Storage stability and solubility of poly(urea‐formaldehyde) microcapsules containing A‐olefin drag reducing polymer

Microcapsules containing α‐olefin drag reducing polymer were prepared by in situ and interfacial polymerization with urea, formaldehyde, and styrene as shell materials, respectively. IR spectrums of prepared shells indicated the formations of poly(urea‐formaldehyde) and polystyrene in the microencapsulating process. The morphologies of uncoated particles and microcapsules were observed by scanning electron microscopy (SEM) which proved that the α‐olefin drag reducing polymer particles were effectively coated. For the purpose of determining the stability of microcapsules in transportation and storage, the static pressure experiment was carried out and lasted for 6 months. In this process, microcapsules with polystyrene as shell material stuck together after 3 months; however, those with poly(urea‐formaldehyde) kept the state of particles. The thermal characteristics of uncoated particles (core), poly(urea‐formaldehyde) (shell), and microcapsules with that as shell material were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) which proved that thermal stable temperature of microcapsules containing α‐olefin drag reducing polymer with poly(urea‐formaldehyde) as shell material was below 225°C, and the mean heat absorbed by microcapsules in the temperature increasing process was 1.5–2.0 W/g higher than that by cores. The evaluation of drag reducing rate of microcapsules showed that the microencapsulating process had no influence on the drag reduction of α‐olefin drag reducing polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Chitosan nanocoating on cotton textile substrate using layer‐by‐layer self‐assembly technique

An attempt was made to deposit a nanocoating onto a cotton textile substrate using a layer‐by‐layer self‐assembly approach. Chitosan, a natural biopolymer with polycationic characteristic, was used as a polyelectrolyte along with poly(sodium‐4‐styrene sulfonate) as an anionic polyelectrolyte for the first time on a textile substrate using this technique. The nanocoated surface was evaluated for surface characteristics such as the contact angle and scanning electron microscopy. The effect of ultrasonication during the intermediate washing steps was explored. Ultrasonication during the washing steps clearly helped in depositing more uniform bilayers onto individual fiber surfaces; this contrasted with the deposition of a continuous coating layer, which was nonuniform and had a lot of surface cracks. The use of this novel method for depositing chitosan onto cotton imparted antimicrobial properties to the fabric without adversely affecting its flexibility, feel, or breathability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of chitosan/urea‐formaldehyde shell microcapsules containing dicyclopentadiene

Microcapsules containing healing agent have been used to develop the self‐healing composites. These microcapsules must possess special properties during the use of composites such as stability in surrounding, appropriate mechanical strength, and lower permeability. A new series of microcapsules containing dicyclopentadiene with chitosan/urea‐formaldehyde copolymer as shell materials were synthesized by in situ copolymerization technology. The microencapsulating mechanism was discussed and the process was explained. Also, the factors influencing the preparation of microcapsules were analyzed. The morphology and shell wall thickness of microcapsules were observed by using scanning electron microscopy. The size of microcapsules was measured using optical microscope and the size distribution was investigated based on data sets of at least 200 measurements. The chemical structure and thermal properties of microcapsules were characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis, respectively. The storage stability and isothermal aging experiment of microcapsules were also investigated. Results indicted that the chitosan/urea‐formaldehyde microcapsules containing dicyclopentadiene were synthesized successfully; the copolymerization occurred between chitosan and urea‐formaldehyde prepolymer. The microcapsule size is in the range of 10–160 μm with an average of 45 μm. The shell thickness of microcapsules is in the range of 1–7 μm and the core content of microcapsules is 67%. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Enhanced mechanical properties of multilayer nano‐coated electrospun nylon 6 fibers via a layer‐by‐layer self‐assembly

We reported the mechanical properties of the polyelectrolyte multilayer nano‐coated electrospun fiber mats with different number of layers. Multilayer nano‐coatings composed of layers of PSS and PAH were successfully deposited onto electrospun nylon 6 fibers via layer‐by‐layer self‐assembly. Compared with pure nylon 6 fibers, the morphology of polyelectrolyte multilayer coated nylon 6 fibers was uniform and smooth. The mechanical properties of polyelectrolyte multilayer coated random and aligned nylon 6 fibers were remarkably enhanced. Moreover, it was found that the higher degree of alignment resulted in higher tensile strength, suggesting the combined effects of the alignment, the surface nanocoating and the formation of internal networks of polyelectrolytes on nylone 6 fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of microcapsules of strong polyelectrolyte couples by one‐step complex surface precipitation

