THE SCIENCE BEHIND PVC
PVC (Polyvinyl chloride) is a thermoplastic polymer composed of chloroethylene monomers with an atactic stereochemistry with occasional syndiotactic structure. The polymer is usually linear with not many branching points, but is still very strong due to the strong intermolecular forces. Phthalate plasticizers, heat and UV stabilizers, and other refining agents are usually added during the industrial polymerization of PVC to enhance the material.
PVC and its additives have multiple health and safety concerns. Degradation is an important limiting factor when constructing PVC. Fatigue induced by various stresses on the material lead to microcracks and deformations on the surface of the material, yielding microparticles which when released to the environment are called microplastics. Concentration of persistent organic pollutants (POP), which are harmful materials not degraded by natural environmental processes, are directly proportional to the level of microplastic pieces emitted, which depend on the plastic medium, the amount of polymerization (i.e. the average molecular weight of single polymer), and the amount and chemical make-up of the additives. PVC usually has a high polymerization number; therefore, the POPs emitted from PVC are usually more toxic as they also have higher molecular weight and become insoluble in water (1). There have been many concerns about the emittance of POPs from PVC to the marine biome as water pipes are often composed of PVC (2). It has even been shown that PVC can absorb POPs on to its surface, thus, exposing POPs to various environments as PVC moves (3). Also, the PVC monomer has been known since the 1970s to be a carcinogen.
The chemical group of phthalates, which has the base of a benzene ring with two ester groups attached in a cis-confromation, is often incorporated at high concentrations in PVC but is not covalently bonded to the polymer matrix, which makes them highly volatile. Several car companies have banned the use of phthalates and even a shower curtain had to be recalled for the risk of toxic inhalation (4). The European Union has lots of regulations on the use of phthalates in commercial products and the waste managment of PVC in general.
Sources:
1 H. Fielder. Persistent Organic Pollutants. Springer, 2003. http://books.google.com/books?id=aQww4alhpA8C&dq=persistent+organic+pollutants&lr=&source=gbs_navlinks_s
2 Andrady, A., Marine Pollution Bulletin, 'Micro-plastics in the Marine Environment.' doi:10.1016/j.marpolbul.2011.05.030
3 A. Bakir, et al. Marine Pollution Bulletin. 64: 2782-9. (December 2012). http://www.sciencedirect.com/science/article/pii/S0025326X12004602
4 http://www.canada.com/cityguides/winnipeg/info/story.html?id=dfe49cb3-b104-4d4a-a449-14e4faf17e2b
PVC and its additives have multiple health and safety concerns. Degradation is an important limiting factor when constructing PVC. Fatigue induced by various stresses on the material lead to microcracks and deformations on the surface of the material, yielding microparticles which when released to the environment are called microplastics. Concentration of persistent organic pollutants (POP), which are harmful materials not degraded by natural environmental processes, are directly proportional to the level of microplastic pieces emitted, which depend on the plastic medium, the amount of polymerization (i.e. the average molecular weight of single polymer), and the amount and chemical make-up of the additives. PVC usually has a high polymerization number; therefore, the POPs emitted from PVC are usually more toxic as they also have higher molecular weight and become insoluble in water (1). There have been many concerns about the emittance of POPs from PVC to the marine biome as water pipes are often composed of PVC (2). It has even been shown that PVC can absorb POPs on to its surface, thus, exposing POPs to various environments as PVC moves (3). Also, the PVC monomer has been known since the 1970s to be a carcinogen.
The chemical group of phthalates, which has the base of a benzene ring with two ester groups attached in a cis-confromation, is often incorporated at high concentrations in PVC but is not covalently bonded to the polymer matrix, which makes them highly volatile. Several car companies have banned the use of phthalates and even a shower curtain had to be recalled for the risk of toxic inhalation (4). The European Union has lots of regulations on the use of phthalates in commercial products and the waste managment of PVC in general.
Sources:
1 H. Fielder. Persistent Organic Pollutants. Springer, 2003. http://books.google.com/books?id=aQww4alhpA8C&dq=persistent+organic+pollutants&lr=&source=gbs_navlinks_s
2 Andrady, A., Marine Pollution Bulletin, 'Micro-plastics in the Marine Environment.' doi:10.1016/j.marpolbul.2011.05.030
3 A. Bakir, et al. Marine Pollution Bulletin. 64: 2782-9. (December 2012). http://www.sciencedirect.com/science/article/pii/S0025326X12004602
4 http://www.canada.com/cityguides/winnipeg/info/story.html?id=dfe49cb3-b104-4d4a-a449-14e4faf17e2b
