Preparation and Properties of PP/Waste EPDM Thermoplastic Elastomers Using Ultrasonically Aided Extrusion

Compounding of waste EPDM from postindustrial scrap with polypropylene (PP) is a possible way to manufacture thermoplastic elastomers to solve a significant environmental problem. Accordingly, the present study considers three compounding methods for manufacturing of PP/EPDM at mixing ratios of 75/25, 50/50, and 25/75 with aid of ultrasonic twin screw extruder (TSE) at ultrasonic amplitudes varying from 0 to 13 μm. These compounding methods included the one step (OS), two step (TS) and dynamic revulcanization (DR) methods. In the OS method, PP and waste EPDM particles were directly compounded using TSE with and without ultrasonic treatment. In the TS and DR methods the waste EPDM particles were fed into TSE and devulcanized without and with ultrasonic treatment. Then, in the TS method, the devulcanized EPDM was compounded with PP using TSE without imposition of ultrasound. In the DR method, the devulcanized EPDM after compounding with curatives was mixed with PP and dynamically revulcanized without imposition of ultrasound in TSE. Die pressure during compounding was recorded and correlated with rheological properties of compounds. Mechanical properties of PP/EPDM blends obtained in the OS and TS methods did not show any improvement with ultrasonic treatment. In the DR method, all PP/EPDM blends showed a significant increase of the tensile strength and elongation with ultrasonic amplitude and a slight decrease of the Young’s modulus. In particular, the tensile strength of 30 MPa and the elongation at break of 400% were achieved at an ultrasonic amplitude of 13 μm for the PP/EPDM blend at a ratio of 75/25. The complex viscosity, storage and loss moduli of dynamically revulcanized PP/EPDM blends increased with the ultrasonic amplitude while the loss tangent decreased. At the same time, results for blends obtained by the OS and TS methods showed an opposite trend in dynamic properties behavior with the ultrasonic amplitude. SEM studies indicated that blends obtained by the DR method with ultrasonic treatment at 13 μm showed the lowest sizes of dispersed revulcanized EPDM particles in PP matrix leading to the excellent performance of these thermoplastic elastomers.