Showing papers in "Polymer Bulletin in 2007"
TL;DR: In this paper, structural evolution of polyacrylonitrile precursor fibers during preoxidation and carbonization was studied using SEM combined with XRD, FTIR, elemental analysis and density measurement.
Abstract: Structural evolution of polyacrylonitrile precursor fibers during preoxidation and carbonization were studied using SEM combined with XRD, FTIR, elemental analysis and density measurement. Crystallite structure of fibers has been completely changed through the process. Crystallite size of fibers firstly increases before 235°, and then decreases with temperature increasing, whereas crystallinity gradually decreases during preoxidation. The combination between fibrils during preoxidation firstly becomes looser, and then gets denser. Meanwhile fibrils at first grow thicker, followed by getting thinner. Homogeneous and granular fracture surface of the resultant carbon fiber is obtained. Fracture morphology during the preparation undergoes transformation from ductile fracture feature to brittle fracture feature, which corresponds to changes of tensile strength and elongation at break from 0.865 GPa to 3.51 GPa, from 9.8% to 1.7%, respectively.
108 citations
TL;DR: In this article, the radiolytic formation of Ag nanoparticles in crosslinked PVA hydrogel was investigated and the reduction of Ag+ ions was performed using strongly reducing species such as hydrated electrons, propan-2-ol and PVA radicals.
Abstract: The radiolytic formation of Ag nanoparticles in crosslinked PVA hydrogel was investigated. The reduction of Ag+ ions was performed using strongly reducing species such as hydrated electrons, propan-2-ol and PVA radicals. Ag+ ions were efficiently reduced in swollen PVA matrix by PVA radicals. Thermal and thermooxidative properties of radiolytically obtained nanocomposites were affected by the content of nanofiller as well as by different routes of preparation.
65 citations
TL;DR: In this paper, a series of moisture curable polyurethane/polysiloxane (PUSR) copolymers with different end-capping agents were prepared based on amine terminated polysiloxanes (PDMS), poly-1,4-butylene adipate glycol (PBA), 4,4′-diphenylmethane diisocyanate (MDI).
Abstract: A series of moisture curable polyurethane/polysiloxane (PUSR) copolymers with different end-capping agents were prepared based on amine terminated polysiloxane (PDMS), poly-1,4-butylene adipate glycol (PBA), 4,4′-diphenylmethane diisocyanate (MDI). The copolymers were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogarvimetric (TGA), X-ray diffraction (XRD), dynamic mechanical thermal analysis (DMTA), X-ray photoelectron spectroscopy (XPS), surface contact angle and stress–strain measurement. Compared with conventional moisture curable PU the PUSR copolymer showed the better thermal stability and surface properties due to the forming of Si-O-Si crosslinking network and the enrichment of siloxane chains on the surface of films , and the tensile strength was not obviously damaged. DMTA results suggested that micro-phase separation was formed in the PUSR copolymer. It was found that the PUSR copolymer with mixed alkoxysilanes as end-capping agents showed better compromised properties than that with single alkoxysilane.
63 citations
TL;DR: In this paper, a novel blend films of soy protein isolate (SPI) and polyvinyl alcohol (PVA) compatibilized by glycerol were fabricated by preparing a solution, and then casting it on a Teflon-coated metal sheet.
Abstract: Novel blend films of soy protein isolate (SPI) and poly(vinyl alcohol) (PVA) compatibilized by glycerol were fabricated by preparing a solution, and then casting it on a Teflon-coated metal sheet. Mechanical, biodegradation and water vapor permeability of the blend properties were systematically investigated with various methods. SEM analysis results release that the SPI/PVA/glycerol film degrades at a slower rate than pure SPI. The mechanical test showed that the stress at yield point, stress at break point and Young’s modulus were decreased and percentage elongation at yield point and percentage elongation at break point and of SPI/PVA were increased obviously than pure SPI films. The blend plastics were softened and became semi-rigid contributing to the plasticization of glycerol and the crystalline partion of PVA was destroyed by glycerol. Water vapor permeability of SPI/PVA/glycerol showed the minimum at the component of SPI/PVA (100/35) compatibilized by 3.5% of glycerol.
