Cellulose dissolution in aqueous NaOH–ZnO: effect of pulp pretreatment at macro and molecular levels

Abstract

This paper discusses the effect of hydrolytic pretreatments on pulp dissolution in the aqueous NaOH–ZnO solvent system. Eight samples were studied. They consisted of a never-dried softwood kraft pulp that was hydrolyzed under seven different conditions as well as the pulp without hydrolysis as a reference. The dissolution of the pulps was evaluated both at the macro level as well as at the molecular level based on their reactivity with 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxo-piperidium (4-AcNH-TEMPO+). The fiber properties (i.e. the extent of fibrillation, amount of fines and fiber width, coarseness, and length) as well as the chemical composition (hemicellulose and cellulose contents) and the viscosity of the pulps was investigated. The results show that hydrolysis at medium consistency (10%) was successful in increasing the solubility of cellulose. Hydrolysis at high consistency (50%), on the other hand, increased the solubility only to some extent. With extended treatment time the fibers formed aggregates and their dissolution became poor. This phenomenon could be overcome by mechanically refining the fibers after the hydrolysis. Moreover, comparison of the viscosity of the pulp over the degree of oxidation revealed that the viscosity needed to decrease below ca. 400 ml/g in order for the outer layers of the fibers to dissolve. Finally, when pulps with similar viscosities where compared against each other, the ones with the higher glucomannan contents formed gels over time. This was true also for the pulp with the lowest viscosity and the highest solubility of the studied samples.

Biosourced spherical microbeads from brewer's spent grain for sustainable personal hygiene products

“…Our results showed that a minimum of 1 wt% ZnO was deemed necessary for the complete solubilization of up to 9 wt% BSG. This observation was surprising when considering the previous studies done on the solubilization of pure cellulose 62,63 in which ZnO is described as an additive that does not directly intervene in the cellulose solubilization mechanism, but rather prevents the spontaneous gelation of solubilized polysaccharides. Moreover, these studies also stated that above 0.5 wt%, the additive reportedly has no further desirable effects and precipitates, contrasting what we observed with our more complex matrix.…”

Do flushed biodegradable wet wipes really degrade?

“…Cellulose has a strong affinity for itself and hydroxyl-containing materials such as water (Khazraji and Robert, 2013). Cellulose exhibits amphiphilic properties, due to its extensive intra and inter molecular hydrogen bonds and simultaneous hydrophobic molecular interactions, which can significantly impact its solubility in water and most organic solvents (Väisänen et al, 2021b).…”

“…For instance, filter paper consists of purified cellulose with a DP of 2900 (Malešič et al, 2005), whilst birch and dissolving pulps have DPs of 1800 and 3600, respectively (Sirviö and Lakovaara, 2021). However, the typically high DP of cellulose is a major obstacle to its chemical breakdown (Väisänen et al, 2021b).…”

“…For cellulose, abiotic hydrolytic degradation involves the molecular scission of its glycosidic bonds, which typically requires industrial acidic or alkaline conditions that are not commonly found in wastewaters (Sharma et al, 2013). Hydrolytic degradation in cellulose is also made dif-ficult due to its high degree of insolubility, inflexible molecular chains, and self-aggregation of fibres with higher hemicellulose content into gelatinous substances in water (Ghasemi et al, 2017;Väisänen et al, 2021a;Väisänen et al, 2021b). Cellulose-based wet wipes exacerbate these issues by aggre-gating in wastewaters and causing blockages (Drinkwater and Moy, 2017).…”

Production of rayon fibres from cellulosic pulps: State of the art and current developments

“…S2, Supplementary data). The latter approach implies to use of specific solvents like N-methyl morpholine-N-oxide (NMMO) (Jedvert & Heinze, 2017;Wang et al, 2016), aqueous solutions combined with ZnO, urea and/or thiourea (Chen et al, 2007;Li et al, 2015;Luo & Zhang, 2013;Väisänen et al, 2021), lithium chloride solution in N,N-dimethylacetamide (DMAc/LiCl) (Hong et al, 1998;Matsumoto et al, 2001;C. Zhang et al, 2014), ammonia/ammonium thiocyanate (NH 3 /NH 4 SCN) (Cuculo et al, 1994), dimethyl sulfoxide/ tetrabutylammonium fluoride (DMSO/TBAF) (Köhler & Heinze, 2007;Wang et al, 2016), dimethyl sulfoxide/benzyl trimethylammonium J o u r n a l P r e -p r o o f fluoride (DMSO/BTMAF) (Köhler & Heinze, 2007), molten inorganic salt hydrates (e.g., LiClO 4 •3H 2 O) Fischer & Thümmler, 2010;Leipner et al, 2000); second generation ionic liquids (Mohd et al, 2017;Morais et al, 2020;Wang et al, 2012;Xu & Wang, 2020), among others.…”