We found that enhanced exfoliation of clay up to 20 wt.‐% in non‐polar polybutadiene (PB) if the PB was blended with a relatively small fraction of hydroxyl‐terminated PB (HTPB). The choice of an intermediate polymer composition to enhance exfoliation was motivated by theoretical predictions of end‐functionalizing effects of Balazs, Farmer, and coworkers. A combination of X‐ray diffraction and rheological measurements were used to optimize HTPB content for enhanced exfoliation. We also observed the competition of the kinetic and thermodynamic processes during the ripening of the exfoliated clay structure.
The preparation of nanofibrillar composite (NFC) materials using single‐polymer nanofibrils as starting materials is described. Such a possibility is offered by (i) the concept of polymer/polymer NFCs, which have recently been manufactured and represent a further development in the field of microfibril‐reinforced composites, and (ii) the opportunity to isolate neat nanofibrils through selective dissolving of the second blend component. The resulting nanofibrillar single‐polymer composites are characterized by superior mechanical properties (the tensile modulus and strength are improved up to 350%), competing with glass‐fiber‐reinforced PET.
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). 相似文献
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
Chemical modification of EVOH in the molten state at 185 °C by a grafting from process of poly(ε‐caprolactone) in batch was studied. 1H NMR was used to characterize the structure evolutions of PCL grafts. In addition to grafting reactions, dynamic covalent transesterification reactions between EVOH residual alcohols and the polyester grafts led to a redistribution of the PCL grafts length. up to 27 and SR up to 80% were obtained. Experiments made in a corotating mini twin‐screw extruder also confirmed these results. The effect of the alcohol to caprolactone ratio and catalyst concentration (SnOct2) on kinetic evolution showed that few minutes were necessary to complete the polymerization. A kinetic model was proposed and adequate conditions for the synthesis by reactive extrusion were defined.
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). 相似文献
Acrylonitrile‐butadiene‐styrene (ABS)/clay nanocomposites have been prepared using two types of ABS with different AN contents and a chemically modified clay, Cloisite 20A. The composites were prepared by melt mixing in a twin‐screw extruder. Their morphological properties were characterized by XRD and TEM. The thermal stability of the polymer nanocomposites was studied using TGA and flammability tests. The results were analyzed in terms of the effect of the clay content and the type of ABS used on the clay dispersion and the thermal stability of the nanocomposites. Experimental results confirmed that better dispersion and intercalation and/or exfoliation can be obtained when using an ABS with a higher AN content. The study using TGA and flammability tests showed that the nanodispersed layers of silicate enhanced the thermal stability of the ABS matrix, and that an ABS with higher AN content was more effective in providing fire retardancy. This suggests that when using higher AN contents, more polar groups are present within the polymer matrix, allowing a more homogeneous dispersion and intercalation of the chain polymers into the organomodified montmorillonite clay (MMT), and even some exfoliation of the nanoclay.
Summary: The phase and thermal characteristics of blends consisting of linear low‐density polyethylene (LLDPE) (0.7 mol‐% hexene copolymer) and poly(ethylene‐ran‐butene) (PEB) (26 mol‐% butene copolymer) have been investigated using optical microscopy (OM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). An upper critical solution temperature of 162 °C was exhibited. The addition of PEB not only slowed the overall crystallization rate of LLDPE but also changed the distribution of lamellar thickness or perfection of LLDPE crystals. The equilibrium melting temperature of LLDPE in the blends was reduced and kept relatively constant in the bi‐phase state. The blends showed a single‐stage degradation and an intermediate thermal stability between those of the individual components. It could be attributed to their homogeneous states at degradation temperatures and the similar decomposing mechanisms of two components. The kinetic analysis of thermal degradation also confirmed the above results.
A blend composition of poly(3‐hydroxybutyrate‐co‐valerate) and polylactide is used as a bioplastic matrix and reinforced with soy hull to engineer novel green composites. A comparative study with soy‐hull‐reinforced polypropylene composite system is performed. A compatibilizer is used to engineer the novel class of green composites with a balanced stiffness and toughness performance with the target to substitute PP‐based composites. The flexural and impact strength along with hydrophobicity of compatibilized composites are improved significantly over the noncompatibilized counterpart. The fiber/matrix interaction is investigated by SEM. These green composites have the potential to substitute PP‐based composites in some applications.
Thermo‐mechanical degradation of LDPE‐based nanocomposites was studied by mainly investigating the rheological properties. For all of the investigated processing conditions, the viscosity of the nanocomposites was higher than that of the pure‐LDPE matrix, but on increasing the severity of the mixing conditions, the difference between the viscosity of the nano‐filled polymer and that of the pure LDPE decreased. The X‐ray traces of the nanocomposites suggest that intercalation has been achieved during the melt, when less‐severe processing conditions were used. At severe processing conditions (longer mixing time, high temperature and shear stress) the thermo‐mechanical degradation was accelerated, possibly due to the loss of mass from the organoclay galleries. The variations of the viscosity in the presence of two organo‐modified montmorillonite (MMt) clays were compared to the ones observed with a MMt clay at different processing conditions.
The influence of an elongational flow on the morphology of PE/clay nanocomposite drawn fibers was studied. An increase of the elastic modulus and the tensile strength as well as a decrease of the elongation at break are observed with increasing draw ratio. The applied elongational gradient orients the polymer chains and the clay particles along the spinning direction. When the applied flow results in the formation and the orientation of exfoliated nanoparticles, a pronounced increase of the mechanical properties is observed. The dispersed clay particles can be broken and oriented by the extensional flow, which might indicate a flow‐induced intercalated/exfoliated morphology transition.