62 citations
TL;DR: In this paper, a modified SEBS elastomer was used to synthesize flexible organic-inorganic hybrid materials, which showed an increased interfacial interaction between organic and inorganic phases.
Abstract: Functional triblock copolymer [polystyrene-b-poly(ethylene-ran-butylene)-b-polystyrene] or SEBS elastomer was used to synthesize flexible organic-inorganic hybrid materials. Modification of elastomer was first achieved via nitration to produce nitrofunctionalized copolymer and its subsequent reduction forming aminofunctionalized copolymer. IR, 1H NMR and 13C NMR spectroscopic analyses provided an evidence of their modified structures. Modified SEBS based hybrid materials were then prepared through solution intercalation technique using layered silicates and in-situ polymerization of metal alkoxides via sol-gel process. In the first attempt, hybrids were prepared by the reinforcement of aminofunctionalized SEBS with organophilic montmorillonite to establish compatibility between organic matrix and inorganic phase. Reinforcement of the modified copolymer was secondly achieved by hydrolytic condensation of tetraethoxysilane using 3-glycidyloxypropyl trimethoxysilane (as a coupling agent) yielding hybrid materials. The chemical interactions between the organic polymer chains and the inorganic networks produced in-situ led to better properties of modified elastomer. Mechanical properties of thin transparent films of these hybrids were measured. Tensile strength of hybrids shows a considerable improvement over pure SEBS as well as aminofunctionalized copolymer in all the systems, which shows an increased interfacial interaction between organic and inorganic phases.
57 citations
TL;DR: In this paper, the shape memory effects of poly(L-lactide) and poly(e-caprolactone) copolymers were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and tensile tests.
Abstract: The thermal properties, crystalline structure and shape memory effects of poly(L-lactide) (PLLA) and its copolymer with poly(e-caprolactone) (PCL) are systematically investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and tensile tests. The influences of composition and intrinsic viscosity on structure and shape memory effects are also revealed. It is found that the PLLA homopolymer and poly(L-lactide-co-e-caprolactone) (PCLA) copolymers exhibit good shape memory effects. The existence of PLLA crystal and amorphous phase play very important roles for shape memory effects. The intrinsic viscosity obviously affects the crystallinity of polymers and further affects the shape memory effects. The shape recovery rate decreases with increasing deformation strain, which is relate to the deformation of PLLA crystal. The recovery stress increase with the increase of the e-CL content and maximum recovery stress is 3.54MPa obtained in the PCLA804 (20wt% e-CL content, Mw=304,400). With the increase of cyclic testing number, the shape recovery rates decrease and the shape retention rates increase at the beginning and then approach to a steady value.
57 citations
TL;DR: This overview focuses on the design, synthesis, and characterization of peptide/protein-containing polymers, which self-assemble into stimuli-sensitive hydrogels, which show a promising future as biomaterials.
Abstract: The overview focuses on the design, synthesis, and characterization of peptide/protein-containing polymers, which self-assemble into stimuli-sensitive hydrogels. Hybrid hydrogels are composed of two classes of molecules, synthetic and biological. They self-assemble from graft copolymers, block copolymers and by association of soluble polymers and protein domains. Genetic engineering provides a powerful tool to produce biomaterials (macromolecules) with precise control of composition, length, and three-dimensional structure. Minimal changes in the composition of the coiled-coil forming protein domains in genetically produced triblock copolypeptides result in dramatic changes in the properties of the copolymers and, ultimately, the self-assembled hydrogels. The application of self-assembling hydrogels as biomaterials has been investigated and has shown a promising future.
53 citations
TL;DR: In this paper, the thermal properties of a series of inorganic-organic diglycidyl ether of bisphenol A/octa(aminpropyl)silsesquioxane (EP/POSS-NH2) composites of were systematically investigated.
