Summary: To improve the interfacial interaction in MMT‐SBR nanocomposites, one type of UOAC was introduced to in‐situ modified MMT before latex compounding with SBR. The influence of the UOAC/MMT ratio on the structure and properties of MMT/SBR nanocomposites were carefully studied by XRD, TEM, and mechanical testing. It was found that through the in‐situ organic modification, a rubber‐intercalated structure of MMT was obtained in the nanocomposites, and the amount of rubber‐intercalated structure strongly depended on the UOAC/MMT ratio. The tensile strength of MMT‐SBR nanocomposites was enhanced dramatically from 4 to 18 MPa by in‐situ organic modification of MMT.
Stress‐strain diagram of SBR/clay nanocomposites. 相似文献
Summary: Fibrillar silicate (FS)/rubber nanocomposites were successfully prepared by directly mixing modified FS with rubber matrix. It is found that FS could be separated into nano‐fibrils with diameters less than 100 nm by the shear forces during mixing. The stress‐strain characteristics of these composites are similar to those for short micro‐fiber/rubber composites (SFRC). Nevertheless, these FS/rubber composites have some outstanding advantages over the conventional SFRC, even though the reinforcing effect of FS is restricted due to its small shape aspect ratio. More importantly, the differences in mechanical properties of the composites in the two different directions show that SBR/FS and NBR/FS composites both exhibit obvious anisotropy, which strongly depends on the preparation process, FS concentration, and rubber matrix. These factors were thoroughly investigated in this paper, and it can be concluded that the anisotropy of the composites was due to the orientation of nano‐fibrils.
Summary: Pyrolytic carbon black (CBp) has been prepared by rubber crumb pyrolysis under nitrogen flow at 700 °C. The CBp obtained by this process had an average surface area of 81 m2 · g?1 and was obtained in 43% yield over the starting rubber crumb. Although the CBp surface area can be increased up to 109 m2 · g?1 by washing away the Zn‐ and Si‐based ashes with HF treatment, the CBp was tested in a standard NR/SBR‐based formulation without any purification and ash extraction. CBp was tested at increasing loading levels as partial or full replacement of a standard N339 furnace carbon black. CBp depresses the physical properties of the rubber compound in a way which is directly proportional to the amount added. The reason of this result and the limited reinforcing effect is discussed in terms of low surface area and low structure in comparison to N339 carbon black as well as in terms of low surface activity, the interference of the ashes and the poor dispersion. Ideas of further development works are outlined.
It has been shown that the mechanical properties of NR/BR/EPDM blends can be improved by using APPS as a modifier. In this paper, it is demonstrated that modification of EPDM with APPS takes place and saturation occurs when the APPS amount reaches 5 wt.‐%. It is shown that the rubber/carbon black affinity improves by using APPS‐grafted EPDM in the blend. TEM and STEM images clearly show that the NR/BR/APPS‐EPDM blend contains a significantly higher content of homogeneous rubber phase than the unmodified NR/BR/EPDM blend. The much better distribution of the carbon black in the APPS‐EPDM phase is considered the main reason for the improvement in properties of the blend.
The preparation of new rubber based nanocomposites by using properly modified organophilic clays is described. A commercial organophilic montmorillonite containing a hydroxylated ammonium ion is reacted with LPBs. The reaction causes a decrease of the polarity of the clay and a great increase of the interlayer distance. The modified organoclays are successfully dispersed into rubber matrices (SBR or BR) by melt blending in an internal batch mixer. SAXS analyses and TEM micrographs revealed the formation of highly exfoliated nanocomposites containing intercalated stacks made of few lamellae.
The fabrication of nanocomposites by organic modification of clay during mixing into NR is reported. NR/OMMT nanocomposites show more intercalation and exfoliation at higher modifier content, increasing the tensile modulus primarily by improved filler reinforcement. Comparison with nominally identical pre‐modified OMMT shows similar microstructures and physical properties. No effect of mixing duration is observed, indicating that modification is rapid. Unlike montmorillonite, unmodified sepiolite disperses well in NR, so organo‐modification improves compatibility but does not affect the nanocomposite microstructure. This means that organo‐sepiolite offers relatively small improvements over sepiolite as a filler for NR.
