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Carbonized cellulose nanofibers as dielectric heat sources for microwave annealing 3D printed PLA composite
Abstract
Filament fused fabrication (FFF) is an extrusion-based 3D printing technology for manufacturing thermoplastic components. One major obstacle facing 3D printed thermoplastic material is the reduced crystallinity resulting from a fast quench when material exiting the 3D printer hot nozzle solidifies quickly at the low-temperature platform, leading to weak mechanical performance. Here, we report an accelerated annealing strategy with the assistance of microwave heating, aiming to enhance crystallinity and mechanical performance of FFF 3D printed polylactic acid (PLA) composite. We selected naturally abundant cellulose fibers as precursors for producing carbonized cellulose nanofibers (CCNFs), and compounded CCNFs with PLA to produce bi-component filament for 3D printing final composite. After being irradiated with microwave, the embedded CCNFs in composite selectively absorbed microwave energy and generated heat. Subsequently, the localized heat transferred to the adjacent PLA regions, triggering amorphous PLA chains to repack and convert to new crystallites. In this work, annealing conditions, including heating method (i.e., oven annealing vs. microwave annealing), time (0–120 min), and temperature (80 vs. 120 °C), were systematically studied to understand the relevant effects on the resulting parameters including composite crystallinity and tensile strength. Microwave annealing method was also compared with conventional oven annealing method and results shows that microwave annealing significantly reduced the required annealing time to reach the maximum crystallinity and tensile strength. Notably, microwave annealing performed below cold crystallization temperature was exceptionally suitable to develop an optimized crystallinity and tensile strength for 3D printed PLA composite.
... They are employed in the chemical industry to treat coatings, vulcanize rubber [13][14][15][16][17][18][19][20][21][22][23][24], and perform hydrothermal synthesis. Autoclaves used in laboratories or for research. ...
... Normally, oven annealing is easy to use where heat propagates from polymer component surface to the interior. However, for most engineering thermoplastic polymers such as PLA, due to the low thermal conductivity and thermal diffusivity, oven heat may take a long time to diffuse inside, which makes process energyconsuming from a practical perspective [16]. They are employed in the chemical industry to treat coatings, vulcanize rubber [13][14][15][16][17][18][19][20][21][22][23][24], and perform hydrothermal synthesis. ...
... However, for most engineering thermoplastic polymers such as PLA, due to the low thermal conductivity and thermal diffusivity, oven heat may take a long time to diffuse inside, which makes process energyconsuming from a practical perspective [16]. They are employed in the chemical industry to treat coatings, vulcanize rubber [13][14][15][16][17][18][19][20][21][22][23][24], and perform hydrothermal synthesis. Autoclaves used in laboratories or for research. ...
In additive manufacturing technologies, fused deposition modelling (FDM) is continuing its advancement from rapid prototyping to rapid manufacturing. However, effective usage of FDM is not performed due to the poor mechanical properties of the 3D-printed components. This drawback restricts their usage in many applications. Much research, such as reinforcing 3D-printed parts with fibers, changing printing parameters (infill density, infill concentration, extrusion temperature, nozzle diameter, layer thickness, raster angle, etc.) are aimed to increase the mechanical properties of 3D-printed parts. This research paper aims to investigate the effect of pressure and temperature on the mechanical properties and consolidation of layers of 3D-printed PLA (Polylactic Acid). Post-treatment was done using a customized autoclave. Autoclave has the capability to maintain 185 °C and 135 bar pressure. Three-dimensional-printed specimens were manufactured using the FDM process with two patterns. Later, the specimens were subjected to various post-treatment processes, then followed with testing and analysis of mechanical properties. Post-treatment process carried out by placing them in an autoclave at certain pressure and temperature conditions. To investigate the repeatability and tolerances, the test series includes a minimum of four to six test specimens. The results indicate that the concentric pattern yields the most desirable tensile, impact, and flexural strength due to the alignment of deposited rasters and better consolidation of layers with the loading direction. The pressure and temperature of the autoclave has a positive effect on the PLA samples, which helped them to reorganize the structure, hence strength properties were enhanced. The test results also compared with injection-molded samples for better understating.
... Besides NCC and CNF, the use of carbonized cellulose nanofibers [131] and TEMPO-oxidized bacterial cellulose [142] are also reported. To improve the compatibility of the nanocellulose with a hydrophobic matrix of PLA, many works report the use of some modification in the cellulose, such as graphitization of CNF with PLA [25,77,130], polymerized lignin surface-modified CNF [134], and the use of TEMPO [137,142]. The most used nanocellulose isolation methods were acid and enzymatic hydrolysis for the isolation of NCC and mechanical processing for isolation of CNF, with contents varying between 0.1 and 5 wt.%, apart from the papers [25,132] which used a maximum of 20 wt.% and 40 wt.% of filler, respectively. ...
... The effect of NCC or CNF addition on the PLA matrix, however, depends on different factors such as amount of filler added and the use of a coupling agent or some cellulose surface modification. According to Dong et al. [130], the incorporation of PLA-g-CNFs improved storage modulus of the composite filaments in both the low-temperature glassy state and high temperature rubbery state. Gregor-Svetec et al. [134], for example, reported that the addition of NFC slightly reduced tensile strength, stretchability, and ability to absorb energy of the filaments, while the initial modulus slightly improved. ...
Growing concerns about environmental issues and global warming have garnered increased attention in recent decades. Consequently, the use of materials sourced from renewable and biodegradable origins, produced sustainably, has piqued the interest of scientific researchers. Biodegradable and naturally derived polymers, such as cellulose and polylactic acid (PLA), have consistently been the focus of scientific investigation. The objective is to develop novel materials that could potentially replace conventional petroleum-based polymers, offering specific properties tailored for diverse applications while upholding principles of sustainability and technology as well as economic viability. Against this backdrop, the aim of this review is to provide a comprehensive overview of recent advancements in research concerning the use of polylactic acid (PLA) and the incorporation of cellulose as a reinforcing agent within this polymeric matrix, alongside the application of 3D printing technology. Additionally, a pivotal additive in the combination of PLA and cellulose, polyethylene glycol (PEG), is explored. A systematic review of the existing literature related to the combination of these materials (PLA, cellulose, and PEG) and 3D printing was conducted using the Web of Science and Scopus databases. The outcomes of this search are presented through a comparative analysis of diverse studies, encompassing aspects such as the scale and cellulose amount added into the PLA matrix, modifications applied to cellulose surfaces, the incorporation of additives or compatibilizing agents, variations in molecular weight and in the quantity of PEG introduced into the PLA/cellulose (nano)composites, and the resulting impact of these variables on the properties of these materials.
... In the scientific literature, many studies have investigated the influence of different heat treatments on 3D-printed parts of different type of materials such as PLA [26,31,32,41,[48][49][50]55,57,71], ABS [26,27,33,42,51,54], nylon [43], PPS [56], PEEK [28,47], PETG [32,[37][38][39], metals (steel [5][6][7][9][10][11]34,64,65,67,75,76,76,77,90,93,99], aluminum [23,24,70,82], Inconel [23,24,95], titanium [8,13,[16][17][18][19]21,61,84,97,101]), and composites [26,41,49,52,53]. ...
... In the scientific literature, many studies have investigated the influence of different heat treatments on 3D-printed parts of different type of materials such as PLA [26,31,32,41,[48][49][50]55,57,71], ABS [26,27,33,42,51,54], nylon [43], PPS [56], PEEK [28,47], PETG [32,[37][38][39], metals (steel [5][6][7][9][10][11]34,64,65,67,75,76,76,77,90,93,99], aluminum [23,24,70,82], Inconel [23,24,95], titanium [8,13,[16][17][18][19]21,61,84,97,101]), and composites [26,41,49,52,53]. ...
