PVC, stabilisation

Whilst lead compounds have been, and still are, the most important class of stabiliser for PVC the metallic soaps or salts have steadily increased in their importance and they are now widely used. At one time a wide range of metal stearates, ricinoleates, palmitates and octoates were offered as possible stabilisers and the efficiency of many of them has been examined. Today only the compounds of cadmium, barium, calcium and zinc are prominent as PVC stabilisers. 

The mechanisms of degradation and the mode of action of the various PVC stabilisers have both been widely studied. Often at least one aspect of their operation is some sort of reaction with the first trace of hydrogen chloride evolved. This removes what would otherwise act as the catalyst for further dehydrochlorination, and hence significantly retards the degradation process. In addition, many stabilisers are themselves capable of reacting across any double bonds formed, thereby reversing the process that causes discoloration and embrittlement. 

The BP Chemicals polymer cracking process is based at Grangemouth in Scotland and uses mixed plastics as the raw material. The reactor uses a fluidised bed which operates at 500 °C in the absence of air, and under these conditions the plastics crack thermally to yield hydrocarbons. These vaporize and are carried away from the bed with the fluidising gas. Solid impurities such as metals from PVC stabilisers accumulate in the bed or are carried away in the hot gas to be captured by a cyclone further along in the plant. PVC decomposes to HCl and this is neutralized on a solid lime absorbent to yield CaCl2 which is disposed of in landfill. The purified gas is cooled to condense most of the hydrocarbon which can be employed as commercially useful distillate feedstock. The light hydrocarbons which are less easy to condense are compressed, reheated and recycled as fluidising gas. 

ESPA (2002) Use, exposure and loss data for the use of mono/di- tin compounds as PVC stabilisers. Communication from the European Stabilisers Producers Association, received 25 February. 

Wieboldt et al. [560] have described SFE-SFC-FTIR analysis of hindered phenol primary antioxidants and phosphite secondary antioxidants in PE. SFE is more selective for the lower-range low-MW polymer than Soxhlet-type extraction. This yields a chromatogram with less interference from low-MW polymer peaks in the region where the additive components elute. As a result, SFE appears to be a better choice than Soxhlet-type extraction for the selective removal of additives from flaked polymer. SFE and dissolution/precipitation methods were compared for a PVC/stabiliser system [366]. 

SEC-RI/UV has also been used to analyse some 26 thioorganotin compounds, organotin carboxylates and chlorides, essentially PVC stabilisers, and some of their main by-products and related compounds (thioesters and dithioesters, n-alkanes) [803]. Not all organotin chlorides were stable in the adopted analysis conditions. N, Ai -ethylene-bis-stearamide and -oleamide in common plastics (ABS, SAN, PUR, LDPE, PA6.6) can be analysed by SEC after derivatisation with trifluo-roacetic anhydride. SEC analysis of fatty alcohol ethoxy-lates (FAE), used as nonionic surfactants, has also been described [759]. 

GC-AAS has found late acceptance because of the relatively low sensitivity of the flame graphite furnaces have also been proposed as detectors. The quartz tube atomiser (QTA) [186], in particular the version heated with a hydrogen-oxygen flame (QF), is particularly effective [187] and is used nowadays almost exclusively for GC-AAS. The major problem associated with coupling of GC with AAS is the limited volume of measurement solution that can be injected on to the column (about 100 xL). Virtually no GC-AAS applications have been reported. As for GC-plasma source techniques for element-selective detection, GC-ICP-MS and GC-MIP-AES dominate for organometallic analysis and are complementary to PDA, FTIR and MS analysis for structural elucidation of unknowns. Only a few industrial laboratories are active in this field for the purpose of polymer/additive analysis. GC-AES is generally the most helpful for the identification of additives on the basis of elemental detection, but applications are limited mainly to tin compounds as PVC stabilisers. 

Applications Since the introduction of commercial GC-MIP-AES systems, organometallic analysis can be performed routinely, e.g. for speciation of organotin compounds used as PVC stabilisers [356], The hyphenated GC-AED technique can be used to improve the efficiency of additive analysis. While on the one hand... 

