Enhanced water absorption of tissue paper by cross-linking cellulose with poly(vinyl alcohol)

Abstract

Abstract: Tissue paper was the only paper grade whose consumption increased during 2020 in Europe. In a highly competitive context, this work explores a strategy based on bisacrylamide cross-linkers and poly(vinyl alcohol) (PVA), seeking to enhance the water uptake of pulps for tissue paper and the key properties of the resulting tissue sheets: water absorption capacity, capillarity, softness, porosity, and strength. For that, α-cellulose from cotton and a kraft hardwood pulp, in parallel, were reacted with N,N'-methylenebisacrylamide, both in the absence and in the presence of PVA. The water desorption rate of the modified polymers was monitored. Pulp blends were then mixed with a conventional softwood pulp (30%) to prepare laboratory tissue paper sheets (20 g m^-2). For cotton cellulose, cross-linking with PVA more than doubled the water uptake, up to 7.3 g/g. A significant enhancement was also obtained in the case of pulps, up to 9.6 g/g, and in the case of paper, to 11.9 g/g. This improvement was consistent with a drastic increase in porosity, and it was not detrimental to paper strength.

Keywords: Cellulose; Cross-linking; Kraft pulp; Poly(vinyl alcohol); Pulp and paper.

Scheme 1

Generic reaction of MBA-mediated crosslinking between two hydroxy polymers

Fig. 1

FTIR spectra of α-cellulose and cross-linked samples of α-cellulose and α-cellulose–PVA, using 0.5 g of MBA per gram of polymer

Fig. 2

Thermograms (a) and DTG curves (b) for the neat and cross-linked α-cellulose polymers

Fig. 3

SEM images of α-cellulose (a), cross-linked α-cellulose (b), α-cellulose + PVA 27 k (c) and α-cellulose + PVA 61 k (d). Magnification × 1000

Fig. 4

Water uptake for the different α-cellulose-based polymers. The amplitude of the tolerance intervals equals twice the standard deviation

Fig. 5

FTIR spectra of BEKP (neat and cross-linked) and BEKP-PVA cross-linked blends

Fig. 6

Thermograms (a) and DTG curves (b) for the neat and cross-linked BEKP materials

Fig. 7

SEM images of BEKP (a), cross-linked BEKP (b), BEKP + PVA 27 k (c) and BEKP + PVA 61 k (d). Magnification × 1000

Fig. 8

Water uptake for the different BEKP-based polymers

Fig. 9

Results of tensile index (a), water absorption capacity (b), and air permeability (c) for the laboratory tissue handsheets of Table 1: B0 (30%BSKP + 70%BEKP); B1 (30%BSKP + 70%MBEKP) and B2 (30%BSKP + 70%MPBEKP). The spheres at panel (a) report the bulk values in cm³/g

Fig. 10

Softness (a) and capillarity (b) for tissue handsheets, B0 (30%BSKP + 70%BEKP); B1 (30%BSKP + 70%MBEKP) and B2 (30%BSKP + 70%MPBEKP). Solid lines in (b) were obtained by fitting Eq. (1) to the experimental data