Application And Properties Of Highly Dispersed GO In Starch And Cement-based Composites

Graphene oxide(GO)has a large specific surface area,wealthy oxygen-containing functional groups,and excellent mechanical properties,which makes it widely used in composite materials.However,some problems,such as complex uniform dispersion and the valuable content of GO sheets in composite materials,limit its practical application.At present,the preparation of highly dispersed GO to improve its uniform dispersion in composites and reduce GO content has become a research hotspot.In this paper,two different highly dispersed GO dispersions were prepared by grafting carboxymethyl cellulose(CMC)and intercalating with an amphoteric polycarboxylate superplasticizer(APC).They were applied to starch-based composite films and cement-based composites to study their effects on the structure and properties of different composites.The specific research work is as follows:(1)Highly dispersed GO dispersion was prepared by amidation reaction of GO,CMC and urea,and its effect on the structure and properties of starch-based composite films was studied.Firstly,GO was prepared by the modified Hummers method,and the mass fraction was controlled to 0.5 wt%.The results showed that the surface of the prepared GO sheet had abundant oxygen-containing groups such as carboxyl,hydroxyl and epoxy functional groups,and the average size of GO was 278 nm,which proved that GO was successfully prepared.Highly dispersed GO-U-CMC(GC)composite dispersion was prepared by grafting CMC onto GO sheets by amidation reaction of GO,CMC,and urea in an alkaline environment.The results show that the average size of GO nanosheets in the GC composite dispersion is the smallest,and the dispersion effect is the best.It can still maintain the uniform and stable dispersion of GO nanosheets in the solution rich in Al3+.Secondly,GC was incorporated into the mixed solution of starch and chitosan,and the starch/chitosan/GC composite film(S/CS/GC)was prepared by the casting method.The results show that GO nanosheets can be uniformly dispersed in the S/CS/GC composite film.The tensile strength of S/CS/GC composite film reached 62.5 MPa at 0.01 wt%GO content,which was 91.7%higher than that of starch film.The water vapour permeability(WVP)is 0.91×10-10 g·m-1·s-1·Pa-1,which was 81.1%lower than that of pure starch film.The S/CS/GC composite film has good water resistance and hydrophobicity,and its surface water contact angle(WCA)can reach 126.6°.At the same time,the results also show that the S/CS/GC composite film has good light transmittance and absorption,shielding ultraviolet light and antibacterial preservation performance.It can absorb and shield 93.5%-96.2%ultraviolet light while maintaining 42.9%-50.3%visible light transmittance.The antibacterial rate of S/CS/GC composite film against Escherichia coli(E.coli)and Staphylococcus aureus(S.aureus)increased by 23.8%and 25.6%,respectively,compared with the control group.The S/CS/GC composite film was used in fruit storage and found to have a noticeable preservation effect.These properties make the S/CS/GC composite film can be widely used as packaging materials in the fields of food and medicine.(2)The preparation of highly dispersed GO by APC and GO intercalation,and its application in cement-based composites were studied.APC was prepared by free radical polymerization of[3-(methacrylamido)propyl]trimethyl ammonium chloride as a cationic monomer with acrylic acid,sodium methacrylsulfonate and polyoxyethylene methacrylate.The water reduction rate was 31.5%,and the mass fraction was 40 wt%.The prepared APC was intercalated with 0.5 wt%GO dispersion at a mass ratio of 50:3.The results show that GO is in a single-layer or few-layer dispersion state in the APC/GO intercalation complex,with a thickness of 4.43 nm and a size of 30 nm,indicating that APC has a good dispersion ability for GO nanosheets,and GO nanosheets in the APC/GO intercalation complex no longer exist in a cluster aggregation state,but are adsorbed on APC multi-branched molecules and present a multi-branched chain dispersion state.The compressive strength of APC/GO paste and mortar samples at 28 d was 100.2 MPa and 69.6 MPa,respectively,which were 99.2%and 61.1%higher than that of the PC blank sample when the GO introduced by APC/GO intercalation composite was 0.0003 wt%of cement mass.The water seepage heights of APC/GO paste and mortar samples at 28 d were 3.5 mm and 4.6 mm,respectively,55.1%and 45.9%lower than those of PC blank samples.The dry shrinkage values of paste and mortar samples with APC/GO were 385×10-6 m and 298×10-6 m,respectively,42.8%and 43.6%lower than those of PC blank samples.In addition,it was also found that GO nanosheets in cement-based composites containing APC/GO could be uniformly dispersed and had a common regulation effect on the morphology and structure of cement hydration products.