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Degradation products of plastics. Polyethylene and styrene-containing thermoplastics--analytical, occupational and toxicologic aspects.

1982; National Institutes of Health; Volume: 8 Suppl 2; Linguagem: Inglês

A Hoff, S. O. Jacobsson, Pirkko Pfäffli, A. Zitting, H Frostling,

Microplastics and Plastic Pollution

The primary study objectives were to compare the thermostability of different commercial grades of polyethylene (PE) polystyrene (PS) impact polystyrene (IPS) poly (acrylonitrile-butadiene-styrene) -- ABS and poly (acrylonitrile-styrene) -- SAN under conditions closely resembling those of industrial processing; to analyze the airborne products formed during the initial stage of the degradation of these plastics at low values of weight loss and develop methods for analyzing the compounds formed; to develop field sampling methods for hygienic measurements; to determine the correlation between the results of the laboratory experiments and the field measurements; and to investigate the effects on biological material in studies of acute and subacute exposures. The different grades of low-density polyethylene (LDPE) high-density polyethylene (HDPE) PS IPS ABS and SAN typically found in the Swedish plastics industry were chosen for the analysis of volatile products. Thermogravimetric analysis was used to compare the thermostability of the thermoplastics in terms of weight loss at low values (up to about 4%). The experiments were carried out with a Cahn RG-HV thermobalance in nitrogen or in air at reduced pressure to eliminate the noise due to aerodynamic effects. The degradation experiments with PE and the styrene-containing thermoplastics PS IPS ABS and SAN reported here were carried out on the thermal degradation unit depicted in Figure 1. The techniques used in the processing of plastics depend to a large extent on the type of products required. PE and styrene-containing thermoplastics generally are processed by methods which utilize heat. The processing temperatures usually vary within the range of 200-320 degrees Centigrade. Thermoplastics degrade at elevated temperatures. The presence of oxygen augments the process. Although degradation during processing can be minimized it cannot be eliminated as evident in this investigation since degradation products also were found in factor air when hygienic measurements were taken. The laboratory experiments conducted in this study proved that linear hydrocarbons are generated during the initial stage of the thermal degradation of LDPE and HDPE. The experiments also revealed that the degradation of PE in the presence of air gives rise to a very complex mixture of oxidated products. Thermal degradation of styrene-containing thermoplastics yielded styrene only as a minor product. Industrial hygiene measurements were carried out during normal work processes with PE and styrene-containing thermoplastics. The measured concentrations were fairly low with the exception of the fume (aerosol) concentrations. Thus the fumes which consisted of degradation products with very high boiling points seemed to form the primary hygienic problem during the processing of these thermoplastics. When available hygienic standards were used the average hygienic effect (concentrations of air impurities relative to the respective hygienic standards) was 1 for the PE processes and 0.5 for the processing of styrene-containing thermoplastics.