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High energy absorption efficiency and biodegradable polymer based microcellular materials via environmental-friendly CO2 foaming for disposable cushioning packaging
This study explores the potential of using a composite material made of polylactic acid (PLA), polybutylene adipate‐co‐terephthalate (PBAT), and rice husk (RH) as an alternative for food containers. Two blends with 10 wt%–20 wt% of PBAT and four composites with 10 wt%–20 wt% of RH reinforcement are evaluated. The composite is created using an internal mixer and is analyzed using torque vs time mixing curves, melt flow index (MFI), thermogravimetric analysis, and differential scanning calorimetry (DSC). The blends exhibit higher crystallinity and superior mechanical properties compared to composites. Adding RH improves sustainability and decreases costs by utilizing agricultural waste but reduces flexural strength. However, the addition of PBAT increases flexibility, making it suitable for pliable material applications. The composite CO4 with 20 wt% of PBAT and RH demonstrates balanced performance in terms of lower MFI, thermal stability, and flexural strength, making it suitable for food tray applications. Further studies are needed to optimize the mechanical and barrier properties of these composites for specific applications.
This study investigates the cell structure control in 50% thermoplastic polyurethane (TPU) and 50% acrylonitrile butadiene styrene (ABS) blend foam using CO 2 as a physical blowing agent, focusing on the effects of variable foaming parameters on the microstructure. Samples measuring 25 × 25 × 1 mm were produced and analyzed for foam structure. The foaming process involved saturating the samples with CO 2 gas at pressures of 4, 5.5, and 7 MPa, followed by rapid pressure release and immersion in a hot glycerol bath. The foaming parameters included varied temperatures (80, 90, and 120°C) and times (5–80 s). Scanning electron microscope (SEM) analysis provided data on cell size and density. Results indicated that increasing the saturation pressure enhanced CO 2 uptake in the ABS/TPU blend, with the CO 2 uptake rate peaking early in the process. Higher foaming temperatures and extended foaming times led to increased cell size, cell density, and expansion ratio. These findings highlight the significant role of process parameters in controlling the cell structure of ABS/TPU blend foams, offering valuable insights into optimizing foam properties for industrial applications.
Highlights
Optimization of foam parameters leads to cell structure control in ABS/TPU composite foams for industrial applications.
Increasing saturation pressure significantly boosts CO 2 uptake in ABS/TPU composite foams.
Increasing the foaming temperature and duration leads to larger cell sizes, higher cell density, and greater expansion ratios in ABS/TPU composite foams.
A molded expanded polystyrene (EPS) cushion is a flexible, closed-cell foam that can be molded to fit any packing application and is effective at absorbing shock. However, the packaging waste of EPS cushions causes pollution to landfills and the environment. Despite being known to cause pollution, this sustainable packaging actually has the potential to reduce this environmental pollution because of its reusability. Therefore, the objective of this study is to identify the accurate design parameter that can be emphasized in producing a sustainable design of EPS cushion packaging. An experimental method of drop testing and design simulation analysis was conducted. The effectiveness of the design parameters was also verified. Based on the results, there are four main elements that necessitate careful consideration: rib positioning, EPS cushion thickness, package layout, and packing size. These parameter findings make a significant contribution to sustainable design, where these elements were integrated directly to reduce and reuse packaging material. Thus, it has been concluded that 48 percent of the development cost of the cushion was decreased, 25 percent of mold modification time was significantly saved, and 27 percent of carbon dioxide (CO₂) reduction was identified. The findings also aided in the development of productive packaging design, in which these design elements were beneficial to reduce environmental impact. These findings had a significant impact on the manufacturing industry in terms of the economics and time of the molded expanded polystyrene packaging development.
The preparation of biodegradable polymer foams with a stable high volume-expansion ratio (VER) is challenging. For example, poly (butylene adipate-co-terephthalate) (PBAT) foams have a low melt strength and high shrinkage. In this study, polylactic acid (PLA), which has a high VER and crystallinity, was added to PBAT to reduce shrinkage during the supercritical molded-bead foaming process. The epoxy chain extender ADR4368 was used both as a chain extender and a compatibilizer to mitigate the linear chain structure and incompatibility and improve the foamability of PBAT. The branched-chain structure increased the energy-storage modulus (G’) and complex viscosity (η*), which are the key factors for the growth of cells, by 1–2 orders of magnitude. Subsequently, we innovatively used the CO2 and N2 composite gas method. The foam-shrinkage performance was further inhibited; the final foam had a VER of 23.39 and a stable cell was obtained. Finally, after steam forming, the results showed that the mechanical strength of the PBAT/PLA blended composite foam was considerably improved by the addition of PLA. The compressive strength (50%), bending strength, and fracture load by bending reached 270.23 kPa, 0.36 MPa, and 23.32 N, respectively. This study provides a potential strategy for the development of PBAT-based foam packaging materials with stable cell structure, high VER, and excellent mechanical strength.
Foam materials are widely used in packaging and buildings for thermal insulation, sound absorption, shock absorption, and other functions. They are dominated by petroleum‐based plastics, most of which, however, are not biodegradable nor fire‐proofing, leading to severe plastic pollution and safety concerns. Here, a fire‐proofing, thermally insulating, recyclable 3D graphite‐cellulose nanofiber (G‐CNF) foam fabricated from resource‐abundant graphite and cellulose is reported. A freeze‐drying‐free and scalable ionic crosslinking method is developed to fabricate Cu²⁺ ionic crosslinked G‐CNF (Cu‐G‐CNF) foam with a low energy consumption and cost. Moreover, the direct foam formation strategy enables local foam manufacturing to fulfil the local demand. The ionic crosslinked G‐CNF foam demonstrates excellent water stability (the foam can maintain mechanical robustness even in wet state and recover after being dried in air without deformation), fire resistance (41.7 kW m⁻² vs 214.3 kW m⁻² in the peak value of heat release rate) and a low thermal conductivity (0.05 W/(mK)), without compromising the recyclability, degradability, and mechanical performance of the composite foam. The demonstrated 3D G‐CNF foam can potentially replace the commercial plastic‐based foam materials, representing a sustainable solution against the “white pollution”.
