Urea-formaldehyde Prepolymer Research Articles

A new synthesis method of flexible microcapsules applied for electrophoresis display

This study prepared a new type of electrophoretic display microcapsule with flexibility and strength, namely gum arabic/gelatin/urea-formaldehyde resin microcapsule, based on polysaccharides as the reaction starting point, combined with proteins and resins. The composition, morphology and thermal stability of the microcapsules were tested by Fourier transform infrared spectroscopy, stereo fluorescence microscopy, scanning electron microscopy and thermogravimetric analysis. It was found that the morphology and stability of the new microcapsules prepared by the method are better than those prepared by the traditional complex coacervation method or the in-situ polymerization method. At the same time, it showed that the rotational speed was between 1000 rpm and 1200 rpm, the concentrations of gum arabic and gelatin were 3 wt%, the reaction pH between 3 and 3.5, the reaction duration is between 150 min and 180 min, the ammonium chloride was 20 wt%, and resorcinol was 6 wt%, the reaction between the urea-formaldehyde prepolymer and the electro-neutralizer formed by gelatin and gum arabic was sufficient, the microcapsule wall structure was uniform and consistent, with a dense resin based structure on the outer layer and a flexible blend structure inside.

Improved performance of soy protein adhesive with melamine-urea-formaldehyde prepolymer.

In recent years, soy protein adhesive, as an environmentally friendly bio-based adhesive, has attracted extensive attention. In this study, in order to ameliorate the bonding quality of soy protein isolate (SPI) adhesive, the melamine–urea–formaldehyde prepolymer (MUFP) was synthesized, and different amounts of it were introduced into the SPI adhesive as a cross-linking agent. Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC), thermogravimetric analyze (TGA), and scanning electron microscopy (SEM) were used to analysis the mechanism of modification. The results of plywood test indicated that the wet bonding strength of the adhesives was first increased and then decreased with an increase in the amount of MUFP additive. FT-IR, TGA, and SEM tests suggested that the introduction of MUFP could promote the establishment of a cross-linking structure in the cured adhesive layer to improve the bonding quality of adhesives, but presence of excessive MUFP could introduce hydrophilic groups and adversely affect water resistance.

Development of ultra-high build self-healing coatings using amino silanized lignin nanocapsules

Self-healing coatings were prepared for corrosion inhibition of mild steel by amino Silanization of lignin nano capsules. In-situ polymerization techniques through sonochemical approach was used for preparation of lignin nano capsules. Coatings have been developed using natural healing materials such as combination of lignin and safflower oil and coupling agents i.e APTES in water borne epoxy curing agent. Successful encapsulation of lignin and safflower oil was carried out via in-situ polymerization with the aid of urea–formaldehyde pre-polymer solution in presence of surfactant polyvinyl alcohol (PVA). Further Functionalization of lignin nanocapsules was done by amino Silanization. TEM and FE-SEM images confirm the encapsulation of nano particles and its histogram gives the average particle size distribution of the lignin nano particle and Capsuleas 106 and 146 nm. Total phenolic content of lignin extract were found to be 936 mg GAE/g. Potentio dynamic polarization studies revealed that the current density decreases to minimum of 3.703E-8A/cm2 with increase in weight percentage of lignin in nanocapsules (1.5 wt%) . Electrochemical Impedance spectroscopy showed a maximum impedance value as 6.44E6 for 1.5 wt% LNC coatings. Immersion studies give better corrosion rate for 1.5 wt% LNC coatings when compared to bare and standard coatings.

Effect of Synthesis Conditions on the Molecular Weight and Activation Energy of Urea-formaldehyde Prepolymer and Their Relationship

The aim of this study is to find out the viscosity change of urea-formaldehyde (UF) resin with the synthesis parameters namely formaldehyde/urea (F/U) mole ratios, pH and temperature. The viscosity of UF resins, related to molecular weight and activation energy is very important factor of their usability. Urea-formaldehyde (UF) prepolymer was synthesized through polycondensation reaction with F/U ratio 0.8, 1.0, 1.2, 1.4, 1.6. The synthesis was carried out by two steps: alkali catalysis at reaction pH 8.3, 90°C for 60 min and thereafter acid catalysis at pH 4.3, 83°C for 15 min. Viscosity of prepolymer was determined at acid catalysis step by simple glass viscometer. Weight average molecular weight (Mw) was calculated from the viscosity data of UF prepolymer using Mark-Houwink equation. Highest Mw (2020.9) of prepolymer was obtained at F/U molar ratio 1.0 and pH 4.3. In addition, it was found that pH 4.0 yielded greater Mw (2049) UF prepolymer among the four reactions which were performed at pH 4.0, 4.3, 4.7, and 5.0. The energy of activation (Ea) of UF prepolymer was also calculated from the measured viscosity at temperature 70, 75, 80 and 85°C. The highest values of Ea were also found at F/U molar ratio 1.0 and pH 4.0 & lowest values was obtained at F/U molar ratio 1.6 and pH 5.0. From the experimental data, it was shown that the values of Ea and Mw were varied comparably with the change of reaction parameters.

