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The authors would like to thank the financial support from Stora Enso and Aalto University. D.S. gratefully acknowledges funding from the Academy of Finland’s Flagship Programme under the projects no. 318890 and 318891 (Competence Center for Materials Bioeconomy, FinnCERES). Prehydrolysis kraft (PHK) pulps account for more than half of the global market of dissolving pulp. Characterized by high reactivity toward dissolution, their performances can still be improved by activation treatments. This study compares the dissolution kinetics in cupriethylenediamine of a hardwood and a softwood PHK pulps before and after their activation by high-solid-content mechano-enzymatic treatments. Three enzyme combinations were tested: endoglucanase (E), xylanase and mannanase (XM), and endoglucanase, xylanase, and mannanase (EXM). Xylanase and mannanase reduced the hemicellulose content of only hardwood (by max. 2.4%). Mixing and carbohydrate depolymerization decreased the dissolution time of hardwood and softwood pulps by a maximum of 63 and 30% with E, 37 and 16% with XM, and 44 and 30% with EXM, respectively. The shortening of the dissolution time was partially hindered by hornification, which increased with hemicellulose degradation. Interestingly, XM accelerated the dissolution while preserving a high weight-average molecular mass.

In this work, a novel acid-based deep eutectic solvent (DES) recycling process was developed for the pretreatment of eucalyptus wood chips in the preparation of high purity dissolving pulp. It was found that a large amount of lignin and xylan in the eucalyptus wood material were extracted in the recycling treatment with lactic acid/choline chloride. The dissolved lignin and xylan in DES were recovered by precipitation in water, and the DES solvent was regenerated by removing the water through evaporation. The residual lignin and xylan in the DES pre-treated wood chips were more readily removed in the subsequent kraft cooking and bleaching processes, yielding a high-purity dissolving pulp (DES-KP). Compared with the conventional prehydrolysis kraft based dissolving pulp (PHK), the DES-KP had a higher α-cellulose (94.02% vs. 89.81%) and a markedly higher Fock reactivity (98.94% vs. 60.97%). In addition, the DES pretreatment was also combined with oxygen-alkali cooking and ECF bleaching process, to prepare a dissolving pulp (DES-BP) with a high pulping yield (44.40%). The DES-KP pulping process was advantageous compared with the conventional PHK process in terms of the biorefinery concept, as the total utilization rate of the biomass of the eucalyptus wood chips reached 69.74%. Therefore, the DES pretreatment is a promising process for efficient biomass utilization in dissolving pulp production.

Compression molded composites were prepared through a water-assisted mixing of an aqueous suspension of poly(ethylene-co-acrylic acid), additive,and pulp fibers [thermomechanical pulp (TMP) or dissolving pulp (DP)]. The lubricating additives used were magnesium stearate (MgSt) and molybdenum disulphide (MoS2). The composite materials had dry pulp contents ranging from 30 to 70 wt% and 5 wt% additive relative to the weight of the pulp. The adsorption of the additives onto the fibers was confirmed by scanning electron microscopy and energy dispersive X-ray analysis. DMA showed that MgSt and MoS2 gave similar interphase properties for the TMP samples at all loading contents, but the combination of MgSt and MoS2 improved the overall properties of the DP-based composites. The tensile modulus, at 70 wt% fiber content (TMP or DP), increased compared to the matrix by a factor of 6.3 and 8.1, without lubricants, and by a factor of 8 and 10.7, with lubricants, respectively. The increase in melt viscosity observed for the lubricated samples was greater for the TMP-based samples containing MoS2. At a lubricant content of 5 wt%, in 30 wt% TMP, the MoS2 behaved as both a lubricant and compatibilizer.

Bamboo dissolving pulp (BP)/chitosan (CS) blend solutions were obtained by adding different weight ratios of BP and CS particles to N-methyl-morpholine-N-oxide (NMMO) solvent. The processing and membrane-forming performances of the blend solutions were studied using a rotating rheometer. The BP/CS blend solutions’ optimal processing temperature was 50 to 70 °C. When the CS weight ratio was 9.09 wt%, the viscosity of the solution decreased, which was conducive to the processing of the membrane. The BP/CS blend ultrafiltration membranes were prepared by phase transformation of the blend solutions. The results showed that the rejection rate of the BP/CS blend ultrafiltration membrane with physically added CS particles was greatly improved compared with that of the regenerated BP ultrafiltration membrane.

A NaOH/urea (or thiourea) solvent system capable of dissolving cellulose at lower temperatures is a breakthrough in cellulose chemistry, and it was reported that cellulose rapidly dissolved when it was added to a precooled aqueous solution of sodium hydroxide (NaOH) and additives. In fact, upon initiating this work, we plan to fabricate pulp fibers based cushioning packaging material based on part dissolution of dissolving pulp in aqueous NaOH/additives solutions, and found certain dissolving pulp added to a precooled aqueous solution did not show better dissolution. Therefore, this work compared the effectiveness of the direct dissolution method and freezing-thaw method in dissolving pulp fiber and pure cellulose. Three aqueous solutions were examined: 7% NaOH/12% urea, 9.5% NaOH/4.5% thiourea, and 8% NaOH/8% urea/6.5% thiourea. The dissolving capacity of three NaOH/additives aqueous solutions was analyzed by polarized optical microscopy and the dissolved cellulose proportion was determined. The results showed that the never-dried softwood dissolving pulp and bamboo dissolving pulp achieved better dissolution using freezing-thaw method than using direct dissolution method in the three aqueous solutions. The dissolving method had a negligible effect on the dissolution of each dissolving pulp in the 8% NaOH/8% urea/6.5% thiourea solution. It seems that the direct dissolution method was more suitable for oven-dried microcrystalline cellulose with a low degree of polymerization (DP) and the freezing-thaw method was more suitable for never-dried pulp cellulose fibers with a higher DP.

Dissolving pulps are high-grade cellulose pulps that have minimum amount of non-cellulosic impurities. Dissolving pulps are the basic source for the manufacturing of several cellulosic products such as viscose, lyocell, cellulose acetates, cellulose nitrates, carboxymethyl-cellulose, etc. Dissolving pulps are mainly manufactured by pre-hydrolysis kraft and acid sulphite pulping. A high reactivity of dissolving pulps is desirable for its eco-friendly utilization for several purposes. Several approaches including mechanical, chemical, ultrasonic, and enzymatic treatments have been employed for the improvement of pulp reactivity. This review mainly focussed on pulp reactivity improvement through enzymatic approaches. Cellulases and xylanase have been proved effective for the improvement of pulp reactivity of dissolving pulp from different sources. The different combinations of cellulase, xylanase, and mechanical refining have been tested and found more effective rather than the single one.

