Rheological behavior of low molecular weight polystyrene composites containing monodisperse crosslinked polystyrene beads

Steady shear viscosities and dynamic moduli of polymer composites, consisting of crosslinked polystyrene beads and low molecular weight polystyrene matrix, were measured in a cone-and-plate rheometer at different temperatures. Viscosities and dynamic moduli were found to be very sensitive to filler loading and measurement temperature. Steady shear viscosities of 30% and 40% loaded low molecular polystyrene composites showed a power-law behavior over the entire range of shear rates. Storage and loss moduli were initially linear with frequency on double logarithmic plots, with limiting slopes of 0.3 and 0.1. At high concentration of filler particles, they showed a flat plateau at low frequencies, indicating that these systems exhibit a yield behavior. A 20% PS composite loaded with beads of high crosslink densities resulted in poor dispersion of beads as a result of poor dispersion of particles. PS beads 1.16 μm in diameter showed a higher viscosity. It is due to the apparent increase in loading resulting from broken particles. At low measurement temperature, filler effects were suppressed by high viscosity matrix and showed a similar rheological behavior to high molecular weight by PS matrix. We suggest that rheological behavior reflects the state of dispersion of beads in the matrix.     

Effects of flake graphite on property optimisation in thermal conductive composites based on polyamide 66

In this study, in order to improve the thermal conductivity of polyamide 66(PA66), PA66 composites filled with flake graphite (FG) were prepared by twin-screw extruder. Effects of filler content, particle size and particle size mixing on thermal conductivity, mechanical and rheological properties of the composites were investigated. The results showed that as FG content increased from 0 to 50 wt-%, thermal conductivity of the composites filled with 100 μm FG gradually increased, whereas mechanical properties and rheological properties decreased. At 50 wt-% loading, thermal conductivity reached 3.07 W/(m K). With the increase of particle size, thermal conductivity and rheological properties of the composites improved, but mechanical properties increased first and then decreased. The composite filled with 100 μm FG had relatively optimal mechanical properties. Particle size mixing can improve thermal conductivity and the maximum value was achieved in the 1:2 mass ratio of 20 and 100 μm particles.     

Cryostructuration of polymer systems. XXIV. Poly(vinyl alcohol) cryogels filled with particles of a strong anion exchanger: Properties of the composite materials and potential applications

A composite material produced from a poly(vinyl alcohol) cryogel with entrapped particles of the strong anion‐exchange resin Amberlite is presented. The properties of the composite material depended strongly on whether the resin was used in OH^? form or Cl^? form. The ion‐exchange filler in OH^? form caused both a significant reinforcement of the composite material and an increase in the gel fusion temperature. These effects were thought to be associated with the additional ionic bonding between the continuous and disperse phases. Beads 200–600 μm in size were prepared from the composite material and used in expanded‐bed ion‐exchange chromatography for the capture of the negatively charged solutes benzoate and lactate from the suspension of negatively charged cells. The plausibility of the approach has been demonstrated on model systems composed of yeast cells and benzoate and with a real fermentation broth produced after lactic acid fermentation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 529–538, 2005     

Preparation and characterization of poly(vinyl alcohol) cryogel‐silver nanocomposites and evaluation of blood compatibility,cytotoxicity, and antimicrobial behaviors

