| Reactivity is one of the most significant parameters for dissolving pulps,which is closely related to accessibility of cellulose.High reactivity of cellulose improves the quality of cellulose-end products and lowers the demands of reactants.Reactivity is used to evaluate the degree about carbon disulfide reacts to hydroxyl on glucose units of cellulose chains.However,increasing the accessibility and reactivity of cellulose is not a simple task.Based on the combination analysis of influence factors of the reactivity and methods of improving reactivity,fiber morphology and chemical composition of different parts of green bamboo(Bambusa oldhami)including tip,middle,root of bamboo,and outer layer(OL),middle layer(ML),inner layer(IL),and nodes from different positions of bamboo were analyzed.The application of bamboo materials for dissolving pulp preparation was evaluated upon the factors about affecting reactivity of bamboo materials.The relationship between parameters of bamboo pulp and Fock reactivity was investigated.The effects of different pulping technologies and alkali concentration of cold caustic extraction on pulp parameters were investigated.Furthermore,the factors affecting reactivity were proposed according to analysis of relationship between different parameters of bamboo dissolving pulp and Fock reactivity.Various methods,including mechanical treatments,acid treatment,surfactant treatment and cellulase treatment,were used to improve the reactivity.And the effects of the above methods on parameters of bamboo dissolving pulp were studied.The present study could provide significant information for the processing and utilization for bamboo material,such as process optimization of dissolving pulp preparation.The study of cellulose pretreatment was important for reactivity improvement on cellulose derivative reaction.The fiber morphology and chemical composition of different parts of green bamboo were analyzed.The results showed that:OL,ML,IL,and notes from different positions of bamboo mainly comprised of cellulose,lignin and hemicellulose;the cellulose content of ML from bamboo root was the highest while cellulose content of IL from bamboo tip was the lowest;the amount of non-cellulose components from OL and IL including lignin,pentosan,ash,extraction,metal ion content were higher than ML;fiber length of ML from bamboo root was the longest;the crystallinity of ML and notes were higher than OL and IL in the middle position;surface density of OL and IL were higher than the ML.XPS results showed that the OL was mainly covered with extraction in the middle position;IL was mainly covered with lignin;ML and notes were mainly covered with carbohydrate.These results indicated that ML had the greatest advantage as the raw material to prepare dissolving pulp.Dissolving pulp uniformity and reactivity will be affected by the difference of different parts of bamboo when it was used as raw material.The reactivity of dissolving pulp was discussed according to different dissolving pulps prepared by different pulping methods and different concentration of sodium hydroxide at the cold caustic extraction stage.The relationship between bamboo dissolving pulp performance and Fock reactivity were analyzed.In the kraft-based pulping(KP)process,lignin was removed from the bamboo chips in the cooking and bleaching process,and hemicelluloses is mainly removed from bleaching process;while in the prehydrolysis kraft(PHK)pulping process,the prehydrolysis step was critical for the hemicelluloses removal,and the lignin removal was mainly removed in the subsequent kraft pulping.From the comparison of Fock reactivity from different pulps,the reactivity of PHK pulp was higer than the KP dissolving pulp.The Fock reactivity of the dissolving pulp was affected by both the hemicellulose,the degree of polymerization and crystal structure.Slightly reduction of the degree of polymerization was beneficial to the improvement of the reactivity.The transformation of cellulose cellulose ? to cellulose ? structure had the disadvantage for Fock reactivity.The formation of cellulose ?type should be avoided in the derivatization reaction.Furthermore,specific surface area,pore diameter,pore volume and degree of hornification were closely related to Fock reactivity.Mechanical treatment was used for improving reactivity of bamboo dissolving pulp.Results showed that the Fock reactivity of the dissolving pulp was improved from 68.3%to 73.2%by PFI refinering about optimal condition of 15,000 revolutions.Fock reactivity of the same dissolving pulp can be increased from 68.3%to 84.0%after beating treatment for optimal condition of 30 min.The Fock reactivity of PFI refinering was higer than that valley beating at the same beating conditions.PFI refinering had important function,which showed fibrillation,lamination or the cell wall destruction.And the treatment resulted in addition of the fines content and specific surface area while decreasing the fiber length,degree of polymerization,and the crystallinity of cellulose.Valley beating also led to variations in the fiber morphology and cellulose structure,and more fiber cutting than PFI treatment.The effects of metal ions and silica on the reactivity of the dissolving pulp were discussed.HCl and disodium edetate dihydrate(EDTA),sodium hexametaphosphate(SHMP),diethylenetriamine pentaacetic acid(DTPA)were used in acid treatment,which was applied to bamboo dissolving pulp.The effects of different pH values,the processing time and chelating agent dosage on the reactivity were discussed by analyzing the pulp performance of Fock reactivity,yield,ash content,brightness and degree of polymerization.The presence of metal ions could have negatively impact on the reactivity,and the negative impact of the iron ion was the obvious.Silica also had the same impact on the reactivity.The results showed that the optimum conditions were 3.0 of pH,45 min of treating time,3.0%of DTPA dosage under the 50 ? of treatment temperature.Fock reactivity increased from 67.2%to 74.1%.The content of iron ion of dissolving pulp decreased from 72.19 mg/kg to 38.11 mg/kg.These results led to increase of the specific surface area,pore diameter and volume.Fiber longitudinal split and fibrillation was occurred.The crystallinity of cellulose slightly increased and the value of O/C increased after acid treatment.Molecular weight of cellulose decreased and the polydispersity index(PDI)decreased from 5.22 to 4.91.Three surfactants,including Turkey Red Oil(TRO),Polyoxyethylene Castor Oil(PCO),Polyether Polyol(PP),were used for improving the reactivity of bamboo dissolving pulp.The effect of TRO on improving the reactivity was the most optimal base on the same treatment conditions.The 1.5%and 0.1%of TRO dose were optimal at the before dry stage(BD)and the before steeping stage(BS),respectively.Surfactant treatment decreased surface tension of the lye.The decrease of surface tension and improvement of Fock reactivity showed high level of correlation,which showed decrease of surface tension was one of the reasons for the increase of the reactivity.Surfactant was added to the dissolving pulp,which weakened the hydrogen bonding between the cellulose molecules and then resulted in the increase of specific surface area,pore diameter and pore volume.Improvement of the reactivity and the changes of pulp propertied by celllulase treatment were analyzed.The results showed that cellulase dosage 0.10 U/g,enzymatic treating time 60 min were chosen as the optimal conditions based on the conditions of pH 4.6,pulp consistency 5%and temperature 55 ?.As a consequence,promising results were obtained after the cellulase treatment,which showed the considerable higher Fock reactivity compared with the initial bamboo dissolving pulp.The Fock reactivity increased from 69.5%to 88.0%with slightly degradation of cellulose.The degree of polymetization of cellulose decreased from 643 to 593.The results of other properties including ?-cellulose,yield,glucose content and molecular weight distribution also supported these conclusions.These results were mainly due to the effects of etching or peeling of fibers primary wall during the cellulase treatment,thus opening up cellulose structure and increasing the accessibility of fibers.The enhancement of accessibility of enzymatic treating pulp was certified by the results from BET specific surface area and scanning electron microscope.Furthermore,the results of X-ray diffraction showed that cellulose crystalline structure was not changed after cellulase treatment.With the increase of dosage of cellulase,the crystallinity increased at first then decreased latter. |
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