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.

Blends of chloroprene rubber (CR) and bromobutyl rubber (BIIR) with low-temperature vulcanization (LTV) technology were found suitable for the encapsulation of temperature-sensitive undersea sensors. Polymeric blends are susceptible to the aging process due to external environments such as heat, oxygen, ozone, light, and mechanical stresses, etc. Hence, the longevity of these blends for hostile seawater applications is a great concern. The marine aging of rubber blends was not investigated much. In this study, the LTV blends with a curing system based on lead and zinc oxides were subjected to accelerated aging in a 3.5% aqueous solution of NaCl from 40°C to 70°C. The retention of tensile strength, % elongation and modulus properties were estimated. It was observed that aging could lead to an initial increase in the modulus and a considerable decrease in ultimate tensile strength and elongation values with an increase in the aging period. Reduction in elongation at break showed a gradual decrease with an increase in both temperature and exposure time. It was observed that the blends with lead oxide cure system were prone to more degradation than ZnO-based blend. A life of 6.5 years and 5.3 years at 25°C for blends based on ZnO and lead oxide cure systems was estimated. The water diffusion coefficient was found to be of the order of 10−12 mm2 s−1 for both blends.

Blend of chloroprene rubber (CR) and bromobutyl rubber (BIIR) is used for encapsulation of piezo sensors used in sea water. Conventional encapsulation method of these sensors involving high temperature vulcanisation (HTV) often leads to deterioration of piezo properties due to thermal degradation. This paper reports a low temperature vulcanisation (LTV) technique carried out at 90 °C for CR-BIIR blend using chlorinated polyethylene (CPE) as compatibiliser and LTV system consisting of modified di-o-tolyl guanidine and thiocarbanilide as accelerators and ZnO as curing agent. The conventionally used scavenger MgO was eliminated and only ZnO was used to boost the cure reaction. Properties specific to sonar sensors, namely, acoustic transparency, electrical resistivity, water absorption and physico‑mechanical properties were evaluated besides evaluation of morphology. The results are found to compare better than the conventional blend. Accelerated thermal ageing at 70 °C for 7 days yielded 97 % retention of tensile strength. The technique was implemented in a PZT hydrophone sensor and was successfully underwater tested.