Many different plasticizers are used in PVC, just as there are many different antioxidant additive packages used in HDPE. Both sets of additives are intended to be consumed (lost) during service-only by being consumed will they function as intended.
Dioctyphthalate (DOP) has been a common plasticizer for different PVC films such as shower curtain, bookbinder cover, etc. for many years. In Flexible PVC for Long Outdoor Life DOP plasticizer was shown to provide excellent durability as the tested 4 mil film lost only 10% of its plasticizer content when evaluated after 40 years at room temperature. Plasticizers used in PVC geomembrane are higher in molecular weight and typically experience 1/2 of the volatility (loss) than do DOP plasticizers so we would extend the life of the film above testing to more than 80 years. The rate of plasticizer loss will be lower in thicker PVC geomembranes (due to increased ratio of mass to surface area) and still lower in buried PVC geomembranes (due to lack of freely circulating air).
The Bureau of Reclamation has installed PVC geomembrane canal liners since 1961 - a good portion of which were 10 mil PVC in the early years. In 10 mil PVC evaluation it was discovered that 40 to 50% of the plasticizer had been lost in 27 year old in service material and that the material was still very flexible. Laboratory tests confirmed that PVC geomembrane would still be flexible even if 75% of the plasticizer content had been lost.
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