Document oZ40vBegyLJ9BEL0ex9YDn93

PACKAGING TECHNOLOGY AND SCIENCE VOL 2 215-226 (19891 Polyvinyl Chloride and its Organotin Stabilizers with Special Reference to Packaging Materials and Commodities: a Review* K. Flgge NATEC Institut fur naturwissenschaftlich-technische Diensta GmbH, Behringttraasa 154, D-2000 Hamburg, SO FRG Polyvinyl ehlorido (PVC) is a tharmopiaatie that has antarad practically all araas of Ufa as a chaap and varaatUa material. Sinoa PVCalso fulfila tha Mghquaiity requirements placad on modom packaging matariala, with raapact to packaging tachniquaa and consumer protection. it la being used to an increasing extant for packaging of food and beverages as wall as pharmaceutical and cosmetic products. Tha various additives required for processing PVC into packaging materials and commodity articles, as wad as improving its properties during usage (e.g. lubricants and stabNfatarsi. are harmlaaa with regard to human and acotoxicoiogicai aspects.-Their use Is non-hanrrious and-is therefore permitted by authorities, in the group of thermo- and Hgtot atabiiizars for PVC, mixtures of mono- and dialkyitin thiogiycoiatas play a major roia. In accordance with legislation, these are allowed to be used in rigid PVC. In addition to their excallant stabilizing affect, they are not hazardous to tha health of consumers of products packed in rigid PVC. Slntiiariy, no health hazards exist to personnel, working in PVC production and processing plants, from volatile components of organotin staMtears provided-that procsssing and environmental pramquisttaa of modem technology era ebasrved. The disposal of household waste that contains used PVC materials--stabiUzad with mixtures of mono- and dialkyitin thiogiycoiatae--does not causa additional difficulties. Keywords: PVC; organotin stabilizers; ecotoxicotogy; packaging materials; waste disposal PART I--INTRODUCTION Plastic materials have entered practically all areas of technology, in commercial and daily life. Thereby because of superior properties and a broad spectrum of characteristics and economic advantages, plastics have been able to displace and/or supplement traditional materials, such as wood, glass and metal. It is certain that they will continue to play an increasingly significant role in future. This is indicated, for instance, by progress in the development of electrically conducting and fireproof polymers, which can be used in the electrical and electronics industries and for fire-proofing technology. Thus, expensive and non-replenishable resources like copper, silver 'Report first presented at the Eighth World Meeting of the ORTEP Airoriarion. 1-2 November 198S. San Francisco. USA. 0894-3214/89AM021S-12S06.00 (01969 by John Wiley & Sons, Ltd. Reproduced by permission of John Wiley and Sons Limited Recartd 3 October 1988 Rented 3 March 1989 22138001 BFG19019 216 K. FIGGE and special metal alloys, as well as less suitable fire-proofing materials, can be substituted by plastics. The development of novel polymers would find increasing application of plastics in other technical areas. This versatile and still expanding field of plastics application, if evaluated objectively, contributes towards improved living conditions of modem society by. for example, providing cheap consumer articles and household utensils, in hygienically safe edible products of high quality, and its medical applications. However, this expansion in plastics application is being regarded to. an increasing extent with suspicion and criticism. There is a tendency by a large section of the public to have a preconceived negative attitude towards even well-proven plas tics. which is being promoted and misused in certain areas. The statements in Table 1 are typical of the technically false statements made by some pressure groups. Such objections to the use of plastics are propagated and supplemented further by novel and equally false arguments. They are presented partly with the intention of verifying biased views, with seemingly plausible arguments for accept ance by an uninformed public. This strategy follows the current trend -- which should not be underestimated -- of an increasing awareness of people with regard to their environment and health. Consequently, these objections and argu ments are resonated in the media and by consumer groups, political parties, municipal bodies and. last but not least, among individual consumers. The success of this anti-plastics campaign is partly the result of inactivity during past decades by both plastics and additive producers as well as processors of the same. Thus, these bodies published only technical data and failed to inform the consumer in an understand able and objective fashion of the important properties of plastics, particularly with regard to aspects of environmental and consumer protec tion. Only after it became obvious that a major part of the public had been adversely influenced against plastics, did the industries concerned start to react with objective arguments. However, this attempt has been only partially successful. This is particularly obvious since numerous negative articles against plastics are still appearing in daily newspapers and journals. It is even more alarming that in some detailed expen judgements recently publicized by private and university institutes, the health and environmental hazards due to plastics have been assumed to be proven facts.