
324 Engineering Materials Technology
acetate is hard, stiff and tough but has poor dimensional stability due to a high
absorption of water. CAB is tougher and more resistant to water uptake and
hence more dimensionally stable. Cellulose acetate propionate is slightly
harder, stiffer and stronger. All three can be extruded and injection moulded.
Cellulose acetate is widely used for spectacle frames, having the advantage
that it can be softened by a slight increase in temperature and hence adapated
to facilitate adjustment to fit the wearer. Other applications are tool handles,
typewriter keys and toys. CAB is used for internally-illuminated