Affecting the bonding between PLA fibrils and kraft pulp for improving paper dry-strength

Abstract

<jats:title>Abstract</jats:title><jats:p>Polylactic acid fibrils (PLAf) were employed as a fiber component in papermaking. The addition of 5 wt % of PLAf to bleached kraft birch pulp increased the tensile index of the resulting 100 g/m<jats:sup>2</jats:sup> paper sheets by 20 % in comparison to sheets produced without PLAf. By heat-treating the paper sheets containing 5 wt % PLAf, a 35 % higher tensile index in comparison to sheets produced without PLAf was achieved. SEM imaging showed that the heat-treatment caused the PLAf to melt, which formed a film on the fiber web. The PLAf was ultrasonicated in an attempt to make its surface more hydrophilic and anionic and thus more compatible with cellulose. Chemical additives (cationic polyacrylamide, polyethylene imine and polyethylene glycol) were added to the PLAf/cellulose pulp mixture in order to increase the binding between the ultrasonicated PLAf and cellulose. Ultrasonication caused the PLAf length to decrease and the PLAf surface charge changed by 36 %, indicating that the PLAf became significantly more anionic. Neither ultrasonication of PLAf nor the chemical additives improved the paper sheets’ stretchability. Polyethyleneimine as an additive in an amount of 1 % increased the tensile index of heat-treated sheets made with 5 wt % of PLAf by 19 %.</jats:p>

Wood fiber-reinforced polylactic acid sheets enabled by papermaking

“…6i, where the polylactic acid fibers and wood fibers were compressed to a flat shape and stacked compactly, forming a level and smooth plate layer on the paper surface. This transformation that happened on the composite paper surface is consistent with results of a previous study (Raunio et al 2020). In the study, it was found that polylactic acid fibers deform, melt, and flow around the plant fibers during the thermoforming treatment.…”

“…These changes in the physical properties of the composite paper are consistent with previous studies (Yang et al 2019;Raunio et al 2020). In these studies, it was found that polylactic acid fibers can fill the pores and gaps in the paper due to heat conduction and pressure, thereby improving the density and mechanical properties of the composite paper.…”

“…Cao and Chen (2010) used a laboratory Hollander beater to refine the polylactic acid fiber and studied the influence on the polylactic acid fiber morphology. Raunio et al (2020) showed that the effect of ultrasonication on the physical structure and surface properties of polylactic acid fiber is similar to that of beating, namely reducing the fibril length and making its surface more hydrophilic and anionic. Yang et al (2018) pretreated the bamboo fiber and polylactic acid with polyvinyl alcohol.…”

“…Research studies have considered the effects of different treatment of polylactic acid and cellulose fiber on the physical strength of polylactic acid/cellulose fiber composite paper (Cao and Chen 2010;Yang et al 2018;Raunio et al 2020). Cao and Chen (2010) used a laboratory Hollander beater to refine the polylactic acid fiber and studied the influence on the polylactic acid fiber morphology.…”

“…In addition to beating, thermoforming is another common and essential treatment to produce polylactic acid (composite) sheet with excellent physical strength (Sousa et al 2019;Yang et al 2019;Raunio et al 2020). This process usually involves relatively high temperature (above 160 °C) and pressure (around 5 MPa) and may last from 30 s to several minutes.…”