Improving the reactivity of kraft-based dissolving pulp for viscose rayon production by mechanical treatments

The capacity of dissolving pulp to react with carbon disulfide under the defined conditions, known as the “Fock reactivity,” is an important parameter in determining the processability, end-product quality, and environmental impact in downstream rayon production. This study was aimed at improving the reactivity of kraft-based dissolving pulp by mechanical treatments, such as grinding and PFI refining, which can induce additional accessible surfaces in the compact cellulose structure via fiber cutting and fibrillation, respectively. Results showed that the Fock reactivity of a kraft-based dissolving pulp was increased from 49.3 to 71.8 % by 6-min grinding treatment under the conditions studied. Such a treatment led to increases in the fines content and specific surface area while decreasing the fiber length, intrinsic viscosity, and the crystalline ratio of cellulose. PFI refining can also result in changes in the fiber morphology and cellulose structure; a 25,000 PFI revolution treatment led to an increase in the Fock reactivity from 49.3 to 58.3 % for the same dissolving pulp.     

Electron treatment of wood pulp for the viscose process

Electron processing is currently being evaluated by several viscose producers for integration into their process. The viscose industry converts dissolving wood pulp into products such as staple fibre, filament, cord, film, packaging, and non-edible sausage casings. These materials are used in the clothing, drapery, hygiene, automobile, food, and packaging industries. Viscose producers are facing increasingly high production costs and stringent environmental regulations that have forced some plants to close. Electron treatment of wood pulp can significantly reduce the amounts of chemicals used for producing viscose and the production of hazardous pollutants. Acsion Industries has worked with companies worldwide to demonstrate the benefits of using electron treated pulp for producing viscose (rayon). This paper describes the viscose process, the benefits of using electron treatment in the viscose process, and Acsion’s efforts in developing this technology.     

Sulfur-free dissolving pulps and their application for viscose and lyocell

In this study, the concept of multifunctional alkaline pulping has been approved to produce high-purity and high-yield dissolving pulps. The selective removal of hemicelluloses was achieved by either water autohydrolysis (PH) or alkaline extraction (E) both applied as pre-treatments prior to cooking. Alternatively, hemicelluloses were isolated after oxygen delignification in a process step denoted as cold caustic extraction (CCE). Eucalyptus globulus wood chips were used as the raw material for kraft and soda-AQ pulping. In all process modifications sulfur was successfully replaced by anthraquinone. By these modifications purified dissolving pulps were subjected to TCF bleaching and comprehensive viscose and lyocell application tests. All pulps met the specifications for dissolving pulps. Further more, CCE-pulps showed a significantly higher yield after final bleaching. Morphological changes such as ultrastructure of the preserved outer cell wall layers, specific surface area and lateral fibril aggregate dimension correlated with the reduced reactivity towards regular viscose processing. The residual xylan after alkali purification depicted a lower content of functional groups and a higher molecular weight and was obviously entrapped in the cellulose fibril aggregates which render the hemicelluloses more resistant to steeping in the standard viscose process. Simultaneously, the supramolecular structure of the cellulose is partly converted from cellulose I to cellulose II by the alkaline purification step which did not influence the pulps reactivity significantly. Nevertheless, these differences in pulp parameters did not affect the lyocell process due to the outstanding solubility of the pulps in NMMO. Laboratory spinning revealed good fiber strength for both, regular viscose and lyocell fibers. The high molecular weight xylan of the CCE-treated pulps even took part in fiber forming.     

Novel concepts of dissolving pulp production

Herein, we report about existing and novel dissolving pulp processes providing the basis for an advanced biorefinery. The SO₂–ethanol–water (SEW) process has the potential to replace the acid sulphite process for the production of rayon-grade pulps owing to a higher flexibility in the selection of the raw material source, substantially lower cooking times, and the near absence of sugar degradation products. Special attention is paid to developments that target toward the selective and quantitative fractionation of paper-grade pulps into hemicelluloses and cellulose of highest purity. This target has been accomplished by the IONCELL process where the entire hemicellulose fraction is selectively dissolved in an ionic liquid in which the H-bond basicity and acidity are adequately adjusted by the addition of a co-solvent. At the same time, pure hemicellulose can be recovered by further addition of the co-solvent, which then acts as a non-solvent. The residual pure cellulose fraction may then enter a Lyocell process for the production of regenerated cellulose products.     