Polyelectrolyte microcapsules are fabricated by a one‐step surface precipitation and by a layer‐by‐layer technique on decomposable colloids. The ternary solvent water/acetone/sodium bromide is adjusted properly keeping dissolved simultaneously the strong polyelectrolytes sodium poly(styrene sulfonate) and poly(vinyl benzyl trimethylammonium chloride). Microcapsules are characterized by confocal laser scanning microscopy and scanning force microscopy. The capsules are dissolvable in the ternary solvent. Other dissolved strong polyelectrolyte couples and template‐free preparation pathways are suggested.     

Microencapsulation of disperse dye particles with nano film coating through layer by layer technique

Throughout the past ten years, comprehensive understanding of fundamental and applied research has focused on functional coating and specifically on microencapsulaion. In this study, weak polycation poly(allylamine hydrochloride) and strong polyanion poly(sodium styrene sulfonate) were used for fabrication of nano film through layer by layer technique on the surface of disperse dye particles. Then micron‐sized particles were surrounded by poly(urea formaldehyde) using in‐situ polymerization. Chemical structure, surface morphology, and size distribution of these novel microcapsules were characterized by Fourier transform infrared spectrometry, differential scanning calorimetry, optical microscopy, and scanning electronic microscopy. Size and surface morphology of the microcapsules can be optimized by selecting proper weight ratio of urea to formaldehyde and core to shell material type, and amount of surfactant and agitation rate. This technology demonstrated good capability in several applications in textile industry, such as dying fabrics because of saving huge amount of water and showing slow‐release property of dye without using dye assistant agents. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

LbL‐coated microcapsules as systems for encapsulation of optical brightening agent

We report the encapsulation of optical brightening agent (OBA) into hollow microcapsules prepared by the controlled Layer‐ by‐Layer (LbL) self‐assembly process, achieved by the sequential adsorption of oppositely charged polyelectrolytes using negatively charged silica template. Loading takes place by spontaneous deposition method which was proved by confocal laser scanning microscopy (CLSM) using rhodamine 6G (Rd6G) as a fluorescent probe. The loading of the OBA into the microcapsules was found to be dependent on the feeding concentration, pH of the medium, and loading temperature. The encapsulation efficiency of OBA decreased on increasing feeding concentration. Maximum loading was observed at pH 4 and amount of OBA loaded decreased with increase in pH. The loaded OBA was released in a sustained manner for 8 h. No degradation of the OBA was observed during the process of encapsulation and release. Polyelectrolyte capsules potentially offer an innovative way of encapsulating large amounts of active materials for a variety of applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Suzuki‐ and Heck‐Type Cross‐Coupling with Palladium Nanoparticles Immobilized on Spherical Polyelectrolyte Brushes

We report on a systematic study of the use of palladium nanoparticles immobilized on spherical polyelectrolyte brushes – Pd@SPB – for Heck‐ and Suzuki‐type coupling reactions. The spherical polyelectrolyte brush particles serving as carriers for the palladium nanoparticles consist of a solid polystyrene core with a radius of 46 nm onto which long chains of cationic polyelectrolytes are grafted. The palladium nanoparticles have directly been generated within this brush layer and the stabilization of the nanoparticles is effected by the colloidal carriers, no further surface stabilization is necessary. We demonstrate that these composite particles present robust catalysts for the Heck‐ and Suzuki‐type coupling reactions. This was shown by carrying out the Suzuki‐ and Heck‐type coupling reactions at relatively low temperatures (Suzuki reaction: 50 °C, Heck reaction: 70 °C). We demonstrate that the catalytic composite particles are not changed by these reaction conditions and retain their full activity for at least four runs. The yields obtained for both reactions are good to excellent. The mild operation conditions of the palladium nanoparticles are traced back to the absence of surface stabilization. Further mechanistic implications are discussed.     

