Migration Vinyl chloride

Raw Materials. PVC is inherently a hard and brittle material and very sensitive to heat it thus must be modified with a variety of plasticizers, stabilizers, and other processing aids to form heat-stable flexible or semiflexible products or with lesser amounts of these processing aids for the manufacture of rigid products (see Vinyl polymers, vinyl chloride polymers). Plasticizer levels used to produce the desired softness and flexibihty in a finished product vary between 25 parts per hundred (pph) parts of PVC for flooring products to about 80—100 pph for apparel products (245). Numerous plasticizers (qv) are commercially available for PVC, although dioctyl phthalate (DOP) is by far the most widely used in industrial appHcations due to its excellent properties and low cost. For example, phosphates provide improved flame resistance, adipate esters enhance low temperature flexibihty, polymeric plasticizers such as glycol adipates and azelates improve the migration resistance, and phthalate esters provide compatibiUty and flexibihty (245). 

CPA. Copolymer alloy membranes (CPAs) are made by alloying high molecular weight polymeries, plasticizers, special stabilizers, biocides, and antioxidants with poly(vinyl chloride) (PVC). The membrane is typically reinforced with polyester and comes in finished thicknesses of 0.75—1.5 mm and widths of 1.5—1.8 m. The primary installation method is mechanically fastened, but some fully adhered systems are also possible. The CPA membranes can exhibit long-term flexibiHty by alleviating migration of the polymeric plasticizers, and are chemically resistant and compatible with many oils and greases, animal fats, asphalt, and coal-tar pitch. The physical characteristics of a CPA membrane have been described (15). 

Photochemistry. Vinyl chloride is subject to photodissociation. Photexcitation at 193 nm results in the elimination of HCl molecules and Cl atoms in an approximately 1.1 1 ratio (69). Both vinyUdene ( B2) [2143-69-3] and acetylene have been observed as photolysis products (70), as have H2 molecules (71) and H atoms [12385-13-6] (72). HCl and vinyUdene appear to be formed via a concerted 1,1 elimination from excited vinyl chloride (70). An adiabatic recoil mechanism seems likely for Cl atom elimination (73). As expected from the relative stabiUties of the 1- and 2-chlorovinyl radicals [50663-45-1 and 57095-76-8], H atoms are preferentially produced by detachment from the P carbon (72). Finally, a migration mechanism appears to play a significant role in H2 elimination (71). 

Double bonds having oxygen and halogen substituents are susceptible to epoxi-dation, and the reactive epoxides that are generated serve as intermediates in some useful synthetic transformations in which the substituent migrates to the other carbon of the original double bond. Vinyl chlorides furnish haloepoxides that can rearrange to a-haloketones. 

The environmental impact of PVC is discussed with reference to the toxicity of vinyl chloride, plasticisers and heavy metal stabilisers, the formation of dioxins and acid rain resulting from the incineration of PVC waste, and plasticiser migration from PVC products. A brief examination is also made of the recyclability of PVC. 18 refs. 

ISO 105-X10 Textiles - Tests for colour fastness - Part XIO Assessment of migration of textile colours into polyvinyl chloride coatings ISO 264 1976 Unplasticized polyvinyl chloride (PVC) fittings with plain sockets for pipes under pressure - Laying lengths - Metric series ISO 265-1 1988 Pipes and fittings of plastics materials - Fittings for domestic and industrial waste pipes - Basic dimensions Metric series - Part 1 Unplasticized poly(vinyl chloride) (PVC-U)... 

Human exposure to migrating substances (e.g., di(2-ethylhexyl)phthalate) may result in reproductive disorders. There is a hazard that vinyl chloride monomers or bisphenol A migrating into food may induce carcinogenic, mutagenic, and teratogenic episodes. 

D Consumers of beverages in polyvinyl chloride (PVC) containers Container Vinyl chloride (residual monomer present in PVC) Migration of vinyl chloride to beverage Ingestion... 

Ando, M. and Sayato, Y. Studies on vinyl chloride migrating into drinking water from polyvinyl chloride pipe and reaction between vinyl chloride and chlorine, Water Res., 18(3) 315-318, 1984. 

Castle L, Gilbert J, Eklund T (1990) Migration of plasticizer from poly(vinyl chloride) milk tubing. Food Addit Contam 7 591-596... 

