Synthesis of fluorine-containing latexes with core–shell structure by UV-initiated microemulsion polymerization

A core–shell structure of fluorine-containing polyacrylate latex was synthesized by UV-initiated two-stage microemulsion polymerization from styrene (St) and hexafluorobutyl acrylate (HFA) in the presence of Irgacure 2959 as hydrophilic photoinitiator at room temperature. The first polymerization stage took 12 min and the second stage took 10 min. The conversions of the first and the second polymerization stages were about 60 and 85 %, respectively. Fourier transform infrared (FTIR) spectra, transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and contact angle analysis were used to characterize the properties of latexes and their films. The DLS analysis results indicated that the size of the fluorine-containing nanoparticle is about 20 nm. The TEM photos showed that the particles have core–shell structure and some of the cores are located in the center and the others deviate from the center of particles. From the FTIR and XPS results, we can infer that the fluorine monomer could be introduced into the copolymer and the fluorine-containing polyacrylate mainly occupies the shell part. The TGA results indicated that the fluorine-containing polyacrylate copolymers exhibited higher thermal stability than that of the fluorine-free one. The contact angle analysis results showed that fluorine monomers make the film surface more hydrophobic.     

Synthesis and characterization of thermosensitive core–shell polymeric nanoparticles

Thermosensitive core–shell nanoparticles were synthesized by semicontinuous heterophase polymerization of styrene, followed by a seeded polymerization for forming a shell of poly(N-isopropyl acrylamide) (PNIPAM). Nanoparticles characterization by scanning transmission electronic microscopy showed core–shell morphology with average particle diameters around 40 nm. An inverse dependence of the particle size with temperature in the range 20–55 °C was identified by quasielastic light scattering measurements. As was expected for core–shell particles with PNIPAM as the shell, a volume phase transition near 32 °C was detected. In spite of thermosensitive properties of core–shell nanoparticles synthesized here, the volume percentage loss values were not so high, probably due to their relatively low content of PNIPAM.     

Preparation and characterization of novel polyethylene/carbon nanotubes nanocomposites with core–shell structure

Preparation of novel polyethylene/carbon nanotubes (CNTs) nanocomposites with core–shell structure was presented. The method involved in situ ethylene polymerization in which nanotube surface was treated with Grignard Agent, followed by reacting with active transition metal compound, TiCl₄. The multiwalled carbon nanotubes (MWCNTs) supported catalysts polymerize ethylene to form polymer nanocomposite. MWCNTs were homogeneously dispersed within polymer matrix, and as expected, the resultant nanocomposites featured core–shell structure which was confirmed by HRTEM. For the nanocomposite, the microscopic examination of the cryogenically fractured surface not only ensured a good distribution of carbon nano-particles in the PE matrix but also revealed the ductile-like fracture. The Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed for the study of covalent sidewall functionalization and chemical bonding environment of MWCNTs, also indicated effective immobilization of titanium catalyst on the MWCNTs surface. The crystalline properties, dielectric property and thermal stability of the nanocomposites were determined by WAXD, impedance analyzer and TGA. The dielectric result showed a slight decline of the dielectric constant of the nanocomposites with increase of the polymerization time, and lower dielectric loss was also observed.     

Synthesis and characterization of highly durable and reusable superabsorbent core–shell particles

Superabsorbent core–shell particles were synthesized via a two-step process. A silica core was prepared by co-condensation of tetraethyl orthosilicate and vinyl triethoxysilane. The vinyl-functionalized silica particles were then polymerized with acrylamide monomer via free-radical polymerization to yield silica-polyacrylamide (PAM) hybrid particles. The crosslinking density and porosity of PAM on the hybrid particles were controlled by adjusting the concentration of the crosslinker, n,n′-methylenebisacrylamide (MBA). The structure of core–shell particles was confirmed by scanning and transmission electron microscopy techniques. The hybrid particles with 3.0%MBA could absorb water up to 70 g/g. These hybrid particles also removed 80% of methylene blue from solution within 24 h and this efficacy was maintained for seven cycles. The weight remaining of the hybrid particles after nine cycles was higher than that of pure PAM after three cycles indicating the high durability and reusability of the core–shell particles. POLYM. ENG. SCI., 60: 306–313, 2019. © 2019 Society of Plastics Engineers     

