Meaning
The migration of low molecular weight additives from the polymer matrix to the surface of a plastic part causes a loss of flexibility and changes in material properties. When plasticizer leaching occurs, the molecules that were originally distributed between the polymer chains to make them flexible diffuse out of the plastic. This results in a material that becomes increasingly brittle and prone to cracking under mechanical stress.
Additive Migration
Concentration gradients and chemical incompatibility drive the movement of these smaller molecules toward the outer boundaries of the plastic. In the case of plasticizer leaching, exposure to solvents, high temperatures, or even prolonged contact with other plastics can accelerate this diffusion process. This migration is particularly common in flexible polyvinyl chloride formulations that use phthalates as softeners.
Part Performance
Stiffness and hardness of the component increase notably as a result of this loss of additives. When plasticizer leaching reduces the concentration of the plasticizer, the glass transition temperature of the polymer rises, making the part brittle at lower temperatures. This can lead to premature failure in flexible tubing, seals, and gaskets.
Additionally, the migrating additives can contaminate the surrounding environment or the liquids flowing through the parts, which is a major concern in medical and food-contact applications.
Processing Impact
Molders must select additives with high molecular weight or chemical resistance to minimize this risk. Utilizing polymeric plasticizers instead of monomeric ones reduces the rate of diffusion, although it can increase raw material costs. Molders also need to optimize the cure or cooling cycle to ensure the additives are locked within the matrix.
