Thermoplastic elastomers from rubber and recycled polyethylene: chemical reactions at interphases for property enhancement

Recycled low density polyethylene (R-LDPE) has been reactively compatibilized with butadiene rubber (BR) by using small additions of reactive polyethylene copolymers and reactive BRs to produce thermoplastic elastomers (TPEs). TPEs were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), rheology measurements, wide-angle X-ray scattering (WAXS) and mechanical testing. WAXS results show that the presence of BR and reactive modifiers does not completely prevent the crystallization of R-LDPE during the TPE formation. Depression of the melting point has been found in all cases. Also in all cases, compatibility is provided by formation of interfacial layers. The best mechanical characteristics are obtained for R-LDPE + BR blends compatibilized with poly(ethylene-co-acrylic acid) (PE-co-AA) and polybutadiene terminated with isocyanate groups (PB-NCO) for PB-NCO = 7.5wt% per PB and COOH/NCO ratio = 1/1. The stress at break and elongation at break are respectively improved by 31 % and 63 %. The PB-NCO modifier participates in co-vulcanization with BR in the rubber phase and reacts at the interface with the PE-co-AA dissolved in the polyolefin phase. As a result, the amorphous phase of R-LDPE is dissolved by the rubber phase and a morphology with dual phase continuity is formed, assuring an improvement of mechanical properties of TPEs.  2004 Society of Chemical Industry