In this investigation, cryogels composed of poly(vinyl alcohol) (PVA) were prepared by repeated freeze‐thaw method. The prepared cryogels served as templates for producing highly stable and uniformly distributed silver nanoparticles via in situ reduction of silver nitrate (AgNO₃) using alkaline formaldehyde solution as reducing agent. The structure of the PVA/Ag cryogel nanocomposites was characterized by a Fourier transform infrared and Raman spectroscopy. The morphologies of pure PVA cryogels and PVA/Ag nanocomposites were observed by a scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The SEM analysis suggested that cryogels show a well defined porous morphology whereas TEM micrographs revealed the presence of nearly spherical and well separated Ag nanoparticles with diameter about 100 nm. XRD results showed all relevant Bragg's reflections for crystal structure of silver nanoparticles. The amount of silver in cryogel nanocomposites and thermal stability were determined by inductively coupled plasma atomic emission spectrometry (ICP‐AES) and thermogravimetric analysis measurements. Mechanical properties of nanocomposites were observed in terms of tensile strength. The antibacterial studies of the synthesized nanosilver containing cryogels showed good antibacterial activity against both gram‐negative and gram‐positive bacteria. The prepared PVA/Ag nanocomposites were also investigated for swelling and deswelling behaviors. The results reveal that both the swelling and deswelling process depends on the chemical composition of the cryogel silver nanocomposites, number of freeze‐Thaw cycles and pH and temperature of the swelling medium. The biocompatibility of the prepared nanocomposites was judged by in vitro methods of percent hemolysis and protein (BSA) adsorption. POLYM. COMPOS., 36:1983–1997, 2015. © 2014 Society of Plastics Engineer     

Removal of organic water pollutant using magnetite nanomaterials embedded with ionic copolymers of 2‐acrylamido‐2‐methylpropane sodium sulfonate cryogels

Magnetite cryogel composites as macroporous crosslinked matrices have received wide attention and attract much interest in the water purification and desalination industry. They can be used to produce effective adsorbents with high adsorption rate, capacity and desorption for water pollutants. In this work, the incorporation of magnetite nanoparticles into cryogels by the in situ method is proposed to increase the dispersion of nanoparticles in the gel composites and to produce effective magnetic materials with high adsorption capacities. Ionic sodium‐2‐acrylamido‐2‐methylpropane sulfonate (Na‐AMPS) monomer was selected to prepare cryogels as the homopolymer or copolymers with 2‐hydroxyethyl methacrylate (HEMA) or N‐vinyl pyrrolidone (VP) by the crosslinking polymerization technique in the frozen state. Magnetite nanoparticles were introduced into the cryogel by the in situ co‐precipitation method after introducing iron cations into the cryogel networks. The surface morphologies, crystal structure, magnetite content, thermal stability and magnetic properties were determined for the cryogels and their magnetite composites. The magnetite cryogel composites show significantly enhanced methylene blue dye removal in short times with higher adsorption efficiencies and good regeneration to form an effective adsorbent for water treatment. © 2017 Society of Chemical Industry     

Preparation,microstructure, and thermal properties of phenolic cryogel composite plates

Phenolic hydrogel plates were successfully fabricated by a microemulsion‐templated sol gel polymerization method. Then, the phenolic cryogel plates were obtained from the hydrogel plates freeze‐dried by the lyophilizer. Ultimately, the phenolic cryogel plates (PCPs) and fiber glass cloth layers were compounded to be the phenolic cryogel composite plates (PCCPs). The pore morphology, mechanical, and thermal properties of the composites were investigated. The experimental results showed that the aerogels made by freeze‐drying method and disposed by acetic acid and tert butyl alcohol had the best microstructure. In addition, it was discovered that the tensile strength of the plates had equally increased for approximately eight times after compounding with the glass fiber cloth layers and the mechanical properties of the 20 wt% and 25% solid content PCPs achieved the optimal value compared with PCPs of other contents. Moreover, it was found that the cryogels had excellent thermostability, and their thermal conductivity decreased with the reducing of the solid contents, what's more, the joining of cloth layers had the increased the composites’ thermal conductivity to some degree. Finally, considering the requirement of low density, good mechanical, and thermal performance, the 20 wt% solid content PCCP had the best comprehensive performance compared with others. POLYM. COMPOS., 38:2294–2300, 2017. © 2015 Society of Plastics Engineers     

内嵌SiO_2纳米颗粒的超大孔复合晶胶的制备(英文)