Oxidation of gaseous styrene by electron beam irradiation

In this research, the absorbed dose, background gases, relative humidity, and initial concentrations were selected as control factors to discover decomposition characteristics of styrene using electron beam irradiation. It was confirmed that a considerable amount of styrene was removed by primary electrons as well as radicals and ions, which were produced after the electron beam irradiation. Moreover, the removal efficiencies of styrene were observed to rise when the initial concentration was lower, moisture content was higher, and the absorbed dose increased. For instance, 50 ppmv styrene showed extremely high removal efficiency (over 98%) at a condition of 2.5 kGy. A small amount of styrene oxide, benzaldehyde, aerosol, CO, and CO₂ were produced as by-products after EB irradiation.     

Changes of biodiesel composition after electron beam irradiation

Journal of Radioanalytical and Nuclear Chemistry - The study of the influence of external factors on FAME is increasingly being taken up with research topics. Under natural conditions, they are...     

Development of an up-flow irradiation device for electron beam wastewater treatment

Electron beam irradiation processing is an available technology to treat sludge, groundwater, surface water and industrial and municipal wastewater. The use of this technology into environmental areas has moved slowly because industry and government are always conservative in the adoption of new processes, especially when they can not observe the efficiency and cost effectiveness of a treatment in a full scale facility.

In this direction the hydraulic system where the water is presented to the electron beam governs the efficacy of this technology. The present work is based on the development of the irradiation device, an up-flow delivery system that alleviates the dependence of energy transfer to the stream with the beam accelerating voltage (penetration capability).

In this work a series of experiments were performed to establish the relationships between accelerating voltage ranging from 0.5 to 1.5 MeV, current, water flow and deposited dose in order to optimize the operating parameters and the selection of a cost-effective commercial electron beam.     

Degradation of prednisone in aqueous solutions by electron beam irradiation

A novel degradation study of prednisone (PRE) in aqueous systems (10 mg L^?1) was performed under electron beam irradiation (EBI) in various conditions. The data demonstrate that the highest degradation caused by EBI was obtained with the oxidation of hydroxyl radicals. The proper amount of hydrogen peroxide could increase the PRE total carbon content removal rate. Nine degradation products of PRE in aqueous solution were preliminarily analyzed using ultra-high performance liquid chromatography in combination with mass spectrometry. Furthermore, the chemical analysis and possible degradation pathway were proposed with the assistance of theoretical calculation results by density functional theory.     

Modification of fluoropolymers by means of electron beam irradiation

High molecular weight polytetrafluoroethylene (PTFE) is transformed to free-flowing micropowder by treatment with electron beams. In case of irradiation in presence of air carboxylic acid fluoride groups are incorporated which rapidly hydrolyze to carboxylic groups in the surface-near regions due to atmospheric humidity. These polar groups reduce the hydrophobic and oleophobic properties so much that homogeneous compounding with other materials becomes possible. In addition to PTFE, copolymers of tetrafluoroethylene with hexafluoropropylene (FEP) and perfluoropropylvinylether (PFA) were modified. In case of identical irradiation conditions, the concentration of carboxylic groups is much higher in FEP and PFA than in PTFE, which is due to the lower crystallinity of the copolymers.

Electron beam irradiation of PTFE was performed in vacuum at elevated temperature above the melting point. The changes in the chemical structure were studied. The concentration of CF₃ branches was found to be much higher as compared to room temperature irradiation.

In a practical test PTFE micropowders functionalized by electron irradiation were compounded with epoxy resins, with polyoximethylene and with polyamides. Such compounds are characterized by very good frictional and wearing behaviour in dry-running tests.     

Biodegradability enhancement of textile wastewater by electron beam irradiation

Textile wastewater generally contains various pollutants, which can cause problems during biological treatment. Electron beam radiation technology was applied to enhance the biodegradability of textile wastewater for an activated sludge process. The biodegradability (BOD₅/COD) increased at a 1.0 kGy dose. The biorefractory organic compounds were converted into more easily biodegradable compounds such as organic acids having lower molecular weights. In spite of the short hydraulic retention time (HRT) of the activated sludge process, not only high organic removal efficiencies, but also high microbial activities were achieved. In conclusion, textile wastewater was effectively treated by the combined process of electron beam radiation and an activated sludge process.     

