This paper presents the first results of a project aimed at investigating the arrangement of polyelectrolyte layers on unalloyed steel. We studied the structure of double and single polymer layers consisting of cellulose phosphate (HP‐PP‐C) and polyethyleneimine (PEI). Layers were characterized by variable angle ellipsometry, AFM and XPS. In particular, XPS indicated the incorporation of iron ions into cellulose phosphate layers, but, in contrast, these ions could not be observed in PEI layers. Results indicated that the homogeneity and qualitative corrosion performance of double layers (HP‐PP‐C/PEI) on unalloyed steel depend on the deposition of cellulose phosphate at the interface with steel.
A simple, easily accessible solvent‐free method for the dispersion of MWCNTs into PET is proposed, based on the preparation of a microparticulate polymer/nanotube masterbatch via cryogenic impact‐milling and its subsequent melt blending with the bulk polymer. Thermal and mechanical properties of nanocomposites prepared using this method were evaluated as a function of nanotube concentration. Thermal stability was improved, and superior crystallization behavior of PET in the nanocomposites was observed. Significant improvements of around 25% in tensile strength and tensile modulus of the nanocomposites was achieved using this strategy, with only 0.25 wt.‐% MWCNT, compared to previous literature data where 1 wt.‐% MWCNT was employed.
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.
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.
By curing bisphenol A‐based benzoxazine in a thermoplastic polystyrene‐block‐poly (ethylene‐co‐1‐butene)‐block‐polystyrene (SEBS) block copolymer, nanospherical polybenzoxazines as small as 150 nm with narrow size distribution are obtained in high yield. This specific condition allows simple and direct formation of nano‐ or microspherical thermoset resins. A model of how the thermoplastic block copolymer chains act as a molecular pocket where the thermoset curing proceeds is presented. It is demonstrated that this mechanism requires (i) a particular block of thermoplastic copolymer which allows specific interaction with monomeric thermoset molecules, and (ii) the curing of thermosets in a molecular assembly structure to confine the phase separation of thermoset prepolymer during curing.
In this comparative study, the charge storage performance of commercial high‐temperature polymer films was evaluated and correlated with their chemical structure. Isothermal surface potential decay measurements after annealing periods at 90 °C revealed that amorphous polyetherimide (PEI) films showed the best charge storage behavior. Polyimide films showed reduced charge storage performance, whereas sulfur‐containing polymer films are not suitable as electrets due to their fast charge decay. Additionally, the effect of water content in PEI films in the range of 0.02–0.79 wt.‐% was studied. Increasing amounts of water decreased the charge storage properties proportionally, but only by a relatively smaller amount: the highest investigated water content of 0.79 wt.‐% reduced the charge by only 30%.
The relative stability of chip‐underfill composite materials was modeled as a function of glass filler concentration between 10 and 70 wt.‐%, filler particle size (between 5 and 25 microns), and the curing temperature of the resin (150 vs. 180 °C), yielding different dynamic viscosity profiles. The stability was gauged using a modified sigmoidal chemorheology model for the dynamic viscosity, and incorporating the time‐dependent viscosity into a model for Stokes' law of sedimentation. We also incorporated a hindered sedimentation term, due to filler concentration due to the higher loadings. Several important findings were observed. First, it appears to be the high concentration of filler that is maintaining the stability of these dispersions during cure. Smaller concentrations of the same particles were predicted to have a larger sedimentation velocity leading to stratification in the resin with time. Second, higher cure temperatures led to a shorter period of sedimentation in a pre‐cured state and resulted in less sedimentation, even though there was probably a slightly smaller viscosity in the pre‐cured condition. While these process models adequately describe the physics of the competitive processes of cure and sedimentation, a full picture may be incomplete without a larger determination of how this also affects polymerization shrinkage and residual shear stress upon cure.
CNF‐reinforced PP nanocomposites were fabricated from CNFs dispersed in a boiling PP/xylene solution. Their thermal properties were characterized by TGA and DSC and shown to exhibit improved thermal stability and higher crystallinity. They were further processed into thin films by compression molding. The electrical conductivity and dielectric property of the PP/CNF nanocomposite thin films were studied. Both electric conductivity and real permittivity increased with increasing fiber loading. Electrical conductivity percolation is observed between 3.0 and 5.0 wt.‐% fiber loading. The rheological behavior of the nanocomposite melts were also investigated. It was found that a small fiber concentration affects the modulus and viscosity of PP melt significantly.
Water‐dispersed graphene oxide sheets were used to prepare graphene/poly(ethylene glycol) diacrylate resin composites by photopolymerization. It was found that graphene sheets undergo excellent morphological distribution within the resin system, giving rise to transparent composites with unaltered thermal properties with respect to the neat resin, that are electrically conductive at loading ratios as low as 0.02 wt.‐% of graphene oxide. The proposed strategy based on photopolymerization provides an easy, energy‐saving and environmental friendly technique that can find a wide application in coating technology, mainly for electromagnetic shielding and antistatic coatings.
A bilayer‐structured PEI/CNF composite fabricated by a facile solution casting method is described, showing dramatically improved static dissipation properties at a rather low loading level. Compared to the conventional monolayer nanocomposite with high static dissipation rate, the bilayer‐structured composite exhibited a 91.4 wt.‐% reduction in CNF loading, while it is volumetric and surface static dissipation rates were ca. 1 000 and 20 times higher, respectively. The interface region in the bilayer structure accounts for such a remarkable improvement. It is believed that this design could significantly benefit the applications requiring high antistatic capability of polymeric materials.
