Degradation modelling hydrolysis reaction

Broadly, stochastic models treat the hydrolysis reaction as a random event. Siepmann et al. (2002) developed a model aimed at describing the degradation of PLGA microparticles and the release of a loaded compound. In this framework, the microsphere (only one-quarter has been considered, for symmetry reasons) has been divided in pixel, representing polymer, dmg, or water. At time equal to 0, water starts to diffuse within the matrix and breaks ester bonds, whereas the solubilized loaded drug (random placed within the matrix) can diffuse out of the device. Each polymer pixel possesses a characteristic lifetime fufetime. which starts to decrease as soon as it comes in contact with water ... 

The article temperature must be known in order to calculate its degradation rate. Solar modules generally are nearly black, so they get hot in the sun. We were interested in applications in which the module might be attached directly to a roof, so the back can be considered to be well insulated. Several temperature models have been described in the literature at various levels of complexity [7-12]. These models generally require empirical constants that we did not have. Instead, we adapted a simple equation that was derived from a dataset of the surface temperature of a black polycarbonate roof panel attached to a closed minivan in Arizona over the course of a year [13]. This is shown as Eq. (3.1) where T od is the module surface temperature, is the ambient dry bulb temperature, and / is the global horizontal irradiance in W/m. As it turns out, the selection of the model is not critical in the case of hydrolysis reactions, as will be shown in the Sensitivity section. 

The degradation experiments were carried out in phosphate buffer solution (PBS) with pH 7.4 at three temperatures 37°C 50°C, and 70°C. Further details of the experimental study can be found in the original paper by Weir et al. (2004). In the fittings, it was assumed that only the -COOH end groups on the short chains act as the catalyst for the hydrolysis reaction. The temperature dependence of the kinetic parameters in the model was assumed to follow the Arrhenius relation. The full set of values for the model parameters that achieved the best fits can be found in the original paper by Gleadall et al. (2012), which are not repeated here. 

Small polymer chains produced from the hydrolysis reaction during degradation are diffusible. The diffusion mechanism of small polymer chains in solute aud the corresponding diffusion coefQcient are of great interest in the area of polymer degradation. A BD model for simulating the diffusion of small polymer chains and calculating the diffusion coefficient is introduced in this section. 

The half-lives for these four compounds taken from the literature allowed the estimation of the Four reaction rates necessai to model their degradation [18], As a first approximation, the rate of hydrolysis of the C-Cl bond of all Four, -triazine compounds was assumed to be the same and to be 5.0 x 10 s on the basis of literature precedence. This approximation seems reasonable as the four structures differ only in the alkyl groups at a site quite remote from the C-CI bond. Furthermore, among the Four reaction steps hydrolysis is the slowest anyway. 

Behrens G, Koltzenburg G, Schulte-Frohlinde D (1982) Model reactions for the degradation of DNA-4 radicals in aqueous solution. Fast hydrolysis of a-alkoxyalkyl radicals with a leaving group in p-position followed by radical rearrangement and elimination reactions. Z Naturforsch 37c 1205-1227... 

At high concentrations, corrosion-resistant reactors and an effective acid recovery process are needed, raising the cost of the intermediate glucose. Dilute acid treatments minimize these problems, but a number of kinetic models indicate that the maximum conversion of cellulose to glucose under these conditions is 65 to 70 percent because subsequent degradation reactions of the glucose to HMF and lev-ulinic acid take place. The modem biorefinery is learning to exploit this reaction manifold, because these decomposition products can be manufactured as the primary product of polysaccharide hydrolysis (see below). 

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