| It is a trend for biomass alternative to synthetic polymers to prepare composite or functional materials that can be applied in the fields of chemical engineering,material and biology.Cellulose and gelatin are both natural macromolecules with abundant availability,biocompatibility,biodegradability and renewablility,etc.Cellulose is one of the most abundant biomass polysaccharides in plants,and its high hydroxyl content endows the cellulose-based materials with high mechanical strength.Gelatin is the most abundant collagen hydrolysate in animals,and the carboxyl group(-COOH),amino group(-NH2)and imino group(-NH-)in its structure provide it excellent hydrophilicity and water vapor permeability.However,the strong hydrogen bond network structure in the intra-and inter-molecular of cellulose,as well as highly crystalline state of aggregation conformation makes it insoluble in water that has become a difficult problem and hinder the development of cellulose/gelatin functional materials.The cellulose/protein composite films obtained using phase separation technology suffer from uncontrollable structure,low transparency,and wrinkling,resulting in the easy aggregation of fluorescent molecules and obvious chromatic aberration when regenerated film is used as the matrix for fluorescent functionalization.In this paper,the gelatin molecules with strong hydration ability were bonded to the cellulose glucose chain by cross-linking copolymerization.Cellulose/gelatin cross-linked polymer microgels with high aspect ratio were prepared.Furthermore,the microgel with controllable size and morphology were obtained by means of alkylation and self-assembly technology,which realized the controllable growth and precise control of assembly size and morphology from nanometer to micrometer.The element composition,chemical bonding state,molecular chain conformation and formation mechanism of the microgel were studied,then the correlation between aspect ratio,morphology of microgel particles and microstructure and property characteristics of the corresponding films were analyzed.In addition,a highly transparent,strong water resistance and tunable photoluminescent cellulose/gelatin cross-linked polymer microgel film and coating material made from organic and inorganic fluorescent molecules-loaded the cellulose/gelatin cross-linked microgel substrates with whisker-like and hollow spherical morphology were investigated.The work includes six parts as follows:(1)Cellulose/gelatin cross-linked microgel(CGM)with whisker-like structure was prepared in NaOH/urea aqueous solution with epichlorohydrin(ECH)as coupling agent via homogenous blending,cross-linking,dialysis and self-dispersion pathway.CGM microgels with with high yield up of 48.6%could be obtained by adjusting the molar ratio of ECH to AGU was not less than 2:1 and the incorporation of gelatin as long as Wgel?20%.Elemental analysis,FTIR and GPC provided an evidence for cross-linking interaction in the inter-and intra-molecules between cellulose and gelatin,and the weight-average molecular weight(Mw)of cross-linked polymer was up to 636.60 kDa with narrow PDI of 1.015.XRD proved the crystallinity of cellulose decreased by cross-linking with gelatin,accompanying with larger amorphous region.DLS found that the Z-average particle sizes of CGM microgels were approximately 83?165 nm and decreased with the increases of the protein content,as well as the microgels had good dispersibility and stability in water.SEM and TEM confirmed that the CGM microgel exhibited whisker-like morphology with monodisperse distribution,uniform particle size and aspect ratio of 12-19.(2)The novel amphiphilic cellulose copolymers(HCGM)were prepared by hydrophobically modified CGM microgel from different long-chain alkyl groups,then the cellulose/gelatin cross-linked microgels with controllable particle size and morphology were obtained using self-assembly technology.By studying self-assembly behavior of HCGM,results demonstrated that the critical micelle concentrations(CMC)of the microgels were in the range from 0.628 to 0.075 mg/mL and decreased with the degree of substitution and lengths of the alkyl chains increase,and the corresponding hydrodynamic diameters(Dh)were 104?1000 nm which increased with the length of alkyl chain changes from C8 to C16 under the same the degree of alkylation.Single vesicle,double continuous or three continuous vesicle aggregates and vesicle cluster microgels could be obtained when the concentration of CGD-1(C12)microgel solution increased from 0.1 mg/mL to 10 mg/mL;rod-like,flower-like,and flower-like cluster could be obtained when the concentration of CGC-1(C16)microgel solution increased from 0.1 mg/mL to 5.0 mg/mL.When the length of carbon chain on the HCGM backbone was short(C8),the microgel could self-assemble into cotton flocculence,rod-like,and sphere with the DSri increased from 0.32 to 0.50.The vesicle,coral,and urchin-like microgels were obtained from the HCGM with slightly longer carbon chain(C12)when the DSH of C12 increased from 0.35 to 0.51,and the flower-like,snowflake and sphere microgels were obtained from that with the relatively longer carbon chain(C16).