemically, biobased PE is similar to PE, thereby making it useable and recoverable on the current technologies as well as future recycling methods like thermolysis (Hees et al., 2019). Ethylene can be produced by number of methods such as conversion of methanol to olefins, ethanol dehydration from sugarcane and biomass steam cracking (Harmsen et al., 2014;Wang et al., 2020). ...
... Thermolysis is the process of pyrolyzing polyolefins that do not have hydrolysable functional groups at temperatures ranging from 200°C to 800°C (based on the catalyst utilised and also, polymer used) in lack of oxygen. In these circumstances, the C-C linkages disintegrate, converting the polymer either back into hydrocarbon oil or gas as feedstock or straight into olefin monomers.Conventional refineries and polymerisation companies can then use this feedstock (Anuar Sharuddin et al., 2016;Hees et al., 2019;Zhao et al., 2020). ...
... T (2022), with increasing tendency [4]. While plastic products form the basis for a high living standard, primarily through their use in medicine, food and water supply, transportation, ITor other technology fields, their end-of-life management needs to be improved [5,6]. Worldwide, millions of tonnes of waste products are mainly disposed of in landfills and only 9 % are estimated to be recycled [7]. ...
... However, the majority of post-consumer plastic waste consists of polyolefins, namely high-density polyethylene (HPDE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and polypropylene (PP), which are primarily used as packaging material due to their outstanding property profiles [15,18]. In addition to their high demand, and their correspondingly high turn-over rates, polyolefins are highly versatile and find application in numerous different fields from light-weight construction to automotive applications, to food-packaging, to earthquake-proof pipes [5,[21][22][23]. Mechanical recycling is a suitable recovery method for polyolefins due to their simple sorting and convenient processing properties [13,15]. ...
... Circular economy comprises several strategies to increase the circularity of a product, namely: designing all stages of materials, products and services from the beginning of their life cycle in order to maximize their useful life as much as possible, and ensuring that no material is wasted [37]. To this end, a product should be reused, repaired, reconditioned, remanufactured or ultimately recycled [38][39][40], if possible, always benefiting society [41] and adding value [42,43]. ...
... However, this wide range of indicators was developed ad hoc [38], presenting different purposes, methodologies and metrics [39,40] and as the Circular Economy is a multifaceted concept, the results of these indicators generate different interpretations [27]. That said, the great diversity of indicators and the ambiguity of their objectives make it difficult to choose which are most appropriate in a specific context or product [43], especially in the packaging sector. ...
Plastic packaging, in the form of films, brought several advantages to the commercialization of products given its lightness and durability. It provided better ergonomics, ease of transport, increased shelf life, and easy handling and use. Despite that, plastic packaging is facing enormous sustainability concerns associated with the traditional practice of linear economy, combined with commonplace irresponsible handling by citizens since it is almost exclusively designed for single-use and its end-of-life (EOL) management is not planned for. To mitigate that, the circularity of plastic packaging must be more clearly studied and evaluated through approaches such as micro-level circular economy (CE) indicators. This paper focuses on the selection of relevant CE micro-indicators specifically for the plastic packaging sector among the plethora of indicators available. Relations are also established between CE micro-indicators and CE guiding principles, as well as the most prevalent Design for X (DfX) approaches, providing new insights into how these different aspects of sustainability can be linked together. Results show three micro-level indicators as the most relevant for circularity calculation in packaging, namely those termed ‘MCI’, ‘VRE’, and ‘CEIP’, because their methodology and approach address most of the CE guiding principles and DfX approaches relevant for the packaging sector. Finally, guidelines and good practices to promote circularity adoption in the plastic packaging sector are highlighted. This work can guide companies aiming to adopt CE micro-indicators in their practical implementation, overcoming the significant knowledge barrier that currently exists.
... Each year, at a rate of about 1 garbage truck per minute dumps at least 8 million tonnes of plastic debris into the ocean. Rapid plastic manufacturing contributes to several environmental issues such as air pollution, land pollution and water pollution which releases a huge amount of carbon dioxide (CO 2 ) into the atmosphere [3,4]. The severe situation challenges mankind, indicating the importance of biodegradable plastics made from biobased polymers to replace petroleum-based plastics. ...
... The second approach is the microbial production of polyhydroxyalkanoates (PHA) [13], polyhydroxybutyrate (PHB) [7] and poly (3-hydroxybutyrate-co-3-hydroxy valerate) (PHBV) [7]. Third by the fermentation process, biobased monomer lactic acid (LA) is produced and is polymerized to produce a biobased polymer PLA [4]. In the fourth method the synthetic monomers are used to produce polymers from petrochemical byproducts, such as polycaprolactone (PCL) [6,7]. ...
Due to its low carbon footprint and environmental friendliness, polylactic acid (PLA) is one of the most widely produced bioplastics in the world. Manufacturing attempts to partially replace petrochemical plastics with PLA are growing year over year. Although this polymer is typically used in high-end applications, its use will increase only if it can be produced at the lowest cost. As a result, food wastes rich in carbohydrates can be used as the primary raw material for the production of PLA. Lactic acid (LA) is typically produced through biological fermentation, but a suitable downstream separation process with low production costs and high product purity is also essential. The global PLA market has been steadily expanding with the increased demand, and PLA has now become the most widely used biopolymer across a range of industries, including packaging, agriculture, and transportation. Therefore, the necessity for an efficient manufacturing method with reduced production costs and a vital separation method is paramount. The primary goal of this study is to examine the various methods of lactic acid synthesis, together with their characteristics and the metabolic processes involved in producing lactic acid from food waste. In addition, the synthesis of PLA, possible difficulties in its biodegradation, and its application in diverse industries have also been discussed.
... By the year 2050, the global production of plastic waste is projected to reach 850 million metric tons, while the surface of the ocean is estimated to harbor more than 150 million metric tons of floating plastic waste [3,4]. The rapid production of plastic exacerbates environmental concerns such as air, land, and water pollution, resulting in the emission of substantial quantities of carbon dioxide [5,6]. Scholars are currently exploring the potential application of biobased polymers in the production of biodegradable plastics, aiming to establish a feasible and ecologically sustainable substitute for conventional petroleum-derived plastics [7]. ...
... With a market share of more than 60% and having the lowest lifecycle environmental impact of all polymers, polyolefins play a crucial role in our daily life (1)(2)(3)(4)(5). Polyolefins are lightweight, cheap, and food contact-approved, which makes them materials of choice for, often single-use, packaging applications and other fast-moving consumer goods. ...
Polyolefins are the most widely used plastics accounting for a large fraction of the polymer waste stream. Although reusing polyolefins seems to be a logical choice, their recycling level remains disappointingly low. This is mainly due to the lack of large-scale availability of efficient and inexpensive compatibilizers for mixed polyolefin waste, typically consisting of high-density polyethylene (HDPE) and isotactic polypropylene ( i PP) that, despite their similar chemical hydrocarbon structure, are immiscible. Here, we describe an unconventional approach of using polypentadecalactone, a straightforward and simple-to-produce aliphatic polyester, as a compatibilizer for i PP/HDPE blends, especially the brittle i PP-rich ones. The unexpectedly effective compatibilizer transforms brittle i PP/HDPE blends into unexpectedly tough materials that even outperform the reference HDPE and i PP materials. This simple approach creates opportunities for upcycling polymer waste into valuable products.
... In particular, to the best of the authors' knowledge, only few studies involving the effect of the operative conditions of the melt-compounding process (such as the temperature profile or screw rotation speed) on the final morphology of PE blends can be found [8,[16][17][18][19][20][21]. Especially, few studies dealing with HDPE/HDPE binary blends exist [8,16,20,21], although these systems are of particular interest when approaching the self-reinforcing composite field, given the possibility of obtaining peculiar shish-kebab crystalline structures, formed via structuring processing [22][23][24][25][26]. In fact, an increasing interest in the effect of unimodal, bimodal or trimodal molecular weight distributions on the final microstructure can be observed [25][26][27][28]. ...
In this work, a multivariate approach was utilized for gaining some insights into the processing–structure–properties relationships in polyethylene-based blends. In particular, two high-density polyethylenes (HDPEs) with different molecular weights were melt-compounded using a twin-screw extruder, and the effects of the screw speed, processing temperature and composition on the microstructure of the blends were evaluated based on a Design of Experiment–multilinear regression (DoE-MLR) approach. The results of the thermal characterization, interpreted trough the MLR (multilinear regression) response surfaces, demonstrated that the composition of the blends and the screw rotation speed are the two most important parameters in determining the crystallinity of the materials. Furthermore, the rheological data were examined using a Principal Component Analysis (PCA) multivariate approach, highlighting also in this case the most prominent effect of the weight ratio of the two base polymers and the screw rotation speed.
... 53 By contrast, breaking down the inert hydrocarbon chains of polyethylene is unselective and requires high temperatures, with low yields of recovered ethylene monomer. 54 The solvolyzable in-chain functional groups of HDPE-like long-chain polyesters can act as predetermined breaking points and facilitate deconstruction of the polymer chain to recover the underlying long-chain monomers. This chemical recycling was demonstrated for PE-18,18 and also the long-chain polycarbonate PC-18. ...
Aliphatic polyesters based on long-chain monomers were synthesized for the first time almost a century ago. In fact, Carothers' seminal observations that founded the entire field of synthetic polymer fibers were made on such a polyester sample. However, as materials, they have evolved only over the past decade. This is driven by the corresponding monomers becoming practically available from advanced catalytic conversions of plant oils, and future prospects comprise a possible generation from third-generation feedstocks, such as microalgae or waste. Long-chain polyesters such as polyester-18,18 can be considered to be polyethylene chains with a low density of potential breakpoints in the chain. These do not compromise the crystalline structure or the material properties, which resemble linear high-density polyethylene (HDPE), and the materials can also be melt processed by injection molding, film or fiber extrusion, and filament deposition in additive manufacturing. At the same time, they enable closed-loop chemical recycling via solvolysis, which is also possible in mixed waste streams containing polyolefins and even poly(ethylene terephthalate). Recovered monomers possess a quality that enables the generation of recycled polyesters with properties on par with those of the virgin material. The (bio)degradability varies enormously with the constituent monomers. Polyesters based on short-chain diols and long-chain dicarboxylates fully mineralize under industrial composting conditions, despite their HDPE-like crystallinity and hydrophobicity. Fundamental studies of the morphology and thermal behavior of these polymers revealed the location of the in-chain groups and their peculiar role in structure formation during crystallization as well as during melting. All of the concepts outlined were extended to, and elaborated on further, by analogous long-chain aliphatic polymers with other in-chain groups such as carbonates and acetals. The title materials are a potential solution for much needed circular closed-loop recyclable plastics that also as a backstop if lost to the environment will not be persistent for many decades.
... Among these, notable approaches include the introduction of inorganic nanoparticles [15][16][17][18][19], radical-induced cross-linking reactions [20,21], and the utilization of silane monomers for cross-linking [22,23]. Regarding the incorporation of inorganic nanoparticles, extensive research has been devoted to enhancing the mechanical properties of polyolefins by integrating nano-silica particles, with a particular emphasis on mesoporous silica [24][25][26]. It is generally observed that silica with a higher surface area leads to improved performance when introduced into waste plastics. ...