Research has been undergoing for years on the development of renewable and green polymers to replace petroleum-based plastics. Herein, inexpensive and sustainable films were made by applying some mild etherification reactions on kraft and dissolving pulps to obtain carboxymethylated fibers (CMFs). CMFs were subsequently dissolved in alkaline solutions then cast, immersed in an acid bath, washed, and dried to form regenerated cellulose-based films, which do not dissolve in water. Pulps were chemically analyzed and films were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), field emission scanning electron microscopy (FE-SEM), and UV–vis, and their physical and strength properties were measured. It was found that kraft pulp films were denser, stronger, more transparent and crystalline, had a smoother surface, and were more water absorbent than the dissolving pulp films due to their higher hemicellulose content. Overall, low cellulose carboxymethylation as a scalable method is promising for making biodegradable, recyclable, insoluble, transparent, and strong films that can compete with cellophane and various plastic products used in packaging.

In this study, eucalyptus raw materials were pre-hydrolyzed and cellulose nanofibrils (CNFs) were prepared. The effect of prehydrolysis conditions on the micro-structure of dissolving pulp-based CNFs was studied, and the hydrogen bond change and crystal structure in CNFs were analyzed by FTIR peak fitting and X-ray diffractometer. The results showed that prehydrolysis would not change the crystal structure of CNFs, but could break up the intermolecular and intramolecular hydrogen bonds of CNFs. An increase in the prehydrolysis temperature would promote the breaking of the intramolecular hydrogen bonds in the amorphous region of CNFs, which leads to an increase in the crystallinity of CNFs. Long-time prehydrolysis treatments not only broke up the intermolecular hydrogen bonds in the amorphous region of CNFs, but also intramolecular hydrogen bonding in the crystalline region. Analyses of SEM and gas adsorption revealed that some nanopores became more and more large, and some small nanopores appeared on the surface of the CNFs with the increase of prehydrolysis intensity. The appearance of large or small nanopores on the surface of the CNFs were likely due to the breakage of hydrogen bonds in CNFs. The intermolecular and intramolecular hydrogen bonds of cellulose could be destroyed by changing prehydrolysis conditions, which resulted in appearance of a lot of nanopores on the surface of the CNFs. The DSC and TGA analyses revealed that the prehydrolysis has a little impact on the thermal stability of CNFs. This work can provide a tunable pathway of micro-structure of CNFs by controlling prehydrolysis process.

The garment industry is the backbone of Bangladesh’s economy, which imports 30000 metric tons of rayon fiber every year. Bangladesh used to have a rayon plant, but it was shut down a long time ago. At present, the establishment of a new rayon plant in Bangladesh has become an objective. As a forest deficient country, non-wood plants need to be explored for rayon grade dissolving pulp production. Therefore, in this paper, prehydrolysis potassium hydroxide (KOH) pulping process has been investigated for dissolving pulp production from rice and wheat straws, corn stalk, dhaincha and jute stick. The lowest prehydrolysis yield was 70.1% obtained for corn stalks and the highest prehydrolysis yield was 92.1% for wheat straw. The KOH cooking of prehydrolysed rice straw, wheat straw and corn stalks with 14% alkali charge produced pulps with kappa numbers of 5.7, 4.5 and 8.8, respectively, while prehydrolysed dhaincha and jute stick needed 18% alkali charge to get a bleachable pulp. Dhaincha showed the highest pulp yield (37.3%) with the highest α-cellulose content (92.24%) and the lowest residual pentosan content (5.37%). Further purification with cold KOH extraction increased purity by 3% for rice straw pulp and by 1% for dhaincha, wheat straw, corn stalks and jute stick pulp. Thus, the dissolving pulp produced in this study by the prehydrolysis KOH process can meet the criteria for rayon grade pulp.

TEMPO-oxidised cellulose fibres are often explored as nano-reinforcement for polymers. However, it is unclear whether micrometre-sized TEMPO-oxidised cellulose fibres also possess similar reinforcing potential. In this work, we report the mechanical response of polypropylene (PP) composites reinforced with TEMPO-oxidised cellulose (TOC) of different fibre widths. Micrometre-sized TOC fibres (TOCF) containing sodium carboxylate (TOCF-Na) and free hydroxyl (TOCF-H) groups, as well as nano-sized TOC nanofibrils (TOCN) were produced from dissolving pulp and incorporated into PP matrix via melt-extrusion. It was found that model PP composites containing micrometre-sized TOCF-Na and TOCF-H possessed the highest tensile modulus of up to 2.5 GPa; 40% improvement over neat PP and 30% increase over PP/TOCN composite. No significant differences in the tensile strength of PP/TOCF-Na and PP/TOCF-H composites were observed when compared to neat PP. The incorporation of nano-sized TOCN into PP however, led to a 6% decrease in tensile strength. Single-edge notched beam fracture toughness test further showed that PP/TOCN composite possessed the lowest fracture toughness of 2.52 MPa m1/2; a decrease of 18% over PP reinforced with micrometre-sized TOCF-Na and TOCF-H. Our study shows that micrometre-sized TOCFs serve as better reinforcement for polymers compared to nano-sized TOCN. This is attributed to the better dispersion of TOCF in the PP matrix. Furthermore, the presence of surface microfibrillation on TOCFs also enhanced the quality of the TOCF-PP interface through mechanical interlocking and local stiffening of the PP matrix.

Three approaches were examined for the reutilization of cold caustic extraction (CCE) lye. The term CCE lye refers here to the used NaOH solution with relatively high alkali content, which could be wasted if not reused properly. The results showed that CCE lye can be effectively applied in deinking, alkaline hydrogen peroxide bleaching, and oxygen delignification processes. The CCE lye improved the physical strength of the dried sheet of pulp, as the tensile index increased by 17.9% to 40.5%, the tear index increased by 2.9% to 22.2%, and the burst index increased by 10.5% to 41.0%. The results demonstrated the feasibility of integrating the CCE process of dissolving pulp production with regular pulping and bleaching processes.

In this laboratory study, a hardwood bleached kraft pulp (HBKP) was converted to dissolving pulp by removing hemicellulose using organic electrolyte solutions (OES), consisting of ionic liquid (1-ethyl-3-methylimidazolium acetate (EminAc)) and a polar organic solvent γ-valerolactone (GVL). The molar ratio of GVL/EmimAc, and temperature have significant effect on the swelling of HBKP fibers, thus the hemicellulose dissolution/removal process. Under the optimal conditions of GVL/EmimAc molar ratio of 4 and 60 °C, hemicellulose was effectively removed, leading to the formation of a dissolving pulp with yield of 76%, cellulose content of 91%, Fock reactivity of 56.8% and viscosity of 723 mL/g. Furthermore, the potential of using EmimAc/GVL/water ternary system to selectively remove hemicelluloses from the same HBKP was studied. The GVL/EmimAc/water ratio of 2:1:1 at 60 °C showed promising results, with yield of 76.7%, and cellulose content of 94.8%.

