Toxicity, pyrolysis products

Peterson JE. 1993. Toxic pyrolysis products of solvents, paints, and polymer films. Occup Med State Art Rev 8 533-547. 

Eating in work areas can result in exposure through ingestion smoking on the job can lead to inhalation of native materials or of toxic pyrolysis products. 

VOCs in paints can provoke respiratory symptoms (wheezing, breathlessness) in asthmatics. Conventional water-based paints with only small amounts of VOCs have also been shown to cause such symptoms, but there were no effects using VOC-free paints. No differences were found in the same study looking at lung function and airway responsiveness. Toxic pyrolysis products in paints and polymer films probably evoke asthma-like symptoms similar to PVC pyrolysis. ... 

Because PTFE resins decompose slowly, they may be heated to a high temperature. The toxicity of the pyrolysis products warrants care where exposure of personnel is likely to occur (120). Above 230°C decomposition rates become measurable (0.0001% per hour). Small amounts of toxic perfiuoroisobutylene have been isolated at 400°C and above free fluorine has never been found. Above 690°C the decomposition products bum but do not support combustion if the heat is removed. Combustion products consist primarily of carbon dioxide, carbon tetrafluoride, and small quantities of toxic and corrosive hydrogen fluoride. The PTFE resins are nonflammable and do not propagate flame. 

The Du Pont HaskeU Laboratory for Toxicology and Industrial Medicine has conducted a study to determine the acute inhalation toxicity of fumes evolved from Tefzel fluoropolymers when heated at elevated temperatures. Rats were exposed to decomposition products of Tefzel for 4 h at various temperatures. The approximate lethal temperature (ALT) for Tefzel resins was deterrnined to be 335—350°C. AH rats survived exposure to pyrolysis products from Tefzel heated to 300°C for this time period. At the ALT level, death was from pulmonary edema carbon monoxide poisoning was probably a contributing factor. Hydrolyzable fluoride was present in the pyrolysis products, with concentration dependent on temperature. 

LLDPE can present a certain health hazard when it bums, since smoke, fumes, and toxic decomposition products are sometimes formed in the process. Exposure to burning LLDPE can cause irritation of the skin, eyes, and mucous membranes of the nose and throat due to the presence of acrolein and formaldehyde (81). Toxicity of LLDPE pyrolysis products depends on temperature, heating rate, and the sample size (82—84). 

In particular, PB and PMP are inert materials and usually present no health hazard. PMP is employed extensively for a number of medical and food packaging appHcations. Several grades conform to FDA regulations and to the health standards of other countries. Flammability of polyolefin resins is equal to that of PP, around 2.5 cm /min (ASTM D635). However, during combustion or pyrolysis, smoke, fumes, and toxic decomposition products are formed and can pose a health hazard. 

Health nd SMety Factors. The lowest pubhshed human oral toxic dose is 430 mg/kg, causing nervous system disturbances and gastrointestinal symptoms. The LD q (rat, oral) is 750 mg/kg (183). Thiocyanates are destroyed readily by soil bacteria and by biological treatment systems in which the organisms become acclimatized to thiocyanate. Pyrolysis products and combustion products can include toxic hydrogen cyanide, hydrogen sulfide, sulfur oxides, and nitrogen oxides. 

The kinetics of thermal decomposition and depolymerisation of various polymers is discussed. The aim of the study was to find reaction conditions where different polymers can be separated from mixtures by decomposing them into their monomers or into pyrolysis products and where chlorine and/or nitrogen are eliminated from the polymers without forming toxic compounds. Data are given for PVC, PS, PE, and PR 13 refs. 

Poisoning from toxic combustion products. In chemical fires, particularly those involving mixtures, an extremely complex mixture of gases and particulates, e.g. smoke may be produced. The composition depends upon the initial compounds involved, the temperatures attained and the oxygen supply, and is hence often unpredictable. Some gaseous compounds may derive from thermal breakdown, i.e. pyrolysis, of the chemicals rather than oxidation as illustrated in Tables 3.9 and 3.10. 

Material balances for the pyrolysis products from HIPS equipped with flame retardants have been given (53). The pyrolysis experiments were performed to some extent in the presence of zeolite catalysts. The zeolites were added in order to remove organic bromine from the products of pyrolysis. In addition to their potential of destroying toxic brominated flame retardants, zeolites have been believed to be suitable to upgrade the pyrolysis products. 

Sorting of plastics is often manual and can cause allergic and health problems. Remarkably, plastic waste is not without a smell, and air extracted from storage and handling is thermally deodorized, e.g. at the Ube Industries gasification plant. Part of the pyrolysis products can be regarded as toxic. 

When PU is based on more volatile diisocyanates than MDI, snch as HDl (hexam-ethylene diisocyanate) or TDl (tolnene diisocyanate), these componnds spoil the gasoline or diesel oil boiling fraction of the pyrolysis oil, respectively. It is possible to eliminate the reactive and toxic diisocyanate products from the pyrolysis oil, either in a lower-temperature pyrolysis step or with the help of an adsorbent [41],... 

Health issues can be related not only to the pyrolysis products of the polymer itself, but also may be related to the compounds that come from the polymer additives. For example, in a study of pyrolysis of high impact polystyrene with decabromodiphenyi ether/antimony oxide added as a flame retardant, it has been shown that toxic polybrominated dibenzofuranes are generated during thermal decomposition in the range of 350-400° C [15]. 

For larger amounts we recommend the gas-phase pyrolysis of 4,5-dicyano-l,3-dithiol-2-one (8) [Eq. (3)], which is readily available from sodium cyanide, carbon disulfide, and phosgene [16]. Both the starting materials and most of the pyrolysis products are extremely toxic, and the price to be paid for large-scale production is hence high. 

Waritz RS, Kwon BK. The inhalation toxicity of pyrolysis products of polytetrafluoroethylene heated below 500 degrees Centigrade. Am Indust Hygiene Assoc J. 1968 19-26. 

Numerical and Experimental Investigation of Pyrolysis and Oxidation of Dioxin Precursors and other Toxic By Products ... 

Kimmerle, G. and Prager, F. K. The relative toxicity of pyrolysis products. Part 1. Plastics and man-made fabrics. J. Combustion Toxicology, 7, No. 2, 42 (1980)... 

Significant effort has recently been put in for the elimination of polymer wastes from electric and electronic equipment (WEEE) by pyrolysis. WEEE includes mainly epoxy resins and styrene polymers. They often contain brominated aromatics, which are highly contaminant. However, their elimination by simple thermal treatments is no longer possible as one of the most important drawbacks in dealing with thermal treatment of WEEE is the likely production of supertoxic halogenated dibenzodiox-ins and dibenzofurans. A pyrolysis method at low temperature range was developed, which limited the formation of such toxic by-products and reduced pyrolysis costs, even at relatively long residence times in the reactor. 

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