Thermoplastic polymers as modifiers for urea‐formaldehyde (UF) wood adhesives. II. Procedures for the preparation and characterization of thermoplastic‐modified UF wood composites

Wood composites were prepared by using wood flour (sugar maple, Acer saccharum March) and thermoplastic‐modified urea‐formaldehyde (UF) suspensions. Thermoplastic (5–10% w/v) was introduced into the UF suspension as an aqueous solution, a self‐stabilized dispersion in water, or as a surfactant‐stabilized latex. The modified suspension was blended with wood flour, and the blend was cured by using a cure cycle that was suitable for all the thermoplastic‐modified UF formulations and unmodified UF controls. The wood flour composites were tested by using a notched Izod impact strength test. All formulations containing surfactant decreased the impact strength by ～ 30–40% relative to the unmodified UF control, whereas the water‐soluble thermoplastic had no effect on the impact strength. The formulations with self‐dispersed thermoplastics all increased the notched Izod impact strength, with the greatest increase being 69% more than the UF control, except in a single instance when the molecular weight of the thermoplastic was very high, which decreased resin flow. Increasing the thermoplastic content from 5 to 10% w/v did not further improve the impact test results. Scanning electron microscopy of the fracture surfaces showed morphological differences in the systems that varied with the thermoplastic and method of thermoplastic addition to the UF suspension.© 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 898–907, 2003     

Thermoplastic polymers as modifiers for urea–formaldehyde wood adhesives. III. In situ thermoplastic‐modified wood composites

Acrylic monomers and free‐radical initiators were dispersed in an aqueous urea–formaldehyde (UF) suspension and polymerized in situ to afford a suspension containing 5 wt % thermoplastic (5 g of thermoplastic/100 mL of suspension). The viscosity of the thermoplastic‐modified UF suspension (65 wt % solids at 25°C) ranged from 240 to 437 cP versus 121 cP for the unmodified UF control. Wood‐flour composites (sugar maple and 50 wt % adhesive) were prepared with thermoplastic‐modified UF suspensions and cured with the same cycle used for the composites prepared with the unmodified UF adhesive (control). The effect of the thermoplastic‐modified UF adhesive was evaluated on the notched Izod impact strength and equilibrium moisture uptake of the wood‐flour composites. The notched Izod impact strength of the composites prepared with modified UF adhesives increased by as much as 94% above that of the control. The increase depended on the initiator and the monomer composition. The modification affected the equilibrium moisture uptake and rate of moisture uptake in the wood‐flour composites. Preliminary results for particleboard prepared with 10 wt % modified UF adhesive (5% thermoplastic in the UF resin) and unoptimized cure conditions confirmed a significant effect of the thermoplastic modification on both the internal‐bond strength and thickness swelling of the particleboard. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermoplastic modification of urea–formaldehyde wood adhesives to improve moisture resistance

Urea–formaldehyde (UF) resins are prone to hydrolytic degradation, which limits their use to indoor applications. This study examined the modification of UF resin with various thermoplastics as a means to increase the moisture resistance of the adhesive. UF adhesives were modified in situ with various hydrophobic and hydrophilic thermoplastic formulations, using either polar or nonpolar initiators. Unmodified and modified UF resins were characterized in terms of viscosity, pH, and gel time in their prepolymer suspension state. Cured solid UF resin plaques were prepared to isolate moisture sorption effects of the cured UF resin from that of the wood component in composites, which dominates their moisture uptake. Relative crosslink density and moisture sorption tests were run on cured UF resin plaques. Results indicated that viscosity increased after modification in most cases, with higher viscosities resulting from formulations using an acidic (polar) initiator. In all cases, activation energies of the curing reactions of thermoplastic‐modified UF suspensions were lower than the unmodified UF. High relative crosslink density compared to the unmodified UF was found for one sample, which correlated well with lower overall moisture sorption. Higher relative crosslink density of cured UF resin plaques appeared to be an indicator of lower moisture uptake. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4222–4229, 2006     

Aqueous and Nonaqueous Colloidal Processing of Difficult‐to‐Densify Ceramics: Suspension Rheology and Particle Packing

