Residual vinyl chloride monomer

Case I Residual vinyl chloride monomer (RVCM) loss during storage of a freshly manufactured PVC product. 

ASTM, D 3749 - Residual Vinyl Chloride Monomer in Poly(Vinyl Chloride) Resins by Gas Chromatography Headspace Technique (2002)... 

ASTM, D 4443 - Determining Residual Vinyl Chloride Monomer Content in PPB Range in Vinyl Chloride Homo- and Co-Polymers by Headspace Gas Chromatography (2002)... 

Devolatilization. Following polymerization of many polymers, removal of residual monomer or solvents is necessary. Ultimately this removal becomes controlled by diffusion from the polymer no matter what type of process is employed (27). Many processes use a steam-stripping operation for this purpose, and others employ devolatilization in a vented extruder. Removal of residual vinyl chloride monomer from poly(vinyl chloride) was an issue of much concern following the discovery that this monomer is a carcinogen. 

PVC, over the years, has been subjected to scrutiny on health and environmental grounds. One issue is the level of residual vinyl chloride monomer in the material that may migrate into food. Vinyl chloride monomer has been determined to be a carcinogen, at least under some conditions. In the polymerization process for PVC, less than 100% of the vinyl chloride monomer (VCM) is converted to polymer. This means that relatively high values of VCM may remain unreacted and trapped in the resin. To remove this residual monomer, the resin is subjected to repeated applications of vacuum. In this manner, VCM concentrations in the resin are reduced substantially. PVC packaging resins currently produced have much lower levels of residual vinyl chloride (under 10 ppb) than those used in containers in the mid-1970s when this concern first surfaced. 

Hence, PVC products should be checked for levels of both VCM and plasticisers, although it is now possible for the residual monomer to be removed completely from polymer matrices, and in most cases residual vinyl chloride monomer levels in PVC worldwide are well below the maximum acceptable levels, typically from undetectable to a few parts per billion (ppb). PVC resins should almost always be supplied nearly free of any residual or unreacted monomers. 

Residual vinyl chloride monomer (ngg range) in vinyl chloride homopolymers and copolymers ASTM D4443... 

Residual vinyl chloride monomer in poly(vinyl chloride) resins ASTM D3749... 

In headspace analysis, the plastic is placed in a vial (at a raised temperature) and the volatiles formed are stripped by a flow of carrier gas. The stripped volatiles are trapped in a suitable sorbent (e.g., using a solid-phase microextraction device) and subsequently thermally desorbed into a gas chromatograph. Process gas chromatographs are used in industrial analysis of volatiles in plastics. An example of this technique is the determination of residual vinyl chloride monomer in plastics in the range of 5-50 g per kg. With direct injection of a polymer solution, there is a danger of side-effects (a loss of reactive monomers due to polymerization in the injection port or an increase in its content due to depolymerization at a high injection temperature). 

D3749 Residual Vinyl Chloride Monomer in Poly (Vinyl... 

Reinforced reaction injection molding Reinforced thermoplastic Room temperature vulcanization Residual vinyl chloride monomer Chlorinated isoprene rubber (DIN)... 

Reference methods for criteria (19) and hazardous (20) poUutants estabHshed by the US EPA include sulfur dioxide [7446-09-5] by the West-Gaeke method carbon monoxide [630-08-0] by nondispersive infrared analysis ozone [10028-15-6] and nitrogen dioxide [10102-44-0] by chemiluminescence (qv) and hydrocarbons by gas chromatography coupled with flame-ionization detection. Gas chromatography coupled with a suitable detector can also be used to measure ambient concentrations of vinyl chloride monomer [75-01-4], halogenated hydrocarbons and aromatics, and polyacrylonitrile [25014-41-9] (21-22) (see Chromatography Trace and residue analysis). 

Vinyl chloride monomer (VCM) is the main substrate for the manufacture of polymers used as packaging materials for food. Since VCM is considered by lARC to be a human carcinogen, monomer levels in PVC food packaging materials are strictly controlled. To ensure a safe product, the residual content of VCM in the finished material or article is limited to one mg per kg in the final product (Council Directive 78/142/EEC). Furthermore, VCM should not be detectable in foodstuflfs. Commission Directives 80/766/EEC and 81/432/ EEC give the method of analysis for official control of the VCM level in food packaging materials and in foods - gas-phase chromatography using the headspace method, after dissolution or suspension of samples in N,N-dimethylacetamide. Both residual monomer content of the polymer and... 

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. 

Inovyl Polyvinyl chloride (emulsion) Vinyl chloride monomer High productivity, high quality grades, low residual VCM, effective condenser usage 2 1991... 