Additive manufacturing (AM) comes in various types of technologies and comparing it with traditional fabrication methods provides the possibility of producing complex geometric parts directly from Computer-Aided Designs (CAD). Despite answering challenges such as poor workability and the need for tooling, the anisotropy of AM constructions is the most serious issue encountered by their application in industry. In order to enhance the microstructure and functional behavior of additively fabricated samples, post-processing treatments have gained extensive attention. The aim of this research is to provide critical, comprehensive, and objective methods, parameters and results’ synthesis for post-processing treatments applied to AM builds obtained by 3D printing technologies. Different conditions for post-processing treatments adapted to AM processes were explored in this review, and demonstrated efficiency and quality enhancement of parts. Therefore, the collected results show that mechanical characteristics (stress state, bending stress, impact strength, hardness, fatigue) have undergone significant improvements for 3D composite polymers, copper-enhanced and aluminum-enhanced polymers, shape memory alloys, high-entropy alloys, and stainless steels. However, for obtaining a better mechanical performance, the research papers analyzed revealed the crucial role of related physical characteristics: crystallinity, viscosity, processability, dynamic stability, reactivity, heat deflection temperature, and microstructural structure.
... The use of microwave (MW) radiation provides an alternative, different and intriguing approach for the heating process, as the energy is given directly to the entire of the composite, rather than depending solely on conduction from the surface [8]. Microwaves are electromagnetic (EM) waves with wavelengths ranging from 1 to 300 mm and frequencies ranging from 300 MHz to 300 GHz [9]. MW heating involves the direct transmission of energy into the composite, which is absorbed by the asymmetric (polar) molecules and converted into heat [10][11][12][13]. ...
... The presence of these inclusions, which are commonly known as "absorbers" has a significant impact on the interaction of composite material with MW radiation [17][18][19][20]. The capability of MW radiation absorbers can improve the MW heater's efficacy in converting electromagnetic energy into thermal energy [9]. The prevailing electromagnetic wave absorbing material includes two parts. ...
In this study, Phenol Formaldehyde (PF) resin was modified with Fe3O4 nanoparticles (NPs) as microwave (MW) absorber nanocomposite in the LVL structure to accelerate MW preheating of the billet. The presence and distribution of Fe3O4-NPs in PF substrate was confirmed by Energy Dispersive X-Ray Spectroscopy (EDS) and Scanning Electron Microscopy (SEM). Differential Scanning Calorimetry (DSC) analysis also proved that existence of Fe3O4-NPs shortened the curing time of PF composite. According to Fourier Transform Infrared (FT-IR) analysis, Fe3O4-NPs had no effect on the functional groups of PF nanocomposite. Temperature variations throughout the microwave preheating process were used to monitor the MW absorption performance. Surprisingly, higher temperatures were recorded for samples containing Fe3O4-NPs. MW preheated LVL's with 3% Fe3O4-NPs were hot-pressed at a higher initial temperature, causing the core layer temperature to reach 100 °C faster. The shear strength and screw withdrawal resistance findings showed that the presence of Fe3O4-NPs had a greater impact on the core layers of LVLs than on the surface layers. Remarkably, MW preheated LVLs containing 2% of Fe3O4-NPs after 8 min of hot-pressing exhibited comparable mechanical characteristics to control samples after 12 min of hot-pressing. These findings show that the PF/Fe3O4-NPs composite improved MW absorption performance while also enhancing LVL mechanical characteristics.
... The quality of parts manufactured by FFF-based AM is highly dependent upon the post-processing. The PLA was reinforced with carbonized cellulose nanofibers (CCNFs), and it was observed that microwave annealing as a post-treatment reduced the standard time for post-processing and increased the mechanical strength [25]. The ABS matrix filled with multiwall carbon nanotubes (MWCNTs) as reinforcement enhanced the tensile strength by 288% [26]. ...
... The reinforcement of metallic particulate is one of the conventional methods of modifying the mechanical/surface properties of the polymeric materials. Previous researchers have worked on the different metallic particles reinforced with thermoplastic composite materials for AM applications [23][24][25][26][27][28][29]. The reinforcement of metallic particles in thermoplastics is required pre-processing like: mechanical/ chemical blending and extrusion process, which increases the processing time and overall manufacturing cost. ...
The quality of 3D printed thermoplastic structures mainly depends upon the various aspects of deposition pattern, processing conditions, and layer bonding. The incomplete layer-to-layer adhesion during the additive manufacturing process is the most critical issue since thermoplastics are bad heat conductors. In this study, aluminum (Al) microfilms have been deposited to promote the adhesion between the additive layers. The composite structures (as per ASTM D 695) of polylactic acid thermoplastic were manufactured by fused filament fabrication (FFF) process and consecutively reinforced with Al spray. The composite structures were subjected to compressive loading to investigate the influence of input process variables like; in-between microfilm layers (1–5 layers), bed temperature (60–100 °C), and infill percentage (40–100%). The results of the study suggested that using microfilm in-between additive layers is a promising technique for improving the compressive properties. The compressive strength has been observed maximum by performing FFF with 3 layers of Al microfilm, 70% of infill percentage, and 100 °C bed temperature. The results are supported by scanning electron microscopy, energy-dispersive spectroscopy, and differential scanning calorimeter analysis. An optimization study was successfully conducted using the analytic hierarchy process, which predicted the optimum parameter settings based on the relative importance of each response variable.
... Viskadourakis et al. reported the fabrication of ABS and PLA based polymer composite using carbon nanostructures as filler for electromagnetic shielding application [48]. Dong et al. fabricated the PLA based composite with cellulose fiber as filler using extrusion based 3D printing technology for microwave application possessing dielectric constant less than 12 in GHz frequency region and dielectric loss less than 15 [49]. Wang et al. fabricated cellulosed added methacrylate malate photocurable resin 3D printed composite for energy storage applications. ...
The Purpose of the research can be rewritten as follows: “The purpose of this research is to study the dielectric response of a 3D-printed polymer composite filled with multiwalled carbon nanotubes (CNTs) and polyurethane-based photopolymer resin. The research also aims to investigate the effect of CNT loading and the post-UV curing process on the dielectric performance.“
3D printed polymer composites are fabricated with CNT fillers at weight percentages of 0.5 wt%, 1 wt%, 2.5 wt%, and 3 wt%. The influence of post-treatment on the dielectric behavior of the 3D-printed samples is investigated by subjecting them to ultraviolet (UV) light. XRD, TGA, DMA, and dielectric spectroscopy are performed to study the crystalline or amorphous nature of the samples, their thermal stability, mechanical properties, and dielectric performance, respectively.
The broad hump in the XRD plot depicts the amorphous nature of the composite material. The thermal stability of the material is found to be less than 50 °C. The study shows that post-curing of the 3D sample with UV light decreases the dielectric constant and increases the dielectric loss. Increasing the CNT percentage causes an increase in both the dielectric constant and loss. The DMA result presented does not show any mechanical improvement due to the filler in the 3D printed samples.
The study demonstrates that the dielectric performance of 3D printed polymer composites can be effectively controlled by CNT loading and UV post-curing. Increasing the CNT percentage increases the dielectric constant and loss, while increasing the UV post-curing time decreases the dielectric constant but increases the dielectric loss. The study provides important insights for the fabrication of 3D printed polymer composites for various dielectric applications.
... In order to counteract such situation, "post-processing" becomes a tool that helps to reduce the problem and improve the mechanical strength of the prototype by annealing the printed objects [2]. Nevertheless, even if annealing allows the internal structure of an object to change from an amorphous to a crystalline state generating a greater stability as well as the strength; the process also causes dimensional changes in the treated object, which becomes a critical factor for some parts that need to be designed with an accurate dimension [3,4]. ...
