Twin-screw Compounder Research Articles

Morphologies, Compatibilization and Properties of Immiscible PLA-Based Blends with Engineering Polymers: An Overview of Recent Works.

Poly(L-Lactide) (PLA), a fully biobased aliphatic polyester, has attracted significant attention in the last decade due to its exceptional set of properties, such as high tensile modulus/strength, biocompatibility, (bio)degradability in various media, easy recyclability and good melt-state processability by the conventional processes of the plastic/textile industry. Blending PLA with other polymers represents one of the most cost-effective and efficient approaches to develop a next-generation of PLA-based materials with superior properties. In particular, intensive research has been carried out on PLA-based blends with engineering polymers such as polycarbonate (PC), poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT) and various polyamides (PA). This overview, consequently, aims to gather recent works over the last 10 years on these immiscible PLA-based blends processed by melt extrusion, such as twin screw compounding. Furthermore, for a better scientific understanding of various ultimate properties, processing by internal mixers has also been ventured. A specific emphasis on blend morphologies, compatibilization strategies and final (thermo)mechanical properties (tensile/impact strength, ductility and heat deflection temperature) for potential durable and high-performance applications, such as electronic parts (3C parts, electronic cases) to replace PC/ABS blends, has been made.

Dual reconfigurable network from a semi-crystalline functional polyolefin

A statistical copolymer p(E-co-GMA) of ethylene and glycidyle methacrylate (4.5 wt%) is considered as a starting point towards semicrystalline networks with exchangeable links. Application of the binomial law to size exclusion chromatographic data suggests that chains deprived of reactive comonomers would represent less than 6 wt% of the total, allowing to expect the formation of high gel-content networks. Experimentally, up to 98 wt% gel is obtained upon modification with 3,3′-dithiopropionic acid (DTPA). The crosslinking reaction can be performed in the molten state through a 2-steps procedure: 1°) x mol. of a commercial grade p(E-co-GMA), y mol. of DTPA and z mol. of triazabicyclodecene (TBD) are sheared in a twin-screw compounder at 115 °C, a temperature right above the melting point of the polymer precursor, without triggerring the epoxy-acid addition; 2°) the thermolatent reactive blend thereby obtained is then crosslinked at 170 °C. Samples with x = 1, y = 1 to 4 and z = 0 to 0.8 were thus prepared and evaluated. The presence of TBD accelerates disulfide exchange reaction, possibly by involvement of the thiolate anion whereas it decelerates the epoxy-acid addition. The final networks present several characteristic properties of vitrimers such as insolubility in xylene above the melting point, thermo-activated stress relaxation and creep. Particular shape memory regimes, related to the semicrystalline vitrimer character and the high insoluble fraction are demonstrated. Eventually, production scale-up using continuous reactive extrusion is evaluated.

A case study on the rotomolding behavior of black tea waste and bio-based high-density polyethylene composites: Do active compounds in the filler degrade during processing?

This study verified the possibility of using waste material from the food industry (black tea) as functional filler of rotomolded biobased high-density polyethylene-based composites. As part of the experimental work, the influence of the materials preparation, i.e., dry blending versus twin-screw extrusion, on the effectiveness of the stabilizing antioxidant effect of the black tea was analyzed. The aim of the work was to verify whether, despite the initial degradation of the structure of the lignocellulosic filler, it would be possible to keep its antioxidant capacity and the stabilizing effect on the polyethylene matrix. The research showed that the filler allowed to stabilize the polymeric matrix during the rotomolding process, despite the appearance of numerous defects in the form of pores and a reduction in mechanical properties, more significant for composites prepared by dry blending, obtaining elastic modulus drops of about 50 %. Furthermore, the pre-processing step by melt mixing results in a significant improvement of the composite's thermo-oxidation stability, with increases in the oxidation induction time (OIT), from 25 min for the HDPE to over 70 min for composites with 5 % black tea, and improved rheological behavior, preventing the crosslinking of the matrix, indicative of its thermo-oxidative degradation. The tea brewing process caused the decrease of antioxidant activity of the filler; however, it did not significantly affect the antioxidant behavior, maintaining its influence on the polymeric matrix when the material is prepared via twin-screw compounding, which was proved to provide better stability, increasing OIT by approximately 20 min later when compared to dry blending.

Compounding, Rheology and Numerical Simulation of Highly Filled Graphite Compounds for Potential Fuel Cell Applications.

