Influence Of Adsorbed Hemicelluloses On Paper Properties And Printability

Lignocelluloses, composed of cellulose, hemicelluloses and lignin, are the major global r esource used for manufacturing pulp. In modern fiber-line process, some hemicelluloses and a main portion of lignin in raw material are removed. Anyway, hemicellulose in pulp brings an important contribution to pulp quality although its content is less than cellulose in pulp. Hemi celluloses can serve as inter fiber bonding agents to increase inter-fiber bonding area and cons equently improve strength properties, such as tensile index, burst index and tear index. Hemic elluloses are able to improve fibre flexibility which promotes the conformability of the fibres and results in some changes during the formation of paper sheet. In addition, hemicelluloses a re also a main component in determining the energy of the fibre surface which affects subsequ ent ink penetration.The present work investigates the effects of hemicelluloses loss from pulp on the structure and printability of paper. The adsorption of native and cationized hemicelluloses onto bleached kraft pulps and CTMP was also investigated. The objective of this work was to investigate the relationship between hemicelluloses content and the formation of paper sheet.The influence of hemicelluloses loss on the paper properties and printability was investigated by selectively extracting part of hemicelluloses from bleached softwood and hardwood kraft pulp. The bulk, surface roughness, and air permeability of paper were found increased as a result of hemicelluloses loss, particularly as the hemicelluloses content in pulp was decreased below 13%. Both the brightness and opacity of the paper were slightly improved due to the removal of hemicellulose. Meanwhile, strength indices decreased as expected. Both ink transfer and print through were reduced with hemicellulose loss. When the print density was lower than 1.6, the dependence of print through on hemicellulose loss at a certain degree of print density was not obvious.The hemicelluloses adsorption was also influence the paper properties, besides the hemicelluloses loss. Firstly, hemicelluloses was isolated from eucalyptus wood and then adsorbed on the bleached kraft pulps and CTMP fibers. It was found that adsorption of hemicelluloses onto softwood kraft pulp was slightly higher than hardwood; however, hemicelluloses with low arabinose content were preferentially adsorbed onto the hardwood fibers. Adsorption onto CTMP was the lowest, although the general phenomenon of native absorption was rather low under the applied conditions. Secondly, the tensile index increased upon hemicelluloses addition and reached a maximum at 4% hemicelluloses dosage, whereas the tear index increased depending on the pulp type. The air permeability and surface roughness of the bleached eucalyptus kraft pulp slightly decreased, however, although the brightness and opacity were not changed. SEM analysis shows that hemicelluloses adsorption increases bleached eucalyptus kraft pulp fibers interaction, whereas the effect of hemicelluloses addition on the beaten pine kraft pulp is unclear. The hemicelluloses adsorption also affected printability. It was found that print through for the bleached eucalyptus kraft pulp hand sheet slightly decreased, but for the bleached pine kraft pulp hand sheet it was unaffected. Print densities were not influenced. Finally, the influences of hemicelluloses surface sizing on the inkjet printing paper on the paper properties and printing quality were investigated. It was found that the tensile and tear strength was increased, but burst strength was not affected. The paper surface roughness and advancing contact angle was decreased. The dot gain percentage of inkjet paper printing was decreased after hemicelluloses surface sizing.To increase their affinity to cellulose, cationic derivatives instead of original hemicelluloses have been used to modify the bleached softwood and hardwood kraft pulps. It was found that the adsorption amount of cationic hemicelluloses on kraft pulp fibers was increased compared to native hemicelluloses adsorption. The adsorption amount of cationic hemicelluloses on bleached softwood kraft pulp fibers was higher than that on bleached hardwood kraft pulp fibers. The cationic hemicelluloses addition in both bleached softwood and hardwood kraft pulps can decrease the bulk, surface roughness and air permeability of paper. The tensile and tear strength was increased with the cationic hemicelluloses addition. For the printability, the print density of bleached softwood and hardwood kraft pulp paper was not affected; nevertheless the print through of bleached hardwood kraft pulp was decreased. The cationic hemicelluloses with high degree of substitution was used as color fixing agent and sized on the inkjet paper surface to investigate the influences on the paper properties and printing quality. It was found that the tensile and tear indices were increased and advancing contact angle was decreased. The dot gain percentage of printing was decreased, especially for magenta and black ink. The lightness and chroma of black ink at dark tone was influenced.The hemicelluloses were reacted with Rhodamine B isothiocyanate(RBITC) to obtain RBITC-Hemicelluloses. RBITC-Hemicelluloses were adsorbed on bleached softwood and hardwood kraft pulps and bleached CTMP fibers and observed with Laser Scanning Confocal Microscope(CLSM). It was found that hemicelluloses can absorbed on fiber surface and partly wicked into the intra-fiber. The inner wall and outer wall of fiber did not make difference.