Development of nanoscale morphology and role of viscoelastic phase separation on the properties of epoxy/recycled polyurethane blends

- Recycled polyurethane can be used as an efficient modifier for epoxy resin.
- The recycled polyurethane improves the tensile strength and modulus simultaneously.
- Fracture toughness increased up to 95% by the addition of recycled polyurethane.
- Viscoelastic phase separation results in ordered nano networks.
- Increased usage of RPU leads to reduction in post-consumer waste.

A novel and cost-effective approach towards the modification of epoxy matrix has been developed using recycled polyurethane for the first time without sacrificing any of the intrinsic properties of the resin. Polyurethane, recycled from waste foam by glycolysis process (RPU), was found to be very effective in improving the properties of the thermosetting resin based on Diglycidyl ether of bisphenol-A (DGEBA). The effect of the addition of polyurethane on the mechanical and viscoelastic properties was analyzed and the morphological changes with the inclusion of varying concentrations of RPU were examined by High Resolution Transmission Electron Microscopy (HRTEM). All the blends remained transparent, even after curing by a reaction induced phase separation process (RIPS) of the epoxy phase and hence suggests the development of microphase separation and nanostructure formation. The nanoscale morphology is very clear even with 15 phr concentration of the recycled polyurethane. The morphology at high concentration (40 phr) of RPU under HRTEM showed very distinct ordered interpenetrating network (IPN) like formation and a phase in phase morphology. The size of the dispersed RPU particles varied from 32 to 80 nm as the concentration of RPU varied from 15 to 40 phr in the epoxy phase. This is the first report where nanoscale morphology development by viscoelastic phase separation (VPS) process. The tensile strength values varied from 57 MPa for neat epoxy to 68 MPa for the 40 phr blend. The fracture toughness was increased by 83% for the addition of 40 phr RPU. The recycled PU can be considered as excellent low cost reinforcing filler for epoxy resin where strength and modulus of epoxy resin could be improved simultaneously with an increase of fracture toughness.

The manuscript deals with the modification of DGEBA epoxy resin using recycled polyurethane obtained by glycolysis of industrial scrap of polyurethane. The nanostructure formation assumed from optical transparency was confirmed by TEM analysis and the phase separation occurs in the nanoscale. The mechanism behind the phase separation was proposed to be viscoelastic phase separation ad this is the first time report on the nanoscopic range of phase separation for epoxy-PU interpenetrating systems.146