Nano-scale core–shell structural casein based coating latex: Synthesis,characterization and its biodegradability

Nano-scale core–shell type particle of caprolactam-butylacrylate co-modified casein (CA-CPL-BA) bearing poly(butylacrylate) core and casein-caprolactam shell was synthesized via emulsifier-free polymerization, and was applied as the film-former in leather finishing. By utilizing potassium persulfate–sodium hydrogensulfite as a redox pair during preparing CA-CPL-BA, the grafting extent was superior to that initiated by ammonium persulfate–sodium hydrogensulfite, potassium persulfate or ammonium persulfate. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis results demonstrated that the average size of neat casein particle was around 700 nm while the resultant CA-CPL-BA latex particles were significantly decreased to about 80 nm in size. Compared with those of neat casein films, enhanced hydrophobicity and higher thermo-stability of the CA-CPL-BA latex film were confirmed by contact angle test and thermal gravimetric (TG) measurement, respectively. Meanwhile, the application performance of the leather samples finished by CA-CPL-BA was proved to be equivalent to that finished by the commercial leather finishing agent product. A possible mechanism of emulsifier-free polymerization for this system was proposed and then proved. Biodegradability tested by soil burial degradation experiments proved that CA-CPL-BA had preferable biodegradability.     

Fabrication and properties of polysilsesquioxane-based trilayer core–shell structure latex coatings with fluorinated polyacrylate and silica nanocomposite as the shell layer

Polysilsesquioxanes (PSQ)-based core–shell fluorinated polyacrylate/silica hybrid latex coatings were synthesized with PSQ latex particles as the seeds, and methyl methacrylate, butyl acrylate, 3-(trimethoxysilyl) propyl methacrylate (MPS)-modified SiO₂ nanoparticles (NPs), 1H,1H,2H,2H-perfluorooctyl methacrylate (PFOMA) as the shell monomers by emulsifier-free miniemulsion polymerization. The results of Fourier transform IR spectroscopy, transmission electron microscopy, and dynamic light scattering suggested the obtained hybrid particles emerged with trilayer core–shell pattern. Contact angle analysis, x-ray photoelectron spectroscopy, and atom force microscopy results indicated that the hybrid film containing SiO₂ NPs showed higher hydrophobicity, lower surface free energy and water absorption, in comparison with the control system (without SiO₂ NPs). Compared with the control system, the hybrid latex film containing SiO₂ NPs in the fluorinated polyacrylate shell layer showed the higher content of fluorine atoms and a rougher morphology on the film surface. Additionally, thermogravimetric analysis demonstrated the enhanced thermostability of PSQ-based nanosilica composite fluorinated polyacrylate latex film.     

Synthesis and characterization of local clay–titanium dioxide core–shell extender pigments

A simple chemical technique has been used to prepare core–shell extender pigments based on Nigerian indigenous clays as core and titanium dioxide as shell. The prepared core–shell extender pigments were characterized using X-ray fluorescence and scanning electron microscopy. The physico-chemical properties of these extender pigments were also evaluated according to ASTM measurements. The study showed that the prepared core–shell pigments were nontoxic and environmentally friendly. They are of low cost and can be incorporated in semi-gloss paints, paper, rubber, and plastic composites without much effect on the volume. The characteristics of these pigments showed that they combine the properties of both their precursors, and have the potential to overcome their disadvantages, e.g., low hiding power of clays and photochemical activity of titanium dioxide.     

Preparation and characterization of CeOx@MnOx core–shell structure catalyst for catalytic oxidation of NO

The CeOx@MnOx catalyst with a core–shell structure was prepared and used for catalytic oxidation of NO. It was found that CeOx@MnOx catalyst showed higher intrinsic catalytic activity than CeMnOx catalyst prepared by citric acid method. Based on the characterization results of N₂ adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS), we may conclude that the excellent catalytic performance of CeOx@MnOx catalyst is related to its low crystallinity, good reducibility, and high concentrations of Mn^4 + and active oxygen species.     

