The Study Of Carbonization Of PI/Gr Composite Films

Polyimide(PI)has been widely used as the precursor of carbon film because of its rigid structure,high carbon yield and retaining the original appearance after carbonization.Although the properties of carbon films prepared by PI can be improved by controlling the pyrolysis conditions and pretreatment precursors,but the pure PI based carbon films have many defects,such as large shrinkage rate,low conductivity and low thermal conductivity.In recent years,the addition of inorganic filler is considered as an effective method,which can improve the performance of PI based carbon film and extend its application.However,the structure of graphene is more complete,which makes it easy to self aggregation,so the dispersion in the PI matrix is poor.Firstly,in this paper,using ultrasonic dispersing method to mix graphene?p-Phenylenediamine(PDA)monomer and Dimethylacetamide(DMAc)to homogeneous suspension,and using in situ and casting film to prepare polyamic acid(PAA)/grapheme(Gr)thin films.PI/Gr composite films was obtained after thermal imidization.The results show that the dispersion of Gr in the PI matrix is still uniform when Gr content is 15%(PI-15Gr),and only a small amount of concentration when Gr content is up to 25%(PI-25Gr).In addition,the thermal decomposition temperature(Td5),residual and electrical conductivity of the PI/Gr films increased with the increase of Gr content,but toughness of the films decreased.Secondly,the PI and PI-15Gr carbon films with different carbonization temperatures and heating rates and the different holding times at 1600? was prepared,changes of carbon film in structure and performance was studied in order to explore the optimal carbonization process for the preparation of two kinds of carbon film.The study on the carbonization temperature shows that the order of PI and PI-15Gr based carbon films is reduced before 800?because of pyrolysis in PI matrix,and the ordered carbon layer structure increases with the increase of temperature after 800?.However,the thermal and electric conductivity of carbon films increases with the increase of temperature.Studying on the heating rate has shown that two kinds of carbon membrane structure in the crystallite size,degree of order and the performance of the surface conductivity,thermal conductivity increases with the heating rate decreases,especially from 10?/min down to 8?/min,the structure and performance of carbon films have more obvious changes.The conductivity and thermal conductivity of the PI carbon film prepared at 2 C/min are up to 2.98×10~4S/m and 10.86 W/m.K,respectively.The conductivity and thermal conductivity of the PI-15Gr carbon film are as high as 5.11×10~4S/m,35.26W/m.K,respectively.The research on the holding times shows that,for the PI carbon film,the longer the holding time(<8h),the better the carbonized structure and properties of the carbon films,the crystallite size is 2.228nm,the R value is 1.324.As for the PI-15Gr carbon film,holding 2h at 1600? can reach the best carbon stucture,crystallite size of 24.398nm,R value of 1.260.It also shows that the Gr can induce the fast and orderly arrangement of the carbonized structure.Finally,the optimum carbonization process of carbonized PI-15Gr film was used to study the effect of the ratio of different drawing and the content of Gr on the structure and properties of carbon films.The results show that the increase of the draw ratio can effectively promote the formation of perfect structure of PI and PI-15Gr carbon films.When the draft ratio is 1.3,the crystallite size is 2.141nm and the R value is 1.420 for PI carbon film,the crystallite size is 25.003nm,and the R value is 1.125 for PI-15Gr carbon film.In addition,the increase of the amount of Gr will reduce the carbonation shrinkage of carbon film on the axial direction,and the carbonation shrinkage of PI carbon film containing 25%Gr is only about 6%.At the same time,the condensed state structure and the electrical conductivity of the carbon film also increased with the increase of Gr.As for PI carbon film containing 25%Gr,the crystallite size is 26.694nm,the R value is 1.154,and the surface conductivity is 5.60×10~4S/m.