A new, nickel‐coated graphite resistance‐change‐based method for gel‐point determination for epoxy‐based thermoset resins is presented and compared with DSC and rheological methods. Gelation times determined by this new method are in very good agreement with conventional techniques; this new method is potentially simpler and less time consuming than existing ones.
The effect of hydrophilic and hydrophobic nanosilica on the morphological, mechanical and thermal properties of polyamide 6 (PA) and poly(propylene) (PP) blends is investigated by extrusion compounding. Depending on the difference between the polymer/nanoparticle interfacial tensions, different morphologies are obtained as highlighted by TEM and SEM. Hydrophobic nanosilica migrates mainly at the PA/PP interface, which leads to a clear refinement of PP droplet size. The macroscopic properties of the hybrid blends are discussed and interpreted in relation with the blend morphology and melt‐mixing procedure. The control over coalescence allows a morphology refinement of the blends and improves mechanical properties.
A novel method to produce uniaxially aligned nanofibers is described, in which a pair of parallel auxiliary electrodes at a positive potential is placed between the needle and the collector electrodes. Charged nanofibers ejecting from the polymer solution are pre‐aligned by the electrostatic repulsion originating from the auxiliary electrodes and deposited on the collector electrodes, forming a narrow mat with the fiber segments strongly curved. By adjusting the conductivity and shape profile of the collector, the curved segments can be straightened longitudinally. A seamless tube composed of longitudinally aligned nanofibers can be obtained. Such seamless tubes may be useful as biomaterials in tissue engineering.
Electroactive macroporous poly[(vinylidene fluoride)‐co‐trifluoroethylene] membranes have been produced by solvent evaporation at room temperature, starting with a diluted solution of the copolymer in dimethylformamide. The pore architecture consists of interconnected spherical pores. This architecture is independent of the membrane thickness. The thickness of the membranes ranges from a few to several hundred µm, using spin coating and evaporation in static conditions, respectively. The pore structure is explained by a spinodal decomposition of the liquid/liquid phase separation and crystallization in the copolymer‐rich phase.
PA6 nanocomposite films with different nanoclay dispersion degrees are prepared by melt compounding and cast extrusion. The dispersion of the MMT platelets (homogeneity and degree of exfoliation) is evaluated qualitatively by TEM and quantitatively by rheology and NMR; it ranges from microcomposites to highly exfoliated nanocomposites. Compared to neat PA6, the optical properties (clarity, gloss, haze) are worse for the microcomposites and better for the nanocomposites. The mechanical properties depend strongly on the exfoliation level. Better exfoliation leads to higher stiffness. The strain at break decreases compared to neat PA6 films even in the case of highly exfoliated nanocomposites films. At low MMT content, the microcomposite has a higher ductility than well exfoliated nanocomposites films.
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 efficiency of epoxy/CNT nanocomposites as photocatalyst on adsorbed, aqueous and gas phases is investigated. Epoxy films containing SWNTs in the range between 0.1 and 0.3 wt% are prepared by means of UV‐induced polymerization and the achieved materials are used as photocatalysts on adsorbed, aqueous, and gas phases. The activity of this new photocatalytic materials is evaluated in the adsorbed state by using the methylene blue target molecule, in the aqueous phase by following the photodegradation of phenol and 3,5‐dichlorophenol, and in the gas phase using nitrogen monoxide as probe molecule. It is demonstrated that the catalyst is suitable for both oxidative and reductive degradation reactions.
Graphene nanocomposites are prepared by chemical reduction of graphite oxide (GO) dispersion with vitamin C in the presence of SAN latex followed by melt compounding. In this process, GO is well dispersed in an aqueous SAN emulsion before reduction. During reduction the SAN latex is adsorbed on the graphene sheets of the chemically reduced GO (CRGO). After melt compounding of such hybrid particles with SAN, the nanocomposites show uniform dispersion of CRGO in SAN resulting in improved stiffness with respect to SAN/graphite. The reduction of GO in the presence of polymer latex represents a versatile route to graphene masterbatches and does not require either drying of GO or thermal GO expansion at high temperatures.
The effect of different bicomponent electrospinning techniques i.e., off‐centered coaxial electrospinning and side‐by‐side electrospinning, on the formation of tight nanocoils (nanosprings) was studied. Since right balance between the longitudinal compressive forces arising from the shrinking thermoelastic components and the rigidity emerging from the stiff component and conductivity is required for nanospring formation, conductive solutions of flexible and rigid components were used for the electrospinning. Under optimum conditions, nanofiber mats with almost 100% nanospring morphology were generated using off‐centered and side‐by‐side electrospinning techniques. Mechanical properties of aligned nanomats with and without nanosprings, produced at different collecting speeds are provided.
The effect of carbon nanoreinforcements of different shapes on the mechanical properties of epoxy‐based composites is studied. It is found that while nanodiamond and fibrous (carbon nanotube and nanofiber) particles provided better tensile properties, platelet (graphene oxide) nanoreinforcements lead to a considerable increase in the fracture toughness of the composites. The trend of the results is explained on the basis of the geometrical characteristics of the reinforcements. The accuracy of several micromechanics‐based criteria for predicting the Young's modulus of composites is investigated for different nanoparticle shapes. The state of dispersion of nanofillers and the fracture surface features of all composites are examined using TEM and SEM.
