Abstract
Oxidative degradation of commercial grade ABS (Acrylonitrile-butadiene-styrene) resin powders was studied by thermal analysis. The instabilities of ABS containing different polybutadiene (PB) contents with respect to temperature were studied by Differential Scanning Calorimeter (DSC). Thermograms of isothermal test and dynamic scanning were performed. Three exothermic peaks were observed and related to auto-oxidation, degradation and oxidative decomposition, respectively. Onset temperature of the auto-oxidation was determined to be around 193 °C. However, threshold temperature of oxidation was found to be as low as 140 °C by DSC isothermal testing. Another scan of the powder after degeneration in air showed an onset temperature of 127 °C. Reactive hazards of ABS powders were verified to be the exothermic oxidation of unsaturated PB domains, not the SAN (poly(styrene-acrylonitrile)) matrix. Heat of oxidation was first determined to be 2,800 ± 40 J per gram of ABS or 4,720 ± 20 J per gram of PB. Thermal hazards of processing ABS powder are assessed by adiabatic temperature rise at process conditions. IR spectroscopy associated with heat of oxidation verified the oxidative mechanism, and these evidences excluded the heat source from the degradation of SAN. A specially prepared powder of ABS without adding anti-oxidant was analyzed by DSC for comparing the exothermic behaviors. Exothermic onset temperatures were determined to be 120 °C and 80 °C by dynamic scanning and isothermal test, respectively. The assessment successfully explained fires and explosions in an ABS powder dryer and an ABS extruder.
Highlights
Acrylonitrile-butadiene-styrene (ABS) copolymer is one of the most common used engineering plastics containing rubber
ABS basic powders with different PB fractions were first screened in Differential Scanning Calorimeter (DSC) dynamic temperature programming
The first peak is attributed to oxidative reaction of PB and the second and third ones are attributed to thermal degradation and decomposition of the matrix phase in ABS, which were almost the same with the characteristic thermograms from SAN copolymer
Summary
Acrylonitrile-butadiene-styrene (ABS) copolymer is one of the most common used engineering plastics containing rubber. The thermal processing induced oxidation mainly occurred within the polymer phase of the ABS copolymer when studied by chemiluminescence (CL); the results pointed out the BD phases were the degrading units [12,13]. Another accident revealed a fire at an ABS fluidized bed dryer by the operation of changing from 25% PB content to 60% PB content in the formulation of ABS basic powder These engineering objectives are: to characterize the exothermic auto-oxidation of ABS powder, to identify the intrinsic hazards of ABS powder in existing processes, to apply the results of thermal analysis to related incidents for the change from lower PB content (25%) to higher PB content (60%) that occurred in the dryer
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