Study On The Preparation Of Water-redispersed Nanocellulose Whiskers

Nanocellulose whiskers (NCW) were prepared by the hydrolysis method. Due to thelarge surface area and abundant surface hydroxyl groups on the NCW, the aggregationphenomena occurred through the hydrogen bonds and Van der Waals force between thenanocellulose particles during the spray drying, which could not be redispersed to its originalNano-size through the physical or chemical methods. Therefore, it was special significant tostudy the preparation of redispersibility NCW.The stability and redispersibility of NCW suspensions could be improved by themodification of NCW with the steric or electrostatic functional groups, which furtherimproved the accessibility and affinity of water molecules onto the NCW. Based on thishypothesis, the physical and chemical methods were used to modify the surface of the NCWwithout changing their intrinsic properties. The mechanisms and factors which influenced thedispersion and stability of the nanoparticles during the preparation process were investigated.Sodium carboxymethylcellulose (CMC-Na) was used to modify the NCWredispersibility. The influence of CMC-Na amount, pH value of the suspensions, ultrasonictime, and inlet temperature of the spray drying on the properties of the redispersibility wereinvestigated. The results showed that NCW water-redispersion suspensions were obtainedwith an average particle size of170nm, a length from50nm to400nm, and a Zeta potentialof45mV, when the amount of CMC-Na was6%, the pH value of the suspensions was7, theultrasonic time was5min, the inlet temperature of the spray drying was160℃, respectively.The NCW modified by CMC-Na were characterized using several analytical techniques suchas FT-IR, SEM, TEM and TGA etc. It was showed that the CMC-Na modified NCW retainedthe basic structures of cellulose and realized the role of the physical package of CMC-Na forNCW.Acrylic acid (AA) and Methacrylate (MA) were used to modify NCW with the graftcopolymerization method. The effects of experimental conditions on the properties of themodified NCW redispersibility were investigated. The acrylic modified NCW werecharacterized using several analytical techniques. It was showed that a length from50nm to300nm, an average particle size of109nm, Zeta potential of43mV for acrylic acid (AA) andan average particle size of98nm, Zeta potential of48mV for Methacrylate (MA) with lightblue appearance were obtained when the solid content of the suspensions was1%, the spraydrying gas flow rate was0.5m3/h, feed flow rate was6mL/min, the molar ratio of AA/NCWis2.5:1, MA/NCW is3:1, respectively. The spray drying principle, DLVO theory, space stability theory, free radicalpolymerization and kinetic equations during the modification and redipersion were studied.On the basis of experimental data, some discuss, such as the intermolecular forces and lightscattering on the preparation, the redispersion and factors which influence the properties ofthe redispersibility of the redipersed NCW aqueous suspensions and the stability mechanisms,were analyzied and studied, which laid the theoretical basis for the application of redispersiblenanocellulose whiskers.