Production of Thermoplastic Starch/MMT‐Sorbitol Nanocomposites by Dual‐Melt Extrusion Processing

A “green” processing method, dual‐melt extrusion, was used to prepare thermoplastic starch/montmorillonite nanocomposites without organic reactions in the solution. XRD demonstrates that sorbitol enlarged the interlayer distance of MMT during the first step. MMT‐sorbitol, formamide and starch were used to obtain TPS/MMT nanocomposites in the second step. XRD and TEM reveal that TPS intercalated the layers of MMT. With increasing MMT content, improvements in thermal stability, tensile strength, Young's modulus and energy break, and a slight decrease of elongation at break, appeared. The effect of water content on the tensile strength and elongation at break was also studied.

     

A Novel Phosphorus‐Containing Poly(ethylene terephthalate) Nanocomposite with Both Flame Retardancy and Anti‐Dripping Effects

Summary: It is a big challenge to improve simultaneously both the flame retardancy and the melt‐dripping resistance of polymeric materials such as PET. In this paper, a novel intumescent flame retardant, DPSPB, was synthesized and blended with copolyester PET‐co‐DDP/O‐MMT nanocomposites, which were synthesized by polycondensation of TPA, EG, DDP, and O‐MMT. The resulting PET‐co‐DDP/O‐MMT/DPSPB nanocomposites exhibit very good flame retardance and dripping resistance, e.g., LOI = 29, UL‐94 V‐0. SEM, XRD, and XPS were used to investigate the relationships between the structures and properties of the composites. It is proved that DPSPB offers excellent protection for the structure of nanocomposites, which is responsible for the good anti‐dripping properties of the nanocomposites.

Residues of copolyesters after combustion: common nanocomposite residue of PDMN (left) and the novel nanocomposite residue of PDMN/DPSPB (right).     

Polysulfone/Clay Nanocomposites by in situ Photoinduced Crosslinking Polymerization

PSU/MMT nanocomposites are prepared by dispersing MMT nanolayers in a PSU matrix via in situ photoinduced crosslinking polymerization. Intercalated methacrylate‐functionalized MMT and polysulfone dimethacrylate macromonomer are synthesized independently by esterification. In situ photoinduced crosslinking of the intercalated monomer and the PSU macromonomer in the silicate layers leads to nanocomposites that are formed by individually dispersing inorganic silica nanolayers in the polymer matrix. The morphology of the nanocomposites is investigated by XRD and TEM, which suggests the random dispersion of silicate layers in the PSU matrix. TGA results confirm that the thermal stability and char yield of PSU/MMT nanocomposites increases with the increase of clay loading.

     

Preparing Exfoliated MMT/Polymer Nanocomposites by Combined Latex Compounding and Spray‐Drying

A facile and easily industrialized approach for preparing highly dispersed MMT/polymer nanocomposites is developed by combining the latex compounding method and a spray‐drying process. Clay particles are successfully delaminated into layers, and layer re‐stacking is effectively prevented. HR‐TEM and XRD results confirm that MMT layers achieve exfoliated or nearly exfoliated dispersion in both MMT/styrene‐butadiene rubber and MMT/PS nanocomposites. Compared with melt‐blended MMT/SBR composites, MMT/SBR nanocomposites prepared by this new strategy exhibit extremely high dynamic modulus.

     

Exfoliated/Intercalated Rubber/Organo‐Montmorillonite Nanocomposites: Preparation and Characterization

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.

     

Improvement of Flex‐Fatigue Life of Carbon‐Black‐Filled Styrene‐Butadiene Rubber by Addition of Nanodispersed Clay

Summary: The flex‐fatigue life of carbon‐black‐filled SBR was dramatically improved by incorporation of 4–5 phr nanodispersed clay. Addition of clay did not decrease the degree of crosslinking of the composite but improved the hysteresis and tearing energy. ESEM observation of the flexing‐fracture morphology indicated that nanodispersed clay layers had the advantage over carbon black in that they could blunt the crack.

