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     

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.     

Simple route to get very hydrophobic surfaces of fibrous materials with core–shell latex particles

The aim of this article is to report the creation of artificial, robust, and very hydrophobic materials with core–shell polyurethane–polydimethylsiloxane or polyurethane–poly(n-butyl acrylate) polymer microparticles. These latexes were prepared by polyaddition in cyclohexane with commercial or synthetic steric stabilizers. An easy one-step method based on the filtration of the colloidal particles was developed to obtain water-repellent fibrous materials such as paper or textiles that maintain stable properties even after several washing/drying cycles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of superparamagnetic β-cyclodextrin-functionalized composite nanoparticles with core–shell structures

In this article, we report an original and feasible protocol for the preparation of superparamagnetic β-cyclodextrin-functionalized composite nanoparticles with core–shell structures via cross linking reaction on the surface of carboxymethyl β-cyclodextrin-modified magnetite (Fe₃O₄) nanoparticles by using epichlorohydrin as a crosslinking agent. The structure and morphology of the prepared composite nanoparticles were studied by Fourier transform infrared spectrometry, X-ray diffraction measurement, transmission electron microscopy and the thermogravimetric analysis. The results show that the prepared roughly spherical composite nanoparticles (diameter about 10–20 nm) with core–shell structures turned out to be magnetite nanoparticles surface-surrounded by a layer of cross-linked CM-β-cyclodextrin polymer. Results of vibrating sample magnetometry testing and inclusive behaviour studying confirmed the superparamagnetism with saturation magnetization value of 52.0 emu/g in an external applied magnetic field of 20000 Oe and inclusion functionality of the composite nanoparticles consisting of magnetite cores and β-cyclodextrin moiety, which implies very important applications in targeting drug delivery technology and separation for specific substances.     

Soft core–hard shell latex particles for mechanically strong VOC-free polymer films

Polymer films cast from aqueous polymer dispersions typically suffer from an inherent lack of mechanical strength when compared to their solvent-borne counterparts. This drawback can be overcome by the use nanostructured hybrid particles that contain both a hard and soft phase. In this work, we demonstrate the use latex particles consisting of a soft core with a multilobed hard shell synthesized by seeded semicontinuous emulsion polymerization with the aim of maximizing the interconnectivity of the hard phase in the resulting polymer film, thus generating films with improved mechanical properties. Films with a minimum film formation temperature (MFFT) close to that of the soft phase are formed while obtaining a Young's modulus up to 4.5 times higher that of a standard homogeneous latex particle. The effect of annealing temperature on film morphology is also investigated, clearly demonstrating that a marked difference in mechanical properties is observed when a percolating network of the hard phase within the film is obtained. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47608.     

Particle size and shell composition as effective parameters on MFFT for acrylic core–shell particles prepared via seeded emulsion polymerization

In this study, acrylic-based copolymer particles were prepared with core–shell morphology and the effect of T_g of the shell, particle size and their bimodal size distribution on minimum film formation temperature (MFFT) were investigated. The main goal was to optimize conditions to obtain latexes with low MFFT and appropriate mechanical properties. These will develop the applicability of such water-borne binders as paints and coatings at ambient conditions. A series of latexes with core–shell morphology with variable T_g of the shell from −56 to 30 °C were prepared and the MFFT, hardness and thermal behavior of the obtained films were studied. Then a series of latexes with particle sizes ranging from 46 to 960 nm were prepared and the effect of particle size on MFFT was studied too. By inducing the formation of secondary nucleation during emulsion polymerization, latexes with bimodal size distribution were obtained and the effect of presence of such particles on film formation was investigated. Results indicate that latexes with appropriate composition and bimodal particle size distribution lead to optimized performance in both mechanical and film formation properties as a proper choice for water-borne coatings.     

