Wood Cellulose Fibers Research Articles

Dissolution mechanisms of wood cellulose fibres in NaOH–water

Four wood pulps and a microcrystalline cellulose were dissolved in a NaOH 8%–water solution. Insoluble fractions and clear solution fractions were isolated by centrifugation and were observed by optical microscopy and transmission electron microscopy. Molecular weight distribution, carbohydrate composition and cellulose II content were measured. The dissolution of wood cellulose fibres in NaOH 8%–water solutions occurs by successive dismantlement and fragmentation steps governed by the swelling and the shearing of the original structure. The cellulose from insoluble and clear solution fractions is in both case converted in cellulose II and the insoluble fractions contain embedded mannans. Besides, the molecular weight distributions of cellulose from insoluble and clear solution fractions reveal the existence of heterogeneities in dissolution capacity of the cellulose chains, independent to the degree of polymerization, which are related to the chemical environment of the chains in the fibre structure.

Structural changes and alkaline solubility of wood cellulose fibers after enzymatic peeling treatment

Two dissolving sulphite wood pulps were treated by an enzymatic peeling protocol and the changes in terms of structure and alkaline solubility were analyzed. The enzymatic treatment leads to a fast and large decrease of degree of polymerization and of crystallinity, showing that the enzymes do not simply act on the fiber surface. The swelling and dissolution behaviour of the treated samples showed that the enzyme mixture used has two effects at short peeling times (i) a digestion of the primary wall which is seen by the near absence of ballooning and (ii) a destructive action on the inside of the fiber which is seen by the large decrease in the degree of polymerization. At long peeling times, the external walls are totally digested and the fiber structure is totally destroyed, as seen by the absence of birefringence. The alkaline solubility of the different treated samples was investigated in a NaOH 8%–water solution. As expected from thermodynamic considerations, there is a direct correlation between the solubility and the degree of polymerization. However, aside thermodynamics, the removal of the external walls and the macrostructural destructuration of the fibers are key factors in the improvement of the dissolution of wood cellulose fibers. At constant intrinsic viscosities of the cellulose materials, the alkaline solubility is almost two times higher when the external walls are removed. The macrostructural destructuration of fibers by enzymes allows a high degree of polymerization to be preserved while keeping a good alkaline solubility.

Growth, Structural, and Optical Characterization of ZnO-Coated Cellulosic Fibers

Rod-shaped ZnO particles were grown over wood cellulose fibers using a two-step process. In the first step, the formation of ZnO seeds at cellulose fibers surfaces was induced by the alkaline hydrolysis of aqueous Zn(II); in the second step, the growth of the ZnO seeds into larger nanoparticles was promoted by the controlled hydrolysis of Zn(II)−amine complexes. In particular, we will report the use of hexamethylenetetramine (C6H12N4) and triethanolamine (C6H15NO3) to grow, respectively, ZnO nanorods and microrods at the cellulose fibers surfaces. Photoluminescence measurements performed on the nanocomposite materials showed the typical excitonic ZnO recombination peaked between 3.38 and 3.34 eV, at low temperature. The full width at half-maximum of the excitonic line is dependent on the ZnO particles morphology and can be as narrow as 30 meV for some of the materials investigated.

Characteristics of Wood Cellulose Fibers Treated with Periodate and Bisulfite

Wood cellulose fibers were oxidized by periodate to obtain dialdehyde cellulose (DAC) fibers. The aldehyde group content, degrees of crystallinity and polymerization, and fiber length of treated fibers were characterized. The tensile strength of the test sheets made of treated fibers was also measured. The results show that periodate oxidation significantly increased the aldehyde group content and the dry and rewet tensile strengths of the test sheets. Sulfonation of the oxidized fibers by bisulfite improved the undried fiber water absorbency and the dry and rewet tensile strengths of the test sheets made of sulfonated fibers.

Swelling and dissolution of cellulose, Part V: cellulose derivatives fibres in aqueous systems and ionic liquids

The swelling and dissolution mechanisms of several cellulose derivatives (nitrocellulose, cyanoethylcellulose and xanthate fibres) are studied in aqueous systems (N-methylmorpholine-N-oxide—water with various contents of water, hydroxide sodium—water) and in ionic liquids. The results are compared with the five modes describing the swelling and dissolution mechanisms of cotton and wood cellulose fibres. The mechanisms observed for the cellulose derivatives are similar to the ones of cotton and wood fibres. Swelling by ballooning is also seen with cellulose derivatives, showing that this phenomenon is linked to the fibre morphology, which can be kept after undergoing a heterogeneous derivatisation.

