Environmental stress cracking of poly(vinylidene fluoride) in sodium hydroxide. Effect of chain regularity

Three commercial samples of poly(vinylidene fluoride) (PVDF) homopolymers w ith different crystallinity degree have been evaluated for chemical stress cracking behavior in 30 wt% sodium hydroxide solution. The polymers were su bmitted to thermal and mechanical analyses before environmental experiments . These were carried out at 23 degrees C on 3-mm-thick PVDF sheets, using t hree different levels of constant strain applied (3%, 5%, 7%). The time for crack appearance decreases with the increase of the degree of crystallinit y. This behavior has been related to the presence of head-to-head VDF addit ions (defect "a"), as well as to the overall chain regularity. The head-to- head sequences inhibit the degradation mechanism because of the dehydrofluo rination reaction activated by alkaline media. The less crystalline PVDF po lymer, with the higher content of head-head VDF additions and a limited num ber of chain-branching defects, presents the best crazing resistance.