The development of degradable plastic foams is in line with the current development concept of being pollution free and sustainable. Poly(lactic acid) (PLA) microporous foam with biodegradability, good heat resistance, biocompatibility, and mechanical properties can be successfully applied in cushioning packaging, heat insulation, noise reduction, filtration and adsorption, tissue engineering, and other fields. This paper summarizes and critically evaluates the latest research on preparing PLA microporous materials by supercritical carbon dioxide (scCO2) physical foaming since 2020. This paper first introduces the scCO2 foaming technologies for PLA and its composite foams, discusses the CO2-assisted foaming processes, and analyzes the effects of process parameters on PLA foaming. After that, the paper reviews the effects of modification methods such as chemical modification, filler filling, and mixing on the rheological and crystallization behaviors of PLA and provides an in-depth analysis of the mechanism of PLA foaming behavior to provide theoretical guidance for future research on PLA foaming. Lastly, the development and applications of PLA microporous materials based on scCO2 foaming technologies are prospected.
Starch/PBAT blends were reactively extruded as masterbatch with the addition of tartaric acid (TA) and epoxide chain extender ADR4468 (ADR). The effects of tartaric acid and chain extender on the mechanical properties and structure of starch/PBAT blends were evaluated. The tensile strength of starch/PBAT blends with TA and TA/ADR increased by 31.4% and 85.6%, respectively. Further, starch, plasticizer, and blowing agent were melt extruded with this blend masterbatch, and the effects of masterbatch on the foamability, morphology, and properties of starch foams were investigated. When the masterbatch content was 10 phr, the obtained foam had the lowest apparent density (445.1 kg m⁻³), and the compressive strength, recovery, and water resistance of the foam were also improved significantly.
Starch and its derivatives have recently emerged as a sustainable and renewable alternative for petroleum-based expanded polystyrene (EPS) and expanded polypropylene (EPP) foam materials. In this study, biodegradable foam materials were prepared from cassava starch using a novel dual modification technique, combining microwave treatment and freeze-drying. The foam materials were prepared from starch solutions microwaved over different intervals. The starch-based foam materials were characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), 13C nuclear magnetic resonance (13C-NMR) spectroscopy, and compression set test. Moreover, the water absorption capacities and density values of the foam materials were measured according to ASTM standards. The biodegradability test was carried out according to the aerobic compost environment test. The lowest water absorption capacities of 65.56% and 70.83% were exhibited for the cassava starch foam sample (MWB) prepared at a 20 s microwave treatment time and immersed in distilled water for 2 and 24 h, respectively. Furthermore, the lightweight cassava starch-based foam materials displayed density ranging from 124 to 245 kg/m3. The biodegradation test exhibited significant biodegradation of over 50% after 15 days for all the foam materials prepared. These results suggest that the dual-modified cassava starch-based biodegradable foams show potential in sustainable packaging applications by replacing petroleum-based materials.
Wet foam can be used as a carrier in the manufacturing of lightweight materials based on natural and man-made fibers and specific additives. Using a foam forming method and cellulose fibers, it is possible to produce the porous materials with large area of end-using such as protective and cushioning packaging, filtering, hydroponic, thermal and sound absorption insulation, or other building materials. In comparison with the water-forming used for conventional paper products, foam-forming method provides many advantages. In particular, since fibers inside the foam are mostly trapped between the foam bubbles, the formed materials have an excellent homogeneity. This allows for using long fibers and a high consistency in head box without significant fiber flocking. As result, important savings in water and energy consumptions for dewatering and drying of the foam formed materials are obtained. In cushioning packaging, foam-formed cellulose materials have their specific advantages comparing to other biodegradable packaging (corrugated board, molded pulp) and can be a sustainable alternative to existing synthetic foams (i.e., expanded polystyrene or polyurethane foams). This review discusses the technical parameters to be controlled during foam forming of cellulose materials to ensure their performances as cushioning and protective packaging. The focus was on the identification of practical solutions to compensate the strength decreasing caused by reduced density and low resistance to water of foam formed cellulose materials.
Due to extensive concerns of tremendous environment pollutions, particularly microplastic as an emerging pollutant, the development and investigate on biodegradable polymer foams raised growing interest and revealed promising application prospects. In this work, carbon nanotubes (CNTs) and graphene nanosheets (GNPs) were introduced into poly (butylene adipate-co-terephthalate) (PBAT) foams to develop micro-nano bimodal cellular structure (BCS) using a supercritical CO2 foaming approach. CNTs and GNPs (CG) network structures were formed in PBAT/CNTs/GNPs nanocomposites by the gradual addition of CG, which made a significant enhancement on their melt viscoelasticity. Systematically, the effect of CG content and foaming temperature on the PBAT cellular structure were investigated. As the CG content increased, BCS was steadily formed in the PBAT/CG foams, meanwhile, their cell size decreased. At last, the generation mechanism of BCS in different PBAT/CG foams was explored.
The use of polymer foams is becoming increasingly important due to the attainable weight reduction and value‐added properties. The development of foam structures is a popular research area as they have outstanding energy absorbing capability, which is related to the special deformation mechanisms of the cell structure (cell wall buckling and collapse of the cells). This property is exploited by the sports industry, where the main task of such products is to protect the health of the athlete and to ensure safe sports conditions. This review provides a comprehensive presentation of the advanced energy absorbing applications of polymeric foams in sports. The article presents in detail the processing technologies of polymer foams, as well as the sports‐specific regulations which contain the requirements for sports products. The impact damping of polymeric foams is typically determined by falling weight impact tests, which were used in several previous studies. However, it is a great challenge to compare the published results, as the test parameters and the tested materials are different. Currently, an unexplored field of research is the detailed study of multilayer sandwich foam structures. Understanding the effect of layer order on mechanical properties would help researchers achieve a major improvement in this field.
Developed a new technical solution for making cushioning packaging materials using greening waste as raw materials. Collect greening wastes that have been pruned or fallen off naturally in the city, crushed and sieved, and then alkalized to obtain crude cellulose powder. Through the addition of additives, the foaming is carried out in a microwave manner, and the buffering packaging material is finally made by drying treatment. The material has been verified by the test of cushioning characteristics, has excellent resilience and impact resistance, and is environmentally friendly and degradable. It can replace the non-degradable cushioning materials on the market, such as polystyrene foam (EPS), etc., to reduce environmental pollution.