As the polymerization proceeds vinyl chloride monomer is consumed and the pressure drops. At about 0.05 MPa gauge pressure (pressure above normal atmospheric) sufficient monomer has been converted to polymer. Unreacted monomer is vented and the residual vinyl chloride is removed by blowing... 

HS-SPME-GC-MS showed that residual methyl methacrylate is released during thermal annealing of PMMA [40]. SPME fiber was carboxen/PDMS. The extraction time and temperature was 2 hours at 70 °C. A multiple headspace extraction method using a carboxen/PDMS fiber was developed for the quantitative determination of vinyl chloride monomer in PVC [41]. To reduce the equilibrium time, the PVC sample was finely ground before the extraction. Quantitative SPME methods have also been developed to determine vinyl chloride in liquid and solid samples [42] and to determine terephthalic acid and vinyl acetate monomers from aqueous solutions [43]. 

Bulk polymerization is the simplest process for producing PVC, since there are no difficulties on the separation and recovery of the residual monomer, or on the finishing of the produced polymer. The most well-known bulk vinyl chloride monomer (VCM) polymerization process these days is the Rhone-Poulenc two-stage process. According to this process, only VCM and oil-soluble initiators are introduced into the reactor, since there is no need for water and suspending agents. Due to the absence of water, productivity is very high, with respect to the other VCM polymerization processes (i.e., suspension, emulsion, solution). 

In the solid polymer approach the residual monomer is partitioned between the headspace and the polymer phase. The monomer concentration in the head space is determined and the original concentration in the polymer is calculated. Since polymer standards of known monomer content are not readily available, the headspace monomer concentration must be related to the original concentration in the polymer either by assuming 100% diffusion of the constituent into the head space or through equilibrium calculations utilising Henry s Law and the appropriate partition coefficient. Berens [1] determined this coefficient for the vinyl chloride-PVC system and applied this to the determination of vinyl chloride in PVC resin powder. Equilibration of residual vinyl chloride with the headspace occurred within one hour when PVC powder was heated to 90 °C. 

Nitrile elastomers and PVC are considered to be harmless when used with good safety practices under normal operating conditions. Residual acrylonitrile monomers, free butadiene, and vinyl chloride monomer levels are limited and controlled by industrial and environment safety standards. Stabilization of nitrile needs to be adequate to prevent spontaneous combustion. Hazardous decomposition products include carbon monoxide, carbon dioxide, nitrogen compounds, hydrogen cyanide, hydrocarbons, vinyl chloride. 

The removal of residual vinyl chloride from poly(vinyl chloride) appears to be fairly difficult. For example, in a patented process, 1 kg of PVC containing 34 gm of residual monomer was heated for 0.5 hr at 433 mm Hg at 85°C with steam. Then, as the resinous mass cooled to 40 C, the pressure was reduced to 55 mm Hg. The residual resin (969 gm) still contained about 3gm of vinyl chloride [14]. While this reduction in residual monomer is impressive, leaving about 0.3% of free monomer in a finished resin may be rather high. Upon injection molding, for example, this monomer may be released to the atmosphere to raise the vinyl chloride concentration to unacceptable levels unless additional ventilation is provided. 

K020—Heavy ends (residue) from the distillation of vinyl chloride in vinyl chloride monomer production... 

Steichen has discussed a modified solution approach for the gas chromatographic determination of residual vinyl chloride, butadiene, acrylonitrile, styrene and 2-ethylhexyl acrylate monomers in their associated polymers by head space analysis (Method 57). 

Poly(vinyl chloride). Poly(vinyl chloride) (PVC) [9002-86-2] is a thermoplastic for building products. It is prepared by either the bulk or the suspension polymerization process. In each process residual monomer is removed because it is carcinogenic. Oxygen must be avoided throughout the process (see Vinyl polymers). 

The molecules join together to form a long chain-like molecule which may contain many thousands of ethylene units. Such a molecule is referred to as a polymer, in this case polyethylene, whilst in this context ethylene is referred to as a monomer. Styrene, propylene, vinyl chloride, vinyl acetate and methyl methacrylate are other examples of monomers which can polymerise in this way. Sometimes two monomers may be reacted together so that residues of both are to be found in the same chain. Such materials are known as copolymers and are exemplified by ethylene-vinyl acetate copolymers and styrene-acrylonitrile copolymers. 

A wide variety of methods have been developed for the detection of residual monomers in polymeric materials. Volatile monomers, for example, acrylonitrile, butadiene, vinyl chloride, etc., are normally determined using headspace GC methods. 

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

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