Biodegradable “asbestos

Since asbestos fibers are all siUcates, they exhibit several other common properties, such as incombustibiUty, thermal stabiUty, resistance to biodegradation, chemical inertia toward most chemicals, and low electrical conductivity. 

We make a mention of phosphate fibers, or more appropriately polyphosphate fibers, that were developed by Monsanto Co. as a replacement for asbestos fibers (Griffith, 1995). Basically, the silicon atoms of asbestos were replaced by phosphorus atoms. These polyphosphate fibers were supposed to be a kind of safe asbestos fiber. However, Monsanto did not commercialize these fibers because of a possible vulnerability to lawsuits. The safety feature of polyphosphate fibers stems from the fact that they are composed of components that are constituents of the human body and are thus biodegradable. The polyphosphate fibers developed by Monsanto were similar to asbestos fibers in terms of their insulating and nonflammable characteristics. 

A synthetic substitute for asbestos without the associated toxicity has been produced in England, [ 4, 5 ]. It represents a current revolution in materials technology. There is good reason to foresee that the industrial chemist may well produce insecticides whose biodegradable life will be days instead of months - and thus reduce materially these objectionable non-point sources of toxicity. 

Polychlorinated biphenyls have very high chemical, thermal, and biological stability low vapor pressure and high dielectric constants. These properties have led to the use of PCBs as coolant-insulation fluids in transformers and capacitors for the impregnation of cotton and asbestos as plasticizers and as additives to some epoxy paints. The same properties that made extraordinarily stable PCBs so useful also contributed to the widespread dispersion and accumulation of these substances in the environment. By regulations issued in the United States under the authority of the Toxic Substances Control Act passed in 1976, the manufacture of PCBs was discontinued in the United States, and their uses and disposal were strictly controlled. Some degree of biodegradation of PCBs in the environment does occur. 

Table 4.1 Chapter 5). Wool fibres have been optimized to allow maximum recovery when unpacked and set. Also, their dissolution in vitro has been of utmost importance since the problems generated by asbestos (see water diffusion and hydrolysis of siloxane bonds Chapters 5 and 7). Biodegradable glass fibres have been developed accordingly (Chattier, 1997). 

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