Plastics are nothing but synthetic organic high polymers. It is important to know the general outstanding properties of plastics to make best use of this an engineering material. It should also be noted that each plastic material has its own peculiar properties to suit the various uses. Hence the success of plastic as an engineering material for a particular purpose will depend upon the correct choice of the variety.
Properties of Plastic Materials
Following are the general properties of plastics.
The plastics are sufficiently strong and can be used for load bearing structural members. The strength of plastics can further be increased by reinforcing them with various fibrous materials.
Plastic as structural material has not gained much popularity because of the following resins.
- High cost of construction
- High temperature susceptibility
- Poor stiffness
- Being subjected to creep under constant load
2. Weather Resistance
The plastics, prepared from phenolic resins, are only good in resisting weather effects. Certain plastics are seriously affected by ultraviolet light.
3. Fire Resistance
Plastics, being organic in nature, are combustible. But the resistance to fire temperatue depends upon the plastic structure.
- Cellulose acetale plastics burn slowly.
- Polyvinyl chloride (PVC) plastics are non-inflammable.
- Phenol formaldehyde and urea formaldehyde plastics are used as fire proofing materials.
Plastics generally possess sufficient durability, provided they offer sufficient surface hardness. Thermoplastic varieties are found to be attacked by termites and rodents.
5. Dimensional Stability
Plastics easily maintain its shape and do not go under plastic deformations.
6. Chemical Resistance
Plastics offer great resistance to moisture, chemicals and solvents. Many plastics are found to possess excellent corrosion resistance. Plastics are used to convey chemicals.
7. Thermal Resistance
The plastics have low thermal conductivity and therefore foamed or expanded varieties of plastics are used as thermal insulators.
8. Working Conditions
All operations like drilling, sawing, punching, clamping etc are carried out easily on plastics, just like wood.
9. Moisture Resistance
This property depends upon variety of plastics used, for example, cellulose plastics are considerably affected by the presence of moisture, whereas polyvinyl chloride plastics offer high resistance to moisture.
Plastics, generally, have low ductility and hence plastic structural members may fail without prior warning.
11. Miscellaneous Properties
In addition to above properties, plastics have following qualities.
- Plastics are available in variety of colors, both opaque and transparent.
- Plastics possess excellent insulating property, so used as electric insulators.
- Plastics are clean, light and shining, so they need not be given any finish such as painting, polishing etc.
- Normally thermo-plastics have low melting point and cannot be used where temperature or heat condition persists.
- They possess good optical and sound absorption qualities.