Extraction, Characterization And Application Of Corn Stalk Nanocellulose

As the main by-products of corn,corn stalk is an abundant agricultural waste with high biological output and low economic coefficient.The annual output is about170 million tons.Most of them are directly burned in the field not only waste biomass energy but also bring serious environmental pollution and other social problems.Corn stalk is composed of root,pith and leaf.As the main part of corn stalk,stem is composed of skin,pith and section.However,the pith has poor compositional homogeneity and a large amount of sugar,which is suitable for feed production,buffer materials and other fields.In this research,corn stalk with no pith was chosen as the main object.The traditional applications of corn stalk include producing sugar,wine,biomass alcohol,catalytic hydrogen production,particle fuel,adsorption material,and the furfural manufacturing.However,with the development of nanotechnology,the research of nanocellulose has attracted more and more attention.Using corn stalk waste to prepare nanocellulose can not only turn waste into treasure but also reduce environmental pollution,which has the high research value and application prospect.In this paper,nanocellulose from the corn stalk was isolated by sulfuric acid hydrolysis method and then mixed with the representative water soluble polymer polyvinyl alcohol(PVA)and polyvinylpyrrolidone(PVP)to prepare composite films.It provided some guidance for the effective application of nanocellulose into watersoluble polymer.The composition and thermal stability of corn stalk was studied.The carbon content of corn stalk with no pith,corn leaf and corn root were 44.88%,45.30% and46.87%,respectively.The content of cellulose of them were 32.73%,35.43% and32.26%,respectively.The initial decomposition temperature of the corn stalk with no pith,corn leaf and corn root were 243.39 ℃,258.09 ℃ and 258.04 ℃,respectively.Cellulose nanocrystals(CNCs)were isolated from corn stalk using sulfuric acid hydrolysis,and their morphology,chemical structure,and thermal stability properties were characterized.The CNCs had an average length of 120.2 ±61.3 nm and diameter of 6.4±3.1 nm(L/D = 18.7).The degree of crystallinity of the CNCs was 76.44% compared with 59.98% of that in the raw corn stalk,while the chemical structure was well kept after sulfuric acid hydrolysis.Thermal stability analysis showed that the degradation temperature of the CNCs reached 239.5?C,which was higher than that of the raw fiber,but lower than that of the extracted cellulose.The average activation energy values for the CNCs,evaluated using the Friedman,FlynnWall-Ozawa(F-W-O)and Coats-Redfern methods,were 312.6,302.8,and 309kJ·mol-1 in the conversion range of 0.1 to 0.8.The isolated CNCs had higher values of activation energy than the purified cellulose,which was attributed to the stronger hydrogen bonds presented in the crystalline domains of CNCs than in those of cellulose.These findings can offer a better understanding on the thermal properties of polymer/CNC composites.Rheological,thermal,mechanical and transparency properties of PVA/PVP/CNC films at different CNCs loading levels(2.5%,5%,10%,and 20w/w %)were evaluated.Viscosity measurement results revealed that the rheology behavior of aqueous polymer suspensions transformed from Newtonian fluid behavior to typical shear thinning behavior with the addition of CNCs.Dynamic mechanical analysis(DMA)results showed that bio-nanocomposites exhibited better mechanical properties compared with the PVA/PVP films.It was also clarified that all the PVA/PVP/CNC films remain transparent due to the nanoscale dispersion of CNCs.The produced films with reduced UV and enhanced tensile properties,suggesting that the PVA/PVP/CNC films are promising materials as the packing materials,which represent a positive effect on the food protection.Poly(vinyl pyrrolidone)(PVP)/cellulose nanocrystal(CNC)/silver nanoparticle composite fibers were prepared via electrospinning using N,N-dimethylformamide(DMF)as a solvent.Rheology,morphology,thermal properties,mechanical properties,and antimicrobial activity of nanocomposites were characterized as a function of material composition.The PVP/CNC/Ag electrospun suspensions exhibited higher conductivity and better rheological properties compared with those of the pure PVP solution.The average diameter of the electrospun fibers decreased with the increase in the amount of CNCs and Ag nanoparticles.Thermal stability of the electrospun composite fibers was decreased with the addition of CNCs.The addition of CNCs resulted an increase of the composite tensile strength,but an decrease of the elongation at break.The composite fibers contained Ag nanoparticles showed improved antimicrobial activity against both the Gram-negative bacterium Escherichia coli(E.coli)and the Gram-positive bacterium Staphylococcus aureus(S.aureus).The enhanced strength and antimicrobial performances of PVP/CNC/Ag electrospun composite fibers make the mat material an attractive candidate for application in the biomedical field.