| Cellulose is the most abundant carbon hydrates polymer in nature，it is also the maincomponent in plant fiber as the raw material of paper. The excellent structure and propertiesof cellulose determines that paper is plastic, biodegradable and renewable, and transparentpaper is widely used in some areas of the society as its good optical performance.The TEMPO/NaBr/NaClO system was applied to eucalyptus wood fiber under alkalinecondition to investigate the fiber characteristics and paper transparency properties when thedosage of NaClO more than8.1mmol/g cellulose. To characterizing fiber surface morphology,length, width, fines, and so on when changing the beating degree of fibers and to investigatethe effect of oxidative condition and fiber properties on paper transparency and strengthcharacteristics. Different aging treatments were applied to paper prepared before to study therelationation between paper reversion and the content of carbonyl group.The results show that:1. Paper transparency is as high as87%when the dosage of NaClO is greater than8.0mmol/g cellulose in TEMPO/NaBr/NaClO system. The pulp suspension became moretransparent, the fiber length decreased by47.5%, fiber width increased by34.3%, finescontent increased eightfold and fiber curl decreased by13.9%. Paper prepared by TEMPOoxidized treatment fibers has a very dense structure; single fiber can hardly see on its surface,transparency is above80%, paper elastic modulus increased6times at the same time.2. The yields of oxidized fiber were less than60%when used fiber beating degree from15°SR to45°SR while the dosage of NaClO reached8mmol/g cellulose. The length offibers after TEMPO oxidization was all decreased and the decline was much more obvious inlow beating degree (15°SR). The influence on width and fines of oxidized fibers aregradually weakened with the increase of beating degree. Fiber surface became smooth, andbrooming disappeared as the dosage of NaClO increasing in oxidized system. Fiber color gotdiluted under the same dyeing condition after oxidation. The carboxyl content of pulp in lowbeating degree increased faster than that in high beating degree under the same condition.3. Paper density increasing when the dosage of NaClO increasing in beating degree of15°SR and21°SR, but when the dosage of NaClO increases to8mmol per gram cellulose, density of all samples up to0.8g/cm3.Transparency of paper incereasd along with theincrease of dosage of NaClO as the beating degree increased from15°SR to45°SR, andwhen dosage of NaClO was8mmol per gram cellulose, all the paper transparency were above86%. But paper transparency was more than80%only in15°SR and21°SR when the dosageof NaClO was6mmol/g cellulose. This also can be observed in optical image below.With theincrease of dosage of NaClO, the surface roughness of paper prepared by free pulp wasdeclining while prepared by half free and half shiny pulp was increased before reduced, andpaper strength of15°SR and21°SR increasing.when the dosage of NaClO increasing, but thesituation was on the contrary in other beating degree The porosity of paper in15°SR and21°SR decreasing when the dosage of NaClO increasing. But porosity values in other beatingdegree were first increases then decreases. TEMPO oxidation would first remove broomingpart on fiber surface and then increase the fiber width to make paper became tighter whichcan be observed from SEM graphs.4. The carbonyl content increased circuitously with the increase of dosage of NaClO, thevalue was increased from0.08to0.77mmol per gram cellulose in15°SR and from0.11to0.68mmol per gram cellulose in45°SR. Optical graphs and Δb datas both show that paperpreparated from15°SR and45°SR had slight discoloration under60℃and8hoursillumination, and had obvious color change after placed in room temperature for10months,and had badly discolored after heating in150℃for24hours. The paper yellowing behaviorwas more serious in15°SR than45°SR, and the sum of carbonyl and carboxyl contentdifference may be the reason of this phenomenon. |
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