Hydrolytic Degradation Rates

In the literature most rate constants are reported as first-order constants. These are pseudo-first-order rate constants, because the concentration of water is so high 

Aside from involvements of phosphorus as phosphates in the biochemistry of living systems, perhaps a second approach is to consider vital uses of phosphates in hundreds of products used daily, throughout most societies on Earth. Toy and Walsh s exceptional book. Phosphorus Chemistry in Everyday Livings gives an interesting approach to all forms of phosphorus applications, including DTA, RNA, and ATR Their approach is directed more toward the usefulness of these compounds rather than their safety when in contact with live forms, but it is a simplified, excellent coverage that will not be repeated here.  

Since phosphate fibers are exclusively in the dominion of inorganic chemistry and therefore the mineral kingdom, these areas will receive our major attention. As a safety issue, inorganic phosphate s use in foods, fertilizers, cosmetics, and pharmaceuticals will be considered. Returning to the fact that bones when dried are a calcium orthophosphate, hydroxyl apatite, approximately Ca5(P04)30H, the alliance of phosphates with life is again established. Most phosphates used in products mentioned above are from this source in one form or another. When a mummy s tomb is opened, about all that is left are phosphates he ate during his lifetime. Phosphates of his bones assisted him in his quest for immortality. 

There is no doubt that much phosphate rock that is mined for fertilizer applications is used for modem humanity to inject itself into a food chain that is sixty million years or more old. Moreover, as Earth s population becomes larger our dependence on this ancient food chain grows more and more critical. It has been estimated that as much as one-quarter of the people should be condemned to starvation within four years, if we discontinued mining phosphates and attempted to live on organic phosphates alone. 

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Surface erosion occurs when the hydrolytic degradation rate of the material surface in contact with water containing catalytic substances such as alkali or enzymes is much higher than the... 

It is of particular interest that PBS has a higher hydrolytic degradation rate than poly(butylene succinate-co-butylene adipate) (PBSA) copolymers, as shown in Fig. 17 (Ahn et al. 2001). It is suggested that the presence of butylene adipate units may promote the hydrophobic nature of copolyesters, which would negatively influence the hydrolytic susceptibility by sterically hindering the access of nucleophiles. 

Thus, considering the high importance of the appropriate hydrolytic degradation rate of PLA when this is utilized for its recycling to lactic acid or as biomedical materials with an optimal degradation rate in the human body (as pharmaceutical matrices), the aim of this chapter is to review the recent studies reported in the literature on the mechanisms, affecting parameters and possible applications of the abiotic hydrolytic degradation of PLA. 

Molecular weight is one of the most crucial factors for the hydrolytic degradation rate of PLA-based materials. Saha et studied the effect of... 

Several researchers have extensively studied the effect of GA and CL units on the hydrolytic degradation rate of LLA-based copolymers, and found catalytic effect in alkaline and neutral media by the use of both comonomers, especially by the incorporation of hydrophilic GA units as compared to the hydrophobic CL. In neutral conditions the degradation rate of P(LLA-co-GA) seems to increase with GA unit content. " Similar evidence was obtained for P(DLLA-co-GA) copolymers under neutraF and acidic media, and they were ascribed to the increase in the bound reactive water content in the specimens at higher content of GA units. The effect of addition of CL units on the hydrolytic degradation of LLA- or DLLA-based copolymers is still not clear. Some researchers reported higher hydrolytic degradation rates in neutral media for nanoparticles based on P(LLA-co-GA-co-CL) (63/27/20) copolymers as compared to nanoparticles based on P(LLA-co-GA) (70/30) copolymers. Conversely, other researchers reported lower neutral hydrolytic degradation rates for block copolymers of PDLLA-Z -PCL, P(DLLA-co-GA-co-CL) and P(LLA-co-GA-co-CL) with the increase in the PCL content. ... 

Zhu and Lei reported that the neutral degradation rate of poly(DLLA-co-adipic anhydride) increased at higher content of adipic anhydride. Nakayama et reported that the addition of 20 mol% of p-methyl-valerolactone (VL) considerably increased the degradation rate of P(LLA-co-p-methyl-VL) copolymers. However, high contents of 8-valerolactone units in PLLA copolymers were found to decrease the hydrolytic degradation rate in neutral media. 

Concerning the use of nanoparticles, Armentano et reported interesting results regarding the effect of carbon nanotubes on the PLA hydrolytic degradation. Indeed, they described a correlation between the hydrophilicily level of carbon nanotubes with the hydrolytic degradation rate of PLA in neutral conditions. 

Andersson, S.R., Hakkarainen, M., Inkinen, S., Sodergard, A., Albertsson, A.-C., 2012. Customizing the hydrolytic degradation rate of stereocomplex PLA through different PDLA architectures. Biomacromolecules 13, 1212—1222. 

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