Highly filled plastics may offer a suitable solution within the production process for bipolar plates. However, the compounding of conductive additives and the homogeneous mixing of the plastic melt, as well as the accurate prediction of the material behavior, pose a major challenge for polymer engineers. To support the engineering design process of compounding by twin-screw extruders, this present study offers a method to evaluate the achievable mixing quality based on numerical flow simulations. For this purpose, graphite compounds with a filling content of up to 87 wt.-% were successfully produced and characterized rheologically. Based on a particle tracking method, improved element configurations were found for twin-screw compounding. Furthermore, a method to characterize the wall slip ratios of the compounded material system with different filler content is presented, since highly filled material systems often tend to wall slip during processing, which could have a very large influence on accurate prediction. Numerical simulations of the high capillary rheometer were conducted to predict the pressure loss in the capillary. The simulation results show a good agreement and were experimentally validated. In contrast to the expectation, higher filler grades showed only a lower wall slip than compounds with a low graphite content. Despite occurring wall slip effects, the developed flow simulation for the design of slit dies can provide a good prediction for both low and high filling ratios of the graphite compounds.

Improvement of the Thermo-Oxidative Stability of Biobased Poly(butylene succinate) (PBS) Using Biogenic Wine By-Products as Sustainable Functional Fillers.

Biobased poly(butylene succinate) (PBS) represents one promising sustainable alternative to petroleum-based polymers. Its sensitivity to thermo-oxidative degradation is one reason for its limited application. In this research, two different varieties of wine grape pomaces (WPs) were investigated as fully biobased stabilizers. WPs were prepared via simultaneous drying and grinding to be used as bio-additives or functional fillers at higher filling rates. The by-products were characterized in terms of composition and relative moisture, in addition to particle size distribution analysis, TGA, and assays to determine the total phenolic content and the antioxidant activity. Biobased PBS was processed with a twin-screw compounder with WP contents up to 20 wt.-%. The thermal and mechanical properties of the compounds were investigated with DSC, TGA, and tensile tests using injection-molded specimens. The thermo-oxidative stability was determined using dynamic OIT and oxidative TGA measurements. While the characteristic thermal properties of the materials remained almost unchanged, the mechanical properties were altered within expected ranges. The analysis of the thermo-oxidative stability revealed WP as an efficient stabilizer for biobased PBS. This research shows that WP, as a low-cost and biobased stabilizer, improves the thermo-oxidative stability of biobased PBS while maintaining its key properties for processing and technical applications.

TECHNOLOGY FOR OBTAINING SUPERCONCENTRATES (MASTERBATCH) BASED ON ALCOHOLYSIS PRODUCTS OF SECONDARY POLYETHYLENE TEREPHTHALATE

Regularities of alcoholysis of secondary polyethylene terephthalate (RPET) by diethylene glycol (DEG) have been studied. It is shown that with an increase in the amount of diethylene glycol taken for alcoholysis from 0.1 mol to 0.4 mol per 1 mol of the elementary unit of HPET, a decrease in molecular weight from 1480 to 707 and the associated melting point from 215 to 145 °C are observed, and also intrinsic viscosity from 0.075 to 0.05 dl/g. The physicochemical properties of the products of alcoholysis of SPET (PAPET) have been determined. It has been revealed that PAPET is slightly colored and this is an undesirable factor affecting the individuality of the color of masterbatches based on them. Washing out with PAPET leads to some increase in the molecular weight values and related other indicators of the final oligomers. The structure of PAPET has been studied by infrared spectroscopy and differential scanning calorimetry. It has been revealed that PAPET synthesized at a molar ratio of SPET : DEG of 1:0.4, in which the dropping point according to Ubellode is 155 °C, is most suitable for obtaining superconcentrates. On the basis of PAPET obtained under these conditions, formulations of black and white masterbatches for polyethylene terephthalate fibers have been developed. To ensure uniform dispersion of white (TiO2) and black (K-354 carbon black) pigments, polyethylene wax was added to the superconcentrates. Masterbatches have been obtained by dry method in a twin screw compounder equipped with a double strand head and a granulator. The technological properties of the developed black and white superconcentrates have been determined, which turned out to be very close to those of the superconcentrates used in production. Conducted production tests of these masterbatches have showed that they are not inferior in terms of performance to similar industrial masterbatches used for dyeing threads.

