Study On The Preparation And Property Of Graphene/PET Composites

Graphene is a novel carbon material with two-dimensional network of sp²-hybridized carbons,which has a series of merits including extraordinary electrical conductivity,superior thermal conductivity properties,high specific surface area,high mechanical strength etc.Graphene is widely used in fields such as biochemistry,catalyst carrier,photo-electricity display,nanocomposite and so on.Polyethylene terephthalate?PET?has many advantages,such as excellent mechanical properties,good dimensional stability,transparency and chemical resistance,etc.It has been widely used in textile fiber,film,packaging and other fields.However,due to its rigid group benzene ring in the PET molecular chain,the crystallization rate of PET is slow,which leads to the low crystallinity during rapid cooling and time consuming molding cycle.Therefore,as a result of above-mentioned,its application in engineering plastics such as buildings and automobiles is limited.In order to give full play to the advantages of PET,graphene is consider as modifier to improve the crystallinity property of PET.A promising composite material with high performance and new application is prepared,which combines the excellent inherent properties of PET and unique features of graphene.In this paper,multifarious silane coupling agents were selected to modify graphene before the synthesis of graphene/PET by direct esterification and in situ polymerization.FT-IR,transmission electron microscopy and laser particle size analyzer were used to characterize the dispersion of graphene before and after modification.The effect of graphene on the molecular structure,molecular weight,thermal properties,crystallinity and shear rheological properties of PET were investigated by FT-IR,intrinsic viscosity test,TG,DSC,POM and capillary rheometer.The results show as below:1.The analysis of the graphene treated with KH550,KH560 and KH792 showed that the graphene flake modified by the silane coupling agent had better exfoliation and loweraggregation,and the dispersion effect was better.KH560 and KH792 showed better dispersion stability compared to that of KH550.However,there is pungent odor during the synthesis when KH550 or KH792 was used,that might due to the decomposition of amino group at high temperature.Therefore,KH560 surface-modified graphene was selected from the viewpoints of coupling stability to graphene-modified dispersion and preparation of composites.FT-IR showed that KH560 was grafted into the graphene layer successfully.2.The graphene/PET composites were prepared by in situ polymerization with different loading of graphene?0,0.075,0.1,0.3,0.5 wt%?.The FT-IR result elucidated that there was no chemical bonding between graphene and PET in the experimental range?the graphene content was lower than 0.5 wt%?.The results of intrinsic viscosity tests showed that the addition of graphene had little effect on the intrinsic viscosity of PET at the same stirring power.When the content of graphene increased to 0.5 wt%,the intrinsic viscosity decreased by only 0.006 d L/g,which indicating a barely effect on graphene to PET molecular weight.3.The addition of graphene improved the density of crystal nuclei in the composite,the crystallization rate and the crystallization peak temperature.In addition,the addition of graphene improved the thermal stability of PET.When the graphene loading was 0.3 wt%,the epitaxial decomposition initiation temperature of graphene/PET was 6.61 ?,higher than that of pure PET and T_m was 9.48 ?.Thus,the growth of nuclei could be initiated with graphene grains as the center at higher temperatures.Graphene improved the crystallizing behavior of PET,and elevated the crystallizing temperature as well as the crystallization rate of PET.The crystallization curve showed a thin and narrow crystallization peak,and a multiple melting endotherms were observed in melting curve.When the graphene loading was 0.075 wt%,the T_p of PET was increased by 34.2 ? and followed a decreasing of ?T by 29.37 ?.Detailed analysis of non-isothermal crystallization at different cooling rates provides evidence that graphene was a nucleating agent and provided a positive effect on crystallinity and crystallization rate.As the cooling rate increases from 5 ?/min to 30 ?/min,the crystallization temperature and crystallization peak shifted to lower temperature.In the meanwhile,the crystallization peak appeared broader,crystallinity subdued and crystallization rate improved.4.The shear rheological properties of graphene/PET showed that the addition of graphene did not change the non-Newtonian nature of PET melt,and still could be categorized as the typical pseudoplastic fluid.However,with the increase of graphene content,the non-Newtonian nature of PET melt,the flow resistance and shear viscosity as well as shear stress also showed an increase.With the increase of shear rate,the shear viscosity of pure PET decreased 36.3% at the shear rate of 6000 s^-1 at 260 ?,and decreased by 36.3% compared to 750 s^-1,moreover,it decreased 49.8% when 0.1 wt% of graphene was loaded.Namely,the shear rate affected shear viscosity of melt more significant due to the appearance of graphene.The activation energy of viscous flow of melt raised with the loading of graphene.The value increased 2.9% when graphene loading increase to 0.5 wt%,compared to the pure PET at the shear rate of 1450 s^-1.The results mentioned above corroborates that there is increase of the viscosity to the temperature sensitivity,however,the effect was not remarkable.