Both α‐cyclodextrin and linear dextrin are used to prepare biocomposites with poly(3,4‐ethylenedioxythiophene). Materials are prepared electrochemically in aqueous solution. Comparison with the pure polymer indicates that the electroactivity and electrostability decrease with the incorporation of the dextrins while the electrical conductivity is retained. The different properties of the two biocomposites suggest that the linear dextrin is mainly located at the surface, whereas the cyclodextrin is homogeneously distributed in the polymeric matrix. Cell adhesion and proliferation assays indicate that the cellular activity is significantly higher in the dextrin‐containing biocomposites.
Polyurethanes based on vegetable oil were synthesized with castor oil and toluene diisocyanate, isophorone diisocyanate or hexamethylene diisocyanate, using dibutyltin dilaurate as a catalyst. The effects of the nature of the diisocyanate on the evolution of the kinetics, as well as the physical and mechanical properties and the thermal stability, of the different synthesized polyurethanes were investigated, and these complement data from the literature on equivalent systems. The polymerization kinetics, degree of swelling and mechanical properties were greatly affected by the diisocyanate nature, whereas the rheological properties and thermal stability were found to be similar for all polyurethanes.
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.
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.
Novel nanocomposites based on conductive Ag nanoparticles and a self‐assembled polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) block copolymer were investigated. Good confinement of the nanoparticles into polystyrene microphase was achieved by the addition of DT as surfactant. The polymeric matrix kept its hexagonal order packed cylindrical structure up to 7 wt.‐% content of Ag nanoparticles. An electrostatic force microscopy (EFM) analysis of well‐dispersed metal‐organic hybrid Ag/SBS films was used to characterize the electric behavior of the conductive nanocomposites.
Factorial design analyses and numerical optimization are performed to establish material compositions (wood flour content, particle size, and impact modifier content) and mechanical property relationships for PLA/wood flour composites. Numerical optimization produces two scenarios based on materials compositions to manufacture composites with similar mechanical properties as unfilled PLA. High wood flour and impact modifier contents are required for composites made with fine wood flour particles, whereas the formulation requires low wood flour content and excludes impact modifiers for composites with coarse wood flour particles. These optimization solutions are validated experimentally.
Cellulose‐based fibers were prepared by electrospinning from cellulose dissolved in NaOH/urea in the presence of a small amount of polyol binders. The as‐spun products were examined with SEM. Pure cellulose solution did not produce fibrous materials, because it often formed spherical nanoparticles with diameters ranging from 100 to 300 nm. However, bicomponent fibrous materials were obtained successfully from mixtures of cellulose and HMPEG or PVA by electrospinning. The cellulose/HMPEG electrospun fibers had average diameters of 400 nm. The content of NaOH and urea as well as the stiffness of cellulose chains were found to have significant effect on the electrospinning process.
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).
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.
A new kind of binary polymer brushes was synthesized from two immiscible polymers, PMMA and PEG, on GPS‐modified silicon wafers. Surface composition, layer thickness, coverage, chain density, wetting ability, morphology and protein adsorption of the binary brushes were investigated by XPS, ellipsometry, AFM and contact angle measurements. The results show that both PMMA and PEG were successfully grafted onto the surface. The surface coverage and the chain density of PMMA and PEG brushes can be controlled by modulating the reaction temperature and time. This kind of binary polymer brushes exhibits a distinct microphase‐separated structure and excellent protein‐preventing property.
Conducting electrospun fiber mats based on PLA and PAni blends were obtained with average diameter values between 87 and 1 006 nm with PAni quantities from 0 to 5.6 wt.‐%. Structural characteristics of fiber mats were compared to cast films with the same amount of PAni and studied by SEM, SAXS, and AFM. Thermal properties of fiber mats and cast films were compared by DSC analyses. Mechanical properties of fiber mats were also evaluated. It was found that electrospinning process governs the crystal structure of the fibers and strongly affects fiber properties. New properties of PLA/PAni blends are reported due to the size fiber reduction.
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.
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.
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.
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.
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.
Hydrophobic association hydrogels (HA‐gels) with almost ideal properties were successfully prepared by micellar copolymerization, and the associated micelles acted as physical cross‐linking points in the network of HA‐gels. HA‐gels exhibit exceptional mechanical properties and transparency. However, the most striking properties are that HA‐gels possess the capability of self‐healing and remolding, which is mainly due to the dissociation and re‐association process of the associated micelles. Dried‐gels, which were prepared by stretching HA‐gels to a certain elongation for a period of time in the air, can be used as shrinkable or thermal sensitivity materials. HA‐gels have a broad selectivity for components, so we have synthesized HA‐gels with variously available properties by changing a corresponding component: thermoresponsive HA‐gels, nanosphere‐composite HA‐gels, and fluorescent HA‐gels. Therefore, we are sure that HA‐gels will be widely used in various fields, such as biology, medication, sensors, optics, and oil exploitation.
New dibenzoylgermanium derivatives are synthesized starting from various dithioacetal protected benzaldehydes by a coupling reaction with different dialkyldichlorogermanes and subsequent oxidative cleavage of the protecting group. The synthesized germanium compounds show a significantly stronger blue light absorption than camphorquinone. During irradiation, the dibenzoylgermanium derivatives undergo photodecomposition under formation of radicals. Therefore, the different dibenzoylgermanium derivatives are used as amine‐free visible‐light photoinitiators for dental cements and composites. Composites based on the different dibenzoylgermanes are storage‐stable and show a significantly improved bleaching behavior over composites with CQ/amine photoinitiators.
Biocides are widely explored in the design of materials and surfaces in order to address a variety of problems, such as biodeterioration, biofouling or infections. Materials with migrating biocides are under scrutiny due to potential health and environmental risks, as well as instability of the antimicrobial activity in time. This paper focuses on the onium‐functionalised polymers in the design of bioactive materials and surfaces, which are capable to kill micro‐organism or efficiently inhibit their growth on contact. The review highlights synthetic and processing routes towards the integration of onium functionalities into solid materials. The influence of materials structure on the antimicrobial activity and possible applications are discussed.
The effect of nanosilica addition on the morphology and mechanical properties of blends of isotactic PP and an ethylene/octene copolymer (EOC) is studied. TEM reveals that the well‐dispersed nanoparticles are localized exclusively in the PP phase. In the presence of a maleated PP compatibilizer addition of nanosilica leads to more finely dispersed EOC domains and a finer co‐continuous morphology. The nanoparticles reduce the rate of coalescence of the dispersed phase domains. The mechanical properties depend on the EOC and PP‐g‐MA content. Tensile and flexural properties are significantly enhanced in the presence of the silica nanoparticles, whereas impact properties are not affected. These enhancements are attributed to the favorable microstructure of the blends.