Modeling the mechanical properties of polypropylene/lignin/flax hybrid composites

Flax and lignin were used to prepare hybrid polypropylene composites. The lignin contents were varied between 0 and 50 vol%, while the amounts of flax used were 0, 10, 20, and 30 vol%. The components were homogenized in a twin-screw compounder and then injection molded into tensile bars. Tensile and impact tests were used to characterize the mechanical properties, and the structures were studied by scanning electron microscopy. The simultaneous effects of reinforcement on composite properties were analyzed quantitatively with models to establish synergies or a coupling effect of lignin. The agreement between measured results and predicted values proved to be excellent. The models were also successfully applied to data published in the literature. Lignin increased the strength from 10 to 20 MPa, and a smaller amount of added flax increased the strength up to 30 MPa. Modeling also established the stronger reinforcing effect of flax; the corresponding B parameters for lignin and flax were 3.7 and 5.9 for strength and 1.0 and 5.2 for impact resistance, respectively. The two reinforcements acted independently; their effects were additive, and synergism could not be detected. Only quantitative analysis and modeling offer reliable information about the effect of components in hybrid materials.

Three-component polypropylene/lignin/flax composites with high natural additive content for structural applications

Hybrid composites were prepared from a polypropylene reactor blend (rPP), lignin and flax fibers. Interfacial adhesion was improved using a functionalized PP (maleated PP, MAPP) coupling agent. Composition changed in a wide range; flax content varied between 0 and 30, while lignin content between 0 and 50 vol% in 10 vol% steps. The components were homogenized in a twin-screw compounder, and injection molded specimens were prepared from the compounds for further testing. The processability of the composites was characterized by the measurement of melt flow rate, while mechanical properties by tensile and impact testing. The combination of lignin and flax fibers yields materials with an advantageous property profile, considerably decreased carbon footprint and acceptable price. The application of flax compensates for the deteriorating effect of lignin on deformability and especially on impact resistance. Significant improvement was achieved in stiffness and strength. In order to obtain this property combination, the application of a coupling agent is necessary because of the poor interaction between PP and natural reinforcements. The compounds developed may successfully compete with materials offered on the market.

In-Line Rheo-Optical Investigation of the Dispersion of Organoclay in a Polymer Matrix during Twin-Screw Compounding.

The dispersion mechanisms in a clay-based polymer nanocomposite (CPNC) during twin-screw extrusion are studied by in-situ rheo-optical techniques, which relate the CPNC morphology with its viscosity. This methodology avoids the problems associated with post extrusion structural rearrangement. The polydimethylsiloxane (PDMS) matrix, which can be processed at ambient and low temperatures, is used to bypass any issues associated with thermal degradation. Local heating in the first part of the extruder allows testing of the usefulness of low matrix viscosity to enhance polymer intercalation before applying larger stresses for clay dispersion. The comparison of clay particle sizes measured in line with models for the kinetics of particle dispersion indicates that larger screw speeds promote the break-up of clay particles, whereas smaller screw speeds favor the erosion of the clay tactoids. Thus, different levels of clay dispersion are generated, which do not simply relate to a progressively better PDMS intercalation and higher clay exfoliation as screw speed is increased. Reducing the PDMS viscosity in the first mixing zone of the screw facilitates dispersion at lower screw speeds, but a complex interplay between stresses and residence times at larger screw speeds is observed. More importantly, the results underline that the use of larger stresses is inefficient per se in dispersing clay if sufficient time is not given for PDMS to intercalate the clay galleries and thus facilitate tactoid disruption or erosion.

Life Cycle Assessment of Olive Pomace as a Reinforcement in Polypropylene and Polyethylene Biocomposite Materials: A New Perspective for the Valorization of This Agricultural By-Product

The main environmental impact of olive oil production is the disposal of residues such as pomace and water vegetation. During the olive oil extraction process, the olive stone is milled and discharged within the olive pomace. However, olive stone flour can be valorized as filler for polymeric composites. A life cycle assessment of the olive pomace valorization was carried out by focusing on the manufacturing process of a biocomposite made of two different thermoplastic matrices, i.e., polyethylene and polypropylene. The functional unit is the production of 1 m2 of a lath made of an olive pomace-based biocomposite. The analysis was carried out with the SimaPro PhD 9.1.1.1 software, and the database used for the modeling was Ecoinvent 3.6. The obtained results reveal that the hotspot of the whole process is the twin-screw compounding of the olive stone fraction, with the polymeric matrix and coupling agent, and that human health is the most affected damage category. It represents 89% for both scenarios studied: olive stone fraction/polypropylene (OSF/PP) and olive stone fraction/polyethylene (OSF/PE). Further research directions include the use of biosourced polymer matrices, which could reduce the impact of olive pomace-based composite manufacturing.

