Fergana polytechnic insitute mechanical engineering faculty department of mechanical engineering and automation

Aging of polymers. 
Over time, the properties of polymers naturally decrease. 
Such a phenomenon is called obsolescence. Wear is affected by the external 
environment (light, heat, oxygen, azone, etc.). 
Polymers are also affected by radiation: polymers are ionized and chemical 
bonds are eroded (destruction). 
Ablation phenomenon. 
Ablation is the removal of 
the mass of polymers by a stream of hot air. The more complex the polymer 
structure, the higher its resistance to ablation. 
16.4. PLASTICS
Artificial materials made of organic binders are called plastics. 
Plastics soften when heated and take the desired shape under pressure and 
retain that shape. This property of plastics is widely used in technology. 
Plastics are multi-component materials, the main component of which is a 
binder (synthetic resin, cellulose ether). Many thermoplastics consist only of a 
binder (polyethylene, organic glass, etc.). Other than the main component - fillers 
(powder, fiber). 
pressed with a binder , a monolithic mass is formed. Fillers increase the 
mechanical properties of plastic, give special properties (antifriction, friction, etc.) 
and reduce the cost of plastic. Plasticizers (oleic acid, stearin, etc.) increase the 
plasticity of plastic. 
If necessary, hardeners (amines), catalysts (peroxides), pigments, inhibitors 
are added to plastics. Different properties can be achieved by changing the 
composition of plastics. 
Depending on the type of binder, plastics are divided into thermo- and reactive 
plastics. 
Depending on the type of filler, plastics are divided into powder (wood 
powder, graphite, talpk, mica, asbestos), fibrous (fabric fibers, cotton), layered 
(sheet), plastics. 
According to the place of application, plastics are divided into strong 
(structural, frictional, etc.) and weak (optical, durable , decorative, etc.) plastics. 

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Plastics have advantages as well as disadvantages. They have a small modulus 
of elasticity, low heat resistance, low thermal properties, and resistance to wear. 
Thermoplastics have the property of softening when heated and hardening 
when cooling. This property is preserved even during repeated heating and cooling. 
Polyethylene. 
Polyethylene is formed when ethylene is polymerized. 
Polyethylene is divided into low and high pressure types. Polyethylene is chemically 
resistant, good dielectric. It has poor resistance to atmospheric and ultraviolet 
effects. Pipes, fittings, sizes, films, ropes, special fittings are made from 
polyethylene. 
Various products are produced from polyethylene by injection molding, hot 
pressing , welding, gluing. 
Polypropylene. 
The properties of this plastic are higher than those of 
polyethylene. 
Polypropylene has low cold resistance, which is its disadvantage. Various 
pipes, pump blades, sizes are made from polypropylene. The technological 
properties of polypropylene are similar to those of polyethylene.