| Reinforcing fillers are usually added into the thermalplastics to improve their mechanical and physical performances. In recent years, nanoscale fillers had attracted more and more attention in polymer modifications field. For plastics used in automobile interiors, the incorporation of nanofillers in polymer matrix could bring both strength and toughness improvement for the materials. With proper modification, some fillers can even bring functional properties such as flame retardancy for polymer matrix. Those properties improvement are very important for the applications of plastics in automobile industry. While for the rubber used in tyres, the nanofillers can not only improve mechanical properties like tensile strength, tear resistance and wear properties, but also lower the total filler content, which potentially reduces the rolling resistance of the tyre and improve the vehicle fuel economy.This thesis mainly focused on the surface modification of halloysite nanotubes and evaluaiton on the properties improvement of polypropylene(PP) based nanocomposites filled by such halloysite clay. Firstly, the surface modifications of halloysite nanotubes and their reinforcing effect for PP were studied. Second, the influences of halloysite nanotubes and their modifications on PP crystallization behavior were also evaluated. Third, halloysite nanotubes were further modified with flame retardant chemicals and mixed with montmorillonite for preparing flame retardant nanocomposites. Meanwhile, the preparation of montmorillonite filled SBR/BR nanocomposites and their applications in tyre treads were also investigated in this thesis. Latex compounding method was firstly modified and optimized for obtaining well dispersed intercalation structure of montmorillonite/SBR. In addition, the influences of traditional fillers on the reinforcements of montmorillonite were also systematically investigated. The main conlusions were summarized as follows:(1) Halloysite was successfully grafted by silanol with both wet and dry modification methods. Among them, wet modification using aqueous solution(WMHA)possessed the best reinforcement as well as highest modification efficiency. Silanol grafting on halloysite surface improved both the filler dispersion and interfacial compatibility in polymer composites, but it didn’t influence the crystallization structure of halloysite and PP composites. The rheologicalbehavior indicated surface modification had improved the halloysite dispersion in PP matrix and enhanced the interfacial bonding. Furthermore, halloysite and its modifications also improved the thermal stability of PP composites, showing elevated decomposition temperatures of PP. Finally, the filler content was determined for 2% by optimizingtrade-offs of these properties.(2) Influences of halloysite and its silanization on the crystallization structure and kinetics of PP composites were investigated by differential scanning calorimetry(DSC) and hot-stage polarized optical microscopy(HS-POM). The results indicated that halloysite dispersed in nanoscale would apparently shorten the induction time for crystallization and accelerate the overall crystallization rate as well as increase the crystallinity of PP. The heterogeneous nucleation effect and promotion forcrystallization of halloysite were further enhanced by surface silanization. Halloysite also increased the crystallization temperature range during the nonisothermal crystallization, accelerating the crystallization transition and forming fine spherulite crystals. The isothermal and nonisothermal crystallization crystallization kinetics were modeled and calculated with Avrami and Ozawa theory, respectively. The nucleation and spherulitic growth were investigated separately by hot-stage polzrized optical microscope(HS-POM). The nucleation rate of halloysite filled PP nanocomposites was much higher than that of pure PP under either isothermal or nonisothermal crystallization, and such promotion effect was further amplified after the halloysite silanization.The linear spherulitic growth rate of PP was independent with the cooling route and rate, filler dispersion and surface conditions, but only determined by the crystallization temperature.(3) Spiralphosphodicholor(SPDPC) was grafted on the inner surface in halloysite nanotubes based on silanization. The grafting process did not affect the dispersion and reinforcing effect ofhalloysite in PP. The resultant FRHA decomposed at 330~370 oC, which was good for the formation of char residues. Montmorillonite was introduced into the halloysite/PP composites as a synergistic agent. Well dispersed montmorillonite formed mixed structure of intercalation and exfoliation and prepared PP composites with elevated strength and modulus.Additionally, montmorillonite sheets also improved thermal stability of the nanocomposites, showing that T5% and T10% were elevated by 25 oC and 13 oC,respectively. Thermal stability was improved with the addition of FRHA, showing increased thermal decomposition activation energy. FRHA facilitated the formation of compact char residue during decomposition, and coordinated with barrier effect of montmorillonite sheets, which obviously enhanced the flame retarndancy of composites. When FRHA was loaded at 14%, the composites reached LOI of 32 and UL-94 of V-0 rating, respectively. Heat and smoke release rates were also largely cut down with the addition of FRHA, implying that the composites possessed good flame retardnacy and smoke suppression effect during the combustion. As the FRHA content increased, the modulus of composite increased while the strength and toughness declined. The reinforcing effect of halloysite was well maintained evenat a loading of 18%.(4) Intercalted montmorillonite/SBR/BRnanocomposites were successfullyprepared through latex compounding method. Newly introduced ethanol solution and ultrasonicaion apparently improved the mixing effiency of the latex compounding and filler dispersion. The optimized processing parameters included a ratio of water: ethanol: clay=1:9:4, and ultrasonication duration of 120 min. Montmorillonite intercalation was not affected by the clay content. When used with carbon black together as fillers in SBR/BR, montmorillonite displayed retardant effect for rubber curing, showing declined crosslink extent and curing rate. Montmorillonite also brought considerable reinforcing effect to SBR/BR rubber, leading to improvement in strength, elongation, tear resistance, hardness, as well as application properties of tyre treads including ice traction, wet traction and dry handling. The montmorillonite loading was optimized as 15 phr by considering trade-offs among mechanical properties and practical performances.(5) Synergistic reinforcing effect was produced by the combination usage of montmorillonite and silica in SBR/BR tread compounds. Similar with silica, montmorillonite could react with Si69 and release ethanol, possessing an even higher reaction rate. When simultaneously filled in rubber, silica favored the dispersion of montmorillonite in rubber and facilitated the transformation of exfoliation from intercalationstructure. Fully exfoliated montmorillonite was formed when the montmorillonite/silica ratiowas 1:4 or lower. Intercalatedmontmorillonite retarded the curing while the exfoliated montmorillonite boosted the curing. Silica uniformly dispersed in rubber, but it displayed relative poorer reinforcing effect if compared with montmorillonite. Generally, the MS14CA3.6 and MS18CA3.6with exfoliated montmorillonite possessed the most balanced properties. The effects ofcoupling agent, Si69, on the processing and properties of rubber compoundes were alsoinvestigated. The coupling agent increased curing extent but lowered curing rate of the rubber compounds. The microstructure and filler dispersion were not affected by Si69 contents. Within this experimental study, MS14CA3.6 was preferred for balancedphysical and dynamic properties. |
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