Characterization of in-House-Developed Mn-ZnO-Reinforced Polyethylene: A Sustainable Approach for Developing Fused Filament Fabrication-Based Filament

This study outlines a sustainable development of Mn-ZnO-reinforced low density polyethylene (LDPE)-based feedstock filament, using twin screw extrusion (TSE) process, for fused filament fabrication-based additive manufacturing technology. Mn-ZnO-based reinforcement, known for its functional properties, has been utilized to tune the thermo-mechanical, morphological, and piezoelectric characteristics of LPDE. Functional feedstock filaments have been manufactured by varying twin screw compounder processing parameters such as barrel temperature (120, 130, and 140 °C), screw torque (0.15, 0.20, and 0.20 N.m) and forced loading (5, 10 and 15 kg). The results of the study suggested that the better mechanical properties of feedstock filament were attained at 140 °C barrel temperature, 0.25 N.m screw torque, and 10kg forced loading in TSE. The result of the tensile properties is supported by Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), piezoelectric property (D33 measurement), shape memory effect and differential scanning calorimetric analysis.

On Mn doped ZnO nano particles reinforced in PVDF matrix for fused filament fabrication: Mechanical, thermal, morphological and 4D properties

This study deals with investigations of mechanical, thermal, morphological and 4D (shape memory, magnetic and piezoelectric) properties of the feedstock filaments prepared for fused filament fabrication (FFF) process by twin-screw compounding of polyvinylidene difluoride (PVDF) reinforced with Mn doped ZnO. The Mn doped ZnO was synthesized by using sol-gel method up to the solubility limit (at first stage) so that the properties of the host, as well as dopant ions, are present in the composition. In the second stage, PVDF composite feedstock filaments reinforced with Mn doped ZnO nanoparticles have been prepared for FFF of biosensor/biomedical sensors/actuators. The results are supported by scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), differential scanning calorimetry (DSC) observations. The results of this study suggest that the optimum set of process parameters for tensile properties is combination of pre-heat treatment, 210 ℃ barrel temperature, 3 % Mn-ZnO loading, and 0.15N.m screw torque. Also the reinforcement of Mn-ZnO in PVDF has led to improved piezoelectric, magnetic, and shape memory properties.

Mechanical and water kinetic parameters of water-absorbed hard wood dust/high-density polyethylene composites

The mechanical (flexural, tensile and impact) properties and water kinetic parameters of water-absorbed hard wood (mangrove) reinforced high-density polyethylene composites were evaluated as untreated and treated mangrove dust (MD). Samples were prepared by mixing high-density polyethylene (HDPE) with MD at 10, 20 and 30% by weight in a twin-screw laboratory compounder and injection moulded into dumb-bell and rectangular-shaped test specimens for flexural, tensile and impact tests. Samples were soaked in distilled water for 1440 h at room temperature and a relative humidity of ~ 65%. The flexural strength and modulus indicated that treated composites exhibited lower decrease in values than their untreated counterparts at water equilibrium points. The dry composites maintained higher values of tensile properties, notwithstanding the treatment. Scanning electron microscopy of impact fractured surfaces showed evidence of improved MD-HDPE interfacial adhesion of treated composites in both dry and water-absorbed conditions. The water kinetics parameters such as the diffusion, sorption and permeability coefficients further show that dry composites are more water-resistant than the wet composites. Overall, the treated composites at dry and moisture-saturated conditions indicated better mechanical and moisture stability than the untreated MD/HDPE composites.

On ZnO nano particle reinforced PVDF composite materials for 3D printing of biomedical sensors

Abstract The inherent piezoelectric and biocompatibility behaviour of polyvinylidene difluoride (PVDF) and excellent biocompatibility, thermal and magnetic responses of zinc oxide (ZnO) nano particles made their blends as a good candidate for biosensor 3D printing. In this study, the co-precipitation method has been used to prepare the nano-sized ZnO particles, which are further reinforced with PVDF on twin screw compounder with the controlling proportion of ZnO, forced loading, and torque. The investigations of mechanical, thermal, morphological, and shape memory effect have been performed on the prepared feedstock filaments to check the effect of controlling parameters. It has been observed that maximum mechanical strength (tensile strength, percentage elongation and modulus of toughness) results without ZnO nano particle reinforcement, 1% reinforced critically reduced the mechanical properties but the mechanical properties of 2% ZnO nanoparticle reinforced PVDF composite were obtained better than PVDF-1%ZnO and less than PVDF-0%ZnO. Thermal analysis shows that increase in the ZnO percentage into PVDF improves the normalized heat capacity (25.16 J/g in PVDF to 33.07 J/g in PVDF-2%ZnO). The energy dispersive spectroscopy (EDS) analysis confirms the presence of ZnO on the fracture surface. The shape memory was found 98.22 % for PVDF-2%ZnO at 25 °C.

