Effects of sunshine duration and precipitation on the degradation of poly (L-Lactic acid) (PLA) have been investigated by applying multiple regression analysis. The analysis showed that the tensile strength of PLA exposed to outdoor can be described by kW and k'U, where k and k' are rate constants of hydrolysis and photodecomposition, respectively, and W is precipitation, U is sunshine duration. The contribution of k'U to the degradation of PLA was 1.5 times of kW. Hydrolysis and photodecomposition tests for PLA were also carried out in laboratory. The activation energy of hydrolysis and photodecomposition were 81.1kJ/mol and 66.9kJ/mol, respectively. These results suggested that the degradation caused by solar radiation was prominent than that by precipitation.
Decomposition reactions of polystyrene and the mixture of polystyrene and phenol resin in 1-methylnaphthalene or, sub-or super-critical water were carried out. Thermal decomposition reactions of polystyrene to monomeric compounds such as styrene and toluene were observed in the reactions at over 350°C. Acceleration effects of polystyrene addition on the decomposition reaction of phenol resin molding materials were observed indicating the possibility that the reactive intermediates from polystyrene contributed to the decomposition reaction of phenol resin.
The paper studied the properties of the polyethylene (PE) based composite substances that was obtained by mechanical milling (MM). Low-density polyethylene and silicon (Si) in the some compositions, and PE and Si by activated carbon (C) additions were mechanically milled by planetary ball-mill in an argon atmosphere. Morphology of the powder obtained by MM was studied by optical microscope and electron microscope. X-ray analysis, DSC and electric resistivity of the samples were measured. MM brought about amorphization of PE in PE-Si powder. The addition of C accelerated the fine dispersing and mixing of PE-Si. The amorphous state in obtained MM PE powders including amorphous and fine carbon and Si are stably kept on through' heating. From the results obtained, the changes of the structure of the composites during MM process were considered as follows. MM brings about the repetition of a forging, a rolling and a folding to samples. This results in the fine mixing in the composite. The phenomena suggest that MM function transforms straight long chain PE molecules into tangled PE molecules.