Heat-treated and functionalized horsetail biosilica reinforced polyhydroxyalkanoate composite fabricated via additive manufacturing: insights into mechanical, wear, and flame-resistant performance

In this research, heat treated and silane functionalized horsetail derived biosilica was incorporated into a polydroxyalkanoate (PHA) matrix to fabricate environmentally sustainable bio composites through fused filament fabrication (FFF) 3D printing. Surface modification enhanced the interfacial compatibility between biosilica and PHA resulting in improved structural reinforcement and load transfer. Among the developed composites, MB2 (2 vol% biosilica) exhibited the highest mechanical properties which includes 53.9 MPa in tensile, 83.4 MPa in flexural, 3.05 J in impact and 78 Shore D hardness, as uniform filler dispersion and strong polymer filler bonding enabled efficient stress distribution. Additionally, tribological evaluation revealed that the composite with 4 vol% biosilica (MP3) provided the best wear resistance achieving the lowest specific wear rate (0.013 mm³/Nm) and the lowest coefficient of friction (0.31) attributed to the improved load bearing capacity during sliding. Moreover, MB3 also demonstrated superior flame retardancy (12 mm/min) due to the development of a compact silica rich char layer that effectively inhibited heat and oxygen diffusion. These findings confirm the potential of surface modified biosilica reinforced PHA composites as high performance, biodegradable engineering materials.