Physical Aging in PS-MWCNT Composite: An Enthalpy Relaxation Study

Abstract

Physical aging behavior of pure polystyrene (PS) film and PS-multi wall carbon nanotube (MWCNT) composite film has been studied by monitoring enthalpy relaxation using differential scanning calorimeter (DSC). The PS-MWCNT film with 2.5 wt % MWCNT was prepared via the solution casting method. In this work, we have studied the physical aging behavior of pure PS and PS-MWCNT composite film. The glass transition temperature (T g) for PS and PS-MWCNT composite as obtained from DSC are 98.2°C and 95.3°C, respectively. To study the physical aging behavior, both the samples were isothermally annealed at an aging temperature (Ta) 84°C for various aging time (t a) from 1 hour to 48 hours. The T g for both the samples increases with aging time. This ascending trend of T g for the aged sample is due to the relaxation of molecular chain mobility. The kinetics of enthalpy relaxation due to physical aging has been studied using Kolrausch-Williams-Watt (KWW) model. By applying this model to the experimental results, we calculate the values of relaxation time (τkww). The values of relaxation time (τkww) as obtained from KWW model are 13.45 ± 0.16 hours and 10.82 ± 0.95 hours for PS and PS-MWCNT, respectively. This shows that the relaxation due to aging in PS is slower than that in PS-MWCNT composite.