Low-temperature vulcanizable chloroprene rubber–bromobutyl rubber blend for encapsulation of undersea sensors: Nonconventional cure systems and reaction kinetics

Abstract

Blends of chloroprene rubber (CR) and bromobutyl rubber (BIIR) are used in making the undersea sensors watertight by a process of encapsulation. The encapsulation process is conventionally done at high temperature approximately 150°C and above using high-temperature vulcanization (HTV). However, the new class of acoustic sensors like polyvinilidenefluride (PVDF) and thin film PZT are highly temperature sensitive and fragile in nature and hence they require low-temperature vulcanization (LTV) process to avoid damages and protect their full functionalities. However, conventional cure systems are not adoptable in LTV process and hence there is a need for the search of alternate cure systems. Not much work has been reported in this area. This article reports a nonconventional cure system vulcanizable with LTV and the associated reaction kinetics for a commonly used CR–BIIR blend for encapsulation of undersea sensors. Formulations have been attempted with cure systems based on red lead (Pb₃O₄) and zinc oxide (ZnO) for CR–BIIR blend in 80:20 weight ratio, instead of zinc oxide, magnesium oxide, and ethylene thiourea system, which are conventionally used in HTV. The cure parameters at low temperature between 70°C and 120°C and the activation energy for cure reactions (E _a) were estimated using MDR 2000 rheometer. Essential prerequisites like water resistance, electrical resistivity, and physicomechanical properties for sensor application are qualitatively analyzed for the blend cured at 90°C. The results reveal that the proposed nonconventional cure systems are able to bring down the cure temperature of CR–BIIR blend to 90°C from 150°C enabling the suitability of the materials for undersea sensor encapsulation.