Preparation Of Cellulose Nanocrystals By ZnCl₂ And Its Application Of Paper Reinforcing Agent

People attach importance to cellulose nanocrystals(CNCs)day by day as they have excellent performance.In this research.CNCs are prepared from pulp with ZnCl2 aqueous solution.The Box-behnken design in Design-Expert software was used for comprehensive analysis and the comparison of main factors affecting the yield of CNCs,including mass of a-cellulose.reaction time,concentration of ZnCl2 aqueous solution and ultrasonic time.The optimal conditions after optimization are as follows:mass of a-cellulose is 1.45g,reaction time is 2.94h,concentration of ZnCl2 aqueous solution is 67.53%and ultrasonic time is 3.22h.The yield of CNCs can reach 98.5%.The determination coefficient reaches0.9967 and the adjusted r-squared is 0.9933,showing the model is fitted to the data.The samples at different periods of the preparation were observed by Fibers Analyzer,Transmission Electron Microscopy(TEM),Atomic Force Microscopy(AFM)and X-ray Diffraction(XRD).The results show that the fibers of the pulp are slender,and there are some fragments of some short fibers.The lengths are mainly between 0.68 and 5.31 mm,and the widths are mainly between 15 and 60?m.The morphology of a-cellulose made of the pulp is almost the same as that of the wet pulp,but there has been some reduction in the lengths and widths of the fibers.The a-cellulose prepared from the pulp becomes microfibrils under the synergy of ZnCl2 solution and mechanical work of the high-speed homogenizer.And the fibers are rod-like and form an interconnected web-like structure.The cellulose colloids forms a loose cross-linked network with fibers lengths of 160?300nm and diameters of 30?50nm by a complete reaction and a tight one with fibers lengths of 160?300nm and diameters of 35?50nm by an incomplete reaction.These cellulose colloids(microfibrillated cellulose)were dispersed by ultrasonic treatment and cellulose nanocrystals with length of 14?40nm and diameter of 10?20nm were prepared.Fourier Transform Infrared Spectrometry(FTIR)spectra shows transition of cellulose ? to ? has occurred during the preparation and the characteristic bands of the ?-cellulose,cellulose colloids and CNCs are the same,which demonstrate they all have basic chemical structure of cellulose.The degree of crystallinity declines from 60.8%to 52.9%.The nano-composite paper is made of paper which is reinforced by CNCs.microfibrillated cellulose(MFC)and CNCs mixed with MFC and tested.The mechanical properties of nano-composite paper were measured.The results show CNCs can increase tensile index and burst index of paper greatly meanwhile decrease tear index.The effect of enhancement of MFC is better than that of CNCs as the mechanical properties and retention of MFC is higher than those of CNCs.The tensile index and burst index increases and the tear index decreases with the dosage of MFC increasing.When the dosage of MFC is 9%,the amount of MFC connected with the pulp fibers reaches the maximum and the enhancement effect of MFC will not increase with the dosage of MFC increasing.Vulcanized paper is enhanced with nanofiber by the addition to vulcanized base paper and the addition to ZnCl2 aqueous solution.Both of the following methods can increase the vulcanized tensile strength.The tensile of vulcanized paper increased obviously with the dosage of MFC in vulcanized base paper increasing by addition to vulcanized base paper.The amount of MFC comnectecd with the pulp fibers reaches the maximum when the dosage of MFC is 10%The tensile strength of vulcanized paper decreases with MFC more than 10%.The enhancement effect of CNCs is better than that of MFC by addition to ZnCl2 aqueous solution as CNCs possesses greater specific area and smaller than MFC so that CNCs can be easier to get inside the fiber of base paper.When the dosages of MFC in the two methods are the same,the enhancement effect of the addition to vulcanized base paper is worse than that of addition to ZnCl2 aqueous solution as MFC in vulcanized base paper was not swelled by ZnCl2 aqueous solution incompletely so that part of hydrogen bonds did not break,which led to the number of its free hydroxyl is fewer than the MFC dissolved in ZnCl2 aqueous solution in the addition to ZnCl2 aqueous solution.