What happens to PVC membranes over time?

• A. Thermal softening reduces rigidity.
• B. Increased resistance to moisture.
• C. Embrittlement due to mineral deposits.
• D. Plasticizer migration can lead to embrittlement and cracking.

Answer: (D)

PVC membranes stay flexible because plasticizers lower the glass transition temperature of the material. Over time, those plasticizers can migrate out of the PVC due to heat, UV exposure, and general aging. As the plasticizers leave, the polymer becomes stiffer, leading to embrittlement. When the membrane is brittle, it can’t tolerate thermal movement or substrate shifts, so small movements cause cracks to form and propagate, compromising the waterproofing. This plasticizer migration causing embrittlement and cracking is the primary aging mechanism for PVC roofing membranes. The other ideas don’t fit long-term service behavior: extensive heat alone would not explain gradual embrittlement, aging doesn’t improve moisture resistance, and mineral deposits don’t drive the same embrittlement process as plasticizer loss.