Overview

Like other plastics, polyvinyl chloride (PVC) is not free from product failure during service. A recent study [1] has shown that the main reasons for failure in plastics, in general are environmental stress cracking, dynamic fatigue, static notch failure, creep-related failure, chemical attack, ultraviolet (UV) attack, heat degradation, and wear/abrasion. These are stated in decreasing order of failure.

Amorphous thermoplastics, such as PVC, are particularly sensitive to environmental stress cracking. The reason for this is probably associated with the open structure that allows high rates of fluid permeation. The influence of hydrogen bonding parameters for 65 fluids on craze and crack initiation has been investigated [2].

Dynamic fatigue, as already explained in Section 4.3.4, is not a strong feature of amorphous plastics and unplasticised-PVC (PVC-U) is particularly sensitive in this area. However, this is well known and allowance is made for this aspect in formulation and design - pressure pipes are an example.

Impact-related failure, in the absence or presence of notches, is probably one of the most common reasons for failure of PVC-U products. This may be due to the use of the incorrect grade/formulation for the service temperature and/or poor product design causing stress concentration effects.

Creep is not so much of an issue with PVC-U, but plasticised PVC (PVC-P) may be subject to creep failure at the areas of jointing.

PVC offers good chemical resistance, as noted in Section 4.11.3, but there should be an awareness of chemicals likely to come into contact with the article...