Effect of the clay amount on the flex fatigue life of the composites.     

Preparation of Polystyrene/Clay Nanocomposites by Free‐Radical Polymerization in Dispersion

Fully exfoliated PS/clay nanocomposites were prepared via FRP in dispersion. Na‐MMT clay was pre‐modified using MPTMS before being used in a dispersion polymerization process. The objective of this study was to determine the impact of the clay concentrations on the monomer conversion, the polymer molecular weight, and the morphology and thermal stability of the nanocomposites prepared via dispersion polymerization. DLS and SEM revealed that the particle size decreased and became more uniformly distributed with increasing clay loading. XRD and TEM revealed that nanocomposites at low clay loading yielded exfoliated structures, while intercalated structures were obtained at higher clay loading.

     

Preparation and Properties of PVC Ternary Nanocomposites Containing Elastomeric Nanoscale Particles and Exfoliated Sodium‐Montmorillonite

Summary: A novel rigid PVC ternary nanocomposite containing NBR‐ENP and untreated Na‐MMT has been fabricated. X‐ray diffraction XRD, TEM and SEM observations revealed that the untreated Na‐MMT was exfoliated and most NBR‐ENPs (about 90 nm) were separately dispersed in the PVC matrix. DMTA and TGA demonstrated that the PVC ternary nanocomposites had a higher glass transition temperature and a higher decomposition temperature than neat PVC, while the toughness increased simultaneously. Combustion tests showed that the exfoliated clay in the PVC/NBR‐ENP/MMT ternary nanocomposites did not improve the flame retardancy after ignition under strong heat flux.

Schematic diagram of the fabrication procedure of PVC/NBR‐ENP/Na‐MMT ternary nanocomposites.     

Intercalated PS/Na+‐MMT Nanocomposites Prepared by Ultrasonically Initiated In Situ Emulsion Polymerization

Summary: A new technique, ultrasonically initiated in situ emulsion polymerization, was employed to prepare intercalated polystyrene/Na⁺‐MMT nanocomposites. FTIR, XRD, and TEM results confirm that the hydrophobic PS can easily intercalate into the galleries of hydrophilic montmorillonite via ultrasonically initiated in situ emulsion polymerization, taking advantages of the multi‐effects of ultrasonic irradiation, such as dispersion, pulverization, activation, and initiation. Properly reducing SDS concentration is beneficial to widen the d‐spacing between clay layers. However, the Na⁺‐MMT amount has little effect on the d‐spacing of nanocomposites. The glass transition temperature of nanocomposites increased as the percentage of clay increased, although the average molecular weight of PS decreased, and the decomposition temperature of the 1obtained nanocomposites moves to higher temperature.

TEM of PS/Na⁺‐MMT nanocomposite prepared by ultrasonically initiated in situ emulsion polymerization.     

Effects of Heat and Pressure on Microstructures of Isobutylene‐Isoprene Rubber (IIR)/Clay Nanocomposites

Summary: In this work, the effects of heat and pressure on microstructures of isobutylene‐isoprene rubber/clay nanocomposites prepared by solution intercalation (S‐IIRCNs) are investigated. Not only are the local intercalated structures monitored by wide‐angle X‐ray diffraction, but the spatial distributions of the silicate particles are also observed by transmission electron microscopy. The changing behavior of microstructures of S‐IIRCNs is strongly dependent on the temperature of the thermal treatment. The observed phenomena are completely different from those in IIRCNs prepared by melt blending (M‐IIRCNs), which were reported in a previous paper. Various experiments suggest that the presence of residual solvent molecules in S‐IIRCN plays a key role on the microstructural change of S‐IIRCNs caused by heat and pressure. The possible microstructural models for untreated and treated S‐IIRCNs are presented, which could well interpret all observed phenomena. Finally, guidelines are proposed for adjusting the curing conditions of the system to achieve the desired intercalated/exfoliated morphology, and a new method for preparing rubber/clay nanocomposites with good dispersion states by melt blending is put forward.