A reactive organic montmorillonite clay (VMMT), modified with (4‐vinylbenzyl) triethylammonium cations, has been prepared and used as a nanofiller to reinforce a corn‐oil‐based polymer resin. The polymer resin was prepared by the cationic polymerization of conjugated corn oil, styrene and divinylbenzene, using boron trifluoride diethyl etherate modified with Norway fish oil as the initiator. The results indicate that the VMMT is intercalated in the corn‐oil‐based polymer resins. When compared with the pure polymers, these novel nanocomposites reinforced with 2 to 3 wt.‐% VMMT exhibit significant improvements in modulus, strength, strain and toughness. Furthermore, incorporating VMMT into the corn‐oil‐based polymer matrix also leads to improved thermal stability of the nanocomposites over the pure resins of up to 400 °C.
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 series of hydrogels based on poly(ethylenglycol) methyl ether methacrylate (PEGMEMA) is synthesized using macromonomers of three different molecular weights, in combination with varied degrees of chemical crosslinking. The effects of PEGMEMA, initiator, and crosslinker concentrations on gel yield and swelling properties are studied. In addition, the chemical structure of the gels is characterized by FTIR and solid‐state NMR spectra. The swelling and rheological behaviors of hydrogels as well as protein partitioning into the gels are discussed in terms of the network mesh size. Low protein sorption and bacteria deposition tendencies indicate that PEGMEMA‐based hydrogels could be highly beneficial for uses as fouling‐resistant materials, for instance, as protective coatings for desalination membranes.
The effect of OMLS incorporation on the thermal properties of PET/LCP blends is studied. Pure and OMLS‐modified PET/LCP blends were prepared by melt‐extrusion using twin‐screw extruder. The morphological analyses of PET/LCP blends show that OMLS addition enhances the phase‐separated structure of the pure blend. A detailed study on the thermal properties of the pure and OMLS‐modified PET/LCP blends were carried out by means of DSC in both conventional and modulation modes. Results show a complex melting behaviour comprises of successive melting and re‐crystallisation. Finally, non‐isothermal crystal‐growth kinetics of pure and OMLS‐modified blends were investigated.
In this study, the effects of processing parameters on the mechanical properties of injection molded thermoplastic polyolefin (TPO) foams are investigated. Closed cell TPO foams were prepared by injection molding process. The microstructure of these foamed samples was controlled by carefully altering the processing parameters on the injection molding machine. The foam morphologies were characterized in terms of skin thickness, surface roughness, and relative foam density. Tensile properties and impact resistance of various injection molded TPO samples were correlated with various foam morphologies. The findings show that the mechanical properties are significantly affected by foam morphologies. The experimental results obtained from this study can be used to predict the microstructure and mechanical properties of cellular injection molded TPO foams prepared with different processing parameters.
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.
In this paper, the effects of different cure regimes on the strain development in an anhydride‐cured epoxy resin were investigated by fiber optical measurements. The course of the strain signal was detected by an embedded fiber Bragg grating sensor in the unconstrainedly curing epoxy. The build‐up of strain was detected for various cure regimes differing in the dwelling times of the first isothermal step, heating rates to the cure temperature, and final curing temperatures, respectively. Characteristic points (gelation, vitrification) of the cure regimes were identified by conversion‐ and Tg‐determinations via DSC and assigned to changes of the FBG signal. The fiber Bragg sensing technique allowed us to find those variables of the cure regimes which mostly affect the strain development and thus, the level of the residual strain. It was established that the dwelling time and heating rate to the cure temperature influence markedly the residual strain whereas the cure temperature affects this value to a lesser extent for the selected cure regimes. So, the above parameters should be selected properly for an optimum cure regime characterized by the build‐up of a minimum residual strain.
The properties of synthetic hydrogels can be tuned to address the needs of many tissue‐culture applications. This work characterizes the swelling and mechanical properties of thiol‐ene crosslinked PEG hydrogels made with varying prepolymer formulations, demonstrating that hydrogels with a compressive modulus exceeding 600 kPa can be formed. The amount of peptide incorporated into the hydrogel is shown to be proportional to the amount of peptide in the prepolymer solution. Cell attachment and spreading on the surface of the peptide‐functionalized hydrogels is demonstrated. Additionally, a method for bonding distinct layers of cured hydrogels is used to create a microfluidic channel.
A physical model of dart impact tests of film manufactured from semi‐crystalline polyethylene resins is developed. The models treat the dart impact tests as a special case of the standard high‐speed stress/strain measurement performed on a polymer sample with a linearly changing cross section. They describe the dart impact strength as a complex function of the parameters that characterize the stress‐strain curve of the resin: stresses and strains at the yield, necking and breaking points. The models correctly predict the range of the dart impact strength (ASTM D1709, ISO 7765) and are suitable for semi‐quantitative characterization and ranking of linear low density polyethylene resins for film applications.
Pulse electric current sintering is used to prepare a compact from resinificated hydrous silk powder. Compacts with no remnant silk powders are formed with 20 wt% added water, 20–40 MPa molding pressure, and >353 K molding temperature. The latter two are much lower than those used for conventional hot pressing. No dependence on molding pressure and temperature are found in XRD or FT‐IR analysis, except for a compact molded at 473 K, for which silk fibroin decomposition is confirmed by DSC, EGA‐MS, and molecular weight measurements. The compact's three‐point bending strength depends on the molding temperature, except for the temperature at which silk fibroin decomposes. The maximum three‐point bending strength resembles that of general‐purpose epoxy resin and is much higher than that of PLA.
