In situ process monitoring of a thermoplastic-based fibre composite using optical fibre sensors

This paper reports the use of optical fibres to obtain real-time information during the processing of thermoplastic-based glass fibre-reinforced polypropylene. The technique used to monitor the melting and solidification process in this study is based on monitoring the modulation of the refractive index of the polymer matrix. Before embedding the sensor in the composite laminate, the cladding layer of the optical fibre was removed to expose the optical fibre core thus allowing intimate contact with the host polymer matrix. As the matrix undergoes melting and solidification cycles, the refractive index of the polymer at the sensor-host interface changes which in turn varies the amount of light transmitted through the optical core. This signal intensity modulation was monitored during the composite processing cycle. Differential scanning calorimetry was carried out to provide a reference for evaluating the validity of the optical fibre data.