PVC stabilizers

Heat stabilizers protect polymers from the chemical degrading effects of heat or uv irradiation. These additives include a wide variety of chemical substances, ranging from purely organic chemicals to metallic soaps to complex organometaUic compounds. By far the most common polymer requiring the use of heat stabilizers is poly(vinyl chloride) (PVC). However, copolymers of PVC, chlorinated poly(vinyl chloride) (CPVC), poly(vinyhdene chloride) (PVDC), and chlorinated polyethylene (CPE), also benefit from this technology. Without the use of heat stabilizers, PVC could not be the widely used polymer that it is, with worldwide production of nearly 16 million metric tons in 1991 alone (see Vinyl polymers). 

Epo>y Compounds. Epoxidized soya oil (ESO) is the most widely used epoxy-type additive and is found ia most mixed metal stabilized PVC formulations at 1.0—3.0 phr due to its versatiHty and cost effectiveness. Other usefiil epoxy compounds are epoxidized glycerol monooleate, epoxidized linseed oil, and alkyl esters of epoxidized tall oil fatty acid. 

By far the most common lead salt used for PVC stabilization is tribasic lead sulfate. It can be found either alone or combined with another lead salt in almost every lead-stabilized PVC formulation. Many of the combinations are actually coprecipitated hybrid products, ie, basic lead sulfophthalates. Dibasic lead stearate and lead stearate are generally used as costabilizers combined with other primary lead salts, particularly in rigid PVC formulations where they contribute lubrication properties dibasic lead stearate provides internal lubrication and lead stearate is a good external lubricant. Basic lead carbonate is slowly being replaced by tribasic lead sulfate in most appHcations due the relatively low heat stabiHty of the carbonate salt which releases CO2 at about 180°C during PVC processing. 

Whereas other metal salts, especially lead stearates and srdfates, or mixtures of Groups 2 and 12 carboxylates (Ba—Cd, Ba—Zn, Ca—Zn) ate also used to stabilize PVC, the tin mercaptides are some of the most efficient materials. This increased efficiency is largely owing to the mercaptans. The principal mechanism of stabilization of PVC, in which all types of stabilizers participate, is the adsorption of HCl, which is released by the PVC during degradation. This is important because the acid is a catalyst for the degradation, thus, without neutralization the process is autocatalytic. 

Figure 9. UV-visible absorption spectra of a stabilized PVC plate, with or without a 70 yin UV cured epoxy-acrylate coating, before and after QUV aging at 40°C...

Chlorine-containing polymers such as poly(vinyl chloride) PVC undergo an autocatalytic dehydrochlorination reaction under the influence of elevated temperature and UV radiation. Since the HCl originating from the dehydro chlorination of the PVC chains is believed to sustain this autocatalytic process, stabilizers that irreversibly bond HCl can thus inhibit the degradation. Heavy metal compounds such as cadmium stearate or lead stearate are currently used for this purpose. However, alternatives are required due to environmental problems associated with the use of heavy metals. Indeed, the largest current application of LDH materials is in the polymer industry, mainly to stabilize PVC [3,229-232]. 

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

Mizuno, K.M., Hirukawa, H., Kawasaki, O., Noguchi, H., and Suzuki, O., Development of Non-Lead Stabilized PVC Compounds for Insulated Wires and Cables, Furukawa Review, 1999, 18, 111-118. 

Internal stabilization is a novel method of enhancing the thermal stability of vinyl polymers. Braun, who proposes this term, reports that metal salts of unsaturated carbonic acids are suitable comonomers acting as internal stabilizers. For example, a copolymer of vinyl chloride with only 0.3 mole % of lead undecylenate has a significantly longer and better thermal stability than externally lead-stabilized PVC. 

To stabilize PVC against the action of heat, it is necessary to prevent dehydrochlorination. If one does, nevertheless, intend to forego the use of stabilizers for the initially discussed reasons, one must use comonomers which not only restrict the length of the polyene sequences but which, at the same time, check the process of dehydrochlorination. 

Now a closer look at the mapping of vinyl PB can be considered. A further refinement of the total PB citations revealed 926 references for vinyl PB, which are mapped in Fig. 4. Here, the aqueous preparation of syndiotatic 1,2-PB is seen along with the use of both syndiotatic and atactic PB in tire beads, silica containing treads, and even medical applications after cross-linking with peroxide or radiation.Mixtures of catalysts have been used to allow amorphous 1,2-PB to be coproduced with syndiotatic PB in the same reactor.Epoxidized vinyl PB can be used to reduce tire rolling resistance, toughen resin, and stabilize PVC... 

The inertness of lead-stabilized PVC can be demonstrated by extraction studies. Eor instance, several studies have shown that the amount of lead extracted from lead-stabilized water pipes is negligible when tested according to the requirements of the EU plastics Directive (2002/72/EC) which specify the maximum amount of lead that can be extracted from plastics in contact with food which includes drinking water [148]. 

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

Stabilizers are almost invariably added to PVC to improve its heat and light stability. The species found effective in stabilizing PVC are those that are able to absorb or neutralize HCl, react with free radicals, react with double bonds, or neutralize other species that might accelerate degradation. Lead compounds, such as basic lead carbonate and tribasic lead sulfate, and metal soaps of barium, cadmium, lead, zinc, and calcium are used as stabilizers. Obviously, they can react with HCl. Epoxy plasticizers aid in stabilizing the resin. Another group of stabilizers are the organotin compounds, which find application because of their resistance to sulfur and because they can yield crystal-clear compounds. 

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