Synthesis and dynamic mechanical study of core–shell structure epoxy/polyacrylate composite particle

A material with high damping property and based on epoxy/polyacrylate (EP/PA) composite particles was synthesized by two-stage emulsion polymerization. Transmission electron microscopy (TEM) showed that the composite particles have a spherical morphology, a core–shell structure and a diameter of 100 nm–130 nm. Fourier transform infrared spectra (FTIR) indicated the cross-linking between EP groups in the core layer and carboxyl groups in the shell layer of the composite particles during film formation. The cross-linking reaction improved the dynamic mechanical property by the interaction of core and shell polymers. The effects of the cross-linking agent and ratio of the two polymers on the damping capacity were studied by dynamic mechanical analysis (DMA). DMA results revealed that a certain amount of acrylic acid could markedly enhance the loss factor (tan δ) and slightly widen the damping temperature range. When the EP/PA ratio was 1:7, peak values for tan δ of the composite materials could reach 2.10, exceeding the value for most damping materials. The result implies that the EP/PA composites have great potential application in damping steel surface coatings.     

Synthesis and properties of microencapsulated phase change material with a urea–formaldehyde resin shell and paraffin wax core

During this study, paraffin wax with low melting point was encapsulated in a urea–formaldehyde resin to prepare a novel microencapsulated phase change material (Micro-P6) for temperature regulation and thermal energy storage. The structure and properties of Micro-P6 were characterized by using Fourier transform infrared spectroscopy, differential scanning calorimeter, laser particle size analyzer, thermogravimetric analysis, contact angle analysis, and scanning electron microscope. The results indicated that the chemical structure of Micro-P6 meets the designed core–shell structure; and the paraffin wax with low melting point was successfully encapsulated by using urea–formaldehyde resin; and the Micro-P6 shows a spherical structure and rough surface, and the average size is 8.0–10.0 μm. Then, the performances of Micro-P6, such as core content, mechanical property, thermal conductivity and durability, were tested. Based on above characterization and performance test, it was indicated that the synthesized Micro-P6 could be used in the field of cementing and construction for temperature regulation and thermal energy storage. The applications of Micro-P6 in the field of cementing and construction will be completed in our next study. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48578.     

Crosslinked polyurethane–epoxy hybrid emulsion with core–shell structure

An epoxy resin was used to prepare crosslinked polyurethane hybrid emulsion through the blocked NCO prepolymer mixing process. Due to their hydrophobicity, the amine chain extender, blocked –NCO, and epoxy are located inside the emulsion particles. Thus, the crosslinking reaction occurs mostly in the interior of the particles. In this way, the crosslinking density of the resin is increased without the use of solidifying agents or heating during film formation, and the stability of the emulsions remains uninfluenced. The effects of the type of amine chain extender and the type, dosage, and addition mode of the epoxy resin were studied in terms of mechanical properties and swelling properties in water and toluene of the cast films. Additionally, the stability of the single-pack hybrid emulsion was studied. The results showed that the sample prepared with diethylene triamine had good stability, chemical resistance, and high mechanical strength. The modulus and water resistance of the films increased with the epoxy resin content, which could reach 20 wt%. The type of amine chain extender affected the stability of the emulsions significantly. The molar ratio of NH/NCO at 1:1 led to the best film performance. The optimal temperature of the chain-extension reaction was approximately 80°C. The hybrid emulsions could be stored for at least 6 months without apparent performance changes.     

Preparation of the stable core–shell latex particles containing organic-siloxane in the shell

In this study, the latex particles with a polyacrylate core and a polydimethylsiloxane shell via 3-(methacryloxypropyl)-trimethoxysilane as the space arm to link the core and shell have been prepared by semi continuous seeded emulsion polymerization. And several key polymerization reaction conditions such as the emulsifier concentration, 3-(methacryloxypropyl)-trimethoxysilane dosages, feeding sequence and the acrylates/siloxanes ratio were detailedly discussed. Then, the optimal condition to prepare stable core/shell particles was selected and a proper preparation process has been established. The as-synthesized particles were characterized by TEM and XPS. The clear core/shell structure of the particles could be observed through analysis TEM. In addition, the results of XPS analyses manifested that siloxanes had been grafted on the surface of the polyacrylate particles and they distributed on the outmost layer of the particles. Finally, the surface hydrophobicity of the film formed by latex particles was investigated by the water absorption ratio measurement. The results indicated the developed latex particle provided with a fair water-repellency property.     

