Solid State Orientation of Thermoplastic Vulcanizates

Die drawing has been used to produce polymeric products with superior mechanical properties by orientation of polymer chains. Although this process has been studied for a variety of thermoplastics and composites, there are no current publications exploring its efficacy to enhance thermoplastic vulcanizates (TPVs). TPVs combine the elasticity and high elongation at break of thermosets while maintaining the processability of a thermoplastic. For the first time, TPVs are die drawn and the effect upon their mechanical and thermal properties is investigated. TPVs based upon ethylene propylene diene monomer (EPDM) and polypropylene (PP) as well as ground tyre rubber (GTR) and PP are prepared by dynamic vulcanization using a twin-screw extruder. In all cases, die drawing leads to an increase in tensile strength and modulus of the material along the drawing direction, often at the cost of elongation at break. At a draw ratio of 2, EPDM/PP TPVs exceed the strength and modulus of neat polypropylene whilst maintaining an elongation at break in excess of 200%. For EPDM/PP, tensile strength increases from approximate to 21 MPa to over 90 MPa using a draw ratio of 4, whilst for GTR/PP this increases from approximate to 15 to approximate to 57 MPa.