Epoxy/BaTiO3 hybrid materials are prepared as good candidates for organic capacitors. The hybrid system is cured by using camphorquinone and a iodonium salt through a free‐radical promoted cationic polymerization using a long‐wavelength tungsten halogen lamp. The cured films are fully characterized. Morphological characterization shows a well‐dispersed inorganic phase within the organic matrix. Electrical characterization demonstrates a linear increase of the dielectric constant with increasing filler content, while low dielectric loss values are obtained.
Electrically conductive, cationically UV‐cured composites were prepared using exfoliated graphite plates (EGP) with cycloaliphatic epoxy resin and polyalcohol binder system. Exfoliated graphite (EG) was obtained from natural flake graphite through chemical and thermal treatment. Sonication of EG in solvent produced EGP. Characterization of graphite samples by XRD showed structural similarity between original graphite and EGP. UV curing behavior was characterized using photoDSC. Electrical resistivity measurements of the composites as a function of EGP concentration showed that at low filler concentration the binder system can influence the electrical percolation behavior. Some formulations showed electrical percolation at less than 1 vol.‐% of EGP filler.
The role of polymer/filler interactions on the mechanical and electrical properties of elastomer nanocomposites is analyzed using dielectric spectroscopy, cyclic stress/strain tests, and online dc‐conductivity measurements. Pristine and deactivated (graphitized) CBs are studied in different rubber matrices. Due to confinement effects, an interphase of strongly immobilized polymer is present between adjacent filler particles, representing stiff but flexible mechanical bonds of the filler network. Under deformation of the sample, these bonds bend and finally break. Cyclic stress/strain measurements are analyzed by fitting the data to a microstructure‐based material model that allows for the evaluation of microscopic parameters of the polymer and filler network.
Novel fluoroalkyl end‐capped oligomer/hydroxyapatite nanocomposites have been easily prepared by the reaction of disodium hydrogenphosphate and calcium chloride in the presence of self‐assembled molecular aggregates formed by fluoroalkyl end‐capped oligomers in aqueous media. The fluorinated hydroxyapatite nanocomposites thus obtained were found to exhibit a good dispersibility in a variety of media, and were applied to the surface modification of glass.
End‐grained wood/polyurethane composites were obtained by a water‐based one‐pot process free of diisocyanates. Wood was impregnated with both PEG and CBC‐functionalized PEG as a coupling agent. A thorough study of the CBC‐mediated end‐groups conversion of PEG was achieved. It came out that functionalization conditions strongly affected the polyurethane chain extension and its grafting onto the wood structure. Antiswelling efficiency measurements showed that the one‐pot procedure allowed to reach comparable dimensional stabilization than the diisocyanate‐based process previously described. Morphological analysis demonstrated that such an improvement was attributable to the formation of cell wall‐bulked WPCs.
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.
Conducting polymer blends based on styrene–butadiene–styrene (SBS) triblock copolymer and polyaniline doped with dodecylbenzene sulfonic acid (Pani.DBSA) were prepared by different procedures: mechanical mixing (MM) and ‘in situ’ polymerization (ISP) methods. The ISP blends exhibited higher levels of electrical conductivity, as compared to MM blends. The scanning electron micrographs of the ISP blend were characterized by the presence of microtubules, which favored the formation of the conducting pathways inside the SBS matrix. From dynamic mechanical and dielectric analysis, it was possible to suggest a higher interaction degree of the polyaniline with the polystyrene phase of the block copolymer. Blends prepared by ISP method displayed also higher dielectric constant and higher dielectric loss factor than blends prepared by MM method.
Poly(propylene)‐clay nanocomposites and poly(propylene) containing conventional inorganic fillers such as calcium carbonate (CaCO3) and glass fiber were used in a comparative study focusing on dimensional stability, structure, mechanical and thermal properties. Micro‐ and nanocomposites were prepared by melt blending in a twin‐screw extruder. The relative influence of each filler was observed from dimensional stability measurements and structural analysis by WAXD, TEM, and thermal and mechanical properties. At equal filler loadings, PP/clay nanocomposites exhibit an improvement in dimensional stability and were the only composites capable of reduced shrinkage in both in‐flow and cross‐flow directions. The flexural modulus of PP increased nearly 20% by compounding with 4% organoclay, as compared to a similar performance obtained by compounding with 10 wt.‐% of CaCO3 or approximately 6 wt.‐% of glass fiber. The HDT and thermal stability of PP were enhanced by using nanoclay as filler.
The crystallization behavior of poly(L ‐lactide) (PLLA) was investigated in the presence of benzenetricarboxylamide (BTA) derivatives as crystal nucleators. BTA‐cyclohexyl (BTA‐cHe) was the most effective nucleating agent, but induced a complete loss of transparency of the processed material. On the other hand, BTA‐n‐hexyl (BTA‐nHe) enhanced crystallization with little increase in haze. PLLA containing BTA‐cHe enhanced PLLA crystallization in α‐form crystal whereas BTA‐nHe enhanced α′‐form (incomplete α‐form) with forming smaller spherulites. TEM revealed BTA‐nHe had completely dissolved in the PLLA matrix in melt and recrystallized during the thermal annealing process. It was also found that the size of the recrystallized BTA‐nHe was in the nanometer range to effectively nucleate the PLLA crystals.