Due to growing concerns about environmental pollution from plastic waste, plastic recycling research is gaining momentum. Traditional methods, such as incorporating inorganic particles, increasing cross-linking density with peroxides, and blending with silicone monomers, often improve mechanical properties but reduce flexibility for specific performance requirements. This study focuses on synthesizing silica nanoparticles with vinyl functional groups and evaluating their mechanical performance when used in recycled plastics. Silica precursors, namely sodium silicate and vinyltrimethoxysilane (VTMS), combined with a surfactant, were employed to create pores, increasing silica’s surface area. The early-stage introduction of vinyl functional groups prevented the typical post-synthesis reduction in surface area. Porous silica was produced in varying quantities of VTMS, and the synthesized porous silica nanomaterials were incorporated into recycled polyethylene to induce cross-linking. Despite a decrease in surface area with increasing VTMS content, a significant surface area of 883 m²/g was achieved. In conclusion, porous silica with the right amount of vinyl content exhibited improved mechanical performance, including increased tensile strength, compared to conventional porous silica. This study shows that synthesized porous silica with integrated vinyl functional groups effectively enhances the performance of recycled plastics.
... At the beginning of the 21st century, polyolefin materials like polyethylene (PE) and polypropylene (PP) comprised nearly half of the global plastic production (Stürzel et al., 2016;Hees et al., 2019;Alsabri et al., 2022;Ali et al., 2021a). These remarkable economic accomplishments represent substantial reaction engineering advancements, high-profile catalyst synthesis, and progressive polymer processing (Ali et al., 2022a;Christianson et al., 2010;Liu et al., 2001). ...
... Bennett and Alexandridis, (2021) currently stated that recycling programs include collection and recycling systems for consumers' plastic waste, product manufacturers to recycle plastic waste generated from production processes, and for sanitation efforts in removing plastic waste from the environment. Utilizing these plastic recycling processes will allow for plastic products to continue to be manufactured and used while reducing the numbers of plastic waste that will end up in the environment (Hees, Zhong, Sturzel and Mulhaupt, 2019). ...
The earth is the home for human; as such it should be cherished by all. The activities of manufacturing firms by burning of fossil fuels and releasing of energy to the atmosphere should be put to a halt, if we intend to live in a healthy environment. The earth cannot be crying for excess usage of its natural resources, and at same time be confronted with pollutions. The activities of improper and unethical waste management processes have affected the progress of manufacturing firms, and if not addressed immediately, achieving sustainable development will be far reached. This study was carried out to examine the relationship between environmental sustainability and the performance of plastic manufacturing firms in Enugu State, Nigeria. The descriptive survey research design method was adopted. The study was conducted in Enugu state of Nigeria which housed seven (7) plastic manufacturing firms and a population element of 1,043, the Borg & Gall formula: n= [(Zx) 2 (e) (N)] was adopted to obtain the sample size for the study. However, the sample size for the study was 200. A structured likert questionnaire was employed. Similarly, the researcher used information from the literatures that were studied to create the instrument. The hypotheses of the study were tested using the Paired Sample T-test included in SPSS version 23. The findings of the study showed that there is a significant positive relationship between recycling and net profit margin, and also that there is no significant relations between incineration and customer satisfaction. However, the study concluded that plastic manufacturing firms should invest in sustainable operational approaches that yield positive impacts to them, and pay less attention to those approaches that does not impact positively to their operations. Based on the findings, the study recommended amongst others that; by implementing efficient collection techniques and creating markets for recovered plastic waste, plastic companies are being urged to improve their recycling infrastructure and waste management systems. This will save them money, increase their organization's cash flow, and provide employment opportunities for people who land fill empty plastic can.
... Among these, notable approaches include the introduction of inorganic nanoparticles [15][16][17][18], radical-induced cross-linking reactions [19,20], and the utilization of silane monomers for crosslinking [21,22]. Regarding the incorporation of inorganic nanoparticles, extensive research has been devoted to enhancing the mechanical properties of polyolefins by integrating nano-silica particles, with a particular emphasis on mesoporous silica [23][24][25]. It is generally observed that silica with a Disclaimer/Publisher's Note: The statements, opinions, and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). ...
Due to growing concerns about environmental pollution from plastic waste, plastic recycling research is gaining momentum. Traditional methods, such as incorporating inorganic particles, increasing cross-linking density with peroxides, and blending with silicone monomers, often improve mechanical properties but reduce flexibility for specific performance requirements. This study focuses on synthesizing silica nanoparticles with vinyl functional groups and evaluating their mechanical performance when used in recycled plastics. Silica precursors, namely sodium silicate, and vinyltrimethoxysilane (VTMS), combined with a surfactant, were employed to create pores, increasing silica's surface area. Early-stage introduction of vinyl functional groups prevented the typical post-synthesis reduction in surface area. Porous silica was produced in varying quantities of VTMS, and the synthesized porous silica nanomaterials were incorporated into recycled Polyethylene to induce cross-linking. Despite a decrease in surface area with increasing VTMS content, a significant surface area of 883 m2/g was achieved. In conclusion, porous silica with the right amount of vinyl content exhibited improved mechanical performance, including increased tensile strength, compared to conventional porous silica. This study shows that synthesized porous silica with integrated vinyl functional groups effectively enhances the performance of recycled plastics.
... The C 6 to C 9 > hydrocarbon range was selected, as C 6 to C 8 is widely used and applicable in gasoline while C 9 > is outside the range of gasoline hydrocarbon (Hees et al., 2019). Gasoline is predominantly a mixture of paraffin, naphthene, aromatics, olefins, benzene, aliphatic, alicyclic, alkanes, isoalkanes, and cycloalkenes (Jia et al., 2021). ...
... This might be made easier if the plastic is developed with recycling in mind, for as by eliminating chemicals that cause deterioration during melting and re extrusion or catalyst deactivation during heating operation. The production of 100% polyolefin plastics and composites without additives is discussed by (Hees et al. 2019). This can achieve by the different catalysts and injection molding techniques. ...
Plastic recycling reduces the wastage of potentially useful materials as well as the consumption of virgin materials, thereby lowering the energy consumption, air pollution by incineration, soil and water pollution by landfilling. Plastics used in the biomedical sector have played a significant role. Reducing the transmission of the virus while protecting the human life in particular the frontline workers. Enormous volumes of plastics in biomedical waste have been observed during the outbreak of the pandemic COVID-19. This has resulted from the extensive use of personal protective equipment such as masks, gloves, face shields, bottles, sanitizers, gowns, and other medical plastics which has created challenges to the existing waste management system in the developing countries. The current review focuses on the biomedical waste and its classification, disinfection, and recycling technology of different types of plastics waste generated in the sector and their corresponding approaches toward end-of-life option and value addition. This review provides a broader overview of the process to reduce the volume of plastics from biomedical waste directly entering the landfill while providing a knowledge step toward the conversion of “waste” to “wealth.” An average of 25% of the recyclable plastics are present in biomedical waste. All the processes discussed in this article accounts for cleaner techniques and a sustainable approach to the treatment of biomedical waste.Graphical abstract
... [4,5] For the case of polyethylene, the chemically inert nature of the hydrocarbon chains in addition to its hydrophobicity further precludes biodegradation. [6] We have previously shown that renewable polyesters with a low density of in-chain functional groups as breaking points in a polyethylene chain can be chemically recycled in a closed-loop by solvolysis with quantitative recovery at mild conditions (120 to 180°C). [7] Unlike the aforementioned and other low crystalline polyesters, [4,8] the in-chain groups do not affect the crystalline structure and the beneficial material properties of polyethylene are retained at the same time. ...
We report a novel polyester material generated from readily available biobased 1,18‐octadecanedicarboxylic acid and ethylene glycol possesses a polyethylene‐like solid‐state structure and also tensile properties similar to high density polyethylene (HDPE). Despite its crystallinity, high melting point (Tm=96 °C) and hydrophobic nature, polyester‐2,18 is subject to rapid and complete hydrolytic degradation in in vitro assays with isolated naturally occurring enzymes. Under industrial composting conditions (ISO standard 14855‐1) the material is biodegraded with mineralization above 95 % within two months. Reference studies with polyester‐18,18 (Tm=99 °C) reveal a strong impact of the nature of the diol repeating unit on degradation rates, possibly related to the density of ester groups in the amorphous phase. Depolymerization by methanolysis indicates suitability for closed‐loop recycling.
... As a consequence, efforts are being made to combat the problem of an increased carbon footprint in the atmosphere by substituting even a small portion of conventional (petroleum-based and nonbiodegradable) plastics, such as poly(ethylene terephthalate) (PET), polyethylene (PE), polypropylene (PP), and polystyrene (PS), with bio-based plastics like starch, cellulose, polyhydroxyalkanoates (PHAs), and polylactic acid (PLA) [68,69]. PLA has no material carbon footprint and produces fewer CO2 emissions when compared to plastics made from fossil fuels. ...
Poly (lactic acid) (PLA) is a promising polymer with its value and potential due to its sustainability, low carbon footprint, and being a superior bio-based polymer compared to other bioplastics. Since it is also a compostable aliphatic polyester, has been frequently subjected to research. Researchers have conducted studies on the compatibility of PLA, which is a bio-based, biodegradable, and compostable, renewable polymer, with traditional petrochemical-based polymers, especially polyesters such as polybutylene terephthalate (PBT), and polyethylene terephthalate (PET). It is highly important that applications of PLA/polyester blends will ensure that the materials developed are not only economically and sustainable but also can meet current and future appropriate needs. PLA-based materials have some disadvantages such as slow biodegradation rate, high cost, and low toughness, and to eliminate mentioned drawbacks generally blends are prepared with petroleum-based polymers. In this review, information about the perspectives with studies for PLA/polyester blends; approaches to the subject, potential application areas, and contributions for the future were given.
... Different fillers bearing unique functional properties can bring customized properties to polyolefin composites. [63][64][65][66] For instance, the outer-shell self-supported Ni-catalyzed in situ ethylene polymerization provides a fascinating route for waste utilization, including fly ash, wood meal, and hollow glass beads ( Figures 6B). [67][68][69] Interestingly, the in situ polymerization route leads to a shortened high-temperature treatment time, which allows the resulting composite to better retain the color of the pine-derived wood meal (See Supporting Information, Figure S38). ...
In situ heterogeneous olefin polymerization has attracted much attention for the synthesis of polyolefin composites. However, the complicated syntheses of specially designed catalysts or the detrimental effects of interactions between catalyst and solid supports pose great challenges. In this contribution, an outer‐shell self‐supporting strategy was designed to heterogenize nickel catalysts on different fillers via precipitation homopolymerization of ionic cluster type polar monomer. These catalysts demonstrated high activity, good product morphology control, and stable performances in ethylene polymerization and copolymerization. Moreover, various polyolefin composites with great mechanical and customized properties can be efficiently synthesized.
... Nonetheless, innovations in catalyst and process technology to enable the thermal degradation/liquefaction and quantitative recovery of low molar mass hydrocarbon oil and gas products are needed. Further, the recyclable hydrocarbon materials meeting the needs of sustainable development would be tailored and integrated into CE [84]. ...
This chapter discusses different aspects of a sustainable circular economy, by reviewing the cumulative knowledge on strategies, approaches, and business models developed to close the cycle involving C-bearing compounds and materials. Some approaches, such as the role of the bioeconomy and of the renewable resources, as well as the introduction of the eco-design, eco-efficiency, and eco-effectiveness concepts, are discussed. A Circular Economy (CE) conceived as a way of minimizing, even avoiding waste generation is most appropriate in a decarbonizing scenario. However, circularity per se is not a warrant for sustainability and other measures need to be in place, to accomplish a sustainable circular economy. Within a decarbonization strategy, closing the carbon cycle becomes a circularity challenge. Unless the electric sector firstly passes through a drastic decarbonization, any electrification strategy will fail or be too slow to achieve the sustainability goals. The difficulties in assessing, monitoring, and measuring advances of circularity are also part of this chapter. Other required changes, such as business model, policies and regulations, social behavior, and product uses, for instance, are also discussed.