The annealing process in FDM printing applying materials such as PLA and HTPLA, is a technique that looks for the improvement of the mechanical characteristics of post-printing products. The aim of the research is to determine the most suitable annealing process that does not generate significant changes in the dimension of the object. To this end, 108 test pieces were manufactured within the applied methodology, which were exposed to combined tests that considered variables such as the type of printing material, the fill level, temperature and coating. Once the experiment was carried out, it was concluded that the most suitable annealing process is in PLA or HTPLA material at 100% filler, exposed to 200°C with plaster stone coating.
... Δ is the measured melting enthalpy, Δ the measured cold crystallisation enthalpy, Δ 0 the melting enthalpy of a theoretical 100% crystalline PLA (93 J/g [18]), and the MMT mass fraction. PLA molar masses were determined by GPC for each formulation after compounding to determine the molar mass degradation regarding MMT mass fraction. ...
This study aims to assess the viability of nanocomposites in fused filament fabrication. Polylactide/organo-modified layered silicate materials have been studied in terms of structure and properties evolution through the whole manufacturing chain, and for thermomechanical optimisation. The method included the optimisation by the composite formulation and by the additive manufacturing process by experimental designs. A competition between flow thinning of the molten composite and stiffness of the input filament with the addition of filler allows an enhanced printability at intermediate loadings. The method provides an optimisation of the final parts, enabling similar or greater tensile properties, while providing better thermal stability, with additively manufactured nanocomposite materials compared to conventionally manufactured polymers.
... 15 During the transformation from organic cellulose molecules to inorganic carbon, the CNF precursor needs to remain in a fibrous morphology at all stages to avoid material heterogeneity and loss of nanomaterial properties. 16 Widely used CNF drying methods include freeze-drying, 17 oven drying, 18 spray-drying, 19 and supercritical fluid drying. 20 However, all of these methods are reported to have problems to obtain dry CNF precursors with individualized fibrous structures. ...
Drying cellulose nanofibril (CNF) from aqueous suspensions often leads to aggregated fibril morphology, negatively affecting its performance in ensuing applications. In this work, we introduced a new solvent drying approach to acquire dry CNF from aqueous suspensions and subsequently pyrolyzed the CNF precursor to obtain carbonized CNF (CCNF) without loss of its fibrous morphology. The fibrous CCNF was dispersed homogeneously in polycaprolactone (PCL) thermoplastic resin, greatly enhancing PCL composite tensile performance. After being further mixed with carbon black (CB), the CCNF helped to minimize CB aggregation due to formation of interconnected three-dimensional (3D) structures. The CCNF/CB/PCL composite exhibited superior electrical conductivity ascribed to electrons transporting more efficiently among CB aggregates. The composite is also suitable for applications such as 3D printed electromagnetic interference (EMI) shielding and deformation sensing. Specifically, the 3D printed EMI shielding composite efficiently absorbed EM radiation in the frequency range of 4–26 GHz, and the 3D printed deformation sensor exhibited excellent sensitivity, durability, and flexibility in monitoring mechanical distortions. Herein, this study sheds light on the development of multifunctional conductive composites embedded with fibrous CCNF from sustainable resources.
... In addition, thermal annealing is intended to increase the crystallinity of semi-crystalline polymers by adding thermal heat in between the transition temperature of the polymer (Tg) as well as the melting temperature (Tm). Thermal annealing stimulates the mechanism of polymer nucleation, which further enables existing crystallites to expand [17]. Furthermore, plant-derived fibres like, kenaf, hemp, flax and bamboo fibres were utilized to improve PLA. ...
Polymers play a vital role in our daily lives. In various fields such as medical, food industry and automotive applications, the use of biopolymers is commonly used. The most widely used polymers and fillers among biopolymers are polylactic acid (PLA) and cellulose, which are biocompatible and biodegradable due to their eco-friendly properties. Extensive usage of cellulose in various forms has been applied in combination to PLA but there is only a few research that has been done by using the 3D printing method. This paper covers the types of biodegradable biopolymer materials, types of coupling agents and plasticizers, mechanical properties and applications. This paper discusses the types of cellulose ranging from micro to nano, including other types and sources of cellulose that have been researched and are compatible with PLA. In order to generate biocompatible polymers with stronger and better mechanical properties, the findings of these experiments are all tied together. These biopolymers are commonly used in the biomedical industry and are expected to improve their benefits in this field.
... However, they may present difficulties in machining more complex structures for bench scale. On the other hand, polymers do not allow calcination processes, but they can be easily cut and machined for bench scale, using for example 3D printers (Dong et al. 2020). ...
The persistence of many micropollutants in water and wastewater is of great concern to the contemporary scientific community. Several types of advanced techniques such as heterogeneous photocatalysis are being used for the degradation of micropollutants in waters from domestic, industrial, and agricultural activities. Thus, structured photocatalytic systems are a great alternative in the development of photocatalytic reactors and continuous water treatment systems, as they present good autonomy during the treatment process. Many aspects such as type and geometry of the catalytic structure to be developed must be carefully chosen for the proper functioning of the system, as well as the best routes by which the photocatalysts will be immobilized. In this sense, this work brings the main photocatalytic coating techniques in low-cost structures for the treatment of water and wastewater contaminated with micropollutants. The methodologies and synthesis parameters that can influence the final result of the coating were highlighted, as well as the ability to reuse photocatalysts and methods for pretreating the structural surface. The dip-coating technique was the most reported among the current works due to its simplicity and, predominantly, the pretreatment techniques of the structure are still cleaning the surface with water, soap, and also some alcohols.
Fused Deposition Modelling (FDM) is one of the additive manufacturing (AM) techniques that have emerged as the most feasible and prevalent approach for generating functional parts due to its ability to produce neat and intricate parts. FDM mainly utilises one of the widely used polymers, polylactic acid, also known as polylactide (PLA). It is an aliphatic polyester material and biocompatible thermoplastic, with the best design prospects due to its eco-friendly properties; when PLA degrades, it breaks down into water and carbon dioxide, neither of which are hazardous to the environment. However, PLA has its limitations of poor mechanical properties. Therefore, a filler reinforcement may enhance the characteristics of PLA and produce higher-quality FDM-printed parts. The processing parameters also play a significant role in the final result of the printed parts. This review aims to study and discover the properties of PLA and the optimum processing parameters. This review covers PLA in FDM, encompassing its mechanical properties, processing parameters, characterisation, and applications. A comprehensive description of FDM processing parameters is outlined as it plays a vital role in determining the quality of a printed product. In addition, PLA polymer is highly desirable for various field industrial applications such as in a medical, automobile, and electronic, given its excellent thermoplastic and biodegradability properties.
This work presents a novel broadband double-cross shape metamaterial structure based on the Carbon Black-Acrylonitrile-Butadiene-Styrene (CB-ABS) composite material. The optimal metamaterial structure with the thickness of 7 mm shows a broadband absorption characteristic in the frequency range of 5.1–40 GHz. Additionally, the low volume filling fraction of the proposed metamaterial structure will be helpful to achieve lightweight broadband absorption performance. Meanwhile, the metamaterial structure can also display a wide-angle absorption performance from 0° to 55° for TE mode and 0°–75° for TM mode. Moreover, this research provides an effective and promising way for the practical application of the lightweight broadband and wide-angle microwave strong absorption metamaterial in the future.
Due to its high temperature (maintain stable performance at 200 ℃), corrosion resistance (resistant to strong acids and alkalis) and high mechanical strength, polyphenylene sulfide (PPS) has been attracting more attention in recent years, but research about PPS and 3D printing reinforced composites remains low. Pure PPS has lower application potential compared to its composites. In this study, carbon nanotube (CNT) reinforced PPS 3D printing filaments with uniform CNT dispersion were prepared and CNT uniformity was ensured by coating maleimide polymers (MIPs). Systematically analyzed CNT (contents between 0 and 0.9 wt%) effects on tribological, mechanical and thermal performance of 3D printing PPS. Compared to pure PPS, tensile and bending strengths increased 26% and 29%, respectively. Crystallinity of PPS printed parts improved through thermal conductivity and diffusivity. Wear rate reduced from 1.14E-3 mm³N⁻¹m⁻¹ to 1.838E-5 mm³N⁻¹m⁻¹. Both fracture and worn surfaces were observed by SEM. As result, this research expects to improve engineering application values of 3D printing PPS.