SYNTHESIS OF SULFUR-CONTAINED MICROCAPSULES AND POTENTIAL APPLICATION IN RUBBER

Microcapsule-based material is potentially utilized in a variety of fields such as pharmaceuticals, food, biology, self-healing materials, etc. More remarkedly, in the rubber-related fields, this outstanding material is able to have a crucial role to play as an alternative of sulfur in compounding and vulcanizing process with regard to the self-healing ability after cracking. In this research, the interface polymerization was applied to generate microcapsules, whose shell was synthesized from Urea-formaldehyde pre-polymer modified by 0.25 wt% melamine containing sulfur (S) as a core substance. When the synthesizing process was carried out at 80 C and stirring rate of 300 rpm in 2 hours, the microcapsule product was spherical with the average size of 115 m and contained 60% of core content that was examined by FTIR, DLS, SEM, TGA and experimented the potential application. As a result, the amount of 8 phr of produced microcapsules utilized in NBR rubber compounds necessitated a longer time to vulcanize rubber at 160 C compared to using 5 phr free S. Besides, the mechanical strength of the microcapsules-contained product was insignificantly changed but bloom-like phenomenon on the rubber surface was markedly improved. It is noticeable that the vulcanized NBR rubber with the presence of these microcapsules are well able to heal its crack or cut when heated up to 150 C in 10 minutes while the free S-vulcanized NBR rubber is definitely unable to be self-healing in the same conditions.

Preparation of porous graphene oxide–poly(urea–formaldehyde) hybrid monolith for trypsin immobilization and efficient proteolysis

Porous graphene oxide–poly(urea–formaldehyde) (GO–PUF) hybrid monolith was prepared by the in situ polycondensation of the urea–formaldehyde prepolymer solution in the presence of GO sheets and ammonium chloride. The amide groups in the residues of asparagine and glutamine in trypsin was allowed to condense with the residual N-hydroxymethyl groups of PUF in the monolith at low pH to fabricate bioreactors for proteolysis. The morphologies and structures of the prepared materials were investigated by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. The results indicate that both GO–PUF hybrid and trypsin-immobilized GO–PUF hybrid mainly consist of irregular micrometer size flakes and pores that are interconnected to form 3D porous architectures. In addition, the feasibility and performance of the novel capillary bioreactors were demonstrated by the digestion and identification of bovine serum albumin, lysozyme, ovalbumin, and cytochrome c. The digestion time was significantly reduced to less than 10s. The digests were identified by mass spectrometry with results that were comparable to those obtained by 12-h conventional in-solution tryptic digestion.

Characterization of Ailanthus altissima Veneer Modified by Urea-formaldehyde Pre-polymer with Compression Drying

Recently, Ailanthus altissima wood has received increased attention in China. Although Ailanthus altissima has a number of advantages, such as fast-growing character and high density, the low dimensional stability is a restraining factor. Chemical modification could be a feasible way to overcome such drawbacks. The aim of this research was to study the physical and chemical properties of Ailanthus altissima veneers treated by urea-formaldehyde pre-polymer impregnation and compression drying. The results showed that this approach not only significantly increased the dimensional stability of wood, but also enhanced the bending strength and compressive strength parallel to the grain. The FT-IR analysis showed that the intensity of hydroxyl (-OH) and carbonyl (C=O) absorption peaks decreased, which indicated that the NH-CH2-OH of the pre-polymer reacted with the wood’s carboxyl and hydroxyl groups. The positions of the XRD peaks did not change, which indicated that the structure of cellulose crystallinity was not noticeably affected by the chemical modification. The TGA showed that the thermal stability of modified wood was improved, while FESEM showed that the wood cell wall and vessels were impregnated with chemicals.

