Effects of a poly(hydroxyalkanoate) elastomer and kraft pulp fibres on biocomposite properties and three-dimensional (3D) printability of filaments for fused deposition modelling

Three-dimensional (3D) printing is a useful technique that allows the creation of objects with complex structures by deposition of successive layers of material. These materials are often from fossil origin. However, efforts are being made to produce environmentally friendly materials for 3D printing. The addition of lignocellulosic fibres to a polymer matrix is one of the alternatives to replace, for instance, glass fibres in composites as reinforcing materials. The fields of biocomposites and 3D printing open innovative application areas for pulp fibres from the pulp and paper industry. In this work, biocomposites of poly(lactic acid) (PLA), poly(hydroxyalkanoate) (PHA) and kraft pulp fibres were prepared in order to find a suitable formulation for filaments for 3D printing. The effect of two different types of kraft fibres (bleached (B) and unbleached (U)) and of PHA on the mechanical and thermal properties of the biocomposites was assessed. The addition of 30% kraft fibres to PLA resulted in an increase of the tensile modulus from 3074 to ∼4800 MPa. In the case of biocomposites containing PHA (50% PLA/20% PHA/30% kraft) the increase in modulus was more moderate (PLA+PHA+U: 3838 MPa, and PLA+PHA+B: 3312 MPa). The tensile strength of PLA (66 MPa) increased to 77 MPa in PLA+kraft biocomposites, while a reduction in strength was observed for PLA+PHA+U (43 MPa) and PLA+PHA+B (32 MPa). Filaments prepared with PLA, PHA and bleached and unbleached pulp fibres showed similar printability of complex geometries, demonstrating that unbleached pulp fibres could also be utilized in the preparation of biocomposites with good mechanical performance and 3D printing properties.