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What Is Phenolic Plastic?
Prior to the mid 1980's, a large percentage of phenolic plastic molding compounds contained asbestos. Asbestos is known to cause mesothelioma, lung cancer and other asbestos-related diseases. Phenolic plastic (phenol-aldehyde resin) is considered to be the foundation of the plastic molding industry. It contributes to a large percentage of all molded plastic products and is used almost exclusively for industrial plastic materials. Phenolic plastic was also first manufactured under the trade name Bakelite, named after the founder and inventor of phenolic plastic, Dr. Leo Hendrik Baekeland. Most applications of phenolic plastic materials benefit from a thermosetting reaction created by a one or two-stage process.
Phenol and formaldehyde are the two major components of phenolic plastic. Phenol, which is carbolic acid, is a by-product of the distillation of coal and, because of this, large quantities can be produced. Phenol is also synthetically produced from benzene. Formaldehyde is normally a gas and is produced by the oxidation of methyl or wood alcohol; it is incorporated in its liquid form to produce phenolic plastic.
Either a one-stage or two-stage process is used to create phenolic plastic. In the one-stage process, equal parts of phenol and formaldehyde are mixed into a kettle. A catalyst such as ammonia or caustic soda is added, the mixture is then heated, and a chemical reaction begins to create a clear amber resin. When removed from the kettle, the resin has a consistency of molasses, and it is cooled in cooling pans or on a hardening floor. At this stage the resin compound is called resol.
The first stage of the two-stage process consists of making a soluble resin called novolak by use of an acid catalyst. Initially, phenol and formaldehyde are poured into the resin kettle, and an excess of phenol is added to the mix. An acid catalyst, such as hydrochloric or sulphuric acid, is then added, heated and mixed, starting the chemical reaction. By neutralization and the addition of an excess of a formaldehyde bearing compound called hexa, this resin is converted to a thermosetting resin. The resin is cooled and hardened on a hardening floor similar to the one-stage process.
After the clear amber resin solidifies on the hardening floor or in cooling pans, it is ground into a fine powder. Both one-stage and two-stage phenolic resin compounds are then ground and mixed with filler materials. Other materials, such as vegetable wax and calcium stearate, are also added to prevent sticking during molding operations.
Filler materials are essential in providing strength and preventing shrinkage in phenolic plastic compounds. Asbestos was commonly used as it provided ample strength and increased heat resistance. Asbestos fibers also improved resistance to moisture, acids and other chemicals. For this reason, asbestos was incorporated as filler in phenolic plastics designated for use in heavy industry or chemical applications.
Asbestos is known to cause mesothelioma, lung cancer and other asbestos-related diseases. Workers who manufactured phenolic plastic molding compound and those who produced molded products from phenol resin materials were often exposed to dangerous asbestos fibers.
Typical Fillers Used in Phenolic Plastic Compounds:
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