Supermacroporous composite cryogels embedded with SiO2 nanoparticles were prepared by radical cryogenic copolymerization of the reactive monomer mixture of acrylamide(AAm) and N,N-methylene-bis-acrylamide(MBAAm) containing SiO2 nanoparticles(mass ratios of nanoparticles to the monomer AAm from 0.01 to 0.08) under the freezing-temperature variation condition in glass columns.The properties of these composite cryogels were measured.The height equivalent to theoretical plate(HETP) of the cryogel beds at different liquid flow rates was determined by residence time distribution(RTD) using tracer pulse-response method.The composite cryogel matrix embedded with the mass fraction of SiO2 nanoparticles of 0.02 presented the best properties and was employed in the following graft polymerization.Chromatographic process of lysozyme in the composite cryogel grafted with 2-acrylamido-2-methyl-1-propanesulfonic acid(AMPSA) was carried out to evaluate the protein breakthrough and elution characteristics.The chromatography can be carried out at relatively high superficial velocity,i.e.,15 cm·min-1,indicating the satisfactory mechanical strength due to the embedded nanoparticles.     

Thermal Decomposition of Energetic Materials 86. Cryogel Synthesis of Nanocrystalline CL‐20 Coated with Cured Nitrocellulose

An unusual energetic composite, in which spherical nano‐dimensional particles of CL‐20 were uniformly coated with HDI‐cross‐linked nitrocellulose, was synthesized by the sol‐gel to cryogel method. Up to 90% solid loading was achieved. The particle size of CL‐20 was determined to be in the range of 20–200 nm by transmission electron microscopy, atomic force microscopy, and X‐ray powder diffraction. The decomposition characteristics of the composite were investigated by DSC and T‐jump/FTIR spectroscopy. The decomposition properties were controlled mostly by nitrocellulose until the percentage of CL‐20 was well above 50%. The drop weight impact sensitivity of the cryogels was essentially independent of the composition.     

Multifunctional PMMA-Ceramic composites as structural dielectrics

We describe the influence of calcium copper titanate (CCTO), and montmorillonite (MMT) on the thermo-mechanical and dielectric properties of poly(methyl methacrylate) PMMA-based composites prepared by an in-situ, thermally activated, radical polymerization for multifunctional structural capacitor applications. MMT was used for its ability to disperse and suspend the CCTO particles through the generation of viscous monomer slurries. X-ray diffraction (XRD) measurements together with transmission electron microscopy (TEM) analysis revealed that the MMT platelets were present in both intercalated and exfoliated morphologies within the polymer matrix. The filler addition was found to improve the thermal stability and the glass transition temperature of PMMA in the composites. Furthermore, the elastic stiffness and dielectric constant of the resultant composites were observed to increase monotonically with filler loading. By contrast, the dielectric breakdown strength of the composite samples was found to diminish with increasing filler loading.     

Complexation of macroporous amphoteric cryogels based on N,N‐dimethylaminoethyl methacrylate and methacrylic acid with dyes,surfactant, and protein

Macroporous amphoteric cryogels based on N,N‐dimethylaminoethylmethacrylate and methacrylic acid p(DMAEM‐co‐MAA) crosslinked by N,N′‐methylenebisacrylamide (MBAA) were synthesized by radical copolymerization of monomer mixtures in cryoconditions. The structure and morphology of cryogels were evaluated by FTIR and SEM. Cryogels exhibited interconnected porous structure with pore size ranging from 40 to 80 µm, which depended on their crosslinking degree. The value of the isoelectric point (IEP) of equimolar amphoteric cryogel determined from the water flux was equal to 4.4, while the IEP of cryogel with the excess of DMAEM units was equal to 7.1. The mechanical strength of equimolar amphoteric cryogels increases with increasing amount of crosslinking agent. The complexation ability of amphoteric cryogels with respect to surfactant, dyes, and protein was demonstrated. The adsorption isotherms with respect to anionic surfactant—sodium dodecylbenzene sulfonate (SDBS) and protein—lysozyme correspond to Langmuir equation, while adsorption isotherms of anionic and cationic dyes—methylene blue (MB) and methyl orange (MO) are well described by Freundlich equation. It was found that the binding ability of p(DMAEM‐co‐MAA) with respect to various low‐ and high‐molecular weight compounds changes in the following order: SDBS > lysozyme ? MO > MB. The preferential adsorption of MB from the mixture of protein and MB was shown. The quantitative release of protein, surfactant and dye molecules from the matrix of cryogels takes place at the IEP of cryogel. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43784.     