*1-2 3 4 5 Consequently, a number of concrete meastfres have been proposed, for instance, to substitute polyvinyl chloride (PVC) -- a plastic that has very wide areas of application -- to the maximum extent by other materials. This view is incompre hensible. particularly since PVC has a longproven record of use in numerous fields of application throughout the world. In the Federal Republic of Germany, it has the second highest tonnage of polymeric material, exceeded only by polyolefins, of the order of 1.2 million tons per year. The easy modification of PVC through the use of additives, which have been evaluated positively over many years, represents a notewor thy technical asset. Table 2 shows the wide range of uses. It is not only used in the building and construction sector, but an increasing trend of its application also concerns the packaging of food stuffs. as well as other consumer articles. In spite of this, PVC is now a permanent focal point of Table 1. Technically false statements made by some pressure groups 1. The production and processing of plastics are wasteful with respect to recourses and energy 2. Owing to the high volatility of starting materials and other ingredients, production and processing of plastics are hazardous for the health of factory workers 3. Plastic materials are dangerous for the environment and health, and. owing to their content of processing aids and other additives, they are potential sources of environmental pollutants 4. Society is faced with health hazards, among others, owing to the use of plastics in packaging and as building and construction materials, for example, through contamination of foods and beverages and of the air in rooms by volatile plastic components 5. Treatment and disposal of household and commercial wastes containing, in addition to vegetable components, glass, metals, paper and cardboard, and considerable quantities of different types of plastics, are problematic and hazardous. 009ETZZ BFG19020 PVC AND ITS ORGANOTIN STABILIZERS 217 Table 2. Industrial application of PVC in different areas of usage in the Federal Republic of Germany PVC (1 ppm) and is quite often below 0.1 mg VC per kg PVC (0.1 ppm). After a short interruption. PVC has once again Industrial sector Fraction (%) received a negative reaction from the media, this is not restricted to the environmental and health Building and construction 58 conscious German media but involves those of Packagings 17 other western and northern European countries, Automobiles 4 the USA and Japan. The latest many sided Electrical engineering Furniture Construction of apparatus and equipment Consumer goods Agriculture Medicine Mining 4 objections to PVC are concerned mainly with its 4 use in the packaging sector. 1-2 These are not only related to the production of 3-6 1-2 PVC starting materials and the PVC produced, but also concern health hazards during the 1-2 processing of PVC, the toxicity of PVC additives, 1-2 risks to the consumer by the use of PVC as food and beverage packaging materials, and the disposal problems of used PVC packaging mate- rials contained in household waste. criticism. mainly in respect of its increasing These arguments against PVC packaging mate application as a packaging material. The main rials have been, raised on a broad front. However, objections are concerned with health hazards and they are only partially' based on objective problems concerned with disposal of PVC-, argument, and. verifiable facts. In most cases, the containing household wastes.As far back as 197A,' arguments, have been selected with the sole the American PVC producer B.F. Goodrich objective of PVC substitution and they totally informed the `Occupational Safety and Health ignore, for instance, improved possibilities of Administration (OSHA)' that the death of_' energetic, and/or material recycling of PVC several staff members due xq liver angiosarcoma ' wastes. , could possibly be related to vinyl chloride (VC) Moreover, the unique advantages of rigid PVC -- the monomer of polyvinyl chloride" (PVC). as. food packaging^ material have not been Thus, both VC and its polymer PVC came into considered, at.au. Two of the prime advantages the public attention for the first time. This can be cited as illustrations. resulting excitement was very intensive and quite often it was demanded that the use of VC. and (i) As shown bv results of numerous consequently that of PVC. should be banned. investigations3-1* both aqueous and fat- Soon, thereafter, it was verified that VC is a cause releasing' foodstuffs (including pure