Observations and characterizations of tensile and fatigue properties of chemically recycled PBT(polybutylene terephthalate)

This study investigated the microstructural evolution and its influence on the mechanical properties of recycled PBT (rPBT), a blend of virgin PBT (vPBT) and chemically recycled PBT, in comparison with those of vPBT. Gel permeation chromatography (GPC) analysis confirmed that the molecular weight and molecular weight distribution of rPBT were maintained at levels comparable to those of vPBT. Nevertheless, under tensile loading, a significant reduction in elongation at break of up to 52% was observed in rPBT, whereas improved fatigue performance was obtained under cyclic loading. Differential scanning calorimetry (DSC) analysis revealed an increase in the glass transition temperature ( T g ) and a decrease in the heat capacity change ( ΔC p ), indicating reduced segmental mobility and an increased rigid amorphous fraction (RAF). Fatigue analysis further revealed delayed compliance evolution in rPBT, suggesting that fatigue damage initiation was suppressed by reduced hysteretic energy dissipation associated with constrained amorphous-phase mobility. Consequently, the accumulation of fatigue damage was delayed, resulting in improved fatigue life. Overall, these results demonstrate that, even when molecular weight is preserved, the mechanical performance of chemically recycled PBT is strongly governed by changes in amorphous-phase mobility.