PFI磨浆对干湿竹浆制备阳离子纳纤化纤维素物化特性的影响

研究了PFI磨浆预处理对干、湿竹浆所制备的阳离子纳纤化纤维素(Q-NFC)物化特性和微观结构的影响规律。选用PFI磨浆处理前后的干、湿竹浆为纤维素原料,依次经过2,3-环氧丙基三甲基氯化铵化学预处理和高压均质机械拆解分离,制备了一系列Q-NFC水分散液;采用电导滴定、紫外-可见光分光光度计(UV-Vis)、旋转流变仪、透射电子显微镜(TEM)及X射线衍射仪(XRD)等手段对系列Q-NFC水分散液进行分析表征。试验结果表明,由湿竹浆所制备的Q-NFC较干竹浆所制备的Q-NFC具有更高的固体收率、表面电荷量、Zeta电位、纳纤化程度及更细的平均微纤直径;经PFI磨浆预处理后,干、湿竹浆纤维表面均发生大量分丝帚化现象,导致纤维在季铵盐化预处理过程中的反应可及性和反应活性增加,从而进一步提高了干、湿竹浆所制得Q-NFC固体收率、表面电荷量、纳纤化程度及透光度等物化特性,但减少了它们的微纤尺寸和聚合度。由此可以说明,PFI磨浆预处理能消除角质化给干竹浆在季铵盐化预处理中带来的不利影响,但是对Q-NFC的结晶指数无明显影响。

The influence of PFI pretreatment on physicochemical characteristics of cationic nanofibrillated cellulose prepared from once-dried and never-dried bamboo pulps

In this work,the effects of the PFI pretreatment on physicochemical characteristics and microstructure of as-prepared quaternizednanofibrillated celluloses(Q-NFC)derived from once-dried and never-dried pulps were investigated.With the once-dried and never-dried bamboo pulps pretreated before and after PFI as raw materials,a series of Q-NFCs were prepared,respectively,through the chemical pre-treatment using 2,3-epoxypropyltrimethylammonium chloride(EPTAC)and subsequent mechanical disintegration via a high-pressure homogenizer.The as-obtained Q-NFCs were characterized by the solid recovery ratio determination,conductometric titration,Zeta potentiometer,degree of polymerization and yield of fibrillation measurement,ultraviolet-visible light spectrophotometer(UV-Vis),rotation rheometer,transmission electron microscope(TEM)and X-ray diffractometer(XRD),respectively.The results showed that,compared to Q-NFC prepared from the once-dried bamboo pulp,the higher solid recovery ratio,surface charge content,Zeta potential,degree of fibrillation as well as finer average cellulose microfibril diameter were achieved for the Q-NFC from the never-dried bamboo pulp.It was clear that the role of hornificationoccurred in the once-dried pulps caused the decrease of the swelling capacity(i.e.water retention value)of fibers and closure of pores.As a consequence,the accessibility of EPTAC and reactivity of cellulose fibers were decreased.However,after the beating pre-treatment via a PFI mill,a high degree of fibrillation occurred on the surfaces of both once-dried and never-dried pulp fibers,which promoted the accessibility to the cationic reagents and reactivity of cellulose fibers in the quaternized pre-treatment process.As a result,it was found that the physicochemical characteristics(such as solid recovery,surface charge content,Zeta potential,degree of fibrillation and light transmittance)of the bamboo pulp-derived Q-NFCs were markedly improved with a decrease in both average microfibril diameter and DP v value.The results demonstrated that the adverse effect of hornification on the subsequent quaternized pre-treatment of the once-dried bamboo pulp was eliminated.But both wetting sates of bamboo pulp and PFI pretreatment had slight effects on CrI values of the resulting Q-NFCs.This fundamental knowledge would be crucial to understand how the hornification of cellulose pulps affects the physicochemical characteristics and microstructure of as-obtained Q-NFCs and would be favorable to optimize the preparation conditions of Q-NFC.