A magnetic microrheometer is used to characterize the development of viscosity at different depths in UV‐cured epoxy coatings. Lateral magnetic particle velocities are tracked at different depths to quantify viscosity gradients. In general, viscosity build‐up is faster near the coating surface, tending to produce a “skin”. The effects of process conditions on the viscosity gradient development, on the rate of viscosity increase, and on surface defects are studied. More severe gradients develop in thicker coatings and in those with higher photoinitiator concentration. Under some conditions, the skin layer wrinkles, indicating the development of local compressive stress. Curing at higher temperature, however, increases cure rates while reducing the viscosity gradients and wrinkling defects.
This work reviews principles of Raman and infrared imaging, as well as applications of the art to understand physiochemical phenomena in polymer systems. Image sequences may be assessed in terms of spatial or spectral changes that occur over time, either within a specific region or across the field of view. As such, the methods have enabled the analysis of diffusion and dissolution processes at polymer interfaces, drug release from polymer matrices, and structural transitions among others. Despite analytical limitations imposed by resolution (spectral or spatial) and sample preparation, Raman and infrared imaging are powerful tools for relating performance attributes to molecular‐level characteristics.
Recycling of thermoplastic wastes consisting of PE/PP/PS/HIPS blends was investigated by using SEBS/EPR and SBR/EPR as compatibilizers. The effect of the binary compatibilizer systems and processing conditions on the mechanical properties and morphology of the blends are discussed. The SEBS/EPR system allowed blends with better mechanical properties to be obtained than the SBR/EPR system; this was attributed to the chemical structure similarity between compatibilizers and recycled materials. The optimal conditions for processing of the recycled thermoplastics (blends) were found to be 190 °C, 14 min of processing time and 3.5 wt.‐% of compatibilizer. The morphology and mechanical properties of the blends were discussed using theoretical phase diagrams and models proposed in the literature, and good agreements between these properties were found.
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.
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.
PET/PEN blends were prepared over the full composition range via a melt mixing process under various processing conditions. This resulted in transesterification reactions and formation of copolymer structures with various average sequence block lengths and degree of randomness (RD) determined by 1H NMR. It was seen that with an increase in time and temperature of mixing copolymer content (TEN%) and RD increased, whereas the , values were decreased. The differences in the extent of transreactions arising from different processing histories showed their systematic influence on rheological characteristics. Moreover due to progress of transreactions during the rheological measurements, convergence was seen in all the rheological characteristics at terminal zones in the high frequency regions. Similar convergence in the copolymer structural parameters was also obtained by NMR analysis. An increase in TEN% led to a systematic increase in viscosity of the blends. A decrease in the , values results in an increase in elasticity and relaxation time due to improvement of blend interface with increase in extent of copolymer formation.
A pronounced and distinctive increase in the conductivity of polyetherimide nanocomposite films containing CNF agglomerates is reported. It is demonstrated that a variation of the CNF network can have a dramatic effect on the AC conductivity of PEI composites. The effect is found in composites containing relatively large and strongly entangled CNF agglomerates, and it is suggested that is is due to a new mechanism of electrical conduction. The observed behavior may reveal the distinctive response of electrons in strongly entangled CNF networks in polymer films to an AC field in contrast to a DC field, and could also result in a negative dielectric response.
Chemical and mechanical experiments are reported to elucidate the macroscopic effects of crosslinker length and composition on the thermomechanical response of acrylate‐based SMPs. To this end, EGA‐based formulations underwent a battery of basic tests which revealed that by increasing crosslinker chain length, polymer Tg can be decreased but there will be increases in compliance, step recoverability, and damping in a glassy state. Addition of methacrylate groups can cause increases in swelling, Tg, storage modulus in shorter chains, and greater damping at a rubbery state. All tested polymers exhibited mild hydrophilicity. PEGDA formulations exhibited good recoverability and could be an option for vascular applications.
Polymer blend films consisting of a tacky and a nonadhesive component are promising candidates for low‐tack applications. Immiscibility of both components results in a phase separation process yielding a tacky matrix with glassy objects embedded. The influence of the blending ratio of the components poly(n‐butyl acrylate) (PnBA) and polystyrene (PS) is addressed. The mechanical information resulting from the tack test shows the possibility of varying the bonding strength of the PSA blend over a wide range. The macroscopic and microscopic structural characterization with optical microscopy and ultrasmall angle X‐ray scattering (USAXS) shows that the blend PnBA/PS exhibits similarities to common filler systems as well as deviates regarding installed structures. Due to the large domain size on a microscopic level, only the tacky component, PnBA, defines the adhesive behavior. The nonadhesive component limits the contact area between the adhesive and the substrate.
To improve the poor mechanical properties of uniaxially ultra‐drawn films along the transverse direction, lamination of two ultrahigh molecular weight polyethylene/ethylene dimethylaminoethyl methacrylate copolymer blend films was carried out in the rectangular elongation direction by a microwave heating method. The characteristics of the successful laminated films were analyzed theoretically and experimentally. The original orientation of the crystallites for the blend films was maintained perfectly after lamination, and the preferential directions intersected each other. The Young's modulus increased symmetrically with respect to the 45 ° direction. This is the first report concerning a drastic improvement of the Young's modulus in the transverse direction for films ultra‐drawn along one direction.
