Two Type Of Layered Silicate/Polymer Nanocomposites

In this dissertation, polymer/layered silicate composites were prepared with two types of layered silicates, such as montmorillonite and talc, respectively. Firstly, nylon 6/montmorillonite (N6/MMT) composites were prepared via melt compounding with the following three different blending sequences: (1) Nylon 6 (N6) was modified by epoxy (EP), then mixed with MMT. (2) Nylon 6, EP and MMT were blended simultaneously. (3) Nylon 6 was compounded with MMT pretreated by EP. The effects of EP contents and blending sequence on melting, crystallization, and mechanical properties of composites were investigated. Secondly, the fully exfoliated thermotropic liquid crystalline copolyester/ montmorillonite (LCP/MMT) nanocomposites were synthesized by in-situ acetylation and melting intercaction condensation polymerization. Finally, the talc/isotactic polypropylene (PP) composites were prepared by melt extrusion with PP and talc modified by in-situ monomer/talc polymerization or adding glycidyl methacrylate/styrene solid-phase-grafted polypropylene (GSP) as compatibilizer. The effects of in-situ monomer/talc polymerization or compatibilizer on crystal structure, melting and crystallization properties of PP matrix, the micro-structure and mechanical properties of talc/PP composites were inverstigatied. And the toughening mechanism of talc on PP was also discussed. Based on experiment results, the conclusions were drawn as following:(1) The intercalated structure nylon 6/montmorillonite (N6/MMT) nanocomposites were prepared; the blending sequences have few effects on the mechanical properties and thermal behavior of N6/MMT nanocomposites. The addition of epoxy decreases the melting temperature (Tm), crystallization temperature (Tc) and relative crystallinity (Xc) of N6 phase in N6/MMT nanocomposites. Due to its plasticizing effect, the epoxy enhances the elongation at break and Izod impact strength of N6/MMT nanocomposites.(2) LCP/MMT nanocomposites exhibit nematic liquid crystalline behavior, and the incorporation of the exfoliated MMT layers throughout the LCP matrix results in very fine but imperfect schlieren texture, and the disinclination becomes blurred. The exfoliated MMT layers have different effects on the glass transitions of the PBT-rich and PHB-rich domains in LCP macromolecules due to their different chain flexibility and structure. With increasing MMT contents, the glass transition temperature (Tg1) of PBT-rich phase in LCP tends to increase, while the Tg2 of PHB-rich phase tends to decrease. Under the induction of LCP, the exfoliated MMT layers are oriented along the force field.(3) After talc was modified with methyl methacrylate (MMA) or butyl acrylate (BA) via in-situ polymerization, the talc/PP composites is intercalated in nano-sized level. The thickness of the PMMA-modified talc layers in the PP matrix is in the range 80 nm to 240 nm, while the PBA-modified talc is even thinner. The modified talc enhances the interfacial action between PP and talc, weakens the nucleation effect of talc on crystallization of PP, and decreases the crystallinity of PP. The oriented talc layers induce orientation of PP crystals during molding process, while the degree of PP crystal orientation decreases after talc is modified with PMMA or PBA.(4) During the processing of PP/talc composites, the talc particle is delaminated to platelets with multi-scale structure ranged from micro- and nano-size in thickness by high shearing force. The compati1izer (GSP) enhances the interfacial interaction between talc and PP matrix, which makes the thickness of talc platelets decrease further. There is an optimal talc contents for the flexural modulus, tensile strength and izod impact strength of PP/GSP/talc composites. With increasing GSP contents, the tensile strengths of PP/GS-PP/talc composites increase obviously, while the flexural modula of composites change little. The Izod impact strength of PP/GS-PP/talc composites is higher than that of PP. Moreover, there is an optimal GSP contents for the Izod impact strength of PP/GS-PP/talc composites.(5) In in-situ polymerization modified talc/PP composites, the delaminated talc layers restrict the formation of crazes in composites. Their two-dimension structure is not beneficial to yielding polymer matrix around talc layers, debonding and cavitating of PP/talc interface, so that the impact strength of talc/PP composites decreases. For PP/GSP/talc composites, two factors, i. e. the multi-scale structure ranged from micro- and nano-size in thickness of talc layers, and enhanced interfacial adhesion between PP and talc due to compati1izer, lead to absorbing more impact energy during fracture, and increasing the toughness of PP/talc composites.