Surface modification of sulfur by vacuum plasma polymerization with acetylene was applied in order to modify its surface properties without losing reactivity for vulcanization. A nm‐thin layer of crosslinked polyacetylene was deposited on the surface of the sulfur powder. Its surface energy was decreased as monitored by wetting in liquids of various polarities. A delay in the onset of weight loss by sublimation in thermal gravimetric analysis was shown by the plasma‐modified sulfur. Scanning electron microscopy showed a core/shell structure of the coated sulfur. In 50:50 blends of styrene‐butadiene rubber and ethylene‐propylene‐diene rubber, the encapsulated sulfur samples resulted in pronounced improvements in the mechanical properties relative to the use of unmodified sulfur.
New talc/PBAT hybrid materials were prepared through reactive extrusion. First, PBAT was free‐radically grafted with MA to improve the interfacial adhesion between PBAT and talc. Then, the resulting MA‐g‐PBAT was reactively melt‐blended with talc through esterification reactions of MA moieties with the silanol functions from talc. Sn(Oct)2 and DMAP were used as catalysts. Interestingly, the tensile properties for these compatibilized composites were improved due to a better interfacial adhesion between both partners. XPS showed the formation of covalent ester bonds between the silanol functions from talc particles, and the MA moieties grafted onto the polyester backbones.
Nanocomposites of linear low‐density polyethylene (LLDPE), with three different amounts of polyhedral oligomeric silsesquioxanes (POSS), were prepared through melt‐mixing in a batch‐mixer at 150 °C. The structure of the prepared nanocomposites was studied by X‐ray scattering and optical microscopy. The surface morphology of the nanocomposites was investigated through field‐emission SEM. The thermal properties of the pure LLDPE and nanocomposites were studied by differential scanning calorimeter (DSC). Thermomechanical properties were assessed on a Paar‐Physics MCR501 rheometer using a solid‐state rectangular fixture. Results exhibited a significant improvement in both the storage and loss moduli of the neat LLDPE upon the incorporation of the POSS particles. A substantial improvement in thermal stability was also observed in the high‐temperature region.
Film‐insert‐molded (FIM) tensile specimens were prepared under various molding conditions to investigate the effects of wall temperature and packing pressure on the residual stress distribution and thermoviscoelastic deformation. The warpage of the specimen increased with increasing mold‐wall temperature difference and decreased with increasing packing pressure. The FIM specimens produced with unannealed films showed the warpage reversal phenomenon (WRP) during annealing and the degree of WRP was affected significantly by the molding conditions and thermal shrinkage of the film. The warpage of the specimen was predicted by three‐dimensional flow and stress analyses and the prediction was in good agreement with the experimental results.
This paper reports the properties of highly oriented nanocomposite tapes based on isotactic PP and needle‐like sepiolite nanoclay, obtained by a solid state drawing process. The intrinsic 1D character of sepiolite allows its exploitation in 1D objects, such as oriented polymer fibres and tapes, where it can be uniaxially oriented upon drawing. A synergistic increase in mechanical properties is presented for highly drawn tapes (λ ≤ 20) and low filler loadings (≤2.5 wt.‐%), which can not be simply explained by micromechanical composite models. Instead, mechanical properties are intimately related to the dispersion state of the nanoclays in PP, the rheological properties of the nanocomposites and the polymer morphology.
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.
A facile technique is presented to prepare discrete µm‐sized spherulitic particles of BAPC in thin polymer films. Unlike in bulk precipitation or spray crystallization, the present technique offers a method to prepare three‐dimensional semicrystalline particles of narrow particle size distribution that can be readily isolated and collected from the glass substrate as discrete particles. We report the effects of polymer molecular weight, polymer type, and the precursor polymer film thickness on the formation of spherulitic particles and their morphologies. The three‐dimensional spherulitic particles prepared in this study have large specific surface areas, higher crystallinity and melting temperature than the bulk precipitated and crystallized polycarbonate particles.
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.
A new completely biodegradable shape‐memory elastomer consisting of PLLCA reinforced by in situ PGA fibrillation is described. The manufacturing processes and shape‐memory effects of the composites are discussed. DMA results reveal a strong interface interaction between in situ PGA fibrillation and PLLCA. Compared with the SMP‐based composites that are commonly used, the shape‐memory test shows that in situ PGA fibrillation can improve the recovery properties of PLLCA; in fact, the shape‐recovery rate increases from 80.5 to 93.2%.