Formation of long chain branches (LCB) in polyethylene (PE), via incorporation of in situ generated vinyl macromonomers, is known to affect material properties dramatically, making their detection and quantification of primary importance. 13C NMR spectroscopy is the archetypal technique for the analysis of polymer microstructure, yet it suffers from major limitations in the analysis of LCB in polyethylene, primarily in terms of resolution. Herein, we propose a simple and effective methodology for detecting and quantifying LCB based on the analysis of C atoms in β-position with respect to the branching point. By analyzing model ethylene/α-olefin copolymers bearing methyl, ethyl, butyl, hexyl or tetradecyl chain branches, we show how the Cβ resonances can be used to discriminate between shorter or longer branches. Importantly, the proposed method allows the most critical discrimination between hexyl-type branches and LCB, with an up to three-fold detection enhancement with respect to previously proposed procedures based on the analysis of the methine carbons. The proposed approach is then tested on a representative industrial sample of HDPE, proving that it is suitable to detect very small amounts of LCB.
The integration of circularity and a sustainable economy framework in supply chain management represents a paradigm shift in waste reduction, especially regarding environmental hydrocarbon pollutants. Circularity fundamentally focuses on establishing closed-loop systems prioritizing items’ durability, reusability, and recyclability. The transition above challenges conventional linear production methods, promoting a regenerative system in which materials are constantly recycled. When firms adopt sustainable supply chain management methods, they may effectively address the challenges of incorporating circular concepts across their whole value chain. The comprehensive approach endeavors to mitigate the ecological consequences of hydrocarbon pollutants and reevaluate the economic framework by harmonizing profitability with ecological accountability. This model aims to usher in a period when firms actively contribute to a circular and sustainable future by implementing waste reduction methods, innovative recycling programs, and improved treatment technologies.
The depletion of fossil resources, coupled with global warming and adverse environmental impact of traditional petroleum-based plastics, have necessitated the discovery of renewable resources and innovative biodegradable materials. Lignocellulosic biomass (LB) emerges as a highly promising, sustainable and eco-friendly approach for accumulating polyhydroxyalkanoate (PHA), as it completely bypasses the problem of “competition for food”. This sustainable and economically efficient feedstock has the potential to lower PHA production costs and facilitate its competitive commercialization, and support the principles of circular bioeconomy. LB predomi nantly comprises cellulose, hemicellulose, and lignin, which can be converted into high-quality substrates for PHA production by various means. Future efforts should focus on maximizing the value derived from LB. This review highlights the momentous and valuable research breakthroughs in recent years, showcasing the biosynthesis of PHA using low-cost LB as a potential feedstock. The metabolic mechanism and pathways of PHA synthesis by microbes, as well as the key enzymes involved, are summarized, offering insights into improving microbial production capacity and fermentation metabolic engineering. Life cycle assessment and techno- economic analysis for sustainable and economical PHA production are introduced. Technological hurdles such as LB pretreatment, and performance limitations are highlighted for their impact on enhancing the sustainable production and application of PHA. Meanwhile, the development direction of co-substrate fermentation of LB and with other carbon sources, integrated processes development, and co-production strategies were also pro posed to reduce the cost of PHA and effectively valorize wastes.
Biodegradable polymers are gaining attention as alternatives to non‐biodegradable plastics to address environmental issues. With the rising global demand for plastic products, the development of non‐toxic, biodegradable plastics is a significant topic of research. Aliphatic polyester, the most common biodegradable polyester, is notable for its semi‐crystalline structure and can be synthesized from fossil fuels, microbial fermentation, and plants. Due to great properties like being lightweight, biodegradable, biocompatible, and non‐toxic, aliphatic polyesters are used in packaging, medical, agricultural, wearable devices, sensors, and textile applications. The biodegradation rate, crucial for biodegradable polymers, is discussed in this review as it is influenced by their structural properties and environmental conditions. This review discusses currently available biodegradable polyesters, their emerging applications, and the challenges in their commercialization. As research in this area grows, this review emphasizes the innovation in biodegradable aliphatic polyesters and their role in advancing environmental sustainability.
The current CO 2 emissions scale (Gton) magnitude is 5–6 orders greater than that of utilization (Mton). CO 2 utilization should focus on its massive consumption, application of sustainable technologies, low-C energy sources and long-lasting products. CO 2 conversion into materials might fulfill these requirements while using C-neutral resources and circularization to avoid waste generation will contribute to achieve sustainability. This article revises reported RD&T on production of CO 2 -derived materials and circularization approaches.
Solar energy is the fastest-growing source of electricity generation globally. As deployment increases, photovoltaic (PV) panels need to be produced sustainably. Therefore, the resource utilization rate and the rate at which those resources become available in the environment must be in equilibrium while maintaining the well-being of people and nature. Metal halide perovskite (MHP) semiconductors could revolutionize PV technology due to high efficiency, readily available/accessible materials and low-cost production. Here we outline how MHP-PV panels could scale a sustainable supply chain while appreciably contributing to a global renewable energy transition. We evaluate the critical material concerns, embodied energy, carbon impacts and circular supply chain processes of MHP-PVs. The research community is in an influential position to prioritize research efforts in reliability, recycling and remanufacturing to make MHP-PVs one of the most sustainable energy sources on the market.
In this work, crystallographic texture evolution in 3D printed trimodal polyethylene (PE) blends and high-density PE (HDPE) benchmark material were investigated to quantify the resulting material anisotropy, and the results were compared to materials made from conventional injection molded (IM) samples. Trimodal PE reactor blends consisting of HDPE, ultrahigh molecular weight PE (UHMWPE), and HDPE_wax have been used for 3D printing and injection molding. Changes in the preferred orientation and distribution of crystallites, i.e., texture evolution, were quantified utilizing the wide angle X-ray diffraction through pole figures and orientation distribution functions (ODFs) for 3D printed and IM samples. Since the change in weight-average molecular weight (Mw) of the blend was expected to significantly affect the resulting crystallinity and orientation, the overall Mw of the trimodal PE blend was varied while keeping the UHMWPE component weight fraction to 10% in the blend. The resulting texture was analyzed by varying the overall Mw of the trimodal blend and the process parameters in 3D printing and compared to the texture of conventional IM samples. The printing speed and orientation (defined with respect to the axis along the length of the samples) were used as the variable process parameters for 3D printing. The degree of anisotropy increases with an increase in the nonuniform distribution of intensities in pole figures and ODFs. All the highest intensity major texture components in IM and 3D printed samples (0° printing orientation) of reactor blends are observed to have crystals oriented in [001] or [001̅]. Overall, for the same throughput, 3D printed samples in the 0° orientation showed greater texture evolution and higher anisotropy compared to IM samples. Most notably, an increase in 3D printing speed increased the crystalline distribution closer to the 0° direction, increasing the anisotropy, while deviation from this printing orientation reduced crystalline distribution closer to the 0° direction, thus increasing isotropy. This demonstrates that tailoring material properties in specific directions can be achieved more effectively with 3D printing than with the injection molding process. Change in the overall Mw of the trimodal PE blend changed the preferential orientation distribution of the crystal planes to some degree. However, the degree of anisotropy remained the same in almost all cases, indicating that the effect of molecular weight distribution is not as significant as the printing speed and printing orientation in tailoring the resulting properties. The 3D printing process parameters (speed and orientation) were shown to have more influence on the texture than the material parameters associated with the blend.
Background
Environmental exposures to non-biodegradable and biodegradable plastics are unavoidable. Microplastics (MPs) and nanoplastics (NPs) from the manufacturing of plastics (primary sources) and the degradation of plastic waste (secondary sources) can enter the food chain directly or indirectly and, passing biological barriers, could target both the brain and the gonads. Hence, the worldwide diffusion of environmental plastic contamination (PLASTAMINATION) in daily life may represent a possible and potentially serious risk to human health.
Objective
This review provides an overview of the effects of non-biodegradable and the more recently introduced biodegradable MPs and NPs on the brain and brain-dependent reproductive functions, summarizing the molecular mechanisms and outcomes on nervous and reproductive organs. Data from in vitro, ex vivo, non-mammalian and mammalian animal models and epidemiological studies have been reviewed and discussed.
Results
MPs and NPs from non-biodegradable plastics affect organs, tissues and cells from sensitive systems such as the brain and reproductive organs. Both MPs and NPs induce oxidative stress, chronic inflammation, energy metabolism disorders, mitochondrial dysfunction and cytotoxicity, which in turn are responsible for neuroinflammation, dysregulation of synaptic functions, metabolic dysbiosis, poor gamete quality, and neuronal and reproductive toxicity. In spite of this mechanistic knowledge gained from studies of non-biodegradable plastics, relatively little is known about the adverse effects or molecular mechanisms of MPs and NPs from biodegradable plastics.
Conclusion
The neurological and reproductive health risks of MPs/NPs exposure warrant serious consideration, and further studies on biodegradable plastics are recommended.
A comprehensive review on the chemical, biological, and mechanical recycling of legacy and emerging polyesters.
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Purpose of Review
This review intends to recapitulate the pretreatment measures of kitchen waste and kitchen wastewater (KWAKWW). Furthermore, this review also separately summarizes the ascendancy of using bacteria, microalgae and microalgae-bacteria consortia to treat KWAKWW, and corresponding emerging reinforcement strategies.
Recent Findings
Tremendous amount of KWAKWW are annually generated in the whole world. Wherein roughly 1.3 billion tons of kitchen waste (KW) are dumped and which were forecasted that would increase to about 2.5 billion tons by 2025. In addition, KWAKWW have the characteristics of high content of refractory organic matter (e.g., oil and cellulose), water (commonly outstrip 70%), and salt, which is difficult for bacteria or microalgae to treat. Consequently, it is essential to perform efficacious pretreatment measures to boost the efficiency of post-treatment. Utilizing bacteria, microalgae, and microalgae-bacteria consortia to treat KWAKWW is considered an efficient strategy due to ascendancy of puissant deep purification ability, excellent resource appreciation effect, and low operation costs. For instance, bacteria could produce leastways four kinds of products through KWAKWW; multiple studies indicated that microalgae generally could remove exceed 70% of nutrients of KWAKWW; one research manifested that microalgae-bacteria consortia retrenched 46% of the demand about dissolved oxygen (DO). Nevertheless, the above microbial treatment systems still have some inherent drawbacks such as poor impact resistance. Fortunately, metabolic engineering and other strengthen strategies can efficaciously upgrade the nutrient removal and resource utilization performance of bacteria, microalgae, and microalgae-bacteria consortia. For example, one research shown that the 1-butanol productivity of original bacteria remarkably increased by 93.48–171.74% draw support from metabolic engineering.
Summary
A total of 221 papers related to the content of this review were searched through Web of Science (http://apps.webofknowledge.com). What is more, specific data that emerged on this review were all extracted from the above-searched papers. The mechanisms and effect of hydrothermal carbonization (HTC) and other four pretreatment measures are introduced by this review in detail. The preponderance of utilizing bacteria, microalgae, and microalgae-bacteria consortia to treat KWAKWW are comprehensively evaluated mainly from the perspectives of nutrient purification and resource utilization. Four state-of-the-art strengthen strategies like machine learning are then introduced. Finally, the current challenges in KWAKWW treatment are summarized from five aspects, and future concrete improvement directions are also provided. Overall, this review outlines the state-of-the-art research progress of KWAKWW treatment by bacteria and microalgae and tenders corresponding implementation schemes for improving KWAKWW treatment effect.