Failure of elastic‐plastic core–shell microcapsules under compression

Characterization of the failure behavior of microcapsules is extremely important to control the release of their core actives by mechanical forces. The strain and stress of elastic‐plastic uninflated core–shell microcapsules at failure (rupture or bursting) has been determined using finite element modeling (FEM) and micromanipulation compression experiments. The ductile failure of polymeric microcapsules at high deformations is considered to occur when the maximum strain in the shell exceeds a critical strain, resulting in their rupture. FEM has been used to determine the maximum strains present in the capsule wall at different deformations for three types of shell material: elastic, elastic—perfectly plastic and elastic—perfectly plastic with strain hardening at large strains. The results obtained were used to determine the failure strain and stress of melamine‐formaldehyde microcapsules, with average population values of ～0.48 and ～350 MPa, respectively. Thus, the elastic‐plastic stress–strain relationship has been determined for the core–shell microcapsules tested. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Preparation of antireflection coatings with novel cationic–nonionic PU‐SiO2 core–shell particle dispersions

A novel polyurethane (PU)‐SiO₂ core–shell particle dispersion was prepared by an acid‐catalyzed sol–gel process using cationic–nonionic PU particle as template. Results of average sizes, polydispersity index, and transmission electron microscope indicated that tetramethylorthosilicate were first diffused to the surface of PU particles, then occurring hydrolysis–condensation reaction to form core–shell particles. Antireflection coating formulation was prepared by as‐prepared core–shell particle dispersion and SiO₂ sol binder. After dip‐coating in the formulation, antireflection coating was formed on glass surface by calcination. Scanning electron microscopy images showed that pores had been formed inside coating after removing PU template particles, and the coating surface could be almost fully closed. In addition, ultraviolet–visible spectrophotometer analysis showed that the maximum transmittance of antireflection glasses can be as high as 98.6% at 548 nm. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45762.     

Layer‐by‐layer assembled hydrogel nanocomposite film with a high loading capacity

The layer‐by‐layer assembly technique is a method that widely used in the preparation of nanostructured multilayer ultrathin films. We fabricated a hydrogel nanocomposite film by alternating the deposition of a core–shell poly[(dimethylimino)(2‐hydroxy‐1,3‐propanedily) chloride] (PDMIHPC)–laponite solution and poly(acrylic acid). The growth of the deposition procedure was proven by ultraviolet–visible spectroscopy and spectroscopic ellipsometry. The surface morphology of the films was observed by scanning electron microscopy. The films could reversibly load and release methylene blue (MB) dye, which was used as an indicator. It took about 4.5 h to reach loading equilibrium at pH 9.0. The loading capacity of the film for MB was as large as 4.48 μg/cm² per bilayer because of the introduction of the core–shell PDMIHPC–laponite as a film component. Nearly 90% of MB was released at pH 3.0 or in a 300 mM NaCl solution within 2.5 h. The loading and release processes were greatly influenced by the ionic strength and pH value of the MB solution. The hydrogel nanocomposite film showed good pH‐triggered loading‐release reversibility and suggested potential applications in controlled drug‐delivery systems and smart materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39352.     

Preparation and properties of microcapsule with EVA core‐PU shell structure

Microcapsule with poly(ethylene‐co‐vinylacetate) (EVA) core‐polyurethane (PU) shell structure was synthesized by interfacial polymerization in aqueous polyol dispersion with ethylene diamine as the chain extender of toluene diisocyanate in poly(vinyl alcohol) aqueous solution as the stabilizing agent. The effects of polyol constituent on the average particle size and distributions, morphologies, color strength, and friction fastness of core‐shell particles were investigated to design microcapsule. The friction fastness of printed fabrics with EVA core‐PU shell microcapsules became the increase to 4–5 grades. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 893–902, 2007     

Ultrasonication‐assisted synthesis of molecularly imprinted polymer‐encapsulated magnetic nanoparticles for rapid and selective removal of 17β‐estradiol from aqueous environment

Molecularly imprinting technique was combined with magnetic nanoparticles to synthesize molecularly imprinted polymer‐encapsulated particles for selective removal and efficient separation of estrogenic compounds from water. The core‐shell‐structured particles were successfully prepared by a novel 2‐h ultrasonication‐assisted synthesis in a mixture of water and organic solvent using dual‐layer surfactant‐modified magnetic particles as core, the most physiologically active estrogenic compound (17β‐estradiol) as template, and widely adapted methacrylic acid as functional monomer. Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and magnetic separation were used to characterize the particles. High‐performance liquid chromatography–tandem mass spectrometry was used for quantitative binding performance analysis at low‐nanogram per milliliter levels. The particles exhibited satisfactory recognition of 17β‐estradiol in water. They possessed great potential for rapid, cost‐effective, and efficient separation of estrogenic compounds from aqueous environment with specificity. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Influence of microcapsule shell material on the mechanical behavior of epoxy composites for self‐healing applications

