The problem of selecting Plastic Material is that of finding the material with suitable properties from the standpoint of intended service, methods of forming and fabricating, and cost.
Plastic Material possessing
New and improved Plastic Material possessing almost any desired characteristic are being introduced continually. There are plastics that do not require plasticizes that have greater flexibility under lower temperatures, and are stable under higher temperatures. Some resist water, acids, oils, and other destructive agents.
Use of Plastics Testifies
The wide use of plastics testifies to their value, However, fundamental limitations should be considered when applying a new material or adapting an old material to new applications.Plastics are inclined toward rigidity and brittleness at low temperatures, and softness and flexibility at high temperatures. They are fundamentally unstable dimensionally with respect to temperature, and are susceptible to distortion and flow when subjected to elevated temperatures. The thermoplastics are particularly susceptible, while the thermosetting plastics are much more resistant, differing, however, only in degree.
Distinction of Plastic Material
The distinction between the thermal stability of the thermosetting and thermoplastic resins is not well defined. A true distinction can be drawn only between individual plastics, rather than between classes of plastics. High temperatures not only seriously reduce the physical properties of plastics, but accelerate the destructive action of external agents to which they are sensitive. Continuous heating also may induce brittleness and shrinkage in heavily plasticized materials by volatilization of plasticizers. The use of one plastic in contact with a dissimilar plastic in a proposed application should be checked first in the light of possible “migration of plasticizer,” sometimes resulting in discoloration or hardening of one of the Plastic Material.
In general, moderate temperatures are required for storage of plastics over long periods；low temperatures are to be avoided because of the low-temperature brittleness of most of the plastics, and high temperatures should be avoided because of the rapid loss of physical properties, volatilization of plasticizers, and the susceptibility of a large number to distortion.Plastics, with only a few exceptions, are extremely sensitive to the effects of water. High-humidity atmospheres induce water absorption and varied resulting effects, depending upon the composition and formulation of the Plastic Material.
Increased Water Content Plasticizes
Increased water content plasticizes some materials, and there is a general lowering of the physical properties. Water absorption is responsible for swelling in certain plastics and the ultimate decomposition of a few. Moist or wet atmospheres may extract plasticizers from heavily plasticized materials and also provide conditions favorable to fungal growth. In recent years, however, new plastics have come into use that have first-class moisture resistance and may contain water indefinitely while resisting other influences at the same time.
Extremely dry environments may cause brittleness in certain plastics as a result of loss of water that normally contributes to their plasticity. Cyclic wet and dry atmospheres are more destructive to plastics than continuous exposure at constant humidity because of the mechanicalstresses induced in the plastics by swelling and shrinking with moisture absorption and moisture emission.
Relatively Constant Moderate
Relatively constant moderate to low humidity are preferred for plastic storage because of the adverse effects of water on the structure and properties of these materials, and the possibility of plasticizer loss by extraction and fungal attack in moist atmospheres.
By steven,a China plastic mold maker dedicated to tooling and injection molding making