Long term performance of polymers for solar hot water applications

Polymer materials used in domestic hot water heating systems must maintain mechanical properties in the working fluid over their target lifetimes. In potable water, chlorine and pH combine to create an oxidative environment, characterized by the oxidative reduction potential (ORP) that can chemically attack a polymer, resulting in permanent loss of mechanical strength and increase in creep compliance. Polymer morphology data and mechanical property data are presented for polysulfone (PSU), polybutylene (PB), polypropylene random copolymer (PP-r) and polyamide 6/6 (PA66) specimens that had been exposed to an aqueous oxidative environment. The data obtained after up to 1500 hours exposure in hot potable chlorinated water (ORP ranging from 550 mV to 825 mV), show that PSU and the polyolefins with antioxidant additives (PB and PP-r) maintain their mechanical properties, while PA66 degrades significantly.