Polymer International Polym Int 53:1693–1703 (2004) DOI: 10.1002/pi.1530 Thermoplastic elastomers from rubber and recycled polyethylene: chemical reactions at interphases for property enhancement Olga Grigoryeva, 1 Alexander Fainleib, 1 Olga Starostenko, 1 Alexander Tolstov 1 and Witold Brostow 2,3∗ 1 Institute of Macromolecular Chemistry of the National Academy of Sciences of Ukraine, 48 Harkivske shose, 02160 Kyiv, Ukraine 2 Department of Materials Science and Engineering, University of North Texas, PO Box 305310, Denton, TX 76203-5, USA 3 Center for Applied Physics and Advanced Technology (CFTA), National University of Mexico, Querataro, Mexico Abstract: 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 = 7.5 wt% 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 Keywords: recycling; dynamic vulcanization; reactive compatibilization; LDPE; BR; TPE INTRODUCTION It is known that thermoplastic elastomers (TPEs) can be produced from polymer blends consisting of non-vulcanized virgin rubber and thermoplastic polymers such as polyolefins. 1–9 The TPE properties can be much improved by a dynamic or in situ curing. 2–5,7,9 During dynamic vulcanization, carried out by intense mixing above the melt temperature of the thermoplastic polymer, the rubber phase will be crosslinked (vulcanized) and finely dispersed (mean particle size of a few microns) in the thermoplastic. The latter takes the role of the matrix. 4 The resulting TPE exhibits rubbery characteristics while maintaining the thermoplasticity of the matrix. As a consequence, the TPE is melt (re)processable. A further benefit of TPEs is that they provide high value-added products if the components are derived from waste sources (‘upcycling’). Preliminary results show that the TPEs can be adopted for certain post-consumer goods. 10 – 12 Since thermoplastic and rubber are usually incompatible, providing component compatibility via an enhancement of interfacial adhesion is needed. 13 – 16 The reactive compatibilization can be realized by several ways. 13,15 In this work, we introduce reactive polyethylene copolymer into a thermoplastic phase and reactive polybutadiene rubber into a rubber phase. 17,18 The functional groups of polymer additives used should be reactive with each other. During intensive mixing of components at an elevated temperature a chemical reaction occurs at the interface, leading to increased adhesion between thermoplastic and rubber phases. The morphology of such compatibilized TPEs should result in a reinforcement of their mechanical properties. EXPERIMENTAL Materials The virgin butadiene rubber (BR) (weight-average molecular weight M w = 21 000 g mol −1 was SKD-2 ∗ Correspondence to: Prof Witold Brostow, Department of Materials Science, University of North Texas, Denton, TX 76203-5310, USA E-mail: brostow@unt.edu Contract/grant sponsor: European Union INCO-Copernicus project; contract/grant number: ICA2-CT-2001-10003 Contract/grant sponsor: US Department of Commerce, Washington, DC (SABIT Program) (Received 19 July 2003; revised version received 4 September 2003; accepted 10 October 2003) Published online 30 July 2004  2004 Society of Chemical Industry. Polym Int 0959–8103/2004/$30.00 1693