Processive catalysts remain attached to a substrate and perform multiple rounds of catalysis. They are abundant in nature. This review highlights artificial processive catalytic systems, which can be divided into (A) catalytic rings that move along a polymer chain, (B) catalytic pores that hold polymer chains and decompose them, (C) catalysts that remain attached to and move around a cyclic substrate via supramolecular interactions, and (D) anchored catalysts that remain in contact with a substrate via multiple catalytic interactions (see frontispiece).
This research aimed to conduct a bibliometric analysis of the existing scientific literature on circular economy (CE) and innovation in the oil and gas industry to determine the most critical concepts, authors, sources, most cited articles and countries mentioned in the field. The study of the literature on CE and innovation is also intended to reveal its underlying philosophical, intellectual and social framework. Scopus publications from 2010 to 2022 were examined for this purpose. First, a quantitative study with tables, graphs and maps summarizes the state of the CE and innovation in the oil and gas business, focusing on the key performance indicators of article output and citation. A total of 799 items were located by the results. Second, an inductive analysis of secondary literature that includes 108 articles was done, and 8 categories were identified: the CE and innovation; the CE and environmental impact; the acceptance of the economy CE by developing nations; the possibility of mainstreaming the CE; the effects of the CE on manufacturing; the effects of the CE on the pandemic (COVID‐19); and the effects of the CE on oil and gas industry.
Plastics have changed human lives, finding a broad range of applications from packaging to medical devices. However, plastics can degrade into microscopic forms known as micro- and nanoplastics, which have raised concerns about their accumulation in the environment but mainly about the potential risk to human health. Recently, biodegradable plastic materials have been introduced on the market. These polymers are biodegradable but also bioresorbable and, indeed, are fundamental tools for drug formulations, thanks to their transient ability to pass through biological barriers and concentrate in specific tissues. However, this “other side” of bioplastics raises concerns about their toxic potential, in the form of micro- and nanoparticles, due to easier and faster tissue accumulation, with unknown long-term biological effects. This review aims to provide an update on bioplastic-based particles by analyzing the advantages and drawbacks of their potential use as components of innovative formulations for brain diseases. However, a critical analysis of the literature indicates the need for further studies to assess the safety of bioplastic micro- and nanoparticles despite they appear as promising tools for several nanomedicine applications.
Significant amounts of fermented food waste are generated worldwide, promoting an abundance of residual biomass that can be used as raw material to extract bioactive peptides, fermentable sugars, polyphenols, and valuable compounds for synthesizing bioproducts. Therefore, generating these high-value-added products reduces the environmental impact caused by waste disposal and increases the industrial economic value of the final products. This review presents opportunities for synthesizing bioproducts and recovering bioactive compounds (employing wastes and byproducts from fermented sources) with several biological properties to support their consumption as dietary supplements that can benefit human health. Herein, the types of fermented food waste and byproducts (i.e., vegetables, bread wastes, dairy products, brewing, and winery sources), pre-treatment processes, the methods of obtaining products, the potential health benefits observed for the bioactive compounds recovered, and other technological applications of bioproducts are discussed. Therefore, there is currently a tendency to use these wastes to boost bioeconomic policies and support a circular bioeconomy approach that is focused on biorefinery concepts, biotechnology, and bioprocesses.
With ongoing miniaturization and weight reduction of portable electronic devices, effective heat dissipation is essential to inhibit malfunctions and premature failure. The application of fillers in a polymer matrix enhances...
Polyethylenes endowed with low densities of in‐chain hydrolyzable and photocleavable groups can improve their circularity and potentially reduce their environmental persistency. We show with model polymers derived from acyclic diene metathesis polymerization that the simultaneous presence of both groups has no adverse effect on the polyethylene crystal structure and thermal properties. Post‐polymerization Baeyer‐Villiger oxidation of keto‐polyethylenes from non‐alternating catalytic ethylene‐CO chain growth copolymerization yield high molecular weight in‐chain keto‐ester polyethylenes (Mn ~50.000 g mol‐1). Oxidation can proceed without chain scission and consequently the desirable materials properties of HDPE are retained. At the same time we demonstrate the suitability of the in‐chain ester groups for chemical recycling by methanolysis, and show that photolytic degradation by extended exposure to simulated sunlight occurs via the keto groups.
Polyethylenes endowed with low densities of in‐chain hydrolyzable and photocleavable groups can improve their circularity and potentially reduce their environmental persistency. We show with model polymers derived from acyclic diene metathesis polymerization that the simultaneous presence of both groups has no adverse effect on the polyethylene crystal structure and thermal properties. Post‐polymerization Baeyer–Villiger oxidation of keto‐polyethylenes from non‐alternating catalytic ethylene‐CO chain growth copolymerization yield high molecular weight in‐chain keto‐ester polyethylenes (Mn≈50.000 g mol⁻¹). Oxidation can proceed without chain scission and consequently the desirable materials properties of HDPE are retained. At the same time we demonstrate the suitability of the in‐chain ester groups for chemical recycling by methanolysis, and show that photolytic degradation by extended exposure to simulated sunlight occurs via the keto groups.
The tremendous efforts made in the research field of solid-state Li-ion batteries has led to considerable advancement of this technology and first market-ready systems can be expected in the near future. The research community is currently investigating different solid-state electrolyte classes (e.g., oxides, sulfides, halides and polymers) with a focus on further optimizing the synthesis and electrochemical performance. However, so far, the development of sustainable recycling strategies allowing for an efficient backflow of critical elements contained in these batteries into the economic cycle and thus a transition from a linear to a circular economy lags behind.
In this contribution, resource aspects with respect to the chemical value of crucial materials, which are used for the synthesis of solid-state electrolytes are being discussed. Furthermore, an overview of possible approaches in relation to their challenges and opportunities for the recycling of solid-state batteries with respect to different solid-state electrolyte classes by means of pyrometallurgy, hydrometallurgy and direct recycling/dissolution-based separation processes is given. Based these considerations and with reference to previous research, it will be shown that different solid-state electrolytes will require individually adapted recycling processes to be suitably designed for a circular economy, and that further improvements and investigations will be required.
In‐situ heterogeneous olefin polymerization has attracted much attention for the synthesis of polyolefin composites. However, the complicated syntheses of specially designed catalysts or the detrimental effects of interactions between catalyst and solid supports pose great challenges. In this contribution, an outer‐shell self‐supporting strategy was designed to heterogenize nickel catalysts on different fillers via precipitation homopolymerization of ionic cluster type polar monomer. These catalysts demonstrated high activity, good product morphology control, and stable performances in ethylene polymerization and copolymerization. Moreover, various polyolefin composites with great mechanical and customized properties can be efficiently synthesized.
In this work, ternary immiscible blends based on poly(lactic acid) (PLA) as major phase and polybutylene succinate (PBS) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHH) as minor phases were prepared through melt blending, aiming at obtaining fully biobased materials with enhanced ductility and toughness as compared to the inherently brittle matrix. Thermodynamic considerations based on the calculation of the interfacial tensions predicted the achievement of a partial encapsulation between the domains of the two minor components embedded in the PLA matrix. The rheological characterization revealed higher melt viscosity and elasticity for all the ternary blends as compared to the PLA matrix and a growing level of interfacial interactions between the different phases when increasing amounts of PBS are incorporated. This last was confirmed through morphological observations, which allowed demonstrating the achievement of an improved homogeneous microstructure for the blends containing 30 and 40 wt.% of PBS, notwithstanding the relatively good interfacial adhesion obtained in all the explored materials. The combined effect of the strong established interfacial interactions and of the uniform morphology resulted in the obtainment of dramatic increments of ductility, tensile toughness and impact strength for all formulated ternary blends as compared to the PLA matrix, and especially for those containing 30 or 40 wt.% of PBS, while maintaining satisfactory levels of stiffness and tensile strength.
We report a novel polyester material generated from readily available biobased 1,18‐octadecanedicarboxylic acid and ethylene glycol possesses a polyethylene‐like solid‐state structure and also tensile properties similar to high density polyethylene (HDPE). Despite its crystallinity, high melting point (Tm = 96 °C) and hydrophobic nature, polyester‐2,18 is subject to rapid and complete hydrolytic degradation in in vitro assays with isolated naturally occurring enzymes. Under industrial composting conditions (ISO standard 14855‐1) the material is biodegraded with mineralization above 95 % within two months. Reference studies with polyester‑18,18 (Tm = 99 °C) reveal a strong impact of the nature of the diol repeating unit on degradation rates, possibly related to the density of ester groups in the amorphous phase
Melt-flow-induced crystallization of polyethylene blends having tailored ultrabroad molar mass distribution affords extended-chain ultrahigh molar mass (UHMWPE) nanophases resembling nanofibers which effectively reinforce the polyethylene matrix. Unparalleled by state-of-the-art high density polyethylene (HDPE), the resulting melt-processable “all-polyethylene” single component composites exhibit simultaneously improved wear resistance, toughness, stiffness and strength. Key intermediates are trimodal blends prepared by melt compounding HDPE with bimodal UHMWPE/HDPE wax reactor blends (RB) readily tailored by ethylene polymerization on supported two-site catalysts. Whereas HDPE wax, varied up to 54 wt.-%, serves as processing aid lowering melt viscosity, UHMWPE varied up to 63 wt.-% accounts for improved blend properties. UHMWPE platelet-like nanophase separate during ethylene polymerization and readily melt during injection molding of RB/HDPE blends producing extended-chain fiber-like UHMWPE nanostructures of 100 nm diameter as shish which nucleate HDPE and HDPE wax crystallization to form shish-kebab-like structures. At 32 wt.-% UHMWPE content shish-kebab-like reinforcing phases account for massive polyethylene self-reinforcement as reflected by improved Young's modulus (+420%), tensile strength (+740%) and notched Izod impact strength (+650%) without impairing HDPE injection molding. All-PE composites exhibit high wear resistance entering ranges typical for polyamide and monomodal UHMWPE which is not processable by injection molding under identical conditions.
Plastics in the marine environment have become a major concern because of their persistence at sea, and adverse consequences to marine life and potentially human health. Implementing mitigation strategies requires an understanding and quantification of marine plastic sources, taking spatial and temporal variability into account. Here we present a global model of plastic inputs from rivers into oceans based on waste management, population density and hydrological information. Our model is calibrated against measurements available in the literature. We estimate that between 1.15 and 2.41 million tonnes of plastic waste currently enters the ocean every year from rivers, with over 74% of emissions occurring between May and October. The top 20 polluting rivers, mostly located in Asia, account for 67% of the global total. The findings of this study provide baseline data for ocean plastic mass balance exercises, and assist in prioritizing future plastic debris monitoring and mitigation strategies.
