Polymers do not corrode or rust is OT true or false
Answers
Answer:
Explanation:
Corrosion on polymers, both plastics and rubber materials, is in many cases similar to metals but in other cases it looks very different. Corrosion attacks on polymers are often hard to discover, the material may look normal but can in fact be embrittled and have lost it´s mechanical strength.
Mechanical stressed polymers applied in chemical environments may initiate cracks on the surfaces. These cracks can thereafter propagate through the material either as a result of the mechanical stresses or in combination with continuing chemical attack. Corrosion of polymers can be divided into either chemical reaction or physical interaction.
Cover made of glassfiber reinforced polycarbonate. High temperature under load in water give cracks that cause leakage.
Chemical reaction
Polymers consist of a network with molecular chains mainly consisting of carbon, hydrogen and oxygen. Corrosion by chemical reaction changes the configuration of the polymer chains. Listed below are some of the environments that causes chemical reactions in polymers.
Heat: Chain scission will occur when polymers are exposed to heat above a specified temperature limit, which is unique for each type of polymer.
UV- radiation: In the presence of oxygen, UV-radiation can cause a breakdown of the polymer chains.
Ozone: Attacks from ozone on unsaturated polymers (e.g. natural rubber) under stress, causes characteristic cracks.
Water: Absorption of water at elevated temperatures causes hydrolysis of certain groups in a polymer chain (e.g. urethane and ester groups). Hydrolysis weakens the polymer since the backbone structure is altered.
Chemicals: It is important to distinguish chemical deterioration caused by chemicals from effect caused by swelling/dissolving which do not alter the chemical structure of the polymer chains. Chemical resistance is highly dependent on the molecule structure of a polymer as for thermoplastics, whether they are amorphous (e.g. PC, PVC, PS, PMMA) or partially crystalline (e.g. PE, PA, PP, POM). Partially crystalline are more resistant to organic substances and solvents than amorphous polymers. Thermosetting resins (e.g. PUR, EP, UP) can, due to their cross-linked structure not be dissolved, but can be subjected to swelling or chemical reaction (e.g. hydrolysis).
Physical interaction
Physical effects on polymers are caused by interaction with the environment. This may lead to swelling, dissolving or leakage of additives. The interaction is dependent on diffusion of substances into the polymer, and the process is in some cases reversible.
Organic substances usually affect polymers through physical interaction, while substances like strong acids or bases normally result in an irreversible breakdown of polymers.
yes it is true...........