The effects of compatibilizers and hydrolysis on the tensile and impact strength, interfacial tension and morphology of the PP/PLA (80/20) blends were investigated. For the PP/PLA (80/20) blends before hydrolysis, the tensile strength of the blends reached a maximum when the polypropylene-g-maleic anhydride (PP-g-MAH) copolymer was added at 3 phr. For the PP/PLA (80/20) blends after hydrolysis, the tensile strength did not change appreciably with the PP-g-MAH content. For the blends with the styrene-ethylene-butylene-styrene-g-maleic anhydride (SEBS-g-MAH) before or after hydrolysis, the tensile strength of the blends decreased with increasing SEBSg-MAH content. The interfacial tension of the PP/PLA (80/20) blend was determined from the relaxation time using the Palierne and Choi-Schowalter models, and showed a minimum value at a PP-g-MAH content of 3 phr in each model. For the PP/PLA (80/20) blends with the SEBS-g-MAH before and after hydrolysis, the increase in impact strength was more significant for the blends after hydrolysis. This suggests that PLA becomes less brittle after hydrolysis. The impact strength suggests that the SEBS-g-MAH is an effective impact modifier to improve the impact strength of the PP/PLA (80/20) blends.
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been associated with diabetes in several epidemiological studies. However, the diabetogenic action of TCDD on pancreatic cells is unclear. Here, we investigated the direct toxic effects of TCDD on a rat insulin-secreting beta cell line. We found that TCDD enhances exocytosis of MTT formazan and lysosomal proteins such as beta-hexosaminindase and Lamp-1. This TCDD-induced exocytosis was abrogated by T-type calcium channel blockers (mibefradil, flunarizine) but not by an aryl hydrocarbon receptor antagonist (alpha-naphtoflavone). Indeed, cytosolic calcium levels were increased by TCDD. Furthermore, TCDD stimulated insulin secretion, which was inhibited by flunarizine. Taken together, our results suggest that TCDD-induced calcium influx via T-type channels regulates vesicular trafficking, such as lysosomal and secretory granule exocytosis, and that TCDD might exert adverse effects on beta cells by continuous insulin release followed by beta cell exhaustion. This could contribute to the link between TCDD exposure and the risk of developing diabetes.
A process designed to synthesize rigid polyurethane foam (PUF) with insulative properties via the modulation of PUF cell size via the addition of clay and the application of ultrasound was assessed. The blowing agents utilized in this study include water, cyclopentane, and HFC-365mfc, all of which are known to be environmentallyfriendly blowing agents. The rigid PUFs were prepared from polymeric 4,4'-diphenylmethane diisocyanate (PMDI) and polyether polyol with a density of 50 kg/m 3 . In addition, rigid PUFs/clay nanocomposites were synthesized with clay modified by PMDI with and without the application of ultrasound. The PUF generated using water as a blowing agent evidenced the highest tensile strength. The tensile strength of the PUF/nanocomposites was higher than that of the neat PUF and the strength was even higher with the application of ultrasound. The cell size of the PUF/clay nanocomposites was less than that of the neat PUF, regardless of the type of blowing agent utilized. It appears that the higher tensile strength and lower cell size of the PUF/clay nanocomposites may be attributable to the uniform dispersion of the clay via ultrasonic agitation. The thermal conductivity of the PUF/clay nanocomposites generated with HCFC-141b evidenced the lowest value when PUF/clay nanocomposites were compared with other blowing agents, including HFC-365mfc, cyclopentane, and water. Ultrasound has also proven effective with regard to the reduction of the thermal conductivity of the PUF/clay nanocomposites with any of the blowing agents employed in this study. It has also been suggested that the uniformly dispersed clay particles in the PUF matrix function as diffusion barriers, which prevent the amelioration of the thermal insulation property.
This article investigates the effects of liquid-type silane additives and organoclay as a solid-type additive on the morphological, mechanical and thermal insulating properties of polyisocyanurate-polyurethane (PIR-PUR) foams. The organoclay likely acted as nucleating agents during the formation of PIR-PUR foams. When the liquid silane additives and organoclay were added, the cell size and thermal conductivity of the PIR-PUR foams appeared to be decreased. However, organoclay did not contribute to reduce the cell size distribution of the foam. PIR-PUR foams synthesized with tetramethylsilane as a liquid-type additive showed a smaller average cell size and lower thermal conductivity than that of PIR-PUR foams synthesized with the other silane additives or with organoclay as a solid-type additive. For the PIR-PUR foam with organoclay/TEMS (1.5/1.5 php) mixture, cell size and thermal conductivity of the foam showed similar to the foam with TEMS. These results suggest that smaller cell size appears to be one of the major factors in the improvement of thermal insulation properties of the PIR-PUR foams. Silane additives did not seem to have a strong effect on the flammability of the PIR-PUR foams. However, heat resistance was more dominant for the foam with the organoclay at the higher temperature.
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