High-definition automated optical analysis was used to observe the morphological changes of bleached hardwood dissolving pulp during oxidation mediated by (2,2,6,6-tetramethylpiperidn-1-yl)oxyl (TE...

Dissolving pulp production is mostly reliant on wood, which drastically depletes forest resources. To prevent the over-exploitation, the efforts were required by considering waste materials utilization. Therefore, a comprehensive assessment to account for environmental impacts was needed. The purpose of this research was to determine the environmental impact of empty fruit bunches (EFB) utilization from oil palms as a promising raw material substitute for wood in the production of dissolving pulp and furfural as co-product. The consequential life cycle assessment (cLCA) was performed by following the methodology in ISO 14040. Inventory for the input–output materials and energies for the proposed integrated dissolving pulp and furfural co-production process was evaluated based on laboratory-scale experiments. Meanwhile, the field survey as a reference for the existing practice in the conventional dissolving pulp industry was conducted. The SimaPro v8.0.5® software was used for the LCA calculation with the Centrum voor Milieuwetenschappen Leiden (CML) environmental impact assessment method. Several environmental impact categories, such as acidification, global warming, eutrophication, and human toxicity potential, were quantified. This study examined three proposed scenarios for dissolving pulp and furfural co-production compared with the conventional dissolving pulp production. In the Scenario 1, 50% of the wood consumption was replaced by EFB and applied to acid prehydrolysis/soda cooking followed by ECF bleaching, with an additional process to co-produce furfural. In the Scenario 2, 100% of wood consumption was replaced by EFB, with the same cooking and bleaching parameters as those in Scenario 1. In the Scenario 3, 100% of wood consumption was replaced by EFB, and the acid was replaced by water in the prehydrolysis process to improve the total environmental performance with the same conditions as the previous scenarios. The Scenario 3 was the most promising scenario and had the lowest environmental impact. This research was conducted to propose EFB, which is environmentally sustainable and economically profitable, as a wood substitute in the co-production of dissolving pulp and furfural. The scenarios were proposed and compared with the existing practices. Based on the cLCA approach, this study recommended the EFB as a promising raw material and referred to Scenario 3 for the environmentally friendly system production.

In this study, aimed at valorization of industrial xylan-rich hemicelluloses (a by-product of dissolving pulp process), water-soluble hemicelluloses were fabricated with mild acetylation in 1-ethyl-3-methylimidazolium acetate ionic liquid (EmimAc) and dichloroacetyl chloride (Cl2AcCl) system by a facile and novel method. The structure of the acetylated hemicelluloses was characterized by FT-IR and NMR spectra. The resultant modified products could fully dissolve in water with the degree of substitution (DS) valued between 0.17 and 0.37. Structural characterization indicated that the modified hemicelluloses were chiefly composed of the (1 → 4)-linked β-D-Xylp backbone with hydroxyl or -COCH3 linked to O-2 and O-3 of the Xylp units. Moreover, the mild acetylation was achieved by one-pot method, in which the hemicelluloses reacted with mixed anhydride produced between EmimAc and Cl2AcCl rather than Cl2AcCl. Rheological behavior measurements revealed that acetylated hemicelluloses solutions showed shear-thinning behavior and indicated lower viscosity compared with those of the referenced hemicelluloses. The excellent water-solubility of industrial hemicelluloses would widen its application field and be easier for its conversion into desired chemicals.

In this paper hemicellulose was separated by using 1-ethyl-3-methylimidazolium acetate (EmimAc, an ionic liquid) -water mixtures from a paper grade market bleached hardwood kraft pulp to produce dissolving pulp. Pure EmimAc dissolves pulp fibers completely in 30 min at ambient temperatures. By adding water (as an antisolvent to EmimAc system) the cellulose dissolution decreases and by optimizing the conditions, hemicellulose is largely removed while cellulose remains as the solid residue (dissolving pulp). At optimal conditions: molar ratio of water to EmimAc of 2, 60 °C, an alpha-cellulose content of 92.2%, with a high yield (78 wt%) was obtained. The viscosity of the solvent mixture decreases by increasing water to EmimAc molar ratio, which improves the mobility of ions, thus, facilitating their penetration into pores and lumens of the fibers during the dissolution process. Cellulose purity increases and purified cellulose yield decreases with the increases in temperature and water content (up to 2 wt%) in the mixture. This study implies that the optimal EmimAc/water mixture is an effective system to separate hemicellulose from hemicellulose/cellulose matrix.

The aim of this study is to present the design, optimization and modelling of a chemical recovery system for a novel CS2-free viscose-type process that entails dissolution of pre-treated dissolving pulp in a continuous-flow reactor in cold alkali and wet spinning of cellulose in sodium carbonate solutions. Technologies already known to other industries for the recovery and reuse of chemicals, such as causticizing, recalcination, recarbonization and freeze-separation, were used. Chemical equilibria simulations were performed with OLI Studio 9.5, with the purpose to select experimental conditions which avoid undesired precipitations in each unit operation. Synthetic solutions mimicking the spent coagulation liquor were used in the laboratorial experiments. The proposed chemical recovery system was shown to be technically feasible and reduce chemical make-ups to a minimum of 45 kg/ton of NaOH and 4 kg/ton of H2SO4. Small amounts of Zn are expected to precipitate during recarbonization of the coagulation liquor at 30 °C and causticizing at 98 °C. Thus, a filter for ZnO particles should be included in the design of the recarbonization unit and a continuous purge of lime mud and input of fresh lime make-up should be needed to keep burnt lime availability at an acceptable level. Overall, the results presented in this study portray a solution to reduce operating costs and the environmental impact of novel viscose-type processes with alkaline spin dopes and wet spinning of cellulose in sodium carbonate solutions.

Cellulose can be directly dissolved in cold alkali without derivatization. However, this requires low cellulose molecular weight, i. e. low pulp viscosity, preferably below 300 mL g−1. This can be achieved by for example acid or enzymatic hydrolysis of the dissolving pulp. However, it would be beneficial to manufacture pulp with sufficiently low viscosity without an additional treatment stage prior to dissolution. Unit processes in pulping can be operated in such a way as to reduce the molecular weight of cellulose. The approach of the study was to modify the conditions in unit pulping processes in order to obtain a low pulp viscosity of fully bleached prehydrolysis kraft pulp. A high charge of alkali in the oxygen delignification reduced the cellulose molecular weight significantly. Increased temperature, 120 °C compared to 98 °C, had also a significant effect on viscosity. By performing peroxide bleaching at acidic pH, the viscosity could be sufficiently reduced even when oxygen delignification was performed at lower temperature. However, for high brightness, a chlorine dioxide stage is needed.

