Foamability of all-green polylactide/rice straw pulp biocomposites through continuous extrusion process: Effects of pulping and reactive compatibilization

In the present work, the processability of poly(lactic acid) (PLA) in the extrusion foaming process was improved by using rice straw (RS) as an agricultural waste. In order to extrude a sustainable lightweight foam, the soda-pulping and bleaching modification were performed on the RS particles, which resulted in the attainment of purified micron-sized cellulosic fibre with higher aspect ratio. The addition of these fibres, with larger interfacial area between filler and matrix, to the PLA melt enhanced the foam void fraction and cell density more than one order of magnitude. The use of a reactive compatibilizer in the biocomposite showed further beneficial effects on the PLA foamability. The used reactive compatibilizer, with the ability of simultaneous reactions with the end groups of PLA macromolecules and hydroxyl groups of the lignocellulosic pulp, in the biocomposite noticeably improved the viscoelastic properties of melt and lengthened the macromolecule relaxation times. As a result, the biocomposite melt with higher melt strength was obtained, which kept the melt integrity during the bubble growth stage, hindered the cell coalescence, and retained a larger volume of gas inside the melt. Contrary to these influences, the compatibilization activity of this additive weakened the heterogeneous nucleation role of the cellulosic fibres. However, by choosing proper pulp loading, the extrusion of a lightweight biodegradable PLA-based biocomposite foam can be feasible, which can be used in interior construction applications.