TEM images of IIR/clay nanocomposites prepared by solution‐intercalation before (left) and after thermal treatment at 160 °C and atmospheric pressure (right).     

Temperature‐Induced Changes in the Surface Wettability of SBR + PNIPA Films

We report a novel rubber film made by a simple mixing method, which realizes a steep temperature dependence of the contact angle of water at a critical temperature of 41 °C. We mixed a common SBR with a known temperature‐responsive PNIPA to make a thermo‐responsive rubber. This rubber film distinctly showed a switch of surface wettability between hydrophilic below 41 °C and hydrophobic above 41 °C. The switching property is possibly controlled by the mixing ratio of PNIPA to SBR, preparation method, added chemicals, and so on. This mixing technique will be applied for the control of surface wetting properties by temperature on various SBR‐like rubber materials, such as wet‐brake performance of automobile tires on a rainy day.

     

Effects of Characteristics of Rubber,Mixing and Vulcanization on the Structure and Properties of Rubber/Clay Nanocomposites by Melt Blending

Summary: Three rubber‐based nanocomposites, natural rubber (NR), styrene‐butadiene rubber (SBR), and ethylene‐propylene‐diene rubber (EPDM) matrixes, were prepared with octadecylamine modified fluorohectorite (OC) by melt blending. X‐ray diffraction (XRD) revealed that the SBR/OC and EPDM/OC nanocomposites exhibited a well‐ordered intercalated structure and a disordered intercalated structure, respectively. In the case of the NR/OC nanocomposite, it exhibited an intermediate intercalated and even exfoliated structure. These results were in good agreement with transmission electron microscopy (TEM) observations. Furthermore, in the NR/OC and SBR/OC systems, the mixing process played a predominant role in the formation of nanometer‐scale dispersion structure, whereas the intercalated structure of EPDM/OC formed mainly during the vulcanization process. The tensile strength of SBR/OC and EPDM/OC nanocomposites loading 10 phr OC was 4–5 times higher than the value obtained for the corresponding pure rubber vulcanizate, which could be ascribed to the slippage of the rubber molecules and the orientation of the intercalated OC. For the strain‐induced crystallization NR, the exfoliated OC efficiently improved the modulus of the NR/OC nanocomposite relative to the pure NR. However, its hindrance on NR crystallization during the tensile process may be the main reason for the decrease in tensile strength of NR/OC.

XRD diffraction patterns of three nanocomposites containing 10 phr organoclay.     

Intercalation of Diphenyl Sulfide into Nanogalleries and Preparation of Poly(p‐phenylenesulfide)‐Based Nanocomposites

Summary: For the reference system of PPS‐based nanocomposites, we investigated the intercalation behavior of DFS molecules into nano galleries based on OMLFs consisting of different types of intercalants and nanofillers with different surface charge densities. The smaller initial interlayer opening led to the larger interlayer expansion, regardless of the miscibility between the intercalant and DFS. We examined the preparation of PPS‐based nanocomposites with and/or without shear processing at 300 °C. The finer dispersion of OMLFs in the nanocomposite was observed when using OMLF having small initial interlayer opening. The delamination of the stacked nanofillers was governed by the initial interlayer opening, whereas the uniform dispersion of the nanofillers was affected by the shear.

Plot of initial interlayer opening versus Δ opening for various OMLFs intercalated with DFS.     

Effect of the Addition of Toluene on the Structure and Properties of Styrene‐Isoprene‐Butadiene Rubber/Montmorillonite Nanocomposites

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.

TEM image of the SIBR/MMT nanocomposite.     