With the enhancement of global environmental protection awareness, new eco-friendly packaging materials have gained more and more attention since the new century. Starch is one of the most potential natural biodegradable materials due to its abundant source, low price, and completely degradable characteristics. Starch-based materials with excellent biodegradability can be widely used by improving their properties. This review starts with the structure of starch and summarizes its phase transition during processing related to the packaging materials. Then, we expound on the development stage of starch-based biodegradable materials and starch modification. This part focuses on the research of starch-based composites formed by starch derivatives, including nano-starch. Besides, extrusion molding and other modern molding methods are described in detail. Through the systematic elaboration of the above contents, the connection among structure, phase transition, and processing can be found, which can better broaden the application of starch-based biodegradable materials. Finally, various applications of starch-based materials and prospects for its future research are discussed. It is hoped to provide the basic theory and reference for the research of starch-based biodegradable materials.
With the urgent need for the development of sustainable materials and a circular economy, a surge of research regarding biobased materials and associated processing methods has resulted in many experimental biobased foams. Although several biobased foams are already shown to have thermal and mechanical properties competitive with expanded polystyrene, there remains a fundamental knowledge gap leading to limited understanding of the principles that determine performance. This review outlines the progress in this burgeoning field, introducing materials selection and processing, comparing performance, examining efforts in modelling physical properties, and discusses challenges in applying models to real biobased systems. The focus is on low thermal conductivity, which is a critical property for temperature-controlled applications such as packaging for refrigerated/frozen foods, medications, and vaccines as well as building materials. Currently, the trend in the field is moving towards fully biobased and compostable foams, though partially biobased polyurethane foams remain the most consistent performers. To illustrate the foam structure-property relationship, thermal conductivity, cell size, and density data were compiled. Given the complexity of biobased foams, heat transfer models aid in identifying crucial variables. However, data relevant to the insulation capability of biobased foams is not fully reported in many references. To address this issue, we employed a dimensional analysis to fill the gaps, revealing a power law correlation between thermal conductivity and relative density. Our approach is not intended as a robust prediction technique, but rather a simple demonstration of how biobased foams data could be utilized to predict the most promising materials and methods.
Biodegradable composites with an open-cell structure were developed to replace petroleum-based buffer packaging materials. To overcome the problem of uneven and insufficient foam in the composites, CaCO3 was used as a nucleating agent to prepare porous composites. At 5 wt% CaCO3, more uniform and dense composite cells with better cushioning performance were obtained. A further increase in the CaCO3 content caused the density of the cells and the cushioning properties of the composites to decrease. The addition of CaCO3 improved the thermal stability and water barrier properties. The moisture absorption was reduced by 15%. X-ray diffraction analysis indicated that the addition of CaCO3 destroyed the crystalline structure of the starch and produced a new crystalline peak, resulting in a significant reduction in the crystallinity. The decrease in the crystallinity of the starch resulted in the formation of a homogeneous slurry that produced a uniform foam in the composites.
Algae has long been used as a food and a potential source of valuable and bioactive compounds due to residues left after the extraction process. Discovery of an alternative approach to the residues contributes to commercial feasibility in algae biorefinery. This study aimed to examine the cellulose composition in macroalgae. The physiochemical characteristics of cellulose and its potential use as a reinforcement to polyurethane (PU) foam were investigated. A green filamentous freshwater algal biomass composed of Cladophora sp. and Microspora sp. was treated via alkalization. The treated algae was use as a filler agent to synthesize PU-composite foams. Morphological, chemical, mechanical, physiochemical and viscoelastic properties of cellulose and PU-composite foam were investigated through field emission scanning electron microscopy (FESEM), Fourier-transform in-frared spectroscopy (FTIR), thermal gravimetric analysis (TGA), X-ray diffraction (XRD) compressive tests, and dynamic mechanical analysis (DMA). A cellulose yield of 37.2% was obtained from Kai algae via alkalization and the crystallinity index was 63.6%. The use of algae and algal cellulose to synthesize PU-composites resulted in foam density increase, while the compressive modulus decreased. The addition of algal cellulose as filler in PU foam significantly reduced the cell size of foam. Using algae at 0.5% (w/v) and algal cellulose at 1.0% (w/v) as filler in PU-composites increased stiffness at 25-50°C and transition temperature and decreased loss modulus. These results indicated that algae and algal cellulose added during PU-composite foam production may be integrated into the foam structure and result in more open cells and softer foam. The PU-composite showed greater shock absorbent capacity than PU foam. The results provided a new alternative approach in algal cell residue utilization in terms of material, which could be useful for the packaging industry.
Polymeric materials produced from petroleum resources are not biodegradable. Because they defy degradation, they end up in the landfills and damage the environment. Synthesized biodegradable polymeric materials (BPMs) have received increasing interest owing to the difficulty in procuring reproducibility when using natural polymeric materials. Modification of natural polymeric materials or via chemical,
microbiological, enzymes mediated and chemo-enzymatic synthesis, a comprehensive range of variegated BPMs can be reaped. Amended natural polymeric materials like starch, cellulose, chitin upshot with enhanced properties, whilst synthetic BPMs like PLA, PGA, PCL, PDS, PLGA are explicitly designed to pursue its coveted applications in multifarious domains, on the whole diagnostics and therapeutics. Synthesized BPMs can be embedded with tailored characteristics to justify the neoteric entails of mankind.
Polymer foams have low density, good heat insulation, good sound insulation effects, high specific strength, and high corrosion resistance, and are widely used in civil and industrial applications. In this paper, the classification of polymer foams, principles of the foaming process, types of blowing agents, and raw materials of polymer foams are reviewed. The research progress of various foaming methods and the current problems and possible solutions are discussed in detail.
In this work, a high-magnification extrusion-foaming technique for biomass-based biodegradable composite materials using water vaporization was examined. Starch was selected as the biomass and polylactic acid was selected as a biodegradable matrix resin. No additional plasticizer or additives were used in this extrusion-foaming process. The foaming ratio was deduced according to the conditions of the extrusion-foaming process to confirm the forming characteristics of the foaming materials. Scanning electron microscopy was performed to examine the morphology of the composite foam. To investigate the potential of the foam cushion as an ecofriendly packing material, we conducted experiments on its static compression and dynamic cushioning properties and examined whether its biodegradability could be controlled by varying the mixing ratio of the materials. Thus, we developed a water-foaming process that is ecofriendly and whose products can be recycled as compost after use.
