Preparation And Mechanical Properties Of CVD Graphene Polymer Composites

Polymers generally have the advantages of high specific strength,good toughness and fatigue resistance,but also prone to stress relaxation and creep,limited strength value and other problems.It is an effective way to improve the performance and expand the application of composite materials by adding the second phase component into the polymer.In recent years,graphene has become an ideal reinforcement filler for polymer composites due to its unique two-dimensional structure and excellent mechanical properties.However,the current research on such composites mainly uses powder graphene materials,such as GO,r GO or e GO.Although powder graphene has the advantages of easy dispersion and low price,its small size and many defects also limit the upper limit of mechanical reinforcement.High quality graphene continuous film materials can be prepared by chemical deposition（CVD）.The characteristics of fewer defects and good continuity are very conducive to the continuous load of force,and theoretically have far better mechanical properties than powder graphene.At the same time,the continuous structure also brings problems such as difficulty in addition and limited molding,making the orderly arrangement and assembly of high-quality continuous graphene in polymer composites still a great challenge.In this thesis,PLA-GO,PLA-G and PAN-G composites were prepared from GO,graphene（continuous monolayer graphene prepared by CVD,G for short）,polylactic acid/dichloromethane（PLA/CH₂Cl₂）and polyacrylonitrile/N,N-dimethylformamide（PAN/DMF）solution,and an innovative molding process and means was adopted.Ordered dispersed graphene-based composites were realized at the laboratory level and their mechanical properties were tested.The main research content is as follows:（1）With Cu as the catalytic substrate,monolayer graphene film materials were successfully synthesized by CVD method.Optical microscopy and Raman characterization showed that the graphene film grown by this method was continuous and defect-less.（2）PLA-G membrane was prepared by spinning PLA/CH₂Cl₂solution on the surface of CVD graphene and a stacking and cross shear rolling method was used to generate ordered PLA-G composite fiber materials.Then,PLA-G composite fiber was applied to 3D printing molding.Tensile tests were carried out on the printed specimens using a horizontal tensile testing machine.The experiments results show that,compared with pure PLA materials,the average（maximum）strength and Young’s modulus of PLA-G were found increased by38.98%（45.07%）and 69.64%（76.47%）with only 0.1%volume fraction of graphene,respectively,and significantly higher than those of PLA-GO.It was proved that the mechanical strengthening effect of continuous graphene film is more significantly than that of fragmentary graphene.（3）The PAN-G film was prepared by spinning PAN/DMF solution on the surface of CVD graphene.PAN-G film was then treated under high temperatures.The influence of graphene additives to the carbonization and graphitization of PAN membrane was studied.Furthermore,the effects of graphene defects on the high-temperature carbonization and graphitization of PAN films were studied by pre-treating graphene using the UV-O₃,Ar and O₂plasma.The results show that graphene can facilitate the graphitization of carbon atoms in its vicinity.Graphene pre-treating by UV-O₃has the most significant effect,which reduces the I_D/I_Gvalue of PAN-G from 0.762 to 0.552in Raman spectrum,and the graphitization degree is obviously improved.By promoting the transition of polymer from amorphous carbon to graphitized carbon,this study could be extended to strengthening the PAN-based carbon fibers.