Thermal degradation of poly(vinyl chloride) blends

Abstract

Poly(viny1 chloride) was mixed with various poly(methacry1ate)s and polycarbonates by combined precipitation from common solutions. The thermal stability of the samples was measured at 180 "C under nitrogen, the HCI evolved was detected by conductometry.UV-Vis-spectra of degraded samples were measured to investigate the influence of the poly(methacry1ate)s on the lengths of polyenes formed during the degradation of poly(viny1 chloride).The experiments show that the nature of the ester group is the dominating factor for the thermal stability of poly(viny1 chloride) in these blends. Poly(n-butylmethacrylate) exhibits the best stabilization for poly(viny1 chloride) in this series. Polycarbonates with a higher glass transition temperature than the temperature of degradation destabilize poly(viny1 chloride).Stabilization experiments with dibutyltin-bis(isooctylthioglyco1ate) show a costabilizing effect of the poly(methacry1ate)s and polycarbonates. ZUSAMMENFASSUNG:Polyvinylchlorid wurde mit verschiedenen Polymethacrylaten und Polycarbonaten durch Ausfallen gemeinsamer Liisungen gemischt. Die thermische Stabilitat der Proben wurde bei 180 "C in einer Stickstoffatmosphare mittels konduktometrischer Messung der abgespaltenen Salzsaure bestimmt. Um den EinfluB der Polymethacrylate auf die Unge der entstandenen Polyensequenzen zu ermitteln, wurden die abgebauten Proben UV-spektroskopisch untersucht.Wie die Experimente zeigen, ist die Estergruppe von dominierendem EinfluB auf die thermische Stabilitat von Polyvinylchlorid in diesen Blends. Poly-n-butylmethacrylat stabilisiert dabei Polyvinylchlorid am besten. Die eingesetzten Polycarbonate haben Glastemperaturen, die iiber der Abbautemperatur liegen; sie vermindern die thermische Stabilitat von Polyvinylchlorid.Stabilisierungsversuche mit Dibutylzinn-bis(isooctylthioglykolat) zeigen einen costabilisierenden Effekt der Polymethacrylate und Polycarbonate.

Principles of Thermal Degradation

“…314 These are essential parameters which affect duration of heat exposure but there are many other data characterizing thermal stability of PVC/PMMA blends. 308 The thermal decomposition temperatures of the first and second stage of degradation in PVC in the blend with PMMA were higher than for pure PVC. Lowering weight loss in the first stage of blend degradation (dehydrochlorination) should be attributed to dilution of HCl producing polymer (PVC) by PMMA.…”

“…Poly(methyl methacrylate) and other methacrylates are used as process aids, 308 and they improve PVC stiffness and heat distortion. 309 There is no single answer regarding blend miscibility because it depends on conditions of its preparation.…”

“…If information on morphological features of both polymers is not available, it is thus difficult to assess why some blends are miscible or immiscible. 278,308,315,316 Figure 4.54 shows that the weight loss is proportional to PVC concentration. Reactive processed blends had single phase morphology and single glass transition temperature.…”

“…313 Acrylic process aids are beneficial in PVC processing because of their ability to promote fusion, increase melt strength, increase melt elasticity, and, for some particular grades, reduce sticking to metal parts. 308 This will suggest that in the coarse mixed blends HCl is absorbed in PMMA, which inhibits catalysis of dehydrochlorination. 278,308,315,316 Figure 4.54 shows that the weight loss is proportional to PVC concentration.…”

Plastics in Heritage Collections: Poly(vinyl chloride) Degradation and Characterization

“…The concentration dependency of evaporation of plasticizer led to some con-troversy, where Braun and et al have shown the relationship not to be linear and having a minimal value based on the chosen plasticizer and possible interactions. 65,66 The highest compatibility of a plasticizer with polymer is designated as the critical concentration, but no studies were found to connect it with the lowest evaporation rate.…”