Aqueous and nonaqueous colloidal processing of zirconium diboride (ZrB₂) and boron carbide (B₄C) has been investigated. The aqueous and nonaqueous ZrB₂ and B₄C suspension formulations have been optimized. The suspensions were cast into green bodies using slip casting. The correlation between the state of dispersion with the rheological properties of the suspensions and the resulting packing density was observed in both aqueous and nonaqueous processing. The attractive interactions between powder particles in water were difficult to overcome with electrical double layer or electrosteric repulsion. Reasonably low viscosity aqueous ZrB₂ suspensions up to 45 vol% solids could be prepared. It was not possible to produce low viscosity (viscosity below 1 Pa·s at shear rate of 100 s^?1) aqueous B₄C suspensions with solid content above 30 vol%. Slip casting of the weakly aggregated ZrB₂ suspensions resulted in low packing densities (~55% relative density) of the green bodies. On the other hand, dispersion of powder particles in nonaqueous media (cyclohexane and dodecane) enabled suspensions with lower viscosities and a higher maximum solid concentration (up to 50 vol%) to be prepared. The well‐dispersed nonaqueous suspensions promoted an efficient particle packing, resulting in higher green densities (64% and 62% relative density for ZrB₂ and B₄C, respectively) compared to aqueous processing. The significantly high green densities are promising to allow densification of the materials at lower sintering temperature.     

Horizontal Dip‐Spin Casting of aqueous alumina‐polyvinylpyrrolidone suspensions with chopped fiber

A novel ceramic processing method, called Horizontal Dip Spin Casting (HDSC), enabled fabrication of tubular ceramic parts with an aligned chopped fiber phase. HDSC was demonstrated using highly loaded aqueous alumina suspensions with >50 vol.% solids loading and ≤5 vol.% water‐soluble polymer employed as a rheological modifier. Chopped carbon fibers were added to the suspensions to attain maximum loadings of 30 vol.%. During forming, cylindrical foam molds were dipped into the suspension while being rotated radially about the long axis. Simultaneously, a doctor blade was placed at a specified distance from the foam surface to facilitate the flow of the suspension to align the fiber and control the thickness of the material that accrued on the mold. Rheological study of alumina‐PVP suspensions with and without chopped carbon fiber showed that the suspensions exhibited a yield‐pseudoplastic flow behavior. The degree of alignment of the carbon fiber phase in the green bodies was characterized for various suspension formulations, carbon fiber contents and forming speeds. Stereological characterization of green body specimens confirmed the effectiveness of HDSC to attain the desired tubular geometry with considerable fiber alignment for a suspension composition containing ≤20 vol.% chopped fibers.     

Rheology of Nano‐Scale Aluminum Suspensions

Nano‐scale aluminum particles are innovative materials which are used increasingly in energetic formulations. In this contribution, the rheological behavior of suspensions with either paraffin oil or HTPB as the matrix fluid and nano‐scale aluminum (ALEX) as the dispersed phase is described and discussed. The paraffin oil/aluminum suspensions exhibit non‐Newtonian flow behavior over a wide range of concentrations, whereas the HTPB/aluminum suspensions exhibit Newtonian behavior (i.e. the viscosity is independent of shear stress) up to a concentration of 50 vol.% aluminum. Both systems have unusual viscoelastic properties in that their elastic moduli are independent of the solids concentration.     

Self‐assembly of pH‐responsive acrylate latex particles at emulsion droplets interface

The self‐assembly of pH‐responsive poly (methyl methacrylate‐co‐acrylic acid) latex particles at emulsion droplet interfaces was achieved. Raising pH increases the hydrophilicity of the latex particles in situ and the latex particle acts as an efficient particulate emulsifier self‐assembling at emulsion droplet interface at around pH 10–11 but exhibits no emulsifier activity at higher pH. This effect can be reversibly induced simply by varying the aqueous phase pH and thus the latex emulsifier can be reassembled. The effect factors, including the aqueous phase pH, the surface carboxyl content, ζ‐Potential of the latex particles and oil phase solvent have been investigated. Using monomer as oil phase, the latex particles could stabilize emulsion droplets during polymerization and cage‐like polymer microspheres with hollow core/porous shell structure were obtained after polymerization. The mechanism of the latex particles self‐assembly was discussed. The morphologies of emulsion and microspheres were characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of oil type on stability of high internal phase water-in-oil emulsions with super-cooled internal phase

This study considered the stability and rheology of a type of high internal phase water-in-oil emulsions (W/O) emulsion. The aqueous phase of the emulsions is a super-cooled inorganic salt solution. The oil phase is a mixture of industrial grade oils and stabilizer. Instability of these systems manifests as crystallization of the metastable dispersed droplets with time. This work focused on the effects of oil polarity and oil viscosity on the stability of these emulsions. Ten types of industrial oils, covering the viscosity range 1.4–53.2?cP, and with varying polarity, were used in combination with polymeric poly(isobutylene) succinic anhydride (PIBSA) and sorbitan monooleate (SMO)-based surfactants. The effect of oil relative polarity on rheological parameters of the emulsion was evident mainly in the emulsions stabilized using polymeric surfactant, whereas the oil viscosity did not show any significant effect. The optimum stability of the emulsions stabilized with SMO was achieved using high polar oils with a viscosity of 3?±?0.5?cP. However, when using the PIBSA surfactant, the best emulsion stability was achieved with low polar, high viscosity oils.     

