Effects of Temperature and Humidity on Plasticizer Migration and Exudation
Effects of Temperature and Humidity on Plasticizer Migration and Exudation
Plasticizers are primarily associated with the PVC matrix through non-covalent interactions, including van der Waals forces and dipole–dipole interactions, rather than permanent chemical bonds. Consequently, exposure to external environmental factors such as elevated temperature, humidity, and mechanical stress can gradually drive plasticizers to migrate from the bulk of the material toward the surface, where they may subsequently be released into the surrounding air, water, or other contacting media. This migration leads to progressive hardening and embrittlement of PVC products, deterioration of mechanical properties and durability, and ultimately a reduction in service life.
Previous studies have identified temperature and humidity as the two most influential environmental factors governing plasticizer migration. Elevated temperature increases molecular mobility, thereby accelerating diffusion within the polymer matrix. Under high-humidity conditions, water molecules progressively penetrate the PVC matrix, increasing the free volume between polymer chains and creating additional pathways for plasticizer diffusion. More importantly, temperature and humidity do not act independently; rather, they exhibit a pronounced synergistic effect, whereby their combined influence on plasticizer migration is substantially greater than the sum of their individual effects.
Microscopic Mechanisms Underlying the Synergistic Effect
1. Synergistic Increase in Free Volume
High temperatures intensify the thermal motion of PVC molecular chains, increasing free volume; high humidity allows water molecules to penetrate, further enlarging the free volume. Their combined action results in a greater increase in free volume than the sum of either factor acting alone.
2. Synergistic Optimization of Diffusion Paths
High temperatures accelerate the diffusion of water molecules within the PVC, making moisture penetration more uniform and profound, thereby forming more continuous diffusion channels throughout the material.
3. Synergistic Weakening of Intermolecular Forces
High temperatures weaken van der Waals forces, while the ingress of water molecules weakens polar interactions. Together, they significantly reduce the binding force between plasticizer molecules and the PVC matrix.
Author: Zicai Pan | QC Supervisor | Zhenjiang R&D Center
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