edible of liver angiosarcoma. But Jit was also evident fats) come only into superficial contact with that, unlike its monomer, the polymer PVC was rigid PVC packaging materials and do not not toxic and could not be replaced, easily on cause any appreciable swelling. Accordingly, technical and economic grounds. Therefore, it in general, there is only a very limited became essential to remove hazards during the possibility that mobile components of rigid processing of VC. as well as reducing the level of PVC packaging material would migrate into residual VC in PVC to the lowest possible extent. the packed foodstuff. For example, the In retrospect, both as a result of protective minimum and maximum total migrates, de regulations that came into effect from 1974 termined in cases of different polymeric onwards, as well as action by PVC producers and packaging materials under identical and processors, this problem was solved within a defined contact conditions, are compiled in relatively short period. Thus, the methodical Table 3.iS The migration values are given in improvements of degassing VC polymerizates mg/dm2 contact area between packaging resulted in a reduction of residual VC to one material and fat-releasing foodstuff. The total thousandth of the amount contained in PVC migrate includes all components that migrate materials produced by methods in vogue IS years from a packaging material into a food previously. The residual VC in processable PVC product under defined contact conditions. It materials today is below about 1 mg VC per kg is clear that fat-releasing foodstuffs packed in 22138003 BFG19021 218 K. FIGGE Table 3. Total amount of components that mi grate from different, plastic packaging materials into fat-releasing foodstuffs itest conditions: 10 days/40 C and one-sided contact between test specimen and test fat HB 307) Plastic packaging material (polymer -t- additive) Total migrate (mg/dm2) Polyvinyl chloride (rigid PVC) Low-density polyethylene (LDPE) High-density polyethylene (HOPE) Polypropylene <PP) Impact-resistant polystyrene (HIPS) Acrylonitrile butadiene styrene copoiymerizete (ABS) * Below detection limit. 8 Dependent on thickness. 0*-2 4-14" 2-9 2-7" 1-6 1-4 rigid PVC materials are less contaminated with migrating components than the other plastics. Consequently, the consumer has the lowest intake of contaminants from plastic packaging via food ingestion when rigid PVC .materials are used exclusively for packaging. These observations are further substantiated by the values compiled in Table 4. which have been calculated from experimentally deter mined migration data and particular assump tions. These values refer to the daily additive intake by an individual consumer and are classified according to different additives of packaging materials.15 Comparing the values in Table 4 shows that if. instead of polyole fins. rigid PVC is used exclusively for the packaging of foodstuffs, the consumer ingests about one-hundredth of the amount of plastic components (additives) as would be the case for polyolefins. (ii) Within the framework of their numerous protective functions, packaging materials have to fulfil two important tasks. On the one hand, they must ensure that packed products reach the consumer without reduction of their characteristic quality, e.g. by retaining their original composition without loss of ingredients. On the other hand, they should protea against external influences that affea quality retaining properties. Thus, iftany foodstuffs, beverages and cosmetics have to be proteaed against loss of flavour, carbon dioxide or water. A particularly difficult packaging problem is that many products, particularly those containing fat. are sensitive to oxygen. On comparing (Table 5) the relative oxygen, carbon dioxide and water vapour permeabilities of a number of polymeric materials (relative to rigid PVC, which is presumed to have a permeability of 1 in each case), it is evident that rigid PVC, offers superior barrier characteristics. Thus, for instance, it is clearly indicated that. Table 4. Daily uptake of migrated components of plastic packaging materials via food consumption; under the assumption that the foodstuffs are each only packaged in one of the listed packaging materials Packaging material Polymer Additive Uptake of migrate by the consumer % by wt. (mg/dayl HOPE PP Rigid PVC Antioxident* BHT* Antioxident* BHT* Steeryl Alcohol Stsbilizer 0.1 0.2 0.1 0.2 0.6 1.0 1.72 6.46 3.83 0.006 0.02 3-(3,5-Di-ferT.-butyl-4-hydroxyphenyi-n-oetadecyl propionate. * 2.6-Oi-teft-butyl-4-methytphenol. 