deplasticization

Deplasticization is the process of removing plasticizers from a plastic polymer, resulting in increased rigidity and a higher glass transition temperature. It describes the reversal of plasticization rather than chemical degradation of the polymer itself. The term is most commonly applied to flexible plastics such as polyvinyl chloride (PVC), where plasticizers like phthalates are used to soften the material.

The mechanism involves diffusion of plasticizer molecules from the polymer matrix into surrounding media or spaces, driven by concentration gradients, temperature, and solvent interactions. Diffusion can be slow and often yields partial recovery of the original, unplasticized state. Factors influencing deplasticization include the polymer’s free volume, the plasticizer’s compatibility and molecular size, processing history, and environmental conditions such as temperature and humidity.

Common methods to induce deplasticization include heat treatment, solvent extraction, or exposure to environments that favor plasticizer migration (e.g., water, certain oils, or organic solvents). The process can be accelerated by using selective solvents or by aging the material under controlled conditions. It is important to differentiate deplasticization from chemical degradation, as the latter involves changes to the polymer backbone.

Characterization of deplasticization typically involves differential scanning calorimetry to monitor shifts in Tg, dynamic mechanical analysis to assess modulus changes, and gravimetric or spectroscopic methods to quantify plasticizer loss. Applications include recycling and reclamation of plastically softened polymers, regulatory testing for leachables, and post-processing conditioning of flexible plastics where a more rigid material is desired.

Limitations include incomplete removal, potential embrittlement, and environmental concerns related to extractable plasticizers.