Urethane/acrylic hybrid latex particles are prepared by miniemulsion polymerization for an application as soft adhesives. The polymerization of the acrylic monomers and grafting of an isocyanate functionalized PU on a hydroxyl functionalized monomer (HEMA) take place simultaneously, resulting in a complex PU/acrylic network while avoiding any macroscopic phase separation. Its structure can be tuned by changing the extent of grafting and a specific model is applied to analyze the final polymer microstructure. The resulting materials have a low level of adhesion but display an exceptionally high resistance to shear. Two parameters are varied: the fraction of HEMA in the monomer composition and the diol concentration.
Artificial turf is robust, playable in all weathers and has a long service life. Polyamide (PA) flooring has excellent resilience but provokes abrasion injuries (friction burn); polyethylene (PE) monofilaments are skin‐friendly but tend to permanent deformation. To maximize resilience while minimizing the risk of skin abrasion, PA‐PE bicomponent fibers are developed. Numeric simulation is applied to find optimized fiber cross‐sections and material combinations, accompanied by melt‐spinning of respective filaments and validation of the model. The resulting artificial grass resembles natural turf with respect to playability and appearance and does not need any granular infill.
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.
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.
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.
Fully exfoliated PS/clay nanocomposites were prepared via FRP in dispersion. Na‐MMT clay was pre‐modified using MPTMS before being used in a dispersion polymerization process. The objective of this study was to determine the impact of the clay concentrations on the monomer conversion, the polymer molecular weight, and the morphology and thermal stability of the nanocomposites prepared via dispersion polymerization. DLS and SEM revealed that the particle size decreased and became more uniformly distributed with increasing clay loading. XRD and TEM revealed that nanocomposites at low clay loading yielded exfoliated structures, while intercalated structures were obtained at higher clay loading.
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.
Dynamic crack propagation routes in composites were investigated using numerical methods. The interfacial strength was characterized by means of the interfacial nodal constrained failure. Five different micro‐damage modes around a broken fiber and the corresponding stress/strain curves were obtained with the interfacial strength increasing. It was proved that the shear stress concentration region appears to be different as the interface varying from weak to strong and that the recovery of fiber load‐supporting with a strong interface is better than that with a weak interface. Experimental work has been done and the available results agree well with corresponding simulation results.
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 novel zirconia polyester nanocomposite is prepared using an in situ approach. Surface‐functionalized zirconia nanoparticles are obtained by attaching 3‐phosphonopropionic acid to the metal oxide. Neat and surface‐covered metal oxide particles are incorporated at the beginning of the polyesterification reaction of isophthalic acid and neopentyl glycol resulting in zirconia/poly(neopentyl isophthalate) (PNI) nanocomposites. TEM shows that the dispersibility of the inorganic filler is improved by covering the zirconia surface with carboxylic acid groups. These results are verified by SAXS. Rheological measurements reveal that the viscosities are increasing compared to pristine PNI at particle loads of 10 wt% (neat zirconia) and 5 wt% (phosphonic‐acid‐capped zirconia), respectively.
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.
Morphological analyses of nanocomposites based on TPU and polyhedral oligomeric silsesquioxanes (POSS) was performed using different techniques (transmission electron microscopy, small‐ and wide‐angle X‐ray scattering, differential scanning calorimetry) as a function of molecular weight of poly(ethylene glycol) (PEG) and PEG/POSS mol ratio. A strong interdependence in crystallisation behaviour between the two (POSS and the soft segments of TPU) specified to be able to crystallise in TPU/POSS was found. The mechanical properties determined by using recording microindentation techniques at room temperature were significantly improved by POSS for two material formulations.
Three types of acrylonitrile‐butadiene‐styrene rubbers with different rubber contents were used in the preparation of PC/ABS/MWCNT composites. It was found that localization of MWCNTs changes from PC to ABS phase when rubber content of ABS varies from 5 to 60%. This is discussed by a combination of thermodynamics and kinetics. Melting sequence and high viscosity of ABS are used to explain the localization of MWCNTs in the high viscosity ABS phase. The relationship between the localization of MWCNTs and the electrical resistivity of the composite is also investigated.
UV‐curable inks based on a poly(ethylene glycol) diacrylate (PEGDA) matrix and containing a dispersion of aqueous Ag nanoparticles in different amounts from 10 to 50% are prepared for the fabrication of inkjet printed resistors. The composition is adapted to the inkjet requirements in terms of viscosity, surface tension, and particle size. The gel content, glass transition temperature, conversion, UV‐Vis absorption, morphology, and DC electrical properties of the materials are characterized. It is found that the NPs dispersed in the polymeric matrix realize a percolating path by aligning themselves in chains, which results in a reduction of the percolation threshold. Thus, resistivity is well beyond the dissipative range.
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.
The selective positioning of clay platelets at the polymer/polymer interface in a blend with drop/matrix morphology has a contrasting effect: on the one hand, it promotes a refinement of the morphology during the intense flows which occur during melt compounding; on the other hand, it induces coarsening in the course of prolonged slow flows experienced during rheological analysis. Rather than to a usual coalescence process, the increase of the average sizes of the dispersed phase is primarily due to a clustering mechanism of clay‐coated droplets, which keep their individuality inside the clusters because of the elastic connotation of the layered interface.
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.
A series of symmetrical and unsymmetrical azoalkanes were synthesized and their potential as a free‐radical source for rheology modification of polyolefins was investigated. The experimental results show that unsymmetrical azoalkanes, in particular N‐cyclohexyl‐N'‐tert‐octyldiazene ( 13 ), can be successfully used for manufacturing controlled‐rheology poly(propylene) and cross‐linked high‐density polyethylene. For example, the melt flow rate of a general‐purpose poly(propylene) (MFR = 14) could be increased to a value of 800 when 0.75 wt.‐% of azoalkane 13 was added during reactive processing. In parallel, it was found that 13 has a remarkable efficiency for free‐radical‐induced cross‐linking of high‐density polyethylene, resulting in similar gel contents to dicumyl peroxide.
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.
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.