In the present work, foamed polypropylene (PP) composites were prepared by chemical foaming technology, and the foaming quality and impact property of the foamed PP composites were studied. The results showed that the foaming quality was significantly improved after the introduction of thermoplastic rubber (TPR) and polyolefin elastomer (POE). Meanwhile, it was found that the impact property depended on the intrinsic toughness and contribution of foams (cells) to the PP composites. Furthermore, the data regarding impact property in low temperature showed that when the temperature was between −80 and −20 °C, the impact properties of the foamed PP composites were higher than that of the unfoamed sample, which was due to the impact property being completely contributed by cells under this condition. Meanwhile, when the temperature ranged from −20 to 20 °C, the impact property of the unfoamed sample was higher, which was due to the PP matrix contributing more to the impact property under this temperature. This work significantly improved the foaming quality of foamed PP composites and provided reliable evidence for the improvement of impact property.
Currently, the fabrication of microcellular semicrystalline polymer foam using supercritical CO2 as a blowing agent constitutes a worldwide interest. In this work, a facile approach of chain extension and batch foaming was proposed to prepare microcellular semicrystalline poly (butylene adipate‐co‐terephthalate) (PBAT) foam using CO2 as a physical blowing agent. With the introduction of chain extender (CE), the weight‐average molecular weight and gel fraction of PBAT samples increased; their crystallization temperature increased from 74.2 to 86.9 °C and their viscoelasticity was improved greatly. Microcellular PBAT foams with the cell size <4 μm and the cell density more than 10¹⁰ cells cm⁻³ were fabricated successfully. With increasing concentration of CE, the cell density and volume expansion ratio (VER) of various PBAT foams increased from 3.4 × 10¹⁰ to 8.7 × 10¹⁰ cells cm⁻³ and from 1.5 to 2.0 times, respectively. With increasing foaming temperature, the cell size and VER increased and the cell density decreased. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47322.
The melt strength of poly(lactic acid) (PLA) is an important factor in preparing foams and blowing films. Aiming to endow PLA with a suitable melt strength via a slight crosslink, a superficial micro-crosslinking method was introduced in which the PLA feed was mixed with benzoyl peroxide (BPO) and crosslinked in a 100 °C oven for 1 h. Additionally, poly(butyleneadipate-co-terephthalate) (PBAT) was blended with the crosslinked PLA (C-PLA) to further improve melt strength and viscosity. The blend foams were prepared using a single-screw extruder and azodicarbonamide as a foaming agent. The properties were characterized by gel fraction, melt flow rate (MFR), rheometry, DSC and SEM. The rheological results showed that the complex viscosity and storage modulus of C-PLA and C-PLA/PBAT blends increased, attributed to the micro-crosslinking and addition of PBAT and indicating an improvement in melt strength. Furthermore, the crystallization of modified PLA was also enhanced. Compared with pure PLA foams, the C-PLA/PBAT blend foams showed larger cells with more uniform shapes and homogenous distribution. This approach to improve the melt strength of polymers with micro-crosslinking and blending with PBAT represents an attractive method for preparing foams with regular cells.
Considering that environmental friendliness and energy conservation are becoming crucial, it is urgent to advance the sustainability of materials in terms of their lifecycle, including synthesis, processing, and application. Herein, covalent adaptable networks were constructed in a polyethylene terephthalate (PET) matrix via a green, external-catalyst-free method within only 8 min, which was realized by sequential transesterification and crosslinking reaction. This synthesis is environmentally friendly given that no toxic solvents or external catalysts are required, and it avoids energy waste. Meanwhile, the vitrimer exhibited an extremely fast relaxation time of 4.8 s, which was realized through the synergistic catalysis of the tertiary amine structure and neighboring group participation. Therefore, the vitrimer could readily change its configuration via fast exchange reactions during processing, which eliminated the residual stress and suppressed the molecular-chain orientation, avoiding shrinkage and warpage. Further, the vitrimer has potential sustainable applications in repairability and shape memory, where on the one hand, due to its stable state resulting from configuration-change foaming processing, the vitrimer foam has attractive self-healing behavior, which is the first time this is reported for foam materials, whereas other foams tend to shrink in the melt state, and hence fail to realize self-healing. On the other hand, due to the quick rearrangement of the crosslinking networks, the obtained vitrimer could be rapidly shape-programmed repeatedly, where its shape-memory behavior could be strengthened or erased by the synergistic effects of its covalent adaptable networks and physical crystalline networks, making it more regulable and concealed in encryption application. Briefly, the synthesis, processing, and application of this vitrimer are constructive to guide the design of novel polymers with improved performance and sustainability.
We developed an image processing algorithm and applied it on high-speed camera recordings to characterize the deformation response of three-layered density-graded foam structures subjected to drop weight testing. Different densities (30, 40, 50 and 70 kg/m3) of weakly cross-linked polyethylene foam sheets were laminated together to achieve varying density distributions along the thickness, and the effect of layer order on the shock absorption capability was evaluated. Foam structures with a higher density top layer and a negative density gradient showed enhanced energy absorption in the initial stage of deformation, which resulted in lower maximum reaction forces. The positive effect of layer order modification was more dominant at higher impact energies. We provided a detailed explanation of the tendencies by investigating the differences in deformation propagation and the changes in the diameter of the deformation zone. The presented method can be utilized to design sports and packaging foam products.