The two-stage pyrolysis-catalysis of high density polyethylene has been investigated with pyrolysis of the plastic in the first stage followed by catalysis of the evolved hydrocarbon pyrolysis gases in the second stage using solid acid catalysts to produce gasoline range hydrocarbon oil (C8–C12). The catalytic process involved staged catalysis, where a mesoporous catalyst was layered on top of a microporous catalyst with the aim of maximising the conversion of the waste plastic to gasoline range hydrocarbons. The catalysts used were mesoporous MCM-41 followed by microporous ZSM-5, and different MCM-41:zeolite ZSM-5 catalyst ratios were investigated. The MCM-41 and zeolite ZSM-5 were also used alone for comparison. The results showed that using the staged catalysis a high yield of oil product (83.15 wt.%) was obtained from high density polyethylene at a MCM-41:ZSM-5 ratio of 1:1 in the staged pyrolysis-catalysis process. The main gases produced were C2 (mainly ethene), C3 (mainly propene), and C4 (mainly butene and butadiene) gases. In addition, the oil product was highly aromatic (95.85 wt.% of oil) consisting of 97.72 wt.% of gasoline range hydrocarbons.
In addition, pyrolysis-staged catalysis using a 1:1 ratio of MCM-41: zeolite ZSM-5 was investigated for the pyrolysis–catalysis of several real-world waste plastic samples from various industrial sectors. The real world samples were, agricultural waste plastics, building reconstruction plastics, mineral water container plastics and household food packaging waste plastics. The results showed that effective conversion of the real-world waste plastics could be achieved with significant concentrations of gasoline range hydrocarbons obtained.
In the past, studies have been performed to follow chain dynamics in an equilibrium polymer melt using low molar mass polymers. Here we show that in linear ultrahigh molecular weight polyethylene entanglements formed during or after polymerization are influencing differently the overall chain topology of the polymer melt. When a disentangled UHMWPE sample is crystallized under isothermal conditions after melting, two endothermic peaks are observed. The high temperature peak is related to the melting of crystals obtained on crystallization from the disentangled domains of the heterogeneous (nonequilibrium) polymer melt, whereas the low melting temperature peak is related to the melting of crystals formed from entangled domains of the melt. On increasing the annealing time in melt, the enthalpy of the lower melting temperature peak increases at the expense of the high melting temperature peak due to the transformation of the disentangled nonequilibrium melt into the entangled equilibrium one. However, independent of the equilibrium or nonequilibrium melt state, the high melting temperature peak is observed when the disentangled samples are left to isothermally crystallize at a specific temperature, although with a decrease in bulk crystallinity. A commercial (entangled) sample, instead, shows both shift in the position of the melting temperature peak and drop in crystallinity. To ascertain that entanglements are the cause for the observed difference, experiments are performed in the presence of reduced graphene oxide (rGON): the melting response of disentangled UHMWPE crystallized from its heterogeneous melt state remains nearly independent of the annealing time in melt. This observation strengthens the concept that in the presence of a suitable filler, chain dynamics is arrested to an extent that the nonequilibrium melt state having lower entanglement density is retained.
The increased use of carbon fibre and glass fibre reinforced polymer in industry coupled with restrictions on landfill disposal has resulted in a need to develop effective recycling technologies for composites. Currently, mechanical, thermal and chemical approaches have been use to recycle composites. This paper seeks to examine the applications of engineering optimisation techniques in the composite recycling and re-manufacturing processes and their relevant systems, providing an overview of state-of-the-art. This paper is based on a comprehensive review of literature covering nearly all the research papers in this area. These papers are analysed to identify current trends and future research directions. The composite recycling is a relatively new area, and the modelling and optimisation work for composite recycling and re-manufacturing techniques and their relevant systems is still in its infancy. Currently, the optimisation work developed in composite recycling mainly focus on the applications of design of experiments methods. These approaches have been applied to improve the quality of recyclates such as carbon fibres. Some of the soft-computing algorithms have been applied to optimise the re-manufacturing at the system level. Based on the existing research, the area of optimisation for composite recycling and re-manufacturing haven't been well explored despite the fact that many opportunities and requirements for optimisation exist. This means significant amount of modelling and optimisation work is required for the future research. More significantly, considering optimisation at the early stage of a system development is very beneficial in terms of the long term health of the composite recycling industry.
Traditional insulation material is thermally insulating and has a low thermal conductivity. The miniaturisation and higher power of electrical devices would generate lots of heat, which have created new challenges to safe and stable operation of the grid. The development of insulating materials with high thermal conductivity provides a new method to solve these problems. The improvement of thermal conductivity would increase the ability to conduct heat and greatly reduce the operating temperature of the electrical equipment, which could reduce the equipment size and extend service life. On the other hand, inorganic thermally conductive particles and the improved thermal conductivity may have great effect on thermal breakdown. In this study, the factors affecting the thermal conductivity of dielectric polymer composites were explored. Intrinsic thermal conductive polymer and particle-filled thermal conductive composites were discussed. Effect of thermal conductivity, shape, size, surface treatment of the particle and prepare process on thermal properties of the composites were illustrated. This study focused on the electrical and thermal properties of thermally conductive epoxy, polyimide and polyethylene composites. Tracking failure caused by thermal accumulation is a typical thermal breakdown phenomenon. The performance of the resistance to tracking failure was studied for these composites. The results showed that thermal conductive particles improved the resistance to tracking failure. Finally, application of thermally conductive epoxy in electrical equipment was discussed.
Nanoparticles are very interesting because of their surface properties, different from bulk materials. Such properties make possible to endow ordinary products with new functionalities. Their relatively low cost with respect to other nano-additives make them a promising choice for industrial mass-production systems. Nanoparticles of different kind of materials such as silver, titania, and zinc oxide have been used in the functionalization of fibers and fabrics achieving significantly improved products with new macroscopic properties. This article reviews the most relevant approaches for incorporating such nanoparticles into synthetic fibers used traditionally in the textile industry allowing to give a solution to traditional problems for textiles such as the microorganism growth onto fibers, flammability, robustness against ultraviolet radiation, and many others. In addition, the incorporation of such nanoparticles into special ultrathin fibers is also analyzed. In this field, electrospinning is a very promising technique that allows the fabrication of ultrathin fiber mats with an extraordinary control of their structure and properties, being an ideal alternative for applications such as wound healing or even functional membranes.
A complete review of the different techniques that have been developed to recycle fibre reinforced polymers is presented. The review also focuses on the reuse of valuable products recovered by different techniques, in particular the way that fibres have been reincorporated into new materials or applications and the main technological issues encountered. Recycled glass fibres can replace small amounts of virgin fibres in products but not at high enough concentrations to make their recycling economically and environmentally viable, if for example, thermolysis or solvolysis is used. Reclaimed carbon fibres from high-technology applications cannot be reincorporated in the same applications from which they were recovered, so new appropriate applications have to be developed in order to reuse the fibres. Materials incorporating recycled fibres exhibit specific mechanical properties because of the particular characteristics imparted by the fibres. The development of specific standards is therefore necessary, as well as efforts in the development of solutions that enable reusers to benefit from their reinforcement potential. The recovery and reuse of valuable products from resins are also considered, but also the development of recyclable thermoset resins. Finally, the economic and environmental aspects of recycling composite materials, based on Life Cycle Assessment, are discussed.
Plastic pollution is ubiquitous throughout the marine environment, yet estimates of the global abundance and weight of floating plastics have lacked data, particularly from the Southern Hemisphere and remote regions. Here we report an estimate of the total number of plastic particles and their weight floating in the world’s oceans from 24 expeditions (2007–2013) across all five sub-tropical gyres, costal Australia, Bay of Bengal and the Mediterranean Sea conducting surface net tows (N5680) and visual survey transects of large plastic debris (N5891). Using an oceanographic model of floating debris dispersal calibrated by our data, and correcting for wind-driven vertical mixing, we estimate a minimum of 5.25 trillion particles weighing 268,940 tons. When comparing between four size classes, two microplastic ,4.75 mm and meso- and macroplastic .4.75 mm, a tremendous loss of microplastics is observed from the sea surface compared to expected rates of fragmentation, suggesting there are mechanisms at play that remove ,4.75 mm plastic particles from the ocean surface.
Flow-induced crystallization has long been an important subject in polymer processing. Varying processing conditions can produce different morphologies, which lead to different properties. Recent studies indicated that the final morphology is in fact dictated by the initial formation of crystallization precursor structures (i.e. shish-kebabs) under flow. In this article, factors that affect the shish-kebab formation in entangled polymer melts are systematically reviewed, including the concept of coil–stretch transition, chain dynamics, critical orientation molecular weight, phase transition during shish and kebab formations. In particular, recent experimental results from in situ rheo-X-ray studies and ex situ microscopic examinations have been presented to illustrate several new findings of flow-induced shish-kebab structures in polymer melts. (1) The shish entity consists of stretched chains (or chain segments) that can be in the amorphous, mesomorphic or crystalline state. (2) The kebab entity mainly arises from the crystallization of coiled chains (or chain segments), which seems to follow a diffusion-control growth process. (3) A shish-kebab structure with multiple shish was seen in the ultra-high molecular weight polyethylene (UHMWPE) precursor. Based on the above results and recent simulation work from other laboratories, a modified molecular mechanism for the shish-kebab formation in entangled melt is presented.
Plastics are inexpensive, easy to mold, and lightweight. These and many other advantages make them very promising candidates for commercial applications. In many areas, they have substantially suppressed traditional materials. However, the problem of recycling still is a major challenge. There are both technological and economic issues that restrain the progress in this field. Herein, a state-of-art overview of recycling is provided together with an outlook for the future by using popular polymers such as polyolefins, poly(vinyl chloride), polyurethane, and poly(ethylene terephthalate) as examples. Different types of recycling, primary, secondary, tertiary, quaternary, and biological recycling, are discussed together with related issues, such as compatibilization and cross-linking. There are various projects in the European Union on research and application of these recycling approaches; selected examples are provided in this article. Their progress is mirrored by granted patents, most of which have a very limited scope and narrowly cover certain technologies. Global introduction of waste utilization techniques to the polymer market is currently not fully developed, but has an enormous potential.
Biomass represents an abundant carbon-neutral renewable resource for the production of bioenergy and biomaterials, and its
enhanced use would address several societal needs. Advances in genetics, biotechnology, process chemistry, and engineering
are leading to a new manufacturing concept for converting renewable biomass to valuable fuels and products, generally referred
to as the biorefinery. The integration of agroenergy crops and biorefinery manufacturing technologies offers the potential
for the development of sustainable biopower and biomaterials that will lead to a new manufacturing paradigm.
In the past a few decades, some modified injection molding technologies aiming to fabricate highly oriented superstructure as "self-reinforcement" phase in injection molded samples, such as SCORIM, DPIM and PVIM, have been extensively proven to be effective in improving mechanical properties of polyolefin. However, there is rare report focus on applying these technologies on reinforcing products with a more complex geometry structure till now. The vibration injection technology is currently researched at lab-scale rather than wildly used in industry. Here we designed a lid-shaped part, of which the geometry structure is completely different from rectangle or dumbbell used in the previous studies, and a novel multi-flow vibration injection technology was hired to control the content of shish-kebab successfully. The self-reinforcement effect induced by shish-kebab was remarkable, indicated by the overall improvement in mechanical properties. This work gave a new insight into the practical application prospect of vibration injection technology.
