Thermal analysis of polymer samples by a round robin method: I. Reproducibility of melting, crystallization and glass transition temperatures

Abstract

The reproducibility of transition temperatures (melting, crystallization and glass transition temperatures) of polymers determined by thermal analysis was examined by a round robin method, in which twenty three laboratories participated. Seven polymer samples were used for the test, which consisted of polyethylene pellet and film, two poly(ethylene terephthalate) fibers, poly(ether ether ketone) pellet, polystyrene sheet and poly(ether sulfone) pellet. Eight types of instrument were employed including 13 power-compensated type differential scanning calorimeters and 8 heat-flux type ones (quantitative differential thermal analyzers). For the first-order transition such as melting and crystallization, the values of the peak melting and crystallization temperatures ( T pm and T pc) and the extrapolated onset and end temperatures ( T im and T ic, and T em and T ec) agreed well among laboratories. The standard deviations (σ n ) were smaller than 3.0 K for T pm, T pc, T im and T em, and T ic and T ec with a few exceptions. However, the onset and end temperatures ( T' im and T' em, and T' ic and T' ec) are so scattered that it is reasonable to use T pm, and T pc, and T im, and T em, and T ic and T ec for the comparison of data obtained for polymers by thermal analysis in separate laboratories. For glass transition, the σ n values were within 3.1 K for the extrapolated onset temperature ( T ig) and the midpoint temperatures ( T mg), but the onset and end temperatures ( T' ig and T' eg) and the extrapolated end temperature ( T eg) were very scattered. Therefore, it is appropriate to use T ig and T mg to compare the data from different sources.