With an exponential rise in the popularity and availability of additive manufacturing (AM), a large focus has been directed toward research in this topic's movement, while trying to distinguish themselves from similar works by simply adding nanomaterials to their process. Though nanomaterials can add impressive properties to nanocomposites (NCs), there are expansive amounts of opportunities that are left unexplored by simply combining AM with NCs without discovering synergistic effects and novel emerging material properties that are not possible by each of these alone. Cooperative, evolving properties of NCs in AM can be investigated at the processing, morphological, and architectural levels. Each of these categories are studied as a function of the amplifying relationship between nanomaterials and AM, with each showing the systematically selected material and method to advance the material performance, explore emergent properties, as well as improve the AM process itself. Innovative, advanced materials are key to faster development cycles in disruptive technologies for bioengineering, defense, and transportation sectors. This is only possible by focusing on synergism and amplification within additive manufacturing of nanocomposites. The combination of additive manufacturing with advanced nanocomposites creates new emerging material properties during processing, morphology evolution and novel functionalities with top level hierarchies that are dictated by print path topology. The synergistic, cooperative properties are key to unique capabilities that are not possible otherwise. This article takes a critical look at recent advances in this area and potential applications in automotive, civil engineering, biomedical, aerospace and space.
Abstract: It is of utmost importance to analyze the plate vibrations in detail, especially in the automotive industry, and to determine the natural frequencies. This is the case for classical plates, but also for composite plates. Most of the structural elements used in composite plates can have irregular shapes and complex structures and this seriously affects natural frequencies. On the other hand, the layered production method, also known as three-dimensional (3D) printing, is based on the principle of knitting materials on top of each other in order to create a 3-dimensional model. The use of this technology has increased greatly in recent years, especially as it is carried out quickly. With this method, parts with complex shapes can be produced, and therefore its use has become widespread in many scientific research and technology fields from machine to automotive, aviation to robotics. In this article, finding and comparing the free vibration frequencies of a PLA-based plate produced with a 3D printer by numerical simulation and experimental tests are examined. First, the tensile tests of the sample produced with a 3D printer with PLA 190x190x1.75 mm to be used in finite element (FE) analysis were performed and the elasticity modulus and stress-strain curves were calculated. Then, natural frequencies and modal shapes are obtained from finite element (FE) methods to characterize the vibration behavior of the plate. The obtained values were tested with the help of a modal shaker in an experimental setup where vibration frequencies were measured. In the comparison, it was seen that the results of the finite element analysis and the experimental results were close to each other.
Iron (Fe) plays a significant role in plant growth, especially in alkaline soil. These days, Nanomaterials are quickly used in modern agriculture. The field experiments were carried out in the Research and Application Farm of the Field Crops Department, Faculty of Agriculture, Van Yuzuncu Yil University, Van, Turkey. The present study was conducted to evaluate the effect of different doses of Nano Iron Oxide (Fe2O3) (0 as control, 0.4, 0.6 and 0.8 g.L-1) and two foliar application on growth of corn (Zea mays var. Tuano) plant at 54 and 69 days after planting (DAP) during 2019 and 2020 seasons under alkaline soil conditions. Three samples were collected and dough stage of corn. Results showed that, the different applied treatments increased plant height, leaf number and total chlorophyll SPAD 74 and 84 (DAP) during the both seasons in comparison to control non-sprayed plants, while at 64 was no difference between control and treated plants by Nano iron oxide. Moreover, corn plants in the dough stage characters (plant height, leaves number/plant and shoot fresh weight) improved due to foliar application of Fe2O3 in both season for all Nano-iron doses. The spraying of Nano iron mitigated negative effects of alkaline soil on maize performance, especially when applied at 0.6 g.L-1 where was the most effective treatment in this respect and caused the maximum increase in comparison to control non-sprayed corn plants. The foliar application of Nano Iron Oxide could be an effective strategy to improve growth of maize under alkaline soil conditions.
Key Words: Nano Iron Oxide, Corn, Alkaline Soil, Dough Stage.
The development of well-designed polylactic acid (PLA) based composite filaments through fused filament fabrication (FFF) is crucial, as PLA printed parts are characterized by a high brittleness. Here we focus on FFF composite formation using ductile poly (butylene adipate-co-terephthalate) (PBAT), the nanoclay cloisite and the chain extender Joncryl. A high modulus, flexibility, toughness and notched impact strength result upon combining PLA/PBAT (80:20; mass basis) with a sufficiently high cloisite amount (1–5 phr) supported by a suited Joncryl amount (0.3 phr). A fine PBAT dispersion is then ensured, as confirmed by scanning and transmission electron microscopy. For high cloisite amounts (e.g. 10 phr) the crystallinity and vicat softening temperature enhance but cloisite aggregation is unavoidable, leading to a strong reduction in tensile strain and toughness. Annealing increases crystallinity thus material strength, rigidity and impact, at least partially overruling the need of a fine dispersion. Novel radar charts are also reported to select an optimal bio-based blend suitable for different end-user applications by adjusting the composition and possible post-annealing of printed products.
Biodegradable poly(lactic acid) (PLA)/poly(butylene adipate‐co‐terephthalate) (PBAT) blends and PLA/PBAT/Al2O3 nanocomposites were fabricated via solution blending. The influence of PBAT and Al2O3 content on the thermal stability, flexural properties, impact strength, and morphology of both the PLA/PBAT blends and the PLA/PBAT/Al2O3 nanocomposites were investigated. The impact strength of the PLA/PBAT/Al2O3 nanocomposites containing 5 wt% PBAT increased from 4.3 to 5.2 kJ/m² when the Al2O3 content increased from 0 to 1 wt%. This represents a 62% increase compared to the impact strength of pristine PLA and a 20% increase compared to the impact strength of PLA/PBAT blends containing 5 wt% PBAT. Scanning electron microscopy imaging revealed that the Al2O3 nanoparticles in the PLA/PBAT/Al2O3 nanocomposites function as a compatibilizer to improve the interfacial interaction between the PBAT and the PLA matrix.
Polylactide (PLA) and silk fibroin (SF) are biocompatible green macromolecular materials with tunable structures and properties. In this study, microporous PLA/SF composites were fabricated under different pressures by a green solid solvent-free foaming technology. Scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric (TG) analysis, and Fourier transform infrared (FTIR) spectroscopy were used to analyze the morphology, structure, and mechanical properties of the PLA/SF scaffolds. The crystalline, mobile amorphous phases and rigid amorphous phases in PLA/SF composites were calculated to further understand their structure-property relations. It was found that an increase in pore density and a decrease in pore size can be achieved by increasing the saturation pressure during the foaming process. In addition, changes in the microcellular structure provided PLA/SF scaffolds with better thermal stability, tunable biodegradation rates, and mechanical properties. FTIR and XRD analysis indicated strong hydrogen bonds were formed between PLA and SF molecules, which can be tuned by changing the foaming pressure. The composite scaffolds have good cell compatibility and are conducive to cell adhesion and growth, suggesting that PLA/SF microporous scaffolds could be used as three-dimensional (3-D) biomaterials with a wide range of applications.