High reactivity of dissolving pulp is the basic parameter for achieving the deeply advanced applications of natural cellulosic fiber in the sustainable society. Here we developed a simple yet effective strategy of microwave treatment to promote the reactive ability of pulp fibers. The microwave radiation can induce the rotation and vibration of water molecules due to the polarization effect, where the water molecules functioned as the “spinning cutter” to collide and attack the cell wall of fibers. The morphologies and structure of fibers were controllably modified to have the rough surface and loose structure, while the cellulose purity and fiber yield were well maintained during the process. A 5 min and 500 W microwave treatment can improve the Fock reactivity of pulp fibers from 49 to 83% with a super-high fiber yield of 99.5%. The effective approach of microwave treatment presents a promising candidate for manufacturing high-performance cellulosic fibers.

The aim of this study was the experimental demonstration and assessment of a novel lignocellulose biorefinery (LCB) for the integration of beech wood-based products as platform and fine chemicals. The process sequence included organosolv pulping followed by pulp bleaching, hydrothermal conversion of hemicellulose to xylose and its purification, fermentation of xylose to malic acid, and base-catalyzed lignin depolymerization (BCD). The resulting products were dissolving pulp, phenolic BCD-oligomers, and malic acid. The state of the art for these technologies is their experimental proof of concept and validation at a laboratory- and pilot-scale and has a technology readiness level (TRL) of 3–4. By integrating and optimizing the single-process steps into one LCB, the TRL could be increased to 5. Based on the findings of the experimental studies, a LCB converting 50,000 dry metric tonnes ($$ \hat{=} $$ = ̂ 38.7 MW) of beech wood annually was simulated with Aspen Plus. Mass and energy balances showed that 14,616 dry metric tonnes of dissolving pulp, 5174 dry metric tonnes of BCD-oligomers, and 4077 dry metric tonnes of malic acid annually could be produced. The total energy efficiency is 40.3%. The calculation of specific production costs demonstrated the marketability of dissolving pulp (1350 €/t) and BCD-oligomers (2180 €/t), whereas malic acid (4750 €/t) is not yet competitive. Environmental assessment showed reduced greenhouse gas (GHG) emissions from the production of BCD-oligomers and malic acid and higher GHG emissions from the production of dissolving pulp compared with the reference products. In total, the examined LCB would contribute to the mitigation of global warming.

In this work, a surface cationized inorganic–organic hybrid foam was produced from porous geopolymer (GP) and cellulose nanocrystals (CNCs). GPs were synthesized from alkali-activated metakaolin using H₂O₂ as a blowing agent and hexadecyltrimethylammonium bromide (CTAB) as a surfactant. These highly porous GPs were combined at pH 7.5 with cationic CNCs that had been synthesized from dissolving pulp through periodate oxidation followed by cationization in a deep eutectic solvent. The GP-CNC hybrid foams were employed as reactive filters in the removal of the anionic dye, methyl orange (MO; 5–10 mg/L, pH 7). The effects of a mild acid wash and thermal treatments on the structure, properties, and adsorption capacity of the GPs with CNCs and MO were investigated. The CNCs aligned as films and filaments on the surfaces of the neutralized GPs and the addition of CNCs improved MO removal by up to 84% compared with the reference sample. In addition, CTAB was found to disrupt the attachment of CNCs on the pores and improve adsorption of MO in the GPs with and without CNCs.

Three industrial Eucalyptus globulus acid sulphite dissolving pulps of different intrinsic viscosity (ca. 490–570 cm3/g) with similar xylan content (2.4–3.0%) were partially (ca. 60%) converted to cellulose II by treatment with 12% NaOH and hornified by drying for 8 h at 105 °C to induce changes in physical structure. All three initial and modified pulps were analysed on their Fock reactivity method and Chinese filterability. These dissolving pulps were also examined for the crystallinity degree and the crystallite dimensions assessed by wide-angle X-ray scattering and the fibril aggregation assessed by solid-state 13C nuclear magnetic resonance. The results showed that the reactivity of the dissolving pulp was negatively correlated with the degree of cellulose crystallinity and depended almost linearly on the lateral dimension of the fibril and the dimensions of the fibril aggregates. In hornified pulps, the effect of cellulose physical structure on reactivity was even more pronounced than the intrinsic viscosity of the dissolving pulp. In addition, no unambiguous dependence between the reactivity and the filterability of dissolving pulps was found. Filterability did not correlate clearly with lateral dimension of fibril or fibril aggregates, but depended only on pulp viscosity.

The influence of drying on cellulose accessibility and enzymatic hydrolysis was assessed. Dissolving pulp was differentially dried by freeze-, air- and oven-drying at 50 °C and subsequently hydrolyzed using the commercial CTec 3 cellulase preparation. It was apparent that drying reduced the ease of enzymatic hydrolysis of all of the substrates with a pronounced reduction (48%) exhibited by the oven-dried pulp. To assess if the ease of hydrolysis was due to enzyme accessibility to the substrate, microscopy (SEM), FTIR spectroscopy, water retention value (WRV), fiber aspect ratio analysis, Simons' stain and the selective binding of Fluorescent Protein-tagged Carbohydrate Binding Modules (FP-CBMs): CBM3a (crystalline cellulose) and CBM17 (amorphous cellulose) in combination with confocal laser scanning microscopy (CLSM) were used. The combined methods indicated that, if the gross characteristics of the substrate limited enzyme accessibility, the cellulases, as represented by the FP-CBMs, could not in turn access the finer structural components of the cellulosic substrates.

A pre-hydrolysis Kraft pulping (PHK) process that was used to make dissolving pulp was enhanced by replacing conventional white liquor (WL) neutralization with green liquor (GL) neutralization prior to Kraft pulping. This resulted in a 10% increase in dissolving pulp production, and significant chemical savings, without compromising pulp reactivity. When the possible influence of the alkaline charge on fibre properties was assessed using methods such as viscosity, Simon's stain, Size Exclusion Chromatography (SEC) and SEM, it was apparent that stronger alkaline treatments (WL) resulted increased cellulose degradation, a lower cellulose DP and a slightly larger surface area. When these methods were complemented with an assay based on the selective binding of site-specific carbohydrate-binding modules (CBMs), it was apparent that green liquor (GL) neutralization resulted in an increase in less-ordered cellulose being exposed. This likely contributed to its higher reactivity despite its lower overall surface area.

