PPG-PEG-PPG/Epoxy systems cured at 100 °C: relationship between miscibility, microstructure, thermal and mechanical properties

Abstract

This article evaluated the thermal, mechanical, morphological and fracture properties of systems with poly (ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) (PPG-PEG-PPG) triblock copolymer, with molecular weight 2000 g•mol−1 and 50% PEG in its composition, in DGEBA/DDM epoxy matrix. Systems with 10, 20 and 30 wt.% copolymer were prepared by in-situ polymerization and curing at 100 °C. In the differential scanning calorimetry (DSC) analysis, the characteristic temperatures of both the copolymer and the matrix in the binary systems were verified, indicating that phase separation had occurred. However, the glass transition temperature referring to the epoxy phase (Tg-E) occurred at lower temperatures than in neat matrix, which indicates partial miscibility in binary systems. The epoxy/copolymer systems presented a Young's modulus higher than the neat matrix, and without loss of mechanical resistance, reinforcing the miscibility of the PEG block in the blends and a microstructure with nanophase separation. When evaluating the fracture surface of the blends by scanning electron microscopy, the presence of deflection and crack immobilization mechanisms was observed, but no phase separation of the copolymer was observed. In this way, the systems studied showed partial miscibility with the formation of nanophases at the curing temperature of 100 °C, influencing Tg-E and improving the stiffness of the matrix.