Synergism in thermal stabilization of polyvinyl chloride

Abstract

Plasticized polyvinyl chloride was thermally stabilized by barium, cadmium, and zinc laurates, epoxidized soybean oil, and monoalkyl diaryl phosphite, and by combinations of these stabilizers. Of 26 possible combinations, 18 showed some improvement, 8 showed useful improvement, 7 showed marked improvement, and 3 systems were outstanding. Of the 26 combinations, 10 showed distinct synergism, based mainly upon combinations of Group II‐B metals with Group II‐A metals, “secondary” stabilizers, or both. Combinations of Group II‐B metals with “secondary” stabilizers were particularly interesting and promising.

Heat stabilizers for poly (vinyl chloride). I. Synergistic systems based on calcium/zinc stearate

“…Contrary to this, the addition of 0.2 phr tris(nonylpheny1) phosphite to the Ca/Zn stearate stabilized system did not result in any significant color improvement. This is in agreement with earlier studies (14,27,29,30). A direct reaction between the phosphite and HCI may also occur: (14, [24][25][26] (R0)SP + HC1-(R0)zPOH + RCI (6) The catalysis of HC1 is thus prevented, as the phosphonate does not promote dehydrochlorination.…”

“…The stabilizing influence of phosphorus compounds has been investigated rather extensively (14, [22][23][24][25][26][27][28][29][30]. Phosphites and phosphines, as well as phosphonates, have been considered.…”

Synergistic interaction in zinc/epoxy/phosphite stabilization of polyvinyl chloride

“…In practical terms, it is the reason zinc soaps are never used alone as stabilizers for polyvinyl chloride. The general behavior, while qualitatively similar to cadmium laurate (16,17), was quantitatively much more dramatic and extreme: initial stability was greater, and catastrophic failure came much sooner and more suddenly.…”

“…When zinc laurate was the only stabilizer, samples failed by catastrophic blackening before the first 15-min samples were removed from the 150°C circulating air oven. Only by taking samples at 1 minute intervals during this initial heat-aging period was it possible to see that zinc laurate did provide excellent stability for a brief period of time before catastrophic blackening (16); this will be called a B-type stability pattern. This brief stabilization was presumably due to esterification of the polymer as described before (9).…”

“…These 5 components may be combined into 2-, 3-, 4-, and 5-component systems, offering 26 such possible combinations. Of these, 10 showed distinct synergistic interaction (16). Classification of these 10 systems led to some interesting implications, but still left the detailed mechanisms unclear.…”