This research work has concerned a study on thermomechanical and crystallization properties of poly(lactic acid) (PLA) composites containing three different types of additives; namely: kenaf fiber (20 pph), Cloisite30B nanoclay (5 pph), and hexagonal boron nitrile (h-BN; 5 pph). The composites were prepared using a twin screw extruder before molding. Crystallization behaviors of the various composites were also examined using a differential scanning calorimetry. By adding the additives, tensile modulus of the polymer composites increased, whereas their tensile strength and elongation values decreased as compared to those of the neat PLA. Heat distortion temperature (HDT) values of the materials slightly increased, for about 3-5 C. However, after annealing at 100 C, HDT values of the fabricated PLA composites rapidly increased with annealing time before reaching a plateau after 10 min. The HDT values of above 120 C were achieved when 20 pph kenaf fiber was used as an additive. The above results were in a good agreement with DSC thermograms of the composites, indicating that percentage crystallinity of the materials increased on annealing and crystallization rate of the PLA/kenaf system was the highest.

This research work has concerned a study on relationship between structure and properties of maleated thermoplastic starch (MTPS)/plasticized poly(lactic acid) (PLA) blend. The aim of this work is to investigate the effects of blending time, temperature, and blend ratio on mechanical, rheological, and thermal properties of the blend. The MTPS was prepared by mixing the cassava starch with glycerol and maleic anhydride (MA). Chemical structure of the modified starch was characterized by using a FTIR technique, whereas the degree of substitution was determined by using a titration technique. After that, the MTPS prepared by 2.5 pph of MA was further used for blending with triacetin-plasticized PLA under various conditions. Mechanical, thermal, and rheological properties of the blends were evaluated by using a tensile test, dynamic mechanical thermal analysis, and melt flow index (MFI) test, respectively. It was found that tensile strength and modulus of the MTPS/PLA blend increased with the starch content, blending temperature, and time, at the expense of their toughness and elongation values. The MFI values also increased with the above factors, suggesting some chain scission of the polymers during blending. SEM images of the various blends, however, revealed that the blend became more homogeneous if the temperature was increased. The above effect was discussed in the light of transesterification. Last, it was found that mechanical properties of the PLA/MTPS blend were more superior to those of the normal PLA/TPS blends.

ABSTARCT: Poly(vinyl chloride) was blended with an acrylic rubber at a variety of blending ratio using a twinscrew extruder. The acrylic rubber was compounded with sulfur and sodium stearate in a two-roll mill prior to the blending. Dynamic vulcanization was performed in a compression mould at 170°C. Mechanical properties of the blends were determined by using a tensile testing machine. Scanning electron microscope was used to examine morphology of these blends. Degree of crosslinking of acrylic rubber in the blends was evaluated by using a differential scanning calorimeter. It was found that the normal blends are miscible regardless of the blending variables. By performing dynamic vulcanization, however, the blends became immisicible, showing a typical dispersed particle morphology, which was accompanied by a remarkable improvement of tensile properties. The screw-rotating speed was an important parameter affecting particle size and crosslink density of the rubber phase, which in turn controlled the tensile toughness of the blends. On the one hand, tensile toughness increased with the speed because of the decreasing particle size. On the other hand, the toughness decreased with the speed because of the decreasing crosslink density of the rubber. As a result, there was an optimum speed for each blend ratio, which corresponded to the maximum toughness.

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