Organotin Compounds as PVC Stabilizers

Izmir Institute of Technology, Chemical Engineering Department, Izmir, Turkey 3.3.1 Introduction 

The first generation tin mercaptide stabilizers were dialkyltin long-chain mercaptans (1), traditional mercaptoacetate products (2), and mercaptoacetic ester products, having an average tin content of 18% in the stabilizer. When a stabilizer with a high content of a monoalkyltin compound derived from a mercaptoethanol ester (3), was demonstrated to provide outstanding early color and color retention in white pipe, the industry quickly accepted this departure from traditional mercaptoacetate products. 

Second generation products were mixed mono-/di-alkyl tin long-chain mercaptans. The stabilizer is synthesized directly from an appropriate combination of mono-n-butyltin trichloride and di-n-butyltin dichloride, which is reacted with a suitable quantity of /-octyl mercaptoacetate and sodium sulfide. Although the tin content in the stabilizer is increased to about 22%, these products are often used in diluted form to aid in their handling, while reducing losses. 

This section deals with the stabilization of PVC by organotin stabilizers having different alkyl groups (methyl, ethyl, n-butyl, n-octyl, etc.) and different ligands (carboxylates, mercaptides, etc.), the mechanism of reaction and the evaluation of stability by yellowness index and conductivity. 

There are three major types of tin stabilizers (organotin stabilizers), distinguished by their respective alkyl groups n-octyl, n-butyl, and methyl  

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The organotins have a wide range of uses, which are largely specific for the different organotins. Thus, mono-and disubstituted organotin compounds are not suitable as biocides, and trisubstituted organotin compounds are not suitable as PVC stabilizers. 

The first organotin compound, Et2Snl2, was reported by Frankland in 1849. Interest in organotin chemistry developed steadily over the next decades, but it was not until the discovery of the industrial uses of organotin species (e.g. as PVC stabilizers and as biocidal species), a century or so later, that this area of chemistry expanded rapidly. 

PVC is imstable imder exposure to light and heat resulting in discoloration and embrittlement. In the early 1940s it was found that this degradation could be prevented by addition of certain organotin derivatives. Presently, about 70% of the commercial organotin compounds are employed as PVC stabilizers in the form of mono and dialkyltin derivatives. Today, many of these stabilizers are based on organotin polymers made by Carraher and coworkers. [63]... 

Similarly, while the main products used as stabilizers in PVC are mono- and disubstituted compounds, owing to the chemistry involved in their production, trisubstituted organotin compounds will comprise a small fraction of the total amount. This could be significant in assessing the toxicity of the compounds (see below). 

Organotin compounds are important industrial chemicals. One major use is as stabilizers for poly(vinyl chloride) (PVC) plastics. These additives, one example of which is dioctyltinmaleate, inhibit degradation of the polymer by heat, light, and oxygen. In the absence of these tin compounds, PVC yellows and becomes brittle. 

Elements Ge, Sn, and Pb form many interesting varieties of organometallic compounds, some of which are important commercial products. For example, EuPb is an anti-knock agent, and organotin compounds are employed as polyvinylchloride (PVC) stabilizers against degradation by light and heat. Some examples and advances are discussed in the present section. 

Butyltin compounds, monobutyltin (MBT) and dibutyltin (DBT) and tri-butyltin (TBT) are widely used for the production of biocides and polymer stabilizers. On a yearly basis, 23, 000 tons of butyltin compounds are used as additives in PVC products. This is about 40% of the world usage of organotin compounds [90]. The negative impact of butyltins on the aquatic environment is well documented and in vitro studies have also shown that they disrupt the immune response in humans [91]. Studies have shown that organotins leach out from PVC and related materials, resulting in the con-... 

Organo-compounds of the group 14 elements include some important commercial products, and we have already discussed silicones in Section 13.10 and Box 13.12. Organotin compounds are employed as polyvinylchloride (PVC) stabilizers (against degradation by light and heat), antifouling paints on ships, wood preservatives and... 

With this background information, it was decided to see how these blends would behave as films. In Table II are tabulated some physical properties of extruded films of PVC/acrylic copolymer blends (9/1, 1/1, and 1/9). In Table III are tabulated physical properties of solution-cast blend films, cast from tetrahydrofuran solution. The cast films contained no lubricants or stabilizers (which were present in the extruded films) nevertheless, their optical property deficiencies were similar to those of the extruded films. The additives used were PVC stabilizer (e.g., organotin compounds), lubricant (e.g., metallic stearates), and plasticizer (phthalate type). 

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