ABSTRACT:We have developed high-performance biomass-based plastics that consist of poly(lactic acid) (PLA) and kenaf fiber, which fixates CO 2 efficiently. Adding this fiber to PLA greatly increases its heat resistance (distortion temperature under load) and modulus and also enhances its crystallization, so the ease of molding this material is improved. Eliminating the short particles from the kenaf fiber improves its effect on the impact strength. Kenaf fiber without the particles exhibits effects on these characteristics of PLA practically comparable to the effects of glass fiber. Furthermore, adding a flexibilizer (a copolymer of lactic acid and aliphatic polyester) to the composites improves their strength. These composites (PLA/kenaf fiber and PLA/ kenaf fiber/flexibilizer) show good practical characteristics for housing materials of electronic products in comparison with petroleum-based plastics used in housing such as glassfiber-reinforced acrylonitrile-butadien-styrene (ABS) resin.

Bio-based polymer composite was successfully fabricated from plant-derived kenaf fiber (KF) and renewable resource-based biodegradable polyester, poly(Llactide) (PLLA), by melt-mixing technique. The effect of the KF weight contents (0, 10, 20, and 30 wt %) on crystallization behavior, composite morphology, mechanical, and dynamic mechanical properties of PLLA/KF composites were investigated. It was found that the incorporation of KF significantly improves the crystallization rate and tensile and storage modulus. The crystallization of PLLA can be completed during the cooling process from the melt at 58C/min with the addition of 10 wt % KF. It was also observed that the nucleation density increases dramatically and the spherulite size drops greatly in the isothermal crystallization with the presence of KF. In addition, with the incorporation of 30 wt % KF, the half times of isothermal crystallization at 1208C and 1408C were reduced to 46.5% and 28.1% of the pure PLLA, respectively. Moreover, the tensile and storage modulus of the composite are improved by 30% and 28%, respectively, by the reinforcement with 30% KF. Scanning electron microscopy observation also showed that the crystallization rate and mechanical properties could be further improved by optimizing the interfacial interaction and compatibility between the KF and PLLA matrix. Overall, it was concluded that the KF could be the potential and promising filler for PLLA to produce biodegradable composite materials, owing to its good ability to improve the mechanical properties as well as to accelerate the crystallization of PLLA.

An intelligent shape-memory polymer was made through the synthesis of poly(lactic acid) macromonomers with furanyl groups and crosslinking with linkers with maleimidyl groups. The thermoreversible covalent bonds formed by the Diels-Alder reaction between these groups made this polymer recyclable (i.e., environmentally friendly). The structure of the polymer was also studied. A defect of the structure, a dissociated moiety of the thermoreversible bonding, was strongly affected by the reaction conditions and was investigated with UV spectroscopy, which was used to monitor the concentration of the maleimidyl groups. The relation between the flexibility of the linker and the strength and inner stress of the polymer was also evaluated. Reducing the number of defects and relaxing the inner stress were found to increase the strength of the shape-memory polymer.

Long/short chain mixed cellulose esters (MCE) are practical, promising polymers with interesting properties. In the molecular design of MCE, using long acyl chains made from renewable resources is important and enhances the value of MCE as sustainable materials. In this study, we focused on two types of renewable long acyl chains for MCE: the aromatic 3-pentadecylphenoxy acetyl (PA) group derived from cardanol extracted from cashew nutshells and the aliphatic stearoyl (St) group made from vegetable oils. Using these long acyl chains and the acetyl (Ac) group as a short acyl chain, we synthesized PA/Ac MCE (P-series) and St/Ac MCE (S-series) in LiCl/DMAc medium. The thermal and mechanical analyses revealed that a mixed substitution of long and short acyl chains prevented the crystallization of the long acyl chain moieties in MCE. The P-series had slightly higher bending strength and glass transition temperature than those of the S-series but showed low impact strength because of the existence of the aromatic ring in the PA group, which caused an increase in the stiffness of the cellulose backbone and the extra intermolecular interaction. However, the S-series without aromatic rings showed remarkably improved impact strength with sufficient balanced mechanical properties for use in durable products due to its composition of low crystalline long acyl chain moieties.

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New flame‐retardant epoxy resin compounds containing novolac derivatives with specific aromatic compounds have been developed. After crosslinking reactions between epoxy resin and hardener, the epoxy resin compounds formed highly flame‐retardant network structures that were obtained by including biphenylene and phenylene moieties in the main chains of novolac‐type epoxy resin and phenol novolac resin hardener. The high flame retardancy is due mainly to the stable foam layers that form during combustion because of the low elasticity at high temperatures and the high pyrolysis resistance of the compounds. Furthermore, the addition of excess phenol derivative hardener not only facilitates the formation of the foam layers by decreasing the crosslink densities but also reduces the amount of flammable substances generated from the epoxy resin compounds during combustion. The use of a multifunctional epoxy resin containing four glycidyloxy groups in the compounds improved characteristics such as heat resistance and strength at high temperatures, while maintaining excellent flame retardancy. Copyright © 2001 John Wiley & Sons, Ltd.

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Plant-derived kenaf fiber (KF)-reinforced poly(e-caprolactone) (PCL) biocomposites were successfully fabricated by the melt mixing technique. The crystallization behavior, morphology, and mechanical and dynamic mechanical properties of PCL/KF composites with various KF weight contents were investigated. The crystallization rate, tensile and storage moduli significantly improved as compared to the virgin polymer. The half times of PCL/KF composite (20 wt % fiber content) in isothermal crystallization at 408C and 458C reduced to 31.6% and 42.0% of the neat PCL, respectively. Moreover, the tensile and storage modulus of the composite are improved by 146% and 223%, respectively, by the reinforcement with 30% KF. The morphology evaluated by SEM indicates good dispersion and adhesion between KF and PCL. Overall, these findings reveal that KF can be a potential reinforcement for the biodegradable polymer composites owing to its good ability to improve the mechanical properties as well as crystallization rate.