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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.

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.

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