A study of the oxidative degradation of polyvinyl formal

Abstract

The investigation of the thermal degradation or pyrolysis of vinyl polymers has been pursued from the theoretical and the experimental standpoint for polystyrene,' polymethyl methacrylate,2 and polythene.3 The degradation of the first two polymers seems to be predominantly a depolymerization, while that of polythene is a process of random chain scission. The methods have been weight loss, viscosity studies, molecular weight distribution, osmotic measurements, and infrared analysis. The oxidative degradation of vinyl polymers has been extensively studied by Tobolsky,' who emphasizes that a combination of analytical methods is necessary for a complete analysis of such a complex process.This paper presents the oxidative degradation of polyvinyl formal at high temperatures, studied by the infrared method in conjunction with weight loss, color development, and chemical analysis. Polyvinyl formal, like many other materials used in electrical insulation, undergoes severe changes in its physical, chemical, and electrical properties when exposed to high temperatures in the presence of air. It changes from a strawcolored resin of good Electrical properties to a deep brown embrittled material of high dielectric constant. Loss of solubility precludes such methods as viscosity measurements as methods of analysis during degradation. However, the infrared spectrum, because of its sensitivity to molecular structure and structural changes, has been valuable in detecting the changes in the polymer during degradation.. EXPERIMENTAL Materials. Commercial polyvinyl formal resin, or Formvar "E" obtained from Shawinigan Products Corporation, was analyzed by the manufacturers to contain 6% free hydroxyl groups, 12% acetate groups, 0.9% moisture, and 0.14% free hydroxyl acid. The hemi-formal content was believed to be insignificant; the molecular weight was approximate!y 22,000. Osmotic measurementst made in this laboratory on dioxane solutions of * The research described in this paper was carried out under sponsorship by the Office t

Effect of oxides on binder burnout during ceramics processing

“…One characteristic of this process is an increasing carbonyl content which is detected by infrared spectroscopy. A free-radical mechanism for the oxidation of poly(vinyl formal) has been proposed by Beachell et al [7]. PVB can also decompose by a cyclic-elimination mechanism to release butyraldehyde, with associated chain breakage to leave aldehyde and unsaturated end-groups (Fig.…”

“…Sacks and co-workers [5,6] have recently completed similar studies on the decomposition chemistry of ceramic green bodies containing PVB. Decomposition of the related polymer poly-(vinyl formal) has been studied by Beachell et al [7], who found that formaldehyde production was responsible for about 25% of the weight loss at 150 ° C. They proposed an oxidative mechanism for the formation of formaldehyde. Changes observed in the infrared spectrum of the polymer included loss of the formal and C-H bands, an early increase in the intensity of the carbonyl band, and the subsequent formation of C=C bands at 1612 and 910cm -1 .…”

Thermal degradation of a poly(vinyl formal)‐containing adhesive film on a polyethylene rubber surface. A photoacoustic fourier transform infrared spectroscopic investigation

“…These attributions were consistent with the earlier infrared results by Beachell et a1. 16 and Chanda et al17 (see Discussion later).…”

Vinyl Acetal Polymers

“…Thermogravimetric analysis indicates significant rate of weight loss, starting about 240 • C in air or about 320 • C in nitrogen for PVF (63,64) compared to about 280 • C in air or up to about 320 • C in nitrogen for PVB (65). In air, significant oxidative degradation occurs at lower temperatures with longer thermal exposure as evidenced by loss of solubility, color development, and increasing T g attributed to the initial formation of unsaturated bonds and cross-linking (64,66). Mechanisms for degradation have also been studied employing combination techniques, including gas chromatography/mass spectrometry and infrared spectroscopy/thermogravimetry (65,67).…”