Degradation modelling crystallinity

From these results, a plausible physical model of starch structure during hydrolysis is presented. The model states that various crystalline states of the constituent starch molecules are present throughout the course of degradation. These crystalline states are associated with the natural state of the... 

It is convenient to start the discussion of degradation models with amorphous polymers. A typical application of amorphous polymers in medical devices is the drug-carrying layer of coronary stents. Calculating the degradation rate of the polymer is the first step to predict drug-release profile from a stent. Furthermore, all semi-crystalline polymers contain an amorphous phase. It is therefore logical to focus attention on amorphous polymers first. Semi-crystalline polymers are considered in Chapter 4. 

Because of its fundamental role as a precursor of vitamin A and the availability of P-carotene standard in crystalline form, the thermal degradation of P-carotene in model systems has been a subject of intense research. 

To our knowledge, the coumarone ketol (XXII) is the first crystalline dimeric lignin degradation product with two complete phenylpropane skeletons which has been reported in the literature 26). On the basis of the model experiments discussed above, the presence of the ketol side chain as well as the phenylcoumarone system in (XXII) indicates that the origin of the product is a sequence of three phenylpropane monomers (XXVIII) in lignin, involving a phenylcoumaran system carrying a gly-... 

The non-pattemed CaCOj films could be observed to crystallize within 1 h by optical microscopy. However the patterned films stayed amorphous for 2-3 h under ambient conditions and were only completely crystalline after 24 h, which is probably due to the use of ethanol in the patterning procedure, as this is known to stabilize ACC (amorphous calcium carbonate). Subsequently cell culture experiments were performed and the results indicated that the CaCOj substrates support rat bone marrow stromal cell attachment, proliferation and differentiation into osteoblast and osteoclast-like cells. Moreover, mineral formation by the osteoblast-like cells was favored on the CaCOj films compared to the developed polymer films. Also, the osteoclast-like cells can degrade the CaC03 films. Therefore, these patterns of CaCOj films can be regarded as suitable 2D model substrates for bone cells. 

Cross-linked potassium Kurrol s is prepared in exactly the same manner as the calcium polyphosphate fibers. The only difference is potassium is substituted for calcium in the preparation of potassium Kurrol s salt. There is strong reason to question whether or not the strange solution behavior of cross-linked potassium Kurrol s salt is a result of cross-linking in the crystalline phase or is a result of ultra long polyphosphate chains mixed with an independent ultraphosphate phase that contains the required cross-linking. All of the observations which led to the belief that the molecule-ions in the crystalline phase were cross-linked can be explained based upon the two phase model where the ultraphosphate phase is rather quickly degraded in aqueous solutions to form acidic groups. 

---