The increasing demand for cellulosic fibres is continuously driven by the growing earth population and requirements of the textile industry. The annual cotton production of ca. 25 million tons is no longer enough to meet the market demands. This market gap of cellulosic fibres is progressively filled by regenerated cellulosic fibres derived from the dissolving pulp. The conventional industrial process of viscose production is far from being environmentally friendly due to the use of hazardous reagents. Alternatively, new trends in the production of regenerated fibres are related to the direct dissolution of cellulose in appropriate environmentally sound recyclable solvents, allowing high quality rayon fibres. This article reviews the sources of dissolving pulps used for the production of viscose and its quality parameters related to the performance of viscose production. The prospective cellulose regeneration processes, both commercialized and under development, are reviewed regarding current and future developments in the area.

The direct dissolution and joint spinning of cellulose and lignin in BmimChc and EmimAc were investigated by using blends of dissolving pulp and kraft lignin as a model for subsequent processing real lignocellulosics wood-TMP and wheat straw. The solubility of cellulose and lignin in the solvents is represented by ternary phase diagrams. The limits of solubility for different cellulose/lignin ratios were found to be an approximately linear function of the lignin content. Air-gap spinning was realized for the model compound with up to 50 % lignin loading with both ionic liquids, whereas TMP and wheat straw could be processed acceptably only with BmimChc. The resulting bicomponent model fibers exhibit a rather high level of tenacity (33 to 46 cN/tex) and modulus (1500–2000 cN/tex). The cellulose fraction is dominating the fiber morphology while the lignin is incorporated in the core and somewhat leached out from the shell region.

In this study, a novel type of high-strength regenerated cellulose composite fiber reinforced with cellulose nanofibrils (CNFs) and nanosilica (nano-SiO2) was prepared. Adding 1% CNF and 1% nano-SiO2 to pulp/AMIMCl improved the tensile strength of the composite cellulose by 47.46%. The surface of the regenerated fiber exhibited a scaly structure with pores, which could be reduced by adding CNF and nano-SiO2, resulting in the enhancement of physical strength of regenerated fibers. The cellulose/AMIMCl mixture with or without the addition of nanomaterials performed as shear thinning fluids, also known as “pseudoplastic” fluids. Increasing the temperature lowered the viscosity. The yield stress and viscosity sequences were as follows: RCF-CNF2 &gt, RCF-CNF2-SiO22 &gt, RCF-SiO22 &gt, RCF &gt, RCF-CNF1-SiO21. Under the same oscillation frequency, G’ and G” decreased with the increase of temperature, which indicated a reduction in viscoelasticity. A preferred cellulose/AMIMCl mixture was obtained with the addition of 1% CNF and 1% nano-SiO2, by which the viscosity and shear stress of the adhesive were significantly reduced at 80 °C.

The presence of lignin hampers the utilization of hemicelluloses in the pre-hydrolysis liquor (PHL) from the kraft-based dissolving pulp production process. In this paper, a novel process for removing lignin from PHL was proposed by effectively recycling catalysts of BiOCl/BiOBr. During the whole process, BiOCl and BiOBr were not only adsorbents for removing lignin, but also photocatalysts for degrading lignin. The results showed that BiOCl and BiOBr treatments caused 36.3% and 33.9% lignin removal, respectively, at the optimized conditions, and the losses of hemicellulose-derived saccharides (HDS) were both 0.1%. The catalysts could be regenerated by simple photocatalytic treatment and obtain considerable CO and CO2. After 15 h of illumination, 49.9 μmol CO and 553.0 μmol CO2 were produced by BiOCl, and 38.7 μmol CO and 484.3 μmol CO2 were produced by BiOBr. Therefore, both BiOCl and BiOBr exhibit excellent adsorption and photocatalytic properties for lignin removal from pre-hydrolysis.

The production of regenerated cellulosic fibres, such as viscose, modal and lyocell, is based mainly on the use of dissolving wood pulp as raw material. Enzymatic processes are an excellent alternative to conventional chemical routes in the production of dissolving pulp, in terms of energy efficiency, reagent consumption and pulp yield. The two main characteristics of a dissolving pulp are the cellulose purity and the molecular weight, both of which can be controlled with the aid of enzymes. A purification process for paper-grade kraft pulp has been proposed, based on the use of xylanases in combination with hot and cold caustic extraction, without the conventional pre-hydrolysis step before kraft pulping. This enzyme aided purification allowed the production of a dissolving pulp that met the specifications for the manufacture of viscose, < 3% xylan, > 92% ISO brightness and 70% Fock’s reactivity. Endoglucanases (EGs) can efficiently reduce the average molecular weight of the cellulose while simultaneously increasing the pulp reactivity for viscose production. It is shown in this study that lytic polysaccharide monooxygenases act synergistically with EGs in the modification of bleached dissolving pulp.

Cellulose is the most abundant renewable resource which has found a diverse range of applications. Cellulose dissolution is a significant property for manufacturing man-made cellulosic fiber through viscose process. Crystalline microfibrillar structure and relatively high ordered packing of polymeric chains contribute to recalcitrance and poor reactivity of cellulose. One of the most common methods to improve cellulose dissolution is cellulase treatment. Herein, cellulase treatment at different doses was studied to explore the correlation of cellulose dissolution with crystallinity. Pulp showed improvement in Fock reactivity and other properties related to viscose application. But contrary to previous studies, cellulose crystallinity as determined by XRD and FTIR did not correlate with Fock reactivity at a higher dose of cellulase. The results indicated some complex mechanism to be involved between the cellulose dissolution and crystallinity than a simple negative correlation. Cellulase treatment at 150 HCU/g resulted in the upgraded pulp suitable for viscose application.

This study investigates a fast dissolution and regeneration pretreatment to produce regenerated cellulose nanofibers (RCNFs) via mechanical disintegration. Two cellulose pulps, namely, birch and dissolving pulps, with degree of polymerizations of 1800 and 3600, respectively, were rapidly dissolved in dimethyl sulfoxide (DMSO) by using tetraethylammonium hydroxide (TEAOH) as aqueous electrolyte at room temperature. When TEAOH (35 wt % in water) was added to the pulp-DMSO dispersion (pulp:DMSO and TEAOH:DMSO weight ratios of 1:90 and 1:9, respectively), 95% of the dissolving pulp and 85% of the birch pulp fibers dissolved almost immediately. Addition of water caused the regeneration of cellulose without any chemical modification and only a minor decrease of DP, whereas the crystallinity structure of cellulose transformed from cellulose I to cellulose II. The regenerated cellulose could then be mechanically disintegrated into nanosized fibers with only a few passes through a microfluidizer, and RCNF showed fibrous structure. The specific tensile strength of the film produced from both RCNFs exceeded 100 kN·m/kg, and overall mechanical properties of RCNF produced from birch pulp were in line with reference CNF produced by using extensive mechanical disintegration. Although the thermal stability of RCNFs was slightly lower compared to their corresponding original cellulose pulp, the onset temperature of degradation of RCNFs was over 270 °C.

