Preparation Of Lignin-containing Nanocellulose And A Mechanism Study On The Effect Of Properties

Cellulose nanofibers(CNFs),nano-scale biomass-based polymer,can be extected from variant resource.Due to its low-price,nontoxic,degradable,good biocompatibility,high specific surface area and high mechanical properties,including Young's modulus and tensile strength.It has been a hot topic for several years.However,the high cost and energy consumption of manufacturing are the obstacle of application widely.To address this concern,a green and low energy process to manufacture novel cellulose nanofibers contains lignin micro-/nano-particles materials was developed in this research.Potential applications of cellulose nanofibers/lignin nanoparticle materials were explored as well.The main research contents have been summarized as following:1.Lignin-containing cellulose nanofibers(LCNFs)with various lignin contents were produced by a grinding process from switchgrass,which were pre-treated via Clean Fractionation(CF).The effect of different fractionation conditions(temperature and time)and passes of grindering on the energy consumption and morphologies of LCNFs were investigated.Results showed that nanosized fibers were found in clean fractionated samples before grinding.After several grinding passes,LCNFs with a similar degree of fibrillation as commercial cellulose nanofibers(CNFs)were obtained from the fractionated materials,which means residual lignin is beneficial to consume less energy during the grinding process.The dimensions and dispersion of LCNFs were significantly influenced by the lignin content in the LCNFs.Longer and well separated nanofibrils were observed from transmission electron microscopy and fluorescence microscopy with appropriate residual lignin(?13.7 ±1.59 %)in the LCNFs compared to those of LCNFs with either lower or higher lignin contents.Therefore,microsized and nanosized lignin particles were successfully obtained in a single process,and they not only facilitated LCNFs dispersion but also help to decrease the energy consumption during the grinding process.2.Three natural hybrid poplar variants with different recalcitrance were pretreated via clean fractionation to remove hemicellulose and partly lignin,then were used to manufacture lignincontain cellulose nanofibers(LCNFs)via grinding process.It can be investigated the influence of the biomass recalcitrance on energy consumption during the production of LCNFs.Some simple measures were demonstrated for characterizing lignocellulose fibers fibrillated at different passes through the grinder.Chemical composition analysis was determined by standard procedures.It can be found that degrees of recalcitrance played important role in lignin-removing.Microscope observation,degree of fibrillation and XRD were determined to estimate the influence of the lignin content and natural factors from different degrees of recalcitrance on LCNFs.Several nano-sized fiber original samples were obtained from clean fractionation.3.Micro and nano-sized lignin particles can be obtained with cellulose nanofibers by ‘one-step'grinding process.The results showed that residual lignin eased fibrillation.After a few passes grinding,LCNFs as same degree of fibrillation as commercial CNFs were obtained from fractioned materials.It is beneficial to save energy consumption in the grinding process.Lignin content is related to length of LCNFs.Longer and individualized nanofibrils were obtained from ca.18 %lignin residual materials than from lower lignin content materials with 13.7 k Wh/kg energy consumption and the yield is 87.9 %.In addation,lignin content contributes to temperature of fibrillation.The more lignin contain,the higher the mechanical temperature.It is because under the high shear force of disks,mechanical free radicals directly increased and ?-? interaction occurred within lignin fragments.4.The LCNFs film were prepared by filtration and heat-pressuring.The role of lignin content on morphology,hydrophilicity,moisture permeability,light transmittance,rheological property and thermal stability of LCNFs film has been investaged.The results haven been showed that the presence of lignin resulted in multi-layers struction of the LCNFs films.This structure contributes on reducing the hydrophilicity and water permeability of LCNFs films.After heat pressuring,pores between the CNFs were also blocked by the softened lignin,water is difficult to penetrate into the interior of the composite through the pores in the vertical direction.Besides,the presence of lignin reduces the light transmission of the film.The effects of lignin on the rheological properties,thermostability and tensile properties of LCNFs were investigated.The results showed that lignin content is higher,LCNFs are more susceptible to frequency changes,and internal hydrogen bonding is weaker.LCNFs with low lignin content have more free radicals on the surface of the nanofibers,and it is easier to form a stable network structure.At low angular frequencies,the molecular chain has more recovery time and space.The LCNFs changed its storage modulus with temperature.When the lignin content was moderate,the storage modulus increases with increasing temperature and the growth trend is stable.When the lignin content was too low(4.46 %),the storage modulus decreases as the temperature increases.The Tan ? value remained basically stable,demonstrating that the LCNFs membrane has good stability.Moreover,after heat pressing,when lignin was in a certain range,tensile properties and thermal stability were increased as the lignin content increases.5.The composites were prepared from lignin-contain nanocellulose and polylactic acid by“master batch” and blending method.The LCNFs samples with various lignin content(4.46 %,9.96 %and 18.6 %)and the bleached nano-cellulose were used,and the addition of nano-cellulose was taken as variable as well.The results showed that the interfacial force increased with the increase of lignin content.When lignin content was 18.6 %,the tensile strength and modulus of the LCNF/PLA composites reached a maximum,and the elongation at break first increased then decreased.The dynamic storage modulus of the composites increased with the increasing lignin content.Lignin connected with cellulose nanofibers via intermolecular hydrogen bonds,and van der Waals force and ester bond interaction force formed between polylactic acid and lignin.After melting,the morphology of lignin changed,its specific surface area increased,and the contact area with nanocellulose filament and polylactic acid increased respectively.The increase of lignin content can increase the interfacial interaction range and improve the interfacial adhesion.The lignin in LCNFs could act as adhesive in the “self-bonding” composited material.