Preparation And Characterization Of Polymer Based Organic/inorganic Nanocomposites And Study On Their Structure-property Relationship

Polymer based organic/inorganic nanocomposites have extracted extensive research interests due to their unique properties. The nanocomposites combine the advantages of the inorganic materials (rigidity, high thermal stability and unique optical, electronic and magnetic properties) and the organic polymers (flexibility, dielectric, ductility and processability), which is different with the single material and conventional composite materials. Moreover, these polymer based organic/inorganic nanocomposites have potential application in mechanical, thermal, electronic, optical, and nonlinear optical fields because the inorganic particles are well dispersed in polymer matrix in nanometer scale.In this thesis, several kinds of polymers and inorganic materials were used to prepare the polymer based organic/inorganic nanocomposites and their structures and properties are also extensively studied.(1) Poly(styrene-co-maleic anhydride)(SMA)/silica and Poly(styrene-co-acrylonitrile) (SAN)/silica hybrids were prepared via a sol-gel route using silicic acid oligomer (SAO) from water glass. The polycondensation behavior of the SAO and the aggregation behavior of the silica particles in the hybrids were investigated. The prepared SMA(SAN)/silica hybrids were characterized by infrared spectroscopy, dynamic light scattering, thermogravimetric analysis, differential scanning calorimetry and scanning electron microscopy. The results showed that the particle size of silica in hybrids increased with increasing silica loading, and decreased dramatically by adding the coupling agents. The decomposition temperature and the glass transition temperature of the hybrids were higher compared with the precursory polymers. The mechanical properties of blends of ABS resin with the hybrids were also tested and the results indicated that the well-dispersed silica particles in the hybrids indeed reinforced the blends. Some nanocompsites based of Acrylonitrile Butadiene and Styrene copolymers (ABS) were prepared in this way.(2) The polyamide-6/silica nanocomposites were prepared via an in situ polymerization route using silicic acid as precursor of silica, which was extracted from water glass. SEM observation showed that the silica particles were welldispersed in the polyamide-6 matrix on nanometer scale, which demonstrated that this method could effectively avoid the agglomeration of the inorganic particles. The coupling agent APTES was added to introduce the interfacial interaction between the silica and the polymer matrix, which lead to more graft of polymer on the silica surface and made the material display higher performance. It was found that the incorporation of the inorganic component significantly increased the melt viscosity, tensile strength, Young's modulus, thermal decomposition temperature, glass transition temperature and Vicat softening temperature of polyamide-6 resin. The reinforcement of the silica particles was clearly demonstrated.(3) The polyamide-6/attapulgite nanocomposites were prepared via an in situ polymerization route with attapulgites pre-modified with cetyltrimethylammonium bromide (CTAB) and toluene-2,4-diisocyanate (TDI). Morphology observation showed that the exfoliated attapulgite fibers were well dispersed in the polyamide-6 matrix on a nanometer scale and formed a percolation network structure. Polyamide-6/attapulgite nanocomposites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), thermomechanical analysis and tensile test. The results showed that the attapulgite fibers can remarkably reinforce the thermal and mechanical properties of polyamide resins and these high performance materials can be used in plastic industry.(4) The rheological behaviors of such Polyamide-6/attapulgite nanocomposites samples were investigated by an ARES rheometer with parallel plate geometry. The storage moduli (G'), loss moduli (G"), and dynamic viscosities of these samples increased monotonically with attapulgite content at low frequencies. The presence of attapulgites caused these nanocomposite melts to have solid-like behaviors and slower relaxation. This behavior can be explained in terms of the development of a grafting-percolated fibrous-silicate network structure. Monte Carlo simulations were performed to determine the critical threshold for attapulgites fibers in three dimensions. The calculated critical threshold from simulations fitted the results of our rheological experiments very well. The confinement effect was evidenced by the thermo mechanical data from DMA (Dynamical mechanical analysis) and TMA (Thermal Mechanical Analysis). From the results it can be concluded that the exhibited properties of thenanocomposites came from the intrinsic structure of the nanocomposites. The nanocomposites showed dynamic modulus reinforcement, suppression of thermal expansion effect, and enhanced barrier property with increasing attapulgite loading, which lead to prepare some functional polyamides products. (5) Resol-type phenolic resin/expanded graphite composites were synthesized via in situ polymerization of the monomer in the presence of sonicated expanded graphite. SEM observation showed that the graphite nanosheets were well dispersed in the phenolic resin matrix on a nanometer scale. The electrical conductivity of the composite was investigated as a function of the expanded graphite fraction. Compared with pure polymer, the electrical conductivity of the composites was dramatically increased and had a value of about 1 S/m at graphite content of 4.0 wt%. These electrically conducting composites have a lower percolation threshold and much higher conductivity than those of composites made by conventional methods.