Novel nanocomposites based on polyurethane and micro fibrillated cellulose

The goal of this study was to fibrillate cellulose from micro to nano scale and evaluate how these microfibers and nanofibrils affected the mechanical and thermal properties of thermoplastic polyurethane. The source of cellulosic material was hard wood cellulose fibers and the fibrillation was done with a high pressure homogenizer. The composite materials were prepared using compression moulding, by stacking the cellulose fiber mats between polyurethane films. The results showed that both microfibers and nanofibrils reinforced the polyurethane and provided better heat stability. The addition of 16.5 wt% of cellulose nanofibrils to PU increased the strength nearly 500% and the stiffness by 3000%. These results are very promising in terms of obtaining fibrils with a novel processing method and by improving the mechanical and thermal properties of polyurethane. This is expected to expand the application areas of polyurethanes.

Grafting of poly (methyl acrylate) onto sulfite pulp fibers and its effect on water absorbance

AbstractTo prepare super water absorbent hydrogels of wood cellulose fibers, poly (methyl acrylate) (PMA) was copolymerized onto softwood sulfite pulp fibers using free radical initiator followed by alkaline hydrolysis. Ceric ammonium nitrate (CAN) was used as the free radical initiator. Effects of various parameters such as fiber concentration, monomer/pulp (M/pulp) ratio, CAN concentration, and reaction time on the grafting yield and on other grafting parameters were investigated. The graft conversion was the same from low to medium fiber concentration. The amount of initiator required was found to be independent of fiber concentration to achieve maximum grafting yield. Different fiber fractions (classified based on their length) have no effect on the grafting yield. The evidence of graft copolymerization was determined by using ATR‐IR spectroscopy. The X‐ray diffraction (XRD) analysis shows that grafting takes place both in amorphous and crystalline regions of cellulose fibers and the decrease in crystallinity of the grafted fibers with an increase in grafting yield was confirmed. The surface morphology of the PMA‐g‐cellulose was characterized by scanning electron microscopy (SEM). The water retention value of the hydrolyzed grafted pulp was determined based on a centrifugation technique. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Swelling and Dissolution of Cellulose Part II: Free Floating Cotton and Wood Fibres in NaOH–Water–Additives Systems

AbstractSummary: The swelling and dissolution mechanisms of native cotton and wood cellulose fibres in NaOH–water are studied. The cellulose fibres exhibit a heterogeneous swelling by ballooning in the best dissolving conditions (−5 °C, 7.6% of NaOH). This corresponds to the mode 3 of the swelling‐dissolution (see companion paper). In this region of the mixture phase diagram, cellulose is only dissolved inside the balloons. A lot of insoluble parts are present. Increasing the temperature and/or the content of NaOH decreases the quality of the solvent. In this case, the cellulose fibres do not show ballooning, but only a homogeneous swelling (mode 4). Three components are tested as additives: urea, zinc oxide and N‐methylmorpholine– N–oxide (NMMO). The swelling and dissolution mechanisms in NaOH‐water and NaOH–water–additives stay the same. Adding urea to NaOH‐water (−5 °C, 7.6% of NaOH) gives the same ballooning mechanisms, but with a larger expansion of the balloons, indicating that the solvent is better. Zinc oxide does not increase the expansion of the balloons, but the kinetics of swelling is faster. NMMO acts as a dissolution inhibitor.

Swelling and Dissolution of Cellulose Part 1: Free Floating Cotton and Wood Fibres in N‐Methylmorpholine‐N‐oxide–Water Mixtures

AbstractSummary: Five modes describing the behaviour of cellulose fibres dipped in a chemical have been identified: Mode 1: Fast dissolution by disintegration into fragments Mode 2: Large swelling by ballooning, and dissolution Mode 3: Large swelling by ballooning, and no dissolution Mode 4: Homogeneous swelling, and no dissolution Mode 5: No swelling and no dissolution In the case of the behaviour of wood and cotton cellulose fibres in N‐methylmorpholine‐N‐oxide (NMMO) and water mixtures, four domains of water content have been identified. Below 17% of water up to monohydrate (13%), the fibres are disintegrated into rod‐like fragments and dissolve (mode 1). In NMMO – water mixtures containing 19–24% water, the cellulose fibres exhibit a heterogeneous swelling by forming balloons (composed of dissolved cellulose holds inside a membrane) separated with non‐swollen sections. The whole fibre will completely dissolve (mode 2) in four successive steps (growth of the balloons, burst of the balloons, dissolution of the non‐swollen sections and finally dissolution of the membrane). With still greater water contents (25–30%), only the ballooning phenomenon is observed, with a partial dissolution inside the balloon (mode 3). Above 35% of water, the fibres swell homogeneously and are not dissolving (mode 4).