Prehydrolysis is an essential step for utilizing biomass, particularly in the Kraft-based dissolving pulp process. Once the hemicellulose was effectively extracted, it can not only upgrade the dissolving pulp, but also arise additional revenue by converting value-added products. Herein, sodium dodecyl benzene sulfonate (SDBS) was used to enhance the hemicellulose removal from poplar wood chips during mild acid hydrolysis. SDBS addition could reduce the surface tension, thus increasing the diffusion of hydrogen ion and promoting the hemicellulose and lignin dissolution. The hemicellulose removal was increased from 42.5 to 54.7% by adding SDBS in comparison with the control under condition of 170 °C and 2 h. Additionally, the lignin removal was increased from 9.6 to 19.1%. Gel permeate chronograph, scanning electron microscope, and heteronuclear single quantum coherence spectroscopy support the positive effect of SDBS addition. The properties of dissolving pulp prepared from surfactant assisted pretreatment are comparable/better than that derived from acid pretreatment. It opened a sustainable and economical way to extract hemicellulose from lignocellulose. A new surfactant assisted acid prehydrolysis process for enhancing biomass pretreatment.

The soluble lignin present in the pre-hydrolysis liquor (PHL) is detrimental for value-added utilization of the PHL from production of kraft-based dissolving pulp. In this paper, the soluble lignin was separated from PHL by activated carbon adsorption and subsequent desorption with methanol. The structural characteristics of the soluble and dioxane lignins (from bamboo-willow material) were analyzed by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA). The FTIR and proton-NMR results showed that cleavage of β-O-4 aryl-ether linkages and demethylation occurred in the lignin structure during the pre-hydrolysis. The main linkages between structural monomeric units of the soluble lignin were β-β, β-5, β-1, and β-O-4. Additionally, the TGA results showed that the residual char yield at 800 °C of the soluble and dioxane lignins were 33.4% and 35.3%, respectively. Therefore, the soluble lignin obtained from PHL possessed thermal stability comparable to that of dioxane lignin, and can be used as a renewable source for carbon fiber.

Cellulase treatment is a promising approach to activate dissolving pulp in terms of viscosity and reactivity. However, the enzyme cost is still too high, which hinders the scale up application. In this study, Tween 80 was introduced into the enzymatic system for improving the cellulase efficiency by improving the enzyme accessibility and its stability. Results show that the cellulose chain scission rate was more than 2 times higher with the addition of Tween 80 (0.1 g/L) in comparison to the control, which is mainly attributed to decreased surface tension (by 28.0% with the addition of 0.1 g/L Tween) and increased relative cellulase activity (by 9% at 48 h and 55°C). As a result, Tween 80 assisted cellulase activation gave a higher cellulasic efficiency in terms of viscosity decrease and Fock reactivity increase. Other pulp properties (alkali solubility, molecular weight distribution) and pulp yield were all favorable, supporting the conclusion that the Tween 80- assisted cellulase treatment process has a great potential to improve the cellulase treatment performance of dissolving pulp.

The cellulose reactivity is a critical parameter in the manufacturing process of viscose rayon with dissolving pulp. In this study, an ultrasonic treatment, which is considered as an environmentally friendly pretreatment technology, was applied to a softwood prehydrolysis kraft-based dissolving pulp for enhancement of accessibility/reactivity in terms of viscose rayon production through cavitation of ultrasound. Results show that the ultrasonic treatment can lead to the decrease of cellulose crystallinity, the increase of specific surface area and average pore diameter in fibers, and the increase of water retention value due to the release of energy induced by the collapse of the gas/vapor bubbles. As a consequence, the Fock reactivity and viscose filterability of dissolving pulp is enhanced significantly after ultrasonic treatment. Other parameters, such as intrinsic viscosity and fiber morphology were also determined.

Hemicellulose separation/removal from cellulosic fibers is critical for manufacturing high-purity cellulose (dissolving pulp). In this communication, a combined system of using both urea and NaOH was studied to enhance the separation/removal of hemicellulose from a softwood sulfite dissolving pulp. The urea/NaOH treatment significantly improves the hemicellulose removal. With a 1% urea concentration and 5% NaOH concentration, the hemicellulose content of resultant pulp decreased from 11.22 to 3.99%, which was compared to 6.56% of the control NaOH treatment (without the addition of urea under otherwise the same conditions). Consequently, the alpha-cellulose content of the urea/NaOH-treated pulp was higher than that from the control NaOH treatment (96.02% and 93.94%, respectively). Additionally, the urea/NaOH process was more selective in terms of removing hemicellulose. The underlying mechanism to account for the improved performance of the urea/NaOH process will be discussed.

The swelling and dissolution of cellulose are key parameters in the production of regenerated cellulose fibers. Since cotton is almost pure cellulose, it has been proposed that the recycling of cotton textiles may be accomplished through incorporating the cotton textiles into the production of regenerated cellulosic fibers. In this study, the supramolecular structure before and after pretreatment was characterized using solid-state carbon-13 nuclear magnetic resonance (13C NMR), and the findings related to the swelling of dissolving pulp and cotton were quantified with a fiber analyzer. The cotton and dissolving pulp samples were subjected to three different pretreatments: mild acid hydrolysis, acid hydrolysis in ethanol, and a hydrothermal treatment. The results showed that cotton was harder to swell than the dissolving pulp. This indicated that either waste cotton requires another type of activating pretreatment than those included in this study or very good solvents if it is to be included in the production of regenerated fibers.

