Models of polymer degradation

The corresponding viscosity ly, if it is then taken to be linear in concentration, will also show a similar exponential decay. More general relations for rj C) will result in rather more complex viscosity decay laws however, within a simulation model this causes no additional difficulty. In all of the results presented below on polymer degradation, the first-order degradation 

---

Kinetic models of polymer degradation based on chain processes have been suggested (4-8). These models and other models for polymer degradation have normally invoked the steady-state hypothesis (9). Barron and Boucher (10) describe a kinetic model for zip kinetics but assume an apparent first order behavior and do not account effectively for the acceleratory phase of the degradation. 

A kinetic model of polymer degradation during extrusion, Polymer Degradation and Stability, 51 (1996), p. 271 - 279... 

Flow-induced degradation is intimately related to the nonequilibrium conformation of polymer coils and any attempt to interpret the process beyond the phenomenological stage would be incomplete without a sound understanding of chain dynamics. To make the paper self-contained and to provide a theoretical basis for the discussion, we have included some fundamental models of polymer dynamics in the next section which may also serve as a guideline for future work in the field of polymer degradation in flow. For the first-time reader, however, this section is not absolutely necessary. Further, any reader familiar with molecular rheology or interested only in experimental results can skip this section, only to go back whenever a reference is needed. 

This volume of Modern Aspects of Electrochemistry is intended to provide an overview of advancements in experimental diagnostics and modeling of polymer electrolyte fuel cells. Chapters by Huang and Reifsnider and Gu et al. provide an in-depth review of the durability issues in PEFCs as well as recent developments in understanding and mitigation of degradation in the polymer membrane and electrocatalyst. 

A better model of thermal degradation by depropagation may be obtained if we distinguish between polymer molecules and radical fragments in the population. Here, we consider radical species being formed from an initial random scission reaction. Once formed, the radical species then undergo... 

Emsley, A. M. and Heywood, R. J. Computer modelling of the degradation of linear polymers. Polymer Degradation and Stability 1995 49 145. 

Inaba, A., Kashiwagi, T., and Brown, J. E. Effects of initial molecular weight on thermal degradation of polyfmethyl methacrylate) Part 1—Model 1. Polymer Degradation and Stability 1988 21 1. 

Van Krevelen DW, "Group Contribution Techniques for Correlating Polymer Properties and Chemical Structure", in Bicerano J (Ed) "Computational Modelling of Polymers", Marcel Dekker, New York, 1992, Chap. 1. Vasile C, "Degradation and Decomposition", in Vasile C (Ed), "Handbook of Polyolefins", Marcel Dekker, New York, 2nd Ed, 2000, Chap. 17. 

P is the number of polymer molecules of degree of polymerization n, R is the number of radicals found in a volume V, R is the number of polymer radicals with degree of polymerization n found in a volume, V. For other definitions, please use the nomenclature associated with Table 15.2. Noting equation 15.14, the kinetics of polymer degradation are very complex. Only the most simple mechanisms have been thoroughly researched. These simplified reactions presented in Table 15.2 are sometimes zero order, more frequently first order, and infiiequently second order in polymer mass. These simplified rate expressions are typically used to model binder burnout. 

Luminescence properties of and phenomena in polymer systems continues to be widely researched in connection with mechanisms of polymer degradation and stabilization, molecular dynamics, solubility, blend miscibility, and solar energy harnessing. A number of interesting reviews have appeared. Molecular dynamics of polymers in solution and in the solid state have been covered, as has excimer formation,photoresponsive polymers,behaviour of polymer gels, and photochromic phenomena. Photoisomerization of enzymes and model compounds has also been discussed in depth, with particular emphasis on proteins and synthetic polymers containing azo-compounds or spirobenzopyrans. ... 

Vergnes and Berzin (2004), Vergnes et al. (1998) of PP model of polymer flow in co-rotating, selfwiping, twin-screw extruders, coupled with degradation reaction kinetics shear rate, viscosity, residence time... 

A general kinetic treatment of polymer degradation by elimination has been presented by Tiidos et al. [170, 197]. The detailed elementary reactions taking place in the course of degradation are not taken into account. The main features of the model are... 

D.W. Grattan, D.J. Carlsson, and D.M. Wiles, Polyolefin photo-stabilisation mechanisms. Reaction of tetramethylpiperidine derivatives in model systems, Polym. Degrad. Stab. 1979, 1, 69-84. 

To make this review self-contained and to provide a foundatitMi for further discussion, we have included the experimental methods and theoretical models of mechanical degradation for linear chains in the second and third sections, respectively. From the fourth to seventh sections, the mechanochemistry of cyclic polymers, graft polymers, star-shaped polymers (star-shaped polymers), dendrimers, and hyperbranched polymers is summarized. In the eighth section, we survey the mechanochemistry of supramolecular aggregates and knotted polymers, where the topology constraints are temporal. We hope our overview can serve as a guideline for the future work in the field of polymer mechanochemistry. 

D.G. Duguay, R.S. Labow, J.P. Santerre, D.D. McLean, Development of a mathematical model describing the enzymatic degradation of biomedical polyurethanes. 1. Background, rationale and model formulation. Polym. Degrad. Stab. 47, 229-249 (1995)... 

Bai, Y. and Keller, T. (2009) Modeling of strength degradation for fiber-reinforced polymer composites in fire. /. Compos. Mater., 43(21), 2371-2385. 

Plastic films exposed to natural weather undergoes photo-oxidative reactions. Sunlight, together with oxygen, initiates the chemical reactions in the polymer matrix. The important aspects of sunlight include sunshine duration, total solar radiation, and UV radiation that may be used in modeling of the degradative processes [6-8],... 

Denq, B.L., Chin, W.Y., Lin, K.F. Kinetic model of thermal degradation of polymers from nonisothermal process. J. Appl. Polym. Sd. 66, 1855-1867 (1997)... 

EFFECT OF POLYMER DEGRADATION WITH A 6 MONTH HALF LIFE ON CUMULATIVE OIL PRODUCTION IN THE BASE CASE TWO LAYER MODEL... 

Mathematical modelling of drug release from biodegradable systems requires consideration of the relative rates of polymer degradation and drug diffusion. Two defined scenarios may be established, as described next. 

---