Thermal degradation begins to be important when polymers are processed and fabricated for use. The threshold temperature for breakdown determines the upper limit of temperature in fabrication and the volatile products of degradation must be known in order to guarantee the safety of workers. These same properties are relevant to the potential use of a polymeric material and, in the extreme case, to the hazards presented by the polymer in a fire situation. However, there are also some useful aspects of thermal degradation. Examination of the breakdown products from polymers is increasingly used as a method of analysis. In a limited number of cases, controlled thermal degradation is important in recycling of plastics waste and in the special case of carbon fibre production, degradative reactions are an essential part of the manufacturing process.

15 – Thermal Degradation

Aspects of the thermal oxidation of ethylene vinyl acetate copolymer

Aspects of the thermal oxidation, yellowing and stabilisation of ethylene vinyl acetate copolymer

The fire-resistance of EVA filled with ternary systems (magnesium hydroxide/zinc borate/ talc) has been investigated. The release of water from Mg(OH) 2 seemed to be the predominant phenomenon which acts in relation to fire-resistance. The presence of talc as a minor component, mainly in binary compositions by partial substitution of Mg(OH) 2 , appeared to enhance the flame-retardant properties. It acts by forming a diffusion barrier which is able to limit the transfer of degradation products and oxygen. Synergism was also noticed between talc and zinc borate at constant Mg(OH) 2 loading in ternary compositions.

Magnesium hydroxide/zinc borate/talc compositions as flame-retardants in EVA copolymer

Ammonium polyphosphate (APP)-based additives and Al2O3 and TiO2 nanoparticles have been incorporated separately or combined at a 15 wt% global percentage in poly(methyl methacrylate) (PMMA). APP–based additive containing melamine phosphate has led to an intumescent behavior during cone calorimeter tests, whereas thermal stability was particularly improved by the use of the oxide nanoparticles. APP with melamine phosphate and Al2O3 combination allowed significant synergism on flame retardance to be achieved, owing to the catalytic action of alumina well-dispersed nanoparticles, which modified the decomposition pathway of PMMA and the formation of a charred and ceramized structure. Aggregation processes in the case of TiO2 seemed to limit the catalytic action of the surface and did not allow synergism for flame retardance to be observed. Copyright © 2006 John Wiley & Sons, Ltd.

A. Jamieson

Papers

The thermal degradation of copolymers of vinyl acetate with methyl methacrylate and other monomers

The thermal degradation of copolymers of methyl methacrylate with methacrylic acid