Vickers microhardness of microfibrillated cellulose/poly (L-lactic acid) composites and associated mechanical properties

Microhardness testing is a quick and efficient way to assess some distinct mechanical properties of polymer composites that are difficult to measure experimentally. This study examined the Vicker’s microhardness of microfibrillated cellulose (MFC)-reinforced poly(L-lactic acid) (PLA) composites with different weight fractions 0.00 wt% to 0.05 wt%. The composites of PLA and MFC were prepared using the solvent casting method. The hardness of samples was measured with indentation loads of 0.098, 0.2452, 0.4903, 0.9807 and 1.971 N. The effects of XMFC in the composites were further assessed by tensile strength test, thermogravimetry test and SEM analyses. The load-oriented indentation size effect behaviour of the composites was studied with well-established theoretical models, namely, Meyer’s Law, Hays – Kendall, elastic/plastic deformation, proportional sample resistance, and modified proportional sample resistance models. The composites exhibited a plastic deformation tendency under indentation loads that closely fit the Hays – Kendall model. The calculated true hardness data were used to determine several distinct mechanical properties, viz. yield strength (Y), elastic modulus (E), brittleness index (B), and fracture toughness (K). The values of Y, E, B, and K changed successively with increasing MFC fraction. In conclusion, Vicker’s microhardness analyses will provide valuable information for selecting the filler‒matrix ratio of cellulose/PLA composites.