Study On The Selective Localization Of Carbon Nanotubes In Immiscible Polymer Blends And Its Influence On Crystalliization Behaivors Of Component

Polymer blending is a convenient and efficient route for the development of new polymeric materials, which can combine the excellent and special properties of the constituent polymers. Many polymer blends are immiscible and their blends exhibit poor mechanical properties. Among various techniques used to compatibilize polymer blends, adding inorganic nanofillers is proved to be one of the most efficient methods. Since their discovery, carbon nanotubes (CNTs) attracted tremendous attention due to their superior mechanical, electrical and thermal properties. CNTs have been proved to be a good nucleating agent for crystallization of polymers. The addition of a few CNTs in semicrystalline polymer can efficiently promote the crystallization by decreasing the nucleation activation energy and accelerating crystallization rate. Polystyrene (PS), polypropylene (PP) and polyethylene terephthalate (PET) are important engineering polymers used in a wide variety of applications, and melt blending of them are of practical significance. In this research, nanocomposites of PS/PP and PS/PET containing Multi-walled nanotubes (MWCNTs) were mainly prepared by direct melt blending. MWCNTs were firstly functionalized to improve the adhesion with polymer matrices, so we can control the localization and dispersion of MWCNTs in immiscible polymer blends. The selective localization of MWCNTs in nanocomposites was realized by the different blending sequences, the use of compatibilizer, etc. Furthermore, the effect of selective localization of MWCNTs on the crystallization and morphology behaviors of nanocomposites were discussed. The main results obtained in this work are listed as follows:(1)The pristine carbon nanotubes were first acidified in nitric acid and then reacted with maleic acid, to introduce carbonyl, carboxyl and hydroxide groups onto the surface of carbon nanotubes and the final products are called Functionalized multi-walled carbon nanotubes (F-MWCNTs).(2)PS/PP blends containing F-MWCNTs were prepared using a twin screw extruder followed by injection molding, the F-MWCNTs was firstly dispersed in solvent to obtain PS/F-MWCNTs master batch and then the master batch was melt blended with different contents of PP and PS to obtain samples with corresponding compositions. For the PS/PP blends without F-MWCNTs, two exothermic peaks were presented in the cooling curve of PP phase, indicating fractionated crystallization of PP. The PS/PP/F-MWCNTs nannocomposites exhibited only one exothermic peak indicating that only bulk crystallization of PP phase occurred during the cooling process. Furthermore, the nanocomposite exhibited higher crystallization temperature compared with the corresponding blends without F-MWCNTs, and the crystallization temperature shifted to higher temperatures at higher content of PP. It proved that F-MWCNTs migrated from the PS phase to the PP phase, and nucleated the crystallization of PP. The DMA results showed that F-MWCNTs exhibited as a plasticizer for both PS and PP, decreasing the glass-transition temperature of both PP and PS in PS/PP/F-MWCNTs nanocomposites. SEM results showed that the presence of F-MWCNTs induced the morphology of the immiscible blends to change from sea-island morphology to co-continuous morphology to a certain degree.(3)Addition of maleic anhydride grafted styrene-ethylene-butylenes-styrene (SEBS-MA) as compatibilizer to 80PP/20PS blends can compatibilize the blends by reducing the interfacial tension and enhancing the interfacial adhesion, and consequently result in smaller dispersed particles with better distribution. The different blending sequences and usage of compatibilizer on the selective localization of F-MWCNTs was discussed. When the F-MWCNTs were first dispersed in PP and then blended with other components, the crystallization temperature of PP phase shifted to lower temperature when SEBS-MA are added, indicating the migration of F-MWCNTs to the SEBS-MA, which characterized high affinity. Due to the migration of F-MWCNTs into the SEBS-MA, less F-MWCNTs remained in the PP phase, leading to decreased temperature of PP phase. The DMA results showed that glass-transition behaviors of PS had not changed, meaning that F-MWCNTs remained on the interface instead of migrating into the PS phase. When the F-MWCNTs were first dispersed in PS and then blended with other components to prepared the nanocomposites, the crystallization temperature of PP in different composites are nearly the same, and the DMA results showed that glass-transition behaviors of PP had not changed, indicating that the F-MWCNTs stayed in the PS phase due to obstruction of F-MWCNTs imposed by the SEBS-MA. For the 80PP-MA/20PS/SEBS-MA/F-MWCNTs nanocomposites with PS master batch, the crystallization behavior of PP-MA showed that F-MWCNTs had better affinity with SEBS-MA than PP-MA in 80PP-MA/20PS/SEBS-MA/F-MWCNTs nanocomposite.(4)The PS/PET/F-MWCNTs nanocomposites were prepared, and the wetting coefficients predicted that the F-MWCNTs should selective localized in PET. And the DSC test showed that F-MWCNTs exhibited obvious nucleating effect for the crystallization of PET. So, for PS/PET/F-MWCNTs nanocomposites, F-MWCNTs have higher affinity with the PET phase, it could migrate from the PS phase to the PET phase. The SEM observations showed that the localization of the F-MWCNTs at the interface and in PET phase, and the experimental results confirmed the results of prediction.