Microchip bioreactors based on trypsin-immobilized graphene oxide-poly(urea-formaldehyde) composite coating for efficient peptide mapping

Trypsin was covalently immobilized to graphene oxide (GO)-poly(urea-formaldehyde) (PUF) composite coated on the channel wall of poly(methyl methacrylate) microchips to fabricate microfluidic bioreactors for highly efficient proteolysis. A mixture solution containing urea-formaldehyde prepolymer and GO nanosheets was allowed to flow through the channels. The modification layer on the channel wall could further polycondense to form GO-PUF composite coating in the presence of ammonium chloride. The primary amino groups of trypsin could react with the carboxyl groups of the GO sheets in the coating with the aid of carboxyl activating agents to realize covalent immobilization. The feasibility and performance of the novel GO-based microchip bioreactors were demonstrated by the digestion of bovine serum albumin, lysozyme, ovalbumin, and myoglobin. The digestion time was significantly reduced to less than 5s. The obtained digests were identified by MALDI-TOF MS with satisfactory sequence coverages that were comparable to those obtained by using 12-h in-solution digestion. The present proteolysis strategy is simple and efficient, offering great promise for high-throughput protein identification.

Study on Urea-Formaldehyde Prepolymer and Hot-Press Treatment of Italian Poplar Wood

Abstract The purpose of this study was to modify Italian poplar (Populus euramevicana cv. ‘I-214’) wood with urea-formaldehyde prepolymer followed by hot pressing. The timbers were impregnated with urea-formaldehyde prepolymer using a pulsed-dipping machine and cured in a hot press. The results showed that the timbers could be easily compressed and cured at temperatures between 90°C and 120°C. The characteristics and quality of the modified wood were up to A grade according to Chinese Standard GB/T 6491‐1999. The air-dried density of modified wood was improved by 58 percent, and the hardness in the transverse, tangential, and radial directions was increased by 67, 210, and 160 percent, respectively. The bending strength was improved by 78 percent; the bend elastic modulus was improved by 66 percent. The water absorption of treated wood decreased relative to that of the untreated timbers. Fourier transform infrared spectroscopy of the modified wood showed a significant reduction in the C=O absorbance at 1,750 cm−1. The peak at 1,645 cm−1 was found to increase as a result of treatment with the prepolymer.

Study on Compressed Wood with Urea-Formaldehyde Prepolymer

In this research, the urea-formaldehyde prepolymer and multilayer hot-press drying was used to obtain modified wood. The timbers were compressed and dried by the multilayer hot-press drying kiln. The combination of chemical modification and hot-press drying can improve the drying rate, which can also enhanced the physical and mechanical properties. Based on the findings, the basic density of modified wood improved 25.2 %, the bending strength and the bend elastic modulus improved 15.6 % and 25.0 % respectively. The dimensional stability of the treatment appeared to be slightly higher than that of untreated samples under the same conditions for processing temperatures and times. The improving dimensional stability of wood mainly was attributed to the prepolymer that changes wood cell wall components such as the degradation of the hemicelluloses and cellulose during hot-press drying treatment. The XRD results indicated that the degree of crystallinity increased to 35.45 %from 31.25 %. The TGA results show that the degradation of the samples can be divided into two step, both of the maximum weight loss velocity temperature of the two step increased to 266 °C, 355 °C from 244 °C and 341 °C.

Chemical and Physical Changes for Dimensionally Stability of Compressed Wood

The objective of this study was to determine the chemical and physical changes of chemical modified on poplar wood. The chemical modifier was impregnated into cell lumen space by pulse-dipping machine to improve the dimension stability and mechanical property of timber. The timbers were compressed and dried by the multilayer hot-press drying to produce the modified timber. The modified timber had better dimension stability than the natural wood when they were immerged water continuous eight-hour. Characteristics of Fourier Transform Infrared Spectroscopy (FTIR) for modified were studied by the FTIR spectrometer. The intensity of hydroxyl absorption peak in the infrared absorption spectrogram decreased significantly, and that of carbonyl decreased lightly, which due to the bond of the function groups of -NHCH2OH of urea-formaldehyde prepolymer react with the wood carboxyl (C=O) and hydroxyl(-OH). The morphologic models of chemical within wood were discovered by SEM.

Preparation of PS/TiO 2/UF multilayer core–shell hybrid microspheres with high stability

In this paper, we report a facile method for preparation of polystyrene/titania/urea–formaldehyde resin (PS/TiO 2/UF) multilayer core–shell hybrid microspheres with high stability through in situ condensation polymerization. The TEM images show that the thickness of UF shells is about 10 nm. The Zeta potential is close to zero. The density of PS/TiO 2/UF could be controlled to 1.85 g/cm 3, which matches well with the non-polar dispersant (tetrachloroethylene). They are well dispersed and remain non-agglomerated even over several months, so they could be potential building blocks to fabricate electrophoretic display. Some parameters such as the ratio of urea–formaldehyde prepolymer (UFP) to PS/TiO 2, the pH value, and the temperature are also investigated.