Study of cryostructuration of polymer systems. XVII. Poly(vinyl alcohol) cryogels: Dynamics of the cryotropic gel formation

Freeze‐thaw treatment of concentrated (>5 g/dL) aqueous solutions of poly(vinyl alcohol) (PVA) (MW 115,000; DD ≈100%) resulted in the formation of opaque gels. The extent of such a cryostructuration process was exhibited in the rheological properties of similar PVA cryogels. The gels' strength depended on the initial polymer concentration in the solution to be frozen and on the conditions of a cryogenic influence. The key factor was the defrostation dynamics: the slower the thawing rate, the stronger the cryogel sample formed, provided other parameters of the process were identical. The observation for the kinetics of the freeze‐thaw–induced gel formation revealed the extreme character of the temperature dependence of the efficacy of PVA cryotropic gelation, the maximum point being in the vicinity of −2°C. It was shown that the effect of the strengthening of PVA cryogels prepared by means of a single‐cycle cryogenic treatment could be reached either with use of as slow as possible thawing regimes, or by the prolonged frozen storage of the samples at “high” subzero temperatures. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2017–2023, 2000     

Microcellular Conductive Carbon Black or Graphene/PVDF Composite Foam with 3D Conductive Channel: A Promising Lightweight,Heat-Insulating,and EMI-Shielding Material

In this study, a lightweight microcellular carbon-based filler/poly(vinylidene fluoride) (PVDF) composite foam is fabricated with a 3D conductive network that is thermally insulating, electrically conductive, and fabricated on a large scale. This composite can be used for high-efficiency thermal insulation and electromagnetic interference (EMI) shielding applications. The prepared composite demonstrates low density, high electrical conductivity, and excellent thermal insulation properties. The structure and density of the conductive network and the carbon-based filler content has a significant influence on the electrical conductivity of the prepared composite foam. Although the composite comprises microcellular PVDF beads of the same density, the conductivity of the composite-comprising strip beads is greater than that comprising spherical beads. In the same conductive network structure, as the size of the microcellular PVDF beads decrease, the conductive network becomes denser, which results in a higher conductivity. Furthermore, with an increase in the conductive filler content, the conductivity improves significantly. Excellent EMI shielding materials with optimal filler content and particle shapes, exhibiting EMI shielding effectiveness of up to 40–50 dB, are developed. The prepared composite foam possesses excellent application potential in the fields of ultra-light thermal insulation, conductivity, and EMI shielding.     

Composites of high density polyethylene and different grades of calcium carbonate: Mechanical,rheological, thermal,and morphological properties

Calcium carbonate (CaCO₃)/high density polyethylene (HDPE) composites were prepared in a HAAKE twin screw extruder, using the experimental conditions defined by the factorial experimental design presented in a prior study. In this study, the effect of different grades (Ca₁ and Ca₂) and CaCO₃ content (varying from 0 to 15 wt %) on the mechanical, rheological, thermal, and morphological properties was evaluated. The results showed that the addition of the filler provoked a decrease on the impact strength, stress at break, and yield stress properties in relation to the pure HDPE. A consequent increase on the modulus of elasticity, indicating an increase on the rigidity of the composite, was observed. It was also verified a tendency to increase the toughness and the viscosity of the composites as CaCO₃ was added. Scanning electron micrographs showed that as the filler was incorporated to HDPE matrix, CaCO₃ particles tended to agglomerate, especially that grade constituted of particles of smaller size. The thermal analysis showed that the addition of mineral filler caused a decrease on the crystallinity degree. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2559–2564, 2006     