APPS has been used to modify EPDM in order to solve the cure incompatibility and heterogeneous filler distribution of NR/BR/EPDM blends for tire sidewall applications. The physical properties of the NR/BR/APPS‐EPDM blends are compared with an NR/BR/EPDM blend and a conventional NR/BR tire sidewall. It is demonstrated that the application of APPS‐EPDM leads to a significant improvement of the tensile properties, tear strength, and fatigue properties. The properties of the NR/BR/APPS‐EPDM blends are equivalent or even superior to those of conventional NR/BR tire sidewall compounds. The dynamic viscoelastic properties of the NR/BR/APPS‐EPDM blends are not quite comparable with the conventional NR/BR sidewall blend, but still greatly improved, compared to using virgin EPDM.
Summary: Poly(butylene succinate‐co‐adipate) (PBSA) and organically modified montmorillonite (OMMT) nanocomposites of three different compositions were prepared by melt‐extrusion in a batch mixer. The structure of the nanocomposites was studied using X‐ray diffraction (XRD) and transmission electron microscopy (TEM) that revealed a coexistence of exfoliated and intercalated silicate layers dispersed in the PBSA matrix, regardless of the silicate loading. The degree of crystallinity of PBSA decreases with the addition of OMMT platelets. Dynamic mechanical analysis revealed remarkable increase in flexural storage modulus when compared with that of neat PBSA. Tensile property measurements exhibit substantial increase in stiffness with simultaneous increase in elongation at break of nanocomposites as compared to that of neat PBSA. The effect of clay loading on the melt‐state linear viscoelastic behavior of mixed intercalated/exfoliated nanocomposites was also investigated.
Elongation at break of compression molded annealed samples of neat PBSA and various PBSACNs. 相似文献
Intercalated polycarbonate (PC)/clay nanocomposites (PCCN)s have been prepared successfully through the melt intercalation method in the presence of a compatibilizer. The internal structure and morphology of the PCCNs has been established by using wide‐angle X‐ray diffraction (WAXD) analyses and transmission electron microscopic (TEM) observations. The morphology of these nanocomposites and degradation of the PC matrix after nanocomposites preparation can be controlled by varying surfactants used for the modification of clay and compatibilizer. The intercalated PCCNs exhibited remarkable improvements of mechanical properties when compared with PC without clay. We also discuss foam processing of one representative PCCN using supercritical CO2 as a foaming agent.
TEM bright field image of intercalated polycarbonate/synthetic fluorohectorite nanocomposite. 相似文献
A novel model is presented for predicting the phase selective filler localization in an equilibrium state for ternary rubber blends of SBR, NBR, and NR. It is based on surface tension data of the rubber components and the filler. Phase‐selective filler localization in ternary rubber blends is determined experimentally by means of FTIR spectroscopy on the basis of the wetting concept. It is found that by preparation of ternary blends with certain silica loadings, pre‐mixed in each blend phase using the masterbatch technology, silica transfer processes between blend phases take place until the equilibrium filler distribution is reached. The sequence of the silica transfer processes can be explained by taking into consideration the formation of a phase‐in‐phase morphology of the ternary blend.
Using previously obtained data on the solubilities of curatives in SBR, EPDM and in NBR, different mixing procedures were performed on 50/50 SBR/EPDM and NBR/EPDM blends. In contrast to a previous phase‐mixing study, the curatives were added to separate phases before final blending, in an attempt to control the curative distributions in the blends for optimal mechanical properties. Fillers were not applied in the system to exclude their influence on the dispersion of the curatives. The properties of such blends compounded by selective phase mixing are superior to those of blends compounded with normal mixing procedures.