Bleached kraft pulps from Eucalyptus benthamii, E. globulus, E. nitens and E. nitens × E. globulus hybrid were prepared in laboratory scale and upgraded to dissolving-grade via cold caustic extraction (CCE) and dilute acid hydrolysis. The CCE reduced the alkali solubility (S18) of bleached kraft pulps from 11.8–16.4% to 4.5–6.3% after extraction with 5% (w/v) NaOH, and to 0.9–1.7% after extraction with 10% (w/v) NaOH. The dilute acid hydrolysis with 3% H2SO4 reduced the intrinsic viscosity of CCE-treated kraft pulps from 800–900 to 110–450 ml/g. E. nitens and E. benthamii displayed the most contrasting values for S18 and intrinsic viscosity after CCE and acid hydrolysis treatments. The X-ray diffraction results showed that the crystallinity index of bleached kraft pulps followed the order: E. benthamii > E. globulus > En × Eg > E. nitens. Regarding cellulose reactivity, the Fock reactivity of the bleached kraft pulps was in the range of 34.7–41.3%. After CCE, the pulps reactivity was reduced to 13.7–25.4%, whereas after acid hydrolysis it was increased to 40.7–87.5%. E. benthamii and E. nitens pulps showed to be the less reactive pulps after pulp activation via acid hydrolysis, whereas E. globulus and the hybrid showed to be the most reactive pulps towards xanthation. It was observed that different Eucalyptus species can lead to kraft pulps with different requirements towards xanthation, and that the inherent features of wood and how they are processed are of outmost importance for the final use of kraft-based dissolving pulp from a given wood species.

Improvements on reactivity and viscosity control of the prehydrolysis kraft (PHK) dissolving pulp in an efficient and sustainable way is of both fundamental and practical interest. In this study, we proposed a novel concept of using a simultaneous treatment consisting of mechanical refining (R) and phosphotungstic acid (PTA) catalysis (defined as R-PTAsim) for this purpose. Results showed that the simultaneous process (R- PTAsim) was more effective in improving Fock reactivity, from 47.2 to 83.5%, while the sequential process (initial refining, followed by PTA catalysis, defined as R-PTAseq) increased from 47.2 to 77.2%. The viscosity of resultant pulps was 411 mL/g and 428 mL/g for the R- PTAsim and the R-PTAseq, respectively. The explanations are: (1) the PTA catalysis induces cellulose depolymerization and morphological changes of fibers, and improves the mechanical refining efficiency, (2) mechanical refining facilitates the diffusion/adsorption of PTA into cellulose fibers and further enhances the PTA catalysis, (3) an enhanced synergistic effect occurs in simultaneous treatment. It was demonstrated that PTA has a high chemical stability and recyclability/reusability. This concept can offer a new pathway for sustainable manufacturing high- quality dissolving pulp.

Recently, cellulose films or nanopapers have aroused great attention due to their potential for utilization in photoelectric materials. In this study, transparent cellulose films were prepared from TEMPO-oxidized cellulose fibers by the casting method after they were ultrasonicated to improve the light transmittance and haze. It was found that powerful ultrasonication initiated severe cellulose fiber flattening, fibrillation, and breakage. Therefore, films with compact structures and smooth surfaces could be prepared, resulting in high transparency and tensile strength. However, excessive ultrasonic treatment caused transmittance haze loss. By controlling the ultrasonic power within the range of 180–360 W, transparent films (transmittance of ~ 90%) with 51–76% haze were obtained.

Sugar-containing hydrolysates as byproducts of dissolving pulp production could be a source of alcohol production, but the presence of fermentation inhibitors hampers this utilization route. In the present study, nine types of phenolic inhibitors were found and their removal by ligninases gave satisfactory results. Laccase removed 73.1% of phenolic inhibitors and produced three new aromatic compounds, whereas the combination of laccase and lignin peroxidase (as a dual-enzyme treatment) resulted in a removal rate of 91.7% without new product formation. Xylose as the main sugar in the hydrolysate was retained with a 90% yield, regardless of the enzymatic treatment, which modified, however, the kinetics of yeast growth. Laccase improved cells’ maximum specific growth rate (v max) from 0.115 to 0.154 and reduced the saturation constant (K s ) from 53.4 to 42.5, whereas the dual-enzyme system improved v max to 0.206 and reduced K s to 42.44. The greater v max and the smaller K s imply a better growth rate, and accordingly, the dual-enzyme system is better suited for removing phenolic inhibitors.

Bamboo-willow is a type of fast-growing wood with a high hemicellulose content. In the present study, the effects of phosphoric acid addition on the main components of bamboo-willow and pre-hydrolysis liquor (PHL) were explored, and subsequently the pre-hydrolyzed bamboo-willow chips were cooked, O–H–P bleached, and acid post-treated to produce dissolving pulp. The results showed that adding phosphoric acid to the pre-hydrolysis stage effectively removed hemicellulose and increased the cellulose content of the pre-hydrolyzed bamboo-willow. The major component of the hemicelluloses was xylan/xylose, which represented approximately 62% to 78% of the total sugars in the PHL. Glucose was the most abundant sugar that was produced, apart from xylose, and represented approximately 12% to 25% of the total sugars in the PHL. Additionally, 73% to 83% of the total sugars in the PHL were in an oligomeric form. The obtained bamboo-willow dissolving pulp could be used to produce viscose rayon with a 92.1% α-cellulose content, 4.77% hemicellulose content, and 675 degree of polymerization.

With the increasing need for bio-based materials developed by environmentally friendly procedures, this work shows a green method to develop shape-controlled structures from cellulose dissolving pulp coated by chitosan. This material was then tested to adsorb a common and widespread pollutant, 2,4-dichlorophenol under different pH conditions (5.5 and 9). Herein it was noticed that the adsorption only occurred in acidic pH (5.5) where electrostatic interaction drove the adsorption, demonstrating the potential to tune the response under desired conditions only. The adsorption was successful in the hydrogel structure with an adsorption capacity of 905 ± 71 mg/g from a solution with 16.6 ppm; furthermore, adsorption was also possible with dried hydrogel structures, presenting a maximum of adsorption of 646 ± 50 mg/g in a similar 16.6 ppm solution. Finally, adsorbent regeneration was successfully tested for both, dry (rewetted) and never-dried states, showing improved adsorption after regeneration in the case of the never dried hydrogel structures.

A pre-hydrolysate is an aqueous stream obtained during the production of hardwood kraft dissolving pulp. It is rich in sugars and contains dissolved organic matters. The purpose of this study is to investigate the optimization of lignin recovery from wood pre-hydrolysates and to characterize the extracted lignin. The optimal conditions for lignin extraction have been determined to be (a) a filtration temperature of 40 &deg, C, (b) a sulfuric acid concentration of 8.5 kg.m&minus, 3, and (c) a coagulation time of 180 min. Using these conditions, high filtration rates have been obtained and the extracted lignin has a low content of impurities (8.3%), a low molecular weight (1270 Da), and a very low polydispersity (Mw/Mn = 1.22). Compared to kraft lignin, the pre-hydrolysate lignin has a much lower molecular weight and could be a potential candidate for niche applications. A high lignin recovery rate is possible (52% of the total lignin content in the pre-hydrolysate).

