Thermal Degradation of Poly Vinyl Acetate

Thermal decomposition of poly(vinyl acetate) results in a loss of acetic acid. The reaction is typical of thermal cleavages of esters. It is facilitated by formation of pseudo six-membered rings as a result of interactions between the p-hydrogens of the alcohol residues and the carboxylic groups  

When double bonds form, adjacent methylene groups become activated. The loss of acetic acid is the main product at temperatures up to 200-250°C. Beyond these temperatures, aromatic pyrolytic compounds form. 

Studies of thermal degradation of copolymers of vinyl chloride with vinyl acetate showed that the copolymers are thermally less stable than the homopolymers [502, 503]. The ratio of hydrochloric acid to that of acetic acid that volatilize remains constant during the degradation. This indicates that neither is evolved preferentially, once the reaction begins [502, 503]. It is interesting to note that degradation studies of a copolymer of vinyl chloride and styrene also demonstrated that the copolymer is less stable than each of the homopolymers [504]. 

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B. Rimez, H. Rahier, G. Van Assche, T. Arttoos, M. Biesemans, and B. Van Mele, The thermal degradation of poly(vinyl acetate) and poly(ethylene-co-vinyl acetate), Part I Experimental study of the degradation mechanism, Polym. Degrad. Stab., 93, 800-810 (2008). 

Discuss the thermal degradation of poly(vinyl acetate)... 

The elimination process that occurs during the thermal degradation of poly(vinyl acetate) (PVAc) has been studied and it has been found that elimination of acetate groups initially begins slowly, but increases as degradation proceeds due to an additional process. The increase in rate was found to depend on the concentration of unsaturated groups in the polymer chain. The activation energy of the initial step was found to be 190 kj/mol, while that for the additional process was 130 kj/mol. The additional process of elimination... 

The thermal degradation of poly (vinyl alcohol) (PVA) usually starts at about 150°C or above, depending on the PVA grade. The degradation process gives rise to the release of water from the polymer matrix, accompanied by the formation of volatile degradation products, such as acetic acid in partially acetylated samples [46]. 

Thus Pavllnec (26) detected grafting in a thermally degrading mixture of PP and poly(vinyl acetate) and Mlzutanl (19) found it In degrading mixtures of PP with PMMA, polystyrene and some related polymers. On the other hand McNeill and Nell (13) have shown that chlorine atoms from degrading poly(vlnyl chloride) are responsible for the accelerated decomposition of PMMA In mixtures of the two. 

Sivalingam, G., Karthik, R., Madras, G. Blends of poly(e-caprolactone) and poly(vinyl acetate) mechanical properties and thermal degradation. Polym. Degrad. Stab. 84(2), 345-351 (2004)... 

Madorsky, S. L., Thermal Degradation of Organic Polymers , Interscience, New York, 1964. A compilation of the existing knowledge on polymers and copolymers of styrene, alkenes, halo-carbons, vinyl acetate, acrylonitrile, butadiene, isoprene, poly(ethylene terephthalate), polybenzyl, polyxylene, phenol, formaldehyde resin and cellulosic polymers Polym, Rev, vol. 7). 

Uyar,T. Tonelli, A.E. and Hacalojlu, ,Thermal degradation of polycarbonate, poly(vinyl acetate) and their blends, Polym. Degrad. Stabil. B 12, 2960-2967 (2006). 

Vinyl polymers are particularly susceptible to thermal degradation. A typical example is rigid PVC, which is impossible to process under commercially acceptable conditions without the use of thermal stabilizers. Unstabilized PVC imdeigoes dehydrochlorination near the melt processing temperature. This involves liberation of hydrochloric acid and the formation of conjugated double bonds (polyene formation). The intense coloration of the degradation products is due to polyene formation. A second example of a polymer that undergoes nonchain-scission reaction is poly(viriyl acetate) or PVAc. When heated at elevated temperatures, PVAc can liberate acetic acid, which is followed by polyene formation. 

Radhakrishnan, C., Alex, R., Unnikrishnan, G., Thermal, ozone and gamma ageing of styrene butadiene rubber and poly(ethylene-co-vinyl acetate) blends. Polymer Degradation and Stability 2006,91,902-910. 

Other polymers which have been the subject of thermal degradation studies include ethylene-vinyl acetate [29, 66, 67], ethylene-vinyl alcohol [68], poly(aryl-ether ketone) [69], poly-2-vinyl-naphthalene-co-methyl maleate [34], polyphenylenes based on diethyl-benzophenone [70], polyglycollide [71-73], poly(a-methylstyrene tricarbonyl chromium [74], polytetrahydrofuran [75], polylactide [76-78], poly(vinyl) cyclohexane [79], styrene-vinyl cyclohexane [80], isopropenylacetate-maleic dianhydride [80], polyethylene glycol containing a 1,3-disubstituted phenolic group [81], poly-2-vinyl naphthalene-co-methacrylate [34], collagen biopolymers [82], chitin graft poly (2-methyl-oxazoline - polyvinyl chloride blends [83], cellulose [32, 83-88] and side-chain cholestric elastomers [89, 90]. 

PTFE increases the decomposition temperature of cadmium oxalate trihy-drate. Moreover, the products of cadmium complex degradation, in turn, increase the temperature at which an intensive degradation of PTFE begins. The thermal decomposition of the highly dispersed copper formate leads to the formation of a metal-polymer composition (20-34% Cu). The maximum on the nanoparticles granulometric composition curve corresponds to 4nm. No chemical interaction between the components was observed. The decomposition of a fine dispersion of palladium hydroxide in polyvinyl chloride (PVC) results in spatial structures with highly dispersed Pd particles (S = 26 m g ) in the nodes. This process increases in the temperature required for complete dehydrochlorination of PVC. The thermolysis of cobalt acetate in the presence of PS, PAA, and poly(methyl vinyl ketone) proceeds... 

A significant enhancement in thermal stability has also been recorded for poly (ethylene-vinyl acetate) (EVA) filled with MWNT compared to unfilled EVA The two degradation steps of the EVA matrix (first the deacetylation and then the volatilization of resulting unsaturated chains) are shifted to higher temperatures with a decrease of volatilization rate of the acetic acid and the formation of a stable char, which is further stabilized through electronic interactions with the nanotubes [54]. 

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