Preparation And Properties Of Graphene Oxide/Poly(Lactic Acid) Composites

Poly(lactic acid) (PLA) is regarded as one of the most promising biodegradable polymer, while the drawback of fragile, impact strength, poor heat-resistance and hydrophilicity limit the wide application of PLA in packaging. Due to the excellent mechanical, thermal conductivity and excellent hydrophilicity, carbon matrix nano-fillers are widely used in polymer modification research. For the large excellent overall performances and specific surface area, Graphene Oxide(GO) is one of the most important derivatives of graphene, graphene oxide also has a similar two-dimensional lamellar structure to graphene, and it has excellent mechanical properties and large specific surface area, which make it become a ideal filler in preparation of high performance composites.In our work, the modified Hummers method was adopted to synthesize graphene oxide, (modified) graphene oxide/poly (lactic acid) composites was prepared by solution mixing method. All samples were characterized by using transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray diffraction and so on. The properties of the (modified) graphene oxide and its composites were tested by electronic universal testing machine, synchronous thermal analyzer and video optical contact angle measuring instrument.In this paper, the solution mixing method was used to synthesize graphene oxide/poly(lactic acid) composites using dichloromethane as solvent. The influence of different graphene oxide content on the properties of composite materials were investigated. Furthermore, the strengthening mechanism of poly(lactic acid) performance enhancements by graphene oxide was discussed. In addition, silane coupling agent KH570 was used to modify graphene oxide, the influence of graphene oxide and modified graphene oxide on the properties of composite materials was discussed when its content was 1.0wt% respectively. The strengthening mechanism of poly(lactic acid) performance enhancements by modified graphene oxide was analysed. The main conclusions are as follows:(1) The high quality graphene oxide with the modified Hummers method was prepared, the graphene oxide dispersed uniformly and stable in aqueous solution after the sonication. The graphene oxide/poly (lactic acid) composites were prepared by solution mixing method, and the effect of different content of graphene oxide on the properties of the composites was also studied. When the graphene oxide content is under 1.0wt%, it can be more dispersed in poly (lactic acid) matrix evenly and agglomeration is not obvious; when the graphene oxide content is higher than 1.0wt%, the agglomeration of graphene oxide in poly (lactic acid) is more obvious, and there are some voids in the matrix of poly(lactic acid).(2) With the addition of graphene oxide, the tensile strength of the composite increases first and then decreases, When the graphene oxide content is 1.0wt%, the tensile strength of the composites is increased by 52%. while the elongation at break decreases with the increase of the content of the graphene oxide.(3) The initial thermal decomposition temperature of poly (lactic acid) matrix added graphene oxide decreases, but the overall thermal stability of poly (lactic acid) increases, the main mass loss temperature of poly (lactic acid) increases from 300?360? to 340?390?.(4) The hydrophilic property of graphene oxide/poly (lactic acid) composites showed that with the increase of the content of graphene oxide, the contact angle of the base material decreased, the water absorption increased, that is, the hydrophilicity enhanced.(5) A coupling agent, KH570 was applied on dealing graphene oxide surface. Then graphene oxide/poly(lactic acid) was prepared by solution blending method. The test results demonstrated that the KH570 was successfully grafted to the graphene oxide surface. In addition, modified graphene oxide in organic solvent obtained a better dispersion, compared with graphene oxide, the contact angle increased and the water absorption rate decreased, namely, the hydrophilicity decreased. This is due to the affinity of silane coupling agent and the reduction of graphene oxide.(6) Composites were investigated regarding the addition of graphene oxide and modified graphene oxide in poly(lactic acid) respectively. Some results have been achieved as shown in the following:When the content of graphene oxide and modified graphene oxide is 1.0wt% respectively, the latter increases by 1.63MPa in tensile strength and decreases by 0.36% in elongation at break than that of the former. In addition, the hydrophilicity of the latter enhances than that of the former with increases slightly in thermostability of the high temperature phase. This is due to the success of KH570 grafted on the surface of graphene oxide; Modified graphene oxide surface is more fold, molecular chain between poly lactic acid and modified graphene oxide result in enhanced mechanical interlocking; modified graphite oxide graphene with poly (lactic acid) between the hydrogen bonding interaction, which enhance the interface between them.