Development of materials that are biobased and environmental sound is one of the goals within the current bioeconomy. This goal comes from an increasing conscientious society that pushes manufacturers and regulators toward a sustainable development. However, to be a feasible alternative, biobased materials should also match or outperform the mechanical performance of fossil-based materials. In this study, wood pulp fiber-reinforced polylactic acid (PLA) biocomposites were prepared, tested, and compared with glass fiber reinforced polypropylene. Pre-extrusion with a kinetic mixer and subsequent injection processing ensured correct dispersion of the reinforcement. The biocomposites showed mechanical properties in line with commercial materials, comparable to composites reinforced with 20% w/w of glass fiber. Micromechanics of PLA-based biocomposites showed the existence of strong interphase between the matrix and the pulp fibers. The interfacial shear strength was around 29 MPa and with a intrinsic tensile strength of the fibers 729 MPa. These materials offer a reliable alternative to oil-based matrices reinforced with mineral fibers. 

Two different series of biobased polyethylene (BioPE) were used for the manufacturing of biocomposites, complemented with thermomechanical pulp (TMP) fibers. The intrinsic hydrophilic character of the TMP fibers was previously modified by grafting hydrophobic compounds (octyl gallate and lauryl gallate) by means of an enzymatic-assisted treatment. BioPE with low melt flow index (MFI) yielded filaments with low void fraction and relatively low thickness variation. The water absorption of the biocomposites was remarkably improved when the enzymatically-hydrophobized TMP fibers were used. Importantly, the 3D printing of BioPE was improved by adding 10% and 20% TMP fibers to the composition. Thus, 3D printable biocomposites with low water uptake can be manufactured by using fully biobased materials and environmentally-friendly processes.

Two biobased polyethylenes (BioPE) and thermomechanical pulp (TMP) fibers were used to produce biocomposites. The impact of TMP fibers on the mechanical properties was assessed in detail. An increase on the viscosity of the melted biocomposites was quantified and was related to the incorporation of the TMP fibers (0–30% w/w). The impact of polyethylene functionalized with maleic anhydride (MAPE) on the mechanical properties was quantified. Compared to neat BioPEs, a maximum increase of tensile strength between 115 and 127% was obtained, for the biocomposites containing 6% w/w of MAPE and 30% w/w TMP fibers. The formulated biocomposites containing 10 and 20% TMP fibers were three-dimensional (3D) printed, by fused deposition modelling. We confirmed that TMP fibers facilitated the 3D printing and correspondingly improved the mechanical properties of the biocomposite materials.

The present study is about the enzymatic modification of thermomechanical pulp (TMP) fibers for reduction of water uptake and their use in bio-based filaments for 3D printing. Additionally, TMP was used as a fiber reinforcing material and poly(lactic acid) (PLA) as the polymer matrix. The hydrophilic TMP fibers were treated via laccase-assisted grafting of octyl gallate (OG) or lauryl gallate (LG) onto the fiber surface. The modified TMP fibers showed remarkable hydrophobic properties, as demonstrated by water contact angle measurements. Filaments reinforced with OG-treated fibers exhibited the lowest water absorption and the best interfacial adhesion with the PLA matrix. Such higher chemical compatibility between the OG-treated fibers and the PLA enabled better stress transfer from the matrix to the fibers during mechanical testing, which led to the manufacture of strong filaments for 3D printing. All of the manufactured filaments were 3D-printable, although the filaments containing OG-treated fibers yielded the best results. Hence, laccase-mediated grafting of OG onto TMP fibers is a sustainable and environmentally friendly pathway for the manufacture of fully bio-based filaments for 3D printing.