(3)The intermolecular chemical bonding state and crystal structure of cellulose/gelatin cross-linked microgels were analyzed by 1H NMR,Raman,XPS and XRD.It was found that gelatin molecule mainly occurred on C2 and C3 positions of cellulose glucose units through C-O-C and C-N-C bonds,and the crystallinity of cellulose was reduced from 80.5%to 6.19%.In addition,long-chain alkyl groups were bonded to the residual hydroxyl groups of C6 position from cellulose glucose unit and the amino groups of gelatin in the form of C-O-C and C-N-C.The second virial coefficient(A2)of microgels were 4.5×10-3?5.4×10-3 mol mL/g using SLS and DLS,and the structure factor(?),persistence length(q),molar mass per unit contour length(ML),and characteristic ratio(C?)of CGM microgel with whisker-like were given as 2.2,11.6 nm,601.0 nm-1,and 23.6,respectively.The above results confirmed that CGM exhibited a stretched rigid chain in aqueous solution,and the cross-linking reaction produced steric hindrance in cellulose molecules.Moreover,the molecular chain conformation parameters(p,q,ML,and C?)of self-assembled microgels with different degree of substitution and alkyl chain length were consistent with those observed by SEM,TEM and AFM.Based on the above analysis,the formation mechanism of controllable cellulose/gelatin cross-linked polymer microgels was provided.(4)Compared with the cellulose/protein composite films prepared via phase separation method,CGM films with whisker-like formed by solution casting exhibited more homogeneous surface and compact cross-section structures,as well as presented higher light transmittance at 400 nm of more than 88%.CGM films with aspect ratio greater than 16.2 showed relative lower swelling ratio and weight loss,as well as displayed higher tensile strength compared with that of water-soluble cellulose derivatives/protein blend films in dry and wet states.However,the low aspect ratio(AR less than 13.2)could improve the adsorption and internal transport of water vapor molecules on the surface of CGM microgel films.The water vapor permeability of films made from microgel particles with different shapes was significantly lower than that of whisker-like CGM films,and the microgel films with coral,urchin,flower-like and snow-like showed lower optical transmittance.However,the microgel films with various particle shapes exhibited high flexibility and strong stability in water,which was confirmed by water resistance parameter.(5)A variety of highly transparent and biodegradable fluorescent films were prepared by loading organic fluorescent dyes and inorganic alkaline earth aluminate pigments onto the whisker-like CGM microgel matrix,respectively.Benefiting from the cross-linking sites,reticular structure,and the abundant hydroxyl,amino and imino groups of the cellulose microgel matrix,the cellulose-based microgel loaded with organic dyes and inorganic pigments displayed good dispersion and stability in the solution,and the resultant composite films emitted bright yellow,orange,yellow-green and blue-green fluorescence characteristics under 365 nm U-V light,respectively,especially cellulose-based microgel stabilized inorganic alkaline aluminate hybrids represented a continuous luminescence of at least more than 10 h in the dark.Moreover,the photochromic and long afterglow mechanism was revealed.The cellulose-based microgel fluorescent dispersion could be coated on metal and glass surfaces to endow them with handwriting.In addition,the fluorescent films have excellent optical stability,high thermal stability,strong resistance to organic solvents,foldability and easy scrollability characteristics.Compared with the existing cellulose-based fluorescent films,the CGM microgel fluorescent film prepared in this paper had higher transmittance(Tr650 nm?91%)and could be completely biodegraded.(6)A series of strong water resistance,tunable fluorescent and flexible composite films could be made from hydrophobic fluorescent dye-encapsulated hollow cavities of cellulose-based microgels.TEM and SEM confirmed the formation of cellulose based microgel with hollow structure.DLS,AFM and UV spectra provided an evidence for the successful encapsulation of FITC in hollow cellulose based microgels.Meanwhile,benefiting from the "anchoring" and"diluting" effect of cellulose based polymer chains as well as the isolation effect of hollow shell,the aggregation and self-quenching of FITC were effectively inhibited as well as the falling off of FITC was prevented,which made the microgel films with different coating amounts display green fluorescence under 365 nm UV light,and the fluorescence intensity was controllable.Moreover,the resultant fluorescent films exhibited strong ultraviolet absorption,excellent optical stability,foldability and easy scrollability characteristics.Compared with the CGM luminescent films,the hollow luminescent films showed stronger water stability.Because of the high stability and easy forming ability of hollow cellulose based fluorescent microgels,fluorescent microgels could be processed into coating materials which were easy to use,durable and widely used.They have potential applications in luminescent devices,smart tags,anti-counterfeiting materials and UV resistant coatings. |
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