Interfacial Modification Of Functionalized Carbon Nanotubes/Bismaleimide Resin Composites

Bismaleimide resin is a high?performance thermosetting polymer with excellent high specific strength,high specific modulus,high temperature resistance,radiation and chemical resistance.Therefore,they are widely used in aerospace,mechanical and electronic fields.In recent years,carbon nanotubes have attracted much attention due to their excellent mechanical,electrical and thermal properties.Adding carbon nanotubes to polymer resins can form polymer nanocomposites with more excellent properties.However,due to the weak van der Waals force between carbon nanotubes and polymer matrix,it is difficult to form effective load transfer.Therefore,the surface of carbon nanotubes is often modified by functionalization to improve the interfacial bonding strength between the carbon nanotubes and the resin and suppress the dispersibility,so that carbon nanotubes/polymer composites possess better mechanical properties.It is worth noting that due to the small scale of the interface and the chemical reaction process involved in the interaction between functional groups and matrix molecules,it is difficult to understand the strengthening mechanism of these materials,however,the numerical simulation method has become a powerful tool to solve the related problems.In this work,the molecular scale models of pristine carbon nanotubes,functional groups-grafted carbon nanotubes(CNT-OH,CNT-COOH)and polymer-grafted carbon nanotubes(CNT-BDM/DABPA,covalent crosslinking of surface functional groups with bismaleimide matrix molecules)reinforced 4,4'-bismaleimidodiphenylmethane(BDM)/2,2??diallylbisphenol A(DABPA,curing agent)resins are established,which considers the crosslinking reaction process that is basically consistent with the experiment,including the modification of bismaleimide resin and the cross-linking reaction of the functional groups on the surface of carbon nanotubes with the resin matrix molecules.Based on the molecular dynamics method,the mechanical properties of BDM/DABPA resins reinforced by pristine carbon nanotubes,functional groups-grafted carbon nanotubes and polymer-grafted carbon nanotubes are calculated,and the interfacial strengthened rule caused by covalent cross-linking of carbon nanotubes and matrix is revealed.The results show that functionalized carbon nanotubes/bismaleimide resin composites have better mechanical properties than the pristine carbon nanotubes as reinforcement phase.The functionalized methods include grafting functional groups and polymer on the surface of carbon nanotubes,and the covalent cross-linking of active functional groups on carbon nanotubes with resin matrix molecules can further enhance the mechanical properties of the resin.That is to say,the enhancement effect of carbon nanotubes is CNT-BDM/DABPA>CNT-COOH >CNT-OH > CNT.The corresponding interfacial interaction energy between carbon nanotubes and matrix is increased from 547.98 kcal/mol to 1373.97 kcal/mol,and the enhancement amplitude is 150.73%.Therefore,polymer-grafted carbon nanotubes as reinforcement phase can improve the poor interfacial bonding strength between carbon nanotubes and bismaleimide resin through interfacial crosslinking,thus effectively boost the interfacial load transfer efficiency.Based on the molecular dynamics method,the effects of 1.09%,1.82%,3.65% and4.63% carbon nanotubes as reinforcement phase on the mechanical properties of bismaleimide resin are revealed.The results suggest that the mechanical properties of pure carbon nanotubes and functionalized carbon nanotubes/ bismaleimide resin composites are increased with increasing the volume fraction of carbon nanotubes.In addition,the strengthening effect of the functionalized degree of carbon nanotubes(0.71%,1.29%,2.47%,3.17%,3.64%)on the composite is analyzed,and the results show that the mechanical properties of bismaleimide resin materials increase with the increase of functionalized degree of carbon nanotubes.This is mainly due to the fact that with the increase of the functionalization degree of carbon nanotubes,the interfacial interaction energy between the reinforcement phase and the matrix increases from 1712.74 kcal/mol to 4954.79 kcal/mol,and the enhancement amplitude is 189.29%,which greatly improves the external load transfer rate between the matrix phase and the reinforcement phase.In this paper,the cross-linking reaction between functional groups on the surface of carbon nanotubes and bismaleimide matrix molecules is achieved by numerical simulation method,so that the long polymer molecular chains(BDM/DABPA)are grafted on the surface of carbon nanotubes to enhance the interfacial bonding between carbon nanotubes and resin.Based on these results,the strengthening mechanism of the volume fraction and functionalization degree of carbon nanotube on the mechanical properties of bismaleimide resin composites is predicted.The research work provides molecular level numerical analysis technology of advanced polymer nanocomposites,which provides technical support for the design and preparation of related materials,and provides valuable reference for its application in aerospace,precision manufacturing and other scientific and technological fields.