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.
A novel zirconia polyester nanocomposite is prepared using an in situ approach. Surface‐functionalized zirconia nanoparticles are obtained by attaching 3‐phosphonopropionic acid to the metal oxide. Neat and surface‐covered metal oxide particles are incorporated at the beginning of the polyesterification reaction of isophthalic acid and neopentyl glycol resulting in zirconia/poly(neopentyl isophthalate) (PNI) nanocomposites. TEM shows that the dispersibility of the inorganic filler is improved by covering the zirconia surface with carboxylic acid groups. These results are verified by SAXS. Rheological measurements reveal that the viscosities are increasing compared to pristine PNI at particle loads of 10 wt% (neat zirconia) and 5 wt% (phosphonic‐acid‐capped zirconia), respectively.
The selective positioning of clay platelets at the polymer/polymer interface in a blend with drop/matrix morphology has a contrasting effect: on the one hand, it promotes a refinement of the morphology during the intense flows which occur during melt compounding; on the other hand, it induces coarsening in the course of prolonged slow flows experienced during rheological analysis. Rather than to a usual coalescence process, the increase of the average sizes of the dispersed phase is primarily due to a clustering mechanism of clay‐coated droplets, which keep their individuality inside the clusters because of the elastic connotation of the layered interface.
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.
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.
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.
This paper investigates thermally activated healing in an epoxy amine network using six thermoplastic modifiers; ethylene vinyl acetate (EVA), poly (ethylene‐co‐glycidyl)‐methacrylate (PEGMA), poly(vinyl‐butyral) (PVB), styrene‐ethylene‐butadiene copolymer (SEBS), acrylonitrile‐butadiene‐styrene (ABS) and polyethylene‐co‐methacrylic acid (EMAA). They all exhibit healing but varied in efficiency, repeatability and mechanism. EMAA, PEGMA and EVA display superior healing or load recovery compared with ABS, SEBS and PVB with increasing healing events. For EMAA and PEGMA this is attributed to a pressure delivery mechanism, while for EVA, it is attributed to increased viscous flow and a highly elastomeric response to damage. Adhesive binding of the fracture surfaces is also critical in restoring load.
Copolymers of 3,4‐ethylenedioxythiophene and 3‐methylthiophene have been prepared by recurrent potential pulses using monomer mixtures with various concentration ratios, their properties being compared with those of the corresponding homopolymers. In addition, different technological applications have been tested for the generated copolymers. Results indicate that the properties of the copolymers are closer to those of poly(3,4‐ethylenedioxythiophene) than to those poly(3‐methylthiophene). Furthermore, the ability of the copolymers to store charge and to interact with plasmid DNA suggest that they are very promising materials.
It is shown that predictions of local mechanical properties in a product can be made from the orientation only using an anisotropic viscoplastic model. Due to processing‐induced crystalline orientations, the mechanical properties of injection‐molded polymer products are anisotropic and exhibit strong variations within a product. The tensile response and the mechanical lifetime under static loading depend strongly on the direction of loading and the location. The deformation kinetics are described with an anisotropic viscoplastic model, and quantitative predictions are made based on coupling of the orientation factor in direction of loading and model parameters. A limited characterization of the morphology within a product is sufficient to determine its local mechanical performance.
An aqueous dispersion of gold nanoparticles was added to an acrylic resin and UV‐cured. The photopolymerization process was followed by means of real‐time FT‐IR spectroscopy. Nanostructured coatings containing a homogeneous dispersion of gold nanoparticles with an average size range of 20–25 nm were achieved. Macroscopic aggregation during polymerization was avoided due to the rapid initiation and kinetic associated with the photopolymerization technique, which allowed the medium to quickly solidify around the dispersion particles.
This review presents the state of the art regarding the improvement of scratch resistance of polymeric coatings. In particular, our attention is focused on the effect of inorganic nanometric fillers on the scratch resistance of organic coatings. Two main strategies are described for the achievement of such nanostructured hybrid organic/inorganic coatings: either a top‐down or a bottom‐up approach.
