Ultrasound injection molding has emerged as an alternative production route for the manufacturing of micro scale polymeric components, where it offers significant benefits over the conventional micro injection molding process. In this work, the effects of ultrasound melting on the mechanical and morphological properties of micro polypropylene parts were characterized. The ultrasound injection molding process was experimentally compared to the conventional micro injection molding process using a novel mold, which allows mounting on both machines and visualization of the melt flow for both molding processes. Direct measurements of the flow front speed and temperature distributions were performed using both conventional and thermal high-speed imaging techniques. The manufacturing of micro tensile specimens allowed the comparison of the mechanical properties of the parts obtained with the different processes. The results indicated that the ultrasound injection molding process could be an efficient alternative to the conventional process.
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 ≈21 MPa to over 90 MPa using a draw ratio of 4, whilst for GTR/PP this increases from ≈15 to ≈57 MPa.
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