Increasing volumes of municipal solid waste (MSW) and decreasing means of disposal are creating a serious problem in the United States. Plastic waste has been identified as a major issue even though it is still only a small portion of the total volume of MSW. In part, that is because of the relatively low rates of environmetal degradation of most plastics; in part, because plastics litter is highly visible and long lasting; in part, because forecasts predict plastics will be an even larger component of MSW in the future. The plastics and solid waste problem is receiving much attention in the United States. Several approaches to solid waste disposal are being investigated, including source reduction, recycling, composting, degradable plastics, incineration, and sanitary landfills. All are being studied intensively to overcome the serious disposal problems associated with increasing amounts of MSW. The results to date, and especially the directions being taken, are encouraging. They indicate solid waste will be disposed by multiple means and the solid waste disposal practices of the near future will be much different from those of the present time.
Degradable plastics were viewed only 1-2 years ago as an exciting new approach to help solve the solid waste problem. However, the finding that sanitary landfills are sterile environments where little degradation takes place has reduced the attraction of degradable plastics. Their attraction has been reduced also by the realization that, although packaging plastics can be made photodegradable, they are not biodegradable - their high molecular weights and structures prevent complete breakdown by organisms in reasonable time periods. Some of the former luster of degradable plastics has been tarnished because several environmental groups have been critical of attempts to take advantage of the public's considerable interest in degradable plastics to sell products which do not meet marketing claims. As a result of all these developments, interest in degradable plastics is low at this time. Other means of solving the problem, notably source reduction, recycling, composting and incineration are more likely to be adopted. Degradable plastics are not likely to play a major role as solutions to the solid waste problem.

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The investigation was undertaken to evaluate the deterioration and the residual life time of O-ring which had been used for 13 years in nuclear reactor. Three O-ring made of silicone which was used for sealing between pressure vessel and “In reactor tube”.
The applied aging factors to the O-rings were estimated by simulation and/or caluculation. Dose was 3.46kGy for the highest sample, temperature was 50°C during on powered, but the sliding friction applied to O-ring was estimated to be a small.
The same type of O-ring as that used in the pressure vessel was irradiated, dose rate was 5.0kGy/h at 70°C for the short time test. The relationship between the changes in mechanical properties of samples and dose was studied. It was found out that more than ten times of dose was necessary to give the same deterioration as that of the O-rings used in pressure vessel.
Referring to data obtained, the O-rings are considered to be able to use until their ultimate elongation go down to 50% and the residual life time of the O-rings was predicted to be 26 years.

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Comparison of waste polyethylene decomposition with and without the zeolite catalyst has been carried out under the conditions of temperature range 160-360°C for 60min. The waste polyethylene having functional groups was almost converted to the cross-linked polyethylene. The molecular weight of degraded polyethylene which was soluble in hot xylene increased remarkably at the elevated temperature. These reaction were inverse to those of undegraded polyethylene decomposition. Formation of cross-linked polymer and increase in molecular weight seems to be specific reaction for waste polyethylene having the >C= O and >C= C< groups. These reactions may possibly be applied to recyclings for the utilization of waste polyethylene.

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