Oxidation and Crumbling

Briefly, antioxidants quench free radicals that are formed in the process of plastic degradation by oxygen and initiated by temperature and UV light, and assisted by moisture, stress, presence of metals, and other catalysts of plastic oxidation. If not intercepted by antioxidants, the polymeric plastic is degraded (depolymerized) so much that it loses its integrity and ceases to be a plastic anymore. It is converted to a loose powderous material, mainly a filler. 

Until recently, the effects of these factors and their qnantitative manifestation were practically nnknown and not even recognized, neither in the WPG indnstry nor in academic research in the area. That is why the acnte deterioration and crumbling of some WPG boards tnrned ont to be qnite nnexpected and puzzling, and resulted in some cases in an avalanche of warranty claims. These cases will be considered in detail in chapter 15. It tnrned ont that the progressive deterioration and crumbling have resnlted from WPG oxidation, and as soon as it was recognized, measures were taken. The OIT (oxidative induction time) parameter was introduced into characterization of WPG products and evaluation of their lifetime in the real world, on real decks. 

Essentially, the OIT value quantitatively describes a lifetime of a composite (or actually any organic-based) material during its accelerated oxidation in pure oxygen at an elevated temperature, such as 190°G. For example, for unstabilized (without added antioxidants) WPG materials the OIT can be as low as 0.3-0.5 min. The lifetime of such WPG boards in the South (Arizona, Texas, Florida) can be as low as only several months. The lifetime in this context is a time period by the end of which the consumer can see there is something wrong with the deck and calls for help. In real terms, the deck owner contacts with the manufacturer and tiles a warranty claim. 

For partially stabilized WPG materials, the OIT can be between I and 10 min (Fig. 1.45). A number of commercial WPG deck boards being sold in the market falls into this range. Depending on the deck profile (solid or hollow) and the board density, and, of conrse, on location/geography/climatic conditions, the lifetime of the deck can vary, but there is a risk that these boards would not live long enough to see the end of their warranty time period, particularly in the South. 

For well-stabilized WPG board, the OIT can be in the range of stabilized plastics (15-100+ min). 

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Oxalic acid-based cleaning agents, 106 Oxidation and crumbling, 36, 493-584 Effect ofUV light, 503 Oxidation and degradation, effect of density, 205... 

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