EFFECTS OF MICROWAVE-ASSISTED CROSS-LINKING ON THE CREEP RESISTANCE AND MEASUREMENT ACCURACY OF THE COAXIAL-STRUCTURED FIBER STRAIN SENSOR

Abstract

Conductive particle reinforced nanocomposite-based strain sensors have been widely investigated owing to their unique material properties. Numerous studies on nanocomposite strain sensors have focused on the enhancement of stretchability, flexibility, and gauge factor (GF) for wearable and health care applications. However, flexible polymer-based strain sensor has a limitation for use in high temperature such as cure monitoring of composite structures due to the semi-crystalline structure of the polymer. The semi-crystalline polymers have a substantial creep when the slippage of the molecular chain at the amorphous region is occurred. Moreover, the slip phenomena are maximized at the high temperature because the mobility of the polymer chain is increased, which results in overestimated strain. The cross-linking process of thermoplastic is one of the possible solutions to reduce creep at high temperature. Conventionally, melt-mixing method has been used for the fabrication of cross-linked thermoplastics. However, the melt-mixing method is not suitable for fabricating fiber shape owing to extremely high viscosity because polymer melting and cross-linking reaction are occurred simultaneously. In this work, microwave-assisted cross-linking method was introduced to overcome the limitation of conventional cross-linking process. The ultra-high molecular weight polyethylene (UHMWPE) core fiber was fabricated by using a dry-jet wet spinning system. Microwave post-treatment was performed under the peroxide bath to enhance the creep resistance through the cross-linking reaction. By using the creep resistance enhanced core fiber, coaxial-structured fiber strain sensor which has multi-layer structured shell parts was fabricated by using a facile dip-coating method. The load carrying capacity and creep resistance of the core fiber were estimated by measuring the tensile strength and minimum creep rate at the high temperature. Sensitivity and linearity of the fiber sensor were checked by means of an electronic test equipment during static tensile test. In addition, accuracy of the fiber sensor at high temperature was evaluated and compared with that of a conventional strain gauge.