Bu derleme çalışmasında, son 10 yılda odun kökenli doğal liflerin polilaktik asit matrisine takviyesi ile oluşturulan kompozit malzemeler üzerine yapılan çalışmalar incelenmiştir. Odun kökenli doğal lifler, güçlü, hafif ve düşük ağırlıkta, yüksek özgül mukavemete sahip, ucuz, çevre dostu ve doğada biyolojik olarak parçalanabilir özelliklerde olduğundan polimer matrisli kompozitlerde kullanımı yaygındır. Genel olarak lifler, odun, sisal, kenevir, keten, kenaf ve bambu gibi bitki kaynaklı doğal malzemelerden elde edilmektedir. Odun unu, odun lifi, selüloz lifi, mikrokristalin selüloz ve selüloz nano parçacıklar gibi elde edilen bu malzemeler, polilaktik asit polimer matrisine takviye edilerek, mekanik özelliklerinin geliştirilmesi sağlanmaktadır. Bu çalışmada, polilaktik asit polimer matrisine odun kökenli malzemelerin takviyesi ile üretilen kompozit malzemelerin mekanik özellikleri, üretim teknikleri, takviye elamanlarının polilaktik asit matrisi üzerine etkileri, ilave edilen takviye oranları, ara yüz malzemelerin etkileri üzerine yapılmış çalışmalar incelenerek, elde edilen tüm bulgular ve sonuçlar özetlenmiştir.
Holographic polymer nanocomposites with upconversion photoluminescence functions have drawn extensive attention. Yet, it still remains challenging to boost the upconversion emission intensity while maintaining a high diffraction efficiency. Herein, we demonstrate a viable approach to fabricating holographic polymer nanocomposites with both high diffraction efficiency and bright upconversion emission by enriching the core-shell structured upconversion nanoparticles (UCNPs) into the constructive regions while enriching the liquid crystal into the destructive regions during photopolymerization. It is found that the mass ratio of oleic acid to H2O (e.g., 2.41–7.65) on the surface of UCNPs plays a critical role to achieve the attractive holographic polymer nanocomposites. Colored holographic images identifiable to the public under room light with four encrypted upconversion emission states (e.g., none, blue, yellow-green and red) are achieved. Moreover, the holographic images are able to show distinct colors at different viewing angles and can be switched by electric fields, showing unclonable features for advanced anti-counterfeiting applications.
Material dielectric properties are important for understanding their response to microwaves. Carbonaceous materials are considered good microwave absorbers and can be mixed with dry biomasses, which are otherwise low-loss materials, to improve the heating efficiency of biomass feedstocks. In this study, dielectric properties of pulverized biomass and biochar mixtures are presented from 0.5 GHz to 20 GHz at room temperature. An open-ended coaxial-line dielectric probe and vector network analyzer were used to measure dielectric constant and dielectric loss factor. Results show a quadratic increase of dielectric constant and dielectric loss with increasing biochar content. In measurements on biochar, a strong dielectric relaxation is observed at 8 GHz as indicated by a peak in dielectric loss factor at that frequency. Biochar is found to be a good microwave absorber and mixtures of biomass and biochar can be utilized to increase microwave heating rates for high temperature microwave processing of biomass feedstocks. These data can be utilized for design, scale-up and simulation of microwave heating processes of biomass, biochar, and their mixtures.
3D printers constitute a fast-growing worldwide market. These printers are often employed in research and development fields related to engineering or architecture, especially for structural components or rapid prototyping. Recently, there is enormous progress in available materials for enhanced printing systems that allow additive manufacturing of complex functional products, like batteries or electronics. The polymer polylactic acid (PLA) plays an important role in fused filament fabrication, a technique used for commercially available low-budget 3D printers. This printing technology is an economical tool for the development of functional components or cases for electronics, for example, for lab purposes. Here we investigate if the material properties of “as-printed” PLA, which was fabricated by a commercially available 3D printer, are suitable to be used in electrical measurement setups or even as a functional material itself in electronic devices. For this reason, we conduct differential scanning calorimetry measurements and a thorough temperature and frequency-dependent analysis of its dielectric properties. These results are compared to partially crystalline and completely amorphous PLA, indicating that the dielectric properties of “as-printed” PLA are similar to the latter. Finally, we demonstrate that the conductivity of PLA can be enhanced by mixing it with the ionic liquid “trihexyl tetradecyl phosphonium decanoate.” This provides a route to tailor PLA for complex functional products produced by an economical fused filament fabrication.
Additive manufacturing through material extrusion, often termed three-dimensional (3D) printing, is a burgeoning method for manufacturing thermoplastic components. However, a key obstacle facing 3D-printed plastic parts in engineering applications is the weak weld between successive filament traces, which often leads to delamination and mechanical failure. This is the chief obstacle to the use of thermoplastic additive manufacturing. We report a novel concept for welding 3D-printed thermoplastic interfaces using intense localized heating of carbon nanotubes (CNTs) by microwave irradiation. The microwave heating of the CNT-polymer composites is a function of CNT percolation, as shown through in situ infrared imaging and simulation. We apply CNT-loaded coatings to a 3D printer filament; after printing, microwave irradiation is shown to improve the weld fracture strength by 275%. These remarkable results open up entirely new design spaces for additive manufacturing and also yield new insight into the coupling between dielectric properties and radio frequency field response for nanomaterial networks.
Poly(ethylene oxide) electrospun nanofibers with a low concentration of embedded gold nanoparticles (AuNP) were subjected to postfabrication annealing via photothermal heating from the nanoparticles. The results, including nanofibrous mat morphology, crystallinity fraction as a function of annealing time and modality, and average crystallite size, were compared with that for conventional heating at the same average temperature. Maximum crystallinity is achieved more quickly under photothermal heating, and higher maximum crystallinity values, approaching the theoretical maxima for an entangled polymer (∼80%), are obtained. Photothermal heating better preserves the unique nanostructured morphology of the nanofibrous mat whereas significant fiber thickening and loss of porosity occur under conventional annealing treatment. With photothermal heating, heat may be predominantly applied within amorphous material within the fiber, which provides energy for the amorphous chains to reorient and then possibly crystallize but while preserving existing crystalline regions as well as the temperature-fragile nanofiber surface. This occurs because nanoparticles are spontaneously segregated within amorphous material due to their characteristic size. In the complex environment of a polymeric nanofiber where crystalline, aligned amorphous, and random amorphous material are all present, further spontaneous segregation of the AuNP to the random amorphous material may occur which enables targeting of this higher barrier to crystallization population, leading to very high final crystallinity fractions.
Metal nanoparticles embedded within polymeric systems can act as localized heat sources, facilitating in situ polymer processing. When irradiated with light resonant with the nanoparticle's surface plasmon resonance (SPR), a nonequilibrium electron distribution is generated which rapidly transfers energy into the surrounding medium, resulting in a temperature increase in the immediate region around the particle. This work compares the utility of such photothermal heating versus traditional heating in gold nanoparticle/poly(ethylene oxide) nanocomposite films, crystallized from solution and the melt, which are annealed at average sample temperatures above the glass transition and below the melting point. For all temperatures, photothermally annealed samples reached maximum crystallinity and maximum spherulite size faster. Percentage crystallinity change under conventional annealing was analyzed using time-temperature superposition (TTS). Comparison of the TTS data with results from photothermal experiments enabled determination of an "effective dynamic temperature" achieved under photothermal heating which is significantly higher than the average sample temperature. Thus, the heterogeneous temperature distribution created when annealing with the plasmon-mediated photothermal effect represents a unique tool to achieve processing outcomes that are not accessible via traditional annealing.
Solvent vapour annealing (SVA) is demonstrated as an attractive method to anneal polymer blend and block copolymer thin films at low temperatures. It is especially suitable for organic electronics, where sensitive materials with strong intermolecular interactions are used. We demonstrate the effect of solvent vapour exposure on the film properties of a perylene bisimide acrylate (PPerAcr) side-chain polymer with strong crystallinity at the perylene bisimide moieties. We record the film thickness, light absorption and fluorescence as a function of the relative solvent vapour pressure. At a certain threshold of relative solvent vapour pressure, we observe a disruption of the p-p stacking, which is responsible for perylene bisimide crystallisation. This leads to an increase in the polymer-chain mobility and therefore to changes in the film morphology. The results are applied to a film of a donor-acceptor block copolymer carrying PPerAcr segments, and the influence of solvent annealing on the nanoscale morphology is demonstrated.
