Molecular evolution during dynamic vulcanization of polyolefin mixtures for lead-free thermoplastic vulcanized


The process of vulcanization has been exploited for decades for rubber production. The original process involves heating natural or synthetic diene polymers with Sulphur which accelerates and activates the formation of crosslinks between the long molecules (macromolecules) resulting in improvement of rubber elastic properties. Also, vulcanization of polyolefins has been widely exploited industrially. Specifically, medium voltage (MV) insulation compounds based on EPDM and EPDM/LDPE blends have been produced. In recent literature, a lead free MV insulation compound was subjected to dynamic crosslinking with peroxide in a melted polypropylene matrix, in the presence of various ethylene polymers, propylene and additives to optimize the ultimate properties. In fact, an analysis of the MV TPV compounds properties revealed that it passed thermomechanical testing for specific operating temperature and short circuit emergency. Nonetheless, it was also shown that a deeper analysis of the molecular evolution and structural morphology during the vulcanization and the role of the various components of the starting mixture was still required.

To address this, Italian scientists from the University of Pisa: Professor Francesco Ciardelli and Stefano Riolo, in collaboration with Dr. Stefano Dossi, Dr. Andrea Galanti and Dr. Andrea Magri at the Mixer SpA company further characterized the thermoplastic vulcanized (TPVs) prepared by MIXER from the molecular viewpoint to the best level allowed by the complexity of the system. Their aim was to reach a control of the final properties based on the feed composition and the structure evolution during the dynamic vulcanization. Their work is currently published in the research journal, Polymers Advanced Technologies.

In their approach, the TPV MV insulation compounds were prepared starting from a peroxide curable lead free MV insulation, which was the actual market benchmark. For this reason, they were extensively investigated in comparison to the standard lead free MV insulation. The researchers then undertook a detailed analysis of the molecular changes induced by the peroxide vulcanization reaction with reference to the different polymers and low molecular weight additives present in the starting mixture.

The results of the dynamic vulcanization process were evaluated and related to the formulation. In addition, the authors found that the presence of the unsaturated polymer (EPDM in their case) highly favored the crosslinking but as shown by their data, the inter chain coupling of saturated ethylene polymers (POE and LDPE) was very modest living a consistent non crosslinked material fraction. This last, with the polypropylene giving degradation rather than crosslinking, granted a good thermoplastic behavior to the TPV.

In summary, the study by University of Pisa and Mixer SpA company scientists presented for the first time at the molecular level, the preparation process and the final properties of new thermoplastic lead-free medium voltage insulation compounds based on the TPV technology. Remarkably, the team achieved their objective, i.e. the design and production of TPVs with better processing behavior and predesigned performances in the final application with particular reference to the possibility of processing them as thermoplastic elastomers.

Molecular evolution during dynamic vulcanization of polyolefin mixtures for lead-free thermoplastic vulcanized - Advances in Engineering

About the author

Dr. Galanti was born in Faenza, Ravenna, Italy, in 1972. He received the B.Sc. and M.Sc. degrees in Industrial Chemistry from the University of Bologna, Bologna, Italy, in 1996.

In 1998 he joined Mixer S.p.A. as Technical Manager. Since 2015 he is the General Director of Mixer S.p.A. coordinating all the technical, commercial and productive activities. His current interests are in rubber compounds for the cable industry.

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About the author

Dr. Magrì was born in Bologna, Italy, in 1982. He received the B.Sc. and M.Sc. degrees in Photochemistry and Chemistry of Materials from the University of Bologna, Bologna, Italy in 2007 and 2010. He specialized in organic semiconductors, optoelectronics, and OLEDs. In 2014 he obtained the Ph.D. degree in Chemistry and Physics from the University of Strasbourg, Strasbourg, France. His field of study includes magnetism and spintronic applications of organic molecules.

In 2011, he joined the Institute of Nanotechnology – Karlsruhe Institute of Technology, Karlsruhe, Germany as Research Scientist. After the academic experience, in December 2015, he joined Mixer S.p.A. as Research and Development Project Manager and Technical Specialist. His main interests include TPV compounds, rubber compounds, mixing and extrusion processes.

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About the author

E-mail: [email protected]

Dr. Dossi was born in Cavalese, Trento, Italy, in 1972. He received the B.Sc. and M.Sc. degrees in Industrial Chemistry from the University of Bologna, Bologna, Italy, in 1998.

He joined Mixer S.p.A. in 1998 as laboratory technician. Currently he is the Raw Materials Lab Manager. His interests are in analytical techniques to characterize raw materials.

About the author

Francesco Ciardelli was Full Professor in Macromolecular Chemistry at the University of Pisa , from 1975 to 2010,and Professor Emeritus of Industrial Chemistry . He was postdoc in UC London and Max-Planck in Germany. Visiting Professor at Berkeley,,Kyoto and Paris., His research results of his research were circulated on the basis of more than 380 papers in international journals ,more than 250 invited presentations,22 industrial patents and 9 books .Since 2010 he became CEO of the SPIN-PET srl devoted to technology transfer to Industry in the field of polymer based advanced materials .Main results were obtained in the formulation of polyolefins adhesives, plastic recycling, blends and composites including nanocomposites .

About the author

Stefano Riolo was born in Siracusa, Italy, in 1987. He received the B.Sc. degree in Industrial Chemistry from the University of Catania in 2011, and the M.Sc. degree from the University of Pisa, Italy in 2014.

In 2015, he joined the SPIN-PET Co. as Technical Specialist for Research and Development in polymer based materilas. He is author of some scientific papers and patents.His main interests include composites , poly olefins and other organic polymers and their compounding by blending and reactive extrusion to compounds and composites with predesigned properties


Francesco Ciardelli, Stefano Dossi, Andrea Galanti, Andrea Magri, Stefano Riolo. Molecular evolution during dynamic vulcanization of polyolefin mixtures for lead-free thermoplastic vulcanized. Polymers Advanced Technologies 2020; vol 31: page 864–872.

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