Thermooxidative degradation of polypropylene (PP) s with a variety of tacticity was investigated in terms of various degradation factors, such as catalyst residue in the PP, molecular weight of the PP, and amount of oxygen existed. Heat treatment was typically carried out in the air at 200°C for 30min, at where the PP powder was varied into the molten state within several minutes. The catalyst residue and molecular weight had slight influence on the thermooxidative degradation of isotactic PP. Thermal stability of three polypropylenes (isotactic PP, atactic PP, syndiotactic PP) having similar molecular weight was investigated under the same conditions. Isotactic PP was degraded drastically compared with atactic PP and syndiotactic PP in the air. The thermal degradation of isotactic PP was depressed greatly under nitrogen. Existence of oxygen was found to induce the thermal degradation, even in syndiotactic PP. Thus, it was found that the influence of the tacticity and oxygen pressure was significant compared with that of the catalyst residue and molecular weight.

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Commercial wooden sashes and smaller wood specimens were finished with 5 kinds of exterior stains (pigmented stains) which were either of the penetrating or semi-film forming type. Finished wood was exposed outdoors and its weather resistance and the performance of the finishes were periodically evaluated by mainly their weight and dimensional changes, and color difference. Weight and dimensional changes in wood samples finishes with penetrating type stains were improved by approximately 20% and 35%, respectively. Finishing with semi-film forming type stains also improved weight changes by about 50 to 60% and dimensional changes by 55%. Exterior exposure of full-sized sashes resulted in large dimensional changes in the cross section of the longitudinal components of the frame. In finished sashes, dimensional changes in the cross section of the longitudinal components were approximately 50% smaller and dimensional changes between the various parts of the sashes were also reduced. Large color changes were observed at the upper surface of horizontal sash frames during exterior exposure and a noticeable difference in color between the horizontal and vertical frames developed over time. However, color differences between sash components was reduced as a result of finishing with exterior stains. From these results, it can be concluded that finishing is a highly effective means of improving the weather resistance of wooden sashes and that water proofing of the cross sections of longitudinal frames and careful finishing of the horizontal surfaces should be undertaken before sashes are exposed outdoors. Property enhancement produced by penetrating type stains was inferior to that of semi-film forming type stains. However, the mode of failure of penetrating type stains was superior to that of film forming type, since wood surfaces treated with the former showed gradual deterioration over time whereas the deterioration of those finished with semi-film forming type stains occurred quite suddenly. Furthermore once films degraded, property enhancement provided by the finish decreased markedly. The first maintenance interval for penetrating and semi-film forming type finishes was similar, approximately two years.

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