This paper focuses on the crystalline structure of injection moulding grade poly(lactic acid) (PLA) and the effect of crystalline structure on the processing. The research is induced by the significant differences in crystallinity of the pure PLA resin, and the injection moulded product, and thus the reprocessing of PLA products. 2 mm thick PLA sheets were injection moulded and re-crystallized in a conventional oven at 60-140°C, for 10-60 minutes to achieve various crystalline contents. The properties of these sheets were investigated by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD). In a processing plant the rejected parts are recycled and reused as raw material for further cycles, accordingly the various crystalline content PLA products were reprocessed as a resin, to investigate the processing itself. When PLA products are reprocessed, due to the adherent feature of amorphous PLA processing difficulties may occur. This adherent effect of the amorphous PLA was investigated and characterized.
This critical review provides a processing-structure-property perspective on recent advances in cellulose nanoparticles and composites produced from them. It summarizes cellulose nanoparticles in terms of particle morphology, crystal structure, and properties. Also described are the self-assembly and rheological properties of cellulose nanoparticle suspensions. The methodology of composite processing and resulting properties are fully covered, with an emphasis on neat and high fraction cellulose composites. Additionally, advances in predictive modeling from molecular dynamic simulations of crystalline cellulose to the continuum modeling of composites made with such particles are reviewed (392 references).
The crystallization and melting behaviors of linear polylactic acid (PLA) treated by compressed CO(2) was investigated. The isothermal crystallization test indicated that while PLA exhibited very low crystallization kinetics under atmospheric pressure, CO(2) exposure significantly increased PLA's crystallization rate; a high crystallinity of 16.5% was achieved after CO(2) treatment for only 1 min at 100 degrees C and 6.89 MPa. One melting peak could be found in the DSC curve, and this exhibited a slight dependency on treatment times, temperatures, and pressures. PLA samples tended to foam during the gas release process, and a foaming window as a function of time and temperature was established. Based on the foaming window, crystallinity, and cell morphology, it was found that foaming clearly reduced the needed time for PLA's crystallization equilibrium.
Poly(lactic acid) (PLA) and PLA grafted cellulose nanofibers (PLA-g-CNFs) mixture were extruded into filaments, and subsequently 3D printed into composites. As-3D printed composites were then thermally annealed at a temperature above PLA glass transition temperature (Tg). Dynamic mechanical analysis, including temperature ramp, frequency sweep, and creep for annealed composites, confirmed the enhanced responses to various viscoelastic factors. Such enhancements were ascribed to the presence of PLA crystalline regions containing both ɑ and ɑʹ phases, which were induced and developed through the annealing treatment. After 3-point bending test at 70 °C, unannealed composites were partially damaged, while annealed composites preserved the originally well-integrated layer structures. Experimental creep and recovery data essentially fitted to the Burger’s model and Weibull’s distribution function, respectively. The calculated parameters (e.g., moduli) from numerical fitting curves demonstrated the synergetic effect of PLA-g-CNFs and annealing treatment on the enahncement of flexural properties for 3D printed PLA composites.
Accelerated curing of high performance fibre-reinforced polymer (FRP) composites via microwave heating or radiation, which can significantly reduce cure time and increase energy efficiency, has several major challenges (e.g. uneven depth of radiation penetration, reinforcing fibre shielding, uneven curing, introduction of hot spots etc). This article reviews the current scientific challenges with microwave curing of FRP composites considering the underlying physics of microwave radiation absorption in thermoset-matrix composites. The fundamental principles behind efficient accelerated curing of composites using microwave radiation heating are reviewed and presented, especially focusing on the relation between penetration depth, microwave frequency, dielectric properties and cure degree. Based on this review, major factors influencing microwave curing of thermoset-matrix composites are identified, and recommendations for efficient cure cycle design are provided.
Semiconducting polymer thin films, which are usually formed by solution-casting from their organic solutions, are critical in the development of flexible and printed electronics. To seek out a method that can further improve the electrical properties of semiconducting polymers and also be industrially applicable is of vital significance. In this study, the impact of zone annealing on the charge-transport properties of diketopyrrolopyrrole-based complementary semiconducting polymer blends in field-effect transistor devices is investigated. An average mobility increased from 0.66 to 0.87 cm2 V−1 s−1, with a highest of 1.6 cm2 V−1 s−1, is observed. It is also demonstrated that zone annealing can be integrated with melt processing to realize a solvent-free process for polymer thin films for organic field-effect transistors (OFETs) and achieve improved charge transport characteristics with a record mobility of 0.54 cm2 V−1 s−1 among melt-processed OFETs. This work provides an alternative, green, and sustainable processing method to advance polymer-based organic electronics.
Understanding the crystallization process of polymer blends is of great importance for designing their process condition, especially when the crystallization occurs during heating, so-called cold crystallization. In this paper, the cold crystallization behavior of Poly (lactic acid), PLA, in its blends with acrylic rubber (ACM) was studied as a function of ACM content, using various techniques including differential scanning calorimeter (DSC), polarized optical microscopy (POM) and rheological methods. It was found that the addition of 10 to 20 wt% ACM to the PLA accelerated its cold crystallization. However, by using a greater amount of ACM up to 30%, the rate of crystallization was not further increased. In the ACM-rich blends, the crystallizable PLA domains were distributed inside the amorphous ACM matrix and consequently confined crystallization occurred. The observed effects are discussed in terms of the interplay between the chain mobility enhancement and the influence of the phase boundaries.
CNFs) via ring-opening polymerization, forming poly(lactic acid) grafted cellulose nanofibers (PLA-g-CNFs). PLA-g-CNFs and pristine PLA were then blended in chloroform and dried to prepare a master batch. PLA-g-CNFs/PLA composite filaments targeted for 3D printing were produced by compounding the master batch in PLA matrix and melt extrusion. The as-extruded composite filaments were subsequently thermal annealed in a conventional oven, and their morphological, thermal, and mechanical properties were evaluated. PLA was successfully grafted on the surface of CNFs as demonstrated by elemental analysis, and the concentration of grafted PLA was estimated to be 33 wt %. The grafted PLA were highly crystallized, contributing to the growth of crystalline regions of PLA matrix. The incorporation of PLA-g-CNFs improved storage modulus of the composite filaments in both low temperature glassy state and high temperature rubbery state. Postextrusion annealing treatment led to 28 and 63% increases for tensile modulus and strength of the filaments, respectively. Simulated Young's moduli from the Halpin-Tsai and Krenchel models were found comparable with the experimental values. The formed composite filaments are suitable for use in 3D printing. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017
Flexible polymer-based dielectric materials that are used to store dielectric energy have widely been used in modern electronics and electric power systems, due to their relatively high energy density, light weight, low cost, etc. However, owing to the growing global environmental issues and a rapid consumption of nonrenewable polymer resources, there exists a strong desire to fabricate flexible dielectric materials using biodegradable materials. Here, we report on flexible dielectric papers based on biodegradable cellulose nanofibers (CNFs) and carbon nanotubes (CNTs) for dielectric energy storage. Highly ordered, homogeneous CNF/CNT papers have been fabricated using a facile vacuum-assisted self-assembly technique. The obtained paper possesses a high dielectric constant of 3198 at 1.0 kHz, thus leading to enhanced dielectric energy storage capability (0.81 ± 0.1 J cm-3), which is attributed to the presence of a low loading of CNTs (4.5 wt%). Moreover, the CNF/CNT papers are mechanically flexible and show improved mechanical strength. These findings enable feasible fabrication of high-performance flexible dielectric materials using ecofriendly materials.