Abstract: The thermal properties of a series of inorganic-organic diglycidyl ether of bisphenol A/octa(aminpropyl)silsesquioxane (EP/POSS-NH2) composites of were systematically investigated. These thermal properties included dynamic mechanical properties, glass transition temperature and thermal degradation temperature. Dynamic mechanical analysis (DMA) and Thermogravimetric analysis (TGA) were adopted. Results showed that the incorporation of POSS into epoxy resin could improve the thermal stabilities of epoxy significantly.
53 citations
TL;DR: The synthesis, characterization and rheological properties in aqueous solutions of three different water-soluble associative polymers (AP’s) (telechelic, multisticker and combined) are reported, with respect to the localization of the hydrophobic groups.
Abstract: We report the synthesis, characterization and rheological properties in aqueous solutions of three different water-soluble associative polymers (AP’s) (telechelic, multisticker and combined). Polymer chains consisting of water-soluble polyacrylamides, hydrophobically modified with low amounts of N,N-dihexylacrylamide and a linear hydrophobic initiator. These have been prepared via free radical micellar polymerization. We compare the properties of these different polymers, with respect to the localization of the hydrophobic groups, using steady-flow experiments. In the semidiluted regime we clearly differentiate two different zero-shear viscosity (η0) -vs- concentration (C) behaviors; a first semidiluted regime unentangled, where the viscosity increases strongly and directly with c and a second regime entangled, where the viscosity increases proportionally to C4, independently of the localization of the hydrophobic group.
47 citations
TL;DR: A new fluorescent initiator fluorescein 2-bromoisobyrate (Flu-Br) was synthesized by using Me6TREN as ligand and CuCl as catalyst by atom transfer radical polymerization as mentioned in this paper.
Abstract: A new fluorescent initiator fluorescein 2-bromoisobutyrate (Flu-Br) was synthesized. The use of Flu-Br as initiator, Me6TREN as ligand and CuCl as catalyst by atom transfer radical polymerization allowed for chain-end fluoresceined poly(N-isopropylacrylamide) (Flu-PNIPAM) in one step. The polymerization reached high conversion (65%) and low polydispersity (PDI) (1.15∼1.28). The linearity plot of the Mn,GPC and Mn,NMR against conversion and the low PDI revealed the well-controlled polymerization by ATRP. In addition, N-isopropylacrylamide (NIPAM) was copolymerized with hydrophilic N,N-dimethylacrylamide (DMAM) using Flu-Br initiator by ATRP. By changing the feed ratio of NIPAM to DMAM, it was very easy to obtain thermo-sensitive fluorescent copolymers with proper lower critical solution temperature (36.0±0.2 °C, 38.0±0.2 °C). The pH dependence on fluorescence intensity of Flu-PNIPAM displayed a similar behavior to the parent fluorescein.
43 citations
TL;DR: In this paper, a U-shaped cloud point curve with a lower critical solution temperature (LCST) centered at ∼30∼°C was observed for chitin gels.
Abstract: On heating, alkali chitin solutions undergo phase separation describing a characteristic "U-shaped" cloud point curve with a lower critical solution temperature (LCST) centered at ∼30∼°C. The process is accompanied by gelation of the polymer-rich phase. A different strategy to induce alkali chitin phase separation/gelation is by applying vacuum to the solution at room temperature during aprox. 72∼h. Once washed to neutrality, chitin gels had a degree of acetylation of ∼30-40% (i.e. they were converted into chitosan). On cooling, these gels exhibit an exothermic peak in micro-DSC and a depression in G " and tan δ traces, evidencing a volume phase transition centered at ∼20∼°C. This transition is observed only within a narrow range of pH ∼7.3-7.6. Variation in the mechanical response as a result of cyclic stepwise changes in temperature between 50 and 0∼°C at pH values from 7.3-7.6, revealed that the G' modulus of the gels increases on heating and decreases on cooling, a behavior that persists over at least four cycles of temperature change. Only marginal changes in G' at pH 8.0 and not at all at pH 12.0 are observed. By contrast, the variation of G " persists throughout the range of pH. This behavior is rationalized in terms of the existence of a fine balance between hydrophobic and hydrophilic interactions at varying temperature and pH, thus effectively controlling swelling and shrinking states of the gel network. The degree of swelling at pH 7.6 reaches a minimum at ∼22-25∼°C. © Springer-Verlag 2007.
