Annealing studies have been carried out to understand the temperature induced microstructural changes in Bakelite (P-120 NEMA LI-1989 Grade XXX) Resistive Plate Chamber (RPC) detector material using Positron annihilation lifetime spectroscopy (PALS), Fourier transform infrared spectroscopy (FTIR), and XRD. The variation of positron lifetime parameters viz., ortho-Positronium lifetime (s 3 ) and free volume size (V f ) increases marginally above glass transition temperature T g as a result of structural changes due to segmental mobility. The drastic increase of free volume parameters above 240 o C attributed to the reduction in strength of CAH bond of the aliphatic bridges and cleavage of methylene bridges of the polymer network, which is supported by the FTIR results. The XRD results show the reduction in crystallinity and average crystallite size of Bakelite on annealing correlates well with the free volume and electrical conductivity. The temperature induced electrical conductivity and activation energy is also correlated with the positron lifetime parameters.Generally, RPCs are operated at high voltages (about 8-10 kV) and due to the variation of temperature under experimental conditions, might lead to changes in microstructural properties of the Bakelite over a period of time. It was noticed that the Bakelite resistivity changes as a function of temperature and humidity. 8,9 This is the indication that Bakelite RPCs are expected Additional Supporting Information may be found in the online version of this article.

Microstructural characterization of nylon 6/short glass fiber (SGF) and nylon 6/polyacrolonitrile based carbon fibers (PAN‐CFs) of 10 to 40 wt% has been performed by positron lifetime technique (PLT). The positron lifetime parameters viz., o‐Ps lifetime (τ3), o‐Ps intensity (I3), and fractional free volume (Fv) of nylon 6/SGF and nylon 6/PAN‐CF composites are correlated with the mechanical properties viz., tensile strength and Young's modulus. The Fv shows negative deviation with the reinforcement of 10 to 40 wt% of PAN‐CF and show positive deviation in nylon 6/SGF from the linear additivity relation. The negative deviation in nylon 6/PAN‐CF composite suggests the induced molecular packing due to the chemical interaction between the polymeric chains of nylon 6 and PAN‐CF. The positive deviation in nylon 6/SGF composite indicates the formation of interface between the polymeric chains of nylon 6 and SGF. The increased crystallinity of nylon 6/SGF and nylon 6/PAN‐CF composites shows the improved mechanical properties of the composites. The hydrodynamic interaction parameter (h), which shows more negative values in nylon 6/SGF than nylon 6/PAN‐CF composites. However, the extent of chemical interaction in nylon 6/SGF is less compare to nylon 6/PAN‐CF composites. This is evident from Fourier transform infrared spectrometry studies. POLYM. ENG. SCI., 58:1428–1437, 2018. © 2017 Society of Plastics Engineers