@lewn,
Regarding the composition of vinyl records; vinyl records are not a stable polymer of just carbon and hydrogen. Vinyl records contain a significant amount of chlorine and oxygen and a variety of additives. The thermoplastic resin used to produce vinyl phonograph records consist of copolymers of vinyl chloride (PVC) and vinyl acetate (PVAc). The ratio of PVAc to PVC varies depending on the particular formulation. The total PVAc/PVC copolymer can be 75-96% of the record weight. The other 4%-25% are additives that are critical to the performance, and stability of the vinyl record. These additives are not covalently bonded to the copolymer matrix but are merely incorporated within the copolymer matrix and therefore can be leeched out. The stabilizers are typically metal salts of fatty acids or similar organometallic compounds. The metals are typically lead, tin, barium and cadmium. Other stabilizers include phenolic antioxidants such as butylated hydroxytolune (BHT)
PVC is not a stable polymer without the addition of these heat and UV stabilizers. Without proper stabilizers, PVC will readily degrade via a dehydrochlorination reaction which liberates HCl and is an autocatylic reaction. Even with stabilizers, PVC can degrade over time but the degradation process is reduced with stabilizers.