Physical aging and thermal aging resistance of polycarbonate/poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene) blends

Abstract

The effect of thermal annealing on the mechanical properties of polycarbonate (PC) was investigated by tensile testing, Izod impact testing, and differential scanning calorimetry (DSC). An endothermic peak appeared in the DSC curve by annealing at various temperatures below T g . The peak area, as a measure of the degree of physical aging, increased with annealing time. The Izod impact strength decreased suddenly just before an endothermic peak became detectable. The results imply that at the very early stage of physical aging, a trigger for the ductile-to-brittle transition may be initiated. By blending hydrogenated styrene-butadiene-styrene block copolymer (SEBS), the embrittlement by annealing was prevented. That is, in the PC/ SEBS blends, the physical aging of PC matrix proceeded in the same way as in neat PC; however, the Izod impact strength did not decrease. This thermal aging resistance seems to originate from the negative pressure effect of SEBS particles that provides dilational stress fields for PC matrix to enhance the local segment motions.

Preparation and characterization of long chain branched polycarbonates with significantly enhanced environmental stress cracking behavior through gamma radiation with addition of difunctional monomer

“…It is well known that the relaxation during annealing leads the system toward equilibrium, which is commonly denoted as an enthalpy relaxation. The regularization of macromolecular chains should make the system harder, 64 which is apparently opposite to our results. Takahara et al mentioned that there were density fluctuations at first followed by a decrease in density in the low density regions during the annealing process for PMMA, which may result in the improvement of local mobility of macromolecular chains.…”

Physical Aging of Polymer Blends

“…For example, polycarbonate has been found to lose its toughness when aged at temperatures below T g . This has been recently confirmed by Suzuki et al (2012) who showed that the Izod impact strength decreased suddenly in the very early stage of physical aging and suggested that annealing may trigger a ductile-to-brittle transition in BPAPC.…”

“…More recent studies have shown that when blending BPAPC with a hydrogenated styrene-butadiene-styrene block copolymer (SEBS), aging of the polycarbonate component proceeded at the same rate as in the pure polymer, but the Izod impact strength did not decrease. This thermal aging resistance was attributed to the negative pressure effect of the SEBS particles leading to enhanced local segment dynamics of BPAPC (Suzuki et al 2012).…”

Physical Aging of Polylactide-Based Graft Block Polymers

“…We observe that t a * is strongly dependent on the volume fraction of the rubbery domain, which is consistent with other reports of physical aging of rubber-toughened materials. 18,67,68 Although this trend is a function of composition, the suppression of embrittlement may also be due to the morphology of the BCPs. Wu previously reported that shear yielding was more favorable for rubber-toughened systems with shorter interparticle distances.…”