All‐polyethylene composites exhibiting substantially improved toughness/stiffness balance are readily produced during conventional injection molding of high density polyethylene (HDPE) in the presence of bimodal polyethylene reactor blends (RB40) containing 40 wt% ultrahigh molar mass polyethylene (UHMWPE) dispersed in HDPE wax. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) analyses shows that flow‐induced crystallization affords extended‐chain UHMWPE nanofibers forming shish which nucleates HDPE crystallization producing shish‐kebab structures as reinforcing phases. This is unparalleled by melt compounding micron‐sized UHMWPE. Injection molding of HDPE with 30 wt% RB40 at 165 °C affords thermoplastic all‐PE composites (12 wt% UHMWPE), improved Young's modulus of 3400 MPa, tensile strength of 140 MPa, and impact resistance of 22.0 kJ/m2. According to fracture surface analysis, the formation of skin‐intermediate‐core structures accounts for significantly improved impact resistance. At constant RB40 content both morphology and mechanical properties strongly depend upon processing temperature. Upon increasing processing temperature from 165 °C to 250 °C the average shish‐kebab diameter increases from the nanometer to micron range, paralleled by massive loss of self‐reinforcement above 200 °C. The absence of shish‐kebab structure at 250 °C is attributed to relaxation of polymer chains and stretch‐coil transition impairing shish formation. All‐polyethylene is prepared by conventional injection molding and its mechanical properties, thermal properties, and nanostructure are influenced by different processing conditions.
Nanophase separation during injection molding of high density polyethylene (HDPE) together with polyethylene reactor blend (RB) additives that have ultrabroad bimodal molar mass distribution and a high content of ultrahigh molar mass polyethylene (UHMWPE), produces thermoplastic all-polyethylene composites reinforced with extended-chain UHMWPE nanostructures formed in situ. Neither alien fibers, inorganic fillers, hazardous nanoparticles nor modified single- and multi-step molding processes are required to convert HDPE into higher performance engineering plastics. The RB40 additive is readily tailored by ethylene polymerization on silica-supported chromium two-site catalysts and contains 40 wt% UHMWPE (Mw = 1.5 × 10⁶ g∙mol⁻¹) dispersed in 50 wt% HDPE wax (Mw = 1.1 × 10³ g∙mol⁻¹). The presence of disentangled nanophase-separated UHMWPE together with HDPE wax serving as a processing aid enables injection molding of all-PE composites with high UHMWPE content of up to 24 wt% without changing processing parameters typical for HDPE. As verified by both scanning electron microscopic analyses of samples etched with hot xylene and thermal analysis, the HDPE matrix is efficiently reinforced by in situ formed polyethylene shish-kebab fibers where flow-induced crystallization yields extended-chain UHMWPE nanostructures as shish nucleating the crystallization of HDPE kebab. For the first time, by etching quenched samples, it was possible to completely suppress kebab formation and to image in situ extended-chain UHMWPE shish with an average diameter of 80 nm. Upon increasing the UHMPE content the average total diameter of shish-kebab fiber-like structures drastically decreases from micron to nanometer range, forming non-woven-like architectures. This self-reinforcement simultaneously improves toughness, stiffness and strength parameters unparalleled by conventional melt-blending HDPE with micron-sized UHMWPE and HDPE wax. Compared to HDPE, the addition of 60 wt% RB40 increases the Young's modulus to 4.2 GPa, tensile strength to 160 MPa and impact strength to 20 kJ/m². This sustainable route to self-reinforced all-PE composite composites preserves the high energy, resource, cost and eco-efficiencies typical for pure hydrocarbon resins. Here, we examine the impact of RB40 addition on in situ nanostructure formation and its correlation with thermal and mechanical properties of all-PE composites.
Indicators used to direct ecomonic policy (GDP, national income, etc.) are based on a number of factors ß but nowhere in their calculation is there an acknowledgement of the degradation of natural resources. The numbers may look good, but continued deterioration of the environment is leading us closer to crises; meanwhile, policymakers and the public are basing decisions on dangerously incomplete information. In Taking Nature into Account, a number of the world's leading experts make the ethical, historical, economic, and ecological arguments for including environmental factors when measuring fiscal health. Initiated by the Club of Rome (an international group of influential businesspeople, statesmen, and scientists), and written in cooperation with the World Wide Fund for Nature, the report reviews existing methodologies and makes recommendations for adjusting the way we think about and measure the economy.
Tailored polyethylene reactor blend additives (RB) with ultrabroad bimodal molar mass distributions comprise nanophase-separated ultrahigh molar mass polyethylene (UHMWPE) uniformly dispersed in polyethylene wax. During injection molding of high-density polyethylene (HDPE) together with variable amounts of the nanophase-separated HDPE wax/UHMWPE (70/30) additive (RB30) flow-induced oriented crystallization affords shish-kebab fiber-like UHMWPE nanostructures accounting for efficient HDPE self-reinforcement. RB additives are readily prepared by ethylene polymerization on silica-supported two-site chromium catalysts which simultaneously produce HDPE wax together with disentangled nanoplatelet-like UHMWPE. The presence of HDPE wax is essential for lowering melt viscosity at high UHMWPE content. Since HDPE wax crystallizes onto extended-chain UHMWPE shish to form kebab structures, high HDPE wax content is tolerated without encountering emission problems and impairing mechanical properties as observed in the absence of UHMWPE. This in situ reinforcement substantially improves HDPE toughness/stiffness/strength balance as reflected by simultaneously increased Young’s modulus (+365%), tensile strength (+392%), and impact resistance (+197%). The performance of self-reinforced polyethylene (PE-SRC) is far superior to that of melt-blended UHMWPE/HDPE and the majority of PE nanocomposites. Neither hazardous UHMWPE nanoparticles nor alien inorganic nanofillers are required.
The word “Waste” normally emphasis something around us which should be re-cycle, re-used, reduced or even eliminated, if possible. A giant amount of waste, such as: electronics/electrical items, manufacturing scrap, discarded constructional materials, polymers from daily needs, etc., is being generated day-by-day, whereas its treatment is lagging. The term zero waste (ZW) is continuously encouraging both producers and consumers to adopt sustainable approaches in order to reduce their expenditures as well as to help in making a better world. In the past, researchers have highlighted numerous techniques to tackle physical waste, however the chemicals which are normally generated from this waste is more critical and limitedly reported. Zero Waste Manufacturing (ZWM) is believed as a roadmap for future of manufacturing by which the burning issue of “Waste” can be tackled. However, ZWM can be supported with recycling and reusability of the produced wastes in another manufacturing process, use of optimization tools and sustainable manufacturing theories, development of precision manufacturing systems, etc. This review article is taken up to discuss various recent sustainable manufacturing ideas applied in the prominent sectors with an aim to either re-cycle/re-use the discarded ones or to produce a fresh part in eco-friendly manners. Special attention is paid to the current trends in machining and a brief case study of sustainable manufacturing of aerospace industry has also been discussed.
In a previous work, it was shown that highly oriented fibres with 10 GPa modulus could be obtained by continuous single-stage melt extrusion of a medium molecular weight polyethylene to which 3% ultra-high molecular weight (M
w ∼ 3 to 5 × 106) material had been added by solution blending. It was demonstrated that a special interlocking shish kebab structure was responsible for the favourable mechanical properties. In the present work, we succeeded in achieving the same effect from an unblended polyethylene by choosing starting materials with an inherently suitable molecular weight distribution. Both the high and low molecular weight tails of the distribution are very influential: the high tail contributes to the formation of extended-chain fibrils (which constitute the backbones of the shish kebabs), while the low tail affects melt extrudability and strength. Melt strength is important because unusually high tensile stresses are required during wind-up. The wind-up stress was measured and found to be an order of magnitude greater than that encountered in conventional melt spinning — where no shish kebabs are formed. The implications of the above findings for polymer processing, crystal morphology and melt rheology are discussed.
Plastic plays an important role in our daily lives due to its versatility, light weight and low production cost. Plastics became essential in many sectors such as construction, medical, engineering applications, automotive, aerospace, etc. In addition, economic growth and development also increased our demand and dependency on plastics which leads to its accumulation in landfills imposing risk on human health, animals and cause environmental pollution problems such as ground water contamination, sanitary related issues, etc. Hence, a sustainable and an efficient plastic waste treatment is essential to avoid such issues. Pyrolysis is a thermo-chemical plastic waste treatment technique which can solve such pollution problems, as well as, recover valuable energy and products such as oil and gas. Pyrolysis of plastic solid waste (PSW) has gained importance due to having better advantages towards environmental pollution and reduction of carbon footprint of plastic products by minimizing the emissions of carbon monoxide and carbon dioxide compared to combustion and gasification. This paper presents the existing techniques of pyrolysis, the parameters which affect the products yield and selectivity and identify major research gaps in this technology. The influence of different catalysts on the process as well as review and comparative assessment of pyrolysis with other thermal and catalytic plastic treatment methods, is also presented.
Aerogels of nanocellulose (NC) prepared by freeze-drying of cellulose nanofibrils (CNF) hydrogels and followed by impregnation with methylaluminoxane serve as nanoporous organic supports for immobilizing single site iron catalysts such as bisiminopyridine iron(II) complexes. The resulting catalyst systems, exploiting renewable biomaterials as organic supports, are highly active in low pressure ethylene polymerization. They afford simultaneous control of high density polyethylene (HDPE) particle morphology and facile NC dispersion within the HDPE matrix. In the early stage of ethylene polymerization, mesoscopic shape replication and NC-mediated templating yield platelets containing an NC core and a HDPE shell, as confirmed by scanning electron microscopy (SEM) of virgin polyethylene powders. Opposite to conventionally dried CNF hydrogels, forming large agglomerates, this facile NC aerogel-mediated in situ NC/HDPE nanocomposite formation is vastly superior to melt compounding of HDPE with NC, failing to produce such fine NC dispersions. On increasing NC content to 3.0 wt%, both Young's modulus (+50%) and tensile strength (+40%) increase at the expense of elongation at break (−80%). According to the SEM analysis of NC/HDPE morphology, the dispersion of NC nanosheets together with the in situ formation of “shish-kebab” polyethylene fiber-like structures accounted for HDPE matrix reinforcement.
Tailoring trimodal polyethylene (PE) molar mass distributions by means of ethylene polymerization on three-site catalysts, supported on functionalized graphene (FG), enables nanophase separation during polymerization and melt processing, paralleled by PE self-reinforcement. Typically, FG/MAO-supported three-site catalysts combine bis(iminopyridyl)chromium trichloride (CrBIP), producing PE wax having high crystallization rate, and quinolylcyclopentadienylchromium dichloride (CrQCp), forming in situ ultrahigh molecular weight PE (UHMWPE) nanostructures, with bis(iminopyridyl)iron dichloride (FeBIP) or bis(tert-butyl cyclopentadienyl)zirconium (ZrCp), respectively, producing HDPE with variable intermediate molar mass. During injection molding, the formation of shish-kebab fiber-like extended-chain UHMWPE structures, as verified by SEM, AFM, and DSC, account for effective self-reinforcement. Only in the presence of high UHMWPE content, PE wax, usually an unwanted byproduct in HDPE synthesis, functions as a built-in processing aid and enables the incorporation of much higher UHMWPE contents (30 wt %) than previously thought to be tolerable in injection molding. Whereas the incorporation of UHMWPE/PE wax blends improves stiffness and strength, the simultaneous FG dispersion accounts for substantially higher impact strength.
A complete review of the different techniques that have been developed to recycle fibre reinforced polymers is presented. The review also focuses on the reuse of valuable products recovered by different techniques, in particular the way that fibres have been reincorporated into new materials or applications and the main technological issues encountered. Recycled glass fibres can replace small amounts of virgin fibres in products but not at high enough concentrations to make their recycling economically and environmentally viable, if for example, thermolysis or solvolysis is used. Reclaimed carbon fibres from high-technology applications cannot be reincorporated in the same applications from which they were recovered, so new appropriate applications have to be developed in order to reuse the fibres. Materials incorporating recycled fibres exhibit specific mechanical properties because of the particular characteristics imparted by the fibres. The development of specific standards is therefore necessary, as well as efforts in the development of solutions that enable reusers to benefit from their reinforcement potential. The recovery and reuse of valuable products from resins are also considered, but also the development of recyclable thermoset resins. Finally, the economic and environmental aspects of recycling composite materials, based on Life Cycle Assessment, are discussed.