Characterization of textile-grade carbon fiber polypropylene composites

In this work, we consider low-cost carbon fiber produced with a textile-grade precursor. The objective of the study is to investigate textile-grade carbon-fiber-reinforced-polypropylene composites (TCF-PP) from compounded pellets for mechanical and thermal characterization. Four sets of pellets with 1%, 5%, 10%, and 15% reinforcement were manufactured using textile-grade carbon fiber (TCF) and polypropylene (PP) by twin-screw compounding. The addition of TCFs through gravimetric feeder directly in the extruder resulted in lower fiber content; however, side feeder has shown good potential. The pellets were further processed in extrusion compression molding to manufacture plaques. An increase in fiber loading has a negligible effect on fiber attrition as fiber length distribution variation between 1% and 15% reinforced pellets was very small. The addition of TCFs in PP showed a significant improvement in mechanical properties. The tensile strength and modulus of the composite were 26% and 161%, respectively, improved by the addition of 10 wt% TCF. Similar results were observed in the flexure test. However, the impact properties were reduced by 25.54% by the addition of 15% TCF.

ZnO nanoparticle-grafted PLA thermoplastic composites for 3D printing applications: Tuning of thermal, mechanical, morphological and shape memory effect

The zinc oxide (ZnO)-grafted polymers have emerged as a prominent material for fabrication of 3D printed biosensor due to its inherent antibacterial, antifungal, room temperature ferromagnetic magnetic behaviour, crystallinity, high thermal conductivity and high exaction binding energy. In this study, ZnO (nanoparticles (NPs)) were grafted with polylactic acid (PLA) using twin-screw compounder for preparations of feedstock filaments. The filaments were prepared by varying input parameters of twin-screw compounder such as ZnO concentration in PLA (0–2%), forced loading (10–15 kg) and torque (0.1–0.2 Nm). Further tests were conducted for thermal properties (on differential scanning calorimetry set-up), mechanical properties (on ultimate tensile testing set-up, Shore D surface hardness, optical photomicrograph-based porosity analysis) and shape memory effect (with stimulus as water under different temperature conditions). The results of the study show that inducing 1% ZnO in PLA led to the formation of highly responsive composite with water as stimulus (at 25°C temperature), mechanically weak, porous, soft surface, while incorporation of 2% ZnO in PLA headed to less porous, harder and responsive composite to the water as stimulus (at 40°C temperature). The proposed combination of ZnO NPs and PLA shows encouraging range of crystallinity, tensile properties and shape memory effect, which made it an eligible candidate for 3D printing applications.

Properties of Styrene-Maleic Anhydride Copolymer Compatibilized Polyamide 66/Poly (Phenylene Ether) Blends: Effect of Maleic Anhydride Concentration and Copolymer Content.

Polyamide 66 (PA66)/poly (2,6-dimethyl-1,4-phenylene ether) (PPE) blends with a ratio of 50/50 (w/w) were produced by a twin-screw compounder. The immiscible blends were compatibilized using two different styrene–maleic anhydride copolymers (SMA) with a low (SMAlow) and a high (SMAhigh) maleic anhydride (MA) concentration of 8 and 25 wt%, respectively. Furthermore, the SMA content was varied from 0 to 10 wt%. The influence of MA concentration and SMA content on the morphological and thermomechanical properties of PA66/PPE blends was investigated. Herein, we established correlations between the interfacial activity of the SMA with blend morphology and corresponding tensile properties. A droplet-sea to co-continuous morphology transition was shown by scanning electron microscopy to occur between 1.25 and 5 wt% in the case of SMAhigh. For SMAlow, the transition started from 7.5 wt% and was still ongoing at 10 wt%. It was found that SMAlow with 10 wt% content enhanced the tensile strength (10%) and elongation at break (70%) of PA66/PPE blends. This improvement can be explained by the strong interfacial interaction of SMAlow within the blend system, which features the formation of nanoemulsion morphology, as shown by transmission electron microscopy. Very small interdomain distances hinder matrix deformations, which forces debonding and cohesive failure of the PPE phase as a “weaker” main deformation mechanism. Due to a lack of interfacial activity, the mechanical properties of the blends with SMAhigh were not improved.