Structure and Dynamic Mechanical Properties of Melt Intercalated Polyamide 6—Montmorillonite Nanocomposites

Summary: Polymer‐layered silicate nanocomposites (PLSN), based on polyamide 6 (PA6) and montmorillonite (MMT) modified with an octadecylammonium salt, were produced via melt compounding in a co‐rotating twin‐screw extruder. Wide angle X‐ray diffraction (WAXD) and TEM revealed a PLSN containing 3.3% by weight (wt.‐%) of MMT to exhibit a mixed exfoliated/intercalated morphology, consisting mainly of individual silicate lamellae together with some intercalated stacks, resulting in a mean value of 1.8 lamellae per particle. In contrast, a PLSN containing a higher level of 7.2 wt.‐% MMT exhibited a more ordered intercalated structure, consisting mainly of a distribution of lamellae stacks with a mean value of 3.8 lamellae per particle. The dispersion of MMT in the PLSN generated very large polymer–filler interfacial areas, resulting in significant increase in the volume of constrained PA6 chain segments. Consequently, significant changes in the ratio of α/γ crystallites and in the thermal behaviour of the matrix PA6 were observed during WAXD, DSC and dynamic‐mechanical thermal analysis (DMTA) studies of the PLSN. In particular, damping data from DMTA showed relaxations between T_g and T_m resulting from amorphous polymer chain segments constrained at the polymer–filler interface, indicating the formation of a continuous phase of constrained polymer. In contrast, a PA6 microcomposite formed using unmodified MMT generated much lower polymer–filler interfacial area, with most of the MMT residing within large, poorly wetted aggregates. Consequently, changes to the thermal behaviour of the matrix PA6 were much less significant than those induced in the PLSN.

Shear storage modulus (G′) versus temperature data for the matrix PA6, the 5T and 10T PLSN and the 5P microcomposite.     

Highly Exfoliated Natural Rubber/Clay Composites by “Propping‐Open Procedure”: The Influence of Fatty‐Acid Chain Length on Exfoliation

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.

     

Novel Cationic RAFT‐Mediated Polystyrene/Clay Nanocomposites: Synthesis,Characterization, and Thermal Stability

Two novel cationic RAFT agents, PCDBAB and DCTBAB, were anchored onto MMT clay to yield RAFT‐MMT clays. The RAFT‐MMT clays were then dispersed in styrene where thermal self‐initiation polymerization of styrene to give rise to exfoliated PS/clay nanocomposites occurred. The RAFT agents anchored onto the clay layers successfully controlled the polymerization process resulting in controlled molecular masses and narrow polydispersity indices. The nanocomposites prepared showed enhanced thermal stability, which was a function of the clay loading, clay morphology, and slightly on molecular mass.

     

Synergism Effect of Montmorillonite and Cellulose Whiskers on the Mechanical and Barrier Properties of Natural Rubber Composites

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.

     

Structural Requirements for the Intercalation of Polyether Polyols into Sodium‐Montmorillonite: The Role of Oxyethylene Sequences

The structural requirements for the preparation of polyether polyol/Na⁺‐montmorillonite nanocomposites, which are used in polyurethane/NaMMT nanocomposites, were evaluated using X‐ray diffraction, thermogravimetric analysis and shear viscosity behavior. Nanocomposites based on homopolyetherols: poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), polytetrahydrofuran (PTHF), block‐type copolyetherols and a SAN‐grafted polymer polyol were prepared. Intercalation was observed only with oxyethylene (EO) units containing polyetherols. The amount of the intercalated polyetherol ranged from 15 to 30 wt.‐%. EO‐sequences of 5 to 6 units proved to be sufficient for intercalation, which suggests a crown‐ether type complexation of interlayer cations.

     

Electroconductive Polyamide 6/MWNT Nanocomposites: Effect of Nanotube Surface‐Coating by in situ Catalyzed Polymerization

Preparation and analysis of morphologic and electrical properties of high‐performance multiwalled carbon nanotube/polyamide 6 nanocomposites was achieved. The MWNTs were surface‐coated by in situ polymerization of ethylene as catalyzed directly from the nanotube surface previously treated by a highly active metallocene‐based complex. The so‐produced polyethylene‐coated MWNTs were melt‐mixed with the PA6 matrix. Pristine MWNTs were also dispersed in PA6. The in situ ethylene polymerization/coating reaction allowed the destructuring of the native bundle‐like aggregates leading to the preparation of nanocomposites with improved properties even at very low nanofiller content.