Study Of Functionalized Graphene And Its Bismaleimide Self-lubricating Composites

Bismaleimide?BMI?,as a kind of thermosetting resin with excellent comprehensive properties has been widely used in polymer composites.While,as a self-lubricating resin material whose inherent brittleness,larger coefficient of friction and poor wear resistance,thus limiting its wide application in self-lubricating composite material field.Graphene as a high performance two-dimensional sheet-like material,can be added to the polymer matrix to improve the mechanical,thermal,tribological properties of its composite materials.At present,the performance of the graphene/polymer composites is mainly effected by the dispersion of graphene in polymer matrix and the interface structure design of graphene-polymer.Meanwhile,the unique two-dimensional structure of graphene determines that its arrangement in the polymer composites also has great impact on the properties of its composites.Based on the above problems,polymer-modified graphene,graphene coated with different morphologies Fe₃O₄nanoparticles and ternary structure magnetic graphene with polyphosphazenes-Fe₃O₄–graphene were designed and synthesized.The effects of different functionalized graphene as well as their arrangement in the polymer matrix on the mechanical properties,hardness,tribological properties and thermal stability of their BMI composites and the possible friction mechanism of them had been studied.Research results are as follows:1.Three kinds of amino-terminated functionalized graphene,hyperbranched polytriazine grafted graphene?HBPT-RGO?,polytriazine coated graphene?HBPT@RGO?and hyperbranched polyphosphazene grafted graphene?HBPC-RGO?were synthesized by different methods.Contrast examined the combination methods,composition,morphology and thermal stability of functionalized graphene.Then,added them respectively into BMI resin and prepared the RGO/BMI,HBPT-RGO/BMI,HBPT@RGO/BMI and HBPC-RGO/BMI composites by casting method.The effects of interfacial bonding between polymer matrix and graphene as well as the chemical structure of graphene on the mechanical properties and tribological properties of the composites were studied in detail.Research results showed that the mechanical,anti-friction and anti-wear properties of BMI composites can be effectively improved by the addition of the three kinds of functionalized graphene.Compared to HBPT-RGO,the method of physical coating polytriazine modified graphene had easy operation,high utilization rate of raw materials and high grafting rate etc.Compared to HBPT-RGO/BMI and HBPC-RGO/BMI composites,HBPT@RGO/BMI composites exhibited more excellent anti-friction properties.At the same time,the HBPC-RGO/BMI composites contain the structure of polyphosphazenes show more excellent mechanical property and anti-wear property compared to the other two kinds of composites.The main reasons are that:?1?the abundant terminal amino groups on the polymer-modified graphene surface can not only make it uniformly dispersed in a resin matrix,but also produce interaction interface between graphene and the resin matrix.?2?Polytriazine coated modified graphene presents less damage to the inherent characteristics of graphene,which can not improve its dispersibility in a resin matrix and increase its mobility during the friction process.?3?The HBPC-RGO contained more stable P?N alternate six-member ring structure and a wealth of active groups,and thus the composite of it showed more stable properties.2.Different size and morphology of Fe₃O₄ nanoparticles were deposited on the surface of graphene by chemical co-precipitation method,prepared the graphene coated with Fe₃O₄ nanosphere?GNS-npFe₃O₄?and the graphene coated with Fe₃O₄ nanorods?GNS-nr Fe₃O₄?.Then,the influence of hybrid nanoparticles on mechanical properties and tribological properties of BMI resin composites was studied.The characterization results shown that,compared to the RGO/BMI composite,GNS-npFe₃O₄/BMI and GNS-nrFe₃O₄/BMI composites have better friction-reducing and anti-wear properties.While,the GNS-nrFe₃O₄/BMI composite compared to the GNS-npFe₃O₄/BMI composite has better friction-reducing property,but poor anti-wear property.This phenomenon may be due to that the graphene easily gathered and superimposed in BMI resin matrix,difficult to form a self-lubricating transfer film during ftiction process,the existence of Fe₃O₄ nanoparticles can prevent its superposed,reducing the friction coefficient of composites.The Fe₃O₄ nanoparticles also have the role of fill and repair friction surface of composites,the graphene and Fe₃O₄ nanoparticles in GNS-Fe₃O₄hybrid nanoparticle can form a synergistic effect of lubrication during friction process to greatly improve tribological property of the composites.At the same time,compared to the GNS-np Fe₃O₄ containing smaller sized Fe₃O₄ nanoparticles,GNS-nrFe₃O₄ are easily precipitated from the resin matrix during the friction process.3.The GNS-Fe₃O₄ composites coated with amino-terminated polyphosphazene were prepared by the method of precipitation copolymerization,and two different morphologies of the ternary complex nanoparticles GNS-npFe₃O₄@PZM and GNS-nrFe₃O₄@PZM were synthesized.And then,the influence of the ternary complex nanoparticles on mechanical properties and tribological properties of BMI resin composites was studied.Characterization results have shown that,GNS-Fe₃O₄@PZM/BMI composite compared to the GNS-Fe₃O₄/BMI composite has better mechanical properties,tribological properties and carrying capacity.This is mainly due to the GNS-Fe₃O₄@PZM compared to the GNS-Fe₃O₄ can be better dispersed in the resin matrix and form a good interface structure between nanoparticles and the resin matrix to improve stress absorbing ability and anti-wear property of the composites.GNS-Fe₃O₄@PZM nanoparticles can precipitate from the resin matrix and form a uniform self-lubricating transfer film to prevent direct contact between metallic rubbing pairs and the composite during friction process,reducing the wear of composite systems.4.The magnetic graphene coated with Fe₃O₄ nanosphere?GNS-npFe₃O₄ or GNS-npFe₃O₄@PZM?were assembled aligned distributed in the resin matrix by magnetic induction method and prepared the aligned GNS-npFe₃O₄/BMI and GNS-npFe₃O₄@PZM/BMI composites.It was first discussed the influence of arrangement and interface structure of graphene on the mechanical and tribological properties of its composites.Characterization results have shown that the aligned composite systems with magnetic field-induced presented higher bending strength and lower friction coefficient compared to the non-aligned composites.This is mainly due to the graphene sheet has a unique structure and outstanding performance anisotropic,when it is aligned distribution in the polymer matrix,ordered structural composite material exhibits a big difference in the different directions.Meanwhile,aligned composites exhibit excellent anti-wear properties under paraffin oil lubrication condition,which is mainly due to paraffin oil itself owns excellent lubricating properties and the friction heat can be quickly transferred during friction process.