Study On The Preparation Of Nanocellulose From Cotton Byproducts And Its Incorporation In Bio-based Nanocomposite

China produces the largest output of cotton and its by-product,like cotton stalks,cottonseeds,etc.Most of them are directly burnt without well recycling.Nanocellulose is an attreactive nanomaterial due to its high strength and length/diameter ratio,biodegradeable and non-toxic.Therefore,incorporation of nanocellulose into the biomass polymer composites is significant and have potential application value.In this paper,nanocellulose was extracted from cotton by-products: cotton stalks and cottonseed hulls using mechanical and chemical treatments.The extracted nanocellulose was incorporated into polyvinyl alcohol(PVA),Poly(glycerol sebacate)and polylactic acid(PLA)to establish biomass composites.The relationship between preparation,structure and property was to figure out an economic recycle methods for cotton by-products.Combination of high-temperature alkaline digestion and acid sodium chlorite bleaching can isolate the pure cellulose of cotton stalks.When the concentration of NaOH was fixed at 12.5%,the obtained cellulose had the highest degree of crystalline(64.9%)and maintained the crystal type I,the content of cellulose was 68.5%.After bleaching with acid sodium chlorite twice,the content of lignin decreased under 0.5%,which mean that the pure cellulose was obtained.Rod-like cellulose nanocrystals was prepared using sulfuric acid hydrolysis,both increasing of the concentration of sulfuric acid and prolonging the reaction time can accelerate the hydrohysis of the amorphous part in cellulose,leading to the smaller size of CNCs.The optimal hydrolysis condition is that: thr ratio of liquid to solid at 15 mL/g,the concentration of sulfuric acid at 65 wt.%,reaction temperature at 50℃,reaction time at 1 hour.The obtained CNCs had diameters of 10-30 nm,lengths of 100-300 nm.TGA analysis indicated that the thermal stability of cellulose was improved after the chemical treatments,but that of the CNCs decreased because of the sulfuric acid.The obtained CNCs was added to the PVA in order to inspect the enhancement effect of CNCs in polymer system.Result showed that the mechanical strength of PVA was greatly improved.When the addition of CNCs was fixed at 3 wt.%,the tensile strength and elongation at break was 40 MPa and 660%,respectively.Both the melt temperature and crystallization temperature increased with the increasing CNCs contents.CNCs was added into the PGS pre-polymer using absolute ethyl alcohol as co-solvent,then the mixture was crosslinked under high temperature in vacuum to form a novel PGS/CNCs bio-elastomer.The effect of CNCs on the structure and properties of PGS was examined through mechanical tests,thermal tests,gel-sol and water absorption analysis and the enhancement mechanism was discussed.Furthermore,considering the bad interfacial compatibility between hydrophilic CNCs and hydrophobic PLA,the acetic acid esterification was performed on the CNCs surface and the mechanical properties of composite before/after modification was compared.Results showed that: the tensile strength and modulus of PGS matrix was largely improved with the increasing addition of CNCs while the elasticity maintained.Gel-sol tests indicated that the crosslinking denity of PGS and content of gel both increased.Prolong the curving time resulted the crosslinking degree of both pure PGS and PGS/CNCs composite,followed with the increase of mechanical properties.Acetic acid esterification improved the compatibility between CNCs and PGS,but tensile strength decreased than pristine CNCs.The addition amount of CNCs had controllability on the degradable rate of PGS.The PGS/CNCs composites reached the highest degradable rate at the addition of 2 wt.% CNCs.Cottonseed hulls were used for the first time to extract three types of CNs,including fibrous cellulose nanofibers,rod-like cellulose nanocrystals and spherical cellulose nanoparticles through mechanical and chemical methods.The morphology,surface ability,crystalline structure and thermal stability were analyzed.XRD results indicated that the crystal type of cottonseed hull cellulose was type I/II hybrid treated with 10% NaOH,and the CNCs had the highest type II proportion because of the stronger resist ability of type II than that of type I to acid.Zeta potential analysis showed that CNCs owned the highest surface charge than SCNCs and CNFs due to the introduction of negative charged sulfuric acid groups.The thermal ability of CNFs was better than that of the SCNCs and the CNCs.Rheology results showed that the rheological behavior of the CN suspensions was strongly dependent on CN concentration and particle morphology.For PVA/CN systems,concentration of PVA/CN suspension,morphology of CNs,and weight ratio of CN to PVA were three main factors that influenced their rheology behaviors.This research reveals the importance of CN morphology and composition concentration on the rheological properties of PVA/CN,providing new insight in preparing high performance hydrogels,fibers and films base on PVA/CN suspension systems.Cellulose nanocrystals(CNCs)were grafted with maleic anhydride(MA)followed by a novel in-situ crosslinking with Poly(lactic acid)(PLA)using dicumyl peroxide(DCP)as the crosslinking initiator.MA-grafted CNCs(MACNCs)exhibited improved dispersion state than that of pristine CNCs in PLA matrix.The in-situ crosslinking reaction further provided a strong bridge of chemical bonding,which greatly enhanced the interfacial adhesion between MACNCs and PLA matrix.Therefore,the resultant PLA/MACNC composite film showed a comprehensive improvement in both the tensile and thermomechanical performance.When the loading of the filler was fixed at 5 wt.%,the crosslinked PLA/MACNC composites had an ultimate tensile strength of 56.3 MPa and Young’s modulus of 1550 MPa,which was 173.2% and 222.7% of these for pristine PLA/CNC composite.The storage modulus in the glassy(30 ℃)and rubbery stage(80 ℃)improved by 53% and 118%,while the glass transition temperature improved by 8.3 ℃ compared with that of neat PLA.2-Bromoisobutyrylbromide and NaN3 were grafted orderly onto the CNCs surface by substituting their hydroxyl groups and FTIR results confirmed the successful synthesis of the CNCs-N3.Using DCC/DMAP as the high efficial catalyst system,the terminal hydroxyl groups of Polycaprolactone diol was esterfied with 4-pentynoic acid.FTIR and 1H-NMR results confirmed that the modified PCL diol with acetylene groups terminated was successfully synthesis.Using CuBr/PMDETA as copper catalyst system,PCL diol macromolecular was directly grafted onto the CNCs surface based on Copper catalyzed azide–alkyne cycloaddition “Click chemistry”.This modified CNCs show great potential in the aspect of PCL reinforcement.