why plasticizers are added with polymers

Any substance added to the polymer system that can increase the plasticity of the polymer system can be called a plasticizer.

The main function of plasticizers is to weaken the secondary bond between polymer molecules, that is, van der Waals force, thereby increasing the mobility of polymer molecular chains, reducing the crystallinity of polymer molecular chains, that is, increasing the plasticity of polymers , Performance is that the hardness, modulus, softening temperature and embrittlement temperature of the polymer decrease, while the elongation, flexibility and flexibility increase.

Plasticizers can be divided into two types according to their mode of action, namely internal plasticizers and external plasticizers.

The internal plasticizer is actually part of the compound. Generally, the internal plasticizer is the second monomer introduced during the polymerization of the polymer. Because the second monomer is copolymerized in the molecular structure of the polymer, the regularity of the polymer molecular chain is reduced, that is, the crystallinity of the polymer molecular chain is reduced. For example, vinyl chloride-vinyl ester acid copolymer is more flexible than vinyl chloride homopolymer. The use temperature range of the internal plasticizer is relatively narrow and must be added during the polymerization process, so the internal plasticizer is used less.

External plasticizer is a low molecular weight compound or polymer. Adding the plasticizer to the polymer that needs to be plasticized can increase the plasticity of the polymer. External plasticizers are generally a kind of high boiling point, hard to volatile liquid or low melting point solid, and most of them are ester organic compounds. Usually, the external plasticizer does not react chemically with the polymer, and the interaction between the external plasticizer and the polymer is mainly the swelling effect when the temperature is increased, forming a solid solution with the polymer. The performance of external plasticizer is relatively comprehensive, easy to produce and use, and it is widely used. Now people generally refer to plasticizers as external plasticizers. Dioctyl phthalate (DOP) and dibutyl phthalate (DBP) are both external plasticizers.