Preparation and characterization of Sebs-Clay nanocomposites

Official URL: http://risc01.sabanciuniv.edu/record=b1124913 (Table of Contents)

In this study, SEBS (styrene-b-ethylene-b-butylene-styrene) clay nanocomposites were synthesized with easy-to-find, cheap ingredients and using convenient, efficient and commercially viable methods. In particular, a combined melt intercalation method and insitu intercalative polymerization method was implemented to produce nanocomposites. The underlying strategy of this approach was to treat clays with appropriately chosen surfactants, namely, those that posessed the ability to intercaltate the basal spacings of the clay. An added subtlety of this study was the incorporation of an engineered polymerization initiator in the nanocomposite preparation, which behaved as an effective surfactant and permitted the uniform initiation of polymerization from even within basal spacings as opposed to being restricted to the clay surface. In the first part of this study, the optimum surfactant for a given reaction condition was determined to be Tequart DSM (N-N dialkyl dimethyl ammonium chloride). Basal spacings noted via WAXD analysis showed that Na-MMT treated with Tequart DSM had reached values of up to 1.9 nm, which exceeded the value of 1.2 nm that is typical of pristine clay. Notably, Tequart DSM delaminated more effectively than Cloisite 15 A, a commercial organoclay (1.38 nm). BTC 1218-50 (Alkyl dimethyl benzyl ammonium chloride ) was also succesful in view that the value noted was about 1.4 nm. Subsequently, an appropriate surfactant-initiator was envisaged and afforded by methylating the watersoluble radical initiator, V-50 (2,2-Azobis-2-methyl propionamide). Methylation was confirmed by the appearance of additional resonances on the 1H-NMR spectrum and by the shift of the melting curve from 173.9 oC to 119.5 oC on the DSC thermogram. While NMR analysis indicated that an average of four methyl groups had been attached to the native structure, DSC thermograms implied high product purity in view that the new melting endotherm was sharp. By applying this in-situ intercalative polymerization strategy to the best surfactant and initiator pair, a Styrene-clay nanocomposite masterbatch was realized. Clay, modified using an equimolar ratio of Tequart DSM and methylated V-50, displayed the greatest interlayer distance of 2.35 nm when characterized using WAXD. While this sample (MC1) gave the best results, the interlayer spacings of other preparations were also notable: Tequart DSM-native V-50 (MC6) gave 2.02 nm, BTC 1218-50-treated V-50 (MC4) gave 1.07 nm, and BTC 1218-50-untreated V-50 (MC2) gave 1.07 nm. In the final part of the thesis, several approaches for the preparation of nanocomposites were tested on a standard unfilled SEBS grade material. Each attempt was melt- mixed with SEBS and compression molded plaques were tested. Thermogravimetric analyses were carried out primarily to verify the anticipated clay content in each of the blends. SEM images in agreement with WAXD data proved that the nanocomposite produced was in fact intercalative. Tensile testing of polymer blends containing 5wt% intercalated clays displayed greater elongation values in all of the nanocomposites when compared with unfilled SEBS. For example, the maleic anhydride grafted SEBS (SEBSMA) sample had the highest elongation value (642,87%). The sample representing our strategy, namely, a MC1 masterbatch (MC1-MB) containing nanocomposite, was more easily elongated than MC1 5% clay sa mples, even though it contained more styrene. Another interesting finding was the decreased tensile strength of the nanocomposities when compared to unfilled SEBS. Lastly, as the clay content was increased, the maximum elongation values were found to decrease. To summarize, the combined melt intercalation method and in-situ intercalative polymerization method did indeed afford nanocomposites with altered properties. Compatibilization through masterbatch preparation or SEBS-MA incorporation consistently improved maximum elongation values. The masterbatch technique also improved the tensile strength of nanocomposites, the reason being apparently related to the extra styrene content in matrix. It follows to reason that the continued development of such an intercalative strategy can greatly improve the compatibility and properties of a wide range of composite materials.