8 Di-n-oxtyltin-di-/mono-n-octyttin-tri (thioglyeolic acid-2-ethyl-n- hexyiestsr). pOOQCTZZ BFG19022 PVC AND ITS ORGANOTIN STABILIZERS Table 5. Relative permeabilitiee of different polymeric packaging materials, with respect to oxygen, carbon dioxide and water vapour (at 20 C) Packaging material (thermoplastic) Gaseoua/Vaporous component Oj CO* H,0 Polyvinylidene chloride (PVCD) Acrylonitrile copolymer (PAN) Polyvinyl chloride (PVC) Polyethylene terephthelate (PETP) 6-Polyamide (PA) Polypropylene (PP) High-density polyethylene (HOPE) Poystyrene (PS) Low-density polyethylene (LDPE) 0.09 0.10 1.0 1.2 1.5 16 20 35 46 0.14 0.12 1.0 0.8 4.3 30 39 100 95 0.02 1.61.0 1.2 5.3 0.18 0.09 3.8 0.24 219 compared with various types of commonly used plastics, rigid PVC is most suitable for packaging 02-sensitive and/or C02containing products. Equivalent properties are only attained with composite plastic materials, produced by combining one of the other plastic materials with, for instance, a layer of PVDC (polyvinylidene chloride). The resulting laminates are more expensive compared with PVC films. These few examples have shown that the discussions regarding substitution of polyvinyl chloride (PVC) in the packaging sector should be carried out with much more caution than has been done up to now. In order to prepare the ground for a more objective discussion of this presumed problem, in Part 11 a short introduction will be given about production, processing and applica tion of PVC as well as about the structure and effects of the organotin stabilizers used. More over. the human and ecotoxicological aspects of PVC and its stabilizers will be discussed. part n--the thermoplastic POLYVINYL CHLORIDE Retrospective glance It was observed in 1835 by Regnault that if vinyl chloride, contained in a glass vessel, is allowed to stand in sunlight, then a white powder is formed. Thereby, he discovered polyvinyl chloride, abbreviated as PVC. Not until 1877, however. was a detailed chemical study of the way in which the monomer combined to form the macromolecule (PVC). i.e. the polymerization mechan ism of vinyl chloride, carried out by Baumann. The first PVC production began in 1912 and was terminated'after the First World War. Subse quently, PVC was forgotten for a time and reappeared only after about 20 years, as a non-combustible substitute for celluloid. During this period, Wick found that the processing of PVC can be improved considerably by using particular additives as well as by using new technological steps. Moreover, he also discovered that the properties of. finished PVC products could be influenced considerably by proper selection of processing conditions. As a result, numerous applications of PVC were established and, from 1935 onwards, industrial production of PVC was started. Industrial production Today, the thermoplastic PVC is one of the most frequently used polymeric materials. With the exception of polyethylene. PVC is the most significant type of plastic in use. The current starting materials for the produc tion of PVC and its copolymers are chlorine and ethylene. These are obtained from sodium chloride (NaCl) and crude petroleum. As Figure 1 indicates, according to production variation, either vinyl chloride (CH2=CHC1) or vinylidene chloride (CH2*CC12) is produced from the two starting materials. The monomer VC is gaseous at room tempera ture and can be liquified under pressure. As a 22138005 BFG19023 220 K. FIGGE Figure 1. Processing diagram for production of polyvinyl chloride (PVC). VC-co- and graft copolymenzates as well as polyvinytidene. chloride (PVOQ result of its reactive double bond. VC can be converted easily to a radical by using an initiator (peroxides, etc.). As shown in Figure 2. this radical can add itself to another VC molecule, thus producing a dimeric VC radical. Finally, this reacts with further monomers to form long chains. The chain growth, the so-called polymerization, is interrupted by combination or disproportionation of two radicals. The length of a polymer chain depends to a considerable extent on the concentration of the initiator that starts radical formation as well as on the reaction conditions (temperature, time). Industrial production of PVC is carried out by four different methods. (i)Emulsion polymerization (E-PVC). In this, the oldest procedure, a system consisting of water, vinyl chloride (VC), emulsifier and water-soluble initiator is stirred in a pressure vessel (autoclave) at elevated temperature. Thereby, the less-water-soluble monomer VC is distributed as fine droplets, whereas the emulsifier forms the so-called `miscella'. The vinyl chloride is confined within this miscella and the polymerization also takes place here. Then, as the confined VC is consumed, new VC diffuses into the miscella from free monomer droplets via the aqueous phase. This process continues until the entire vinyl chloride is polymerized. Thus, the miscella is gradually convened to solid polymer panicles (latex panicles). By means of nozzle spraying in a stream of hot air. the water is evaporated and the E-PVC is obtained as a powder. (ii) Suspension polymerization (S-PVC). This proixdure produces more than 80% of the PVC. The vinyl chloride monomer is distri buted, as in the previous procedure, in an aqueous phase as droplets by using protec tive colloids. Contrary to the emulsion procedure, the polymerization in larger VC droplets is staned by VC-soluble radical forming agents and occurs in the organic phase. The PVC grains are separated from BFG19024 22138006 PVC AND ITS ORGANOTIN STABILIZERS Cl Initiator radical (I) + CH2= CHC1-- I -CH2~C i H CH?