Elastomeric EPDM fibers with diameters of 200–400 nm are prepared by coaxial electrospinning of PVP/EPDM fibers, subsequent vulcanization of the polymers and finally removal of the outer PVP layer using ethanol. The initially applied PVP layer restricts the elastic recovery of the EPDM fibers. The crosslinking density of the EPDM fibers reaches 8.44 × 10?5 mol · cm?3. The original morphology of EPDM is preserved after removing the PVP layer. The ultrafine EPDM fibers are expected to be useful in many fields, such as brittle plastics toughening, as well as applications in extremely high or low temperatures.
Summary: Styrene‐isoprene‐butadiene rubber/montmorillonite nanocomposites were synthesized by the addition of toluene into clay and living anionic polymerization. These silicate layers (B‐M) were exfoliated within 30 min after polymerization initiation, whereas the layers in the nanocomposites prepared without using toluene (A‐M) were only partially exfoliated and not well‐dispersed in the matrix. The results of TEM and X‐ray diffraction revealed disperse silicates and a strong interaction between the terpolymer matrix and clay in the B‐M nanocomposites. The B‐M‐exfoliated nanocomposites exhibited higher decomposition and glass transition temperatures, storage moduli, tensile strengths and elongations at the break than those of the pure terpolymer and A‐M. With an organophilic montmorillonite (OMMT) content of 3 wt.‐%, the exfoliated nanocomposite exhibited the best thermal stability and mechanical properties. In addition, GPC and 1H NMR results showed that the introduction of OMMT caused a slight increase in the of terpolymer, but hardly affected the microstructure of the terpolymer independent of the preparation method. Thus, the addition of toluene plays an important role in enhancing the dispersion of OMMT, which leads to the improvement of the structure and properties of the B‐M nanocomposites.
A series of nanocomposite films based on natural rubber (NR), Na+‐montmorillonite (MMT), and cellulose whiskers (W) was prepared, keeping a total filler content equal to 5 wt.‐%. In the binary NR/MMT system, small stacks of intercalated montmorillonites were homogeneously dispersed within the polymer matrix whereas they were clearly lying in the vicinity of cellulose whiskers in the ternary NR/MMT/W blends. The effects of MMT and W on mechanical and gas barrier properties of the nanocomposite films were investigated. A significant increase of the rubbery modulus was obtained upon filler addition. The reinforcing effect was particularly important for the nanocomposite film reinforced with 1 wt.‐% MMT and 4 wt.‐% W. The improvement of the gas barrier properties observed upon filler addition was explained by a tortuosity effect. The calculated tortuosity values indicated that the simultaneous use of MMT and W could greatly slow down the gas diffusion rate in NR. Formation of MMT‐W subassembly should be responsible for this synergism effect.
The effect of mercapto‐ and anhydride‐functionalized ethylene propylene diene rubber (EPDM) or ethylene–vinyl acetate (EVA) copolymers on the vulcanization kinetics of natural rubber/EPDM blends was investigated using the oscillatory disk rheometer. The mercapto groups in both EPDM and EVA copolymers resulted in a significant decrease of the curing time. The Coran's model was applied to set the kinetic constants within each distinct step of the vulcanization process. The highest curing velocity was perceived in a blend containing 2.5 phr of mercapto‐functionalized EVA. The functionalized EVA, especially that which was functionalized with anhydride groups, also displayed a lower solvent uptake on blending, which would imply an increase of the crosslink density as well a covulcanization phenomenon.
A high degree of exfoliation of MMT in NR is achieved by using the so‐called “propping‐open approach” in which a stepwise expansion of the interlayer spacing of MMT takes place. The nanostructure is characterized by WAXD and TEM which indicate different extents of clay dispersion depending on the fatty‐acid chain length. Curing kinetics of different nanocomposites is studied and interestingly low activation energies of the vulcanization process are observed in the case of NR/EMMT nanocomposites. The incorporation of EMMT dramatically affects composite properties whereas DMA indicates significant reduction of tan δ peak height and the tensile strength approximately doubles from 14 to 30 MPa with only 5 phr EMMT.