The design of supported two- and three-site catalysts for ethylene polymerization and tailoring nanophase-separated polyethylene reactor blends represents the key to the development of advanced all-polyethylene nanocomposite materials exhibiting substantially improved performance and high resource-, eco- and energy efficiency. Two or three different single-site catalysts independently produce high density polyethylene (HDPE), ultrahigh molecular weight polyethylene (UHMWPE) and PE wax on the same catalyst support. Since this catalyst-mediated nanophase separation prevents UHMWPE entanglement, typical for conventional homogeneous reactor blends, much higher UHMWPE content up to 30 wt.-% is incorporated in the presence of PE wax without impairing injection molding. During melt processing the shear-induced oriented UHMWPE crystallization affords shish-kebab-fiber-like nanostructures. This accounts for effective PE self-reinforcement paralleled by simultaneous improvement of stiffness, strength and toughness. Hence, this strategy holds great promise for converting commodity PE into high performance plastics and single component PE composites, entering the performance range currently claimed by glass fiber reinforced PE.
Lamellar and pillared ZSM-5 zeolites (L-ZSM-5 and PI-ZSM-5, respectively) were synthesized and tested in the catalytic cracking of low-density polyethylene (LDPE). The introduction of silica pillars into lamellar ZSM-5 caused a high increase in the Si/Al ratio (from 33 up to 64) and the generation of uniform mesopores with size about 3.5 nm. Both samples provided quite similar LDPE conversions at the three reaction temperatures investigated (340, 360 and 380ºC) despite the lower concentration of acid sites in PI-ZSM-5, which is assigned to the improved active centres accessibility due to the pillaring treatment. Significant activity was observed even at the lowest temperature, with LDPE conversions in the range 27% – 36%, which indicates that 2D ZSM-5 zeolites are convenient catalysts for polyethylene cracking. The main products of LDPE catalytic cracking were C2 – C5 olefins with a selectivity 60 – 70% denoting that an end-chain cracking mechanism is predominant. 2D ZSM-5 samples were subsequently compared with nanocrystalline (n-ZSM-5) and hierarchical ZSM-5 (h-ZSM-5) zeolites. Pyridine adsorption followed by FTIR measurements showed significant differences not only in terms of acid sites concentration but also on the Brønsted/Lewis acid distribution among the samples. When the LDPE cracking conversion was referred to the zeolite mesopore/external surface area, a good correlation was observed with the concentration of Brønsted acid sites but not when considering just the Lewis ones. This interesting fact suggests that Brønsted acid sites are mainly the active centers for the cracking of the LDPE chains, concluding that, in addition to the accessibility, the acidity nature plays a major role in this type of reaction.
Design and synthesis of efficient drug delivery systems are of critical importance in health care management. Innovations in materials chemistry especially in polymer field allows introduction of advanced drug delivery systems since polymers could provide controlled release of drugs in predetermined doses over long periods, cyclic and tunable dosages. To this end, researchers have taken advantages of smart polymers since they can undergo large reversible, chemical, or physical fluctuations as responses to small changes in environmental conditions, for instance, in pH, temperature, light, and phase transition. The present review aims to highlight various kinds of smart polymers, which are used in controlled drug delivery systems as well as mechanisms of action and their applications.
The production and properties of high-modulus and high-strength polyethylene fibres are described. Low molecular weight (LMW-PE) fibres are produced by melt spinning of fibres with controlled morphology, followed by hot drawing to a high draw ratio. Ultra high molecular weight (UHMW-PE) fibres of high stiffness and strength are produced by solution(gel)-spinning followed by drawing to high draw ratios. Solvent-free processing routes and solid/melt routes for UHMW-PE fibres are also described. Commercial applications for both LMW-PE and UHMW-PE fibres are discussed.
IntroductionTechnology EvolutionSpherizone TechnologyTechnology ComparisonEnvironmental ConsiderationsReferences
The interplay of single- and multi-site catalysts with nanoparticles, nanostructure formation, and polymer crystallization represents the key to the development of advanced polyolefin materials for sustainable development. In polymerization filling technology, catalysts are supported on a great variety of nanofillers. In contrast to melt compounding, effective nanoparticle dispersion is readily achieved during catalytic olefin polymerization, independent of polyolefin molar mass. Novel families of in situ-formed polyolefin carbon hybrid materials are based upon single- and multi-layer graphene. Supported multi-site catalysts produce reactor blends as all “polyolefin” nanocomposites, reinforced by in situ-formed shish–kebab-like ultrahigh molecular weight polyolefin nanofibers.
The in-line development of crystalline morphology and orientation during melt extrusion of low density polyethylene (LDPE) tape at nil and low haul-off speeds has been investigated using Small-Angle X-Ray Scattering (SAXS). The processing parameters, namely haul-off speed and distance down the tape-line have been varied and the resulting crystalline morphology is described from detailed analysis of the SAXS data. Increasing haul-off speed increased orientation in the polymer tape and the resulting morphology could be described in terms of regular lamellar stacking perpendicular to the elongation direction. In contrast, under nil haul-off conditions the tape still showed some orientation down the tape-line, but a shish-kebab structure prevails. The final lamellae thickness ( ∼50 Å) and bulk crystallinity (∼20%), were low at, for all processing conditions investigated, which is attributed to the significant short-chain branching in the polymer acting as point defects limiting lamellae crystal growth.
A self-made low frequency vibration injection molding device was adopted to explore the mechanical properties and morphology for iPP injected moldings. The morphology and mechanical properties of samples produced by conventional injection molding (CIM) were used to compare with those obtained by vibration injection molding (VIM). For VIM the main processing parameters are vibration frequency and vibration pressure amplitude, the range of vibration frequency is 0-3 Hz, and the range of pressure vibration amplitude is 0-59.4 MPa. During the injection and pressure holding stages for CIM the injection and holding pressures are always constant, but for VIM an additional pulsing pressure vibration is exerted on the melt in the runner system and mold cavity, causing compression and decompression on the melt and shearing at the melt-solid interface, and it progresses from surface to core of the dumbbell specimen during solidification stage. In this work, the isotactic polypropylene material was plasticized and pumped into the melt chamber by a single screw extruder. During injection and pressure holding stages for the VIM, the melt was vibrated about 25 s in the dumbbell specimen mould and then cooled down in about 20 s. The melt injection temperature and mould temperature are set at 190°C and 40° respectively. The injection pressure for CIM and the base pressure for VIM was 39.5 MPa. The VIM samples were injected at different vibration frequencies and pressure vibration amplitudes, respectively. To prepare VIM samples treated under different vibration frequencies, the vibration pressure amplitude was set at 19.8 MPa, and for VIM samples teated under different vibration pressure amplitudes, the vibration frequency was set at 0.7 Hz. With application of melt vibration technology the mechanical properties of iPP injection moldings were improved. The tensile strength and impact strength increase with the increasing of pressure vibration amplitude, while the elongation at break decreases. The tensile strength increases with increasing frequency in the low frequency range, but the breaking elongation decreases . When the vibration frequency is above 0.47 Hz, the elongation at break begins to increase with increasing vibration frequency, and the tensile strength is also simultaneously improved. Injected at 190°C the mechanical strength increases from a conventional value of 41.3 MPa to 48.4 MPa obtained at 0.7 Hz of vibration frequency and 59.4 MPa of pressure vibration amplitude, and the corresponding increase percentage is 17.2%. DSC, SEM and WAXD were used to investigate the structure and morphologies of core regions of injection-molded samples. SEM studies show that the core region of samples mainly consists of sperulites, they may deform and orient along the flow direction and decrease their size in the vibration injection process. DSC curves display that the melt peaks of vibration injection moldings shift to high temperatures compared with those of conventional samples, and the maximal increase percentage of crystallinity for vibration samples is 12.1%. WAXD shows that γ-form crystals are obtained easily at low vibration frequencies and large pressure vibration amplitudes. The orientation of sperulites, increased crystallinity and existence of γ-form crystals are beneficial to improvement of the mechanical properties of iPP vibration injection-molded samples.
There has been a growing interest and effort over the last few years in the development of novel food packaging concepts, which can play a proactive role regarding product preservation, shelf-life extension, and even improvement. Several strategies have been devised to exert a positive action over the packaged foodstuff, including retention of desirable molecules (i.e., aldehydes, oxygen) and release of substances (i.e., carbon dioxide, aromas). These new developments have been generally termed active packaging technologies. However, many of these emerging active packaging technologies are finding in the versatility and special properties of plastic materials an efficient vehicle to exploit and enhance their commercial interest. This overview examines the most recent developments and technologies designed to include the active principle within the plastic packaging materials and generally termed active plastics technologies. Due to the novelty of most of these active packaging developments, the scope of this article has mainly been focused on peer-reviewed literature as this offers, in principle, a more objective description of these new technologies.
The catalytic ethylene polymerization on dual-site catalysts, supported on functionalized graphene, enables nanostructure formation in polyethylene reactor blends by in situ formation of uniformly dispersed ultrahigh molecular weight polyethylene (UHMWPE) nanoplatelets and in situ formed aligned UHMWPE shish-kebab nanofibers. For tailoring bimodal molar mass distributions, the quinolylsilylcyclopentadienylchromium(III) complex (Cr-1), producing UHMWPE with M-w > 3 X 10(6) g mol(-1), is blended together with bisiminopyridine complexes of either chromium(III) (CrBIP), producing polyethylene (PE) wax (2 X 10(3) g mol(-1)), or iron(II) (FeBIP), producing PE with M-w = 2.0 x 10(5) g mol(-1). Hence, the FeBIP/Cr-1 and CrBIP/Cr-1 molar ratios govern the PE/UHMWPE weight ratio without affecting the average molar mass of the individual PE fractions. In sharp contrast to conventional UHMWPE/PE reactor blends, the UHMWPE content is substantially increased up to 17 wt % without impairing melt processing. In the case of graphene-supported FeBIP/Cr-1, SEM and TEM analysis reveal that UHMWPE nanoplatelets are formed during polymerization. This is attributed to graphene-mediated mesoscopic shape replication. During injection molding, the UHMWPE nanoplatelets are transformed into aligned UHMWPE shish-kebab nanofibers, thus enabling efficient polyethylene matrix reinforcement.
In this work, all-polypropylene composites (all-PP composites) were manufactured by injection moulding. Prior to injection moulding, pre-impregnated pellets were prepared by a three-step process (filament winding, compression moulding and pelletizing). A highly oriented polypropylene multifilament was used as the reinforcement material, and a random polypropylene copolymer (with ethylene) was used as the matrix material. Plaque specimens were injection moulded from the pellets with either a film gate or a fan gate. The compression moulded sheets and injection moulding plaques were characterised by shrinkage tests, static tensile tests, dynamic mechanical analysis and falling weight impact tests; the fibre distribution and fibre/matrix adhesion were analysed with light microscopy and scanning electron microscopy. The results showed that with increasing fibre content, both the yield stress and the perforation energy significantly increased. Of the two types of gates used, the fan gate caused the mechanical properties of the plaque specimens to become more homogeneous (i.e., the differences in behaviour parallel and perpendicular to the flow direction became negligible).