Cold caustic extraction (i.e. CCE) is an essential technique for removing hemicellulose from paper-grade pulp and thus obtaining high-purity dissolving pulp in pulp and paper industry. The generated wastewater from the CCE process contains large amounts of valuable hemicellulose which should be properly treated in a cost-effective way. Therefore, in this research, the hemicellulose has been used as a raw material for preparing hemicellulose-graft-polyacrylamide (hemi-g-pAAm) hydrogel particles for efficiently adsorbing methylene blue (MB) from aqueous solutions. The mass transfer kinetic behaviours of hemicellulose during a multiple CCE process were also studied. The MB adsorption kinetic test results showed that the removal efficiency can be higher than 90% for the simulated wastewater containing 500 mg/L of MB. Of note, the maximum removal capacities for the wastewater samples containing 500 and 1000 mg/L of MB could be reached up to ∼1800 and ∼2300 (mg/g) respectively with the equilibrium time of ∼40 min. Compared to other reported materials, the superior adsorption performance of the prepared hemicellulose-based hydrogel proved its great potential for application in the wastewater treatment of dye industry.

The direct dissolution and joint spinning of cellulose and lignin from NMMO-water were investigated by using dissolving pulp and purified KRAFT lignin. Compared to the rather narrow dissolution window of cellulose in the NMMO-water system, lignin with concentrations up to 15 wt.-% was shown to dissolve in a range from 30 % NMMO to 70 % NMMO at room temperature. The quasi-ternary phase diagram of cellulose-lignin-(NMMO-monohydrate) is represented by a cross section at 95 °C. Dry-jet wet spinning was realized for the cellulose-lignin compound up to 50 % lignin loading. The spinnability decreases with increasing lignin content. SEM and TEM investigations of the fibers exhibit a core-shell structure with a dense core and a porous shell with lower lignin content. In accordance with the X-ray fiber diagrams, it can be concluded that cellulose governs fiber formation and fiber properties while lignin acts mainly as a filler in the core region.

Pretreatment is an essential process for the extensive utilization of lignocellulose materials. The effect of four common organic acid pretreatments for Kraft dissolving pulp production was comparatively investigated. It was found that under acidic conditions, hemicellulose can be effectively removed and more reducing sugars can be recovered. During acetic acid pretreatment, lignin that was dissolved in acetic acid could form a lignin-related film which would alleviate cellulose hydrolysis, while other organic acids caused severe cellulose degradation. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD) were used to characterize the pretreated chips in the process. Lignin droplets were attached to the surface of the treated wood chips according to the SEM results. The FTIR spectrum showed that the lignin peak signal becomes stronger, and the hemicellulose peak signal becomes weaker with acid pretreatment. The XRD spectrum demonstrated that the crystallinity index of the wood chips increased. The acetic acid pretreatment process-assisted Kraft process achieved higher yield (31.66%) and higher &alpha, cellulose (98.28%) than any other organic acid pretreatment. Furthermore, extensive utilization of biomass was evaluated with the acetic acid pretreatment-assisted Kraft process. 43.8% polysaccharide (12.14% reducing sugar and 31.66% dissolving pulp) and 22.24% lignin (0.29% acetic acid lignin and 21.95% sulfate lignin) were recovered during the process. Biomass utilization could reach 66.04%. Acetic acid pretreatment is a promising process for extensive biomass utilization.

Processive endoglucanase EG1 and its core domain, EG1(CD), were used to pretreat the commercial dissolving pulp to improve cellulose reactivity. The Fock reactivity of the pulp which was treated with EG1 and EG1 (CD) at 50 U/g enzyme loading increased from 74.3% of the control to 90.6% and 88.4%, respectively. Refining also improved the Fock reactivity of the pulp, but not as effective as EG1 or EG1(CD) treatment. Refining prior to EG1 or EG1(CD) treatment could slightly further improve the Fock reactivity, to 91.6% and 90.0%, respectively. After enzymatic treatment and (or) refining, the water retention value, differential scanning calorimetry and alkaline solubility analysis indicated that enzyme treatment, especially by EG1, significantly increased the accessibility of fibers to reaction reagents. Combined with the characteristics of soluble reducing sugar produced by EG1 treatment and the changes of degree of polymerization, it is inferred that a small fraction of cellulose crystallization regions are destroyed in the enzymatic hydrolysis process due to the processive acting ability of EG1, and some microchannels in the fiber cell wall were created, which is similar to the effect of “drilling holes”, so that the reaction reagent can reach the inside of the cell wall evenly, thus obviously improving the reactivity of the dissolved pulp.

Choline chloride-based deep eutectic solvents are widely used in biomass processing. In this work, four different green solvent mixtures were used as pre-treatment of acid sulphite dissolving pulp with the hypothesis of increasing the possibilities to produce viscose fibres and decreasing the use of the harmful and toxic carbon disulphide in the process. The experiments were performed at two different pulp to solvent mass ratios. Pulp quality parameters were also measured to determine the suitability of the pre-treatment: α-cellulose, viscosity, lignin and pentosan content. In addition, X-ray diffraction analysis of pulps at the best solid to liquid ratio was performed to obtain the influence of the crystallinity index. Best results were obtained with the use of lactic acid, with reactivity values close to 94%, giving a reduction of CS2 usage of 15.83%. Furthermore, a linear relationship between the crystallinity index calculated by the XRD and reactivity with a regression factor of 0.87 was found.

Reactivity of dissolving pulp is one of the main parameters to determine its availability to be transformed into viscose. It is related to the use of carbon disulphide (CS2). An industrial sequential totally chlorine free bleaching process is used as case study. It is carried out in two stages: (1) Alkaline extraction (EOP) and (2) peroxide bleaching (PO). In order to assess how to decrease the use of carbon disulphide, several experiments were performed at laboratory scale for the two stages mentioned before by modifying the operating conditions: NaOH and H2O2 dosages, time and temperature. Reactivity using a modified Fock’s method and pentosan content was analysed along with quality pulp parameters: α-cellulose, viscosity and lignin content (kappa number). Results showed that reactivity increases through the bleaching process and varies with the chemical dosage in both stages. Pulp obtained at the best conditions had the following characteristics: reactivity, 95.3%; α-cellulose 91.17%; intrinsic viscosity, 448 mL/g; kappa number, 1.81 and pentosan content 2.86%, and as a result, CS2 usage was reduced by 11.88%. At the best conditions obtained in this work, NaOH dosage in PO stage was reduced to zero and temperature was slightly lower, when compared with industrial operating conditions.