Acrylonitrile butadiene styrene (ABS) nanocomposites with organic modified montmorillonite (OMMT) were prepared by melt intercalation. ABS nanocomposite filaments for fused deposition modeling (FDM) 3D printing were produced by a single screw extruder and printed by a commercial FDM 3D printer. The 3D printed samples were evaluated by tensile, flexural, thermal expansion and dynamic mechanical tests. The structure of nanocomposites were analyzed by TEM and low angle XRD. Results showed that the addition of 5 wt% OMMT improved the tensile strength of 3D printed ABS samples by 43% while the tensile strength of injection moulding ABS samples were improved by 28.9%. It was found that the addition of OMMT significantly increased the tensile modulus, flexural strength, flexural modulus and dynamic mechanical storage modulus, and decreased the linear thermal expansion ratio and the weight loss of TGA. These novel ABS nanocomposites with better mechanical and thermal properties can be promising materials used in FDM 3D printing.
To upgrade Indonesian lignite by significantly reducing moisture and volatile matter content for the preparation of quality coal water slurry (CWS) gasification fuel, carbonaceous materials with high dielectric permittivity were employed to accelerate heating rate via microwave irradiation. The physicochemical properties of lignite upgraded through microwave irradiation with the addition of activated carbon and graphite were investigated through Fourier transform-infrared spectroscopy, X-ray photoelectron spectra and N2 adsorption porosimetry. The oxygen functional groups of the upgraded lignite decreased remarkably, whereas coal rank increased. Furthermore, the atomic ratio of oxygen to carbon and the molar ratio of carbonyl to the aromatic groups of the lignite upgraded with the aid of activated carbon were both lower than those of lignite upgraded with the inclusion of graphite. On the contrary, the aromaticity and aromatic-to-aliphatic ratio of the first type of upgraded lignite were both higher than those of the second type. The hydrophilic functional groups on the surfaces of lignite upgraded with the aid of activated carbon were lower in number than those on the surfaces of lignite upgraded with the inclusion of graphite; the opposite was true given hydrophobic functional groups. The maximum solid concentration of CWS prepared from upgraded lignite with activated carbon-assisted microwave irradiation increased markedly from 41.3 wt% to 66.6 wt%.
This Perspective provides a critical analysis of the current knowledge concerning solvent vapor annealing (SVA) of block polymer thin films. Herein, we identify key challenges that will be important to overcome for future development of SVA as a practical, reliable, and universal technique for the valorization of block polymer thin films in a wide range of technologies. The Perspective includes a brief background on thin film block polymer self-assembly, a historical account of the SVA technique, an overview of the SVA fundamentals that are necessary to develop a more comprehensive picture of the overall process, and summaries of relevant and important contributions from the recent literature. We also offer our outlook on SVA and suggest important future directions.
We describe here the first report for developing microphase-separated structures in poly(styrene-block-isoprene) (PS-b-PI) block copolymer nanoparticles by microwave annealing in a nonsolvent, water. A random structure in the nanoparticles successfully transformed to thermodynamically stable structures within several minutes though it takes several days by using the conventional thermal annealing process.
Increasing research activity on cellulose nanofibril-based materials provides great opportunities for novel, scalable manufacturing approaches. Cellulose nanofibrils (CNFs) are typically processed as aqueous suspensions because of their hydrophilic nature. One of the major manufacturing challenges is to obtain dry CNFs while maintaining their nano-scale dimensions. Four methods were examined to dry cellulose nanocrystal and nanofibrillated cellulose suspensions: (1) oven drying, (2) freeze drying (FD), (3) supercritical drying (SCD), and (4) spray-drying (SD). The particle size and morphology of the CNFs were determined via dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and morphological analysis. SCD preserved the nano-scale dimensions of the cellulose nanofibrils. FD formed ribbon-like structures of the CNFs with nano-scale thicknesses. Width and length were observed in tens to hundreds of microns. SD formed particles with a size distribution ranging from nanometer to several microns. Spray-drying is proposed as a technically suitable manufacturing process to dry CNF suspensions.
Poly(lactic acid) is a biobased and compostable thermoplastic polyester that has rapidly evolved into a competitive commodity material over the last decade. One key bottleneck in extending the use of PLA is the control of its crystallinity. Understanding the crystallization behavior is particularly crucial to control PLA's degradation rate, thermal resistance as well as optical, mechanical and barrier properties. PLA crystallization has also been a particularly rich topic from a fundamental point of view because of the existence of the two enantiomeric forms of lactic acid that can be used to control the crystallization rate but also to form high melting point stereocomplex structures. This article presents an overview of the current understanding on the fundamentals of PLA crystallization in quiescent conditions and on the practical means to enhance its rate. Data from the abundant literature on PLA crystallization were compiled and analyzed to provide comprehensive relationships between crystallization kinetics and the main molecular structure characteristics of PLA. In addition, the most promising efforts in enhancing PLA crystallization kinetics through plasticization or heterogeneous nucleation were reviewed.
The zone-annealing method has been used to prepare uniaxially oriented ultra-high modulus polyethylene films from single crystal mats of ultra-high molecular weight polyethylene. The maximum dynamic modulus and tensile strength at room temperature of superdrawn films were 232 and 6 GPa, respectively. The present paper discusses the advantages of the zone-annealing method, the determination of the optimum conditions for zone drawing and zone annealing, and the changes in superstructure and mechanical properties with processing.
Block copolymer (BCP) microphase separation at surfaces might enable the generation of substrate features in a scalable, manufacturable, bottom-up fashion provided that pattern structure, orientation, alignment can be strictly controlled. A further requirement is that self-assembly takes place within periods of the order of minutes so that continuous manufacturingprocesses do not require lengthy pretreatments and sample storageleading to contamination and large facility costs. We report here microwave-assisted solvothermal (in toluene environments) self-assembly and directed self-assembly of a very low molecular weight cylinder-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS) BCP on planar and patterned silicon nitride (Si3N4) substrates. Good pattern ordering was achieved in the order of minutes. Factors affecting BCP self-assembly, notably anneal time and temperature were studied and seen to have significant effects. Graphoepitaxy to direct self-assembly in the BCP yielded promising results producing BCP patterns with long-range translational alignment commensurate with the pitch period of the topographic patterns. This rapid BCP ordering method is consistent with the standard thermal/solvent anneal processes.
We report the dielectric and viscoelastic relaxations in undiluted amorphous poly(d,l-lactic acid) (PLA). Three dielectric relaxations designated as αn, αs, and β are observed in order of decreasing temperature. The relaxation time for the αn relaxation increases with increasing molecular weight and is assigned to the normal mode relaxation due to the component of dipole vector aligned in the direction parallel to the chain contour. The αs relaxation is observed about 30 K above the glass transition temperature Tg (= 310 K) and is assigned to the local segmental mode due to the transverse component of the monomeric dipoles. The β relaxation is seen in the glassy state and is assigned to the secondary relaxation. From the relaxation strengths for the αn, αs, and β relaxations, the effective dipole moments for those relaxation processes are determined and compared with the parallel and transverse components of the dipole moment calculated theoretically with the semiempirical molecular orbital methods. The dielectric relaxation time for the normal mode increases with molecular weight M with the power of 3.5 in the range of molecular weight above the characteristic molecular weight Mc (= 13 000). The molecular weight between entanglements is calculated to be 7700 from the shear modulus in the rubbery plateau region. It is found that the dielectric normal mode relaxation time agrees approximately with the viscoelastic terminal relaxation time. The relaxation spectra for the viscoelastic relaxation are much broader than those for the dielectric relaxation as observed previously for polyisoprene.