= CHC! ---------------- 221 HH i/ (CHi=CHCl)n i-ch2-c-ch2-o ---------------- Cl Cl Figure 2. Radical homopolymerization of vinyl chloride (VC) HH I CH2-C-CH7-C- 1 `1 Cl Cl Cl ch2-c- H the aqueous phase by centrifuging and are then dried. (iii) Mass polymerization (M-PVC). This proce dure produces about 10% of PVC. The vinyl chloride monomer is directly polymerized in batches by using radical-forming agents. Since there is no requirement for the addition of water or other suspension agents, the drying step is omitted in this procedure, in contrast to the previously described emulsion and suspension polymerizations. (iv) Micro-suspension polymerization (Micro-SPVC). This procedure is similar, in principle, to the suspension polymerization described in (ii). However, in this case, a much finer droplet formation of vinyl chloride monomer in the aqueous phase is attained through special formulation and more intensive dis persion. On the basis ot these production methods, the current annual world production capacity of PVC amounts to 18 million tons. This is classified in Table 6 according: to the different economic regions of the world.14 World-wide, about 1S.5 million tons of PVC was processed in 1987. The production develop ment in western Europe during past decades has been characterized by a steady increase untii 1979. a drop in 1981 and then subsequent growth at a rate lower than that of other plastics (Figure 3).16 The level of production in western and northern Europe during the 1980s amounted to an average of 80% installed capacity. This incomplete utilization of available production capacity resulted mainly from the concentration and restructuring processes in the western Euro pean PVC industry, leading to a reduction in the number of PVC producers in this region from 27 to 16 during 1981-1986. Table 6. Production capacity (1987) of polyvinyl chloride (PVC) In different economic regions of the world Economic region Production capacity 10* (t/year) North America Western Europe (ind. Scandinavia) Central and South America Asia (excluding Japan and China) Japan Eastern Europe and China Africa Total 4.2 5.1 1.1 1.7 2.6 3.0 0.3 18.0 The production capacity of the seven PVC producers in the Federal Republic of Germany is around 1.4 million tons of PVC pef year. After a drop during 1981-1982. the present utilization of capacity is again above 85%, which means an annual production of about 1.2 million tons PVC. Since 1983, the PVC consumption in the Federal Republic of Germany has again reached a level of more than 1 million tons per year. This corres ponds to a per-head PVC consumption of nearly 18 kg per year. Modification In order to attain improved processing character istics or special application profiles, polyvinyl chloride is either modified during the production process or is provided with additives before processing. This will be discussed elsewhere in more detail. The first route mentioned offers the possibility of polymerizing vinyl chloride in the presence of 22138007 BFG19025 222 K. FIGGE curope U.S.A. Japan Figure X Trend of PVC production in western end northern Europe. USA and Japan during 1979-1986 other individual monomers (copoiymerization) or to graft vinyl chloride onto other monomers that have already been pre-polymcnzed (graft polymerization). In this connection, more than 100 comonomers have been subjected to technical examination. As can be seen from the following list, only relatively few co- and/or graft polymerizates have been found to possess technical significance: (vi) graft copolymerizates of vinyl chloride, in combination with: (a) ethylene/vinyl acetate copolymerizates (EVA); (b) ethylene/propylene rubber (EPM(PEP)); (c) ethylene/propylene/diolefin terpolymers (EPDM), (d) polyacrylic add ester. (e) polyethylene, poiybutadiene. (i) vinyl chloride/vinyi acetate (and/or vinyl isobutyl ester) copolymerizates: (ii) vinyl chioride/aaylic acid ester copolymeri zates; (iii) vinyl chloride/unsaturated dicarboxyiic add ester copolymerizates, e.g. copoiymerization of VC with dibutyl maleic add ester; (iv) vinyl chloride/vinylidene chloride (VDC) copolymerizates (copolymerizates with 560% VDC content are processed to pack aging films, specially used in laminates as a barrier layer against oxygen and water); (v) vinyl chloride/olefine copolymerizates (copolymers consisting of VC and olefins, such as ethylene, propylene or isobutylene, possessing improved processing properties. In particular. VC/propylene copolymerizates containing 1-25% propylene increase ther mostability, flowability and impact resist ance. Since an inner plasticization of PVC occurs, low-molecular-weight plasticizers can be omitted); In addition, the PVC can. be subjected to post-chlorination after polymerization, producing