Modeling of Twin Screw Extrusion of Polymeric Materials

An issue of modeling of twin-screw extrusion of polymeric materials is reviewed. The paper is written in honor of Prof. James L. White who was a pioneer in studying this issue. A global approach to process modeling is presented which includes solid polymer transport, polymer plasticating, and the flow of molten polymer. The methodology of CFD modeling of twin-screw extrusion is presented as well as the examples of this modeling which show the details of the process. Optimization and scaling of twin-screw extrusion are also covered. And finally, the future prospects of developments and research of twin screw extrusion is discussed.

Improving the Oxygen Barrier of Polyamide Food Packaging by Using Nanoclay

The effect of nanoclay additive on polyamide film oxygen permeability is investigated from the perspective of possible use as a laminate component for low-cost food packaging material. Montmorillonite nanoclay was melt-mixed in an industrial grade polyamide by twin-screw extrusion and the mixture was hot-pressed to a ~50 µm thick film. The film with 10 wt.% of nanoclay loading showed a 17 % decrease in the oxygen transmission rate (OTR), as compared to the pristine polyamide film (72 and 87 cm3/m2∙24 h, respectively). Despite the relatively high loading of the filler the obtained OTR exceeds that of the food packaging preferred upper limit of 10 cm3/m2∙24 h. XRD measurements confirmed the near-complete exfoliation of the nanoclay platelets. The platelets were found to be at an average angle of 9.5 degrees relative to the film’s surface plane. To comply with the requirements for food packaging, this angle needs to be decreased down to 0.4 degrees. To achieve this, different film-making methods enabling better control over the filler particles’ orientation need to be explored. Nanoclay addition increased the films’ yield strength (23 % for 10 wt.% film) and stiffness, while not affecting the films’ optical appearance.

Influence of Twin-Screw Extrusion on The Dispersion of Nanoclay in Vinylester Composites

This paper reports the dispersion of nanoclay in vinylester using co-rotating twin screw extrusion and ultrasonication for preparing nanoclay/vinylester gel coat. Two sets MMT/vinylester specimens, namely Type 1 and Type 2 were prepared for comparative studies. While Type 1 specimens were prepared using ultrasonication only, Type 2 specimens were prepared using both ultrasonication and twin-screw extrusion. Type 2 specimens showed lower levels of nanoclay intercalation and higher levels of exfoliation. By using the MMT/vinylester gel coat so prepared by the two different routes, MMT/vinylester/glass specimens were fabricated and tested for mechanical properties. Type 2 based nanocomposite specimens showed greater values of ultimate tensile strength, flexural strength, interlaminar shear strength and impact strength. Scanning Electron Micrographs (SEM) of tensile fractured Type 2 based specimens showed less agglomeration of nanoclay than that of Type 1 based specimens.

Preparation and Characterization of Polybutylene Succinate Reinforced with Pure Cellulose Nanofibril and Lignocellulose Nanofibril Using Two-Step Process

This study reports the preparation of a polybutylene succinate (PBS) film reinforced with pure cellulose nanofibril (PCNF) and lignocellulose nanofibril (LCNF) by a two-step process that consists of solvent dispersion and twin-screw extrusion. Compared to the conventional one-step process, this method offered improved mechanical properties. The addition of 5% CNF increased the tensile properties up to 18.8%. Further, the effect of the lignin content was also studied by using LCNF as a reinforcement. The LCNF was prepared with and without a deep eutectic solvent (DES) pretreatment to gain LCNF with a lignin content that varied between 5, 19, and 30%. The mechanical properties results show that a 5% addition of LCNF to the PBS matrix increased its tensile strength and elastic modulus. Further, the morphological and thermal properties of the composites were also studied in detail.

Valorisation of Bagasse Cane by-Product: Effect of Cellulosic Fibers and Coupling Agent on Thermal, Mechanical and Rheological Behaviours of Reinforced Polypropylene