Self-Diffusion in Two- and Three-Dimensional Powders of Anisotropic Domains: An NMR Study of the Diffusion of Water in Cellulose and Starch

The pulsed field gradient stimulated echo NMR technique is applied to the study of water diffusion in biological porous materials (a sheet of wood cellulose fibers and a packed bed of potato starch granules) consisting of randomly oriented domains with an anisotropic supermolecular organization. Expressions are presented for the probability distribution of apparent diffusion coefficients due to two- and three-dimensional powder distributions of domain orientations. The distributions are converted to echo attenuation curves with a method taking cross relaxation between the water and the solid matrix into account. Using a model in agreement with the structure and domain orientation known from other experimental techniques, it is found that the mean diffusion coefficient and degree of anisotropy (ratio between water diffusivity parallel and perpendicular to the structure director) at a level of hydration corresponding to approximately 90% relative humidity are (1.68 ± 0.03) × 10-11 m2/s and 6.4 ± 0.9 for cel...

Micromechanical characterization of cellulose fibers

The work presented here aims towards the characterization of micromechanical properties of individual cellulose fibers. In particular, our interest is in determining the elastic modulus, tensile strength and tensile elongation of cotton and wood based cellulose fibers. Testing is conducted at a microscale, on single fibers of a few millimeters in length and tens of microns in width, a scale so chosen because such fibers are commonly used as industrial raw materials. An in-house microtensile fiber tester was designed and fabricated. A fine resolution stepper motor (10 nm per step) provides the actuation for the microtensile load frame and load in the fibers is measured by a high sensitivity load cell (0.01 mN resolution). The entire assembly is placed below a zoom stereo microscope for the dual purpose of aiding in specimen mounting and visually recording the experiment. After calibration of the device, good results were obtained when testing both the cotton and wood based cellulose fibers. Average Young's moduli of 4 GPa and 2 GPa were found for the two fibers, respectively. However, a large variation in failure stress was found for the fibers of both kinds, necessitating a statistical analysis assuming a Weibull distribution of failure. Based on this, mean strengths of 496 MPa for cotton cellulose fibers and 164 MPa for wood cellulose fibers were obtained.

Determination of pore sizes in wood cellulose fibers by 2H and ′H NMR

Determination of pore sizes in wood cellulose fibers by ²H and ′H NMR

Future prospects for wood cellulose as reinforcement in organic polymer composites

AbstractWood cellulose, a versatile and renewable natural resource, has potential for use as a reinforcement for synthetic organic polymers. During the past 80 years a number of materials using the reinforcing properties of wood cellulose have found major markets. Forms of wood cellulose proposed as reinforcements include: wood fibers, cellulose fibers, microfibillar, and microcrystalline cellulose. Recent attention has been given to them as fillers/reinforcements in thermoplastics and elastomers. Most cellulosic composites derive their existence from their comparatively low materials cost and the filling rather than reinforcing properties of cellulose. However, cellulose chains have a potential stiffness much higher than glass and in the same range as superstiff aramid fibers. This paper examines the state of the art of combining wood cellulose with synthetic organic polymers to from composites and considers new ways for better using cellulose's reinforcing potential.

Reinforcement of Epdm Elastomers Through Discontinuous Unregenerated Wood Cellulose Fibers

Reinforcement of Epdm Elastomers Through Discontinuous Unregenerated Wood Cellulose Fibers

Mulches for Grass Establishment on Fill Slopes1

AbstractEleven mulch treatments were evaluated during the fall of 1966 on a 2:1 northeast‐facing fill slope seeded to smooth bromegrass (Bromus inermis Leyss.). Mulch materials included wood cellulose fiber, excelsior, jute netting, emulsifiable asphalt used separately and as an anchorage for corncobs, woodchips, prairie hay, and fiberglass. Plots protected with an excelsior mat yielded the best seedling grass.Eight mulch treatments were evaluated on a 2:1 east‐facing fill slope during the fall of 1967. Mulch materials included an emulsifiable polymer, compost, wood cellulose, jute netting, excelsior, and asphalt‐anchored mulches of excelsior, woodshavings, and bark dust. Plots protected with an excelsior mat or jute netting yielded the best seedling grass.