so-called `chlorinated PVC (C/PVC)', which, instead of a normal chlorine content of 56.7% (homopolymeric composition), has a 62-69% chlorine content, giving it a higher thermal stability and lower flammability. Finally, it should also be mentioned that processable PVC can be mixed and/or blended with other polymers, e.g. chlorinated polyethylene, polyethylene copolym erizates, ABS and MBS polymerizates. resulting in the so-called polyblends. Thus, by means of a spedfic modification of polyvinyl chloride, a number of disadvantageous characteristics of the polymer, e.g. low thermal stability, high melt viscosity, low flexibility, etc., can be compensated. Processing In the following; instead of describing different processing techniques, such as calendering and fj BFG19026 SO09ET2r: PVC AND ITS ORGANOTIN STABILIZERS 223 extrusion, blow and injection moulding, more attention will be given to the selection of crude PVC types and their furnishing with additives for making semi-finished goods, such as films, sheets and workpieces or finished products, such as cups, bowls and bottles. According to type and intended use of the semi-finished or finished product, the optimum processing method is selected. Thereby, special demands are placed on the properties of PVC compounds used (the ready-to-use blend consists of PVC and suitable additives); for example, flowability and workability. These requirements can be met by proper selection of crude PVC. namely of emulsion, suspension or mass polymer, as well as by the addition of suitable processing aids (additives). In the course of selecting a particular type of crude PVC, in addition to the polymerization procedure, the K value -- which is a measure of average degree of polymerization and of the related so-called internal viscosity -- as well as the bulk density of the PVC are of particular significance. The different types of processing aids arid other additives that are available for making processable PVC mixtures are shown in Figure 4. Stabilizers and lubricants are essential compo nents. Accordingly, special PVC initial blends having differing contents of additives and varying K values are produced to meet the demands of the different processing conditions. A review of the processing methods and the application of crude PVC types is given in Table 7. Owing to the similarities of their characteris tic profiles, it is difficult to make a qualitative differentiation between S-PVC and M-PVC. However, where special requirements are placed on the PVC finished product, for example, when high transparency is required, mainly M-PVC is used. On the other hand, only plasticized PVC mixtures from S-PVC are used for making cables, and Micro-S-PVC is preferentially used for paste processing. The most frequently used method for processing PVC compounds in the Federal Republic of Germany, with a share of 60%, is.the extrusion moulding of pipes, films, profiles, etc. It is followed by calendering (films) with a share of 23% and by paste processing (synthetic leather, floor coverings, etc.) with a share of about 10%. Injection moulding, blowing of hollow bodies and compression moulding play a less significant role. These and other methods of processing PVC compounds are linked with the different temperature-dependent constitutional states of PVC. These are shown in Figure S. The PVC materials cannot be deformed below the 22138009 ------ essential lor processing ....... additives which can be used at discretion Figure 4. Preparation of PVC compounds for processing according to different methods BFG19027 224 K. FIGGE Table 7. Um of PVC produced by different methods and their application in varioua types of product manufacture* Manufacturing method Type of PVC ^ S-PVC M-PVC Micro-S-PVC E-PVC Rigid Plastic Rigid Plastic Rigid Plastic Rigid Plastic Extrusion: pipes/hoses window frames cables shaeta/films Blow moulding Injection moulding Calendering Roll coating Moulding Spread coating/casting pastes Powder sintering ++ ++ ++ + ++ ++ + ++ *++, mainly; + lesser; - without significance. ++ - ++ ++ ++ ++ + + ++ - - ++ ++ + + + - + - + - + + + + - - - + -- -- +- --- ++ + -- -- ++ + + - +* ++ -- glass transition temperature. Dependent on the type of PVC, this temperature is between 75 C and 82 *C. Below this temperature. PVC products can be used in practice (application range) and can only be machine processed, e.g. by drilling, milling, sawing, etc. Above the glass transition temperature, in the so-called softening range, the tearing tension of PVC increases steeply, reaching a maximum at about 95-100C in the thermo-elastic region. On further increase in temperature, it is again reduced (range II/III). These temperatures en able the formation of PVC products by, for example, deep-drawing, rolling or stretching. If the temperature is increased even further, one exceeds range III of the so-called thermal 'pm' E E i/i D TO3 E a<u x: CO Temperature (C)t Figure 8. Individual states of PVC as wen as