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Surface Chalking upon Weathering of Dark-Colored PVC Articles and Relevant Stabilizers
Summary
Researchers studied how different chemical stabilizers affect the weathering and surface discoloration of dark-colored PVC products exposed to outdoor conditions. They found that certain acid scavengers were effective at preventing the chalking effect caused by UV degradation, while others actually made it worse. The study provides practical guidance for making PVC products like window frames and shutters more durable and longer-lasting.
PVC items are environmentally friendly as, unlike polyolefins, they are mainly based on chlorine, one of the most abundant elements on earth. However, in the eco-design context, articles' durability plays the crucial role, contributing to the enhancement of their sustainability. In this framework the research on additives capable of increasing the weatherability of outdoor articles is essential. The theory section of the paper reviews the mechanisms of weathering leading to PVC degradation that undermine the durability of items such as window frames or roller shutters. The weathering of PVC items is a complex phenomenon involving photo-chemical and secondary chemical reactions, that yields the formation of conjugated polyene sequences underskin in absence of oxygen and carbonyls in the surface. Here the chain scission of the polymer backbone occurs, bringing the disintegration of the surface of the item and causing the typical discoloration called chalking, especially evident in dark-colored articles. In the experimental section of the paper the effect of different acid scavengers on the item weathering has been studied with natural outdoor and two accelerated exposures, xenon-arc and Q-UV testing devices. Results confirm that some acid scavengers are efficient in preventing chalking, but some are ineffective or even detrimental. Thus, the PVC formulations of durable articles upon weathering still depend on a complex choice of the appropriate ingredients, and several outdoor and indoor accelerated weathering tests are needed to predict the articles' lifetime.