Barrier Properties And Related Properties Of NR/Montmorillonite Nanocomposites

Polymer-layered silicates nanocomposites play important roles in the polymer modifying field due to their unique properties, especially excellent barrier property. The study on gas barrier properties and relating aging resistance, flame retardant properties, thermal stability and solvent resistance has important theoretical and practical significance. In this thesis, the gas barrier property and relating preperties such as aging resistance, flame retardant properites, thermal stability and solvent resistance of nature rubber/ montmorillonite nanocomposites were systematically investigated. The relationship between the barrier properties and the structure of the nanocomposites was discussed. The barrier mechanism of the nanocomposites was explored.Sevaral NR/modified MMT nanocomposites have been prepared via direct mixing intercalation method. These modified MMTs have specific reactive functional groups on the surfaces of the platelets or between them. XRD analysis proved the interlayer expansions for all these modified montmorillonites and also for the NR/EMT composites. The apparent crosslinking densities, the mechanical properties and thermal stabilities of NR/modified MMT nanocomposites have been enhanced compared with NR/unmodified MMT composite. Organic modified montmorillonites can improve the gas barrier properties of the nanocomposites remarkably. Among the nanocomposites, NR/EMT composite has the lowest gas permeability. With the increase of the EMT amount, the gas permeability is decreased until the content of EMT is 10phr. The effect of temperature on gas permeability follows Arrhenius Equation, and the permeation activation energy of the vulcanizates is increased in the order of NR/EMT>NR/MMT>NR, which indicats better gas barrier properties of NR/EMT composite than pure NR and NR/MMT composite.NR/EMT/RH nanocomposite was prepared via in situ reactive intercalationin mechanical mixing process. XRD results showed that the modifier RH can expand the layer distance of the nanocomposite from 1.71nm for NR/EMT to 2.05nm for NR/EMT/RH composite. TEM results indicated that in NR/EMT/RH composite the EMT platelets were dispersed in NR matrix with oriented arrangement in 100nm~200nm long and 10~50nm thick. The tight chemical bondings and hydrogen bondings in the interfacial regions between EMT and NR were formed, and the apparent crosslinking density of NR/EMT/RH nanocomposite was increased. The special nano layered structure, tight interfacial combination and increasd crosslinking density of the NR/EMT/RH nanocomposites retarded and barricaded the gas molecules and solvent molecules across the membrane of the vulcanizate and improved the gas barrier properties and solvent resistance of the nanocomposites. The EMT platelets in oriented arrangement retarded and barricaded effectively transportation of heat and light and diffusionin of oxygen and ozone in the vulcanizate, so the nanocomposite exhibits excellent aging resistance to thermal oxygen, ultroviolet ray and ozone, improved flame retardant properties, and thermal stability have also been improved. The analysis of thermal degradation indicated that all the reactions of the systems of NR, NR/EMT and NR/EMT/RH were first-order reactions, but NR/EMT/RH nanocomposite had highest activation energy thermal stability.NR/EMT/GMA nanocomposite was prepared via in situ reactive intercalation- mechanic mixing method. XRD showed that the modifier GMA can assist the nano intercalation of the EMT by expanding the layer distance from 1.71nm for NR/EMT to 1.79nm for NR/EMT/GMA. TEM results indicated that EMT platelets intercalated in the NR matrix with oriented arrangement in about 100~200nm long and 40~80nm thick. FTIR and other experimental data verified that the unsaturated double bonds in glycidyl methacrylate (GMA) can crosslink with NR molecular chains, the epoxy groups of GMA can conduct nucleophilic substitution with hydroxyls on interfaces of EMT. These reactions made EMT chemically combine with NR matrix on the interfaces and increased the crosslinking density of NR/EMT/GMA nanocomposite. These morphologic features of NR/EMT/GMA nanocomposite ensured the signicant improvements on gas barrier properties, aging resistances to thermal oxygen, ultraviolet rays and ozone, flame retardant properties, thermal stability and solvent resistance. The relationship between the thermal stability and flame retardant properties/thermal-oxygen aging resistance was investigated thermal degradation analysis. The results indicated not only the barrier of heat and oxygen by platelets of EMT played a role in the property improvement, but also the reacton of GMA with NR and EMT contributed the change of the structure of nanocomposite and enhance of activation energy that ensured the thermal stability and flame retardant properties improvements.