Heavy reliance on petrochemical-based plastic foams in both industry and society has led to severe plastic pollution (the so-called "white pollution"). In this work, we develop a biodegradable, recyclable, and sustainable cellulose/ bentonite (Cel/BT) foam material directly from resource-abundant natural materials (i.e., lignocellulosic biomass and minerals) via ambient drying. The strong resistance to the capillary force-driven structural collapse of the preformed three-dimensional (3D) network during the ambient drying process can be ascribed to the purpose-designed cellulose− bentonite coordination interaction, which provides a practical way for the locally scalable production of foam materials with designed shapes without complex processing and intensive energy consumption. Benefiting from the strong cellulose−bentonite coordination interaction, the Cel/BT foam material demonstrates high mechanical strength and outstanding thermal stability, outperforming commercial plastic polystyrene foam. Furthermore, the Cel/BT foam presents environmental impacts much lower than those of petrochemical-based plastic foams as it can be 100% recycled in a closed-loop recycling process and easily biodegraded in the environment (natural cellulose goes back to the carbon cycle, and bentonite minerals return to the geological cycle). This study demonstrates an energy-efficient ambient drying approach for the local and scalable production of an all-natural cellulose/bentonite foam for sustainable packaging, buildings, and beyond, presenting great potential in response to "white pollution" and resource shortage.
Because of its rather low melt strength, polylactide (PLA) has yet to fulfill its promise as advanced biobased and biodegradable foams to replace fossil-based polymer foams. In this work, PLA vitrimers were prepared by two-step reactive processing from commercial PLA thermoplastics, glycerol, and diphenylmethane diisocyanate (MDI) using Zn(II)-catalyzed addition and transesterification chemistry. The transesterification reaction of PLA and glycerol occurs with zinc acetate as the catalyst, and chain scission will take place due to the alcoholysis of the PLA chains by the free hydroxyl groups from the glycerol. Long-chain PLA with hydroxyl groups can be obtained and then cross-linked with MDI. Rheological analysis shows that the formed cross-linked network can significantly improve melt strength and promote strain hardening under extensional flow. PLA vitrimers still maintain the ability of thermoplastic processing via extrusion and compression. The enhanced melt strength and the rearrangement of network topology facilitate the foaming processing. An expansion ratio as large as 49.2-fold and microcellular foam with a uniform cell morphology can be obtained for PLA vitrimers with a gel fraction of 51.8% through a supercritical carbon dioxide foaming technique. This work provides a new way with the scale-up possibility to enhance the melt strength of PLA, and the broadened range of PLA applicability brought by PLA vitrimers is truly valuable in terms of the realization of a sustainable society.
Packaging with plastic films is the most common preservation technique used to extend the shelf life of shiitake mushrooms. However, due to ‘white pollution’, it is essential to develop biodegradable films with efficient preservation properties. Here, the effects of biodegradable polybutylene adipate (PBAT)/poly(lactic acid) (PLA) blend films on the quality of shiitake mushrooms were investigated. The mushrooms were stored for 14 days at 4 ± 1 ℃. The results showed lower CO2 level inside the PBAT/PLA film, but the O2 level was comparable to that in low-density polyethylene (LDPE) package. PBAT/PLA treatment effectively prevented condensation of water vapor inside the package, and could significantly (p < 0.05) slow down the respiration rate, inhibit caps opening, improve phenolic contents and PAL activity, maintain firmness as well as delay senescence. In addition, due to the suitable relative humidity inside the PBAT/PLA film, it was more effective in reducing microbial counts and preserving the appearance of the shiitake mushrooms, thus extending more than 4–6 days of shelf life compared to the LDPE film. These results suggested that besides the in-package gas composition, it is also important to control the level of water vapor permeability to avoid condensation and decelerate degradation of packaged fresh shiitake mushroom. This environmental-friendly PBAT/PLA film exhibited high versatility in shiitake mushroom packaging.
Microelectronic is developing towards high frequency (GHz) and high speed (Gpbs), putting forward high requirements for low dielectric materials. The most efficient method for fabricating low dielectric materials is the incorporation of air into matrix via supercritical CO2 foaming. Herein, a low dielectric thermoplastic perfluorinated polymer is selected to be the matrix and another low dielectric perfluorinated polymer which is capable to form in-situ nanofibrils is selected to regulate the matrix viscoelasticity. Supercritical CO2 foaming method is then applied to introduce a large amount of low dielectric air into nanofibrill modified perfluorinated polymer. Owing to supercritical CO2 as a residue-free foaming agent (residue impurities in matrix originated from foaming agent would increase dielectric loss significantly at GHz) and its strong interaction with perfluorinated polymer (ensure large expansion ratio of the obtained foams to introduce a large amount of low dielectric air in matrix), the lowest dielectric loss of 0.00015 (among the existing polymeric materials) is then obtained by supercritical CO2 foaming of in-situ nanofibril modified perfluorinated polymer. Furthermore, the hydrophobic and oilphobic properties of the perfluorinated polymer were enhanced by supercritical CO2 foaming to form a cellular structure; simultaneously, the corrosion resistance to strong alkali and V0 flame retarding properties of the ultra-low dielectric foam were maintained resulted from the perfluorinated cell walls. Therefore, such superior comprehensive performance of this ultra-low dielectric perfluorinated foam made from supercritical CO2 foaming enables it the best alternative for the next-generation high-frequency (GHz to THz) and high-speed (sub Tbps) signal transmission substrate in electronics.
Expanded polypropylene (EPP) foam, is widely used in the field of packaging, automotive and toys, etc., and its preparation process is mainly obtained by semi-continuous autoclave bead foaming. Because foamed beads can be fabricated into complex 3D components and have excellent structural controllability. In contrast, a novel method for continuous production of expanded PP foamed beads is developed via supercritical CO2 (scCO2) extrusion foaming coupling with a wind cutting device, then the real-time cell growth and pelletizing processes of the extruded bead foams are revealed by using a high-definition camera for the first time. Interestingly, the processes of solubilization, compounding, pelletizing and foaming can happen in a one-step process through the above method, which can greatly shorten the production time, save energy consumption, and promote structural diversification. Besides, the transformation of foamed beads, like spherical, cylindrical and dumbbell-shaped, can be achieved by adjusting the pelletizing speeds based on the Barus effect. Furthermore, the steam-chest molding of the extruded foamed beads into foamed product shows that it is possible to sinter the beads at a low steam pressure (2.0 bar). In addition, the as-prepared foamed products can withstand constantly treading by an adult, and the surface of the foamed product rises only ~7.5 °C after prolonged heating, illustrating the outstanding mechanical and thermal insulation properties. Finally, it can be imagined that the related technical route has important scientific significance for the development of other polymeric bead foaming systems.
