Preparation And Application Of Old Newspaper Based Lignin Containing Nan-Cellulose

As a kind of green polymer material,lignin containing nano-cellulose not only has the intrinsic characteristics of natural cellulose,but also has many excellent properties,such as large specific surface area,high aspect ratio,high mechanical strength,good biocompatibility and so on.Its lignin particles have the advantages of improving the hydrophobicity and solvent compatibility of cellulose,so it has potential application value in the field of composite materials.In this paper,lignin containing cellulose nanocrystals(LCNC)with different lignin content were produced from old newspapers using sulfuric acid hydrolysis process,and the products were used in reinforcing polyvinyl alcohol(PVA)hydrogel.The effects of different LCNC addition on the properties of composite hydrogels were investigated.Then,acidolysis precipitated lignocellulosic solid residues(LCSR)were mechanically defibrillated into lignin containing cellulose nanofibrils(LCNF)by ultrasonic assisted grinding method,which were blended with polylactic acid(PLA)matrix to prepare LCNF/PLA composite film.The influence of LCNF with different lignin content on the performance of composite films were explored.The main research results are as follows:Preparation of LCNC with different lignin contents.Firstly,by controlling the bleaching intensity,three waste pulps with different lignin content were prepared,and then three kinds of lignin contents of LCNC(LCNC-DPL:cellulose nanocrystals with low lignin content;LCNC-DPH:cellulose nanocrystals with medium lignin content;LCNC-DP:cellulose nanocrystals with high lignin content)were produced by sulfuric acid hydrolysis and dialysis.XPS analysis showed that the lignin content of the above three LCNC samples were 8.33%,13.54%and 19.29%,respectively.SEM,TEM and EDX results indicated that three LCNC samples displayed typical rod-like fibers with the average length and width of 140 nm and 11 nm,respectively.Lignin showed small globular-like particles on the surface of LCNC.Furthermore,the studies demonstrated that the cellulose type I structure was still retained in the three LCNC samples.With increasing lignin content,the crystallinity decreased and the hydrophobicity and thermal stability improved.Reinforcement effect of lignin containing cellulose nanocrystals composite polyvinyl alcohol hydrogel.The LCNC/PVA composite hydrogels were prepared by mixing the three kinds of LCNC and PVA,respectively.It was found that the incorporation of LCNC significantly ameliorated the viscoelasticity and compression performance of PVA hydrogel,and the rheological and compressive properties of the composite hydrogels improved with the increase of LCNC addition.When adding 1wt.%of LCNC-DP in PVA hydrogel,the G?_max and G?of the composite hydrogel were 16 and 18 folds that of pure PVA,respectively.At the 20%strain level,the compressive stress of PVA/1%LCNC-DP was 8 times that of pure PVA.The main reason was that mechanical entanglement was created after mixing LCNC and PVA in the formation of composite hydrogels.The presence of PVA and LCNC could form three types of complexes,namely PVA-PVA,PVA-LCNC and LCNC-LCNC,throughout the whole process.The lignin particles on the surface of LCNC acted as a bridge between PVA and LCNC,averted the self-aggregation of LCNC,limited the assembly of LCNC and PVA chains,formed a porous network structure,which was conducive to the transmission of compression stress.Meanwhile,the existence of porous network structure increased the viscoelasticity of composite hydrogels,so that the composite hydrogels had excellent rheological properties.Futhermore,with the increase in the lignin content of LCNC in the hydrogels,the pore size of the hydrogels reduced dramatically(from 4.26?m to 1.52?m),the thermal stability of the hydrogels improved obviously.In addition,the swelling behavior of the hydrogels was markedly enhanced by adding low dosage(0.1 wt.%)LCNC,and the swelling ratio of PVA/0.1%LCNC-DPL was as high as 1374%.Preparation of LCNF with different lignin content.LCNF(LCNF-DPL:cellulose nanofibrils with low lignin content;LCNF-DPH:cellulose nanofibrils with medium lignin content;LCNF-DP:cellulose nanofibrils with high lignin content)were produced by mechanical defibrillated of acidolysis precipitated LCSR via ultrasonic assisted grinding method,the lignin contents of the above three LCNF samples were 7.95%,13.9%and 19.5%,respectively.Morphology analysis displayed that some interconnected nanofibrils or single fibril network could be observed in the three LCNF samples.Lignin existed as small globular-shaped particles located between the cellulosic fibrils.The average diameter of the three LCNF samples were 19.8,17.9 and 16.1 nm,respectively.With increasing lignin content,the thermal stability and hydrophobicity of LCNF improved incrementally,and the crystallinity reduced gradually.Enhancement effect of lignin containing cellulose nanofibrils composite polylactic acid film.The LCNF/PLA composite films were synthesized by blending the three LCNF samples and PLA,respectively.It was discovered that the addition of LCNF dramatically increased the mechanical properties of PLA film,and the higher the lignin content,the better the mechanical properties of composite films.The tensile strength,elongation at break,Young's modulus of PLA/LCNF-DP composite films with the highest lignin content were 99.3 MPa,14.5%,10.3 GPa,which increased by 263.7%,417.9%,505.9%compared with pure PLA,respectively.This was because in the process of composite films formation,lignin and cellulose are combined well by hydrogen bonds and dipole-dipole interactions,and the van der Waals interactions occurred among the non-polar grous of lignin and PLA,and the polar groups of lignin formed hydrogen bonds with the ester groups of the PLA matrix,which obviously heightened the adhesion between LCNF and PLA matrix.The brittle fracture of PLA film gradually changed into ductile fracture,so as to improve its mechanical properties.Moreover,the addition of LCNF significantly enhanced the thermal and water vapor barrier properties of PLA films,also strengthened its UV-shielding performance.When LCNF-DP with high lignin content was added into PLA,the composite film could shield most of the UVA spectrum and 100%of the UVB,UVC spectrum.