Particle‐laden liquid jet impingement on a moving substrate

The impingement of high speed jets on a moving surface was studied. The jet fluids were dilute suspensions of neutrally buoyant particles in water–glycerin solutions. At these low particle concentrations, the suspensions have Newtonian fluid viscosity. A variety of jet and surface velocities, solution properties, nozzle diameters, mean particle sizes, and volume fractions were studied. For each case the splash‐deposition threshold was quantified. It was observed that for jets with very small particles, addition of solids to the jet enhances deposition and postpones splash relative to a particle‐free water–glycerin solution with the same viscosity. In contrast, jets with larger particles in suspension were more prone to splash than single phase jets of the same viscosity. It is speculated that the change in character of the splash response for the jets with larger particles in suspension occurs when the particle diameter is comparable to the lamella thickness. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4673–4684, 2017     

α‐Alumina nanospheres from nano‐dispersed boehmite synthesized by a wet chemical route

In this work, stable aqueous suspensions of nano‐boehmite were developed through a hybrid wet‐chemical route that uses hyperbranched dendritic poly(ethylene)imine (PEI) as template material for boehmite formation aiming at the development of a deagglomerated α‐alumina nanopowder after calcination. The method involves firstly the interaction between the Al precursor and PEI followed by the hydrolysis and polycondensation reactions. The study was aiming to investigate the effect of solids content and pH during reactions on both the stability of the final suspension and the morphology of the resulting nanocrystals. For this purpose, the suspensions were evaluated through viscosity measurements, zeta potential analyses, FT‐IR, DLS and sedimentation studies, whereas after the proper centrifugation, drying, and calcination steps, the as‐received nanocrystals were evaluated through SEM, TEM and XRD studies. In addition, the boehmite nanopowder was studied using Thermogravimetric and Differential Thermal Analysis, whereas its sinterability was evaluated by dilatometric measurements. The investigation showed that the conditions employed affect greatly both the morphology of nanocrystals as well as the dispersion and the stability of the suspensions. The boehmite suspension with the optimum dispersion and stability can lead, after calcination at 1050°C, to a fine deagglomerated α‐alumina nanopowder with a mean size at about 10 nm.     

Study on the molecular behavior of hydrophobically modified poly(acrylic acid) in aqueous solution and its emulsion‐stabilizing capacity

In this article, molecular conformation and aggregation behavior of partly hydrophobically modified poly(acrylic acid) (HMPAA) in aqueous solution has been studied by mesoscale simulation approach dissipative particle dynamics for the purpose to find out how the chemical structure and environmental conditions effect its capacity. It has been found that, as a kind of pH‐sensitive polymer, the chemical structure variation of HMPAA carried by adjusting pH and grafting degree influence the taking place of intermolecular and intramolecular associations, which induced the formation of molecular network and help to maintain high bulk phase viscosity of its aqueous solution in larger pH range or under higher salinity comparing with PAA. There exists an optimum grafting degree, above which the increase of the possibility of the intramolecular associations enhance the coiling of the polymer chain and result in destroy of the network. The experimental determination of properties of aqueous solutions of poly(acrylic acid) (U10) and poly alkyl acrylate (U20), such as the bulk phase viscosity and oil/water interface tension, accord well with the molecular simulation conclusion, by which the mechanisms of elevated stability of surfactant‐free O/W emulsion stabilized by the HMPAA comparing with PAA has been discussed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Single‐pack,self‐curable,aqueous‐based polyurethane dispersion containing a disperse dye

An organic‐solvent‐soluble disperse dye was introduced into an aqueous phase by a reaction with a self‐emulsified, aqueous‐based polyurethane (PU), and this resulted in the formation of a homogeneous, aqueous polymeric dye dispersion. This aqueous polymeric dye was stable in a water phase with excellent color extension upon application. It was formulated with a latent curing agent, polyaziridine (e.g., TMPTA‐AZ), as a single‐component, self‐curable, aqueous polymeric dye. The curing reaction took place between PU carboxylic acid and the latent curing agent upon drying. A self‐cured polymeric dye was obtained with excellent color extension and fastness and resistance to organic solvents and water after drying. This single‐component, self‐curable, aqueous‐based PU system containing a dye has potential for printing, writing, and dyeing applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 2006 © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3741–3747, 2006     