Polyester as the most produced thermoplastic after polyolefin, an urgent issue is to strengthen its environmentally friendly characteristic in processing, application, and recycling. However, the performance of polyester would significantly...
Foams with excellent mechanical performance are extremely valuable, as playing a key role in structural materials. However, it is still a significant challenge to simultaneously strengthen and toughen foam materials. In this work, a novel strategy combining nano-fibrillation network and supercritical carbon dioxide (scCO2) solid-state foaming was proposed as follows: 1) In designing micro-scale cellular structure, chain extension and fibrillation technologies were synergistically adopted to improve the matrix viscoelasticity for cell stability, scCO2 solid-sate foaming was then adopted to improve cell nucleation and cell growth. The combination of the above technologies helps to obtain a microcellular foam with large expansion ratio and small cell size; 2) In designing nano-scale hierarchical structure of crystalline and multiphase, flexible fibrils were dispersed in cell walls to compensate for matrix's brittleness and hence increased the foam impact strength, the crystals in cell walls improved the bending strength of cell walls and hence increased the foam compression strength. Herein, the obtained microcellular foam has simultaneous improvements in compression strength from 1.7 MPa to 2.7 MPa and impact toughness from 0.26 KJ/m² to 0.46 KJ/m² while maintaining a low foam density of 0.13 g/cm³.
Ultra‐low density nitrile butadiene rubber (NBR)/polyvinyl chloride (PVC) composite foams that exhibit satisfactory compressive behavior and energy absorption characteristics were prepared by one‐step compression molding. The properties of the NBR/PVC foams, including the density, hardness, cell morphology, compressive behavior, energy absorption characteristics, and shock absorption characteristics, were studied with various concentrations of azodicarbonamide (AC). Further that, the ideality factor and the energy absorption efficiency of the NBR/PVC foams at a low stress for application in compression and energy absorption were determined. The results revealed that the densities of polymeric foams were crucial in determining the uniformity of cell size and energy absorption characteristics of the composite foams. With increasing AC content, the density of the NBR/PVC foams decreased linearly, whereas the uniformity of cell size and the foaming ratio increased; furthermore, the hardness and compression modulus gradually decreased, and the linear elastic region in the compressive stress–strain curves became narrow. When the applied stress was less than 100 kPa, the foams with a high AC content exhibited higher energy absorption compared to foams with a low AC content capacity because of the deformed cell wall and lower elastic modulus; however, the relation between AC contents and energy absorption was complicated above 100 kPa. The optimum springrate ratio was found at the concentration of 25 phr of the AC blowing agent. Ultra‐low density NBR/PVC foam with high cell quality, well compressive behavior, and energy absorption characteristics was successfully fabricated. The effects of AC agent content on properties of the NBR/PVC foams, particularly compressive behavior and energy absorption characteristics, were thoroughly investigated.
Poly (butylene adipate-co-terephthalate) (PBAT) foams display serious shrinkage problems when supercritical CO2 is utilized as the blowing agent. In this work, a series of fully biodegradable PBAT/polybutylene succinate (PBS) foams were prepared by using supercritical CO2. The introduction of PBS improves the mechanical and crystallization properties. In the foaming process, PBS causes the deterioration of melt strength, promotes the cell nucleation, and decreases the cell wall thickness, facilitating the formation of open-cell structure. Owing to the synergistic effect of the increased open-cell content and the improvement of stiffness, 80/20 blend of PBAT and PBS exhibited the highest expansion ratio of 18.4 without shrinkage. PBS plays multiple essential roles in the foaming and shrinking process with CO2 green blowing agent, providing a widely applicable anti-shrinkage strategy, which also affords shed light upon the large-scale preparation of the biodegradable polyester foams.
Due to abundant disposable insulation materials causing serious environmental problem, degradable poly (butylene adipate-co-terephthalate) (PBAT) foam is a solution. To enhance the degradation rate and improve supercritical foaming for PBAT, poly (butylene succinate) (PBS) was selected in this work to blend with PBAT. PBAT/PBS foam with foam density lower than 0.1 g/cm³ and cell size smaller than 40 μm was successfully obtained, whose thermal conductivity was only 34 mW/m·K and specific compressive strength was over 3000 N·m/kg with an extremely fast degradation rate (97% material degraded within 10 days). The designation strategy is as follows: PBS’s fully aliphatic hydrocarbon structure ensures faster degradation rate than PBAT; PBS’s better molecular chain regularity accelerates crystallization for PBAT/PBS blend which ensures larger strength for blend foams; crosslinking structure and micro-phase separation structure in PBAT/PBS blend ensures better cell growth and hence larger expansion ratio, that is better thermal insulation performance.
Petroleum-based polymers have served the packaging industry in numerous ways as films, pouches, rigid containers, foamed containers, and other components for food, medical, and other packaging applications. However growing concerns about environmental impact, awareness of greenhouse gas emission and their adverse effects, increased oil prices, and disposal and landfill issues are forcing researchers and the industry to develop sustainable packaging. Bio-based materials, those derived from biological sources rather than petroleum sources, are ideally suited to meet these new sustainability requirements. Although bio-based materials such as paper have been used for packaging extensively, packaging with increased functionality and performance is needed. Therefore, the movement toward sustainable packaging will include both improving current biobased packaging, and development of new biobased materials such as biopolymers. The aim of this mini review was to offer a summary of the current state of biobased packaging as well as provide insight into current and future trends of sustainable paper- and bioplastic-based materials for packaging industry.
Development of industrialization has brought convenience to people's lives; however, it has also brought serious harm to the environment, where, water pollution is the most obvious. Here, a polybutylene adipate terephthalate (PBAT) open-cell foam doped with iron-pillared bentonite (IPB) is prepared by using sugar as a pore-forming agent and solution phase separation, and then combined with a solution dipping method to coat the foam surface with a polyacrylamide/SiO2, which makes the PBAT foam superhydrophilic. The static adsorption effect of superhydrophilic IPB-doped PBAT open-cell foam on methylene blue (MB) and Cu²⁺ is studied. The adsorption isotherm fitting shows that the adsorption conforms to the Langmuir model and it has biased toward monolayer adsorption. The adsorption kinetics fitting confirms that the adsorption process is in line with the pseudo-second-order adsorption model, which is dominated by chemical adsorption. The modified PBAT open-cell foam has an adsorption effect on Cu²⁺; however, it has weak cyclic adsorption capacity. It shows a good cyclic adsorption ability for the cationic dye MB and it has >95% photodegradation efficiency of the MB after five time's cyclic adsorption. The superhydrophilicity makes the foam to have better applications in oil–water separation.
