| Abstract: | Polyvinyl chloride compounds rupture prematurely in contact with environmental stress cracking (ESC) agents such as plasticizers. This effect shows a considerable deviation in a stress rupture plot (log stress vs log time) from the expected stress rupture in the absence of ESC agents. PVC and polymers in general dilate under a stress, increase free volume, and allow diffusion of the ESC agent and plasticization of the polymer. However, we show ESC failure is not dependent alone on molecular size of the ESC agent when comparing di-2-ethylhexyl adipate (DOA), di-2-ethylhexyl phthalate (DOP), and tri-2-ethylhexyl trimelitate (TOTM). Therefore this suggests that ESC failure is not strictly associated with diffusion of the ESC agent into the free volume of the PVC, but rather flaws and stress concentrations play a large role. Higher molecular weight PVC retards rupture, both in air and in contact with the ESC agent. However, the safe way to design PVC parts is to avoid ESC contact with stressed PVC rather than using high molecular weight PVC. Part design can play an important role in preventing these premature failures by keeping the ESC agent away from contact with stressed PVC. |
