Subject: why do PVC molds break down in the presence of oils and fats?

student interning at shoe manufacturer where they use PVC soles. the PVC 
has and additive butadiene-acrylonitrile and the copolymer goes by the 
name CHEMIGUM P83. when plain PVC was used for soles, shoes in kitchen 
environments where there was oil and fat were corroded in a month. when 
the PVC copolymer was then used, the shoes soles in the kitchen 
environments lasted for only up to 6 months before corrosion. 
i have been asked to explain what is the cause of this corrosion of the 
PVC soles. i was heading in the direction that the fatty acids present on 
the kitchen floor is causing a reaction with chlorine from the PVC. the 
chlorine atom is substituting the hyrdroxide molecule on the carbonyl 
carbon or the hyrdrogen atom on the alpha carbon of the fatty acids. the 
removal of chlorine from the PVC is breaking down its structure corroding 
the soles.  

Re: why do PVC molds break down in the presence of oils and fats?