Temperature-controlled conversion from Fe–Si particles to integrated Fe–Si/SiO2 core–shell structure particles during fluidised bed chemical vapour deposition

In the synthesis of ferromagnetic/SiO₂ core–shell structures, the minimum formation conditions and evolution mechanism are worth investigating. In the present study, to determine the minimum formation temperature of an integrated Fe–Si/SiO₂ core–shell structure during chemical vapour deposition in a fluidised bed, the effects of deposition temperature on the structural and magnetic performances of SiO₂ insulation coatings on Fe–Si particles were investigated. Thermodynamic calculations and differential scanning calorimetry were used to understand the thermal decomposition of C₈H₂₀O₄Si. The results of the theoretical and structural studies showed that the minimum deposition temperature of the amorphous SiO₂ insulation coating on the Fe–Si particle surface was ~880 K and that the Fe–Si/SiO₂ composite structure started to convert into an integrated Fe–Si/SiO₂ core–shell structure after the deposition temperature was raised above 920 K. The increase in the thickness of the SiO₂ insulation layer due to the increased deposition temperature was studied using X-ray diffraction and scanning electron microscope analyses. The results of X-ray photoelectron spectroscopy showed that four and five types of electronic structures existed in the SiO₂ insulation shell for silicon and oxygen, respectively, and that only 32.74 at.% of the oxygen from the Si(OSi)₃(OH) group interacted with the Fe–Si alloy surface. The results of the performance test indicated that the integrated Fe–Si/SiO₂ core–shell structure led to a substantial enhancement in the electrical resistivity of the particles and reduction in their saturation magnetisation, but hardly affected the coercive force.     

Mechanical properties and fracture behavior of high-performance epoxy nanocomposites modified with block polymer and core–shell rubber particles

The mechanical properties, thermomechanical properties, and fracture mechanic properties of block-copolymer (BCP), core–shell rubber (CSR) particles, and their hybrids in bulk epoxy/anhydride system were investigated at 23 °C. The results show that fracture toughness was increased by more than 268% for 10 wt % BCP, 200% for 12 wt % of CSR particles, and 100% for hybrid systems containing 3 wt % of each, BCP and CSR. The volume content of nanoparticles influences the final morphology and thus influences the tensile properties and fracture toughness of the modified systems. The toughening mechanisms induced by the BCP and CSR particles were identified as (1) localized plastic shear-band yielding around the particles and (2) cavitation of the particles followed by plastic void growth in the epoxy polymer. These mechanisms were modeled using the Hsieh et al. approach and the values of G_Ic of the different modified systems were calculated. Excellent agreement was found between the predicted and the experimentally measured fracture energies. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48471.     

Preparation of core–shell impact modifier particles for PVC with nanometric shell thickness through seeded emulsion polymerization

The improvement in toughness of rigid polymers like poly(vinyl chloride) (PVC) has been of great interest for developing their applications. This could be provided by designing impact modifiers which could be blended with the polymeric matrix. Here, core–shell type impact modifier particles with different glass transition temperatures of the shell and specifically, with nanometric shell thickness were prepared through seeded emulsion polymerization. The core consisted of polybutadiene particles and the shell was made of poly(methylmethacrylate-co-butyl acrylate) that was grafted onto the surface of the seed particles. The polymerization reaction was optimized and the resulting latex particles were well characterized by several techniques such as DSC, DLS, SEM, and TEM. It was found that the core–shell particles have diameters of about 350–360 nm, including the shell with thickness of almost 20–30 nm and glass transition temperatures ranging between 70 and 120 °C. The prepared particles were blended with PVC and the corresponding impact strengths of the moldings were measured by means of Izod impact test. The impact results revealed that by decreasing T _g of the shell in impact modifier particles, the impact resistance of the molded sheets increased remarkably. Also the brittle–ductile transition temperatures (BDTT) of the prepared blends were studied and an increase in BDTT was found with lowering T _g of the shell.     

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.     

New modelling approach to liquid–solid reaction kinetics: From ideal particles to real particles

Typical features of liquid–solid reactions were reviewed: reaction kinetics, mass transfer effects and particle morphology. It was concluded that classical liquid–solid models based on ideal, non-porous geometries (sphere, infinite cylinder, slab) cannot satisfactorily describe real reactive solid particles with various surface defects, such as cracks, craters and limited porosity. Typically a too low reaction order for the reactive solid is predicted by the classical models. The surface morphology can be revealed by electron microscopy, which gives inspiration to develop new mathematical models for reactive solids.     

