Degradation mechanical behavior

Table 21.1 summarizes the reported hydrolytic degradation of PLA-based materials. The degradation mechanism, behavior, and rate depend on material and media-related... 

By varying the material parameters, the hydrolytic degradation mechanism, behavior, and rate can be controlled. In other words, these parameters are carefully manipulated when PLA-based materials are biomedically and environmentally applied by using the hydrolyzability function. In the following section, the hydrolytic degradation conditions are temperature of 37°C and pH of about 7, unless otherwise specified. 

Much recent ongoing work has focused on the chemical degradation mechanisms and revealed that radical attack is the root cause of the membrane decomposition. However, there is still a lack of fundamental understanding of the mechanisms for the degradation of mechanical strength, which is related to the membrane failure mode responsible for the sudden death behavior of fuel cells. 

There is little question that one of the most active research areas in materials science is studying interfaces. In the past, emphasis in materials science has been placed on relating the bulk properties to the structure and composition of the solid. Today, efforts are in progress that relate surface reactivity and stability to the crystallographic orientation and composition, primarily at the S/G interface. Since a fundamental understanding of interfacial behavior and degradation mechanisms at an atomistic level is necessary if short-time test data are to be extrapolated to 30-year lifetimes, careful studies at the S/S, S/G, and S/L interfaces are required (4). 

Furthermore, the effect of hydrated fillers on polymer fire retardancy will depend not only on the nature of the filler, including its particle characteristics (size, shape, and purity) and decomposition behavior, but also on the degradation mechanism of the polymer, together with any filler/ polymer interactions that might occur, influencing thermal stability of the polymer and possible char formation. 

Materials often exhibit unique properties, processing challenges, and degradation mechanisms that are inherently electrochemical in nature. For example, the sintering of high-technology ceramics is closely related to the behavior of ionic defects in solid electrolytes. 

The degradation follows an apparent first order reaction with an initial rate (up to 2000 hours exposure in a QUV apparatus) that is faster than the subsequent rate. An assessment of the kinetic data in terms of proposed reaction mechanisms and concurrent changes in properties such as dynamic mechanical behavior can serve as a preliminary basis for evaluation of the material s ability to retain useful properties for time periods consistent with certain design requirements for solar energy system applications. 

J.A. Burdick, C. Chung, X. Jia, M.A. Randolph, R. Langer, Controlled degradation and mechanical behavior of photopolymerized hyaluronic acid networks. Biomacromolecules 6 (1) (2005) 386-391. 

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