Journal of Thermoplastic Composite Materials

Agave Americana (agave) and Agave sisalana (sisal) fibres belong to the same family of natural fibres. Both the fibres were treated with alkali. Interestingly, alkali-treated agave fibres displayed a clean and smooth surface, whereas alkali-treated sisal fibres showed a rough surface due to the rupture of alkali-sensitive bonds. This indicated that the sisal fibres are more susceptible to alkali treatment as compared to agave fibres. The experimental studies of chemical composition, Fourier transform infrared spectroscopy and X-ray diffraction were also carried out. Both alkali-treated agave and sisal fibres were used to reinforce polyfurfuryl alcohol (PFA) matrix. The effect of these fibres on the mechanical and thermo-mechanical properties of PFA composites was examined. Mechanical, thermal and thermo-mechanical properties of the composites were studied. The results indicated the improvement in mechanical and thermal properties of the reinforced PFA.

Pineapple leaf fiber (PALF) was treated by silane and isocyanate treatments at 0–20% prior to being used as reinforcement in low-density polyethylene (LDPE) and polypropylene (PP) composites. The reactive groups of silane and isocyanate on PALF surface were confirmed by Fourier transform infrared spectroscopy. Scanning electron micrographs also showed the fiber surface coated with layers of treated chemicals as compared with the untreated one. These surface treatments reduced the water absorption of PALF. The physical properties of the PALF-reinforced composites were investigated. The resulting composites possessed higher tensile strength and lower crystallinity than the untreated composites. Silane treatment gave better PALF/LDPE composites in terms of composite strength as compared to isocyanate treatment. For treated PALF/PP composites, fiber pullout was reduced both silane and isocyanate treatments.

Composite filaments of thermoplastic polyurethane (TPU) and single-walled carbon nanotubes (SWCNTs) have been fabricated via extrusion process and their properties were studied using various characterization techniques. Twin-screw extruder has been used for making the composite filaments and the processing parameters like temperature, screw speed, and pressure were optimized. Thermal, morphological, mechanical, and electrical properties were studied by varying the weight percentage of SWCNTs. Raman shift of SWCNTs is observed for the CNTs dispersed in TPU matrix. Thermal analysis shows that there is an increase in the degradation and melting temperature of the TPU/SWCNTs blends. With the addition of SWCNTs as small filler loadings of 1 wt%, the tensile strength of the blended materials increased from 13 MPa to 21.6 MPa. The electrical conductivity of the composite filaments starts with the addition of 0.01% of SWCNTs. The highest value of electrical conductivity (3.7 × 10⁻⁷ S cm⁻¹) obtained with 2 wt% of SWCNTs. This melt extrusion process method could open up for the preparation of new high-performance nanotube composite materials.

Chemically modified sisal fibers are used to reinforce high-density polyethylene to seek applications in electrical appliances and car industry requiring light composite materials with superior mechanical and dielectric properties. Conventional methods of chemical modification using sodium hydroxide are used together with new modifications using benzoyl chloride and benzoyl peroxide in order to improve the compatibility between the hydrophilic fiber surface and the hydrophobic polymer matrix. Mechanical properties have been improved by more than 50%, and improved thermal and electrical properties are achieved using the resulting microcomposite material. The resulting microcomposite can accordingly find its way in electrical appliances and in the car industry replacing metallic parts especially those requiring high dielectric constant and superior mechanical properties.

Magnesium hydroxide (MH) was added into high-density polyethylene (HDPE)/ethylene vinyl-acetate (EVA) copolymer blends with various MH contents (30–60 wt%) to improve the flame retardancy of HDPE/EVA blends. The flammability, morphology of charred residues, thermal stability, crystallization, and mechanical properties of HDPE/EVA/MH composites were investigated by UL-94 test, limiting oxygen index (LOI), cone calorimeter test (CCT), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and tensile test. The data obtained from LOI, UL-94 test, and CCT revealed that the addition of MH provided improvements in flame retardancy by increasing the LOI values, UL-94 rating, and reducing heat release, carbon monoxide and carbon dioxide emissions along with delayed ignition with increasing the content of MH. The UL-94 V-0 rating and high LOI value were achieved with the incorporation of MH at a loading level higher than 50 wt% in HDPE/EVA blends, which suggested that the formation of intact, consolidated, and thick residue structures on the surfaces of MH-filled composites prevented the underlying polymer materials from burning. DSC results showed that the crystallinity of HDPE/EVA blends increased with increasing the content of MH, resulting in the enhancement of the strength of HDPE/EVA/MH composites. The thermal stability of HDPE/EVA blends decreased due to the addition of MH.

An experimental study was conducted to investigate the effects of temperature and strain rate on tensile behavior of polybutylene terephthalate and polyamide-6 reinforced with short glass fibers. Tension tests were performed in several mold flow directions, at a range of temperatures between −40°C and 125°C, and a range of strain rates between 5 × 10⁻⁵ s⁻¹ and 5 × 10⁻¹ s⁻¹. Mathematical relationships were developed to represent the stress–strain response, as well as tensile strength and elastic modulus in terms of strain rate and temperature. Time–temperature superposition principle was also employed to superimpose the effect of temperature and strain rate on tensile strength. A temperature-dependent shift factor of Arrhenius type is suggested, which is independent of the mold flow direction. Mechanisms of tensile failure were also identified from fractured surface of specimens.