Preparation Of Graphene By Mechanical Exfoliation And Its Application In Functional Composites

The monoatomic layer and two-dimensional crystal structure of graphene give it excellent mechanical,electrical and functional properties,and have received extensive attention in the scientific community.With the deepening of research,the broadspectrum antibacterial function of graphene has been further explored,which provides more possibilities for its application in biomedical fields.However,most commonly used graphene is prepared by chemical oxidation.Because the limitations of the preparation method lead to a large number of defects on the surface of the graphene and its incomplete crystal structure,the intrinsic properties of the aforementioned graphene are difficult to be perfectly represented.At the same time,the residue of the strong acid and strong oxidant used in the preparation process on the graphene surface further limits its application in the biomedical field.In addition,the surface of this kind of graphene is rich in oxygen-containing functional groups,which will cause oxidative stress in human cells and face various biosafety risks.Therefore,the preparation of high-quality graphene with complete crystal structure and less defects on its surface is the research focus and challenge in this field.On this basis,it is necessary and urgent to carry out the preparation and performance study of graphenepolymer functional composites for biomedical materials.In this paper,graphene with a complete crystal structure was prepared based on mechanical exfoliation.Through the interface and compatibility of graphene and polymer substrates,we have designed a variety of biomedical composites with excellent functional properties.The mechanism of mechanical exfoliation of high quality graphene and the construction and performance of graphene-polymer functional composites were systematically studied.The specific research contents are as follows:Firstly,a high concentration of graphene dispersion was prepared by using natural polymer milk protein molecular chain assisted ultrasonic exfoliating flake graphite.The dispersed graphene has a small number of layers and a complete structure,showing good biosafety.The graphene powder obtained by freeze-drying the dispersion does not undergo serious agglomeration because of the modification and isolation of ?-casein and ?-lactoglobulin in milk protein,and can be quickly dispersed in water.On this basis,a new type of cotton/graphene composite antimicrobial dressing was prepared by the dipping-coating method.The dressing has good antibacterial properties due to the sharp edges of the graphene on it which can cause mechanical damage to the bacterial cell membrane.Based on the biosafety of cotton/graphene composite antibacterial dressings,the effects of cotton/graphene composite antibacterial dressings and common medical dressings on the healing of large-area wounds in mice were compared.The results show that the cotton/graphene composite antibacterial dressing can significantly shorten the healing cycle of mouse wounds.Secondly,it is expected to further improve the efficiency and sample quality of graphene production by physical mechanical exfoliation method.Inspired by the preparation of graphene by the "tape method",high-quality graphene was prepared by continuously exfoliating flake graphite on a three-roll mill using natural honey as a viscous exfoliating medium.The yield of the preparation method and the monolayer rate of graphene are higher than the conventional mechanical exfoliation method previously reported.The polyvinyl alcohol(PVA)/graphene composite fiber with different content of graphene prepared by a solution compounding and gel spinning technique using the above graphene.This composite fiber has good mechanical properties and its highest tensile strength is nearly three times that of pure PVA fiber.The graphene composite fiber also exhibits excellent antibacterial,anti-ultraviolet radiation and reliable biosafety.Infected wounds of mice were treated with PVA/graphene composite fibers and common medical surgical sutures,respectively,and the effects of two surgical sutures on the wound healing cycle of mice were compared.The results showed that mice wound with PVA/graphene composite fibers had a shorter wound healing cycle.This result is related to the ability of PVA/graphene composite fibers to provide reliable mating support for the skin at the wound site and its excellent antimicrobial properties.Thirdly,polydimethylsiloxane(PDMS)was used as a viscous exfoliating medium to exfoliate graphite on a three-roll mill and "one-step" preparation of PDMS/graphene composite wearable and implantable strain sensors was achieved.Uniformly dispersed graphene not only provides a conductive network path for the sensor in the PDMS matrix,but also significantly increases the tensile strength of PDMS by transferring stress,changing the direction of crack growth and shielding effect of the tip.This sensor with a rich conductive path prepared by a simple method can not only achieve less than 1% strain detection,but also accurately detect strains up to 225%.In the paper,a PDMS/graphene composite sensor with excellent antiultraviolet radiation function and good skin adhesion is used as an "electronic skin" to accurately monitor the movement of finger joints and knee joints.In addition,PDMS/graphene composite sensors have good biosafety and have potential application prospects in implantable sensing devices in the biomedical field.