SCORIM (shear controlled orientation in injection moulding) is a new technology using pairs of reciprocating pistons connected to the runner system to impose shear in the mould during the holding and packing stages; this provides important control over part properties. A computer simulation is set up, and solved numerically to assist with development and exploitation of this novel process. The one-dimensional transient model considers the cooling and solidification of polymer melt, contained between infinite plane parallel plates, whilst subjected to reciprocating shear flow. A non-Newtonian, temperature-dependent viscosity is used, together with temperature-dependent thermal properties and latent heat of solidification. Two operating modes are considered: (1) flow driven by a fixed pressure gradient; (2) an initially fixed flowrate, which falls after a limiting pressure gradient is reached. Results are shown, based on data for a moulding grade polypropylene; these include details of temperature and velocity fields, pressure and flowrate profiles, and frozen-in material strains, which are related to material alignment. In mode (1) operation, flowrate falls rapidly as solidification proceeds. This is not hindered significantly by viscous heating. Frozen-in strain has its maximum value close to the wall, and falls in a series of oscillations to zero on the central plane. In mode (2), if the limiting pressure gradient is too high, viscous heating can prevent cooling, leading to a dynamic thermal equilibrium. In other cases, where cooling is completed, frozen-in strain can show a complex, oscillatory profile, corresponding to a layered structure in the moulding with alternating regions of higher and lower alignment.
Flow-induced crystallization of high-density polyethylene and polypropylene films has been studied in a slit die equipped with optical windows to allow direct visual observation of the process. Mechanical and thermal property measurements and morphological analyses verify the presence of self-reinforced, extended-chain structures in the extrudate. By controlling the location of the crystallization front inside the die but near the exit, continuous extrusion was possible at lower pressures than previously reported. Birefringence measurements of the melt flow indicated the feasibility of an optimal die geometry to maximize oriented structure development during continuous extrusion while minimizing pressure buildup.
Recently, it has been shown that by using a single-site catalytic system having titanium as a metallic center, it is possible to tailor the entanglement density in the amorphous region of a semi-crystalline ultra-high molecular weight polyethylene (UHMWPE). This route provides the possibility to make high-modulus, high-strength uniaxially and biaxially drawn tapes and films, without using any solvent during processing. In this publication, it is shown that a single-site catalyst having chromium as metallic center, proposed by Enders and co-workers, can also be tuned to provide control on the entanglement density during synthesis of the UHMWPE. However, to achieve the goal some modifications during the synthesis are required. The synthesized polymers can be processed in the solid state below the equilibrium melting temperature, resulting in uniaxially drawn tapes having tensile strength and modulus greater than 3.5 N/tex and 200 N/tex, respectively. Rheological studies have been performed to follow the increase in entanglement density in melt state with time.
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Research on "post-metallocene" polymerization catalysis ranges methodologically from fundamental mechanistic studies of polymerization reactions over catalyst design to material properties of the polyolefins prepared. A common goal of these studies is the creation of practically useful new polyolefin materials or polymerization processes. This Review gives a comprehensive overview of post-metallocene polymerization catalysts that have been put into practice. The decisive properties for this success of a given catalyst structure are delineated.
The Fischer-Tropsch synthesis is at the heart of the Biomass-to-Liquids (BTL) process. Feasibility studies published in open literature typically consider cobalt-based catalysts for the Fischer-Tropsch synthesis. Here, we present an overview on the history and development up until the present for both cobalt- and iron-based Fischer-Tropsch catalysts. The role of the support material and various other additives to the catalyst formulation are discussed in detail with regard to activity, catalyst deactivation, and selectivity. Tentative explanations for e.g. the observed size dependency in cobalt-based catalysts and phase transformations in iron-based Fischer-Tropsch catalysts are offered. The productivity of cobalt-based catalysts at high conversion level is currently higher than that of iron-based catalysts. Nevertheless, it is argued that iron-based catalysts may be an attractive option for the BTL-process, since it is much cheaper, impacting on the cost of the process due to inevitable process set-ups in industrial operation. Improvement of current iron-based catalysts is however desired.
Dwindling fossil resources, surging energy demand and global warming stimulate growing demand for renewable polymer products with low carbon footprint. Going well beyond the limited scope of natural polymers, biomass conversion in biorefineries and chemical carbon dioxide fixation are teamed up with highly effective tailoring, processing and recycling of polymers. “Green monomers” from biorefineries, and “renewable oil”, gained from plastics' and bio wastes, render synthetic polymers renewable without impairing their property profiles and recycling. In context of biofuel production, limitations of the green economy concepts are clearly visible. Dreams and reality of “green polymers” are highlighted. Regardless of their new greenish touch, highly versatile and cost-effective polymers play an essential role in sustainable development.
Highly active single- and dual-site catalysts supported on silica nanofoams (NF) enable the control of both polyethylene (PE) morphology and tailoring of bimodal PE molar mass distribution in catalytic ethylene polymerization. In a templating process, aqueous polystyrene (PS) nano suspensions are mineralized and calcinated at 600 °C, thus producing NF with specific surface area of 1200 m2/g and average pore diameter varying between 20 and 80 nm. Mineralization of the aqueous PS nano suspensions in a water-in-oil emulsion affords spherical NF with average diameter of 40 μm and control of pore size. The methylalumoxane- (MAO-) tethered NF immobilizes single-site catalysts such as metallocene (nBuZr), bisiminopyridine iron(II) (Fe) and constrained geometry chinolyl cyclopentadienyl chromium(III) complexes (Cr-1). Immobilization of binary blends of Fe/Cr-1 and nBuZr/Cr-1 affords NF-supported dual-site catalysts. The catalyst activity, PE particle size and molecular weight distribution varies as a function of the NF pore size. Typically, macroporous NF (pore size of 75 nm) are effective supports for Cr-1, producing ultrahigh molecular weight polyethylene (UHMWPE, Mw > 106 g/mol). Dual -site catalysts such as nBuZr/Cr-1 on mesoporous NF (pore size of 20 nm) enable tailoring of bimodal PE molar mass distribution with UHMWPE content increasing with increasing Cr-1/nBuZr molar ratio.
This document is the Accepted Manuscript version of a Published Work that appeared in final form in
Macromolocules, copyright © American Chemical Society after peer review and technical editing by the publisher.
To access the final edited and published work see: http://dx.doi.org/10.1021/ma200667m
The catalytic cracking of HDPE (high density polyethylene) at 500 °C using a spent FCC catalyst agglomerated with bentonite (50 wt %) has been studied in a conical spouted bed reactor. The reaction is carried out in continuous regime (1 g min–1 of HDPE is fed) with no bed defluidization problems. The results obtained, namely, total conversion, and high yields of gasoline (C5–C11 fraction) (50 wt %) and C2–C4 olefins (28 wt %), are explained by favorable reactor conditions and good catalyst properties. These results are compared with those for a catalyst prepared in the laboratory by agglomerating a commercial HY zeolite (SiO2/Al2O3 = 5.2). The conical spouted bed is a suitable reactor for enhancing the physical steps of melting the polymer and coating the catalyst with the melted polymer. Furthermore, high heat and mass transfer rates promote devolatilization, and short residence times minimize secondary reactions from olefins by enhancing primary cracking products. The meso- and macroporous structure of the spent FCC catalyst matrix enhances the diffusion of long polymer chains, whereas the zeolite crystals have micropores that give a proper shape selectivity to form the lumps of gasoline and light olefins. Because of long use in reaction–regeneration cycles, the moderate acidity of the spent FCC catalyst minimizes the secondary reactions of hydrogen transfer, and so restricts the formation of aromatics and paraffins, as well as the reactions of overcracking and condensation and, therefore, the coke formation. The spent FCC catalyst exhibits a low deactivation rate and is regenerable by coke combustion with air at 550 °C. Consequently, the use of a catalyst with the sole cost of a simple agglomeration and the production of value added product streams make the process of polyolefin catalytic cracking a promising option for refinery integration.
The present review is aimed at exploring the field of the catalytic cracking of polyolefins over solid acids, focusing on the role played by the catalysts toward the synthesis of fuels and chemicals as well as on the reaction systems currently used. Initially, conventional solid acids, such as micrometer sized crystal zeolites and silica–alumina, were used to establish the relationship among their activity, selectivity, and deactivation in the polyolefin cracking and the inherent properties of the catalysts (acidity, pore structure); however, the occurrence of steric and diffusional hindrances for entering the zeolite micropores posed by the bulky nature of the polyolefins highlighted the importance of having easily accessible acid sites, either through mesopores or by a high external surface area. This fact led toward the investigation of mesoporous materials (Al-MCM-41, Al-SBA-15) and nanozeolites, which allowed increasing the catalytic activities, especially for the case of polypropylene. Further advances have come by the application of hierarchical zeolites whose bimodal micropore–mesopore size distribution has turned them into the most active catalysts for polymer cracking. In this regard, hierarchical zeolites may be regarded as a clear breakthrough, and it is expected that future research on them will bring new achievements in the field of catalytic cracking of polyolefins. In addition, other materials with high accessibility toward the active sites, such as extra-large pore zeolites, delaminated zeolites, or pillared zeolite nanosheets, can also be considered potentially promising catalysts. From a commercial point of view, two-step processes seem to be the most feasible option, including a combination of thermal treatments with subsequent catalytic conversion and reforming, which allows the catalytic activity to be preserved against different types of deactivation.
Photocatalytic reduction of CO2 into hydrocarbon fuels, an artificial photosynthesis, is based on the simulation of natural photosynthesis in green plants, whereby O2 and carbohydrates are produced from H2O and CO2 using sunlight as an energy source. It couples the reductive half-reaction of CO2 fixation with a matched oxidative half-reaction such as water oxidation, to achieve a carbon neutral cycle, which is like killing two birds with one stone in terms of saving the environment and supplying future energy. The present review provides an overview and highlights recent state-of-the-art accomplishments of overcoming the drawback of low photoconversion efficiency and selectivity through the design of highly active photocatalysts from the point of adsorption of reactants, charge separation and transport, light harvesting, and CO2 activation. It specifically includes: i) band-structure engineering, ii) nanostructuralization, iii) surface oxygen vacancy engineering, iv) macro-/meso-/microporous structuralization, v) exposed facet engineering, vi) co-catalysts, vii) the development of a Z-scheme system. The challenges and prospects for future development of this field are also present.
This review highlights recent developments and future perspectives in carbon dioxide usage for the sustainable production of energy and chemicals and to reduce global warming. We discuss the heterogeneously catalysed hydrogenation, as well as the photocatalytic and electrocatalytic conversion of CO2 to hydrocarbons or oxygenates. Various sources of hydrogen are also reviewed in terms of their CO2 neutrality. Technologies have been developed for large-scale CO2 hydrogenation to methanol or methane. Their industrial application is, however, limited by the high price of renewable hydrogen and the availability of large-volume sources of pure CO2. With regard to the direct electrocatalytic reduction of CO2 to value-added chemicals, substantial advances in electrodes, electrolyte, and reactor design are still required to permit the development of commercial processes. Therefore, in this review particular attention is paid to (i) the design of metal electrodes to improve their performance and (ii) recent developments of alternative approaches such as the application of ionic liquids as electrolytes and of microorganisms as co-catalysts. The most significant improvements both in catalyst and reactor design are needed for the photocatalytic functionalisation of CO2 to become a viable technology that can help in the usage of CO2 as a feedstock for the production of energy and chemicals. Apart from technological aspects and catalytic performance, we also discuss fundamental strategies for the rational design of materials for effective transformations of CO2 to value-added chemicals with the help of H2, electricity and/or light.