Small angle X-ray scattering investigation of deformation in PMMA toughened with core–shell particles

Abstract

Tensile deformation of PMMA toughened with core–shell particles has been investigated by in situ small angle X-ray scattering (SAXS). Each core–shell particle consisted of a PMMA core surrounded by a rubber shell, encased in a thin PMMA outer layer. Toughened PMMA (RTPMMA) specimens containing low and high particle concentrations were compared. The samples were tested under uniaxial tension at strain rates of 0.5 and 5.0 mm min^-1, at room temperature (20°C). The SAXS pattern of each undeformed RTPMMA specimen consisted of circular concentric fringes which correspond to the form factor of the core–shell particles. Highly localised failure within the particles was observed when low particle concentration samples were deformed beyond the yield point. This localised failure occurred at the poles of the particles at, or adjacent to, the core/shell interface. As the sample was stretched further, the failure was then seen to extend either side of the poles around, or alongside, the interface. In contrast, when the particle concentration was high, the particles stretched considerably without failing. No evidence for crazing was seen in the SAXS patterns obtained from these RTPMMA samples tested under the conditions used. Crazing was therefore not considered to be a major deformation mechanism.     

Preparation and properties of core–shell silver/polyimide nanocomposites

A new series of core–shell structured silver/polyimide (PI) nanocomposites was prepared by in situ polymerization followed by the chemical imidization of poly(amic acid) (PAA, precursor of PI) at a low temperature. The TEM images showed that the silver cores of the nanocomposites were encapsulated with homogeneous shells with thickness of 4 and 8 nm at silver contents of 90 and 60 %, respectively. The shell thickness was controlled by varying the content of PAA. FTIR spectroscopic analysis indicated that the imide ring formation occurred after the chemical imidization. The Ag/PI nanocomposites showed excellent thermal stability and exhibited only 10 % weight loss at 300 °C in the air. Moreover, percolation was observed at silver weight fractions close to the critical value, and the maximum dielectric permittivity of the nanocomposites was 120, which is about 40 times higher than that of pristine PI.     

Electrospun composite fibers of polyvinylpyrrolidone with embedded poly(methyl methacrylate)–polyethyleneimine core–shell particles

Composite fibers consisting of poly(methyl methacrylate)–polyethyleneimine (PMMA–PEI) core–shell particles embedded in polyvinylpyrrolidone (PVP) were successfully fabricated by the electrospinning method. The electrospun fibers were produced using 18?% w/v aqueous PVP solution blended with 2?% w/v PMMA–PEI particles at various pH (1, 2, 3, and 4) with a fiber collection distance set at 10?cm. The applied electrical voltages (10, 12, 14, and 16?kV) significantly affected the morphology and diameter of the prepared composite fibers (141–353?nm). The smallest composite fibers were obtained from the spinning mixture at pH 2 and a voltage of 14?kV. The composite fibers would potentially be applied as drug and bioactive compound carriers.     

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 of PBT/POE-g-GMA/PP ternary blends with good rigidity–toughness balance by core–shell particles

Compared with poly(butylene terephthalate)/glycidyl methacrylate grafted poly(ethylene–octene) (PBT/POE-g-GMA) binary blends, supertough PBT-based ternary blends with little rigidity loss were successfully obtained by adding rigid polypropylene (PP) into PBT/POE-g-GMA blends to construct core–shell particles during melt blending. The effects of PP content and type on the phase morphology and mechanical properties of the blends were systematically investigated. Theoretical predictions and scanning electron microscopy observation showed that a core–shell structure was formed in PBT matrix with PP as the core and POE-g-GMA as the shell. The mechanical property tests showed that POE-g-GMA and PP had significant synergistic toughening effect. When PP with high melt flow index (H-PP) was used, PBT/POE-g-GMA/H-PP (70/15/15) blends possessed the highest Izod notched impact strength, which was 1.9-fold compared with PBT/POE-g-GMA (70/30) binary blends, while the tensile performance loss was little. The essential work of fracture tests was performed to evaluate the fracture resistance of different samples. The results demonstrated that PBT/POE-g-GMA/PP ternary blends possessed much better resistance to crack propagation than PBT/POE-g-GMA binary blends. The decrease of interparticle distance and the fibrillation of core–shell particles activated intense matrix shear yielding, which was the reason for the high crack resistance of ternary blends. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48872.