The Plasticizing Principle Of Plasticizers
Plasticizing principle of plasticizer
Plasticizers are divided into internal plasticizers and external plasticizers.
Internal plasticizer: The second monomer is introduced during the polymerization of the polymer. Since the second monomer is copolymerized in the molecular structure of the polymer, the crystallinity of the polymer molecular chain is reduced. Another type of internal plasticization is the introduction of branches (or substituents or grafted branches) on the polymer molecular chains. Branches can reduce the interaction between the polymer chain and the chain, thereby increasing the plasticity of the plastic. Since the second monomer has a stable combination of chemical bonds with the polymer chain segment, it is not extracted by the medium, but in view of process and cost, the use temperature range of the internal plasticizer is relatively narrow and must be added during the polymerization process. Usually used only in slightly flexible plastic products.
Outer plasticizers: Generally high-boiling, less volatile liquids or low-melting solids added to the polymerization system. The vast majority of ester organic compounds, usually do not chemically react with the polymer, the interaction with the polymer at the elevated temperature is mainly swelling, forming a solid solution with the polymer.
Plasticizers can be divided into two types, internal plasticizing and external plasticizing, according to their principle of action and mode of action.
Internal plasticization: Block copolymerization or graft copolymerization of heterogeneous monomer molecules, thereby reducing the intermolecular attraction, such as copolymerization of vinyl chloride and vinyl acetate.
External plasticization: With the help of some low-molecular substances with solvating power, they are incorporated into the resin molecules to increase the distance between the molecules so as to reduce the intermolecular force between the resin molecules. As a result of plasticization, the intermolecular attraction force decreases. Softens the plasticized resin while lowering the resin processing temperature.
The generally accepted theory is described as follows:
The plasticization of polymer materials is caused by the weakening of the aggregation between polymer chains in the material. The insertion of plasticizer molecules into the polymer molecular chains weakens the attraction between polymer chains, resulting in an increase in the mobility of the polymer chains and a decrease in the crystallinity of the polymer chains, thus increasing the plasticity of the polymer. .
When a plasticizer is added to a polymer, there are the following forces in the polymer-plasticizer system: a. The interaction force between polymer molecules and polymer molecules (I);
b, the intermolecular forces of the plasticizer itself (II);
c. Forces between plasticizers and polymer molecules (III).
In general, plasticizers are small molecules, so (II) is small and may not be considered. The key lies in the size of (I).
If it is a non-polar polymer, (I) is small, plasticizers are easily inserted, and the distance between polymer molecules can be increased, and the intermolecular forces can be weakened, which can play a good plasticizing effect; Polymers (I) are large and plasticizers are not easy to insert.
The use of polarizer-based plasticizers is required to allow the polar groups to interact with the polar groups of the polymers instead of the interpolar polar interactions of the polymers, so that (III) increases, thereby weakening the intermolecular space. The force to achieve plasticization.
The main role of plasticizers is to weaken van der Waals forces between polymer molecules, increase the mobility of polymer chains, and reduce the crystallinity of polymer chains, that is, increase the plasticity of plastics. The elongation, flexibility, and flexibility of plastics are improved, while the hardness, modulus, softening temperature, and embrittlement temperature all decrease.