Study On The Process Of Bleaching Of Eucalyptus APMP PULP And Its Mechanism

In this paper,based on the improvement of the bleachability of eucalyptus APMP pulp,study on the bleaching process, bleaching agent and bleaching additives.And have a Preliminary study on its mechanism. The study results are as follows:(1)Studied in the five optimized bleaching processes:H2O2bleaching(P), peracetic acid (Pa), sodium borohydride (B) and sodium dithionite (Y) with single or two stages combination of bleaching, and optimize the bleaching process.Theresults showed that:P and Pa bleached whiteness were74.84%ISO56.29%ISO, whiteness of B and Y bleaching, respectively56.74%ISO,54.87%ISO; With two stages bleaching,brightness of Pâ†'B combination bleaching up to80.58%ISO,the brightness Pâ†'Y of and Pâ†'Pa combination bleaching were79.24%ISO,78.52%ISO respectively. Viscosity of Pâ†'B, Pâ†'Y, Pâ†'Pa decreased to630mL/g and635mL/g,652mL/g. The tensile, tear, burst index of the three two-stage bleaching have been improved.(2)Tetraacetylethylenediamine (TAED), urea peroxide (UP) as bleaching additives for further improving the pulp brightness by strengthen the H2O2bleaching process. Whiteness of H2O2with TAED,UP reached to78.41%ISO,79.04%ISO respectively,increased3.95%ISO,4.58%ISO compared with H2O2single-stage bleaching. Whiteness of Pâ†'B two stage bleaching with urea peroxidewas83.17%ISO.The viscosity of H2O2with TAED was697ml/g,higher than that of H202bleaching, and the viscosity of H2O2with UP was670ml/g.Physical properties of H2O2-TAED, H2O2-UP bleaching were increased,such as tensile index increased5.4%,5.1%respectively, tear index increased7.0%,10.0%respectively, the bursting index increased13.2%,18%respectivelycompared with separate H2O2bleaching.Thus,bleaching additives can not only improve the whiteness but the physical strength as well.(3)Analyzed the changes of lignin in bleaching by infrared spectroscopy.The results as follows:after H2O2bleaching, There have a reduction in conjugated carbonyl condensation guaiacyl and the guaiacyl methoxy ether bond vibration, an aromatic ring structure, the ester carbonyl group C=O, C-H deformation vibration.Among them, conjugated carbonyl was the most damaged.During NaBH4bleaching, Major reduction in lignin structure were conjugated carbonyl condensation guaiacyl and guaiacyl aromatic ring structure; and the emergence of new C=O stretching vibration. After H2O2and NaBH4two stages bleaching, the absorption peaks of C=O stretching vibration of the ester carbonyl group, non-conjugated carbonyl group or a carboxyl group disappeard.The absorption intensity of a beta-glycosidic bond vibration O-H-plane bending vibration in two-stage bleaching with additives was higher than those that bleaching without additives.(4)Analyzed the changes of fiber morphology before and after bleaching through fiber analyzer, the results showed that:fiber length decreased slightly width increased, fines content increased greatly after bleaching; after adding bleach additives, fiber length increased slightly as well as fines content, the fiber width remained, fines content of bleaching with addictives was less than that of without bleaching addictives.(5) Obtained by GC-MS:The organic pollutants of NaBH4and Pa bleaching waste both containe styrene, tributyl phosphate,dibutyl phthalate, hydrocortisone acetate structure, and the content of NaBH4was lower than that of Pa.The NaBH4bleaching major role in lignin side chain carbonyl and quinoid structure, Pa bleaching undermine not only the lignin side chain structure, but also the aromatic ring structure. Two types bleaching waste of TAED-H2O2and UP-H2O2, they both have styrene,tri-n-butyl phosphate,4-hydroxy-3-methoxybenzaldehyde (vanillin), oxato cyclododecane-2-ketone, palmitic acid. Analyse the waste characteristic of TAED-H2O2and UP-H2O2, it indicated that the TAED strengthened damaging the lignin structure of the side chain unsaturated bond and Urea peroxide reinforced damaging phenolic structure and the the aryl structure in H2O2bleaching process.