Evaluation of glass-transition temperature and influence of low-temperature condition on the moduli of acrylonitrile-butadiene rubber

Abstract

Medium acrylonitrile-butadiene rubbers (ABR) (30–45% acrylonitrile (ACN)) are commonly used in several sealing components for the aerospace industry due to their wide range of thermal stability (−40 °C to +108 °C), good abrasion, lightweight viscoelastic and tear resistance properties. Since sealings manufactured using a popular method, viz., moulding followed by milling, has several cons, like difficulty in transferring the used moulds to other supplementary working units, increased manufacturing cost due to increased processing steps and time, etc. There is a need for advanced and green manufacturing methods, like abrasive water jet machining, to produce intricate shapes/sizes in single or batch-size elastomeric components during failure or damage. Several researchers have suggested machining ABR at low-temperature (cryogenic) conditions instead of room temperature, which helps to get good quality machined surface due to the increased modulus of ABR. Hence, the low-temperature study of ABR is imperative due to the prominent market for cryogenic machining of ABR. In this direction, it is necessary to explore the effect of low temperature on ABR’s thermal and dynamic mechanical properties, which is essential for successfully developing the components required for several aerospace applications. The primary focus of the work is to explore the effect of low temperatures (–50 °C to 100 °C) on ABR’s storage and loss modulus. The low-temperature properties of ABR are enhanced by adding a sulfur accelerator followed by Zinc oxide activators to achieve optimum vulcanisation. The glass-transition temperature (Tg) range was measured using profound characterisation techniques such as Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analyser (DMA). The result shows that the transition phase occurred from –36.59 °C to –12.65 °C, which resulted in a phase change of ABR34 from rubbery to glassy (tough) due to a noticeable increase in the observed modulus values.