Preparation Of Carboxylated Graphene Oxide And Its Application In Polylactic Acid

As a biodegradable material,polylactic acid(PLA)has attracted widespread attention of researchers,but the shortcomings of low ductility,poor thermal stability and low crystallinity have severely limited its application.However,as a derivative of graphene,graphene oxide(GO)has excellent mechanical properties,barrier properties,and thermal stability,making it an ideal nanofiller to improve all aspects of PLA performance.However,the incompatibility between GO and PLA will lead to poor performance.Therefore,this work introduced low molecular weight polyethylene glycol 200(PEG200)to improve the compatibility between them.Due to the surface reaction sites of GO are limited,so GO must be carboxylated.At first,GO was modified by carboxylation,and carboxylated graphene oxide(GC)was prepared.The best modification scheme was studied.Secondly,low molecular weight polyethylene glycol(PEG)was loaded on GO and GC by esterification,and nanofillers GO-g-PEG and GC-g-PEG were prepared respectively.Then,PLA/GO-g-PEG nanocomposites and PLA/GC-g-PEG nanocomposites were prepared by melt blending with PLA.Through a variety of testing and characterization methods,the morphology,structure and properties were studied,and the optimal loading capacity of nanofiller was explored,which provided a new theoretical basis for the optimization of material properties.The main work is as follows:(1)In the experiment of carboxylation modification of GO,the effect of different content of chloroacetic acid on the content of carboxyl functional groups on GC surface was studied.Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD)analysis verified that chloroacetic acid can convert the part of the hydroxyl groups on the GO surface to carboxyl groups.X-ray photoelectron spectroscopy(XPS)and thermal weight loss(TGA)analysis proved that when the mass fraction of chloroacetic acid was 50 times that of GO,the content of carboxyl functional groups on the GC surface could reach the maximum.(2)In the PLA/GO-g-PEG nanocomposite system,FTIR,XRD,and TGA tests were first performed to prove that PEG was successfully grafted onto GO,and then the content of GO-g-PEG was examined for PLA/GO-g-PEG nanocomposite properties.The results showed that with the increase of GO-g-PEG content,the elongation at break of PLA/GO-g-PEG nanocomposites showed a trend of first increase and then decrease.The elongation at break reached the maximum,about22%,and the tensile strength was reduced to 60 MPa.DSC analysis shows that with the increase of GO-g-PEG content,the T_g and T_cc of PLA/GO-g-PEG nanocomposites will decrease,and the crystallinity will increase,the highest is 37.8%.In addition,when the GO-g-PEG content was 0.4 wt%,the initial decomposition temperature of PLA increased by about 17°C.(3)Similarly,in the PLA/GC-g-PEG nanocomposite system,the successful preparation of GC-g-PEG was proved by the same characterization method,and then the optimal loading of GC-g-PEG was studied.The results show that when the content of GC-g-PEG is 0.3 wt%,the elongation at break of PLA can reach about 31%and the tensile strength is 59 MPa.Increasing the content of GC-g-PEG will reduce the elongation at break of PLA to about 17%.The DSC test results show that the T_gand T_cc of the PLA/GC-g-PEG nanocomposites will first decrease and then increase with the increase of GC-g-PEG content,and the lowest will be 56.2°C,and the crystallinity will be Increase,the maximum is 44.1%.TGA test shows that when the GC-g-PEG content is 0.3 wt%,the initial decomposition temperature of PLA can be increased by about 23°C.(4)Comparing with the two nanocomposites,it can be found that GC-g-PEG can achieve better improvement with less loading.This is because GO can provide more reaction sites for PEG after carboxylation,which can not only enhance the interfacial interaction between the nanofiller and PLA,but also improve the dispersibility of the nanofiller in the polymer matrix.