High-yield Pulping Properties Improvement From Bamboo Chips By Partial Removal Of Parenchyma Tissues

The bamboo resources are very rich in China.It is indicated by the China’s paper industry plan in the "13th Five-Year" period that the production of bamboo pulp will be encouraged and promoted.With the high yield pulping process having many obvious advantages,such as high utilization efficiency for fiber resources,less capital investment and easier effluent treatment and so on,it is recognized that the application of high-yield pulping process shall be one of the important measures for the healthy development of bamboo pulping industry in China.In this dissertation,with bamboo chips being sampled from Chitianhua paper mill,Chishui city,Guizhou province,the pulping properties of bamboo by chemi-mechanical and semi-chemical processes were investigated;the bleach abilities of bamboo chemi-mechanical pulps were evaluated;both pulping and bleaching process conditions were optimized;the pulping waste water characteristics and pollution load of the above technological process were analyzed;and the possibility of comprehensive utilization of lignin in the cooking liquor from semi-chemical processes was investigated preliminary at the end.Parenchymal portion（called’bamboo powder’）was partially removed from bamboo by compression of bamboo chips and screening,with a removal rate of 11.4%,the accepts called‘bamboo bundles’.Chemical composition and fiber morphologies were analyzed,and the results showed that,ash content in bamboo bundles decreased by 38.6%of that in bamboo chips,cellulose content increased by 4.71%;Ash content in bamboo powder is almost 3 times of that in bamboo chips,pentosane content is 1.5 times of that in bamboo chips;the average fiber length of bamboo bundles is equivalent to that of bamboo chips,it proves that almost less fiber damaged to shorten fibers by compression operation.The 3 types of chemical impregnation methods,i.e.alkaline peroxide,alkaline sulfite and caustic soda,were applied to produce bamboo chemi-mechanical pulps.The specific refining energy consumptions were recorded and calculated,the initial pulp brightness measured;bleachabilities of chemi-mechanical pulps by different chemical impregnations were investigated,physical strength and optical properties of bleached pulps measured on basis of hand-sheets;effluents from pulping processed were collected and characterized.Results show that,there are significant differences on pulping properties of bamboo bundles by using these 3different chemical impregnations:A)by alkaline peroxide impregnation,the lowest specific refining energy consumption of 1368kWh/t used,a highest pulp brightness of 36.3%ISO achieved,the lowest effluent generated and more dense pulps produced;B)by alkaline sulfite impregnation,higher specific refining energy consumption of 1668kWh/t used,and darken pulps produced;C)by caustic Soda impregnation,the specific refining energy consumption ranked between those of other two impregnations,acceptable initial pulp brightness of31.9%ISO,the bulkiest pulps of 3.43cm³/g produced.Chemi-mechanical pulps from bamboo bundles were prepared by using alkaline peroxide impregnation,bleachabilities of bamboo CMP pulps were investigated by using different stage-combinations peroxide bleaching sequences.Results show that,at the same peroxide dosage of 12%,bleached bamboo pulps with a brightness of 72.1%ISO are obtained by using a 3-stages（2%/4%/6%H₂O₂）combination bleaching sequence,only brightness level of 66.8%reached by a 2-stages（2%/10%H₂O₂）combination bleaching sequence.CMP pulps were pre-activated by peroxide acetic acid,followed with hydrogen peroxide bleaching stage,the optimized bleaching conditions illustrated as A)Pre-activation stage:peroxide acetic acid dosage 2%,pH 6,consistency20%,temperature 70℃,retention time 60 min B)Hydrogen peroxide bleaching sequence:I-stage hydrogen peroxide dosage 8%,sodium silicate 2%,diethylene triamine pentaacetic acid（DTPA）0.2%,soda 5.5%,consistency 20%,temperature90℃,retention time 60 min,and the brightness of bleached pulps reaches up to 70.5%ISO.After hydrogen peroxide bleaching,additional reducing bleaching stage with Formamidine sulfinic acid（FAS）or Na₂S₂O₄ was employed（3-stages hydrogen peroxide bleaching followed with 1-stage FAS or Na₂S₂O₄ reducing bleaching）,at the hydrogen peroxide dosage of 10%（2%/4%/4%）and FAS dosage of 2%,bleached pulp brightness reaches up to 76.2%ISO;at the same hydrogen peroxide dosage,while Na₂S₂O₄ dosage of 2%,brightness is 73.2%ISO,with contrast to traditional bamboo CMP bleaching,the very good brightness level has been achieved by this study.The market of unbleached tissue and sanitary paper products enlarged very fast,because of softness of Semi-chemical pulp fiber,which can be used as furnishes for production of unbleached tissue and sanitary paper products.On other hand,at a pulp mill integrated with chemical pulping line and alkali recovery plant,black liquor from semi-chemical pulping pre-concentrated by evaporation or membrane treatment prior to alkali recovery system.Semi-chemical pulping properties of bamboo bundles were compared by using Soda/AQ and Alkaline sulfite pre-cooking operations.Results show that,alkaline sulfite cooking produce semi-chemical pulps with higher yield and higher Kappa number than Soda/AQ cooking;by extension of cooking time,pulp yield and Kappa number decreased by both cooking processes;higher physical strength pulps can be produced by Soda/AQ cooking,at the same time pollutant load of its cooking spent liquor are higher too.The possible utilization of semi-chemical cooking spent liquor were tried.The spent liquor was thickened by ultrafiltration and evaporation and used as partial replacement of phenols during production of resin.IR spectrum and TG analysis were used,the average molecular weight of lignin fragment in spent cooking liquors are lower containing with lots of active functional groups as hydroxyl,methoxyl groups etc.The thermal stability of resin slight decreased because of introducing the recycled lignin in the spent liquor.