Thaddeus Maloney

Fibre porosity development of dissolving pulp during mechanical and enzymatic processing

Dissolving grade pulps are used as raw material for manufacture of regenerated cellulose fibres and their use is constantly growing. Despite intensive research, there is still a need to develop cellulose dissolution-regeneration processes that would be economically viable, fulfil the pre-conditions of sustainability and would be able to meet the strict product quality requirements. The basis for creation of such a process is in deep understanding of the biomass structure and factors affecting the cellulose modification and dissolution. In this paper, the effects of the mechanical and enzymatic pre-treatments on the pore structure and alkaline solubility of dissolving grade pulp are discussed. Formation of micro- and macropores in the pulp fibres during mechanical shredding was found to correlate with the susceptibility of the fibres to enzymatic hydrolysis. The fibre porosity development during the processing was studied by a modified solute exclusion approach, which revealed differences between the effect of mild enzyme or acid hydrolysis on the pore structure of fibres. The dissolution of the modified fibres in NaOH/ZnO was evaluated and found to correlate with overall pore volume and accessible surface area analysed by the modified solute exclusion method.

Network swelling of TEMPO-oxidized nanocellulose

Abstract: This study examines the swelling of TEMPO-oxidized nanofibrillated cellulose (NFCTEMPO, shortly NFC) on both the particle and interparticle levels. The sum of the intraparticle and interparticle swelling is referred to as the network swelling. A centrifugal method, based on a modification of the water retention value test, was used to measure the network swelling of NFC, a pigment, and some pulp fibers. It was found that the network swelling of NFC is highly dependent on its concentration within a fiber matrix. The particle swelling of NFC and pulp fibers was analyzed by differential scanning calorimetry (DSC) and solute exclusion. The counterion for the NFC varied among the Na+, H+, and Ca2+ forms. The counterion has a very large effect on the particle and network swelling of NFC, with Ca2+ giving the lowest swelling and Na+ the highest swelling. An industrially feasible method for changing the counterion of NFC from the nominal Na+ to the Ca2+ form, and thus improving dewatering properties, is given.

Influence on Pore Structure of Micro/Nanofibrillar Cellulose in Pigmented Coating Formulations

Nano and microfibrillated cellulose (NFC and MFC, respectively, collectively termed MNFC) is known to interact strongly with water, related to its high polarity and surface area. The swelling behaviour acts to form a gel with high water retention properties. The observation that nanocellulose could possibly be used in paper or other coating formulations, as a co-binder, for example, raises a question about the possible effects it could have on coating pore structure. In this study, we analyse the pore structure of pigmented coatings, liquid absorption and permeability, in respect to the influence of partially substituting traditional co-binder carboxymethyl cellulose with MNFC. The contrast between polar water and non-polar liquid, such as alkane, is used to probe the water interactive and extractable in-coating (internal) gel-formation properties of the nanocellulosic materials. These contrasting liquids are important in many processes, such as offset printing, but also in respect to exposure of coatings in general to environmental factors in application. Results show that permeability to liquid water is dramatically reduced when nanocellulosic material is present, though water can permeate by diffusion through the nanocellulose gel network. Long timescale exposure to water during absorption leads to extraction of any soluble salts remaining after the chemical treatment of the fibrillar material during production. Inert alkane, on the other hand, can absorb and permeate freely without interactive hindrance from the nanocellulose, with no extractive effect. Such a construct could in principle be considered for use as an oil-water differential membrane or for slow release concepts in aqueous systems by loading soluble deliverable materials within the nanocellulosic gel.

Dissolution enthalpies of cellulose in ionic liquids.

In this work, interactions between cellulose and ionic liquids were studied calorimetrically and by optical microscopy. Two novel ionic liquids (1,5-Diazabicyclo[4.3.0]non-5-enium propionate and N-methyl-1,5-diazabicyclo[4.3.0]non-5-enium dimethyl phosphate) and 1-ethyl-3-methylimidazolium acetate-water mixtures were used as solvents. Optical microscopy served in finding the extent of dissolution and identifying the dissolution pattern of the cellulose sample. Calorimetric studies identified a peak relating to dissolution of cellulose in solvent. The transition did, however, not indicate complete dissolution, but rather dissolution inside fibre or fibrils. This method was used to study differences between four cellulose samples with different pretreatment or origins.

Micro nanofibrillated cellulose (MNFC) gel dewatering induced at ultralow-shear in presence of added colloidally-unstable particles

Aqueous nanogels are notoriously difficult to dewater. An example of such a gel is that of a suspension of micro nanofibrillated cellulose, in which water is both bound to the fibrillar surface and held within the interfibril matrix. We demonstrate a phenomenon in which dewatering of nanocellulose based gel-like suspensions can be induced by adding a colloidal particulate component, which itself can undergo autoflocculation when suspended in water. The mechanism is exemplified by the addition of undispersed precipitated calcium carbonate, which in equilibrium remains stabilised in the gel, but when the gel mix is exposed to ultralow shear, acting below the yield stress, demixing of the combination between the nanofibrils and the autoflocculating pigment leads to separation of the unbound water phase. This novel mechanism is proposed to enhance the dewatering capability in general of complex gel-like water-holding suspensions.

Impact of mechanical and enzymatic pretreatments on softwood pulp fiber wall structure studied with NMR spectroscopy and X-ray scattering

Dissolution of wood pulp can be enhanced by applying certain pretreatments before exposing the fibers to solvents. We have analyzed effect of mechanical and enzymatic pretreatments on softwood fiber wall structure using nuclear magnetic resonance (NMR) spectroscopic methods, small and wide angle X-ray scattering (SAXS, WAXS). NMR diffusometry was used to estimate the effect of pretreatments on average pore sizes at micrometer size scale and for the connectivity of the porous network. A proton NMR experiment was used to quantify the nonfreezing water content inside the fiber wall, and solid state NMR

The investigation of rheological and strength properties of NFC hydrogels and aerogels from hardwood pulp by short catalytic bleaching (Hcat)

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The effect of the outermost fibre layers on solubility of dissolving grade pulp

13C cross polarization (CP) magic angle spinning (MAS) spectroscopy was used to observe the effect of pretreatments on crystallinity and lateral fibril dimensions of cellulose fibrils, and in combination with fiber saturation point measurement to calculate the average pore size at nanometer size scale. Both WAXS and CP–MAS NMR experiments confirmed that there were no changes in crystallinity nor in fibril lateral dimensions due to pretreatments. The pretreatments caused an increase in the amount of nonfreezing water, suggesting an opening of the pore system. According to diffusion experiments there are only minor changes in micrometer scale pore network due to pretreatments. SAXS results indicated that enzymatic treatment increased the microfibrillar distance, and there was also an increase in cross relaxation rate of magnetization from water to cellulose protons as observed by NMR. These were interpreted to be due to opening of microfibrillar bundles, leading to an increased accessibility of water.