synthetic resins
A group of complex, partially amorphous, organic
semi-solid or solid substances that are produced
by chemical reaction or by polymerization of
relatively simple compounds. Synthetic resins are
comparable to natural resins in various physical
properties but are considered to be superior to
them in that they are more uniform, possess
greater clarity, durability, flexibility and
resistance to chemical change. The synthetic
resins include: 1) formaldehyde condensation
products of phenol, urea, and melamine; 2)
reaction products of polyhydric alcohols and
polybasic acids (alkyd and polyester resins); 3)
polymerization products of acrylic acid and its
derivatives (acrylic resins) or styrene
(polystyrene): and 4) polymers of butadiene and
its derivatives, or copolymers, with other
materials (synthetic elastomers, etc.).
According to the manner in which they react to
heat and pressure, synthetic resins are classified
broadly as being either thermoplastic or
thermosetting. Although the cellulose polymers,
cellulose acetate, cellulose nitrate, and ethyl
cellulose, are prepared from natural materials
and, therefore. do not conform to the definition
of a synthetic resin, they are nonetheless classed
along with them. These resins also find use in
papermaking as adhesives in coating and
laminating. as barrier materials, and as agents to
impart special properties to paper, e.g., improved
wet and dry strength. Synthetic resins are also
used extensively in the application of finishes to
the grain surface of leather. (17 , 306 )
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