Studies On The Preparation And Properties Of Liquid Crystalline Epoxy Composites

In comparison with ordinary epoxies,liquid crystalline epoxy resins(LCERs),which combine the thermosets and liquid crystal formation capability,have become attractive for enhanced properties such as anisotropic orientation,high modulus and tensile strength,and low coefficient of thermal expansion.A series of research is conducted in this paper and get a lot of important conclusions,including that synthesis and curing behavior,structure-properties relationships of liquid crystalline thermosets,the blending system with both LCER and a common diglycidyl ether of bisphenol A,the effect of liquid crystalline epoxy structure on exfoliation of clay.The study results were shown as follows:1.4-(2-((oxirane-2-carbonyl)oxy)ethoxy)benzoic acid dimethyl benzalazine ester(OBDBA)and liquid crystalline epoxy 4-(4-oxiranyl-methoxyl)-benzoicacid cholesterol ester(OAC)are synthesized structurally characterised by infrared(IR)and nuclear magnetic resonance(NMR)spectroscopy.The mesogenic behaviours of the monomers are measured by differential scanning calorimetry(DSC)and polarised optical microscopy(POM).The result indicating that OBDBA presented various textures in the extensive temperature range and cholesteric structure is observed in the range of 130 ??215 ? in the OAC measure.2.Dynamic cure behaviors of OBDBA and OAC with different curing agent are investigated by DSC,methyl nadic anhydride(MNA)and phenylenediamine(PDA)is employed to cure OBDBA and OAC,respectively.The textures of OBDBA/MNA and OAC/PDA system were studied by means of POM during isothermal curing process at different temperature,indicating many differences are observed as a function of local degree of order in networks.The polydomain structure of this system is confirmed further by X-ray diffraction(WAXD).Mechanical and thermal properties of LCT with different textures are researched and the optimum performance is proven in smectic structure thermosets.The fracture surface derived from impacting test are observed by scanning electronic microscopy(SEM),indicating that the properties are influenced by different liquid crystal texture.3.The LCERs and epoxy resin blending system is prepared by co-polymerisation. Information about distribution of liquid crystalline epoxy resin is investigated by the FT-IR Imaging System and the texture of the blending system during curing reaction process is observed by POM,indicating that molecules of liquid crystalline epoxy resin can agglomerate to form anisotropic domains.The improvement in mechanical and thermal properties of diglycidyl ether of biphenol A(DGEB A)modified with liquid crystalline epoxy was achieved.In addition,the theory of combining silver-craek shearing-zone with bridge-link anchor is proposed by analyzing the broken section of liquid crystalline epoxy toughening DGEBA system.The utility of MMT as additives to prepare nanocomposite has been an effective way to enhance performance of epoxy resin.It is very difficult to achieve complete exfoliation of this layered silicate in polymer matrices,which has been an obstacle that prevents the development of this polymer nanocomposites.The liquid crystalline epoxy grafted clay is synthesized in this paper and the new method which called "solution compounding" process is developed for preparing epoxy/clay nanocomposites with completed exfoliated structure.The mechanism of exfoliation is explored by monitoring the change of morphology of organoclay(001)during each stage of processing with X-ray diffraction(XRD).The clay platelets uniformly dispersed and highly exfoliated in the whole epoxy matrix are observed using transmission electron microscopy(TEM).The mechanical properties and heat resistance properties of the nanocomposite materials are tested,indicating that the properties of nanocomposite materials with certain content MMT compared with pure epoxy resin are improved markedly.