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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.

The white-rot fungus Trametes versicolor grown in submerged culture produced two laccase isoenzymes, LacI and LacII. Addition of insoluble lignocellulosic materials into the culture medium increased the total laccase activity. The proportion of laccase isoenzymes also changed depending on the lignocellulosic material employed, with ratios of activity LacII/LacI from 0.9 (barley straw) to 4.4 (grape stalks). Besides, this proportion played an important role in the dye decolourisation.

The concept presented in this paper is the utilisation of the natural flavonoids present in cotton as anchors to attach other phenolic compounds to the fiber surface. Laccase can catalyze the oxidation of flavonoids in solution producing quinones that can be further polymerised and grafted onto surface of the cotton providing yellow to brown colouration, depending on the external flavonoids used and on the reaction conditions. Factors such as temperature, time of reaction, pretreatment of cotton, mechanical agitation and the role of an organic solvent were studied in order to improve this laccase colouration reaction. After dyeing, colour measurements and fastness tests (washing, friction and weathering fastness) were performed. A strong mechanical agitation, an increased reaction temperature (from 30 to 50 • C), and the addition of an organic solvent improved dyeing. The natural flavonoids present on cotton were found to play an important role on the grafting reaction, improving dyeing and colour fastness. Since the traditional bleaching pretreatment of cotton removes these natural flavonoids from cotton, the proposed laccase colouration reaction could be carried out without a previous bleaching treatment resulting in a more environmentally friendly process.

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