Influence of grafting conditions on the properties of polyacrylamide-based cation-exchange cryogels grafted with 2-acrylamido-2-methyl-1-propanesulfonic acid

The effects of grafting conditions on the properties of a novel cation-exchange cryogel by grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) onto polyacrylamide-based cryogel (pAAm cryogel) using potassium diperiodatocuprate (Cu(III) solution) as initiator were investigated experimentally. The basic cryogels were saturated with the initiator solution followed by the solution of monomers to get the expected sulfo groups under various grafting conditions, such as concentrations of monomers and initiator, graft reaction time, graft temperature and the volume ratio of Cu(III) to NaOH. The results showed that these factors influenced the liquid dispersion behaviors and the flow resistance as well as the protein binding capacity of the grafted cryogels. Protein binding capacity increased with the increase of concentration of AMPSA and Cu(III), the graft temperature and the graft reaction time in a wide range under the present conditions. Compared with these factors, the volume ratio of Cu(III) to NaOH in the initiator solution in the considered situations had a relatively weaker influence on the cryogel microstructures and protein binding capacity. The maximum binding capacity of lysozyme reached 2.5 mg/mL cryogel in these grafted cryogels.     

Preparation and characterization of polyacrylamide cryogels produced from a high‐molecular‐weight precursor. I. Influence of the reaction temperature and concentration of the crosslinking agent

A new type of cryogel was prepared through a reaction of high‐molecular‐weight polyacrylamide (viscosity‐average molecular weight ≈ 3 × 10⁶ Da) with glutaraldehyde in a moderately frozen aqueous medium. The influence of the crosslinking agent concentration and temperature of the reaction on the gel fraction yield, swelling characteristics, and morphology of the cryogels was investigated. The dependence of the gel fraction yield on the reaction temperature was bell‐shaped. The recognized regularities of the formation of this new type of polyacrylamide cryogel based on a high‐molecular‐weight precursor were very similar to those observed earlier for polyacrylamide cryogels synthesized through the cryopolymerization of monomeric precursors. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Low-cost production of mesoporous carbon/carbon composite cryogels

A carbon/carbon (C/C) composite cryogel was prepared by dispersing cotton fibers (CF) in a resorcinol and formaldehyde (RF) sol, followed by solvent exchange with t-butanol, freeze drying and pyrolysis under inert atmosphere. The mass ratio of CF to RF was increased from 0% up to 25% to observe the mesopore structure change of C/C composites under a selected RF synthesis condition. The porous structures were characterized by nitrogen adsorption and mercury porosimetry, and their structure was observed by a scanning electron microscope (SEM). The mesopore diameter of the C/C composites increases slightly with the increase of CF content. The preparation can increase the mesopore volume and also reduce the production cost compared with carbon cryogels prepared without CF. The SEM images show that nanoporous gel spheres appeared after the freeze drying step. These spheres are converted to be nanoporous carbon spheres with surrounding nanocages, and CF are converted into carbon fibers at the same time by pyrolysis.     

Effect of amphiphilic compatibilizers on the filler dispersion and properties of polyethylene—thermally reduced graphene nanocomposites

Compatibilizers of different chemical structures and specifications were used to enhance the filler exfoliation in nanocomposites of polyethylene and thermally reduced graphene prepared by melt mixing route. The mechanical performance of the compatibilized nanocomposites was observed to be better than PE/G nanocomposites due to enhanced extent of filler exfoliation and distribution. Highest increase of 45% in tensile modulus and 13% in peak stress was observed in the composites. Overall, from the mechanical, rheological, thermal, and calorimetric properties, the compatibilizers with best performance were ethylene acrylic acid (EAA) copolymer and chlorinated polyethylene (CPE25). Furthermore, the extent of filler exfoliation was observed to increase with increasing EAA content thus confirming positive interactions between EAA and thermally reduced graphene, though no specific chemical interactions could be detected. The composite properties were observed to reach maximum around 7.5 wt % EAA content, followed by reduced performance due to extensive matrix plasticization. The observed behaviors were a result of interplay of opposing factors like filler exfoliation due to compatibilizer addition and matrix plasticization due to its lower molecular weight, thus the observed optimum comaptibilizer amount was specific to the compatibilizer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42484.     

