Shear enhancement of mechanical and microstructural properties of synthetic graphite and ultra‐high molecular weight polyethylene carbon composites

• Published in: Journal of applied polymer science 2022-05, Vol.139 (20), p.n/a
• Main Authors: Favreau, Hannah J., Miroshnichenko, Kateryna I., Solberg, Peder C., Tsukrov, Igor I., Van Citters, Douglas W.
• Format: Article
• Language: English
• Subjects: Composite materials; Computed tomography; Ductility; Equal channel angular pressing; Failure; Grain boundaries; Graphite; Materials science; Mechanical properties; Molecular weight; nano27 synthetic graphite; Particulates; Polyethylene; Polymers; Tensile strength; Ultra high molecular weight polyethylene
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.52175

Ultra‐high molecular weight polyethylene (UHMWPE) has a variety of industrial and clinical applications due to its superb mechanical properties including ductility, tensile strength, and work‐to‐failure. The versatility of UHMWPE is hindered by the difficulty in processing the polymer into a well consolidated material. This study presents on the effects of shear imparted by equal channel angular pressing (ECAP) on UHMWPE composites containing Nano27 Synthetic Graphite (N27SG). Ductility and work‐to‐failure improvements up to ~60–80% are obtained in sheared N27SG‐UHMWPE composites as compared to non‐sheared N27SG‐UHMWPE controls of the same composition. Microscopy reveals increased fusion at particle boundaries and smaller voids in the sheared materials. Micro‐computed tomography results indicate different distribution of N27SG particulates in ECAP samples as compared to CM indicating enhanced grain boundary interactions. Tradeoffs are not avoided as ECAP samples were lower in conductivity as compared to compression molded (CM) billets of the same weight percent. However, ECAP samples were able to be doped with more N27SG allowing for an ~170% increase in conductivity over CM samples of the same work‐to‐failure. This work shows that ECAP is a viable processing method for obtaining stronger, more ductile conductive composite materials. Equal channel angular pressing (ECAP) is found to be a superior method for processing graphite based ultra‐high molecular weight polyethylene composites over compression molding. For a given tensile toughness, ECAP allows increased conductivity of ~170%. Tensile testing, electric conductivity testing, and microstructural testing reveal that ECAP improves intergranular distribution of carbon nano‐materials without changing the crystalline microstructure.