Land-fill test of poly (L-lactic acid) blended with wheat bran (PLA/Bran blend) was carried out at two places, Kanazawa and Tsukuba (Japan). The test pieces were prepared by injection molding method. The mechanical properties in the blend sample considerably decreased with exposure time as compared with that of non-blended PLA. Further the molecular weight of PLA in the blended one decreased in one month. On the other hand, that of non-blended PLA hardly decreased under the same conditions. The number of microorganism on the surface of the blended test piece was from 100 to 10000 times as many as that on the non-blended one. The decrease of mechanical properties in the blend can be attributed to the effect of microorganism. Additionally, any clear difference was not observed in the results between Kanazawa and Tsukuba, though the humidity and the temperature of these places in the atmosphere were different from each other in winter.
In order to improve the erosion resistance to electric discharge of epoxy resin insulator with high tracking resistance, the surface of silica filler was modified with three types of chemicals, i.e. methyl series silane, titanate, and epoxy series silane. The treated filler and the composite containing the filler were charac terized on its hydrophobic property, and the fluidity, the mechanical properties and the erosion resistance, respectively. It was found that the treatment with methyl series silane did not improve the erosion resistance. On the other hand, the modification with titanate and epoxy series silane resulted in remarkable improvement. The binding strength between the filler and resin was suggest d to be increased by molecular entanglement and/or covalent bond leading to the high erosion resistance.
Microbial removal of nitrogen in wastewater was performed by biodegradable polycaprolactone (PCL) and the following results were obtained. Nitrogen in wastewater could be effectively removed by PCL, e.g. more than 70 % of total nitrogen (TN) was removed on the average after ten weeks. PCL degraded linearly with immsering time and its weight loss was ca.44 % after 10 weeks. The thickness of PCL plate decreased similarly from 0.5 mm to ca.0.2-0.3 mm, but it kept the original form. During the reaction, biofilm (microbial film) was formed on the surface of the plate and saturated at ca.1.0 mm. Increase in total organic carbon (TOC) and inorganic carbon (IC) in wastewater was observed. Slight changes in pH and suspended substances (SS), and formation of ammonium nitrogen and nitrite nitrogen were occurred. Measurement of molecular weights and spectroscopy such as IR and UV-V indicated that biodegradation of PCL occurred on its surface.