Stabilisation of PVC

OWEN, E. D. (Ed.), Degradation of Stabilisation of PVC. Elsevier Applied Science, London-New York (1984)... 

Ba Zn based systems now have the majority market share for stabilisation of PVC-P in Europe due to extensive formulation development based on increasing the barium content and the important role of new and existing organic co-stabilisers (414). Suppliers include Akros. 

The mechanism of stabilisation of PVC by calcium/zinc stabilisers is briefly discussed and the development of highly efficient, solid and liquid calcium/zinc stabilisers based on novel types of calcium, zinc, calcium-zinc or calcium-zinc-phosphite intermediates for PVC is reported. These new stabilisers are capable of providing PVC compounds having equivalent or improved static heat stability when compared with commercial barium-zinc stabilisers even without the addition of high cost costabilisers. Data in graph form on PVC compounds containing these stabilisers are included. 33 refs. 

This work aims to produce mixed calcium carboxylate stabilisers for use in place of calcium stearate for the stabilisation of PVC. The new stabilisers are based on mixed salts of stearic acid with derivatives of phthalic or maleic acid and also with branched alpha, alpha-branched carboxylic (C12-C16) acids, noted for their lower cost and adequate effectiveness. Test results are examined in detail for the performance of these stabilisers in terms of service properties, processability, and stabilising action. 2 refs. (Translated from Plasticheskie Massy, No.5, 2000, p.19)... 

Recent developments in the use of organic costabilisers for stabilisation of PVC are reviewed, with particular attention to a new class of polyketones (pyrrolidine-2,4-diones) recently patented by Akcros Chemicals. The... 

E. D. Owen, Degradation and Stabilisation of PVC, Applied Science Publishers, Barking, 1984. 

Unlike the well researched subject of the stabilisation of PVC, only a few researchers have investigated the dehalogenation of plastic waste. The studies which have been performed [2] have come up with the following results ... 

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. 

In addition to stabilisers, antioxidants and ultra-violent absorbers may also be added to PVC compounds. Amongst antioxidants, trisnonyl phenyl phosphite, mentioned previously, is interesting in that it appears to have additional functions such as a solubiliser or chelator for PVC insoluble metal chlorides formed by reaction of PVC degradation products with metal stabilisers. Since oxidation is both a degradation reaction in its own right and may also accelerate the rate of dehydrochlorination, the use of antioxidants can be beneficial. In addition to the phenyl phosphites, hindered phenols such as octadecyl 3-(3,5-di-tcrt-butyl-4-hydroxyphenyI)propionate and 2,4,6-tris (2,5-di-rcrt-butyl-4-hydroxybenzyl)-1,3,5-trimethylbenzene may be used. 

The polymetallosiloxanes above may in fact be considered as variants of a series of polymetalloxanes which are akin to the silicones but which contain, for example, tin, germanium and titanium instead of silicon. Of the poly-organostannoxanes, dibutyl tin oxide finds use as a stabiliser for PVC and as a silicone cross-linking agent. Polyorganogermanoxanes have also been prepared (Figure 29.13). 

KemI (2000) Organotin stabilisers in PVC — Assessment of risks and proposals for risk reduction measures. Stockholm, National Chemicals Inspectorate (Report No. 6/00). 

In a reactor at low pressure (0.2-0.3 MPa) and moderate temperature (375 °C) the PVC is chemically and thermally degraded. A particular feature of the process is that the chlorine in the PVC reacts in part with the fillers in PVC and is neutralised with the formation of CaCl2. In similar vein, metal stabilisers in PVC are converted into the respective metal chlorides (lead, cadmium, zinc and/or barium). At current PVC waste compositions these chlorides consist of 60% lead which can be purified and re-used. The reaction in the end results in the following solid, liquid and gaseous products. 

Progress in the field of polymer/additive analysis in the last three decades can best be illustrated by an old recipe for the direct determination of organotin stabilisers in PVC [142] ... 

While additive analysis of polyamides is usually carried out by dissolution in HFIP and hydrolysis in 6N HC1, polyphthalamides (PPAs) are quite insoluble in many solvents and very resistant to hydrolysis. The highly thermally stable PPAs can be adequately hydrolysed by means of high pressure microwave acid digestion (at 140-180 °C) in 10 mL Teflon vessels. This procedure allows simultaneous analysis of polymer composition and additives [643]. Also the polymer, oligomer and additive composition of polycarbonates can be examined after hydrolysis. However, it is necessary to optimise the reaction conditions in order to avoid degradation of bisphenol A. In the procedures for the analysis of dialkyltin stabilisers in PVC, described by Udris [644], in some instances the methods can be put on a quantitative basis, e.g. the GC determination of alcohols produced by hydrolysis of ester groups. 

Organotin stabilisers in PVC compositions were determined by means of TLC [518]. The determination of inorganic species (down to ppb range) by TLC has been reviewed on several occasions [519,520]. Instrumental methods successful in the quantitative estimation of inorganic TLC zones directly on the plate are densitometry, fluorimetry, radiometry, planimetry and visual methods. In the framework of recycling studies, in particular as to metal stabilisers in PVC, Braun and Richter... 

Braun and Richter [923] have described an application of CE in additive analysis, namely quantitative analysis of heat stabilisers in PVC, such as Irgastab 17A and 18 MOK-N, which are metal-based (in the past usually Cd, Ba and Pb, now nontoxic Ca, Zn and Sn). Quantitative metal analysis is of interest for PVC recycling purposes. Various alternative approaches are possible for such quantitative analysis, such as XRF [924], polarog-raphy [925] and AAS [923], The performance of AAS, CE and complexometric titrations in the analysis of the heavy metal content in PVC was compared [923]. For all methods investigated the metals must be separated from the polymer and transferred into an aqueous phase. 

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