Nowadays, silicon represents the most important material used for microelectronic applications. In this paper, both H–Si (111) surfaces and H–Si powders are used to initiate a multifunctional acrylate photopolymerization. The polymers formed are characterized by IR spectroscopy. This should be the way to create either an acrylate polymer coating on a Si wafer or a polymer film containing covalently linked silicon particles.
Novel nanocomposites prepared by melt mixing of MWCNTs in a hot‐melt adhesive PCL‐based polyurethane are investigated. The nucleating effect of MWCNTs and the confinement they cause to polymer chains are considered. The broadening of the glass transition is indicative of a growth of the immobilized amorphous fraction adhered to MWCNTs. In the molten state the formation of a combined polymer/MWCNT network is observed. Practical requisites of hot melt adhesives, such as adequate melting temperature, crystallization degree, and viscosity are preserved when MWCNTs are added. Improvement of strength at room temperature and welding rate during cooling, are observed.
The fabrication of tissue engineering scaffolds based on the polymerization of crosslinked polylactide using leaching and batch foaming to generate well‐controlled and interconnected biodegradable polymer scaffolds is reported. The scaffold fabrication parameters are studied in relation to the interpore connectivity, pore morphology, and structural stability of the crosslinked PLA scaffold. In vitro cell culture and in vitro degradation are used to analyze the biocompatibility and biodegradability of the scaffolds. The new crosslinked PLA thermoset scaffolds are highly suitable for bone tissue engineering applications due to their complex internal architecture, thermal stability, and biocompatibility.
Cardanol, a well known natural resource, was used to produce a polymer resin in the presence of formaldehyde, catalyzed by H2SO4. Before reticulation, PAni · H2SO4 was blended with the resin. The blended material was cast into poly(propylene) cups and kept inside a desiccator under vacuum until complete water evaporation. The final in situ polymer blend was solid and could not be dissolved in ordinary solvents, indicating that a reticulated material had been obtained. Samples prepared similarly were then characterized, showing that the produced blends can be used as pressure sensing materials.
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 new melt‐processable PTFE material is presented and characterized that provides new and economical solutions in polymer technology while bridging the gap between perfluorinated PTFE and fluorothermoplastic materials such as perfluoroalkoxy resins. Thermal transitions, MW and MWD, and microstructures of the melt‐processable PTFE materials are investigated and compared to standard PTFE, modified PTFE, and PFA materials. The influence of the polymerization type used for the preparation of the melt‐processable PTFE (emulsion and suspension polymerization) on the MWD and the comonomer distribution are discussed.
The aim of the present contribution is to understand how ionic strength, brought by the addition of salt to laponite/PEO nanocomposite dispersions, influences the texture and adhesion characteristics at nano‐ and microscales in multilayered nanocomposite films prepared from such dispersions. At the nano‐scale, SAXS and XRD measurements indicated that the clay platelets orient parallel to the film plane and that the polymer chains intercalate the clay platelets regardless of salt addition. A gradual transition from an agglomerated structure, containing polymer‐rich and clay‐rich domains, to a fine‐balanced structure with smaller distinct details without excess PEO was observed, via AFM, on the exposed edges of cryo‐microtomed films with increasing ionic strength.
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.
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.
This review reports on recent advances in the design of biodegradable polymers built from petroleum and renewable resources using reactive extrusion processing. Reactive extrusion represents a unique tool to manufacture biodegradable polymers upon different types of reactive modification in a cost‐effective way. Partially based on our ongoing research, ring‐opening polymerization of biodegradable polyesters will be approached as well as the chemical modification of biodegradable polymers, particularly natural polymers. The development of environmentally friendly polymer blends as well as (nano)composites from natural polymers, including natural fibers and nanoclays, through reactive extrusion, as an efficient way to improve the interfacial adhesion between these components, will be also discussed.
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 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.
Extrusion flow experiments of linear and branched syndiotactic poly(propylene)s were carried out. The work was focused on flow instabilities. Ionized radiation was employed to induce long chain branching in linear samples. Sharkskin and melt fracture were postponed in the case of slightly long branched samples, which possess an enhanced melt elasticity compared to linear samples. For the most elastic samples the nature of the flow instability changed: sharkskin disappeared and melt fracture was observed instead. The correlation between sharkskin and melt strength results is discussed.
Near‐monodisperse, size‐controllable, poly(methyl methacrylate)‐pigment nanoparticle composites were produced using electrohydrodynamic atomization (EHDA). The geometric mean diameters of the composite particles were in the 0.91 to 1.90 µm‐diameter range with geometric standard deviations of approximately 1.05 to 1.12. Increasing the polymer volume fraction and liquid flow‐rate resulted in an increase in the diameter of the composite particles, which agreed well with droplet scaling relations for EHDA. The results here demonstrate that EHDA can be used for polymer‐nanoparticle‐composite production and as an alternative to conventional inkjet printing.
Acrylic‐epoxy interpenetrating polymer networks were prepared by means of UV curing. The photopolymerization process was investigated via real‐time FTIR spectroscopy. The hybrid, cured films showed a broad tan δ peak in DMTA demonstrating the high damping properties of the hybrid, cured formulations. A decrease on shrinkage was achieved by increasing the epoxy‐resin content in the photocurable formulation, with a consequent increase in adhesion properties.
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.
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.
A simple process is described for preparing transparent composite sheets from soy‐oil‐based biopolyurethane (BioPU) with microcrystalline cellulose (MCC). The sheets are prepared by the reaction of a mixture of soy‐oil‐based polyol and petrochemical polyol with polymeric methyldiphenyl diisocyanate (pMDI) in the presence and absence of MCC reinforcement by compression molding. MCC is well dispersed in the PU matrix, and characteristic peaks for MCC and BioPU are shown by the FTIR spectra. Mechanical properties are substantially improved with increasing MCC content. DMA and TGA results show better thermal stability in comparison to the neat BioPU sheets.
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.
An electrospinning method to obtain well‐aligned self‐assembled PVDF fibers in the form of yarn structures is presented. Post‐treatments such as stretching at 100 °C and annealing improve the tensile modulus and strength of the fibers by 17 and 41%, respectively. The results reveal that post‐treatment on fiber yarns induce crystallinity and β‐crystalline phase formation, which in turn impart a noticeable effect on the strength and stiffness of the fibers. An ≈10% improvement in the ferroelectric β‐crystalline phase fraction is estimated for the post‐treated yarns. Such yarn structures with improved strength and ferroelectric β‐phase content can be useful for nanoscale and microscale electronic devices.
