An investigation of mechanisms of synergistic interactions in PVC stabilization

Abstract

synopsisSynergism in poly(viny1 chloride) stabilization has been studied by measuring rates of hydrogen chloride evolution from samples of polymer in the presence of stabilizers in di-(a-ethylhexyl) phthalate solution in an inert atmosphere. Barium, cadmium, calcium, and zinc laurates, when used alone, allow escape of hydrogen chloride well before stoichiometric uptake is achieved, whereas synergistic mixtures of calcium-zinc and barium-cadmium laurates absorb almost the theoretical quantity of hydrogen chloride. Cadmium and zinc laurates replace labile chlorine atoms in the polymer backbone by ester groups, reducing formation of long polyene sequences: barium and calcium laurates delay the formation of cadmium and zinc chlorides, apparently by reconverting them into their respective laurates. Polyols function by forming complexes with the prodegradant cadmium and zinc chlorides, but contrary to popular belief phosphites possess little activity in this respect. Instead, they slow down the rate of polymer degradation by removal of labile chlorine atoms, by reaction with hydrogen chloride, and by peroxide decomposition.

Chlorinated poly(vinyl chloride) stabilization by pentaerythritol/calcium‐zinc stearate mixtures: The fate of pentaerythritol

“…Pentaerythritol (Pe) is an important secondary stabilizer which forms complexes with zinc chloride to delay the appearance of ‘zinc burning’ [15]. Briggs and Wood [16] and Wang et al [17] reported that Pe had some synergistic effect with CaSt 2 /ZnSt 2 caused by the formation of undetermined complexes with the reaction products of calcium and zinc stearates. Abbås and Sörvik [18] considered that the excellent static stability caused by Pe might be partly attributed to its direct reaction with HCl.…”

Principles of Stabilization

“…24 From this discussion we can already observe the possibility that various forms of stabilizer reaction products with HCl may react among themselves. Possibilities for a reaction of this type were mentioned in so many papers [7][8][9][25][26][27][28] (although without proof, as found elsewhere 13 ) that there is little doubt that this is a true mechanism of PVC stabilization. Possibilities for a reaction of this type were mentioned in so many papers [7][8][9][25][26][27][28] (although without proof, as found elsewhere 13 ) that there is little doubt that this is a true mechanism of PVC stabilization.…”

“…Phosphites are thought to be able to react with zinc chloride according to the scheme below: 8,23 The only other known reaction of metal chlorides has been discussed in Section 11.1 with exchange of chlorine between zinc or cadmium chlorides and carboxylates of calcium and barium, respectively. Phosphites are thought to be able to react with zinc chloride according to the scheme below: 8,23 The only other known reaction of metal chlorides has been discussed in Section 11.1 with exchange of chlorine between zinc or cadmium chlorides and carboxylates of calcium and barium, respectively.…”

“…If one compares these functions with, let's say, the action of tin stabilizers, it may be assumed that phosphites act in a similar fashion; the true effect is different. Figure 11.32 shows that aryl phosphite practically does not react with HCl, whereas aliphatics 6,7,8,9,10,11,12,49,53,72,213,253, 613, 675, HiPure 4; Akcrostab CH-300, CH-301; Interstab CH-55 None of the phosphites shows a substantial induction period which is a typical characteristic of stabilizer.…”

“…The comparative influence of three phosphites on color changes follows the same pattern as their influence on dehydrochlorination (Figure 11.31) and it also can be explained by the differences in the strength of acids formed in the process of reaction with HCl. 56 The following reaction scheme has been previously proposed: 8 It is agreed that phosphites are also able to replace labile chlorine atoms and thus affect the dehydrochlorination rate, 23,24,56,[286][287][288]295 but disagreement existed concerning the type of group containing labile chlorine atoms that is able to react with phosphite. Figure 11.34 implies that there is a concentration at which zinc stearate is the most effective.…”