Fully biodegradable chain‐extended poly(butylene adipate‐co‐terephthalate) (CPBAT)/acetylated cellulose nanocrystals (ACNCs) nanocomposites were prepared by the melt compounding process. The dispersibility of CNCs in deionized water was improved through the surface acetylation, which was observed by atomic force microscope and transmission electron microscope. The chain extender was added to the PBAT matrix to improve the melt strength and viscoelasticity of PBAT. The ACNC nanoparticles which served as bionano‐reinforcing fillers were introduced into CPBAT to further improve the crystallization behaviors and rheological properties of CPBAT/ACNCs nanocomposites. Finally, the CPBAT/ACNCs nanocomposite foams were prepared via batch supercritical CO2 foaming process. The cell structure and morphology of various CPBAT/ACNCs foams were investigated by scanning electron microscope. It was found that the introduction of ACNC nanoparticles led to a reduction of cell size, an increase in cell density and in the uniform cell distribution owing to the heterogeneous cell nucleation effect of ACNCs. Meanwhile, the volume expansion ratio (VER) of CPBAT foams reached to 9.21 times, the highest VER reported for PBAT foam in the current literature. Also, the thermal conductive properties of nanocomposites and foams also were studied by a laser thermal conductivity analyzer. Schematic diagram for the fabrication process of various PBAT specimens.
This study investigates the influence of air bubbles inclusion on the foaming of water
blown and water-pentane blown rigid polyurethane and polyisocyanurate foams. It was
observed that, when a large number of air bubbles were included in the reacting
system during the mixing stage (fast mixing), no further bubble nucleation from water
reaction or pentane evaporation occurred. In this case, foam morphology was solely
dictated by the mixing stage and by later bubble coarsening. Instead, when no air
bubbles were included during mixing (slow mixing), nucleation of new bubbles from
CO2 (from water-isocyanate reaction) and pentane was observed. Furthermore, both
bubble coalescence and Ostwald ripening were observed as mechanisms responsible
for the foam morphology coarsening, the latter being less effective in the case of
polyisocyanurate foams.
Foaming behavior of thermoplastic polyurethane (TPU) is extremely difficult to be regulated due to the special microphase-separation structure. Therefore, organic montmorillonite (O-MMT) was applied in TPU foaming to regulate cell nucleation, growth and stabilization simultaneously: (1) strong interfacial interaction between O-MMT with TPU could not only facilitate O-MMTs’ nanoscale dispersion but also ensure a similar cell nucleation at various O-MMT loading, which effectively decoupled the complicated influences of cell nucleation and growth on TPU foam's shrinkage; (2) TPU/O-MMT topological network was constructed by O-MMT loading, regulating cell growth and corresponding decreasing cell size; (3) -OH group on O-MMT surface could hydrogen bond with TPU molecular chains in soft/hard segments, stabilizing TPU molecular chains and finally reducing foams' shrinkage. Combining hydrogen bonding and topological network resulted from O-MMT, it enables us to optimize TPU foam structure by controlling cell nucleation, growth and stabilization simultaneously, the optimal O-MMT loading was 1 wt%.
A combination of solution casting and melt extrusion technique was used to fabricate Boron nitride (BN)-filled Polylactic acid (PLA)/polybutylene adipate terephthalate (PBAT) blend composites. The BN particles were surface treated with a silane coupling agent and functionalization was confirmed via spectroscopic analysis. Field emission scanning electron microscopy confirmed that the BN surface treatment improved the particle adhesion with the polymer matrices and acted as a compatibilizer for the polymers. Moreover, changes in the particle orientation in the blend composite yielded improved thermal conductivity in different directions. The inclusion of the treated BN particles enhanced the in-plane (∼1.1 W m⁻¹k⁻¹) and through-plane (∼0.8 W m⁻¹k⁻¹) thermal conductivity of the composites as compared to the neat PLA. In addition, the storage modulus of the composite become more than 3 GPa that is twice that of the PLA/PBAT blend with a reasonable tensile property. In general, compared with the PLA/PBAT blend, the blend composites exhibited superior thermal and mechanical properties.
In this work, biodegradable starch/cellulose composite foams were fabricated at 220 °C by compression moulding gelatinised starch containing cellulose fibres as a reinforcing agent and citric acid as a cross-linking agent. It was found that the stiffness, tensile strength, flexural strength, and hydrophobicity of the starch/cellulose composite foams increased, and water absorption capacity decreased with an increase in the concentration of citric acid. The tensile strength increased from 1.76 MPa for 0 % citric acid to 2.25 MPa for the starch/cellulose composite foam crosslinked with 5 % (w/w) citric acid. Similarly, the flexural modulus also increased from 445 MPa to 601.1 MPa, and the flexural strength from 3.76 MPa to 7.61 MPa, for the composite foam crosslinked with 5 % (w/w) citric acid. The crosslinked composite foams showed better thermal stability compared to the non-crosslinked composite foam. The resulting composite foams could be used as a biodegradable alternative to expanded polystyrene packaging.
High-performance poly(lactic acid) (PLA) foam has been recognized as a promising material because of its biodegradability. However, low flexibility and foamability of PLAs has limited its use in different fields. In this study, a blend-toughening technology was used to toughen PLA and prepare flexible foams. The mechanical properties of PLA blends were evaluated, and the cellular structure of these foaming blends was characterized. The results show that the blending components significantly affected the overall mechanical properties and foaming behavior of PLA. The toughness of PLA was enhanced by adding poly(butylene adipate-co-terephthalate) (PBAT) and rigid particles. The rheological behavior of PLA was also affected by adding PBAT. Therefore, the cellular structure of the PLA foams was affected. A constitutive model was also used to fit the experimental results of the compression property of the PLA foam.
