When polyethylene pipes are used for hot water application of tap water and heating, they contain a large amount of antioxidants so that they can endure high temperature for a long time.

In addition, some pipe manufacturers add extra antioxidants to the pipes for the purpose of prolonging the lifetime, but in many cases, the pipes don’t last as long as they expect. These days, when polymerizing the material of PE pipe for hot water application, they are starting to use Metallocene catalyst as an alternative to Ziegler-Natta catalyst, which has been conventionally used as a good method. In this study, we molded the material (non-cross linked) into PE pipe for hot water application and assessed its durability in hot water circulation test, which provides a similar situation to actual usage environment. Then we examined the influence of the resin structure on the speed of the antioxidant consumption based on the results obtained.

There are mainly two grades of polyethylene pipes for hot water supply and heating.

The excellent molecular structure polyethylene resins having resistance to stress crack growth are used because hot water is flowed for a long time in both polyethylene pipes.

Furthermore, various additives are mixed to prevent the thermal degradation of polyethylene pipes at the elevated temperature. In this study, the stress rupture test and the continuous hot water circulation test were con-ducted using extruded polyethylene pipes mixed two kind of polysilane and a nucleating agent. As a test results, the time to failure of polyethylene pipes mixed two kind of polysilane was longer than that of a polyethylene pipe without additives. The time to failure of polyethylene pipes mixed a nucleating agent is similar to that of a poly-ethylene pipe without additives. According to precise observation at the failure part, it was found that there was a small degraded colored layer at the inner surface of polyethylene pipes mixed two kind of polysilane compared with polyethylene pipes without additives. In addition, it was found that the generation and the growth of degraded colored layer and small cracks was delayed due to diffusion of polysilane to the inner surface and to protection of adhesion of metal oxides such as copper oxide and iron oxide.

We investigated about accelerated weathering tests suitable for EEA resin. Anchor clamp covers were examined as samples. Accelerating factors were calculated by comparison of accelerated samples and used samples (used for 23-40 years). Tensile stress and oxidized layer’s thickness were measured for the comparison. The measuring method of the oxidized layer’s thickness on EEA was developed for this investigation. Accelerated weathering tests were performed by using carbon arc light and “super Xe light” (3 times higher irradiance than sunlight). The deterioration products of the samples accelerated by super Xe light is different from the used samples. This difference does not occur when the carbon arc light is used. We have concluded that the accelerated weathering test using carbon arc light is suitable for EEA resin, and further study is needed for using super Xe light.