Construction Of Platform For Click Functionalization Of Pulp Fibers

With features such as high selectivity,rapid rates and high yield,click chemistry has been extensively applied in various fields like organic synthesis,medicines.polymers etc.The most famous click reaction is copper(1)catalyzed azide—alkyne 1,3 dipolar cycloaddition(CuAAC).When applied in functionalization of pulp fibers,brilliant perspectives of CuAAC could be envisioned.Functional groups with click reactivity,like azide and alkynyl.are required to be incorporated into pulp fibers when click reactions are employed in the functionalization/modification of pulp fibers and their derivatives preparation.Pulp fibers as reaction substrates and hydroxyls as originally reactive sites,approaches based on different types of reactions are designed to prepare pulp fibers with click reactivity.The main contents are outlined below:1.Preparation of Yne-eth-PFs by Williamson etherificationPulp fibers as reaction substrates,propargyl groups were incorporated into pulps fibers and corresponding Yne-eth-PFs with CuAAC click reactivity were therefore obtained through Williamson etherification with propargyl bromide(PgBr).Effects of NaOH activation and etherification parameters on degree of substitution were investigated.The results showed that PgBr/AGU(the molar ratio of PgBr to anhydrous glucose unit AGU)was a crucial factor in adjusting the content of propargyl groups.Yne-eth-PFs were characterized by FTIR and XPS.Information obtained from the instruments confirmed the CuAAC between Yne-eth-PFs and 4-azidobenzoic acid under Cu(I)catalysis system.2).Yne-im-PFs based on combination of selection oxidation and Schiff base reactionDialdehyde pulp fibers,DAPFs,were prepared by selective oxidation using NaIO4 and used as substrates for Schiff base reaction.Effects of Na1O4/AGU,temperature,time and buffer system on the aldehyde content and yield were studied.The results showed that aldehyde content increased with the increase of NaIO4/AGU,at the same time degradation of pulp fibers deteriorated.The aldehyde content decreased when the reaction time was longer than 4h,elevated temperature simultaneously increased the aldehyde content and accelerated the degradation of fibers.DAPFs with premium aldehyde content and yield were prepared when distilled water was used as buffer system.Degree of polymerization,water retention values and handsheets of DAPFs prepared using different NaIO4 dosage were measured.DAPFs showed characteristic peak ascribed to aldehyde groups in the FTIR spectra and the crystalline changes were characterized by XRD.DAPFs as substrates,aldehyde groups as reactive sites,Schiff base reaction between DAPFs and ethynyl aniline(EAn)were employed to incorporate ethynyl groups;hence Yne-im-PFs were obtained.The effects of reaction parameters on the ethynyl content were investigated,and the reaction results of DAPFs with o-,m-,p-ethynyl anilines were studied.For DAPFs with different contents of aldehyde groups,the effects of reaction parameters were different.Ethynyl content of Yne-im-PFs increased with the increase of EAn dosage and the trend of increase of ethynyl content was much obvious for DAPFs with high aldehyde content.Raising temperature had more notable effect on DAPFs with high aldehyde content than that of DAPFs with low aldehyde content.It took a short interval for DAPFs with low aldehyde content reach reaction equilibrium,but much longer time for DAPFs with high aldehyde content.Yne-im-PFs with ethynyl groups content higher than 2.5 mmol/g could be obtained under appropriated conditions.CuAAC beteween Yne-im-PFs and 4-azidobenzoic acid were carried out and Yne-im-PFs@N3BCOOH were obtained.FTIR and XPS showed that ethynyl groups were successfully incorporated into Yne-im-PFs after Schiff base reaction,Yne-im-PFs and 4-azidobenzoic acid underwent CuAAC under Cu(I)catalysis system as expected.This combinational method is simple to operate,green and environment friendly,and completely proceeds in aqueous suspension.3).Ep-gt-PFs prepared by graft copolymerization and alkynyl/azido functionalized pulp fibers prepared by ring open reactionPulp fibers as substrate and ceric ammonium nitrate(CAN)as initiator;Ep-gt-PFs were prepared by graft from strategy between cellulose and glycidyl methacrylate(GMA).Ep-gt-PFs could serve as platform for epoxy-thiol click reaction,and also as intermediates to prepare alkynyl/azido functionalized pulp fibers through ring open reaction.Effects such as GMA dosage,initiator dosage,reaction time and temperature on epoxy content and graft percent were investigated,and the results showed that epoxy content and graft percent have similar trends of variation.Epoxy content increased with the increase of GMA dosage however decreased with the increase of initiator dosage.Effects of temperature and time were not obvious.Epoxy content of Ep-gt-PFs could be as high as 2.5 mmol/g under appropriate conditions.FTIR inferred that graft copolymerization introduced epoxy groups into Ep-gt-PFs.FTIR and XPS showed that Ep-gt-PFs were of click reactivity.Ring opening reactions between Ep-gt-PFs and propargyl bromide(PgAm)and NaN3 were employed to prepare alkynyl functionalized pulp fibers(Yne-o-gt-PFs)and azide functionalized pulp fibers(N3-o-gt-PFs).In preparation of Yne-o-gt-PFs,prolonged time,elevated temperature and increase of PgAm were all able to improve the alkynyl content;increase of total amount of epoxy groups would slowly increase the alkynyl content of Yne-o-gt-PFs.In preparation of N3-o-gt-PFs.elevated temperature and increase of total amont of epoxy groups were effective to improve the alkynyl content whereas prolonged time and increase of NaN3 dosage had no obvious effect.FTIR and XPS confirmed that Yne-o-gt-PFs and N3-o-gt-PFs successfully incorporated alkynyl groups and azido groups,respectively,and were both with click reactivity.4).Graft copolymerization of PMA and pulp fibers towards Pr-gt-PFsIn pulp fibers suspension,CAN as initiator initiating the graft copolymerization between propargyl methacrylate(PMA)and pulp fibers,propargyl functionalized pulp fibers(Pr-gt-PFs)were prepared by a one step reaction.The experiments results showed that increase of PMA dosage and initiator dosage were able to increase the graft percent,elevated temperature and prolonged time were also beneficial to graft percent.Under the preset conditions,the temperature had better not be higher than 50? and reaction time no longer than 5 h.FTIR showed that pulp fibers successfully grafted PMA and the products Pr-gt-PFs preserved propargyl groups.CuAAC of Pr-gt-PFs between NaN3 and DPPA were carried out,and the instruments analysis confirmed that Pr-gt-PFs were with click reactivity.