Synthesis of superhydrophobic core–shell mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSNPs) have been used in variety of applications due to their morphology and porous structure. This work reports the one-pot synthesis of ultrahydrophobic MSNPs using N-cetyl-n,n,n trimethyl ammonium bromide as a cationic surfactant template and ethanol (EtOH) as a cosolvent to form mesopores in the MSNPs. The effects of EtOH on the size and the pore structure of the MSNPs were studied by scanning electron microscopy and transmission electron microscopy. The results show that an addition of EtOH led to an enlargement of the MSNPs and a change in pore structure from a lamellar structure to a radially oriented structure. Co-condensation with two different types of fluoroalkyl silanes; trimethyl(fluoromethyl)silane, and trichloro(1H,1H,2H,2H-perfluorooctyl)silane provided low surface energy MSNPs with a core–shell structure. An assembly on the surface of these F-MSNPs generated nanostructure surface roughness rendering an improvement in surface wettability with water contact angle of 158.6°, which is a characteristic of oleophobic and ultrahydrophobic material.     

Development and characterization of a lignin–phenol–formaldehyde wood adhesive using coffee bean shell

In the present study, the possibility of development of a wood adhesive using coffee bean shell lignin (Cbsl) has been explored. Cbsl-modified phenolic adhesive has been prepared by replacing phenol with lignin at different weight percents. The optimization of weight percent lignin incorporation was carried out with respect to mechanical properties. It was found that up to 50 wt% of phenol could be replaced by Cbsl to give lignin–phenol–formaldehyde adhesive (LPF) with improved bond strength in comparison to control phenol–formaldehyde (CPF). Optimized LPF and CPF adhesives were characterized by IR, DSC and TGA. The IR spectrum of LPF showed structural similarity to CPF. Thermal stability of LPF adhesive was found to be lower as compared to that of CPF. DSC studies revealed a higher rate of curing in the LPF adhesive.     

Synthesis of multifunctional core–shell toughening agent with light stability and its application in polycarbonate

A light stabilizer compound of 2-(2′-propionyloxy-5′-methylphenyl) benzotriazole (AMB) was synthesized by the esterification of the 2-(2′-hydroxy-5′-methylphenyl) benzotriazole with acryloyl chloride (AC), and the AMB was then copolymerized with the methyl methacrylate (MMA), butyl acrylate (BA), and silicone monomers (D4) to prepare the silicone light toughener of poly(D4-MMA-BA-AMB). Effects of the AMB monomer on the conversion and polymerization stability and the toughening and photostabilizing effects of the poly(D4-MMA-BA-AMB) on the polycarbonate (PC) were studied. The prepared multifunctional toughening agent was characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analyzer, transmission electron microscopy, dynamic light scattering analyzer, and ultraviolet absorption spectroscopy. Results show that the prepared poly(D4-MMA-BA-AMB) toughening agent possessed core–shell structure and could effectively absorb the ultraviolet rays. Although the addition of the poly(D4-MMA-BA-AMB) toughening agent had a negative effect on the tensile strength of the PC, it could greatly improve the low-temperature notched impact strength, toughness performance, and yellowness performance of PC products after UV irradiation. Compared with the silicone toughening agent, the toughening agent of the poly(D4-MMA-BA-AMB) had better anti-ultraviolet property for the PC/poly(D4-MMA-BA-AMB) composite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48747.     

Synthesis and film performances of SiO2/P(MMA-BA) core–shell structural latex

In this study, we have successfully synthesized silica/poly(methyl methacrylate-butyl acrylate) (SiO₂/P(MMA-BA)) core–shell nanocomposite colloids via in situ emulsion copolymerization using cationic 2,2′-azobis(2-amidinopropane)dihydrochloride (AIBA) as the initiator and the 3-Glycidoxypropyl-trimethoxysilane (GPTMS)-modified SiO₂ nanoparticles as the seeds. The SiO₂ nanoparticles embedded can reach as high as 60 wt%. The nanocomposite film presents almost the same high transparency as the pure polymer film (>90% transmittance in visible range), and displays significantly improved mechanical and UV weathering resistant properties over its pure polymer film.     

