Evolution and removal mechanism of the chromophores of Neosinocalamus affinis mechanical pulp in the hydrogen peroxide bleaching process
The application of bamboo in high value-added paper products is limited due to the difficulty of preparing high-brightness(＞78％)chemical-mechanical pulp.Based on the current bleaching chemi-mechanical pulp manufac-turing process,i.e.,alkaline hydrogen peroxide with ethanol-water media bleaching(AHEWB)system,the facile mild bleaching system has been proven to be an effective approach to break through the brightness limitation of the Neosinocalamus affinis mechanical pulp(NAMP)over 80％.In this study,bleached NAMPs(B-NAMPs)were pre-pared in three different systems,e.g.,two-stage bleaching process with conventional hydrogen peroxide dosage(90 kg/t)in aqueous system,four-stage bleaching process with high hydrogen peroxide dosage(180 kg/t)in aqueous system,and four-stage bleaching process with high hydrogen peroxide dosage(180 kg/t)in AHEWB system,re-spectively.The UV-Vis and Raman spectra of different B-NAMPs,as well as the 2D-HSQC of their milled wood lig-nin(MWL)and the pyrolysis gas chromatography mass spectrometry(Py-GCMS)of bleaching residues were carried out to distinguish the characteristics of B-NAMP's chromophores and bleaching residues.The results showed that the content of benzene-conjugated structures in B-NAMP decreased during the bleaching process.However,furan-conju-gated structures that could not be disrupted and solubilized in aqueous systems were generated during the bleaching section with high chemical dosages.Moreover,the Py-GCMS results of bleaching residues confirmed that the solubility of furan-conjugated structures was significantly improved in the AHEWB system,while the ring-opening reactions of benzene ring structures were simultaneously boosted.It was hypothesized that the trace amounts of ethoxy-late ions from ethanol ionization under alkaline conditions played a key role in selectively severing the chemical bonds within the furan-conjugate structure and NAMP,further achieving its dissolution.The findings of this study may pro-vide a theoretical basis for the development of a feasible cost-effective bleaching process for bamboo mechanical pulp and the extraction of lignin from biomass by selectively breaking chemical bonds.
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维普
