Preparation And Research Of TEMPO Oxidation Nanocellulose And Its Composite Film

Cellulose is the most abundant biopolymer on Earth.Nanocellulose is a product formed by nano-crystallization of cellulose.It has excellent properties such as high strength,biocompatibility,renewable and degradable,and has broad application prospects.Nanocellulose prepared by conventional methods has many problems,such as high energy consumption,low efficiency,small aspect ratio,and easy agglomeration,which limit its application in matrix materials,energy storage materials,packaging materials and reinforcement materials.In this paper,nanocellulose was prepared by TEMPO oxidation method,and the effect of alkali pretreatment on the preparation of nanocellulose was studied.Nanocellulose was combined with polyvinyl alcohol(PVA)to prepare high performance and environment friendly biomass-based composite membrane.The specific research contents are as follows:(1)Nanocellulose was prepared from larch pulp using a TEMPO-NaBr-NaClO catalytic oxidation system combined with mechanical treatment.The obtained nanocellulose was in the form of cellulose nanofibrils(TOCN),with a diameter of 5-10 nm,a length up to several microns and has good dispersibility.The yield of TOCN prepared by this method was 76.6%,the carboxyl group content was 0.91 mmol/g,and the cellulose I-type crystal structure was still maintained.(2)The effects of NaOH pretreatment conditions on the morphology,crystalline structure and subsequent oxidation degree of pulp cellulose were studied by single factor experiment.The optimal pretreatment conditions were as follows:NaOH concentration of 7%,pretreatment time of 12 h,and pretreatment temperature of 23?.XRD results show that the cellulose pulp pretreated with NaOH still maintained the cellulose I-type crystalline structure,and the crystallinity decreased.SEM and TEM results showed that appropriate NaOH pretreatment could promote cellulose surface differentiation to form microfibrils,thus improve the efficiency of oxidation,the diameter of the obtained TOCN was reduced to 3-5 nm,while the length was still maintained at the micron level,and the dispersion was improved.The carboxyl content of TOCN was increased from 0.91 mmol/g to 1.20 mmol/g.(3)The TOCN/PVA composite film was prepared by solution casting method.The FTIR analysis results of the composite film showed that the combination of TOCN and PVA was chemical.The effects of the ratios of PVA and TOCN on the mechanical properties,oxygen barrier properties and hydrophilic properties of the composite film were studied.The results showed that when the TOCN ratio in the composite membrane is ?10 wt%,the fracture mode of the film was ductile fracture,when the TOCN content was 5%,the tensile strength of the composite film reached the maximum value of 94 MPa,which was 44.6%higher than that of pure PVA film(65 MPa).The minimum oxygen permeability coefficient is 1.08 cm3·cm/m2·d·0.1MPa,which is 89.8%lower than that of pure PVA film.The contact angle reached the maximum value of 57.7°,which was 54.6%higher than that of pure PVA film(26.2°);When the TOCN ratio in the composite membrane is>10 wt%,the fracture form of the film was brittle fracture.When the TOCN content was 70%,the tensile strength of the composite film reached the maximum value of 159 MPa,which was 9.7%higher than that of pure TOCN film(145 MPa).The oxygen transmission coefficient is 0.48 cm3·cm/m2·d·0.1 MPa,which is 12.7%lower than that of pure TOCN film.The contact angle of the composite film reached the maximum value of 67.0°,which was 38.8%higher than that of pure TOCN film(41.0°).