Molecular and structural analysis of epoxide‐modified recycled poly(ethylene terephthalate) from rheological data

Abstract A multifunctional epoxide chain extender (ADR4370S) was used to increase the molecular weight of recycled poly(ethylene terephthalate) (R‐PET). The extension processing was carried out by melt mixing reaction. The effects of ADR4370S content on the molecular structure [molecular weight, molecular weight distributions (MWDs), branching, and gel‐like structures] of modified R‐PET were rheologically investigated. The results showed that the complex and apparent viscosity of the modified R‐PET were larger than those of unmodified one. The solid‐like behavior of R‐PET was enhanced after the reactive modification. The increments of balancing torque, reaction peak, and shear‐thinning behavior became more pronounced by increasing the concentration of ADR4370S. Reactive modification was characterized by the presence of long‐chain branching resulted in a wider MWD. Modified Cole–Cole plots demonstrated a shift toward higher storage modulus values at a given loss modulus value for the modified R‐PET samples. High concentration of ADR4370S (>1.5 wt%) resulted in a polymeric structure near the sol–gel transition point whose linear viscoelastic properties obeyed scaling law. The relaxation time was prolonged with the amount of ADR4370S increase. The decrease in the melt point and crystallization temperature of the modified R‐PET was correlated to the presence of chain branching. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers