Bulk degradation

Ouhadi, T., Stevens, C., and Teyssie, P., Study of poly-e-caprolactone bulk degradation, J. Appl. Polym. Sci., 20, 2963-2970, 1976. 

Yoshimori, T. Autophagy a regulated bulk degradation process inside cells. Biochem. Biophys. Res. Commun. 313 453-458, 2004. 

It can be calculated that the apparent activation energy during linear pyrolysis (as opposed to bulk degradation) would then be about 15 kcal./mole (see below). Thus, the value of 16 kcal./mole determined by Schultz and Dekker (85) and Coates (22) with their linear pyrolysis experiments agrees well with bulk degradation experiments. 

Calculation of the rate of decomposition in the solid phase shows that it is significant only when Te/f approaches Ts. Thus, Teff Ts, and the apparent activation energy during linear pyrolysis is half of that measured in bulk degradation experiments. This conclusion can also be inferred from the relations given in Ref. 35.]... 

Although these low temperature bulk degradation experiments provide insight into the detailed mechanism of AP decomposition, it is doubtful whether kinetic rates obtained from such experiments can be extrapolated over many orders of 10 to the temperatures typically encountered at the propellant surface, especially since degradation in bulk is not the same as degradation at the surface of the sample. 

Natural rubber oligomers with (i-pinene terminal units have been synthesized by Gutierrez and Tlenkopatchev via metathesis depolymerization [151]. The bulk degradation of natural rubber in the presence of (i-pinene, as chain-transfer agent, and C4 (0.1 mol% related to polymers with Mn between 490 and 1,700 kDa) produced monoterpene-terminated oligomers in yields between 80% and 90%. The results were further confirmed with model CM reactions using (i-pinene and (Z)-3-methyl-2-pentene. 

The influence of water and the phosphoric acid solution becomes clearly demonstrated when one compares the TTF results obtained in air, water and a phosphoric acid solution,. At low stresses (0.6 MPa), hydrolysis, i.e. chemical bulk degradation of the copoly(ester ester) by water and the phosphoric acid solution, is responsible for the failure. However, at higher stress levels, the significant difference in TTF between the aqueous environment and air points to the existence of ESC. The reduced lifetime in the phosphoric acid solution compared to water suggests an increased effect of acid. 

A load of 0.6 MPa results in a TTF of 315 hours in water and 246 hours in phosphoric acid solution. These times are comparable to the 276 hours after which the feilure stress is halved due to hydrolysis so we conclude that the failures obtained at this low stress of 0.6 MPa are only due to bulk degradation. 

Hydrogels that are based on natural products are more acceptable from the standpoint of toxicity-related issues and are therefore preferable to azo-based polymers. However, chemical derivatization, if performed without proper understanding, can lead to modifications of the hydrogels to products that will not degrade readily in the colon because it is possible that the new structures will not be recognized by the colonic bacterial enzymes for degradation. Also, bulk degradation is preferred to surface erosion because it... 

Metiers, A. T., Anseth, K. S., Bowman, C. N. A statistical kinetic model for the bulk-degradation of PEG-b-PLA hydrogel networks. Journal of Physical Chemistry B. 2000, 104, 7043-7049. 

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