the course of tearing tension and shear modulus as a function of temperature BFG19028 PVC AND ITS ORGANOTIN STABILIZERS 225 brittleness, reaching finally the melting range IV at 170ooC. The PVC melt is moulded by such processes as calendering, extruding, etc. in the so-called thermoplastic region between 170 C and 220#C, yielding products such as films, profiles, etc. that are resistant to deformation. However, it should be noted that the thermal instability of pure PVC begins far below the melting temperature, namely from about 110 C upwards.17,1 This thermolysis of PVC consists, to a major extent, of hydrogen chloride elimination in the technically interesting temperature region between 120 C and 220 C. This HC1 elimination leads to polyene segments in the polymer and discoloration of the same from yellow to brown and finally black.19 Simultaneously, the double bonds introduced into PVC are oxidized in the presence of oxygen to hydroxyl and carbonyl groups, and cracked in the last phase. This process leads to degradation of polymer chains and thus to a deterioration of the physical and chemical properties of PVC. Depoiymerization reactions leading to vinyl chloride formation were not observed. Generally, so-called thermal stabilizers have to be added to crude PVC. These additions prevent thermal degradation of the polymer during high-temperature processing. In addition to the thermostabilizing effect, these additives should possess the following properties and/or fulfil given requirements such as: (i) optimum dispersion in PVC; (ii) compatibility with all other components of the formulation; (iii) low volatility and no plate-out tendency; (vj) tasteless and odourless with respect to food packaging materials: (v) physiologically harmless with respect to packaging materials and other articles according to legislative requirements (e.g. low tendency towards migration into pack aged product); (vi) low ecotoxicological potential; (vii) light-stabilization of PVC products; (viii) producing crystal-dear PVC for transparent packs or wrappers; (ix) permanent maintenance, of physical, che mical and electrical properties of finished PVC products. Table- 8. The most important groups of thermo- and light stabilizers and their consumption figures in western Europe during 1M7 Stabilizer groups Stabilizer consumption (10t) (%) Lead compounds Oxides, sulphates, phosphites and carboxyiates Mstaf soaps Zn. Ca/Zn. Ba/Zn. Bs/Cd, Ba/Cd/Zn carboxyiates (steerstes. octoatss, ate.) Organic tin compounds Mono-n-octyltin-tris-/di-n-octyttin bit (2-ethyi-n-hexyi-thiog(yco(ste) Monomathyttin-tris-/dimethyltin bis (2-ethyi-rvhaxyi-thioglycolate) Organic compounds, free from motals Aminocrotonic acid aster (with adcohois `CU) Oiphenyithiourea 2-phenyt indole Total 48.0 56.0 28.5 31.9 9.5 11.0 0.5 0.5 87,5 99.4 BFG19029 226 K. FIGGE No known stabilizer possesses by itself all these characteristics to the extent required for proces sing and application in practice. Consequently, optimum stabilizers have to be selected according to different processing procedures and applica tion areas. In fact, quite often synergetic mixtures of several stabilizers are used. The four most important groups of thermo- and light stabilizers, including several characteristic representatives, as well as their consumption figures in western Europe, are given in Table 8>21 The use of lead- and cadmium-containing stabilizers are facing increasing opposition owing to their presumed human and ecotoxicoiogical effects. This ignores the fact that stabilizer systems containing heavy metals contribute to wards excellent thermo- and light stability of PVC and that the stabilized PVC is not used for packaging foodstuffs, medicines, etc. Despite this, attention is drawn to the fact that although cadmium-containing systems are relatively small compared with lead-containing stabilizers, in the Federal Republic of Germany alone about 4501 of Cd are used annually in the form of PVC stabilizers. If the quantity of cadmium-containing pigments in PVC is ignored, the above amount of Cd corresponds to about 25% of the total cadmium consumption in the Federal Republic of Germany. However, in view of the quite considerable quantity of heavy metals used and the fact that cadmium can enter the human body via aquatic, air and soil-plant routes, the Cd-containing soaps, used nowadays only for stabilization of durable rigid PVC items such as window profiles, shutters and facade elements, are classified as being objectionable. This has been recognized by the plastics processing industry, which is making every effort to substitute the Cd-as well as Pb-containing stabilizers with Ba-Sn and/or Ca/ Sn compounds. REFERENCES 1. Schieffer B. and Vogt. K. Substitution von Polyvinylchlond. WARTIG Chemieberatune GmbH. Lahntal IBRD) (February 1988). 2. Brahma. E.. Eder. G. and Greiner. B. Papier Kunststoff Verpackungen -- Eine Mengen -- und Schadstolfbetrachtung. 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