Meaning
The addition of low molecular weight compounds to a polymer matrix is used to decrease its glass transition temperature and increase flexibility. This material modification, called plasticization, alters the intermolecular forces between the polymer chains, allowing greater chain mobility. It increases the ductility, impact strength, and ease of melt processing for otherwise rigid resins.
The process occurs either through the addition of external chemical plasticizers or by the absorption of environmental moisture.
Processing Benefit
In melt processing, plasticization lowers the melt viscosity of the resin, reducing the energy required for extrusion. Lower viscosities permit lower operating temperatures, which protects heat-sensitive polymers from thermal degradation. This reduction is particularly useful for polyvinyl chloride, which degrades near its processing temperature.
The improved flow also allows the filling of complex, thin-walled moulds.
Performance Shift
The resulting mechanical changes must align with the intended application of the moulded part. While plasticization increases toughness and elongation at break, it decreases the tensile strength and modulus. This trade-off must be managed by the part designer.
If a component requires structural rigidity, the presence of plasticizing agents will lead to premature failure under load.
Additive Selection
Formulators select plasticizers based on compatibility and low volatility. Incompatible additives migrate to the surface. This migration causes stickiness and loss of properties.
High molecular weight polymer plasticizers resist this movement.