Recently more attentions are growing every day towards the valorisation of industrial by-product especially those generated through agriculture and food industries, as the demands of bio-based resources for the necessary transition from fossil hydrocarbon sources to natural based products are increasing. This paper focuses on the potential effect of chemical treatments and modification as well as fibers loading on the thermal, mechanical, and rheological behaviour of reinforced Polypropylene (PP). During this work, fibers were prepared using alkali and bleaching treatments and then characterized using different analysis such SEM, X-ray, FT-IR and TGA/DTG. The composite materials were elaborated using twin-screw extrusion followed by injection molding by mixing PP with 5 to 10 Wt.% of raw bagasse cane (RBC), alkali bagasse cane (ABC) and bleached cellulose microfibers (BCM) as well as cellulose microfibers with Styrene-(ethylene-butene)-styrene three-block co-polymer grafted with maleic anhydride (SEBS-g-MA) as coupling agent. The result achieved from this study shows that the use of different type of fibers led to significant decrease in thermal degradation of PP. The mechanical results show a significant improvement in Yung’s modulus, tensile strength and hardness of the reinforced PP compared to neat PP. However, a remarkable decrease was obtained in elongation at break and toughness for all reinforced composites compared to neat PP. Besides, higher and low torsion modulus was obtained for PP reinforced with BCM and SEBS-g-MA-BCM, respectively.Statement of Novelty: This study aims to valorise bagasse sugar cane by-product as a lignocellulosic source for the isolation of cellulose fibers. Innovative composite materials were prepared based on polypropylene.

Properties of Mosquito Repellent-Plasticized Poly(lactic acid) Strands

Poly(lactic acid) (PLA) is an attractive candidate for replacing petrochemical polymers because it is fully biodegradable. This study investigated the potential of PLA as a sustainable and environmentally friendly alternative material that can be developed into commercially viable wearable mosquito repellent devices with desirable characteristics. PLA strands containing DEET and IR3535 were prepared by twin screw extrusion compounding and simultaneously functioned as plasticizers for the polymer. The plasticizing effect was investigated by thermal and rheological studies. DSC studies showed that the addition of DEET and IR3535 into PLA strands reduced the glass transition temperature consistent with predictions of the Fox equation, thus proving their efficiency as plasticizers. The rheology of molten samples of neat PLA and PLA/repellents blends, evaluated at 200 °C, was consistent with shear-thinning pseudoplastic behaviour. Raman studies revealed a nonlinear concentration gradient for DEET in the PLA strand, indicating non-Fickian Type II transport controlling the desorption process. Release data obtained at 50 °C showed initial rapid release followed by a slower, near constant rate at longer times. The release rate data were fitted to a novel modification of the Peppas-Sahlin desorption model.

On synergistic effect of BaTiO3 and graphene reinforcement in polyvinyl diene fluoride matrix for four dimensional applications

This work presents the synergistic effect of BaTiO3 and graphene (Gr) reinforcement in polyvinyl diene fluoride (PVDF) matrix by chemical-assisted mechanical blending (CAMB) for possible 4D applications. The PVDF matrix was prepared (in form of filament) by solvent casting followed by twin-screw extrusion (TSE) as CAMB process. The filament was used on fused deposition modelling (FDM) setup for preparing standard flexural and pull-out specimens. The mechanical testing revealed that the parts printed with 100% in-fill density (ID), 70 mm/s infill speed (IS), and 45° in-fill angle (IA) has shown better flexural strength (FS). For pull-out properties, part printed at IS 90 mm/s, 0° IA, and 100% ID have shown better results. Further optimized settings of FS were used to 3D print thin cylindrical discs followed by electric poling (for possible piezoelectric properties). The results of X-ray diffraction (XRD) and Fourier transmission infrared spectroscopy (FTIR) analysis show more β-phase formation in the electrically poled sample as compared to non-poled specimen. Moreover, XRD spectra show the homogenous dispersion of doped material in the PVDF matrix. The piezoelectric coefficient (d33) 30.2pC/N was observed on 3D printed specimen (prepared from filament processed with CAMB), suitable for 4D applications.

Fiber Length Distribution in Twin-Screw Extrusion of Fiber-Reinforced Polymer Composites: A Comparison between Shear and Extensional Mixing

New extensional mixing elements (EME) for twin-screw extrusion were applied to compound glass fibers (GF), carbon fibers (CF) or polyethylene terephthalate fibers (PETF) reinforced polymer composites with polymer matrix of polypropylene (PP) or polyethylene oxide (PEO) and the resulting fiber degradation upon processing was evaluated and compared with compounding via shear flow-dominated kneading blocks (KB). Composites structures were characterized in terms of fiber length and distribution, and cumulative length ratio, at five locations along the mixing zone. Although significant fiber breakage was achieved for both configurations, it was markedly lower in composites processed using the EME, because whereas the high shear stress kneading motion in the KB degrades fibers significantly, fiber breakup is significantly minimized by the alignment induced by the EME prior to flow in the high-stress regions.