Tin stabilisers

There has been a revival of interest in recent years in antimony mercaptides as alternatives to the organo-tin stabilisers. This stems from the low level of toxicity and the strong synergism with calcium stearate. However, compared to the... 

ETINSA (2003) Tins Input to EUSES — Levels of TB T found In the environment Summary repert ef relevant studies previded to Risk Policy Analysts Ltd by the Eurepean Tin Stabilisers Asseciatien, Octeber. 

Yoder R (2003) Electrospray ionisation mass spectrometer study ofdioctyitin compounds in solution. Report provided to Risk Policy Analysts Ltd by the European Tin Stabilisers Association, May. 

This presentation covers various aspects relating to stabilisers. These include the structure and mission of the ESPA, the EC Green Paper on stabilisers published on 27th July 2000 and the resolution of the EU Parliament relating to lead and cadmium stabilisers adopted on 3rd April 2001, current EU legislative status of cadmium and lead, key milestones of the PVC Industry Voluntary Commitment relating to stabilisers, scenario of lead replacement in Western Europe, alternatives to lead, plastics additives with approval for direct food contact, tin stabilisers for PVC and issues concerning zinc. EUROPEAN COMMISSION... 

The dielectric strength of polyethylene has been measured as a function of additive concentration while in stabilised polymers the depth of degradation was found to be uniform . HALS have been found to be effective stabilisers for UV cured coatings and do not influence the cure rate . Bleached wood pulps can be effectively stabilised by ascorbic acid and wool by hydroxy-benzotriazoles and HALS . Hydroxybenzotriazole stabilisers also protect wood pulp and polyurethanes by co-reaction . The spectroscopic properties of monomeric and polymeric benzotriazoles have also been compared . UV absorbers are effective in clear coats and when grafted to wood . Dihydroxybenzophenone stabilisers inhibit the chain scission in the photodegradation of poly(methoxyacrylophenone) while tin stabilisers have also been found to photostabilise PVC . 

Because of DCOIT s low water solubility and good UV stability, it makes it ideal for external environments (Figure 45) and permanently or often moisture saturated products such as pool liners, awnings, tarpaulins and so on. Furthermore once released to the environment it is readily degraded which makes it an environmentally favourable alternative to OBPA. Degradation can also be seen with some mercapto tin stabilisers and other reducing agents. 

Among these heat stabilisers, those containing tin (such as tin mercaptides, and tin carboxylates or maleates) are considered to be the most efficient, and can be used in a wide variety of applications. Metallic tin is harmless but there are suspicions that organotin-compounds can be toxic to the central nervous system and the liver. However, tin stabilisers have a low capacity for migrating, and hence they are still considered to be safe. Tin stabilisers such as methyl and octyl tins are used in food contact applications. For PVC, it is believed that tin stabilisers act as HCl scavengers (generating tin chloride) as well as an antioxidant. Thio-tin compounds (preferred for rigid pipe extrusions and profiles (for window frames) of PVC) may develop an odd odour due to sulfur. 

B. B. Cooray and G. Scott, The role of tin stabilisers in the processing and service performance of PVC, in Developments in Polymer Stabilisation - 2, Applied Science Publishers, 1980, Ch. 2. 

The type of tin compound favoured in PVC stabilisers varies in different parts of the world. In Europe, 60% of the tin stabilisers used are octyl compounds, including those used in potable water pipes, and 30% butyl. In North America, where tin is widely used in pipe, foam and window profiles, 50% of the tin stabilisers are methyl, and most of the rest are butyl. Methyl and octyl compounds are FDA approved in some cases and allowed in food packaging. In Asia, 50% of tin stabilisers are methyl, and 40% octyl. In Japan, octyl tin is preferred for food packaging and potable water pipe, while butyl tin is used in construction applications. 

Crompton has introduced Mark 2000 organotin stabilisers for PVC window frames, to overcome processing problems in high-speed extrusion lines. The company also markets a sulfur-free tin stabiliser called Mark 2289, specifically for PVC window profiles that are subject to intense simshine, as in desert areas of the United States. It is said to protect against heat and UV to some extent as well. 

Many other chemicals have become more expensive because of increases in the price of upstream intermediates. Tin stabilisers are affected by the rising price of tin metal and epoxy derivatives are also affected, with basic epoxy resins going up by about 200 euros/tonne in Eiuope in mid-2004. Some phenohc derivatives have also risen dramatically in price. A snapshot over two or three months diuing mid-2004 shows substantial price increases being announced by leading suppliers for impact modifiers, waxes, silica, phosphorus flame retardants and, as indicated earlier, brominated types. Plasticiser producers were also attempting price increases for DINP and DEHP. 

Rohm and Haas has closed its Semoy (France) factory for making methyl tin stabilisers, and is relying on its Cincinnati, US plant. 

There are 130 additives currently under restriction, including the tin stabilisers used in PVC, the polyolefin antioxidant Irganox 1076, and process aids of the bis-ethoxylated amine type. 

Udris [53] examined methods for the recovery and identification of tin stabilisers in excess plasticiser (90 to 95%). The plasticisers included diisooctyl phthalate and mixtures of diisooctyl phthalate and tritolyl phosphate in various proportions. 

Good samples of dialkyltin dichlorides were isolated by this method from mixtures of tin stabilisers with diisooctyl phthalate and tritolyl phosphate the dialkyltin groups have been identified in dibutyl tin dinonylmaleate, dioctyltin dilaurate, dibutyltin dinonylthioglycollate and dioctyltin thioglycollate. 

If mixed tin stabilisers are believed to be present, for example, a thio-compound and a dialkyltin dialkylcarboxylate, it is advantageons to acidify the acetone filtrate after removal of the dialkyltin oxides with hydrochloric acid, evaporate most of the acetone on a water-bath under an air-jet, cool and extract by shaking with diethyl ether. The ether extract then contains hemiesters, acids, and so on, liberated from the other types of tin stabilisers originally present and can be examined further. Although reaction products produced by... 

Metal salts present in tin stabilisers can be identified by diluting the sample with diethyl ether, centrifuging (or filtering) and examining the precipitate by IR spectroscopy and by emission spectroscopy (for metals). 

Wolska [59] reviewed recent advances in the application of XRF spectroscopy to the determination of antimony, bromine, copper, iron, phosphorus, titanium, and zinc, in various plastics. The ED2000 high-performance EDXRF spectrometer mannfactured by Oxford Instruments can determine up to 80 elements qualitatively and up to 50 elements quantitatively between sodium and uranium in various materials, including polymers [60]. X-ray fluorescence methods are available for the determination of tin stabilisers in PVC [61, 62]. 

Studies on the migration of methyl and octyl tin stabilisers from PVC show that comparing the predicted migration to the determined migration for the additives, the model overestimates migration in all cases for 10 days at 40 °C. Flowever, for the higher temperature test there is a significant underestimation (Table 14.3). 

One of the most effective fungicides is probably copper 8-quinolinolate, which is effective in low concentrations, and resists weathering and leaching well. However, it imparts a green colour to PVC compounds and is thus only suitable for use in dark coloured compounds. A PVC compounder wishing to minimise microbial or fungal attack should therefore formulate using phosphate plasticisers, lead or tin stabilisers and avoid the use of low temperature plasticisers such as sebacates or adipates. 

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