Thermal conductivity of several geopolymer composites and discussion of their formulation

We fabricated 50.8-mm cube-shaped samples of metakaolin geopolymer (GP) composites with various additives chosen to increase or decrease the thermal conductivity of the composite. Sodium-based GP (NaGP) and GP composites were more conductive than potassium-based GP (KGP) composites for a given phase fraction of filler, but the maximum amount of filler phase was higher with KGP due to the lower viscosity of the KGP mixture. The highest thermal conductivity achieved was about 8 W/m K by KGP + 44-vol% graphite flakes, whereas NaGP + 27 vol% graphite flakes reached 4.7 W/m K. The thermal conductivity was strongly affected by the moisture remaining in the composite, which appeared to have a greater effect at higher filler content. On the other hand, the size of alumina particles (6, 40, or 120 μm) did not have any apparent effect on thermal conductivity for the same filler content. Larger particles caused less change in mixture viscosity, though, thus permitting incorporation of higher filler phase fractions and therefore higher thermal conductivity.     

Structural,morphological and thermal characterization of poly (2-hydroxyethyl methacrylate-co-acrylonitrile) (P (HEMA-co-AN)) Cryogels: evaluation of water sorption potential and cytotoxicity

Cryogels are macroporous hydrogels which are synthesized through cryogelation method. In the present study cryogels of poly (2-hydroxyethyl methacrylate-co-acrylonitrile) (P (HEMA-co-AN)) were synthesized by copolymerization of 2-hydroxyethyl methacrylate (HEMA) and acrylonitrile (AN) monomers by redox polymerization using cryogelation technique. The synthesized cryogels were characterized by FTIR, SEM, XRD, DSC and TGA techniques. Different compositions of the cryogels were prepared by varying concentrations of the monomers and redox initiators in the feed mixture. These cryogels were then subjected to swelling studies and porosity determination. The swelling behavior was studied as function of concentration of the monomers, redox initiators, temperature, pH, and simulated biological fluids. The prepared cryogels were also characterized for their network parameters using water sorption data. The biocompatibility of P (HEMA-co-AN) cryogel was evaluated by in vitro cytotoxicity test. The results indicated that the P (HEMA-co-AN) cryogel had macroporous morphology and exhibited good water absorption capacity. Moreover, the cryogel was thermally stable and biocompatible in nature.     

Hyaluronic acid microneedles-laden collagen cryogel plugs for ocular drug delivery

Particle loaded hydrogels have shown to provide prolonged delivery of drug in a controlled manner. We propose that embedding drug-loaded hyaluronic acid (HA) microneedles in supermacroporous collagen type-I (Col-I) cryogel plugs may enhance the hydration and provide prolonged release of drug for ocular diseases. In this study, we have fabricated Col-I cryogel and HA-microneedles embedded Col-I cryogel at sub-zero temperature using 4S-arm Star-PEG as a crosslinker. The fabricated novel Col-I cryogels have shown supermacroporous morphology with solvent uptake capacity of nearly 90% due to large pore volume and high interconnectivity. These features of the cryogel enable the release the drug in a controlled and sustained manner. The fabricated cryogels have demonstrated nearly 50% degradation in simulated tear fluid within 15 days of duration. Moreover, the microneedles incorporated cryogels have shown prolonged release of required therapeutic concentration of drug that may satisfy the present dire need for antibacterial drug delivery in eyes. The variation in the drug release kinetics from Col-I cryogel and HA-microneedles-laden-Col-I cryogels have been studied in different release media (PBS and Simulated tear fluid).