Lifetime predictions, polymer weathering

Lifetime of polymers exposed to natural euvironmeut cannot be predicted accurately because of complexity of the natural weathering phenomenon and multitude of weather parameters interacting simultaneously [7]. A brief discussion of the important factors that mainly contribute to degradative processes during natural weathering follows. 

In principle, the computational approach to the kinetics of the complex photooxidation process can give meaningful insight into the effects of outdoor weathering of hydrocarbon polymers. For clear amorphous linear polyethylene, the model suggests that the optimum stabilizer would be a molecularly dispersed additive in very low concentration which could trap peroxy radicals. An additive which decomposes hydroperoxides would also be effective but would require higher concentrations. The useful lifetime of unstabilized polyethylene is predicted to vary from a few months in hot weather (100°F) to almost two years in cool weather (45°F), which correlates well with experimental results and general experience. 

The standard tests for assessing the durability of polymers in outdoor exposure (and other degradative environments) have been listed and discussed by Brown [5]. He concluded that the standard tests are of little value in predicting service lifetime and discussed some of the reasons for this. He also noted the lack of correlation between the results of natural weathering and laboratory weathering, a topic also discussed by other authors [2, 4, 5]. 

A number of studies have been conducted to investigate how well SLP accomplishes these goals for selected polymer-based materials [1 ]. From these, reasonable estimates of lifetime were obtained as compared to actual values of time to failure observed for outdoor exposures. Some of the predictions covered the entire degradation pathway, for which changes in material properties generally followed a trend similar to that measured during outdoor weathering. The SLP methods employed varied somewhat from study to study and all used measured climate data to test their models. 

Mechanisms of Photooxidation of Polyolefins Prediction of Lifetime in Weathering Conditions, In Polymer Durability, American Chemical Society Publication, 1996... 

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