Ethylenediamino bridged bis(β‐cyclodextrin)/ poly(DL‐lactic‐co‐glycolic acid) nanoparticles prepared by modified double emulsion method: Effect of polyvinyl alcohol on nanoparticle properties

This study continues long‐standing efforts to develop protein delivery systems based on cyclodextrin‐conjugated polyester in our laboratory. The crude products of ethylenediamino bridged bis(β‐cyclodextrin)‐conjugated poly(DL ‐lactic‐co‐glycolic acid) were used in this study to make full use of unreacted reactant. With bovine serum albumin (BSA) as a model protein, the encapsulation effects (the encapsulation efficiency and particle size) of nanoparticles were similar to those of using pure conjugated products. Besides, a water‐in‐oil‐in‐water emulsification technique was conveniently modified. By adding polyvinyl alcohol (PVA) in the internal aqueous phase, a more stabilized emulsion was formed. Consequently, less PVA (～ 0.05%) was needed in the outer aqueous phase and less PVA (0.14 g/g nanoparticles) remained in the nanoparticles. This modification resulted in improved encapsulation efficiency (～ 89–94%) of BSA and an enlarged particle size (340–390 nm). Furthermore, the burst release of BSA at the 1st day was less pronounced (7–12% of the encapsulated amount) than that of nanoparticles with no PVA added in the internal aqueous phase. Degradation studies using transmission electron microscope and gel permeation chromatography suggested that the mechanism for protein release was mainly through nanoparticles erosion. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermoplastic 3D Printing—An Additive Manufacturing Method for Producing Dense Ceramics

In our new approach—thermoplastic 3D printing—a high‐filled ceramic suspension based on thermoplastic binder systems is used to produce dense ceramic components by additive manufacturing. Alumina (67 vol%) and zirconia (45 vol%) suspensions were prepared by ball milling at a temperature of about 100°C to adjust a low viscosity. After the preparation the suspension solidified at cooling. For the sintered samples (alumina at 1600°C, zirconia at 1500°C), a density of about 99% and higher was obtained. FESEM studies of the samples' cross section showed a homogenous microstructure and a very good bond between the single printed layers.     

Comb‐like polymer with sulfo groups and its dispersion and rheological properties in aqueous ceramic suspensions

Two types of new comb‐like polymers were formed as dispersants for aqueous ceramic suspensions with isoprenyloxy poly(ethylene glycol ether), acrylic acid, maleic anhydride as the main starting materials. During the synthesis, one comb‐like polymer introduced sodium methylallyl sulfonate (SMAS) into the reaction media, whereas the other did not. The chemical structure and molecular weight were characterized by Fourier transform infrared spectroscopy and gel permeation chromatography. The effects of the polymers on the dispersion, ζ potential and rheological properties of the kaolin suspensions are discussed in detail. The results indicate that SMAS facilitated chain transfer, controlled the effective charge density of the surface, and increased the electrostatic repulsion force. The kaolin suspensions displayed shear‐thinning behavior on the basis of the electrostatic and steric effects of the comb‐like polymers. The apparent viscosity decreased from 1088 to 258 mPa s with the assistance of the SMAS‐prepared comb‐like polymer as a dispersant. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44563.     

A new tri‐functional azetidine compound for self‐curing aqueous‐based PU system

A mono‐azetidine compound had been demonstrating a ring opening reaction with carboxylic acid (e.g., trimethylacetic acid, TMAA) and that resulted in an amino ester bond formation at ambient temperature. A triazetidine compound (trimethylolpropane tris(1‐azetidinyl)propionate, TMPTA‐AZT) was obtained via Michael addition of azetidine (AZT) to trimethylolpropane triacrylate (TMPTA). The carboxylic groups of anionic aqueous‐based polyurethanes (PU) served as internal emulsifier, which stabilized PU dispersion and also served as PU curing sites. The triazetidine compound (TMPTA‐AZT) was introduced into anionic aqueous‐based PU dispersion as a new latent curing agent and that mixture became a single‐component self‐curable aqueous PU system. A crosslinked PU film was obtained from this PU system on drying at ambient temperature. The final polymer performance properties demonstrated the crosslinking behaviors of this new curing agent, TMPTA‐AZT, with carboxylic ion‐containing aqueous‐based PU resins. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Templating synthesis of non‐spherical polymer particles and their effect on the fracture toughness of an epoxy‐amine network

