Preparation And Properties Of Functionalized Multi-walled Carbon Nanotube/Polyamide6Composites Through Ultrasonic-assisted Extrusion

In order to improve the performance of nylon6/MWCNTs composite, this paperprepared nylon6/MWCNTs by ultrasonic assisted melt extrusion on the basis of surfacemodification of MWCNTs. Mainly studied the effect of ultrasonic vibration on the propertiesof nylon6matrix, the effect of surface modification of MWCNTs on the properties of nylon6and the effect of ultrasonic vibration on the properties of composites. The main conclusionsare listed as follows:Carboxyl and isocyanate are grafted onto MWCNTs via mixed acid and TDI modifiedroute. The characterization of treated MWCNTs was carried out by FTIR,SEM,etc. Theresults shows carboxyl and isocyanate are bonded on the MWCNTs. Acidification makes theMWCNTs campact.. After the introduction of isocyanate, the structure of MWCNTs becomesfluffy.The effect of ultrasonic oscillations on properties of nylon-6were studied. The resultsshow that ultrasonic vibration improves both the crystallinity and the proportion of α-phasecrystals of PA6. The inherent viscosity, viscosity average molecular weight and melt viscosityget reduced. Moreover, ultrasonic wave has little impact on mechanical properties.The effect of ultrasonic oscillations on the cross section morphology of composites wasinvestigated by SEM.（1）The functionalized MWCNTs disperse more evenly in the nylon6,because the modified MWCNTs enhance the interfacial effects with nylon6matrix.（2）Afterapplying ultrasound, the size of the MWCNTs become smaller, the distribution range becomelarger and the dispersion are more evenly.The effect of ultrasonic oscillations on the tensile properties of composites were studied. （1）The unmodified MWCNTs reduced the tensile strength of nylon6,and decreased with theincrease of the MWCNTs content. Because the unmodified MWCNTs have a poorcompatibility with nylon6. With the increase of modificied MWCNTs content, the tensilestrength firstly increase to a maximum and then decrease with the increase of MWCNTscontent. This shows that the modified MWCNTs enhance the interfacial effects with nylon6matrix, but when the content of MWCNTs is too high，it will have a reunion, which cause thematerials to produce defects.（2）After introducing ultrasonic vibration, the tensile strengthand tensile modulus of the composites have a certain degree of improvement.Because ultrasonic vibration can promote the dispersion of MWCNTs in nylon6matrix andimprove the compatibility with nylon6matrix.The effect of ultrasonic oscillations on the dynamic mechanical properties（DMA） ofcomposites were studied（.1）After adding MWCNTs, the storage modulus and glass transitiontemperature of the composite are improved. But the increasing degree of the storage modulusare effected by the content and the modified method of MWCNTs. When the MWCNTs is0.5wt%, the storage modulus: nylon6/TDI modified MWCNTs>nylon6/acidifiedMWCNTs>nylon6/unmodified MWCNTs.（2）After the introduction of ultrasonic vibration,the energy storage modulus of the composite are improved, it shows that ultrasonic vibrationhas promoted the compatibility of MWCNTs and nylon6matrix.The effect of ultrasonic oscillations on the mechanical properties of composites wasinvestigated by X-ray diffraction（XRD）（.1）After adding MWCNTs, the diffraction peak ofγ crystalline form disappears, the intensity of α crystalline form diffraction peak increase andthe total crystallinity increase. This suggest that the addition of MWCNTs favors theformation of α crystalline form, and promote the γ crystalline form transforming into αcrystalline form.（2）After introducing ultrasonic vibration, the crystallinity of the nylon6/unmodified MWCNTs increases while the nylon6/modified MWCNTs reduces. On the onehand, the ultrasonic vibration makes the MWCNTs aggregates size decrease and promotes thedispersion of MWCNTs in the nylon6matrix. On the other hand, ultrasonic broken chainreaction can improve the response rate of matrix and MWCNTs surface functional groups. For the unmodified MWCNTs, it has a poor compatibility with nylon6matrix, the heterogeneousnucleation effect of MWCNTs is dominant. For the modified MWCNTs, it has a stronginterface reaction with the nylon6, the limitation on the nylon6molecular chain plays aleading position.The effect of ultrasonic oscillations on the mechanical properties of composites wasinvestigated by differential scanning calorimetry（DSC）.（1）After adding MWCNTs, the γcrystalline melting peak in lower temperature disappeared, the double melting endothermaltranslates single melting endothermal, the crystallization temperature and crystallizationincrease, which is consistent with the XRD analysis.（2）Introducing ultrasonic vibration, thecrystallization of nylon6/unmodified composites increases while the nylon6/modifiedMWCNTs reduces, which is consistent with the XRD.