Thermo-oxidation and degradation of polymers Jozef Rychlý Polymer Institute Dúbravská cesta 9, Bratislava, Slovak Republic Polyfriend workshop, september 5, 2013, morning

Polymers utilised practically usually have unknown residual stability and the unknown concentration of additives – trajectory of the service life of the material Polyfriend workshop, september 5, 2013, morning

Possible harmful effect on polymer products Polyfriend workshop, september 5, 2013, morning

Acid hydrolysis of cellulose chains – example of combination of cross reaction of hydrolysis and free radical oxidation on terminal groups formed subsequently from hydrolytic attack Polyfriend workshop, september 5, 2013, morning

Chemical degradation is accompanied by the reduction of the molar mass, increase of the molar mass due to crosslinking, or it occurs as polymer analogous reaction typical by unzipping of side groups of the macromolecular chain. Degradation (physical) may involve also the physical processes like recrystallisation, denaturation (proteins). Ageing, (corrosion) is related to the long term degradation due to weathering and involves both. Polyfriend workshop, september 5, 2013, morning

Chemical degradation Polymers are organic and inorganic materials composed of structural units – mers – kept together by chemical bonds. Their stability properties are detemined by long entangled chains and by free volume. Small change such as disruption of the chain may change the properties significantly. Polyfriend workshop, september 5, 2013, morning

Physical degradation Loss of properties due the change in position of macromolecular chains and additives in the volume without necessary chemical change. Polyfriend workshop, september 5, 2013, morning

Foil from low density polyethylene in advanced stage of its degradation Polyfriend workshop, september 5, 2013, morning

Dissociation energies of bonds A-B in kJ/mol that may form the skeleton of the macromolecular structure in polymers. Polyfriend workshop, september 5, 2013, morning

Degradation starts by the formation of active sites (radicals, ions, excited states) on the macromolecular chain. Polyfriend workshop, september 5, 2013, morning

Tests of oxidation stability Oxidation stability tests follow from Bolland Gee scheme: Time or temperature evolution of concentration of hydroperoxides, DSC, thermogravimetry, chemiluminiscence, analytical determination of carbonyls, mechanical properties changes, etc. Polyfriend workshop, september 5, 2013, morning

Bolland-Gee scheme for free radical mechanism of polymer degradation valid to temperatures ca 250 oC, (P and Z denote macromolecular chains of the different length, InH is chain breaking inhibitor, D peroxide decomposer, P., Z. are polymer radicals Polyfriend workshop, september 5, 2013, morning

Induction time, the easiest way of the characterisation of the polymer stability Polyfriend workshop, september 5, 2013, morning

Polyfriend workshop, september

Examples Polyfriend workshop, september 5, 2013, morning

1. Original and aged samples of polyether and polyester urethanes daylight (0-15 days), 1000 Wm -2, 25°C/50% RH Polyfriend workshop, september 5, 2013, morning

Structural segments of polyurethanes Polyfriend workshop, september 5, 2013, morning

The comparison of non-isothermal thermogravimetry for reference sample polyether urethane 1 and polyester urethane 2 in nitrogen and oxygen, the rate of heating 5 o C/min. Points denote the theoretical fit. Polyfriend workshop, september 5, 2013, morning

Comparison of nonisothermal thermogravimetry and DSC records for polyether (sample 1) and polyester (sample 2) polyurethane foams, oxygen, the rate of heating 5 o C/min Polyfriend workshop, september 5, 2013, morning

Chemiluminescence and DSC measurements in oxygen for non-aged samples 1 and 2. The rate of heating 5 o C/min. Polyfriend workshop, september 5, 2013, morning

Obvious conclusion! Polyester urethane are hydrolytically less stable than polyether urethane while polyether urethanes are less stable towards light induced degradation. Polyfriend workshop, september 5, 2013, morning

Characterisation of aged polyurethanes Polyfriend workshop, september 5, 2013, morning

Conclusion Degradation is inevitable symptom of the polymer service life. It can be slowed down, with much more pronounced induction time, but it cannot be avoided. The detailed knowledge on the kinetics is always necessary! Polyfriend workshop, september 5, 2013, morning