Effect of Mulches on Microclimate and Turf Establishment1

SynopsisModeration of soil temperature and conservation of soil moisture by straw, wood cellulose fibers, and sawdust resulted in quicker turf establishment than no mulch or elastomeric emulsion treatment of summer seedings of Kentucky 31 fescue, Kentucky bluegrass, and Redtop. Irrigation improved all treatments, but was most beneficial to grasses mulched with straw, wood cellulose fibers, and sawdust.

Nitrogen Adsorption of Solvent-exchanged Wood Cellulose Fibers: Indications of “Total” Surface Area and Pore Size Distribution

Nitrogen Adsorption of Solvent-exchanged Wood Cellulose Fibers: Indications of “Total” Surface Area and Pore Size Distribution

INVESTIGATION UPON DISSOLVING PULP (PART VIII)

With the same samples described in parts V, VI and VII, the morphological transformation of wood cellulose fibers during sulfite cooking, hot alkaline purification and hypochlorite bleaching was investigated by modifying Heide's phosphoric acid method. (K. Heide, Faserforsch. u. Textiltechn., 3, 469 (1952)).The swelling and dissolution state of cellulose fiber at each pulping stage in 78, 79 and 80% H3PO4 was observed by phase-contrast microscope. Simultaneously, the determination of haze value of cellulose solution in 79.5% H3PO4 was also carried out as a newly proposed method by us for estimation of cellulose reactivity.The results ware as follows:1. The swelling and dissolution state of sulfite-cooked cellulose fiber (further delignified with NaClO2)in phosphoric acid was improved with decrease in its average D. P. during the sulfite cooking.2. As a result of subsequent chlorination, hot alkaline purification and hypochlorite bleaching, the state of swelling and dissolution of cellulose was further improved. The final hypochlorite bleaching, however, did not contribute too much to its improvement as the former did. Though the influence of DP of the original sulfite cooked pulps upon the state of swelling and dissolution of cellulose in phosphoric acid was gradually decreased with the subsequent pulping processes, its effect was still slightly observed in final bleached pulps.3. The determination of the haze value of cellulose solution in 79.5% H3PO4, newly proposed by us, may be a good method for quantitative estimation of reactivity of cellulose.The results by this method was very much consistent with that of microscopic observations, and also with the results reported in Part VII on clogging constant (Kw) of viscose prepared from these samples.

INVESTIGATION UPON DISSOLVING PULP. PART VI

With the same samples described in parts V, VI and VII, the morphological transformation of wood cellulose fibers during sulfite cooking, hot alkaline purification and hypochlorite bleaching was investigated by modifying Heide's phosphoric acid method. (K. Heide, Faserforsch. u. Textiltechn., 3, 469 (1952)).The swelling and dissolution state of cellulose fiber at each pulping stage in 78, 79 and 80% H3PO4 was observed by phase-contrast microscope. Simultaneously, the determination of haze value of cellulose solution in 79.5% H3PO4 was also carried out as a newly proposed method by us for estimation of cellulose reactivity.The results ware as follows:1. The swelling and dissolution state of sulfite-cooked cellulose fiber (further delignified with NaClO2)in phosphoric acid was improved with decrease in its average D. P. during the sulfite cooking.2. As a result of subsequent chlorination, hot alkaline purification and hypochlorite bleaching, the state of swelling and dissolution of cellulose was further improved. The final hypochlorite bleaching, however, did not contribute too much to its improvement as the former did. Though the influence of DP of the original sulfite cooked pulps upon the state of swelling and dissolution of cellulose in phosphoric acid was gradually decreased with the subsequent pulping processes, its effect was still slightly observed in final bleached pulps.3. The determination of the haze value of cellulose solution in 79.5% H3PO4, newly proposed by us, may be a good method for quantitative estimation of reactivity of cellulose.The results by this method was very much consistent with that of microscopic observations, and also with the results reported in Part VII on clogging constant (Kw) of viscose prepared from these samples.