This work aims at improving the interfacial bonding between polyamide‐12 and CNFs. CNFs were oxidized and dispersed in polyamide‐12 giving rise to polymer nanocomposites. The oxidation caused an increase in the specific surface area and structural defects of the fibers, as indicated by surface area and Fourier‐transform Raman spectroscopy. The nanocomposites exhibited improved thermal and thermo‐oxidative stabilities. The oxidized nanofibers had marginal effect on the crystallinity and crystallization of the polyamide‐12. An over‐proportional enhancement of stiffness due to the fibers could be achieved. In spite of these improvements the fiber/polymer adhesion should be further improved.
Nanocomposite materials based on a HBP and silica are produced using either a dual‐cure sol/gel and photopolymerization process or by mixing silica nanoparticles with the HBP. In both cases the conversion of the HBP is independent of composition and obeys a time‐intensity superposition with power‐law dependence on UV intensity. Optimization of the dual‐cure process leads to transparent sol/gel composites with ultrafine structures. These materials systematically outperform the particulate composites, including an increase of the glass transition temperature of 63 °C and a process‐induced internal stress as low as 2.5 MPa. Nano‐sized gratings are produced from the sol/gel composites by low‐pressure UV nanoimprint lithography.
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.
A dual‐cure latex is prepared by mixing an amide‐functionalized latex with a latex that has both acetoacetoxy and unsaturated acrylic functionalities. The amide‐functionalized latex provides a thermal cure with the acetoacetoxy groups of the other latex via Michael addition. The partially polymerized triacrylates in the acrylate‐functionalized latex provide active sites for photocuring. Thermoset latex films are prepared by blending amide‐ and acrylate‐functionalized latexes in varying amounts. The effect of the photosensitizer (camphorquinone) concentration on thermal and mechanical properties is studied. The highest tensile modulus and elongation is observed in a 50:50 wt% amide/acrylate‐functionalized latex blend.
The efficiency of melamine cyanurate and a clay filler for improving the flame retardancy and other physical properties of polyamide 6 was examined. Partially intercalated‐exfoliated morphologies were obtained. Nanocomposites suffered from polymer degradation during compounding, while the molecular weight was enhanced in the case of the flame retarded samples. Silicates were shown to restrain crystallization, whereas melamine cyanurate induced heterogeneous nucleation. Both additives positively influenced the tensile modulus of the prepared samples, decreasing their ability to elongate. With respect to the UL94 flammability test, melamine cyanurate was proved to be not sufficiently capable of increasing the tendency of nanocomposites to drip, negatively affecting flammability.
Increasing interest in competitive, sustainable, and biodegradable alternatives to petroleum‐based plastics has encouraged the developmentof protein‐based plastics. The formation of a homogeneous protein melt during extrusion occurs through: denaturation, dissociation, unraveling, and alignment of polymer chains. The presence of covalent cross‐links is unfavorable, decreasing chain mobility, increasing viscosity and preventing homogenization. Proteins have high softening temperatures, often above their decomposition temperatures. To avoid degradation, the required chain mobility is achieved by plasticizers. By understanding a protein's physiochemical nature, additives can be selected that lead to a bioplastic with good processability. The final structural and functional properties are highly dependent on the protein and processing conditions.
A systematic study of the effects of , flow rate, voltage, and composition on the morphology of electrospun PLGA nanofibers is reported. It is shown that changes of voltage and flow rate do not appreciably affect the morphology. However, the of PLGA predominantly determines the formation of bead structures. Uniform electrospun PLGA nanofibers with controllable diameters can be formed through optimization. Further, multi‐walled carbon nanotubes can be incorporated into the PLGA nanofibers, significantly enhancing their tensile strength and elasticity without compromising the uniform morphology. The variable size, porosity, and composition of the nanofibers are essential for their applications in regenerative medicine.
Novel soy protein/polystyrene nanoblends with core‐shell structures were successfully prepared by introducing nano‐sized PS into soy protein through emulsion polymerization. The nanoblends showed core‐shell structures, with the core being of PS and the shell of sodium dodecane sulfonate and soy protein polypeptides, when investigated by electron microscopy. Nanoblends containing high levels of PS (>30%) exhibited characteristic infrared spectrum bands, X‐ray diffraction peak, and glass transition, since PS microsphere aggregated to form independent PS domains. Mechanical strength and water resistance were effectively improved by introducing PS. An effective structure‐performance relationship was thereby established to describe the nanoblends.
