Mechanical and piezoresistive properties of GNP/UHMWPE composites and their cellular structures manufactured via selective laser sintering

In this study, we describe the development of composites comprising ultra-high molecular weight polyethylene (UHMWPE) reinforced with graphene nanoplatelets (GNP), specifically designed for additive manufacturing (AM) of self-sensing structures through selective laser sintering (SLS). We employed ball-milled GNP/UHMWPE powder feedstocks to fabricate standard test specimens and 2D cellular structures with varying GNP content. A comprehensive assessment of their mechanical and piezoresistive properties was carried out under uniaxial tensile loading. The incorporation of 1.5 wt% GNPs into UHMWPE demonstrated a notable increase in crystallinity by -28 % and a significant reduction in porosity by about 98 %. These enhancements contributed to a substantial improvement in both strength (-21 %) and elastic modulus (-40 %). Moreover, the introduction of 1.5 wt% GNPs resulted in the formation of electrically percolated composites characterized by prominent piezoresistive behavior. These composites exhibited gauge factors ranging from 9.6 to 18 under uniaxial tensile loading. During cyclic tensile loading, the GNP/UHMWPE composite displayed hysteresis in its piezoresistive response due to viscoelasticity, impeding an immediate return to its original state. Additionally, the gauge factors of the 2D cellular structures generally demonstrated lower values compared to those of the parent composite, scaling proportionally with the effective elastic modulus.