Preparation And Performance Of Elephant Grass Nano-cellulose Film

The development of green,sustainable and biodegradable materials has received increasing attention due to the gradual depletion of fossil resources and the concern for environmental sustainability.Biodegradable natural polymers are considered as potential substitutes for fossil petroleum resources.Among them,cellulose is the most popular because of its abundant reserves on the earth,non-toxic and renewable properties.Nano-sized cellulose has the advantages of high specific surface area,high strength,low density,easy film formation,degradability,and biocompatibility,which lead to potential value-added applications in the fields such as biomedicine engineering,food,sensors,packaging,optical and electronic devices.The traditional method for extracting and preparing cellulose nanofibrils（CNF）from lignocellulose is inorganic acid-base pre-treatment combined with mechanical disintegration,but this method is harmful to the environment,and the cost of acid-base recovery and treatment is high.Therefore,it is of great significance to develop an environmentally friendly method for preparing CNF materials.Solid acid is an emerging catalyst with the advantages of high activity,recyclability and little harm to equipment.In cellulose extraction and nano-processing,solid acid can be used to solve the potential problems of inorganic acid.The eutectic solvent（DES）is a two-component or three-component eutectic mixture composed of a hydrogen bond acceptor and a hydrogen bond donor with a certain stoichiometric ratio,and its freezing point is significantly lower than the melting point of each component of the pure substance.They have the advantages of strong solubility,high stability,low vapor pressure,easy preparation,easy recycling,non-toxic,biodegradable,and low cost.They are ideal green chemicals for preparing nano-cellulose materials by pre-treatment of lignocellulose.In this paper,the energy plant elephant grass is used as the raw material,and DESs and the solid acid derived from coffee grounds（SC-SO₃H）catalyst are combined for pre-treatment to extract cellulose.Single-factor experiments were carried out on the extraction efficiency of cellulose under different reaction temperature,time,solid-liquid ratio and catalyst conditions.In addition,the recycling efficiency of the recovered SC-SO₃H catalyst was explored.Then,the CNF was prepared by the ultrasonic disintegration,and the CNF film was further obtained by the suction filtration.Moreover,a series of MWCNT/CNF composite films were prepared by adding multi-walled carbon nanotubes（MWCNT）with different mass ratios.The cellulose purity obtained by the optimized DESs/SC-SO₃H pre-treatment method was 79.3%,and the yield was 25%.The catalytic performance of the recovered solid acid was slightly reduced.The purity of the cellulose obtained in the fourth reuse was 76.6%,and the yield was 27.3%.After ultrasonic processing,the CNF was obtained with a high aspect ratio,good dispersion and uniform size（diameter of 2–6 nm,length of 800–1000 nm）.The obtained CNF film showed as transparent,and had good mechanical properties and thermal stability with tensile strength and elongation at break of 79.8 MPa and 13.5%,respectively,and the maximum decomposition temperature of 336℃.The prepared MWCNT/CNF composite films not only presented the excellent mechanical properties of CNF film,but also displayed good electrical conductivity.As the content of MWCNT increased,the electrical conductivity was enhanced.When the content of MWCNT was 12.5%,the electrical conductivity was measured to be 6892.6 S·cm^–1.This thesis developed a new method for green extraction and preparation of CNF from elephant grass using DESs/SC-SO₃H and ultrasonic blasting,and successfully prepared CNF films and MWCNT/CNF conductive films with good performance,which offered a reference for the development and utilization of nano-cellulose materials,and provided a theoretical basis for the high value-added utilization of elephant grass.