A similar situation pertains in the PVC stabiliser sector, where environmental restrictions have acted as an incentive to PVC reformulation (replacement of the commonly used liquid and solid Ba/Cd and solid Pb stabiliser systems). Producers of heat stabilisers for PVC nowadays strive to create products that are heavy-metal-free and provide strong weatherability and... 

Stid-Chemie, Application Note Sorbacid , Heavy Metal Free PVC Stabilisation, Stid-Chemie AG, Moosburg, Germany (2001). 

Frye and his co-workers have continued their tracer investigations of PVC stabilisation (67) and claim to have synthesised (68) a whole series of compounds Bu2SnY2 with labelled butyl groups, labelled tin atoms or labelled Y groups where Y = oxo-octylthioglycollate, mono-methyl-maleate, 2-ethylhexanoate or /S-mercapto-propanoate. They sought to learn a) Do any chemical reactions occur between stabiliser and polymer b) If so what are their natures c) Do the reactions contribute to polymer stabilisation ... 

Fundamentally new types of PVC stabilisers are dyalkyltinmalcatcs of the following structure ... 

Vulcabond Stabiliser-Aid B2 has been introduced by Akcros Chemicals as the first of a new generation of PVC stabilisers for PVC-coated fabrics. This new range of base and top-coat stabilisers is suitable for all plastisol applications. A pot life of 20 hours is now possible with Vulcabond Stabiliser-Aid B2. The new stabiliser offers... 

The study of PVC stabilisation by stannic compounds in the presence of HC1 scavengers shows that the essential stabilisation process is nucleophilic substitution of the allylic chlorine by the thioglycolate or mercaptopropionate groups. It is claimed that their capability to form complexes with HC1 and transport this degradation catalyst to HC1 scavengers are essential for the marked synergism observed between these two types of stabilisers. 14 refs. 

Ontario, 12th-14th Oct.1999, p.52-8 ENVIRONMENTAL ASPECTS OF LIQUID MIXED-METAL PVC STABILISER DEVELOPMENT Burley J W... 

Prague, 27th-19th Oct. 1999, paper 19, pp.6 INCREASING ROLE OF ORGANIC COSTABILISERS IN PVC STABILISATION... 

Brighton, 20th-22nd April 1999, p.350-9 MECHANISM OF PVC STABILISATION Fisch M H Bacaloglu R Witco Corp. 

New York City, 2nd-6th May 1999, p.3569-73. 012 MECHANISM OF ORGANOTIN STABILISATION OF POLYVINYL CHLORIDE. IV. PVC STABILISATION BY ALKYLTIN ALKYL MERCAPTOPROPIONATES Fisch M H Bacaloglu R Dooley T Witco Technical Center (SPE)... 

A series of alkyltin 2-ethylhexyl mercaptopropionates is synthesised and their structure and equilibria with alkyltin 2-ethylhexyl thioglycolates and alkyltin chlorides studied by IR and 119Sn NMR. Compatibility with PVC is determined using DMA analysis of glass transition temperatures. The implications of these results on PVC stabilisation are discussed. 19 refs. 

II. SIGNIFICANCE FOR PVC STABILISATION OF STRUCTURE AND EQUILIBRIA OF ALKYLTIN THIOGLY COL ATES/CHLORIDES Fisch M H Bacaloglu R Biesiada K Brecker L R Witco Corp. 

Toronto,27th April-2nd May 1997,p.3496-502. 012 RECENTLY-DEVELOPED NON-LEAD PVC STABILISERS FOR WIRE AND CABLE... 

Risk reduction is a world wide problem and of course a concern to the field of PVC stabilisers. The replacement of lead stabilisers in wire and cable applications is demonstrated. Newly developed non-lead stabilisers (RUP-series) are shown to offer excellent heat stability, electrical and mechanical properties compared with traditional wire and cable formulations. The overall processability is shown with experimental and actual results. The gradual increase in use of ADKs and other non-lead stabilisers in the USA and Japan demonstrates industry s concern for the public demand in saving the environment without direct laws banning the use of lead. JAPAN... 

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