Preparation and characterisation of biocomposites containing thermomechanical pulp fibres, poly(lactic acid) and poly(butylene-adipate-terephthalate) or poly(hydroxyalkanoates) for 3D and 4D printing

Wood fibres are hygroscopic and swell when immersed in water. This effect can be used to create shape-changing structures in 3D printing. Hence, wood fibre reinforced filaments have the potential to be used in four-dimensional (4D) printing. In this work, biocomposites based on granulated or milled thermomechanical pulp (TMP) fibres and poly(lactic acid) (PLA) were prepared and evaluated based on their tensile properties. Poly(hydroxyalkanoates) (PHA) or poly(butylene-adipate-terephthalate) (PBAT) were included in the biocomposite recipes to assess their effect on the melt flow index (MFI) and tensile properties. Clear effects of the TMP fibre morphology on MFI were quantified. Biocomposites containing 20 wt% PBAT turned out to be stronger and tougher than the ones containing PHA. Based on that, filaments for 3D and 4D printing were manufactured. Interestingly, the tensile strength of 3D printed specimens containing milled TMP (TMPm) fibres was about 33% higher compared to those containing TMP fibre granulate (TMPg). Using hot water as the stimulus, the 3D printed specimens containing TMPg showed a greater reactivity and shape change compared to TMPm specimens. [Display omitted] •Differences in TMP fibre morphology affect the melt-flow-index of biocomposites.•PBAT elastomer ensures the manufacturing of strong and tough biocomposites with enhanced flow properties for 3D printing.•3D printed parts with shorter TMP fibre fragments showed greater tensile strength and were less brittle.•Mono- and bi-material 3D printed biocomposite causes shape morphing properties, using water as an external stimulus.