Preparaton Of Micro-nano-cellulose By NMMO Pretreatment And Its Application In Papermaking

Cellulose is the most abundant natural macromolecule carbohydrates.The obtained micro-nano-cellulose(MNC)by fibrillating have the advantages of light weight,high strength,large specific surface area and low coefficient of thermal expansion,can be widely applied in the papermaking,food,electronic equipment and other fields.MNC has both the properties of micron cellulose and nano-cellulose,can be potentially applied in papermaking.In this paper,bleached softwood pulp was used as raw material.4-Methylmorpholine N-oxide(NMMO)solution with water content of 20wt% pretreatment combined with high-speed mixing had been used for the preparation of MNC.The pretreatment conditions were optimized by the swelling rate as the evaluation criteria and MNC was analyzed and characterized.The effect of MNC dosage on paper reinforcement and filler retention was analyzed by sheets with pulp fiber.Cellulose nanofibrils(CNFs)were prepared from MNC by ultrasonic treatment.The morphology and properties of CNFs were characterized by modern analytical technique,and the effect of MNC on the properties of coating and coated paper was studied.The results show:1.Bleached softwood pulp was used as raw material.NMMO solution with water content of 20wt% pretreatment combined with high-speed mixing had been used for the preparation of MNC.The effect of reaction temperature,time and fiber concentration on the swelling rate of fiber was discussed.The optimum condition was as follows: the reaction temperature was90?,the time was 2h,and the fiber concentration was 2%.In this condition,the swelling rate of the fiber was 63.70%.The MNCs were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),particle size analysis,infrared spectroscopy(FITR),X-ray diffraction(XRD)and thermogravimetric analysis(TG).The results showed that the diameter of the prepared MNC were mainly distributed at 100-1000 nm and the average diameter was 336 nm,consistent with the definition of micro-nano cellulose.The chemical structure of MNC did not changed obviously.The crystal type of MNC transform from cellulose?to cellulose?,and crystallinity is 74.65%.The initial thermal degradation temperature of MNC is 274.3?,which means MNC still maintained good thermal stability.2.The sheets were prepared by mixing MNC with bleached softwood pulp with two beating degrees(15°SR and 45°SR).The effect of MNC dosage on the physical properties of sheets was analyzed.With the increase of MNC dosage,the drainability of the slurry decreased;the tightness and transparency of sheets increased and the permeability of paper decreased significantly.When the MNC dosage increased from 0% to 20%,the tensilestrength,folding strength and broken strength of sheets were significantly improved.3.The composite filler was prepared by pre-mixing MNC with precipitated calcium carbonate(PCC).The effects of MNC suspension concentration,stirring speed and CPAM dosage on PCC adsorption capacity were studied.The optimum preparation condition was as follows: the concentration of MNC was 5%,the stirring speed was 600 rpm,and the CPAM dosage was 0.06%.In this condition,PCC adsorption capacity can reach 82.354%.And the effect of PCC and composite filler filling on the sheets properties was investigated.The results showed that the composite filler has higher retention rate than PCC filler,when the filler content was 60%,the retention rate was as high as 80%.Composite filler has poor drainability,and provide paper with improved tensile strength.4.The cellulose nanofibrils(CNFs)was prepared from MNC by ultrasonic treatment.The CNFs were characterized by TEM,particle size analysis,FITR,XRD,TG.And the light transmittance and tensile strength of CNFs films were studied.The results show that the diameter of the prepared CNFs were mainly distributed at 10-50 nm and the average diameter was 15.8nm and the length is 500-700 nm.The crystal type of CNFs was between cellulose I and II,the crystallinity was 72.78%.The initial thermal degradation temperature of CNFs was263.5?,and CNFs still maintained good thermal stability.The CNFs films have a transmittance of more than 90% and a tensile strength of 133 MPa.CNFs were added to paper coatings to study the effect on the rheological properties of coatings and the properties of coated paper.The results showed that when the content of CNFs was 2%,the viscosity of the coating was 709mpa·s,the surface strength of the coated paper was 4m/s,the smoothness was174 s,increasing by 47.56 fold,40% and 47.46% respectively compared with CNFs content of0%.Due to the hydrophilicity of CNFs,the addition of CNFs reduces water resistance of the coated paper.