TL;DR: Quaternized carboxymethyl chitosan (QCMC) was prepared through the grafting reaction of carboxy methyl chitosa with 3-chloro-2-hydroxypropyl trimethylammonium chloride (CTA) in 2-propanol medium under basic condition as discussed by the authors.
Abstract: Quaternized carboxymethyl chitosan (QCMC) was prepared through the grafting reaction of carboxymethyl chitosan (CMC) with 3-chloro-2-hydroxypropyl trimethylammonium chloride (CTA) as a quaternizing agent in 2-propanol medium under basic condition. The synthetic conditions for QCMC were as follows: 40.0% of NaOH aqueous solution as catalyst; reaction temperature, 60.0 °C and reaction time, 10.0 h; NaOH/CMC, 0.50; CTA/CMC, 1.50 (mass ratio). The characterization by FT-IR and 1H NMR demonstrated that QCMC was a typical amphoteric chitosan derivative in which the carboxymethyl group and the quaternary ammonium group were both introduced into the chitosan molecular chain. QCMC was applied to flocculate a simulated wastewater containing 40.15 mg/L Cd(II) or 15.62 mg/L Cr(VI) respectively. The results indicated that the appropriate pH value for removal of Cd(II) and Cr(VI) were ca 8.5 and 5.0, and the appropriate corresponding mass concentrations of QCMC was 140 mg/L and 120.0 mg/L, respectively. Under these conditions, the removal ratio of Cd(II) and Cr(VI) may reach 99.7% and 94.4%, respectively.
TL;DR: In situ gelling system prepared in this study can be used for a weekly peptide delivery system and it seemed that surface gelation was the main cause of drug release control.
Abstract: One of the main routes of peptide and protein delivery is parenteral The need for daily or repetitive injection of these parenteral formulations is the main cause of patient non-compliance The objective of this study was to prepare a controlled delivery system for peptide and proteins to increase patient compliance Biodegradable triblock copolymers of PLGA and PEG (PLGA-PEG-PLGA) were synthesized and characterized using various content of glycolide Solutions of PLGA-PEG-PLGA containing calcitonin as a model peptide were prepared and drug release from the sol-gel systems was evaluated in two different incubation conditions Zero order release kinetics was achieved for up to 100 hours No significant burst release effect was observed It seemed that surface gelation was the main cause of drug release control The release data fitted to Higuchi’s modeling and showed good correlation It can be concluded that in situ gelling system prepared in this study can be used for a weekly peptide delivery system
TL;DR: In this paper, Dendritic star poly(L-lactide)s (PLLAs) were prepared by ring opening polymerization using a hyperbranched aliphatic polyester as the core.
Abstract: Dendritic star poly(L-lactide)s (PLLAs) were prepared by ring opening polymerization using a hyperbranched aliphatic polyester as the core. The stars were characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance spectroscopy (NMR). The result shows the star PLLAs have narrow molecular weight distribution and the length of arms can be well controlled in terms of the molar ratios of L-lactide to the initiator. The structure and thermal properties of the star polymers were investigated by means of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). XRD shows that the formation of star structure does not alter the structure of crystal of PLLA. The results of DSC indicate that the glass transition temperature (Tg) and the crystallinity of the star polymers increased with increasing the lengths of arms. It is identified that the crystallization of PLLA was effectively suppressed by the formation of star topology.
TL;DR: Microwave assisted glycolysis of polyurethane (PU) flexible foam wastes at atmospheric pressure in "split-phase" condition is reported in this article, where glycerin, sodium and potassium hydroxides were used as gating agent and catalysts, respectively.
Abstract: Microwave assisted glycolysis of polyurethane (PU) flexible foam wastes at atmospheric pressure in “split-phase” condition is reported. Glycerin, sodium and potassium hydroxides were used as glycolysing agent and catalysts, respectively. Decomposition and dissolution of the foam was studied in different reaction condition. Results showed successful polyol recovering in short reaction time in comparison with conventional heating method. Finally, the recycled polyol was identified by FT-IR, 1HNMR and 13CNMR spectroscopy methods, being compared with virgin one.
TL;DR: In this paper, a review is given concerning the nature of crosslinks in thermoreversible gels and eight possibilities of crosslink formation in these gels can be found, e.g. by means of crystallisation of parts of polymer molecules, by liquid-liquid phase separation in solution and in bulk, by hydrogen bridging, by complexation of polymer chains, by helix formation, by chemical equilibrium reaction or by interactions between side-chains.
Abstract: A review is given concerning the nature of crosslinks in thermoreversible gels. In these gels the crosslinks can be formed e.g. by means of crystallisation of parts of polymer molecules, by liquid-liquid phase separation in solution and in bulk, by hydrogen bridging, by complexation of polymer chains, by helix formation, by chemical equilibrium reaction or by interactions between side-chains. One example will be given for each of these eight possibilities of crosslink formation.
TL;DR: In this article, two-step processing of high density polyethylene (HDPE) and ultra high molecular weight polyethylenes (UHMWPE) was used for blown films.
Abstract: Blends of high density polyethylene (HDPE) and ultra high molecular weight polyethylene (UHMWPE) were prepared by two-step processing way. Middle molecular weight polyethylene (MMWPE) as a fluidity modifier and compatilizer was added into UHMWPE in the first step, and then modified UHMWPE and HDPE were blending extruded to prepare the HDPE/UHMWPE/MMWPE blends used for blown films. The mechanical test of the blown films revealed that when the content of MMWPE in modified UHMWPE was 40wt% and the content of UHMWPE in the blends was 20 wt%, the film had the optimal mechanical properties. The tensile strength and tear strength of the film increased by 50% and 21%, respectively, compared with those of pure HDPE film. Rheological curves indicated that the melt torque and the apparent viscosity of the HDPE/UHMWPE/MMWPE blends made by two-step processing way both greatly reduced than other blends. The results from DSC suggested that the blends by two-step processing way may form more stable and perfect co-crystallization. PLM (polarized light microscopy) and SEM micrographs revealed that two-step processing way can improve the surface morphology of the films and make the dispersion of UHMWPE particles in HDPE increase.
TL;DR: In this article, the thermal properties of trans-polynorbornene, cis-polynbornene and hydrogenated polynorbornene were examined and its reversibility tested.
Abstract: The thermal properties of trans-polynorbornene, cis-polynorbornene and hydrogenated polynorbornene were examined and its reversibility tested. Trans-polynorbornene samples, formed in various solvents, exhibit a softening range, from ambient temperature until 375 °C. However, syndiotactic cis-polynorbornene samples show a narrower melting range (between 150 and 375 °C). The fusion enthalpies of cis-polynorbornene samples are around 300-400 J/g. The temperature of decomposition is ca. 456 °C (minimum peak DSC) for trans-polynorbornene and ca. 466 °C, 10 °C higher, for cis-polynorbornene. The solvent used for the polymerization of norbornene has a negligible influence in the melting temperature range or in the decomposition temperature. The treatment with 2,6-di-tert-butyl-4-methyl-phenol during the isolation of polynorbornene leads to materials with different thermal properties. Trans-polynorbornene isolated without 2,6-di-tert-butyl-4-methyl-phenol exhibited an exothermic peak accompanied by an slight increase in weight (1-2%), while samples treated with 2,6-di-tert-butyl-4-methyl-phenol do not show these features.
TL;DR: In this paper, it was shown that the addition of 5 wt. % of organo-modified montmorillonite into recyclate leads to a 3D network structure with secondary plateau of G' at lowest frequencies.
Abstract: Formation of physical network in PET/organoclay nanocomposites leads to significant improvement of processing and utility properties. The state of dispersion of silicate platelets in PET by melt mixing depends on shear forces as well on surface chemical treatment of the filler. The level of dispersion was determined by X-ray diffraction analysis and transmission electron microscopy. Melt rheology was used to examine the presence of network particles. It was shown that the addition of 5 wt. % of organo-modified montmorillonite into recyclate leads to a 3D network structure with secondary plateau of G’ at lowest frequencies. XRD and TEM experiments supported the conclusion.
TL;DR: In this article, the swelling behavior in water-dioxane mixtures of hydrogels containing N-isopropylacrylamide (NIPAM) and N,N-dimethylacryamide (DMAM) is investigated as a function of dioxane content and temperature.
Abstract: The swelling behaviour in water-dioxane mixtures of hydrogels containing N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMAM) is investigated as a function of dioxane content and temperature. The composition of the hydrogels, reported as the mol percentage of DMAM units, x, varies from 0 up to 100. It is found that the hydrogel containing only NIPAM units, GPNIPAM, deswells significantly in the water-rich region, while the hydrogel containing only DMAM units, GPDMAM, presents a pronounced deswelling in the dioxane-rich region. This deswelling becomes less significant with decreasing the DMAM content x, when using the hydrogels of the copolymers GP(NIPAM-co-DMAMx). This swelling behaviour of the hydrogels results from a combination of the lower critical solution temperature-type cononsolvency behaviour of poly(N-isopropylacrylamide) with the upper critical solution temperature-type cononsolvency behaviour of poly(N,N-dimethylacrylamide) in water-dioxane mixtures.
TL;DR: In this paper, the effects of steady shear flows on intermolecular interactions in dilute and semidilute aqueous solutions of hyaluronic acid (HA) are reported.
Abstract: Effects of steady shear flows on intermolecular interactions in dilute and semidilute aqueous solutions of hyaluronic acid (HA) are reported. Pronounced shear thinning behavior is observed for solutions of HA at high shear rates, and no hysteresis effects are detected upon the subsequent return to low shear rates. With the aid of the asymmetric flow field-flow fractionation (AFFFF) technique, it is shown that mechanical degradation of the polymer does not take place in these shear viscosity experiments, even at high shear rates. The low shear rate viscosity of a semidilute HA solution decreases by approximately 40% when the temperature is increased from 10 °C to 45 °C. It is shown that when a dilute HA solution is exposed to a low fixed shear rate (0.001 s-1), a marked viscosification occurs in the course of time and prominent intermolecular complexes are formed. It is argued that shear-induced alignment and stretching of polymer chains promote the evolution of hydrogen-bonded structures, where cooperative zipping of stretched chains generates a network. At a higher constant shear rate (0.1 s-1), the viscosity decreases as time goes because of the alignment of the polymer chains, but the higher shear flow perturbation prevents the chains in dilute solutions from building up association complexes. The viscosity of an entangled HA solution is not changed in the considered time window at this shear rate, but the network structures breakdown at the highest shear rate (1000 s-1), and then they are restored upon return to a low shear rate.
TL;DR: In this article, the influence of blend composition and processing conditions on phase morphology development of polypropylene (PP)/ethylene-octene copolymer (EOC) was investigated by scanning electron microscopy (SEM) in detail.
Abstract: Blends of polypropylene (PP)/ethylene-octene copolymer (EOC) was studied. The influences of blend composition and processing conditions on phase morphology development of the blends were investigated by scanning electron microscopy (SEM) in detail. The minor composition formed the dispersed phase and the major composition formed the continuous phase, and the blends formed interpenetrating co-continuous morphology just at the intermediate concentration. The effect of concentration on phase coarsening was explained by the increase of dispersed phase coalescence with dispersed phase concentration’s increase. Phase coarsening and phase fine dispersing were studied. The effect of mixing time on phase morphology development of the blends was investigated, the PP/EOC (80/20) blends has already formed a well-established droplet/matrix morphology after 1.5 min of mixing, and the similar blends phase morphology persisted until 11 min of mixing. The most prominent phenomenon is that the dispersed phase domain deformed from spherical droplet to elliptical droplet, even fibrillar or sheet morphology as the rotor speed increased. The increase of shear rate and elasticity ratio was applied to interpret this phenomenon.
