Study On Green Preparation Of Micro/Nanofibrillated Cellulose And Its Enhanced Application

With the continuous improvement of people's environmental awareness,the renewable resources industry is continuously rising.The researchers'attention has been widely attracted by nanocellulose with its unique advantages such as high specific surface area,high tensile strength,renewability and biocompatibility.At present,chemical methods are the most common method for preparing nanocellulose,but there are still some disadvantages such as large pollution and difficult treatment of waste liquid.In this paper,micro/nanofibrillated cellulose?M/NFC?were successfully prepared by mechanical milling method and enzymatic-mechanical method,respectively,using a masson pine fiber as a raw material.M-M/NFC?M-M/NFC1 and M-M/NFC2?prepared by mechanical grinding method was applied to enhance the mechanical properties of paper,and EM2-M/NFC obtained by mechanical-enzymatic method was used to improve the mechanical properties of polyvinyl alcohol?PVA?fibers.The paper mainly included the following aspects:?1?Using Masson pine fiber as raw material,M/NFC were obtained by mechanical grinding method and mechanical-enzymatic method.The results showed that the M-M/NFC?M-M/NFC1 and M-M/NFC2?prepared by mechanical grindingare fibrillar,with an average length of 698?m and 460?m,respectively;their water retention value were much higher than those of Masson pine fibers,which were respectively 226.8%and 245.8%,and the curl index,Kink index and fiber thickness are lower.this conclusion provided a favorable basis for the application of M-M/NFC in paper reinforcement.EM2-M/NFC obtained by mechanical-enzymatic method was in the form of a long rod with an average diameter of about 15.4?m;Compared with the mechanical grinding method,EM2-M/NFC had better dispersibility and water absorption,which were respectively 74.27 m V and 352.4%.EM2-M/NFC was also excellent in thermal stability and crystal structure,which were respectively 338.6°C and 72.5%,confirming that EM2-M/NFC could be applied to PVA fibers in the form of a reinforced phase.In addition,M/NFC retained the basic chemical structure of Masson pine fibers.?2?The paper was reinforced by using M-M/NFC as the reinforcement layer,and a cellulose paper-based/M-M/NFC/hydrophobic nano silica multilayer paper with good mechanical properties and high barrier properties was obtained through simple lamination and spraying processes.The results showed that the multilayer paper of the surface and cross-section were flatter and denser,and there was no obvious boundary between the layers,which had good hydrophobic properties;when solid content of M-M/NFC2 was 70 g/m²,Dry/wet tensile strength of multilayer paper?SM-M/NFC2-70?were up to 6.3 k N/m and 2722 N/m,respectively increased by 56%and 2277%,and water vapor transmission rate(378.24 g?m^-2?day^-1)and oxygen transmission rate(9.687 cm³?m^-2?day^-1?atm^-1)were the lowest,which were considered to have excellent mechanical properties and good barrier properties.Z-directional tensile strength indicated that the interlayer bonding force was strong between the cellulose paper base and the M-M/NFC layer.This result provided a theoretical basis for the application of M-M/NFC in paper reinforcement.?3?Using EM2-M/NFC as a filler,EM2-M/NFC was blended into the PVA solution by a simple blending method.Based on the wet spinning process,PVA composite fibers with high mechanical strength and good thermal stability were obtained.The results showed that the mixed spinning dope added with EM2-M/NFC were all non-Newtonian fluids,typical pseudoplastic fluids,and are characterized by viscosity,which have the characteristics of shear thinning.When the shear rate was 100 s^-and the temperature was 50°C,the viscosity tends to be stable.At this time,it was the spinning rate and coagulation liquid temperature in wet spinning.When the addition of EM2-M/NFC and the draft ratio were 7 wt.%and DR=5,respectively,PVA composite fiber with the addition of 7wt.%had a smoother appearance,denser internal structure and reduced cross-sectional filaments.When the addition of EM2-M/NFC and the draft ratio were 7 wt.%and DR=3,EM2-M/NFC7 not only reached 9044 MPa and 573 MPa in elastic modulus and tensile strength,which were 12.8 times and 1.84 times higher than pure PVA?DR=2.5?,respectively,but also its strain at break was still 46.0%,showing good mechanical properties.The addition of EM2-M/NFC could increase the crystallinity and thermal stability of PVA composite fibers.FTIR showed that PVA and EM2-M/NFC were hydrogen bonded.This conclusion provided a theoretical basis for the engineering application of EM2-M/NFC in the textile field.