| The preparation of nylon-6 nanocomposites with layered silicate reinforcementsby direct melt processing has attracted increasing attention in recent years, and theeffects of the silicate platelets on the crystallization behavior of the nanocompositesnylon-6 matrix have also been of interest.The crystallization behaviors, mechanical properties and drawing-inducedcondensed-state structural changes of nylon-6 and nylon-6/montmorillonitenanocomposite during different crystallization and annealing have been investigatedby X-ray diffraction.Wide-angle X-ray diffraction (WAXD) studies of nylon-6 films isothermallycrystallized above 170 ℃or annealed at 200 ℃ and then quenched in ice waterrevealed a strong or a weak crystalline peak at 2θ = 28.5°, respectively. Thecrystalline peak at 2θ = 28.5° did not appear when the isothermally crystallized orannealed nylon-6 films were cooled in air. It might attribute to that the nylon-6 filmis quenched from a high temperature after isothermal crystallization, and the orderedstructure will be maintained at a low temperature. However, if the nylon-6 film iscooled in air, the ordered molecular chains will be converted into the disordered statewith time. Hence, the "high temperature crystalline peak" (HTCP) can be observedin the quenched film instead of the air-cooled film. The addition of montmorillonitechanges the condensed-state structure of nylon-6. All nylon-6/montmorillonitenanocomposite films exhibited the strong crystalline peak at 2θ = 28.5°, whichcoincided with the occurrence of internal stresses during isothermal crystallization orannealing. It attributes to that the platelets of montmorillonite dispersed in nylon-6act as strong heterogeneous nucleating, capable of increasing crystallizationtemperatures and crystallization rates in comparison to neat nylon-6. Therefore, theappearance of α peak and HTCPs at low temperature may be caused by theheterogeneous nucleation of silicate platelets at high temperatures. Annealing above140 ℃ resulted in a crystalline double peak between the α1 and α2 peaks, whichcould be attributed to that the meso-stable γ phase of nylon-6 having beentransformed into the stable α phase during annealing.Nylon-6 and nylon-6/montmorillonite nanocomposite were drawn with the rateof 5 mm/min at room temperature, 140 ℃ and 200 ℃, which showed that theelastic modulus of the materials decreased gradually with drawn temperatureincreasing. The elastic modulus of nylon-6/montmorillonite nanocomposite wasalways higher than that of nylon-6 below 200 ℃. While temperature increased theyield strength was decreased. However, the yield strength ofnylon-6/montmorillonite nanocomposite was higher than that of nylon-6 during thewhole temperature range, which indicated that the addition of montmorilloniteenhanced the mechanical properties of nylon-6 not only at room temperature but alsoat high temperature, which attributed to the strong interaction between nylon-6 andmontmorillonite. However, with temperature increasing, the enhanced effect ofmontmorillonite was decreased, which attributed to the mobility of nylon-6molecular chains increased and the interaction decreased between montmorilloniteand nylon-6 matrix at high temperature.In order to understand the structure changes of nylon-6 and nylon-6/mont-morillonite nanocomposite, Debye diffraction has been investigated. Nylon-6 andnylon-6/montmorillonite nanocomposites were drawn to two times original length forcomparison at same temperature. It has been found that while temperature increasedthe orientation of nylon-6 and nylon-6/montmorillonite nanocomposite wasimproved;but at the same temperature, the addition of montmorillonite did not haveobvious effect on the orientation of nylon-6. |
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