The crystalline structure of poly(L-lactide) (PLLA) have been found to quite depend on the crystallization temperatures (Tcs), especially in the range of 100−120°C, which is usually used as the crystallization temperature for the industrial process of PLLA. The analysis of wide-angle X-ray diffraction and Fourier transformed infrared spectroscopy revealed that 110°C is a critical temperature for PLLA crystallization. At Tc < 110°C and Tc ≥ 110°C, the α′ and α crystals were mainly produced, respectively. Besides, the structural feature of the α′-form was illustrated, and it was found that the α′-form has the larger unit cell dimension than that of the α-form. Moreover, the crystallization kinetics of the α′ and α crystals are different, resulting in the discontinuousness of the curves of spherulite radius growth rate (G) versus Tc and the half time in the melt-crystallization (t1/2) versus Tc investigated by Polarized optical microscope and Differential scanning calorimetry, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Grazing incidence X-ray scattering (GIXS) is used to characterize the morphology of poly(3-hexylthiophene) (P3HT)–phenyl-C61-butyric acid methyl ester (PCBM) thin film bulk heterojunction (BHJ) blends as a function of thermal annealing temperature, from room temperature to 220 °C. A custom-built heating chamber for in situ GIXS studies allows for the morphological characterization of thin films at elevated temperatures. Films annealed with a thermal gradient allow for the rapid investigation of the morphology over a range of temperatures that corroborate the results of the in situ experiments. Using these techniques the following are observed: the melting points of each component; an increase in the P3HT coherence length with annealing below the P3HT melting temperature; the formation of well-oriented P3HT crystallites with the (100) plane parallel to the substrate, when cooled from the melt; and the cold crystallization of PCBM associated with the PCBM glass transition temperature. The incorporation of these materials into BHJ blends affects the nature of these transitions as a function of blend ratio. These results provide a deeper understanding of the physics of how thermal annealing affects the morphology of polymer–fullerene BHJ blends and provides tools to manipulate the blend morphology in order to develop high-performance organic solar cell devices.
The photovoltaic action of plastic solar cells based on P3HT/PCBM- (poly[3-hexylthiophene-2,5-diyl]/[6,6]-phenyl C61 butyric acid methyl ester)-composites depends strongly on structure of the active layer. In this work, the impact of P3HT-crystallinity on optical absorption of P3HT/PCBM-films was investigated. We observed, that both P3HT-crystallinity and optical absorption of thermally annealed films are increased in comparison to the not annealed ones. The highest crystallinity was achieved for films annealed at 125 °C. Further increase of annealing temperature leads to decrease of P3HT crystallinity. It is shown that the absorption coefficient of the films at low photon energies is proportional to the area under the X-ray-diffraction peak, which is a measure for the degree of film crystallinity.
The miscibility of high molecular weight poly(l-lactide) PLLA with high molecular weight poly(ethylene oxide) PEO was studied by differential scanning calorimetry. All blends containing up to 50 weight% PEO showed single glass transition temperatures. The PLLA and PEO melting temperatures were found to decrease on blending, the equilibrium melting points of PLLA in these blends decreased with increasing PEO fractions. These results suggest the miscibility of PLLA and PEO in the amorphous phase. Mechanical properties of blends with up to 20 weight% PEO were also studied. Changes in mechanical properties were small in blends with less than 10 weight% PEO. At higher PEO concentrations the materials became very flexible, an elongation at break of more than 500% was observed for a blend with 20 weight% PEO. Hydrolytic degradation up to 30 days of the blends showed only a small variation in tensile strength at PEO concentrations less than 15 weight%. As a result of the increased hydrophilicity, however, the blends swelled. Mass loss upon degradation was attributed to partial dissolution of the PEO fraction and to an increased rate of degradation of the PLLA fraction. Significant differences in degradation behaviour between PLLA/PEO blends and (PLLA/PEO/PLLA) triblock-copolymers were observed.
Carbonaceous materials are amenable to microwave heating to varying degrees. The primary indicator of susceptibility is the complex permittivity (ϵ*), of which the real component correlates with polarization and the imaginary term represents dielectric loss. For a given material, the complex permittivity is dependent upon both frequency and temperature. Here we report the complex permittivities of three activated carbons of diverse origin over the frequency range from 0.2 to 26 GHz. Dielectric polarization–relaxation phenomena for these materials are also characterized. Measurements were made using a coaxial dielectric probe and vector network analyzer based system across the temperature region between 22 and 190 °C.
For a long time polymers have supplied most of common packaging materials because they present several desired features like softness, lightness and transparency. However, increased use of synthetic packaging films has led to a serious ecological problems due to their total non-biodegradability. Although their complete replacement with eco-friendly packaging films is just impossible to achieve, at least for specific applications like food packaging the use of bioplastics should be the future. The aim of this review was to offer a complete view of the state of the art on biodegradable polymer packages for food application.
The purpose of this paper was to carry out microwave induced pyrolysis of oil palm biomass (shell and fibers) with the help of char as microwave absorber (MA). Rapid heating and yield of microwave pyrolysis products such as bio-oil, char, and gas was found to depend on the ratio of biomass to microwave absorber. Temperature profiles revealed the heating characteristics of the biomass materials which can rapidly heat-up to high temperature within seconds in presence of MA. Some characterization of pyrolysis products was also presented. The advantage of this technique includes substantial reduction in consumption of energy, time and cost in order to produce bio-oil from biomass materials. Large biomass particle size can be used directly in microwave heating, thus saving grinding as well as moisture removal cost. A synergistic effect was found in using MA with oil palm biomass.
Block copolymer self-assembly is an innovative technology capable of patterning technologically relevant substrates with nanoscale precision for a range of applications from integrated circuit fabrication to tissue interfacing, for example. In this article, we demonstrate a microwave-based method of rapidly inducing order in block copolymer structures. The technique involves the usage of a commercial microwave reactor to anneal block copolymer films in the presence of appropriate solvents, and we explore the effect of various parameters over the polymer assembly speed and defect density. The approach is applied to the commonly used poly(styrene)-b-poly(methyl methacrylate) (PS-b-PMMA) and poly(styrene)-b-poly(2-vinylpyridine) (PS-b-P2VP) families of block copolymers, and it is found that the substrate resistivity, solvent environment, and anneal temperature all critically influence the self-assembly process. For selected systems, highly ordered patterns were achieved in less than 3 min. In addition, we establish the compatibility of the technique with directed assembly by graphoepitaxy.
We report on the rapid production, characterization, and spectral properties of highly uniform, ultra narrow semiconductor (ZnS, ZnSe, CdS, CdSe) nanorods and nanowires by microwave irradiation. Quantum-confinement effects are manifested in the light absorption and the PL of the rods and wires. The uniformity of the rods and of the wires is demonstrated in their spontaneous assembly into highly ordered 2D supercrystals. We also observed the stepwise growth of the rods originating from nearly spherical nuclei.
ABS/montmorillonite nanocomposites for fused deposition modeling 3D printing
ABS/montmorillonite nanocomposites for fused deposition modeling 3D printing. Mater Des.
2016;102:276-83.
Morphology and crystalline characteristics of polylactic acid
- S M Bhasney
- P Bhagabati
- A Kumar
- V Katiyar
Bhasney SM, Bhagabati P, Kumar A, Katiyar V. Morphology and crystalline characteristics
of polylactic acid [PLA]/linear low density polyethylene [LLDPE]/microcrystalline cellulose
[MCC] fiber composite. Compos Sci Technol. 2019;171:54-61.
Fast Assembly of Ordered Block Copolymer Nanostructures through Microwave Annealing
- X Zhang
- K Harns
- N Wu
- J Murphy
- J Buriak
Zhang X, Harns K, Wu N, Murphy J, Buriak J. Fast Assembly of Ordered Block Copolymer
Nanostructures through Microwave Annealing. ACS Nano 2010;4(11):7021-9.