Construction,Structures And Properties Of Gel Materials Based On Regenerated Cellulose

Cellulose hydrogels and aerogels are two important structure forms of cellulose-based materials.Gel materials prepared with cellulose not only possess the properties of traditional gels,such as the good swelling property,superior mechanical strength and optical transparency of hydrogels and the porous structure,low density,high porosity,high specific surface area and low thermal conductivity of aerogels,but also they are renewable,degradable and environmental friendly.Therefore,the study of cellulose gels meets the requirements of green chemistry and the current energy development policy,and thus is of great practical significance.However,the current cellulose gels preparation process is companied by tedious preparation procedures,strict preparation conditions,highly consumption of chemicals or complicated post treatment.This work presented a facile and "green" approach to make cellulose-based gels.The cellulose hydrogels with adjustable structures and properties and the cellulose aerogels with controllable morphologies were obtained.Furthermore,an inorganic enhancement component was added to obtain cellulose/organic/inorganic hybrid gels,whose structures and properties as well as the structures-properties connections were examined.In addition,this work also studied the rheological behaviors of these two gel systems,which provided useful information for the preparation of the gel materials with stable structures and propertiesThis work employed the "green" solvent NaOH/urea system to dissolve cellulose and to prepare cellulose-based gel materials.Based on solid nuclear magnetic resonace carbon spectroscopy(13C NMR),infrared spectroscopy(FT-IR),wide angle X ray diffraction(XRD),scanning electron microscopy(SEM),thermogravimetric analysis(TGA),rheometer,texture instrument,ultraviolet visible spectrometer(UV)and elemental analysis,the structures and properties of cellulose hydrogels and aerogels were characterized.The major results are presented as below.1.N,N’-Methylenebisacrylamide(MBA)was used as crosslinker to make cellulose hydrogels at room temperature.The cellulose/MBA hydrogel was prepared by a "one-step" approach,without any initiator and catalyst.The formation mechanism and formation process of gelation were detailed presented for the first time.The cellulose hydrogel with adjustable structures and properties can be obtained by changing the amount of MBA.Compared with pure cellulose hydrogel,the MBA cross-linked cellulose hydrogels showed significantly improved mechanical properties,transparency and water swelling ratio.This work provides a simple,economical and"green" way to the preparation of cellulose based hydrogels.2.A series of cellulose/MBA aerogels with different morphologies,such as the disordered three-dimensional network structure,the evenly dispersed macroporous structure and the one-dimensional fiber structure,were obtained by adjusting the cross-linking degree of aerogels and the concentration of cellulose.Compared with the pure cellulose aerogels,cellulose/MBA aerogels showed significantly improved porosity,water absorption,mechanical stability,stability in water and the adsorption capacity of methylene blue(MB)and Cu2+,but possessed much lower density of 0.0083 g/cm3.The obtained cellulose/MBA aerogel provides a good matrix for the further functionalization of cellulose based aerogels.3.This study for the first time revealed the gelation kinetic study of cellulose/MBA sol and the changes of the rheological parameters(viscoelasticity,compound viscosity and loss angle tangent)of the stable state cellulose/MBA gel as the change of time,frequency,stress and shear rate.Rheological kinetic studies showed that MBA significantly accelerated the gelation process.Studies of storage modulus(G’),loss modulus(G"),composite viscosity(η*)and loss angle tangent(tanδ)of the hydrogels,which were placed at room temperature for 4 h after they reached the sol-gel point,showed that the hydrogels had reached a stable state and the elastic behavior played a dominant role(G’>G").The frequency dependence of G’ and G"of the stable state hydrogels indicated that the gel with higher MBA content formed a more stable network structure.The trend of complex viscosity(η*)of the stable state hydrogels with the change of frequency indicated that MBA cross-linked with cellulose effectively forming a network structure,which experienced irreversible destroyed by high frequency scanning.The stress scanning results showed that MBA improved the strength of the gel.Shear rate scanning revealed that the gel with low MBA content had stronger shear resistance than that with high MBA content4.Cellulose/MBA/GO hydrogels were prepared with MBA as cross-linking agent and graphene oxide(GO)as reinforcement without any initiating factors for the first time.Two kinds of hydrogels,i.e.,the freshly prepared hydrogels and swelling equilibrium hydrogels,were prepared.Based on the studies of transparency,mechanical properties,water swelling ratio,water retention,and texture properties for the two state hydrogels,this work explicated the formation process of the hydrogel and the connection between the structures and properties of the hydrogels.The experimental results showed that MBA and GO played an important role in improving the properties of the hydrogels.Compared with hydrogels without GO,the mechanical strength,elasticity,gumminess and chewiness of cellulose/MBA/GO hydrogels were improved significantly.Hydrogels with different transparency,mechanical strength and texture properties can be obtained by adjusting the amount of GO.5.This study firstly examined the rheological parameters of cellulose/MBA/GO sol and the rheological behaviors of stable state cellulose/MBA/GO gels.The results showed that GO improved the elasticity modulus(G’),the compressive strength and the stability of the three-dimensional network of the hydrogels obviously.The obtained stable hydrogels were then washed,soaked and freeze-dried to prepare cellulose/MBA/GO aerogels.The structures and properties of the aerogels were characterized.Results showed that the cellulose/MBA/GO aerogels have low density(0.0089-0.0105 g/cm3),high porosity(98-96.3%)and good morphologic recovery(98%).Compared with the pure cellulose aerogels and the aerogels without GO,the adsorption capacity of the cellulose/MBA/GO aerogels to MB and Cu2+ was improved significantly.This work provides a simple,economical and "green" approach for the preparation of cellulose/organic/inorganic hybrid aerogels.The cellulose/MBA/GO aerogels have potential applications in the fields of dye and heavy metal adsorption.