TL;DR: Entirely amino acid-based polymers were prepared by side-chain attachment to polysuccinimide derived from the thermal polycondensation of aspartic acid that makes them promising candidates as base materials of controlled drug delivery systems.
Abstract: Entirely amino acid-based polymers were prepared by side-chain attachment to polysuccinimide derived from the thermal polycondensation of aspartic acid. Following deprotonation of various amino acid ester hydrochlorides by a secondary amine, the restored primary amino groups initiated the ring-opening of succinimide to form amide bonds. 1H and 13C NMR measurements revealed that the mole fraction of the introduced amino acid side chains could be controlled by the reaction time, while no hydrolysis of methyl ester groups was observed. The synthesized polymers contain exclusively amino acids, which makes them promising candidates as base materials of controlled drug delivery systems.
TL;DR: In this article, a split-phase glycolysis of isocyanate derived cold cure foams, with glycerin as a new gating agent, is reported.
Abstract: In this communication, “Split-Phase” glycolysis of isocyanate derived cold cure foams, with glycerin as a new glycolysing agent, is reported. The process was simple and economically attractive among material recycling processes. Glycerin was used as a destroying solvent and sodium hydroxide as the catalyst, respectively. In order to study the ability of glycerin as a glycolysing agent and for selecting a system to obtain high quality recovered polyol, the effects of various reaction times were investigated and the characterization and comparison of upper and lower phases were performed by using instrumental (FT-IR, 1HNMR and 13CNMR) and classical methods.
TL;DR: In this article, group transfer polymerization (GTP) chemistry was employed for the preparation of polymethacrylate networks of controlled structure (quasi-model networks) of three different types: (a) regular quasi-model network, in which all polymer chains were linked at their ends, leaving, in principle, no free chain ends, (b) crosslinked star polymer quasi model networks, where star polymers were interlinked via half of their chains, letting the other half free (dangling), and (c) shell-crosslinked polymer quasi-
Abstract: Group transfer polymerization (GTP) chemistry was employed for the preparation of polymethacrylate networks of controlled structure (quasi-model networks) of three different types: (a) regular quasi-model networks, in which all polymer chains were linked at their ends, leaving, in principle, no free chain ends, (b) crosslinked star polymer quasi-model networks, in which star polymers were interlinked via half of their chains, letting the other half free (dangling), and (c) shell-crosslinked polymer quasi-model networks, in which the outer part of the network contained polymer arms (dangling chains) Combination of hydrophilic and hydrophobic monomers led to amphiphilic networks whose aqueous swelling behavior was characterized gravimetrically
TL;DR: In this article, a superswelling poly [N-vinyl pyrrolidone/2-(methacryloyloxyethyl)trimethyl ammonium chloride], poly(NVP/METAC) hydrogels were prepared by free radical polymerization using ethylene glycol as crosslinker.
Abstract: A superswelling poly [N-vinyl pyrrolidone/2-(methacryloyloxyethyl)trimethyl ammonium chloride], poly(NVP/METAC) hydrogels were prepared by free radical polymerization using ethylene glycol dimethacrylate as crosslinker. The hydrogels were characterized by FT-IR spectroscopy and their surface morphology was determined using Scanning Electron Microscope (SEM). The influence of feed composition of both the monomers and crosslinker on equilibrium swelling and dye adsorption properties of the hydrogels were examined. The equilibrium swelling ratio and binding ratio of the hydrogel/dye systems greatly depends on the METAC and crosslinker concentration in the gels. The effects of pH of the medium and initial dye concentration on the adsorption were also studied. The binding ratio of the hydrogel/dye system increases in the following order: OR-II>RO-14>RO-13.
TL;DR: In this paper, the effect of zinc stearate (ZnSt2) as a dispersion additive on the morphology and properties of the ABS/MHSH composites was studied.
