Degradation rate, compositional effects

The ESRI experiments described in our publications and summarized in this chapter led to spatially resolved information on the effect of treatment conditions, amount of stabilizer, and polymer composition on the degradation rate. In the heterophasic systems studied in our laboratory, ESRI has identified specific morphological domains where chemical processes are accelerated. The combination of ID and 2D spectral-spatial ESRI experiments led to mapping of the stabilizer consumption on two length scales within the sample depth on the scale of a few mm, and within morphological domains on the scale of a few gm. 

Fig. 5.20. Effect of polymer composition (1 % in benzene) on degradation rate.

Typically, composite deck boards are porous. The pores are formed by steam and by volatile organic compounds (VOC) during extrusion. Composite boards are partly foamed, and the pores are typically opened and connected to each other, forming chains of cavities. That is why composite materials absorb water, unlike many plastics. Air oxygen flows in, through these pores, and effectively oxidizes composite materials from inside, particularly at elevated temperatures, which often takes place on decks. Water, which is always present in composite materials, serves as a catalyst for the oxidation. Metals, which are often present in composites (as constituents of colorants, lubricants, biocides, fillers), also serve as efficient catalysts of oxidative degradation of composites. As a result, rates of oxidative degradation of composites are 50-100 times faster than those for their constituent plastics. 

Polymer chemists use DSC extensively to study percent crystallinity, crystallization rate, polymerization reaction kinetics, polymer degradation, and the effect of composition on the glass transition temperature, heat capacity determinations, and characterization of polymer blends. Materials scientists, physical chemists, and analytical chemists use DSC to study corrosion, oxidation, reduction, phase changes, catalysts, surface reactions, chemical adsorption and desorption (chemisorption), physical adsorption and desorption (physisorp-tion), fundamental physical properties such as enthalpy, boiling point, and equdibrium vapor pressure. DSC instruments permit the purge gas to be changed automatically, so sample interactions with reactive gas atmospheres can be studied. 

Main applications of thermal analysis are (1) Soil and clay analysis (2) Determination of Glass transition (3) Compositional effects on glass transition (4) Heat capacity determination (5) Characterization of polymer blends (6) Study the effects of additives added to polymer (7) Polymer degradation analysis (8) Crystallinity and crystallization rate study and (9) Reaction kinetic studies. 

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