A fluorinated acrylic resin was synthesized for use as a co‐monomer with a commercially available epoxy resin for UV‐cured interpenetrating polymer network preparation. Hybrid IPN networks were achieved with morphology ranging from a co‐continuous IPN to complete phase separation simply by changing monomer ratios. Highly hydrophobic coatings with good adhesion properties on glass substrates were obtained.
Shape‐memory properties such as shape fixity and recovery ratio of amorphous starch‐based materials extruded under normal conditions were evaluated for the case of single and cyclic recovery processing. This study focused on the effect of moisture as a stimulus for the activation of recovery. A high recovery ratio (Rr > 90%) was obtained at high relative humidity, at deformation ratios up to 200%. In the case of plasticized starch with a glycerol content of 10%, the recovery ratio was close to 50% because crystallization limited the shape recovery. Results were compared to those obtained with synthetic or bio‐based shape‐memory polymers such as semi‐crystalline PU or PLAGC. Efficient shape memory properties for a non‐modified biopolymer are highlighted in this study.
An easy and robust approach for the production of long‐term‐stable silver nanoparticle dispersions with narrow size distribution (mean diameter ≈3–5 nm) has been developed. Amphiphilic‐modified hyperbranched polyethyleneimines with core/shell architecture were used as macromolecular templates and carriers. We systematically investigated the antibacterial performance and morphology of thin silver‐loaded hyperbranched polymer coatings on poly(ethylene terephthalate) prepared by different wet coating techniques. Furthermore, the influence of the density of the hydrophobic shell, varied by the degree of amidation between 50 and 70%, was studied with respect to the silver release behavior, wetting properties and antibacterial activity of the silver/hbp hybrid surface coatings.
Magnetic organosilica nanoparticles are synthesized by grafting MPB‐POSS/MMA‐based block copolymers from magnetic iron nanoparticles via surface‐initiated ATRP. The hybrid nanoparticles consist of a magnetic iron core and a PMMA/POSS composite shell. A small amount of the nanoparticles is added as “smart additive” in casting PMMA sheets for localized surface modification. It is demonstrated that the particles are readily brought to the surface of the cast piece by applying a magnet field to the molding. At 1 wt% loading, the sample has a 50‐time higher particle content in a 100 µm‐thick surface layer than in the bulk. The indentation hardness of the modified surface is increased by 30%.
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.
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.
Air and 5 wt.‐% BSA solution are used as a model system to generate protein‐coated microbubbles, which are significantly smaller in diameter than the processing needle apertures. The effects of processing parameters (applied voltage and flow rate) on the bubble size distribution and stability are studied. The optimal processing conditions are also explored in terms of heating of the solutions and prepared structures. Both individual microbubbles and porous films were successfully prepared using this method which has significant potential for the preparation of microbubbles for drug delivery systems, porous coatings, thin films, scaffolds and ultrasound contrast agents. The versatile nature of the method implies that many macromolecules and other active agents can be used.
An experimental correlation between the non‐linear behaviour of commercial polyethylene melts in LAOS flow, and the pressure fluctuations associated with melt flow instabilities developed in capillary rheometry are presented. Polyethylene melts with enhanced non‐linear behaviour under LAOS conditions present larger pressure fluctuations during capillary extrusion, and consequently, larger surface distortions on the extrudate. The combination of both methods can be a tool to predict the development of melt flow instabilities in the extrusion process of polyethylene melts, and can elucidate their correlation with material structural properties ( , MWD and topology).
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.
The impact of the deformation conditions, specifically the temperature, on the shape‐memory behavior and characteristics of epoxy SMPs is studied. By simply varying the temperature during deformation (i.e., the programming step of the SM effect), the ultimate strain of the formulated epoxy was improved three‐ to five‐fold, thereby providing for an increased range of reachable deformation strains during SM thermo‐mechanical cycling. This research unveils newly developed epoxy‐based SMPs with improved deformability range and high strength with intrinsically good thermal and chemical stability.
Soft coatings are widely used to tailor the surface chemistry of materials without altering their bulk properties. However, the strength of adhesion between the coating and the substrate must be high enough for long‐term applications. This has become a major challenge in the medical field, especially for polymer‐coated stents, mainly due to several coating failures reported after mechanical expansion during clinical implantation. In this work, the applicability of current polymer‐metal adhesion tests to polymer‐coated stents is discussed. The small punch test was proposed as an adhesion test that allows fundamental studies on the adhesion and coating properties. This adhesion test was applied to thin fluorocarbon coatings deposited by plasma on 316L stainless steel.
