PVC Heat Stabilizers

In spite of its inherent thermal instability (see Section 15.3.4), PVC possesses several attractive properties, such as economy of production and processing, and the ease of variation of its properties, with appropriate blending with other polymers or additives, from hard and tough materials to elastomeric ones. Currently, PVC ranks second only to polyolefins in terms of worldwide production among industrial polymers. This technical success is the result of considerable research in the field of degradation and stabilization of this polymer since its introduction as a commodity plastic in the middle of the 20th century. 

The low thermal stability of PVC originates from the presence of labile structures and of the autocatalytic deleterious effect of the hydrochloric acid evolved. Thermal stabilizers for PVC consist principally of metal carboxylates and organotin compounds (primary stabilizers), used in combination for preventive and curative functions. As with degradation, uncertainties continue to exist in the exact stabilizing mechanisms of these additives. There is evidence that organotin derivatives stabilize PVC by substituting the labile allylic chorine with a more thermally stable thioether group [Eq. (96)]. 

Hydrogen chloride is bound with metallic (Zn, Ca, Ba) organic acid salts with formation of the metal chloride and the corresponding free fatty acids. The formation of polyene sequences can be prevented by combination reactions with thiol or mal-eate derivatives. Although efficient in blocking the degradation, most of the inor- 

In recent years, metal-free stabilizer systems have been developed because of environmental concerns of traditional lead and tin stabilizers. Chemically regarded nitrogen-based molecules are used, for example, P-aminocrotonates, dihydropyrimidines [15], trialkanolamines, as well as their reaction products and salts, for example, the perchlorate salt [16], etc. (Fig. 11.11). Owing to their good compatibility with other stabilizers, organic-based stabilizers are predestinated to be used in PVC recycling in case restabilization is needed [17]. 

The most important costabilizers in PVC formulations used mainly in combination with mixed metal salts are alkyl-aryl-phosphites to improve early color. Epoxy compounds, for example, epoxidized fatty esters such as epoxidized soy bean oil, react directly with HCl or substitute labile chlorine atoms, for example, in the presence of zinc ions. Furthermore, the epoxidized fatty esters act as plasticizers. Polyols such as pentaerythritol or dipentaerythritol and P-diketones act as complexing agents and deactivate the negative effect of the formed zinc chloride. Hydrotalcites 

The stability of PVC formulations is tested, for instance, according to ISO 305 by static heat tests, where test specimens are aged at constant temperature and mainly color changes (e.g.. Yellowness Index) are recorded. Alternatively, to assess the performance of heat stabilizers, the time until the dehydrochlorination reaction takes place can be measured, for example, through pH change (ISO 182). Combined thermal and shear stress is analyzed via dynamic tests such as two-roll mill processing or multiple extrusion. 

As explained already, there is a distinct synergism between Ca/Zn stabilizers. Whereas Zn salts show a very good initial color, the time until HCl formation (discoloration) upon heating is considerably short. Ca salts offer a very 

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Cadmium oxide is used in storage battery electrodes. Its solution, mixed with sodium cyanide, is used in electroplating baths. Other uses are in PVC heat stabilizers as an additive to nitrile rubbers and plastics to improve heat resistance and in ceramic glazes and phosphors. 

Phenolic antioxidants - [ALKYLPHENOLS] (Vol 2) -m mixed metal stabilized PVC [HEAT STABILIZERS] (Vol 12)... 

TM for a series of PVC heat stabilizers for extruding, injection molding, calendering, and blow mold-... 

Just like the ability to bind HCl, this exchange reaction is a general characteristic of all efficient PVC heat stabilizers and stabilizer systems. An essential condition of this exchange reaction, is of course, that the transferred groups - in this case a mercaptocarbonic acid ester group - have a lower tendency to be eliminated than the chlorine atom. 

Synpron . [Syn. Prods.] Antimtmy mercaptide, dibutyltin dilaurate, or metallic stearates PVC heat stabilizer, lubricant, i ocess aid. 

PVC foaming PVC heat stabilizers PVC miscible blends PVC other blends... 

In the following part, the most important classes of additives (antioxidants, PVC heat stabilizers, light stabilizers, and flame retardants) are presented, as well as general information on chemical structures and mechanisms, on testing methods, and on use examples in selected polymer... 

Figure 11.12 Scheme of the synergistic activity of Ca/Zn PVC heat stabilizers. 

Figure 11.13 Stabilization efficiency of organic-based PVC heat stabilizers.

Mold-Release Agents Plasticizers Stabihzers Antioxidants PVC Heat Stabilizers UV Stabihzers Thermoplastic Materials Thermoset Materials Classified Directory of Suppliers (Primary Equipment, Auxiliary Equipment, Materials, Chemicals and Additives, Specialized Services)... 

Uses Chem. stabilizer for PVC heat stabilizer for plastisol coatings provides good initial vise, and vise, stabilization Properties Lt. amber liq. mild phenolic odor Mark TT ptco]... 

Uses Plasticizer/stabilizer for epoxy, PVC, paints plasticizer/synergist for PVC heat stabilizers plasticizer in food-contact polymers coupling agent for S/B block copolymers pigment dispersant in PVC-P in closure-sealing gaskets for food containers in food-contact polysulfide polymer/polyepoxy resins... 

PVC heat stabilizers are used to protect polyvinyl chloride against thermal dehydrochlorination during processing and during use above room temperature. Similar additives are sometimes useful in other halogenated systems as well. 

Other Organohalogens. Thermal instabihty is also a problem in other polymers such as chlorinated polyethylene, chlorinated PVC, polyvinylidene chloride, chlorinated rubber, and chlorinated and brominated flame-retardants. PVC heat stabilizers may help here, too, but require careful adjustment for optimum performance in each system. 

Market Volume. The total market for PVC heat stabilizers may be about 100 million pounds in the United States and 1 biUion pounds worldwide, half for organotin and half for metal soap-epoxidized fatty ester-organic phosphite systems. 

The addition of heat stabilizers improves the thermal stability of polymers. One group of commercially available PVC heat stabilizers are Ca/Zn stabilizers. According to the Erye-Horst mechanism (Thomas 1993), the zinc fatty acid salt reacts with PVC by an esterifying displacement of chlorine. Stabilization arises from substimtion of labile chlorine atoms with more stable carboxylate groups (Scheme 14.2) ... 

There are about 40 suppliers of light stabilizers worldwide. Some of these companies also produce antioxidants and PVC heat stabilizers. Of these 40 or so suppliers, only Ciba Specialty Chemicals is a significant player in every region of the world with the broadest product line of light stabilizers. Selected global suppliers of light stabilizers are given in Table 4.18. 

Advastab, PVC heat stabilizers, Morton International Inc., Morton Plastics Additives... 

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