Thermal analysis techniques for characterization of polymer materials
Routine DSC and TGA techniques, used to characterise polymer thermal stability, have been further used for assessment of comparative thermal stability of various polymer materials and for prediction of material lifetimes. The following materials were investigated: (1) commercial and experimental polymer materials – results for poly(vinyl chloride) (PVC) and bisphenol A polycarbonate (PC) are presented; (2) a polydimethylsiloxane–polytetrafluoroethylene (SIL–PTFE) coating system; and (3) commercially available linear low density polyethylene (PE-LLD), unmodified and modified chemically and physically. The plot of reciprocal temperature of initial decomposition 1/Tdi vs log heating rate Î² has been recommended for assessment of comparative thermal stability. The lifetime of polymer materials was calculated from the plots of log time-to-failure, log tf, vs reciprocal temperature 1/T, where tf values were obtained using Tdi from TGA measurements or directly from the oxidation induction time (OIT) data as criteria for initial deterioration of polymer thermal stability. The following sequences of increasing thermal stability were found for investigated materials: PVC âª PC; SIL < SIL–PTFE 20% < SIL–PTFE 50% âª PTFE; (B) PE-LLD, grafted < (A) PE-LLD, unmodified < (C) PE-LLD, filled. The lifetime of polymer materials predicted from the plots of log tf vs 1/T are in reasonable agreement with experimental data and users' observations, e.g. approximately 1 year for PC and unmodified PE-LLD both at 373 K (100 °C) and for PVC at temperature of outdoor conditions about 298 K (25 °C).