Assessing wood pulp reactivity through its rheological behavior under dissolution

Recent years have witnessed an increasing interest in man-made cellulosic fibers, whose production generally requires cellulose dissolution and regeneration. Cellulosic fibers are difficult to dissolve. Thus, the recalcitrance of wood pulp can be an estimate of its reactivity. Pulp reactivity is usually assessed via complex and time-consuming laboratory simulations of the viscose process. This study proposes a faster and more convenient approach. The dissolution-based torque reactivity (DTR) test measures the evolution of the rheological properties of a pulp suspension under dissolution in cupriethylenediamine. Reactivity is quantified in terms of initial dissolution rates (IDR) and dissolution times (DT). This study describes the measurement protocol for the DTR test and its application to some commercial pulps and a series of pulps hornified to different extents. The IDR and DT values were compared with other pulp features, including degree of polymerization, molecular weight distribution, specific surface area and water retention value. The DTR test proved to be reasonably precise and fast to carry out. Graphic abstract

Improving dissolving wood pulp quality using Brown-stock fractionation

Dissolving wood pulp (DWP) contains high levels of cellulose and has various applications. Production of dissolving wood pulp is accompanied by various challenges such as equipment operational problems and high bleaching costs. These are mainly due to lignin and other impurities contained in wood. Further, these impurities impose threats to the dissolving pulps applications such as the viscose process and the manufacture of finished rayon products. Removal of these contaminants at the early production stages proved effective in meeting by the challenges. Hydrocyclones achieve the separation of heavy and light pulp components in a process known as fractionation. In the case of dissolving wood pulp, hydrocyclones fractionate the pulp fibres into coarse fibres and fine fibres known as fines. Fines are the reject materials and are associated with impurities such as wood resins. Wood pulp was fractionated at 0.8% consistency using a Kadant laboratory hydrocyclone at mass reject rates of 5% and 11%. Pulp properties and application properties were determined and compared to unfractionated pulp. The fractionated pulps showed higher cellulose contents and lower levels of fines and associated resins. Bleaching of the fractionated pulps under a standard ODEDH bleaching sequence showed higher levels of delignification, as measured by brightness, and more favourable application properties. These findings were used to optimise the bleaching sequence by reducing the amount of chlorine dioxide applied in the second chlorine dioxide stage. The optimised bleaching sequence produced pulps with satisfactory fibre and application properties.

Textile qualities of regenerated cellulose fibers from cotton waste pulp

Cotton is not the answer to meet the rapidly growing demand for textile fibers. Wood-based regenerated cellulose fibers are an attractive alternative. Since wood is a candidate to replace fossil raw materials in so many applications of the circular economy, other sources need investigation. Cotton linters work in the viscose process – can cotton waste be used to make dissolving pulp? We describe the textile qualities of lyocell fibers from (i) pure cotton waste pulp and (ii) blending with conventional dissolving pulp. The staple fibers were tensile tested, yarns spun and tensile tested and knitted, and tested for shrinkage, water and dye sorption, abrasion resistance, fuzzing and pilling, staining and fastness. TENCEL® staple fibers and off-the-shelf TENCEL® yarn were used as references. The results show that the two study fibers had tenacity and an E-modulus that exceeded the staple fiber reference. Also, the study yarns were at least as good as the spun reference yarn and the commercial off-the-shelf yarn in terms of wet tenacity. Single jerseys made from the study yarns shrunk less upon laundering, which is surprising since they could absorb at least as much water at a comparable rate as the references. Dyeability, staining and color fastness, durability and pilling tendency showed that the two study fiber tricots performed at least as good as the references. This study suggests that cotton waste is a promising candidate for special grade pulp to suit niche regenerated fiber products or to spice up conventional wood-based dissolving pulp.

Characterization of dissolving pulp by fibre swelling in dilute cupriethylenediamine (CUEN) solution in a MorFi analyser

The swelling of dissolving pulps has been investigated by a new method based on the MorfiR analyser, which is measuring the width variation of thousands of fibres in a cupriethylenediamine (CUEN) solution in a few minutes. Pulps from various origins were analysed coming from softwood, birch wood, eucalyptus wood, kraft pulps, sulphite pulps and ECF and TCF bleached pulps, which were modified by several treatments including chemical (cold caustic extraction, hypochlorite) or enzymatic (cellulase) methods. The swelling was much affected by the crystalline form of cellulose and the hemicellulose content but did not depend neither on the cellulose DP nor on the fibre structure (hardwood vs. softwood). The dissolving pulp reactivity in the viscose process was also assessed by swelling in dilute solutions of cupriethylenediamine (CUEN) instead of the Fock’s method.

Preparation and Properties of Viscose Rayon/O-carboxymethyl Chitosan Antibacterial Fibers

Antimicrobial viscose rayon/O-carboxymethyl chitosan fibers (VCMFs) were manufactured by spinning the mixture of O-carboxymethyl chitosan (O-CMCS) xanthate and cellulose xanthate via the viscose process. The structure, morphology and mechanical properties were investigated by infrared, scanning electron microscopy, transmission electron microscope and tensile test. The results show that the blend fibers of cellulose and O-CMCS were satisfactorily prepared and the two polymers were mixed homogeneously. VCMFs display striation along the fiber similar to those of viscose rayon fibers, and their mechanical properties are close to that of viscose rayon. With O-CMCS blended, VCMFs showed good moisture absorption and antibacterial activity against E.coli.