Investigation of mechanical and physical properties of chemically foamed Polylactic acid for the purpose of plant growth

Abstract

This study was to investigate the mechanical and physical properties of chemically foamed Polylactic acid (PLA) for the purpose of plant growth in horticulture. PLA is a biodegradable polymer that shows promising suitability in varied fields by incorporating certain chemical foaming agents (CFA). For this study, we blended PLA with varied CFA concentrations using hot melt extrusion (HME) and then characterized the batches of PLA/CFA blends to optimize plant growth. The conducted studies (i.e., density, water holding content (WHC), foam expansion, porosity, and air-filled porosity (AFP) demonstrated that the addition of CFAcould improve the structural properties of PLAand support plant growth by enhancing water retention based on the porous structure in the finalized blends. In addition, a saturation point can be observed beyond which the additional CFA has no significant effect on the density, porosity, or water-holding capacity of the PLA matrix. Regarding the mechanical performance, a negative impact of CFA concentration can be seen, where the tensile strength reduced from 32.61 MPa to 15 MPa, and Young's modulus decreased from 0.792 GPa to 0.365 GPa for the finalized blends. In addition, an elevated potential of Hydrogen (pH) value can be seen based on the increasing CFA concentrations, where a pH7 can be found in the 0 wt% and a pH8.4 can be found in the 50 wt% CFA. This high pH value decreases the mineral nutrients and, therefore, a growth inhibition can be seen. Overall, this study advances the understanding of foamed PLA as a potential alternative to peat as a growing media and lays a foundation in sustainable plant growth substrate, including a substituted foaming agent such as critical CO₂ extrusion and an addition of a controlled-release fertilizer to promote the effectiveness of PLA matrix.