Structure And Properties Of Layered Silicate/Rubber Nanocomposites Prepared By Melt Blending

In recent years, polymer/layered silicate nanocomposites haveattracted great interest, both in industry and in academia. Compared withconventional composites, they often exhibit remarkable improvement inmaterials properties, such as mechanical properties, gas barrier property,flame retardant resistance, etc. On the other hand, there has beenconsiderable interest in theories of preparation and the relation ofproperties and microstructure.The melt blending method is carried on in this paper. The influenceof matrixes and vulcanizing additives on dispersion of clay layers isdiscussed and then the effect of crosslinking density on the microstructureand mechanical properties of nanocomposites is researched to find someinteresting results. On the base of it, ablating properties ofnanocomposites with high OMMT (organic montmorillonite)'s loadings are tentatively explored. At last, melt blending method is partly improvedby mixing organic modifier (amine salt), pristine montmorillonite andrubber matrix.Followed contents have been studied in this paper:1. Different polar and saturated matrixes are investigated to find thedifference of dispersion of OMMT. Through XRD and TEMcharacterization, different matrixes have found different effect on thedispersion of clay layers: for unsaturated matrixes, well intercalatedstructure of clay can easily be prepared by two-roll mill, because of thestronger interaction between rubber macromolecule and OMMT; whilefor saturated ones, scarce of enough intercalating driving force, the welldispersion of clay is difficult to achieve.For saturated EPDM, Influence of ethylene contents are researched.Because neither PP segments nor PE segments in EPDM chains can formstrong interaction with clay layers, changing ethylene content has littleinfluence on the dispersion of OC. However, by XRD analysis, with highethylene content, the macromolecules more easily to from strain-inducedcrystallization, so the mechanical properties, especially tensile propertiesof nanocomposite have efficiently improved.2. The effect of additives is discussed. By XRD and FTIR, SA(stearic acid), one of the common additives using sulphur cuing system,can esterify with carboxyl groups of SA and hydroxyl groups of OC, which is driving force for SA intercalating interlays of clay. Carried onthis conclusion to vulcanite to further discuss synergetic effect of SA andrubber matrixes, it is found that even using OMMT pretreated by SA,saturated rubber is still different to intercalate between interlayers. Thegenuine structure should be: single layers and smaller aggregates of SAintercalating into OC dispersed in matrix, and macromolecules can notform the real stable intercalated structure. For unsaturated matrix, matrixchains can easily directly intercalate into interlayer to form intercalatedstructure, even without any assistance from other additives.Mixing SA and OMMT powers at high stirring speed and puttingthem in oven for a while, SA-OC can be prepared. Adding it into matrixas fillers, disregard the polar or saturation, the dispersion became muchbetter than the sample through the common processing step: addingOMMT to rubber, then SA, separately.3. The effect of crosslinking density on the microstructure andmechanical properties of nanocomposites is researched. XRD analysisshowed that changing crosslinking density can not change the dispersionof OMMT. Since crosslinking network have much effect on the mobilityof macromolecules, then on the ability of clay layers' orientation andmacromolecules' orientation and crystal, little change in crosslink meanslarge change of tensile properties for OMMT/EPDM nanocomposite:reduce of crosslinking density lead to remarkable increase of strain-induced crystallization and then improve tensile properties. ForOMMT/SBR nanocomposite, in which strain-induced crystallizationdifferently appeared, improving crosslinking density can cause moremodules, large elongations, while tensile strength will become better atfirst stage, and then become worse, which is more like traditionalcomposite instead of OMMT/EPDM nanocomposite.4. Some properties of nanocomposites with high OMMT loadingsare investigated. Compared with samples with common OMMT loadings,this kind of nanocomposite can not show better entropy elasticity asrubber, and the stress-strain curves is more like plastics, which have veryhigh module, which should be contributed to restrict of mobility of rubberchains.Analysis ablating properties, rate of ablated remains is increaseswith more OMMT added. When OMMT is much enough, the rate ofcarbon in ablated remains become stable. Because carbon is kept in thecavity formed by clay layers, the cavity is determined by the amount ofclay layer. On the premise that layers are many enough to form theframework of ablated remains, the ratio between cavity (the carbon in it)and layers is stable. The surface of ablated remains continuously becomesmooth and shape become more integrated with more OMMT added.5. Melt blending method is partly improved by mixing organicmodifier, pristine montmorillonite and rubber matrix. By TEM analysis, The sample without modifier is just micro-composite, while those onesdirectly adding modifier and MMT to rubber, using the MMT pretreatedby water and modifiers or un-drying OMMT are all nanocomposite. Atthe same time, the amine salt have large effect on the vulcanize character.