Thermal degradation of polymers

FIGURE 6.7 Effect of adding dioctyl phthalate (DOP) (a plasticizer), squares, or imidazoliuiii ionic liquid additives (bmimPF6 or hmimPF6), circles, to PMMA on Tg [5]. Reproduced by permission of the Royal Society of Chemistry. 

Some other useful observations regarding Tg and T are that for polymers with a symmetrical repeating unit, such as polyethylene —(CH2—CH2)— and poly(vinylidene chloride), or Saran , (CH2—CCI2)—, 1/2 (for absolute Ts) for unsymmetrical 

PVC is an example of a polymer that self-catalyzes its thermal degradation. Beginning at temperature around 160 °C, HCl is formed as a byproduct of thermal degradation, and, even worse, the acid catalyzes further degradation of PVC. This is why PVC is not used for high-temperature applications, and even for moderate temperatures, a thermal stabilizer is normally added. 

For multiple species in three dimensions, these simultaneous differential equations for heat and mass transport are very complex and require numerical solution [6,7]. As a result of this complexity, we will discuss only simple geometries in the balance of this chapter and determine the rate limiting steps for these geometries. But, first, we present a detailed discussion of polymer degradation reactions. 

Side Chain (or Substituent) Reaction Main Chain Cross-Linking C clizadon then Carbon Formadon 

Scission leads to a decrease in the molecular weight, of the polymer 

TABLE 15.1 List of Polymers That Depolymerize during Thermal Degradation  

Notes El = end initiation, RCS = random chain scission, WLS = weak link scission. FRI = free radical initiation, RI = random initiation, CS = chain scission. 

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In contrast to the extensive work of the pure thermal degradation of polymers, less fundamental chemical information is available on the mechanism of oxidative degradation of polymeric materials. As another point of... 

Polymers have inherently high hydrocarbon ratios, making liquefaction of waste plastics into liquid fuel feedstocks a potentially viable commercial process. The objective is to characterise the thermal degradation of polymers during hydrogenation. LDPE is studied due to its simple strueture. Isothermal and non-isothermal TGA were used to obtain degradation kinetics. Systems of homopolymer, polymer mixtures, and solvent-swollen polymer are studied. The significant variables for... 

Thermal degradation of polymers can occur by three mechanisms (see Chapters 11 and 12) ... 

The chemistry of the solid-state polycondensation process is the same as that of melt-phase poly condensation. Most important are the transesterification/glycolysis and esterification/hydrolysis reactions, particularly, if the polymer has a high water concentration. Due to the low content of hydroxyl end groups, only minor amounts of DEG are formed and the thermal degradation of polymer chains is insignificant at the low temperatures of the SSP process. 

R. D. Ritchie, Symposium on "High Temperature Resistance and Thermal Degradation of Polymers"... 

In the presence of oxygen the thermal degradation of polymers is complicated by oxidation reactions, making the course of the reaction rather obscure. 

Thermal Degradation of Polymers for Molded Integrated Circuit (IC) Devices... 

The oxidative stability of the exposed surface of most organic polymers is less than that in inert conditions and within solids. A description of the many known variations of thermal degradation of polymers is beyond the scope of this book. 

Goodings, E. P., Thermal Degradation of Polymers, p. 211, Society of Chemical Industry, London, 1961. 

Shulman GP (1965) Thermal degradation of polymers I. Mass spectrometric thermal analysis. Polym Lett 3 911... 

Camino, G. Costa, L. Trossarelli, L. Thermal degradation of polymer-fire retardant mixtures Part III— Degradation products of polypropylene-chlorinated paraffin mixtures, Polymer Degradation and Stability, 1982,4(2), 133-144. 

Modeling Thermal Degradation of Polymers by Population Balance Methods... 

Voluminous literature data exists on the thermal degradation of polymers. It was, e.g., established that characteristic parameters of the polymer degradation are determined by the way of preparation of a particular sample. It has been postulated that the less stable samples contain weak links in the macromolecule. However, the nature of these links is not well defined it is known that the weakest links in polymer chains are peroxidic bonds. In hydrocarbon polymer stored in air, a certain concentration of peroxides will always be present as well as of free radicals derived from the decomposition of peroxides. 

Table 21.1 summarises the most important data about the thermal degradation of polymers these data are mainly taken from Madorsky and Strauss and from Korshak et al. (1968,1971) and Arnold (1979). 

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