In-situ Preparation, Structure And Properties Of Nylon11/silica Nanocomposites

Polyamide11(PA11) is an engineering plastics with excellent performance, suchas low water absorption and high low-temperature impact strength. PA11was mostlyused as automobile pipe-laying and municipal gas pipe as well as offshore oilfieldapplication.But with the increasing request of low cost and high mechanical properties,pure PA11resin can not fully satisfy various usages. Nanoparticles have a lot of newcharacteristics. Using nanotechnology in modification of polymers, nanocomposits with somespecial properties or polymers with more outstanding properties can be gained. Consequently,nylon11/silica nanocomposites, and nylon611/MMT nanocomposites were in-situpolymerized using silica and MMT as fillers.In the first part, silica was prepared via the vitriol precipitation method usingcheaper water glass as raw material．The influence of the reactant concentration(water glass, H2S04, Na2S04) and processing, parameters (reaction temperature,stirring rate, solvent washing reaction) on the morphology and properties of silicawere investigated systemically and optimized the synthesis technology．The structure,particle size and its distribution, and surface physical properties were alsocharacterized．PA11/silica nanocomposites (PSN-X, where X represent the weightpercentage of silica) were in-situ polymerized using11-amino undecanoic acid andwet silica as raw materials, and its morphology structure, thermal stability, rheologicalbehavior, crystallization properties, mechanical properties and barrier properties wereinvestigated by scanning electron microscopy (SEM), fourier-transform infraredspectroscopy (FTIR), thermo-gravimetric analyzer (TGA), capillary rheometer,differential scanning calorimeter (DSC) and polarizing microscopy (POM),respectively. The main results were listed as following:1. PEG6000was used as surfactant to control the minienvironment for the coprecipitation reaction,in which the formed precipitates were bundled by PEG6000and kept the precipitates from aggregating．The result showed that the average size ofprimary nanosilica particle was about20～45nm.2. Hydrophobic nanosilica was prepared by"one-step" precipitation method,thatis,silane coupling agent KH570was added into the reaction mixtures during the laststage of synthesis．The affinity of hydrophobic nanosilica with polymer matrix wasexpected to be improved．The activation coefficient of silica is100％,the averagesize of primary silica particle is about20-45nm. The XRD indicated that thenanosilica was still amorphous non-crystalline structure after the treatment withsurfactant PEG6000and silane coupling agent KH570．FTIR and TG analysisshowed that the surface active agents PEG6000and silane coupling agent KH570isgrafted to the surface of nanosilica by chemical bond rather than by simple physicaladsorption．TEM photographs illustrated that the aggregation of nanosilica wasimproved significantly after the treatment with surfactant PEG6000and silanecoupling agent KH570．3. Silica of small particle size and narrow distribution was prepared byoil-in-water microemulsion, and was uniformly dispersed in PA11matrix duringin-situ polymerization. Strong interaction was observed between PA11and silica.With the increasing silica content, the inherent viscosity gradually decreased and theinitial temperature of weight loss improved slightly. The addition of silica contributedto improve the tensile strength, flexural strength, thermal stability and barrier propertyof PA11, while it also led to reduce the impact strength and elongation at break.4. Rheological properties of PA11/silica nanocomposites were investigated bycapillary rheometry. The experimental results showed that both PA11and PA11/silicananocomposites were pseudoplastic fluid and exhibited shear-thinning behavior.Non-newtonian index increased with the silica content increasing. In case of aconstant shearing rate, apparent viscosity of all PA11/silica nanocomposites exceptPSN-5was lower than that of pure PA11. The reduction of the viscous activationenergy with the increasing shearing stress indicated that nanocomposites can beprocessed over a wide temperature at a constant shearing stress. 5. Crystallization and melting behavior of PA11and PA11/silicananocomposites were investigated by differential scanning calorimeter. It was foundthat silica acted as the nucleating agent of PA11, the Avrami equation was suitable todescribe the isothermal crystallization of PA11and its nanocomposites,while both theAvrami equation modified by Jeziorny and Mo's method well described thenonisothermal crystallization kinetics. Additionally, the equilibrium meltingtemperature and the activation energy of nonisothermal crystallization fornanocomposites were calculated from Hoffman-Weeks equation andHoffmann-Lauritzen theory.In the second part, nylon611/MMT nanocomposites were in-situ polymerizedusing11-amino undecanoic acid, nylon6prepolymer and montmorillonite as rawmaterial. The structure, intrinsic viscosity, morphology, barrier properties, mechanicalproperties and thermal stability were characterized by scanning electron microscopy(SEM), fourier-transform infrared spectroscopy (FTIR),thermo-gravimetric analyzer(TGA),, respectively. The main results were listed as following:1. Organoclays were thoroughly exfoliated and dispersed homogenously in the nylon6/11matrix at low organoclay loading, but Intercalated and stacked silicates layerswere observed at high organoclay loading. It was also found that strong interactionoccurred between organocaly and nylon611chains.2. The viscosity-average molecular weight of nylon611/organoclay nanocompositeswas reduced with the increasing MMT content since that the organoclay blockades theactive ending-group of the monomers.3. The tensile strength and elongation at break was increased with the initial additionof MMT and then decreased with the further increasing MMT content. With theincreasing MMT loading level, the tensile modulus and impact strength werecontinuously increased and reduced, respectively.4. The barrir properties of nanocomposites were improved with the incorporation ofMMT, as indicated by the fact that the water absorption and oil absorption werereduced by twofold and2.5times versus pure nylon611. the onset temperature of weight loss was also increased by10℃.