Summary: This study investigated the physico‐mechanical properties, odor and VOC emission of bio‐flour filled PP bio‐composites with different pozzolan contents. On increasing the pozzolan content, the tensile and flexural strengths of the bio‐composites were not significantly changed, whereas the impact strength and water absorption increased slightly and the odor intensity decreased due to the absorption of thermal degradation gases of PP and bio‐flour at the pore surface of the pozzolan. The VOC emission of the bio‐composites, analyzed by GC‐MSD, was mainly due to PP oxidation and the thermal degradation of bio‐flour during the extrusion process at high manufacturing temperatures. With increased pozzolan content, other organic compounds of the bio‐composites were not significantly changed, but the toluene emission of the bio‐composites was decreased. SEM and SEM/EDX mapping techniques were employed to investigate the porous form and the pozzolan distribution in the bio‐composites. From these results, we concluded that the addition of pozzolan in the bio‐composites was an effective method for reducing their odor and VOC emission without any reduction in mechanical properties.
Temperature‐responsive PVCL homopolymers and functional PVCL polymers containing carboxylic acids are prepared in organic and aqueous solutions. PVCL bulk polymers are characterized using 1H NMR, photometry, ATR‐FTIR, and thermal analysis. A finite phase transition at 37–40 °C occurs in aqueous solutions of PVCL and PVCL‐COOH. PVCL and PVCL‐COOH polymers are electrospun into fibers ranging from 100 to 2300 nm in diameter. PVCL/cellulose bi‐component films are obtained by electrospinning of CA and PVCL followed by alkaline hydrolysis. These tunable thermo‐responsive PVCL/cellulose nanofibers have potential applications in developing affinity membranes.
A 1‐D through‐the‐thickness transient heat transfer model is built to simulate the curing process of thick‐walled glass‐fibre‐reinforced anionic polyamide‐6 (APA‐6) composites. The temperature and the degree of polymerisation through the thickness of the composite are calculated and compared to the experimentally obtained results. The kinetic models describing the polymerisation behaviour of APA‐6 are implemented in the model. The kinetic model not taking into account the convection in the polymerisation process shows the best results. It is found that the predicted temperature profiles agree well with the experimental data.
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. 相似文献
Developing co‐continuity in a polymer blend determines a multiphase system with enhanced properties which originate from the synergism of its constituents. Filling a blend with nanoparticles is a promising route to guide its morphology and eventually affect the co‐continuity transition. We add different kinds of nanoparticles to an HDPE/PEO blend to study how they affect the morphology of the blend as function of their surface properties and form factor. We find that PEO drop size is drastically reduced by particles adsorbed at the HDPE/PEO interface. However, we show that a drastic shifting of the co‐continuity threshold may only be achieved when particles affect the rheology of the interface.
MWCNT‐based composites have been successfully synthesized via layer‐by‐layer self‐assembly of crosslinked polyphosphazene nanoparticles on the surface of MWCNTs. The amino‐terminated CNTs were characterized by XPS, FT‐IR spectroscopy, EDS, XRD and TEM. The degree of functionalization could be controlled by simply changing the mass of hexachlorocyclotriphosphazene with 4,4′‐diaminodiphenyl ether. The activity of the surface amino groups was confirmed by the reaction of these groups with HAuCl4. In addition, the effects of the mass of HCCP and ODA ratios on the content of the surface amino groups was also investigated.
The consumption of 10‐undecene‐1‐olate (UOA) during its continuous re‐feeding in the metallocene‐catalyzed copolymerization with propene was investigated by ATR‐FTIR spectroscopy in‐line monitoring through evaluation of the integral absorbances of the characteristic IR bands. For the quantitative determination of the comonomer concentration during the copolymerization reaction with and without continuous re‐feeding of UOA, multiple calibration functions based on the chemometric partial least squares method were applied. For the first time, a direct correlation between the consumption of an olefin and the addition of a polar comonomer during a metallocene‐catalyzed copolymerization was demonstrated. By means of this technique, a relatively constant molar stoichiometric ratio of the comonomer and propene over the whole polymerization time was achieved, which is very important in obtaining copolymers with defined random structure and, thus, from the point of view of reaction engineering, constant product quality.
This paper investigates the effect of both the clay loading and the monomer feed rate on the morphology and properties of poly(styrene‐co‐butyl acrylate)‐clay nanocomposites prepared in emulsion polymerization. Analysis by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) of the nanocomposites prepared by batch polymerization showed that the polymer clay nanocomposites (PCNs) with 1–3 wt.‐% clay loading resulted in intercalated structures, while exfoliated structures were obtained at 10 wt.‐% clay loading. The polymerization was also carried out with semi‐batch polymerization. The morphology, thermal stability, and mechanical properties of nanocomposites obtained were found to be more strongly dependent on the clay/polymer ratio than the monomer feed rate.
Transparent polyimide (PI) and chemically modified graphene nanocomposite films are prepared from solutions of pyromellitic dianhydride (PMDA)/4,4′‐oxydianiline (ODA) poly(amic acid) with various amounts (0.2–0.8 wt%) of graphene carboxylic acid (GCA) in DMAc. The GCA is synthesized by modifying chemically oxidized graphene (COG) with many carboxylic acid groups (–COOH) and is well‐dispersed in DMAc, the organic solvent most frequently used for PI synthesis. The GCA sheets in the PI/GCA composite films are well‐dispersed and aligned two‐dimensionally in the direction parallel to the PI films, which enhances the mechanical properties of the nanocomposite films.
