Material Degradation Mechanism

A surface erosion mechanism takes place when the hydrolytic degradation rate of the material surface in contact with water (containing catalytic substances such as alkalis and 

Material-Based Indexes Nonmaterial-Based Indexes 

FIGURE 21.2 Hydrolytic chain cleavage mechanisms of PLLA in alkaline (a) and acidic (b) solutions. Adapted from Ref. 79. Copyright 2001, with permission from Elsevier. 

On the other hand, as reported by Vert and coworkers, in the cases of PDLLA [96], PLLA [23, 28], poly(L-lactide-co-glycolide) (poly(L-lactic acid-co-glycolic acid) (P(LLA-co-GA))) [123], P(DLLA-co-GA) [123], PDLLA-Z -PEO [198], and PLLA-Z -PEO-Z -PLLA [205], NHD proceeds via 

FIGURE 21.3 Expected processes of hydrolytic degradation of water-insoluble (a) and water-soluble (b) oligo(DL-lactide)-grafted dextrans in a phosphate-buffered solution. Reprinted from Ref. 133. Copyright 2005, with permission from Elsevier. 

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Fig. 14 Algorithmic approach for accounting the feedback between a performance model and a model describing the materials degradation mechanisms...

Clearly, finding a single accelerated-life-test to evaluate materials against all the possible environmental hazards and materials degradation mechanisms is unrealistic. Each material or device needs to be evaluated by a series of tests to elucidate its possible degradation processes. Experience has shown that our ability to predict what test to use when field failure data are not available falls well short of needs. In reality, the corrosion engineer must rely on past experience to make an educated judgment about potential failure scenarios and which accelerated-life-tests to run. 

The use of wedge-shaped samples is an appropriate testing method to study the influence of geometry effects on the material degradation mechanism by high-temperature corrosion. 

Strength, particularly where the material will be subjected to fatigue loading or is susceptible to degrading mechanisms such as hydrogen-induced cracking ... 

Among the oxidative breakers, alkali, metal hypochlorites, and inorganic and organic peroxides have been described in literature. These materials degrade the polymer chains by oxidative mechanisms. Carboxymethylcellulose, guar gum, or partially hydrolyzed polyacrylamides were used for testing a series of oxidative gel breakers in a laboratory study [180]. 

Composite materials, such as glass, carbon and aramid reinforced plastics, are principally used for their mechanical rigidity and strength. The most significant degradation mechanisms are therefore also mechanical or have mechanical consequences. Even when... 

Xie, T., Hayden, C., Olson, K. and Healy, J. 2005. Chemical degradation mechanism of perfluorinated sulfonic acid ionomer. In Advances in materials for proton exchange membrane fuel cell systems, Pacific Grove, CA, Feb. 20-23, abstract 24. 

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