In this article, we have studied the effect of microcapsule shell material on the mechanical behavior of self‐healing epoxy composites. Liquid epoxy healant was encapsulated in melamine‐formaldehyde (MF) and urea‐formaldehyde (UF), using emulsion polymerization technique to prepare microcapsules of different shell walls. The core content of the microcapsules, as determined by solvent extraction technique was found to be 65 ± 4%, irrespective of the shell wall of microcapsule. Morphological investigations reveal a rough texture of the spherical microcapsules, which was attributed to the presence of protruding polymer nanoparticles on the surface. Epoxy composites containing UF and MF microcapsules (3–15% w/w) were prepared by room temperature curing and their mechanical behaviour was studied under both quasi‐static and dynamic loadings. The tensile strength, modulus, and impact resistance of the matrix was found to decrease with increasing amount of microcapsule in the formulation, irrespective of the shell wall material used for encapsulation. Interestingly, substantial improvement in the fracture toughness of the base resin was observed. Morphological investigations on the cracked surface revealed features like crack pinning, crack bowing, microcracking and crack path deflection, which were used to explain the toughened nature of microcapsule containing epoxy composites. Our studies clearly indicate that the microcapsule shell wall material does not play any significant role in defining the mechanical properties of the composites. In addition, presence of secondary amine functionalities in UF and MF shell wall do not interfere with the reaction of epoxy with triethylene tetramine hardener during the curing process. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40572.     

Expansion space and thermal stability of microencapsulated n‐octadecane

5.0–50.0 vt% of cyclohexane was mixed with 95.0–50.0 vt% of n‐octadecane as the oil‐phase during the emulsion process in the in situ polymerization of melamine‐formaldehyde. By heat‐treating the microcapsules in an oven at 100°C, the cyclohexane was removed and expansion space was formed inside the microcapsules. The microcapsules were characterized by using FTIR, SEM, DSC, TGA, and gas chromatography. When the microcapsules are heat‐treated at temperatures higher than 180°C, Tm, ΔHm, Tc, and ΔHc of the microcapsules decrease. The attenuation of enthalpy of the microcapsules containing expansion space is obviously lower than that of the control sample, however. The permeability of the microcapsule shell decreases with the increase of cyclohexane content. There is a maximum between the thermal stabilities of the microcapsules and the cyclohexane contents. The microcapsules synthesized with 30.0–40.0 vt% of cyclohexane have the highest thermal stabilities, with 230°C and 289°C in air and nitrogen atmosphere, respectively. The thermal stable temperatures are approximately 67°C and 102°C higher than that of the control sample, respectively. The expansion space inside the microcapsules allows the n‐octadecane to expand in the temperature rising process and exert lower pressure to the shell, therefore keeping the shell intact and increasing the thermal stabilities of the microcapsules. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 390–396, 2005     

Preparation of Cinnamon Oil‐Loaded Antibacterial Composite Microcapsules by In Situ Polymerization of Pickering Emulsion Templates

In this study, the cinnamon oil (CMO)‐loaded antibacterial composite microcapsules with silicon dioxide (SiO₂)/poly(melamine formaldehyde) (PMF) hybrid shells are effectively and facilely constructed by in situ polymerization of SiO₂ nanoparticle–stabilized Pickering emulsion templates. The morphological structure, composition, and thermal performance of the microcapsules are determined by scanning electronic microscopy, Fourier transform infrared spectroscopy, and thermal gravimetric analysis. In addition, in vitro CMO release and antimicrobial investigations of the microcapsules are also performed, respectively. The results demonstrate that the microcapsules own an approximately spherical shape with a core–shell structure. Moreover, the micro‐encapsulation of CMO clearly increases its thermal stability, and meanwhile results in obtaining microcapsules with the controlled CMO release and visibly long‐term antimicrobial effects. All the results show that in situ polymerization based on templating Pickering emulsions is an attractive method to construct antibacterial essential oil–loaded microcapsules, which can be served as promising antibacterial materials.     