Ionic liquid extraction method for upgrading eucalyptus kraft pulp to high purity dissolving pulp

High purity cellulose from wood is an important raw material for many applications such as cellulosic fibers, films or the manufacture of various cellulose acetate products. Hitherto, multi-step refining processes are needed for an efficient hemicellulose removal, most of them suffering from severe cellulose losses. Recently, a novel method for producing high purity cellulose from bleached paper grade birch kraft pulp was presented. In this so called IONCELL process, hemicelluloses are extracted by an ionic liquid–water mixture and both fractions can be recovered without yield losses or polymer degradation. Herein, it is demonstrated that bleached Eucalyptus urograndis kraft pulp can be refined to high purity acetate grade pulp via the IONCELL process. The hemicellulose content could be reduced from initial 16.6 to 2.4 wt% while persevering the cellulose I crystal form by using an optimized 1-ethyl-3-methylimidazolium dimethylphosphate-water mixture as the extraction medium. The degree of polymerization was then reduced by a sulfuric acid treatment for subsequent acetylation of the pulp, resulting in a final hemicellulose content of 2.2 wt%. When pre-treating the pulp enzymatically with endoxylanase, the final hemicellulose content could be reduced even to 1.7 wt%. For comparison, the eucalyptus kraft pulp was also subjected to cold caustic extraction and the same subsequent acid treatment which led to 3.9 wt% of residual hemicelluloses. The performance in acetylation of all produced pulps was tested and compared to commercial acetate grade pulp. The endoxylanase-IONCELL-treated pulp showed superior properties. Thus, an ecologically and economically efficient alternative for the production of highest value cellulose pulp is presented.     

Use of electron beam for the production of hydrogel dressings

The electron beam irradiation technique has been utilized to prepare hydrogel wound dressings. The composition of the dressings is based on polyvinylpyrrolidone (PVP), poly(ethylene glycol) (PEG), and agar. Increasing the irradiation dose leads to an increase in the gel fraction; this increase is due to increased crosslink density. The gel fraction% decreases as the PEG concentration increases. The maximum swelling% decreases with increasing the irradiation dose, but increases with increasing the PEG concentration. This relationship can be utilized to modify the gel properties as gel fraction% and maximum swelling of the hydrogel. The prepared dressings could be considered as a good barrier against microbes.     

Enzymatic and alkaline treatments of hardwood dissolving pulp

Dissolving pulp was solubilized in 9% NaOH, resulting in 32% solubilization of the pulp. Most of the pulp hemicelluloses were solubilized during this treatment. During the alkaline treatment the cellulose crystalline form was converted from cellulose I to cellulose II. The alkaline insoluble residue was further treated with cellulases in order to render it more alkaline soluble (two-step process). The cellulose II was readily hydrolysed by Trichoderma reesei endoglucanases. Considerably higher hydrolysis yields and lower viscosities were obtained in the hydrolysis of the alkaline insoluble residue as compared with the original pulp. Compared with direct enzymatic treatment with subsequent solubilization in alkali, the overall alkaline solubility of the two-step process was slightly higher at the same enzyme dosage. However, when compared at the same hydrolysis levels, slightly lower overall alkaline solubilities were obtained in the two-step method. 0969--0239 © 1998 Black ie Academic & Professional     

Cyclization and crosslinking of polybutadiene in solution by electron beam irradiation

Effects of electron beam irradiation on liquid polybutadiene in n-hexane solution were studied at ?10°C. With irradiation, crosslinking of the polymer and loss of double bond by cyclization took place at the same time. These reactions were retarded by the addition of DPPH or triethylamine which indicated that both radical and cationic mechanisms contributed to this system.     

Effect of electron beam irradiation on physico-chemical properties of pullulan

Many widely used polymers undergo main chain scission or crosslinking when exposed to radiation. Effects of electron beam irradiation at different doses up to 500?kGy on the biodegradable pullulan polymer films have been investigated by ultraviolet?Cvisible (UV?CVIS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) techniques. UV?CVisible study shows increase of optical absorbance with increase of doses, attributing to the formation some groups or radicals. FTIR and TGA results reveal the processes of both crosslinking and degradation of polymer taking place depending upon the dose of e-beam radiation. The surface morphology of the film is found to be altered by the e-beam radiation as indicated by SEM micrographs.