Polymeric materials degradation mechanisms

In contrast to the extensive work of the pure thermal degradation of polymers, less fundamental chemical information is available on the mechanism of oxidative degradation of polymeric materials. As another point of... 

It Is well known that mechanical properties of polymeric materials are greatly deteriorated by UV exposure (2-j)). The nature of this deterioration was determined using non-strained samples which were photooxidized at 37°C. Engineering stress-strain curves as a function of UV exposure are shown in Figure 1. The numbers next to each curve represent days of UV exposure. In terms of degradation, the points of interest are ... 

To a plastic producer (i.e. processor), melt index is one property that is needed in order to evaluate whether the same process can be used irrespective of whether it uses virgin or recycled polymers. This will tell if it is possible to process the recycled polymeric materials in the same set-up as usual. Several other properties are needed in order to quality mark the materials. The melt index is related to what final tensile properties a product obtains, this in turn has an impact on the expected life-time. The purity of a recyclate stream with respect to the amount of foreign polymer in the stream has an impact on melt-index, but will also be an important factor for the final mechanical properties. Another very important property is the amount of low molecular weight compounds, which may be of vastly different types. Typically such an analysis will show the presences of additives and their degradation products, degradation products of the polymeric matrices, traces of solvents, initiators, or catalysts, compounds related to the use of the plastics and others. 

The changes in mechanical properties due to degradation and/or blending, contamination, antioxidant consumption and general use (e.g. oxidation processes) of the polymeric material during first service life are some of the characteristics that determine if the material should be recycled mechanically or disposed of in another way (e.g. energy recovery). A successful recycling is strictly dependent on the purity and uniformity of the plastic waste. 

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