Abstract: Halogen-free and flame-retardant acrylonitrile–butadiene–styrene copolymer (ABS) composites were prepared using magnesium hydroxide sulfate hydrate (MHSH) whisker as a flame retardant, and the effect of zinc stearate (ZnSt2) as a dispersion additive on the morphology and properties of the ABS/MHSH composites was studied. The morphology observation by using scanning electronic microscope (SEM) indicates that the addition of zinc stearate could improve the dispersion of the MHSH whisker in ABS matrix. Cone analysis results show that the heat release rate (HRR) and mass loss rate (MLR) of the composites decrease considerably with increasing MHSH whisker content. The composite with zinc stearate has lower HRR than the composite without zinc stearate, indicating the better dispersion of MHSH whisker could improve the flame retardancy of ABS composites. SEM observation results show that the char residue of ABS/MHSH composites retain its fibrous appearance. Thermogravimetric analysis (TGA) shows that the presence of MHSH enhanced thermal stability of the composites obviously. The viscoelastic behavior of the composites was measured by using a parallel plate rheometer. With increasing MHSH whisker content, the viscosity, storage modulus of the composites increase at low frequency zone, and ABS/MHSH composites exhibit more distinct solid-like response at terminal zone than ABS. The presence of zinc stearate leads to slight increases in the storage modulus.
TL;DR: In this paper, the synthesis of in-situ hydrophobic functionalized ZnO nanoparticles via an emulsion process is systematically investigated, and different parameters are varied, such as precursor salt concentration and ultrasonification, to optimize the size and the size distribution of the particles.
Abstract: The synthesis of in-situ hydrophobic functionalized ZnO nanoparticles via an emulsion process is systematically investigated. Different parameters are varied, such as precursor salt concentration and ultrasonification, to optimize the size and the size distribution of the ZnO particles. Particles with a size below 25 nm and surrounded by a hydrophobic polymer shell can be easily obtained. The influence of the polymeric shell on the compatibility with different polymeric matrices is described. Due to the small size of the inorganic particles and the excellent hydrophobization, highly transparent inorganic/organic nanocomposites can be obtained by spin-coating and extrusion.
TL;DR: In this paper, the authors used FTIR, X-ray diffraction, elemental analysis, ultramicrotomy and optical microscopy to study the slow evolution of stabilization indices and structure changes with increasing the temperature in the rearmost zone.
Abstract: Temperature in the rearmost stabilization zone has an important impact on the final stabilization degree of PAN precursor fibers during industrial successive pre-oxidation and on their structure and properties. FTIR, X-ray diffraction, elemental analysis, ultramicrotomy and optical microscopy were used to study the slow evolution of stabilization indices and structure changes with increasing the temperature in the rearmost zone. The results show that cross linking reaction happens above 240 °C in the rearmost stabilization zone, leading to a quick increase of oxygen content and aromatization index and the formation of cross-linking rigid structure. Especially for the sample treated at 275 °C, the cross-linking structure induces a compact sheath layer in the fiber which impedes the oxygen atoms diffusion inward. By changing the temperature in the rearmost stabilization zone, the oxygen content, chemical structure and aromatization index can be accurately controlled.
TL;DR: O,O'-diallylbisphenol A (BA), allyl epoxy resins and epoxy acrylate resins are adopted to copolymerize with 4,4'-bismaleimidodiphenyl methane (BDM) resins.
Abstract: O,O’-diallylbisphenol A (BA), allyl epoxy resins and epoxy acrylate resins are adopted to copolymerize with 4,4’-bismaleimidodiphenyl methane (BDM) resins and modify mechanical properties and processing charicteristics. The new modified BMI resin systems have more than two times improved impact strength without a great decrease in excellent dielectric properties or thermal and hot–wet resistance of neat BDM resin. Composites based on modified BMI resins and reinforced by glass fibre and quartz fibre possess excellent mechanical properties. The fracture surfaces of the composites are examined by scanning electron microscopy (SEM). It is indicted that modified BMI resin matrix composites put up typical toughness rupture and the adhesion efficiency in interface of composites is fine. When the test frequency scope is from 1 GHz to 20 GHz, the dielectric constant and dielectric loss of composites almost hold the line. After 100 h in boil water, mechanical and dielectric properties of composites are higher than 85% retention of their original values.