The very high value of Cm for vinyl chloride is attributed to a reaction sequence involving the propagating center XVIII formed by head-to-head addition [Hjertberg and Sorvik, 1983 Llauro-Darricades et al., 1989 Starnes, 1985 Starnes et al., 1983 Tornell, 1988]. Intramolecular migration of a chlorine atom (Eq. 3-114) yields the secondary radical XIX that subsequently transfers the chlorine atom to monomer (Eq. 3-115) to yield poly(vinyl chloride)... 

The results suggests that the copolymer has a graft structure and that the mastication medium involves three kinds of domains. The first is the inner domain of poly(vinyl chloride) which is only slightly penetrated by monomer. Polymerization is initiated by macroradicals created in the PVC domain causing the formation of a true copolymer. Short radical segments arising from transfer reactions migrate into the third external domain which consists practically entirely of pure monomer and there initiate polymerization. The second domain is the surface of the resin particle which is swollen by monomer. The free radicals created by bond rupture appear in this second domain. 

Di(2-ethylhexyl) adipate is a liquid of low volatility, widely used as a plasticizer in flexible poly(vinyl chloride) products, notably food films, as well as in other plastics and in a number of other minor applications, such as lubricants and cosmetics. Occupational exposure may occur by inhalation of di(2-ethylhexyl) adipate as an aerosol during its manufacture and its use. Meat-wrapping workers may be exposed while cutting poly(vinyl chloride) film across a heated cutter. Food is the major source of exposure of the general population to di(2-ethylhexyl) adipate because of migration from poly(vinyl chloride) packaging, particularly into fatty foods such as cheese and meat. 

As a second example, there is a wide variety of breakdown products and oligomeric products that may be formed from the reactive monomers that are the building blocks of plastics. For plastics, the general assumption has been that any side-reaction products and breakdown products are likely to be significantly less toxic than the monomers, and so restricting the migration of the monomer was accepted as an indirect way to limit any hazard from the oligomers also. Whilst this approach is probably acceptable for addition polymers, such as those made from the unsaturated monomers vinyl chloride, butadiene and acrylonitrile where the unsaturated monomer is far more noxious than their products, the validity of this means of indirect control is questionable for condensation polymers such as polyesters and for polyethers formed from epoxide monomers. 

Studies on the Sn reactions of the vinyl chloride, 3-chloro-l-pentafluorosulfanyl-prop-l-ene (10), demonstrated that weak base nucleophiles reacted in an 5 2 reaction.14 When stronger base nucleophiles such as CN were used, double-bond migration occurred via an allyl anion (Scheme 5). MP2/6-31++G supported the different reaction with CN . 

FayadNM, Sheikheldin SY, Al-Malack MH, et al. 1997. Migration of vinyl chloride monomer (VCM) and additives into PVC bottled drinking water. J Environ Sd Health Part A A32(4) 1065-1083. 

As a consequence of EU Directive 78/142/EEC, which introduced a limitation of vinyl chloride monomer both as residual amount in final articles (QM lmg/kg) intended to come into contact with foodstuffs and in migration to food (SML not detectable LOD 0.01 mg/kg), the corresponding necessary analytical methods were developed between several European expert laboratories and laid down as agreed methods in EU Directives 80/766/EEC and 81/432/EEC, respectively. This piece of the EU harmonization process was too time- and work-consuming to continue in this way. The vinyl chloride Directives therefore remain a unique feature in EU food packaging legislation since this was found to be impractical for generalization. 

Polymer Science Series B 44, Nos. 1-2, Jan./Feb.2002, p.45-9 IR SPECTROSCOPY STUDY OF PLASTICIZER MIGRATION FROM POLY(VINYL CHLORIDE)-BASED COMPOSITIONS... 

THERMAL DEGRADATION OF POLY(VINYL CHLORIDE) PLASTISOLS BASED ON LOW-MIGRATION POLYMERIC PLASTICIZERS... 

PLASTICISER MIGRATION AND STRUCTURAL CHANGES IN AN AGED POLY(VINYL CHLORIDE) COATING... 

It is well known from diffusion theory that different types of polymers have different diffusion behaviours. For example, the polyester type polymers like poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN) and polycarbonate (PC) as well as rigid poly(vinyl chloride) (PVC), which have a high glass transition temperature, are low diffusive polymers. The migration of potential contaminants in these polymers will result in low migration values. In contrast, polyolefins like high density polyethylene (HDPE), polypropylene (PP) or low density polyethylene (LDPE), which... 

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