Thermoplastic Vulcanizates Based on Maleated Natural Rubber/Polypropylene Blends: Effect of Blend Ratios on Rheological, Mechanical, and Morphological Properties Charoen Nakason, Sitisaiyidah Saiwari, Azizon Kaesaman Department of Rubber Technology and Polymer Science, Faculty of Science and Technology, Prince of Songkla University, Pattani 94000, Thailand Maleated natural rubber (MNR) was prepared and used to formulate thermoplastic vulcanizates (TPVs) based on various MNR/PP blends. The influence of mixing methods on the TPVs properties was first stud- ied. We found that mixing all ingredients in an internal mixer provided the TPVs with better mechanical prop- erties. The final mixing torque, shear stress, and shear viscosity of the TPVs prepared with various blend ra- tios of MNR/PP increased with increasing levels of MNR in the blends. This may be attributed to higher shear viscosity of the pure MNR than that of the pure PP. Furthermore, as evidenced in SEM micrographs, the TPVs are two phase morphologies with dispersed small vulcanized rubber domains in the PP matrix. Therefore, the higher content of PP caused the more molten continuous phase of the flow during mixing and rheological characterization. Tensile strength and hardness of the TPVs increased with increasing levels of PP, while the elongation at break decreased. Fur- thermore, the elastomeric properties, in terms of ten- sion set, increased with increasing levels of MNR in the blends. This may be attributed to decreasing trends in the size of vulcanized rubber particles dis- persed in the PP matrix with an increasing concentra- tion of MNR. POLYM. ENG. SCI., 46:594 – 600, 2006. © 2006 Society of Plastics Engineers INTRODUCTION Thermoplastic elastomers (TPEs) based on polyolefin rubber-thermoplastic compositions have developed along two distinctly different classes. One class consists of a simple blend and classically meets the definition of a ther- moplastic elastomeric olefin (TPO). In the other class, the rubber phase is dynamically vulcanized, giving rise to ther- moplastic vulcanizates (TPVs) or dynamic vulcanizates (DVs). The TPVs are characterized by finely dispersed, micron-sized, crosslinked rubber particles distributed in a thermoplastic matrix [1]. Most polyolefin TPEs are based on synthetic rubbers such as ethylene–propylene– diene monomer (EPDM), ethylene propylene rubber (EPR) and butadiene acrylonitrile rubber (NBR), or a modification of them. Interest in natural rubber (NR) and thermoplastic blends has increased recently because of abundance of NR and unique properties of the blends. These materials are known as thermoplastic natural rubbers (TPNRs). Not only raw NR has been used to prepare TPNRs, but the modified form of it has also been widely studied. Eoxidized natural rubber (ENR) is one of the most recognized modified forms currently used to prepare TPNRs by blending with thermo- plastics such as poly(vinyl chloride) [2, 3] and poly(ethyl- ene-co-acrylic acid) [4]. Graft copolymers of NR with PMMA [5, 6] have also been used to prepare TPNRs. In this work, an attempt was made to prepare TPNRs based on maleated natural rubber and PP blends via the dynamic vulcanization process. The effect of the blend ratios on the rheological, mechanical, and morphological properties of the TPVs was investigated. EXPERIMENTAL Materials The polypropylene used as a thermoplastic blend com- ponent was an injection-molding grade MD with an MFI of 12 g/10 min at 230°C and a specific gravity of 0.91 g/cm 3 and was manufactured by the Thai Polypropylene, Rayong, Thailand. The natural rubber used was air-dried sheet (ADS) manufactured by a local factory operated by Khun Pan Tae Farmer Co-operation (Phattalung, Thailand). The maleic anhydride used to prepare the graft copolymer of maleic anhydride and natural rubber or maleated natural rubber (MNR) was manufactured by Riedel-de Haen, Seelze, Germany. The toluene used as a solvent was man- ufactured by Lab Scan, Ireland. The zinc oxide used as an Correspondence to: C. Nakason; e-mail: ncharoen@bunga.pn.psu.ac.th Contract grant sponsor: National Metal and Materials Technology Center, NSTDA; contract grant number: MT-B-46-POL-18 –199-G. DOI 10.1002/pen.20498 Published online in Wiley InterScience (www.interscience.wiley. com). © 2006 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2006