Thermal curing behavior of modified urea‐formaldehyde resin adhesives with two formaldehyde scavengers and their influence on adhesion performance

AbstractThis study investigated, by differential scanning calorimetry, the thermal curing behavior of urea–formaldehyde (UF) resins modified with two formaldehyde scavengers and its impact on the adhesion performance of particleboard bonded with modified UF resin adhesives. As the concentration of the two scavengers [i.e., urea–formaldehyde prepolymer (UFP) and urea solution (US)] increased, the gel time, peak temperature, and onset temperature of the modified UF resins did not change significantly for UFP‐modified UF resins, but these parameters increased for the US‐modified UF resins. These results indicated that the reactivity of the UF resin modified with UFP was maintained, but it deteriorated for the US‐modified UF resins. The formaldehyde emission of particleboard bonded with the modified UF resin decreased with an increase in the scavenger concentration. UFP was more effective than US in scavenging the formaldehyde emission and in achieving adhesion to the UF resin. The results showed an optimum UFP level of 20% in the UF resin for maintaining a balance between the formaldehyde emission and adhesion of the particleboard, and they indicated that both the thermal curing behavior of scavenger‐modified UF resins and the properties of particleboard bonded with them must be taken into account in the evaluation of a formaldehyde scavenger system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Synthesis and properties of paraffin capsules as phase change materials

Capsules containing paraffin as phase change core were in situ synthesized by the absorption and polymerization of urea–formaldehyde prepolymer onto the core in the presence of hydrolyzed styrene–maleic anhydride copolymer as emulsifier in aqueous phase. The particle size and shell content were controlled. A series of capsules in the form of powder have been synthesized with high thermal enthalpy capacity due to the high crystallization of the core paraffin. They were stable against coalescence after heating/cooling cycles. The capsules can find potential applications such as in energy conservation, functional heat fluid and heat protection materials.

Comparative 13C‐NMR and matrix‐assisted laser desorption/ionization time‐of‐flight analyses of species variation and structure maintenance during melamine–urea–formaldehyde resin preparation

AbstractThe preparation of an industrially used sequential formulation of a melamine–urea–formaldehyde resin was followed by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry and 13C‐NMR analysis. The analysis allowed us to identify and follow the appearance, increase, decrease, and disappearance of a multitude of chemical species during the preparation of both the initial urea–formaldehyde (UF) phase of the reaction and the subsequent reaction of melamine with the UF resin that formed. The analysis indicated that (1) the increase and decrease in the species that formed proceeded through a cycle of the formation and degradation of species occurring continuously through what appeared to be a series of complex equilibria, (2) even at the end of the reaction a predominant proportion of methylene ether bridges was still present, (3) some small proportion of methylene bridges already had formed in the UF reaction phase of the resin even under rather alkaline conditions, and (4) the addition of melamine to the UF prepolymer induced some noticeable rearrangement of methylene ether bridges to methylene bridges. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Preparation of microencapsulated phase-change materials (MCPCMs) by means of interfacial polycondensation

Microcapsules for energy storage and/or heat transfer applications containing phase-change materials (PCMs—including n-pentadecane, n-eicosane and a paraffin wax) were successfully produced by emulsifying the PCMs as small droplets in an aqueous, water-soluble urea-formaldehyde pre-polymer solution substantially free of emulsifier while polymerizing the pre-polymer at the interface by acid-catalyst. The core/shell structured microcapsules were also characterized with size distribution analysis, scanning electron microscopy, FTIR spectrometry and differential scanning calorimetry.

The relation between narrow-dispersed microcapsules and surfactants

Electric ink display is one of the prospect technologies in paper-like display. In this paper, electric ink microcapsules are prepared by means of an in situ polymerization and complex coacervation. In order to obtain the microcapsules in a uniform size distribution, this study focused on the inter-facial tension between tetrachloroethylene and water solution, the dispersion of the core droplets and the microencapsulation with different kind of surfactants. By measuring the inter-facial tensions between water and tetrachloroethylene, it is found that urea-formaldehyde (UF) pre-polymer presents certain surface activity due to the inter-facial tension descending from 43 mN m−1 to 35 mN m−1. Because the surface activity of pre-polymer is not valid, the water-soluble emulsifiers can occupy on the surface of the droplets and prevent the UF resin depositing there. The analysis of the size distribution shows that the UF microcapsules are multi-dispersed. Furthermore, the influence of anionic surfactant of SDS on the size distribution of the core droplets is also investigated. The average diameters of the core droplets prepared with 0.005 wt% and 0.012 wt% SDS are ∼50 µm and 28 µm, respectively. That reveals the existence of SDS not only decreases the droplet diameters, but also makes the size distribution centralized. Because the surface of the core droplets is charged due to the absorption of SDS anionic, the Gelatin and Gum Arabic (GA) coacervating layer is easy to form there. The size of the GA microcapsules prepared with 0.003 wt% SDS is ∼65 µm. Finally; the responsive behaviour of the microcapsules to electric field is also investigated.

