Isothermal Crystallization Behavior And Mechanical Properties Of Nylon 6/montmorillonite Nanocomposite

We processed nylon 6/montmorillonite nanocomposite by melt intercalationthat organically modified montmorillonite and nylon 6 were mechanically mixedand the extruded by a twinscrew etruder. Organically modified montmorillonitewas synthesized by a cation exchange reaction between Na-montmorillonite andoctadecylammonium salt. The X-ray diffraction patterns of composite containing5wt.% montmorillonite didn't show any peaks corresponding to montmorillonite,which indicated that intercalated montmorillonite layers through themelt-extrusion process are exfoliated into nanoscale layers and randomlydispersed in the nylon 6 matrix. X-ray diffraction scans of nylon 6 crystallized at different crystallizationtemperatures reflected the changes in the structure of nylon-6. Form 60℃ to100℃,γ-phase is dominant in nylon 6. As the crystallization temperature isincreased to above 100℃, α-phase appears and increases, butγ-phase decreasesand disappears. At 180℃, the two peaks of α-phase shift to lower angle. Besides,the diffraction pattern of nylon 6 crystallized at 180℃ shows an interestingfeature. The small crystalline peak at 2θ=28.9°becomes suddenly a very stongpeak and shifts to smaller diffraction angle. This peak appears at high temperature,so we call it "high temperature crystalline peak". We also find the peak in - 52 -吉林大学硕士学位论文nanocomposite and suggest that the peak may arise from stress-induced whennanocomposite is quenched form 180℃ prior to isothermal crystallization. The addition of montmorillonite modifies the crystalline style of nylon 6.The diffraction patterns of the nanocomposites exhibit the high temperaturecrystalline diffraction features of pure nylon 6 even at lower temperature. thestrong crystalline peaks of α-phase indicate that the α-crystalline phase ispredominant in the whole temperature range. The unknown high temperaturecrystalline peak maintains unchanged in intensity. Unlike nylon 6, thenanocomposites have not obvious transformation except increasing the degree ofcrystallinity and crystalline size. All these may be due to restricting of chainmobile by addition of montmorillonite. Nylon 6/montmorillonite nanocomposite is drawn under room temperature,90,150 and 200℃ at a constant deformation rate of 2 cm/min that has beeninvestigated using X-ray diffraction (XRD) and differential scanning calorimetry(DSC). Elevating temperature results in substantial decrease in stiffness for bothmaterials and with increasing drawing temperature, the nanocomposite exhibits amore pronounced modulus decrease response compared to the neat nylon 6. Yieldstrength decreases with temperature for both materials. However, the drop ofyield strength of nanocomposite is more notable than that of nylon6. Elongationat break for both materials is increasing with increasing drawing temperaturethough that of nanocomposite is shorter than that of nylon 6 in the wholetemperature ranges. The above results show that the addition of montmorillonitecan not only increase strength and modulus of nylon 6 at room temperature butalso improve them at high temperature, indicating that there is a interactionbetween the matrix and the montmorillonite in the whole temperature ranges.However, the reinforcing effects decreases with increasing temperature, which - 53 -吉林大学硕士学位论文should be attributed to the increase in the mobility of molecular chains and thedecreasing interactions between nylon-6 matrix and montmorillonite platelet. In order to compare with the nanocomposite, the nylon 6 samples weredrawn up to the same train values as the strain at break of nanocomposite drawn atdifferent drawing temperatures. For nylon 6, XRD indicate the intensity of (200)αis increasing and that of (202/002)α is decreasing with increasing drawingtemperature along the equatorial direction. In the meridian d...