engleski

Photostabolity of Polyurethane Elastomers based on various Types of Diisocyanates

The effect of UV irradiation on the mechanical and thermomechanical properties of polyurethane (PU) elastomers and their morphology was studied.The chemical changes in the PU elastomers exposed to UV irradiation were studied by means of FTIR.The PU elastomer wer based on an aromatic isocyanate (4, 4'-MDI) and a cycloaliphatic isocyanate (H12MDI).POly(caprolactone) glycol of 1250 MW aws the polyol used an 1, 4-butanediol was the chain extender.The elastomers were prepared in a two step procedure.First, prepolymers were prepared from poly(caprolactone) glycol by reacting with the corresponding isocyanate at NCO:OH ratios 2:1 and 4:1. The prepolymers were then chain-extended with 1, 4-butanediol and the mixtures were press-molded in a platen press at 100oC.The results showed that the stability of the investigated PU elastomers depended on the chemical structure of the diisocyanate and the soft/hard segment ratio, .The processes of photooxidative degradation are more prevalent in PU elastomers based on the cycloaliphatic isocyanate than those based on teh aromatic isocyanate.In the case of PU elastomers based on cycloaliphatic isocyanate it was found that the photodegradative processes were enhanced with increasing hard segment concentration.The degree of photooxidative degradation of PU elastomers, as studied by FTIR, correlated very well with the extent of morphological changes and changes in mechanical properties.Althougt PU elastomers based on the aromatic isocyanate undergo color changes, they exhibited better retention ofmechanical properties compared to those based on the aliphatic isocyanate.

polyurethane elastomers; photostability; UV irradiation

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