Synthesis of functional microcapsules containing suspensions responsive to electric fields

A sort of functional microcapsules, which contain a suspension responsive to electric fields, is prepared by in situ polymerization of urea and formaldehyde. The suspension is made up of pigment phthalocyanine green (PPG) and tetrachloroethylene. In order to solve the particles' separation from the suspension during the microencapsulation and to obtain microcapsules applying to electronic ink display, the dispersibility of the particles, the contact angles between the particles and the tetrachloroethylene, and the influences of different emulsifiers on the microencapsulation are investigated. It is found that the dispersion extent and lipophilicity of the PPG particles are improved due to their surface modification with octadecylamine. The contact angles between the modified PPG particles and the tetrachloroethylene increase, and the PPG particles modified with 2 wt% octadecylamine have the best affinity for tetrachloroethylene. The interfacial tension between C 2Cl 4 and H 2O with urea–formaldehyde prepolymer descends from 43 to 35 mN/m, which indicates that the polymer has certain surface activity. However, water-soluble emulsifiers have an important influence during the microencapsulation because they can absorb on the surfaces of internal phase and prevent the resin of urea–formaldehyde from depositing there. From the SEM images of shell surface and cross section, the microcapsules have relatively smooth surfaces and the average thickness is about 4.5 μm. When the microcapsules are prepared with agitation rates of 1000 and 600 rpm, the mean diameters of the obtained microcapsules are 11 and 155 μm, respectively. The particles in the capsules move toward positive electrode with a responsive time of several hundred milliseconds while providing an electric field.

Preparation of Microcapsules Containing Two-Phase Core Materials

Urea-formaldehyde (UF) microcapsules containing two-phase core materials in which phthalocyanine blue BGS (beta-CuPc) particles were homodispersed in tetrachloroethylene (TCE) were prepared by in situ polymerization. The effects of the various process parameters, including the type of surface modifier, the viscosity of UF prepolymer, the type of water-soluble surfactant, and the concentration of oil-soluble surfactant in the capsule core on the dispersity of beta-CuPc particles in TCE and the properties of the capsule wall and the adsorption of beta-CuPc particles on the internal surface of capsule wall were experimentally investigated. It was shown that using octadecylamine (ODA) to modify beta-CuPc particles resulted in a significant increase of the dispersing extent (DE) and the electrophoresis velocity of the particles in TCE (about 4 and 20 times more than that of unmodified). In addition, the optimal reaction conditions of the synthesis UF prepolymer were obtained by the orthogonal test. On the other hand, as the oil/water interfacial tension of emulsion was big enough, the microcapsule formed. The concentration of Span-80 in TCE was no less than 0.062 mM; the adsorption of beta-CuPc particles on internal surface of wall were restrained. Finally, the microcapsules in which beta-CuPc particles possess reversible response to dc electric field were obtained.

In situ pultrusion of urea–formaldehyde matrix composites. I. Processability, kinetic analysis, and dynamic mechanical properties

AbstractWe conducted a feasibility study on the pultrusion of a glass‐fiber‐reinforced urea–formaldehyde (UF) composite using a proprietary method. The UF prepolymer synthesized in this study was prepared from blends of UF monomer and a curing agent (NH4Cl).The process feasibility, kinetic analysis, and dynamic mechanical properties of the glass‐fiber‐reinforced UF composites by pultrusion were investigated. From investigations of the long pot life of the UF prepolymer, the high reactivity of the UF prepolymer, and excellent fiber wet‐out, we found that the UF resin showed excellent process feasibility for pultrusion. A kinetic model, dα/dt = A exp(−E/RT)αm(1 − α)n, is proposed to describe the curing behavior of a UF resin. Kinetic parameters for the model were obtained from dynamic differential scanning calorimetry scans with a multiple‐regression technique. The dynamic storage modulus of the pultruded‐glass‐fiber‐reinforced UF composites increased with increasing die temperature, filler content and glass‐fiber content and with decreasing pulling rate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1242–1251, 2002