TEMPO-mediated Oxidation Of Bleached Softwood Pulp And Preparation Of Nanofiber Based Aerogel Microsphere

With the development of industry,people's voice on environment protection is much bigger due to the high social environment pressure.Hence,seeking a kind of cleaner production resources is imminent.Cellulose is one of the main research objects in pulping and papermaking industry because it is abundant,non-toxic and biodegradable.The system of TEMPO/NaBr/NaClO was used to modify the fully bleached kraft softwood,and then nanofiber based aerogel microspheres were prepared.During the experiment,temperature and the amount of oxidizing agent were studied to find the relationship between oxidative product and oxidation rate.What's more,it was researched to get the influence of carboxylate content and fiber size on nanofiber based aerogel microspheres.SEM was used to observe the morphology of aerogel microspheres and AFM was used to observe the morphological changes of nanofibers.The results were as follows:(1)Some alkali soluble substances had effects on the content of aldehyde and carboxylate during the TEMPO-mediated oxidation.The variations of aldehyde and carboxylate were erratical when the pulp was without pretreatment.However,the content changed regularly while the pulp was treated with 17.5% sodium hydroxide,because the alkali soluble substances were wiped off and the pulp only contained ?-cellulose fiber.(2)The amount of sodium hypochlorite had influence on the content of aldehyde and carboxylate.Aldehyde content was increased rapidly and then increased slowly,but carboxylate content was on the contrary.The aldehyde content could be up to 200 ?mol/g when sodium hypochlorite was 1.2 mmol/g.The falling range of aldehyde was as same as the increasing range of carboxylate.It declared that TEMPO-mediated oxidation was two steps,it was a long response to convert hydroxyl to aldehyde and it was a fast reaction for carboxylate group.(3)The oxidative temperature had influence on oxidative product and rate.Content of aldehyde was decreased when sodium hypochlorite was over 1.2 mmol/g.Under the temperature of 5?,10? and 15?,the falling speed was similar,but it was quite different with 25?,the falling speed was very quick on 25?,because high temperature accelerated the oxidative rate and improved the convertion of aldehyde to carboxylate.Lower temperature was in favor of aldehyde production and high temperature was benefit for carboxylate content.(4)Carboxylate content had direct influence on the fiber sizes,what's more,it also affected the preparation of aerogel microspheres.When the content of carboxylate was 0.9769 mmol/g,it needed at least 12 min to treat the oxidized fiber,but it just need 3 min to treat the fiber when carboxylate contents were 1.12 mmol/g and 1.4096 mmol/g.Nanofibers,which treated 12 min and containing 0.9769 mmol/g,had same fiber sizes with that in carboxylate content 1.12 mmol/g and treated 3 min;nanofibers,which treated 20 min and containing 0.9769 mmol/g,had same fiber sizes with that in carboxylate content 1.12 mmol/g and treated 6min.(5)Aerogel microspheres were prepared by the TOCN,carboxylic content affects the formation and distribution of microspheres.Under the same ultrasonic conditions,the higher carboxylic content it had,the better aerogel microspheres would be.Deforming effects were followed the sequence as 1.4096 mmol/g,1.12 mmol/g,and 0.9769 mmol/g,respectively.The dispersion and particle size of microspheres were not good when the content of carboxylate was low,but aerogel microspheres had good dispersion when the nanofibers had high carboxylate content.(6)TEMPO-oxidized cellulose fiber could be changed by different strength of ultrasonic wave.So,it could provide the condition for its application.