Hydrolytic degradation biodegradation mechanisms

The hydrolytic degradation of PLAs and copolymers has been intensively studied, and, as a result, there are more than 250 papers related to this issue [188,189]. The degradation mechanism, behaviour, and rate depend on material- and media-related factors, which are summarized in Table 8.3. In addition, the methods used to monitor the hydrolytic degradation of biodegradable polymers are summarized in Table 8.4. Detailed information regarding the hydrolytic degradation of PLA-based materials can be found in the related review articles [188-190],... 

Table 8.5 Critical thickness (Lcritiail) of biodegradable polyesters where hydrolytic degradation mechanism changes from bulk erosion to surface erosion [200], (Reprinted from Biomaterials, vol. 23, von Burkersroda et al., Why degradation polymers undergo surface erosion or bulk erosion, pp. 4221-4231. Copyright Elsevier, 2002.)...

No high volume applications of PHAs exist at present there are only trials and small pilot productions. Two perspective areas of applications are consida-ed here, namely health care and packaging. In the field of medical and pharmaceutical applications, the hydrolytic degradation of PHAs is required as the main degradation mechanism, while in environmental applications, enzymatic degradation mechanisms (biodegradation) are relevant. 

Montmorillonite (MMT), a smectite clay, is probably the most extensively studied nanomaterial in terms of mechanical, thermal, fire retardant or crystallization behavior of polylactide, especially when these nanoparticles are organically modified allowing the achievement of intercalated and exfoliated nanocomposites.These nanocomposites show enhanced properties as compared to microcomposites and pristine polymer. However, biodegradation and hydrolytic degradation of PLA in the presence of nanoclays has been investigated to a small extent. 

Pratt, L., Chu, C., Auer, J., Chu, A., Kim., J., Zollweg, J. A. and Chu, C. C., The effect of ionic electrolytes on hydrolytic degradation of biodegradable polymers mechanical and thermodynamic properties and molecular modeling. Journal of Polymer Science Part A Polymer Chemistry 31, 1759-1769 (1993). 

TABLE 21.4 Critical Thickness (Lcriticai) of Biodegradable Polyesters, Above which Hydrolytic Degradation Mechanism Changes from Bulk Erosion to Surface Erosion [150]... 

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