Nanocellulose has generated a great deal of interest as a source of nanometer-sized reinforcement, because of its good mechanical properties. In the last few years, nanocellulose has also attracted much attention due to environmental concerns. This review presents an overview of recent developments in this area, including the production, characterization, properties, and range of applications of nanocellulose-based biodegradable polymers, thermoplastic polymers, and porous nanocomposites. After explaining the unique properties of nanocellulose and its various preparation techniques, an orderly introduction of various nanocellulose-reinforced biodegradable polymers such as starch, proteins, alginate, chitosan, and gelatin is provided. Subsequently, the effects of nanocellulose on the properties of thermoplastic polymers such as polyamides, polysulfone, polypropyrol, and polyacronitril are reported. The paper concludes with a presentation of new finding and cutting-edge studies on nanocellulose foam and aerogel composites. Three different types of aerogels, i.e., pristine nanocellulose-based aerogels, modified nanocellulose-based aerogels, and nanocellulose-based templates for aerogels, are discussed, as well as their preparation techniques and properties. In the case of foam composites, the research focus has been on two major preparation techniques, i.e., solvent-mixing/foaming and melt-mixing foaming, their respective challenges, and the properties of the final composites. In some cases, a comparison study between cellulose nanocrystals and cellulose nanofiber-reinforced biodegradable polymers, thermoplastics, and porous nanocomposites was carried out. Considering the vast amount of research on nanocellulose-based composites, special emphasis on such composites isprovided at the end of the review.
A supercritical CO2 (scCO2) foaming technology was used to develop a PLA foam with a thermal conductivity as low as 30 mW/m-K. The PLA foam’s larger optimal expansion ratio and strong infrared (IR) block ability greatly helped to achieve this outcome. Unlike the PS foams, in which non-biodegradable carbon particles are often added to block the IR thermal radiation, the PLA foams’ intrinsic IR-absorbing characteristic, which acted via the ester group in the PLA molecular chain, further enhanced its environmental impact. Overall, environmentally-friendly PLA foams, made by using the non-toxic scCO2 foaming method, offer a sound alternative to PS foams.
There is growing interest in biodegradable polymers (BP), in particular poly(butylene adipate-co-terephthalate) (PBAT), due to environmental problems associated with the disposal of non-biodegradable polymers into the environment. However, high production cost and low thermo-mechanical properties restrict the use of this sustainable material, making its biodegradability advantageous only when it is decisively required. The addition of different compositions of monomers and selective addition of natural fillers have been reported as alternatives to develop more accessible PBAT-based bioplastics with performance that could match or even exceed that of the most widely used commodity plastics. This review explores the recent progress of the applications and biodegradation of PBAT. The addition of natural fillers and its effect on the final performance of the PBAT-based composites is also reported with respect to improving the properties of composites. The advance of polymerization reaction engineering combined with sustainable trend offers great opportunities for innovative green chemical manufacturing. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers
Lignocellulose agricultural residue from peach palm trees (Bactris gasipaes kunth), also well-known as “pupunha”, was employed as reinforcing filler of biodegradable matrix based on poly(butylene adipate-co-terephthalate) (PBAT) in order to develop new green composites for food packaging applications. Then, milled fibers (1.6 mm) were prepared with or without surface treatment with glycidoxypropyl-trimethoxy silane (GPTMS) and introduced into PBAT matrix. The mechanical, dynamic mechanical and rheological properties of these composites were investigated. The presence of fibers, mainly the functionalized one led to an increase of the mechanical performance of the corresponding composites. Finally, the preparation of polymer composite foams for possible packaging applications was also investigated under supercritical carbon dioxide (ScCO2) which acts as environmentally friendly blowing agent. The foamed materials were characterized by SEM microscopy and creep-recovery testing.
Poly(butylene adipate-co-terephthalate) (PBAT) was first chemically modified via free radical grafting with maleic anhydride (MA) and the MA-g-PBAT graft copolymer was then used as a matrix material to obtain cellulose nanocrystal (CNC)-reinforced MA-g-PBAT bio-nanocomposites via reactive extrusion process to accelerate efforts to develop functional bioabsorbable polymer nanocomposites with improved properties. The molecular structure of the PBAT after chemical modification with maleic anhydride was confirmed by 1H NMR and FTIR spectroscopy. The morphological observation of the nanocomposites revealed that the CNCs were finely dispersed in the matrix. Thermal analysis of the hybrids showed an improvement of the thermal stability of the nanocomposites upon increasing the CNC content. In addition, it was found that the CNC nucleated crystallization of the PBAT in the nanocomposites. Extensive melt rheological characterization of the nanocomposite samples revealed a significant improvement of the viscoelastic properties of the matrix due to the strong interfacial adhesion of the CNC particles to the PBAT. Further, development of the non-terminal characteristics of the viscoelastic material functions and exhibition of yield stress were correlated with the evolution of a 3D-netowork nanostructure of CNCs in the matrix. This CNC nanostructure was interpreted in the framework of scaling theory of fractal elastic gels, and found to be consistent with the structure of open-porous flocs. Tensile testing of the samples showed considerable improvement in the modulus and ultimate strength of the samples with increasing the CNC content. In addition, a positive shift of the glass transition temperature was found in dynamic mechanical analysis. Finally, in-vitro biocompatibility using Thiazolyl blue tetrazolium bromide (MTT) assay and cell adhesion studies with L929 fibroblast cells revealed no cytotoxic effect of CNCs, confirming the biocompatibility of the nanocomposites and the associated significant improvement of cell adhesion, suggesting the potential applicability of this nanocomposite in biomedical and tissue engineering applications.
We developed an advanced bimodal polystyrene (PS)/multi-walled carbon nanotube (MWCNT) nanocomposite foam with a very low thermal conductivity of 30 mW/m-K without using any insulation gas. The MWCNTs significantly decreased the radiative thermal conductivity of the foams with the high infrared (IR) absorption capability and increased the optimal expansion ratio of the foams to minimize the total thermal conductivity. The radiative blocking effect of MWCNTs was quantitatively modeled by calculating the IR absorption index of the unfoamed nanocomposites and calculating the IR extinction coefficient of the foamed nanocomposites. In addition, a theoretical model to analyze the optimal expansion ratio in synergistic bimodal nanocomposite foam was developed for the first time. The calculated values were in good agreement with the experimental data to verify the superior heat-blocking characteristics of the MWCNTs in the bimodal cellular morphology.