Preparation and characterization of silica sol/fluoroacrylate core–shell nanocomposite emulsion

The silica sol/fluoroacrylate core?Cshell nanocomposite emulsion was successfully synthesized via traditional emulsion polymerization through grafting of KH-570 onto silica particles. Comparing the performance of the polyacrylate copolymer, the fluorinated polyacrylate copolymer and the silica sol/fluoroacrylate core?Cshell nanocomposite emulsion, we can come to a conclusion that the silica sol/fluoroacrylate core?Cshell nanocomposite emulsion presents significantly excellent performance in all aspects. The products were characterized by Fourier transform infrared (FTIR), photon correlation spectroscopy (PCS), transmission electron microscopy (TEM), thermogravimetry (TGA), Contact angle and UV?Cvis analyses techniques. The chemical structure of polyacrylate copolymer, fluorinated polyacrylate copolymer and silica sol/fluoroacrylate nanocomposite were detected by FTIR. The size and stability of emulsion latex particles were determined by PCS technique. TEM analysis confirmed that the resultant latex particle has the core?Cshell structure, obviously. The water absorption and contact angle data also showed that the silica sol/fluoroacrylate nanocomposite film has good hydrophobic performance. TGA analysis indicated the weight loss of the silica sol/fluoroacrylate nanocomposite film begins at around 350?°C which testifies its good thermal stability. The UV?Cvis spectroscopy analysis showed that the silica sol/fluoroacrylate nanocomposite film possess UV?Cvis shielding effect when the added volume amount of KH570 modified silica sol is up to 5?mL. Therefore, the excellent properties of hydrophobicity, thermodynamics and resistance to ultraviolet provide the silica sol/fluoroacrylate nanocomposite film with potential applications in variety fields. In addition, the formation mechanism of core?Cshell structure silica sol/fluoroacrylate nanocomposite latex particles was speculated.     

Synthesis and characterization of CuInSe<Subscript>2</Subscript> core–shell quantum dots

A synthesis of 1-dodecanetiol stabilized colloidal quantum dots of CuInSe₂ exhibiting photoluminescence in the range of 700–900 nm has been described. The effect of the shell on the energy levels of electrons in CuInSe₂–ZnS and CuInSe₂–ZnSe core–shell quantum dots has been investigated by quantum mechanical calculations.     

Phase evolution and lightweight application of dolomite@Al2O3 spherical particle with core–shell structure

Dolomite@Al₂O₃ spherical particles with core–shell structure were fabricated by using the dolomite powders as the core and wrapping corundum powders on their surface. The phase evolution and microstructure of the dolomite@Al₂O₃ spherical particles with different firing temperatures were studied. As the spherical particles fired at different temperatures, the dolomite in the spherical core decomposed into MgO and CaO. Due to the Kirkendall effect, MgO and CaO diffused into the shell of the spherical particle and left Kirkendall holes in the core. The holes produced by the Kirkendall effect and the decomposition of dolomite act together to form a hollow structure in the center. And during the diffusion process, MgO and CaO reacted with corundum to generate spinel and calcium hexaaluminate. A small amount of spinel and calcium hexaaluminate can form a ternary compound Ca₂Mg₂Al₂₈O₄₆. Moreover, simulation software Factsage and Abaqus were used separately to help prove the phase evolution and the introduction of spherical particles to the properties of refractories. To test the lightweight effect of dolomite@Al₂O₃ spherical particles on refractories, it was introduced into spinel–corundum refractories as medium particles in different content and fired at different temperatures. The results show that after firing at 1650°C for 3 h with introducing 30% dolomite@Al₂O₃ spherical particles, the samples can reach a high compressive strength (128 MPa), high refractoriness under load (1683°C), and low thermal conductivity (1.79 W (m K)⁻¹).