Structure And Properties Of Crosslinked Epoxy Resin TGDDM: A Molecular Dynamics Simulation

Thermosetting epoxy resins have been widely used in many fields like transportation, mechanical, integrated circuit because of its excellent thermodynamic performance and stability. With the rapid development of the aerospace industry, the higher requirements of performance in epoxy resin has been put forward. Many researchers have devoted to improve the existing epoxy resin, curing agent and curing recipe. In this thesis, molecular simulation method was employed to investigate the influences of crosslink density, curing agent, SWCNTs and FSWCNTs on structure and properties in crosslinked epoxy resin TGDDM. This study can be used to guide the future development of advanced thermosetting epoxy resin.A perl script for automatically and dynamically constructing crosslinked bonds between epoxy resins and curing agents and bring down polymers' temperature has been developed. This script was applied to an epoxy resin system composed of TGDDM and DDS. The effects of crosslink density on thermomechanical properties and structures have been investigated. Results show that, with the increases of crosslink density, system density, glass transition temperature(Tg) and elastic modulus show an increase trend. Total potential energy, angle energy and torsion energy reduce with crosslink density's increase, however, non-bond energy like vdw and electronical energy increase with it. Mean square displacement(MSD) and Fraction Free Volume(FFV) can be used to measure the mobility of molecule, the MSD of system shows a heighten phenomenon with crosslink density's increase. The reason is that the crosslinking process pull end groups together and reduce molecular mobility's decrease. The same trend of FFV was also been predicted. Radial distribution function(RDF) was been used to analyze the distribution of atoms.In order to predict the curing agent structure influences on epoxy resin's structure and properties. Different curing agent like DDS, DDM, MPD and DETDA have been applied to cure TGDDM with molecular dynamic simulation. By comparing the elastic modulus of these system, it is found that the DDS system shows a biggest value in modulus, in the meanwhile, the DETDA system's modulus is the smallest. The magnitude of Tg of these curing system is DDS>MPD>DDM>DETDA. MSD and FFV has been employed to qualitative predict molecular chain segment motion ability, the magnitude relation of elastic modulus show a contrary trend with MSD and FFV results. Cohesive energy density(CED) has been adopted to analyze the relationship between molecular inter-atomic forces and the Tg. The larger the CED, the higher the Tg. Mechanical properties in different temperatures of four systems have been analyzed to estimate systems' heat resistance. DDS and MPD curing systems show a good heat resistance ability.The nano filler of SWCNTs and FSWCNTs' influences on epoxy resin's structure and properties has been predicted by Molecular Dynamic simulation. By comparing with neat epoxy resin, results show that the nano filler SWCNTs facilitates the Tg of curing system increases about 20 K, but decreases the mechanical properties. Nano filler SWCNTs promotes both Tg and elastic modulus of the systems. FFV analysis shows that nano filler can make the FFV value reduce compared with neat epoxy. Mechanical properties in different temperatures of nano filler systems have been analyzed to estimate systems' heat resistance. The adding of SWCNTS does not facilitate heat resistance of epoxy. The FSWCNTs curing systems show a good heat resistance ability.