Novel procedure for laboratory scale production of composite functional filaments for additive manufacturing

Successful 3D printing by material extrusion of functional parts for new devices requires high quality filaments. Uniform homogeneity and good dispersion of particles embedded in filaments typically takes several cycles of extrusion or well-prepared feedstock by injection molding, industrial kneaders or twin-screw compounding. These methods need specific production devices that are not available in many laboratories non-specialized in polymer research, such as those working on different material science and technology topics that try to connect with additive manufacturing. Therefore, laboratory studies are usually limited to compositions and filler concentrations provided by commercial companies. Here, we present an original laboratory scale methodology to custom-prepare the feedstock for extruding magnetic composite filaments for fused filament fabrication (FFF), which is attainable by a desktop single-screw extruder. It consists in encapsulating the fillers in custom made capsules that are used as feedstock and reach the melting area of the extruder maintaining the same concentration of fillers. Results have shown that our approach can create smooth and continuous composite filaments with good homogeneity and printability with fine level of dimensional control. We further show the good dispersion of the particles in the composite filament using X-Ray Tomography, which enabled a 3D reconstruction of the spacial distribution of the embedded magnetic particles. The major advantage of this new way of preparing the composite feedstock is that it avoids the hassle of multiple extrusion runs and industrial machinery, yet providing uniform filaments of well controlled filler concentration, which is predictable and reproducible. The proposed methodology is suitable for different polymer matrices and applicable to other functional particle types, not just limited to magnetic ones. This opens an avenue for further laboratory scale development of novel functional composite filaments, useful for any community. This democratization of complex filament preparation, including consumers preparing their own desired uniform novel filaments, will facilitate to unify efforts nearing 3D printing of new functional devices.

Strong and super thermally insulating in-situ nanofibrillar PLA/PET composite foam fabricated by high-pressure microcellular injection molding

Strong, thermally insulating and biological PLA foams derived from cost-effective and environmentally friendly process are needed for saving resources and improving energy efficiency. PLA’s brittle feature and poor foaming ability are currently the major challenges which strongly restrict developing high-performance PLA foams. Herein, a scalable, cost-effective and environmentally friendly route by combining in-situ nanofibril reinforcement with high-pressure microcellular injection molding (HPMIM) was developed for producing high-performance PLA foams. Nanofibrillar PLA/PET composite was prepared by coupling twin-screw compounding and melt spinning. The presence of PET nanofibrils with an average diameter of 114.8 nm greatly improve PLA’s crystallization, viscoelasticity and melt strength, thereby enhancing its foaming ability. Thus, sub-microcellular nanofibrillar PLA/PET composite foam with an average cell size of 322.8 nm was produced using HPMIM, which shows dramatically enhanced mechanical properties than the pure PLA foam. Remarkably, the Izod and Gardner impact strengths of the HPMIM-fabricated PLA/PET foam are respectively more than 7-fold and 6-fold higher than those of the PLA foam fabricated by regular microcellular injection molding. Moreover, nanofibrillar PLA/PET composite foams with expansion ratio varying from 3.8-fold to 26.2-fold were fabricated. Thanks to the unique nanostructured cell walls with numerous micro/nano fibrils and voids, these nanofibrillar PLA/PET composite foams with large expansion ratios show outstanding thermally insulating properties. The 26.2-fold PLA/PET composite foam exhibits a thermal conductivity of 26.8 mW/m·K, much better than that of current polymer foams. The scalable and environmentally friendly method combined with the unique foam structure opens up new perspectives for developing high-performance multifunctional porous materials.

Percolative polyurethane-polypyrrole-straw composites with enhanced dielectric constant and mechanical strength

Percolative polyurethane composites utilizing surface modified paddy straw particles as filler and exhibiting enhanced dielectric constant and tensile strength, low dissipation and reduced water absorption have been presented. A thin coating of Polypyrrole (PPy) conducting polymer over paddy straw (St) micro particles was accomplished via vapour phase polymerization. Composites were prepared by using a lab scale twin-screw compounder and injection moulding system to mimic the actual industrial processing conditions. At 30 phr, PPy coated particles filled composites exhibited 133 % and 26 % increment in dielectric constant (13.61, 1 KHz) and tensile strength (58.3 MPa) respectively with reduced water absorption by 51.3 % (264 h) at room temperature as compared to their counterparts filled with uncoated particles. The successful preparation of these lightweight composites with improved performance paves the way for low cost, sustainable and eco-friendly materials for high end applications including electronics and sensors.