Flexible non‐spherical polymer particles were successfully produced via concentrated emulsion polymerization. LUDOX TM‐50 (colloidal silica, 50 wt% suspension in water) was introduced into the continuous phase to strengthen the template and inhibit monomer diffusion between the continuous and dispersed phases. The extent of non‐spherical shape was identified by the roundness value. Transmission electron micrographs showed that the higher the volume fraction of the dispersed phase became, the more non‐spherical were the poly(butyl acrylate) (PBA) particles. As an application, the effect of the non‐spherical particles on the fracture toughness of a modified epoxy‐amine network was studied. Scanning electron micrographs showed that the introduction of the non‐spherical PBA particles improved efficiently the impact strength of the cured epoxy resin. Copyright © 2006 Society of Chemical Industry     

Effect of Sucrose on Fabrication of Ceramic Foams from Aqueous Slurries

Ceramic foams with porosity exceeding 90% were prepared by direct foaming and casting of aqueous suspensions containing cetyl trimethyl ammonium bromide (CTAB) as a foaming agent. Foaming of the suspensions, particularly with lower viscosity, was initially non-homogeneous but the foam appeared to homogenize with milling time. Addition of sucrose to ceramic suspensions resulted in lowering of the suspension viscosity, stabilized the foams by reducing drainage of the suspension, and minimized coalescence of bubbles leading to lower cell sizes in sintered foams. Ceramic foams prepared from sucrose based suspensions were strengthened to such an extent that foams with porosity above 90% could be machined in the green state.     

Porous Mullite Ceramics Formed by Direct Consolidation Using Native and Granular Cold‐Water‐Soluble Starches

In this article, the processing and microstructures of porous mullite bodies prepared by modifying the conventional route of the starch consolidation casting method were studied. The proposed route, called the “soluble route”, involves the use of native starches (i.e., potato, cassava, and corn starches) and a synthesized granular cold‐water‐soluble (GCWS) starch. Stable aqueous mullite‐starch suspensions (0.25 starch volume fraction of 40 vol% total solids) were prepared by mixing. The total starch content was a mixture of ungelatinized native starch and GCWS starch with a 1:10 ratio of GCWS starch to total starch. Steady‐state shear flow properties of the suspensions were analyzed by measuring viscosity. The addition of CGWS starch increased the starting suspension viscosity and thus prevented the particle segregation. Porous mullite bodies were obtained by heating (80°C, 2 h) the suspensions in metallic molds and by drying (40°C, 24 h) and sintering (1650°C, 2 h) the green disks after burning out the starch (650°C, 2 h). Green bodies obtained before and after the burning‐out process, and the sintered disks were characterized with density and porosity measurements (Archimedes method) and microstructural analysis by scanning electron microscopy. The phases generated after the sintering process were determined by X‐ray diffraction analysis, and pore size distributions were studied by Hg‐porosimetry. The obtained results showed that the use of the GCWS starch made the shaping of homogeneous mullite bodies without cracks or deformations possible along with the development of controlled porous microstructures.     

PEG 400/Paraffin oil non‐aqueous emulsions stabilized by PBut‐Block‐P2VP block copolymers

For the preparation of PEG 400 in paraffin oil non‐aqueous biocompatible emulsions, the stabilization efficiency was compared for two well‐defined poly(butadiene)‐block‐poly(2‐vinylpyridine) (PBut‐block‐P2VP) block copolymers, with similar molecular weights but different compositions. The PBut₁₂₈‐block‐P2VP₅₀ and PBut₁₈₉‐block‐P2VP₃₇ samples, designated as copolymer A and B, respectively, are self‐organized in paraffin oil as micelles with a P2VP core and a PBut corona. The PEG 400/paraffin oil emulsion characteristics were determined as a function of the copolymers concentrations and phase ratios. Higher static and shear stabilities were obtained for emulsions stabilized by copolymer B than for those obtained in the presence of copolymer A . A further difference concerns the droplet size, relative viscosity, and loss modulus values obtained at a given dispersed phase volume fraction. At constant copolymer concentrations, it appeared that copolymer B , with a longer PBut sequence, is a more efficient emulsifier and stabilizer than copolymer A . © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41390.