Nanoparticles based on Al(III) and Zr(IV) melamine phosphate and sulfate, respectively, are prepared. Cone calorimeter measurements reveal that compared to an unfilled polyacrylate matrix the polyacrylate‐based nanocomposites containing the novel nanoparticles display significantly improved flame‐retardant properties as evidenced by the corresponding values for the peak heat release rate, the time‐to‐ignition, the values for the peak rate of heat release, the total heat evolved, the time to the CO peak and the CO yield. Concomitantly, the mechanical properties of the acrylate‐based composite coatings, i.e., the Martens and surface hardness, can also be significantly improved.
Structural parameters of the filler network have been evaluated by fitting quasi‐static stress/strain cycles to the dynamic flocculation model. It is found that the size of filler clusters as well as the strength of filler–filler bonds increase with filler loading and carbon black activity (specific surface). This correlates with the behavior of the tear resistance obtained for pulsed loading under high‐severity conditions, implying that the characteristics of the filler network govern the fracture properties of filled elastomers. The behavior of the power law exponent of fatigue crack propagation versus tearing energy can be explained by flash temperature effects in the crack tip area.
Cyano‐OPV moieties were covalently incorporated into a PETG backbone to create ductile amorphous polymers which change their PL and absorption color as a function of deformation. The cyano‐OPV concentration was systematically varied, and the composition was related to the material's optical response. This approach afforded PETG/dye copolymers which upon annealing display characteristics of aggregated dye molecules. The materials exhibit a significant color change upon compression, consistent with disassembly of the dye aggregates. This mechanochromic response is irreversible and can be detected by the unassisted eye.
Novel polyurethane (PU) composites were prepared, based on hybrid inorganic/organic phosphazene‐containing microspheres. The FT‐IR spectra have shown that the microspheres have been linked with PU matrix. The microstructure of the composites is investigated by SEM. In comparison with PU, the glass transition temperatures and thermal stability of the composites are increased. The results from tensile testing of the composites have indicated that tensile strength is improved and elongation at break is almost invariable. The investigation on the surface properties of the composites showed that the water contact angles are obviously increased by adding 2 and 4 wt.‐% microspheres to the matrix.
Based on an in situ template method, branched phosphazene‐containing nanotubes were synthesized via a controlled two‐step adding technique of acid acceptors. Structural and morphological characterizations of the as‐synthesized products were performed by SEM, TEM, EDX and FTIR. The results showed that the branched nanotubes were had inner and outer diameters of 8 and 50–150 nm, respectively. In addition, a formation mechanism for the nanostructures was proposed.
A variety of polymer parts used in microsystems technology is produced by injection molding. For dimensioning and design of these products, both the material properties and changes during the life cycle have to be taken into account. The aging behavior of parts with decreasing dimensions or of parts processed under different cooling conditions is discussed in terms of their morphological and mechanical long‐term properties. The results indicate that a decreasing part size leads to higher post‐crystallization and higher thermo‐oxidative degradation. This leads to size‐dependent changes in mechanical properties. Adjusted process conditions by application of thermal low‐conductive mold materials can favor the process‐related properties and thus the long term properties can be improved.
A comparative study of the preparation and properties of composites of PCL with cellulose microfibres (CFs) containing butanoic‐acid‐modified cellulose (CB) or PCL grafted with maleic anhydride/glycidyl methacrylate as compatibilizers, is reported. The composites are obtained by melt mixing and analyzed using SEM, DSC, TGA, XRD, FT‐IR, NMR and tensile tests. An improved interfacial adhesion is observed in all compatibilized composites, as compared to PCL/CF. The crystallization behavior and crystallinity of PCL is largely affected by CF and CB content. Composites with PCL‐g‐MAGMA display higher values of tensile modulus, tensile strength and elongation at break.
Supercritical CO2 has been used as a blowing agent to foam poly(styrene‐co‐acrylonitrile)‐based materials in a single screw extruder specially adapted to allow fluid injection. The cellular morphology depends on foaming temperature, more regular cells being obtained with decreasing extrusion temperature. In a second step, a natural and an organomodified nanoclay have been added for the purpose of imparting some flame resistance to the foamed material. The filler efficiency in reducing sample combustion rate appeared to be dependent on its delamination level inside the matrix and better results were obtained when the organomodified clay was first delaminated in the polymer in an efficient twin screw extruder using water assistance, prior to foaming in the single screw extruder.
CNT/NR composites were fabricated based on a CNT treatment using an acid bath followed by ball‐milling with HRH bonding systems. Thermal properties, vulcanization characteristics and mechanical properties of the CNT/NR composites were characterized. Compared to CB, the incorporation of CNTs into NR was faster and the energy consumption was less. The over‐curing reversion of CNT/NR composites was alleviated. After acid treatment and ball‐milling, the dispersion of CNTs in the rubber matrix and the interaction between CNTs and the matrix was improved. The performance of the CNT/reinforced NR composites was enhanced by the incorporation of the treated CNTs as compared to neat NR and CB/NR composites.
Newly developed shape memory (SM) epoxies are unveiled with an improved deformability range, high strength with intrinsically good thermal and chemical stability, high thermal transition (i.e., SM transformation temperature), and qualitatively excellent SM characteristics, thereby providing a synthetic route for adding attractive properties to commonly used industrial and commodity resins. The impact of chemical composition on the failure strains of these SM epoxies is shown and the resulting SM behavior is discussed.
The first reported use of two‐dimensional mesh thermoplastic fibers in an epoxy matrix for mendable composites is presented, yielding 100% restoration of GIC, failure energy, and peak loads over repeated damage‐healing cycles. SEM imaging and EDS mapping showed different surface structures between CFRPp and CFRPf and confirmed strength recoveries were attained by delivery of EMAA to the fracture plane which enabled the fractured surfaces to rebind after heating to 150 °C for 30 min.