Interfacial polymerization of polyaniline and its layer‐by‐layer assembly into polyelectrolytes multilayer thin‐films

The layer‐by‐layer (LbL) self assembly deposition technique was used to prepare multilayer thin films of anionic polyaniline‐blend‐poly(sodium 4‐styrenesulfonate) (PANI‐PSS) and cationic poly(diallydimethylammonium chloride) (PDADMAC). Anionic polyaniline was prepared by the interfacial polymerization of aniline monomer in the presence of PSS which acted as template to provide water solubility. The PSS to PANI concentration ratios used in the synthesis step was found to have a major effect on the final PANI‐PSS synthesis, its self assembly and the electrical properties of the prepared films. The optical and electrical properties of the films were measured by ultraviolet‐visible spectroscopy (UV‐Vis) and a 4‐point probe setup, respectively while the thickness of the films was measured by atomic force microscopy (AFM). Results showed that the optimum condition for the film growth and optimal conductivity were obtained with different synthesis conditions. These results suggest that the PSS concentration used for interfacial synthesis of PANI must be finely tuned depending on the type of application aimed by the user. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization core‐shell particles and application for E‐Ink

the core‐shell particles were prepared by dispersion copolymerization. The core‐shell particles were characterized with Fourier‐transform infrared spectroscopy, Transmission electron microscope and scanning electron microscope. The dispersion stability and electrophoretic performance of core‐shell particles were studied in the mixed medium of tetrachloroethylene and cyclohexance. Microcapsules containing the core‐shell particles were prepared by coacervation. Results showed that the core‐shell particles had good dispersion stability and it had no electric response, which could be used as grounding particles for E‐Ink. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1195–1199, 2007     

Mechanical properties and thermal stability of double‐shell thermal‐energy‐storage microcapsules

Double‐shell‐structured microcapsules encapsulating phase‐change materials (micro‐PCMs) with an average diameter of 5–10 μm were successfully fabricated with a melamine–formaldehyde resin as the coating material. The mechanical properties of the obtained piled micro‐PCMs, tested under compression, were evaluated with a pressure sensor. Typical stress–strain curves showed that both the single‐shell‐ and double‐shell‐structured microcapsules had yield points and maximum point pressures. The morphological changes in the shell surface confirmed the existence of yield points by scanning electron microscopy. When the pressure was beyond the yield point, the microcapsules showed conventional plastic behavior, and the double‐shell structure was more mechanically stable than the single‐shell one. Differential scanning calorimetry analysis results revealed that the properties of the phase‐change materials experienced no variation after coating with a single‐shell‐ or double‐shell‐structured polymer. Thermogravimetric analysis showed that the double‐shell‐structured micro‐PCMs experienced a weight loss of only about 5% from 86.3 to 232°C but did so more rapidly from 232 to 416°C. Thermoregulation was determined with periodical heating and cooling tests. The data showed that the micro‐PCMs changed temperature in a narrow range of 20–25°C with a time lag of 20 min to reach the maximum or minimum temperature in comparison with a reference temperature of 18–28°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1295–1302, 2007     

Core–shell structure design of pulverized expandable graphite particles and their application in flame‐retardant rigid polyurethane foams

Pulverized expandable graphite (pEG) and melamine ? formaldehyde (MF) resin core ? shell structure particles (pEG@MF) as specific flame retardants for rigid polyurethane foam (RPUF) were synthesized by encapsulating pEG particles with a layer of MF resin via in situ polycondensation. The initial feed weight ratio of pEG and MF prepolymer was found to be the key factor affecting the shell forming process, and the shell growth can be regarded as a combination of ‘raspberry‐like’ and conventional ‘core–shell’ formation mechanisms. With the encapsulation of a well formed MF shell, the expandability of pEG particles was significantly enhanced from 42 mL g^–1 to 76 mL g^–1 and thus the pEG@MF particles showed good flame‐retardant performance in RPUF. The RPUF/pEG@MF composites passed the V‐0 rate and the limiting oxygen index was remarkably increased from 21 to 28 vol% by adding only 10 wt% pEG@MF particles; both the expandability and available expandable graphite content played an important role in controlling the flame‐retardant performance of pEG@MF particles. With a loading of fine sized pEG@MF particles, desirable mechanical and thermal insulation properties of RPUF/pEG@MF composites were achieved by preserving the complete cell structure of RPUF and screening the high thermal conductivity of the pEG particles with the thermally inert MF resin shell. The exciting application of the novel pEG@MF particles indicates that the core–shell structure design of expandable graphite can serve as promising solution for fabricating halogen‐free flame‐retardant RPUF composites with high performance. © 2013 Society of Chemical Industry