Polyamide 6 (PA6)/phosphorylated silica nanocomposites were synthesized during PA6 extrusion through in situ formation of the inorganic phase without solvent. This synthesis is based on the hydrolysis-condensation reactions of diethylphosphatoethyltriethoxysilane (SiP) as a functional inorganic precursor in combination with or without tetraethoxysilane (TEOS) dispersed in the molten PA6. This synthesis is carried out during PA 6 matrix extrusion that means at high temperature and under shear. The characterization of the in situ synthesized PA6/phosphorylated silica nanocomposites by solid 29Si Nuclear Magnetic Resonance (NMR), Small Angle X-ray Scattering (SAXS) and Transmission Electron Microscopy (TEM) coupled with Energy Dispersive X-ray spectroscopy (EDX) demonstrated the possibility to directly create in less than 5 min at 220 °C a phosphorylated silica uniformly dispersed in the PA6, i.e. in the form of well dispersed particles or aggregates of sub-micron range. The influence of silicon and phosphorus on the thermal and fire retardant behaviour was investigated by thermogravimetric analysis (TGA), cone calorimeter and UL94 tests. The fire retardant behaviour was modified with a formation of a char and a peak heat release rate (PHRR) decrease by more than 50% for the SiP based nanocomposite compared to the pure PA6. 相似文献
Poly(vinyl alcohol) (PVA), hydrogel was prepared by using glutaraldehyde as a cross-linking agent. The blend semi-synthetic hydrogel film, consisting of PVA and chitosan, was prepared from a solvent-casting technique and characterized for their intermolecular interactions using infrared method. The swelling and reswelling behaviors, as well as mechanical properties of the synthetic and semi-synthetic gels were examined by weighing and tensile testing, respectively. Cross-linking the two types of polymer with glutaraldehyde produces a film with lower crystallinity and smaller swelling and reswelling degrees, but having improved mechanical properties. Also, the two types of films show a pH-dependent swelling characteristic. It was found that, the reswelling properties of synthetic hydrogels can be improved by blending PVA with certain ratio of natural polymer. This blending film, can be improve sandy soil properties for cultivation, such as, controlled release of water. 相似文献
Among the methods available to reduce water production during oil recovery, injecting a gelling system composed of a polymer and a crosslinker has been widely used. In this study, a Plackett-Burman design was used for screening a large number of factors such as concentrations of polymer, crosslinker, pH, temperature, and presence or absence of NaCl, CaCl2, MgCl2, KCl, thiourea, sodium lactate, and nanoclay on the gelation time of sulfonated polyacrylamide nanocomposite hydrogels by rheological tests. Among these factors, temperature, pH, and CaCl2 concentration were found to have the greatest effect on the gelation time. The effects of these three factors and their interactions on the gelation time were then determined by using central composite design of response surface method. As a result, the interactions of CaCl2 concentration with temperature and pH were considerably more than the interactions of pH and temperature on the gelation time. At low pH (3 < pH < 7), the gelation time decreased by decrease of pH while at CaCl2 concentration of 3750–11250 ppm and at 7 < pH < 11, the gelation time increased with the increase of pH. It was found that temperature was the most effective parameter to control the gelation time. 相似文献
Microdevices designed for practical environmental pollution monitoring need to detect specific pollutants such as dioxins. Bisphenol A (BPA) has been widely used as a monomer for the synthesis of polycarbonate and epoxy resins. However, the recent discovery of its high potential ability to disrupt human endocrine systems has made the development of smart systems and microdevices for its detection and removal necessary. Molecule‐responsive microsized hydrogels with β‐cycrodextrin (β‐CD) as ligands are prepared by photopolymerization using a fluorescence microscope. The molecule‐responsive micro‐hydrogels show ultra‐quick shrinkage in response to target BPA. Furthermore, the flow rate of a microchannel is autonomously regulated by the molecule‐responsive shrinking of their hydrogels as smart microvalves.
High‐porosity interconnected, thermoresponsive macroporous hydrogels are prepared from oil‐in‐water high internal phase emulsions (HIPEs) stabilized by gelatin‐graft‐poly(N‐isopropylacrylamide). PolyHIPEs are obtained by gelling HIPEs utilizing the thermoresponsiveness of the copolymer components. PolyHIPEs properties can be controlled by varying the aqueous phase composition, internal phase volume ratio, and gelation temperature. PolyHIPEs respond to temperature changes experienced during cell seeding, allowing fibroblasts to spread, proliferate, and penetrate into the scaffold. Encapsulated cells survive ejection of cell‐laden hydrogels through a hypodermic needle. This system provides a new strategy for the fabrication of safe injectable biocompatible tissue engineering scaffolds.
This communication describes the first application of cycloaddition between an in situ generated nitrile oxide with norbornene leading to a polymer crosslinking reaction for the preparation of poly(ethylene glycol) hydrogels under physiological conditions. Hydrogels with high water content and robust physical strength are readily formed within 2–5 min by a simple two‐solution mixing method which allows 3D encapsulation of neuronal cells. This bioorthogonal crosslinking reaction provides a simple yet highly effective method for preparation of hydrogels to be used in bioengineering.