Fabrication of composite polymer particles by stabilizer-free seeded polymerization

This paper reports the fabrication of polymer composite particles through stabilizer-free seeded polymerization. Various monomers were polymerized in the presence of submicron sodium styrene sulfunate-functionalized polystyrene seed particles without using swelling agent, emulsifier, or stabilizer. It was found that stable monodisperse composite particles are obtained even without using any ionic comonomer provided that the used monomer is nonpolar enough to facilitate swelling of the seeds. Utilizing the proposed method, copolymerization of styrene/divinyl benzene was successfully performed, resulting in highly crosslinked composite particles. Interestingly, Janus amphiphilic particles were achieved after the extraction of polystyrene by toluene from the particles. Overall, it is demonstrated that the proposed approach can be adopted as a facile and green process for the fabrication of various composite Janus particles

Lightweight high-density polyethylene/carbonaceous nanosheets microcellular foams with improved electrical conductivity and mechanical properties

The high-density polyethylene (HDPE) nanocomposites were prepared by using graphite nanosheets (GNS) and expanded graphite (EG), followed by foaming with subcritical CO2 used as an environmentally benign and nonflammable foaming agent. The partially exfoliated GNS and EG endow the prepared microcellular nanocomposite foams with high electrical conductivity, improved mechanical properties, as well as density reduction up to ca. 20 %. Interestingly, insulator-to-semiconductor transition of microcellular nanocomposite foams shifts to lower nanofiller content compared to that of bulk nanocomposites. Whether the nanofiller is GNS or EG, its incorporation leads to uniformly small cells, resulting in a remarkable enhancement in ductility without sacrificing toughness. It has demonstrated that foaming of HDPE nanocomposites with EG or GNS provides tough and lightweight microcellular foams, exhibiting the potential for use in conductive high-performance lightweight nanocomposite systems

Lightweight flexible polyurethane/reduced ultralarge graphene oxide composite foams for electromagnetic interference shielding

Multifunctional flexible polyurethane (PU)/reduced ultralarge graphene oxide (rUL-GO) composite foams with low density in the range of similar to 53-92 kg m(-3) were fabricated through the in situ polymerization of PU in the presence of rUL-GO. The incorporation of 1 wt% rUL-GO gave the insular flexible PU composite foams a high electrical conductivity of 4.04 S m(-1), and an excellent electromagnetic interference (EMI) shielding efficiency of similar to 253 dB (g(-1) cm(-3)) at 8-12 GHz. Achieving such a high specific EMI shielding efficiency as well as a low percolation threshold, combined with the method of foam preparation, results in a uniform dispersion and very high aspect ratio (>20 000) for the rUL-GO nanosheets. Furthermore, by the introduction of rUL-GO, the Young's modulus and tensile strength of the PU composite foams also improved significantly without reducing the flexibility. TGA experiments also indicated the enhanced thermal stability of the composite foams

Transition behavior, surface characteristics and film formation of functionalized poly (methyl methacrylate-co-butyl acrylate) particles

Carboxylic functionalized poly(methyl methacrylate-co-butyl acrylate) particles were synthesized by soap free emulsion polymerization using sodium salts of itaconic acid and acrylic acid. Transition behaviors of these latexes in terms of glass transition of matrix and cluster were found to be completely different from those synthesized by solution polymerization. This disparity was attributed to the difference between co-monomers sequence distribution along the chains. Distribution of functional groups in the latexes was determined by conductometric titration. Film formation process of the latexes was also examined and interpreted based on the density of surface functional groups, transition behaviors, and particle size. AFM images revealed that, as the amount of these ionic co-monomers increases, more ordered films are obtained, while the particle inter-diffusion is greatly retarded. A dimensionless parameter indicating relative roughness of the films further supported the aforementioned findings. (C) 2014 Elsevier B.V. All rights reserved

Transition behavior, surface characteristics and film formation of functionalized poly(methyl methacrylate-co-butyl acrylate) particles

Carboxylic functionalized poly(methyl methacrylate-co-butyl acrylate) particles were synthesized by soap free emulsion polymerization using sodium salts of itaconic acid and acrylic acid. Transition behaviors of these latexes in terms of glass transition of matrix and cluster were found to be completely different from those synthesized by solution polymerization. This disparity was attributed to the difference between co-monomers sequence distribution along the chains. Distribution of functional groups in the latexes was determined by conductometric titration. Film formation process of the latexes was also examined and interpreted based on the density of surface functional groups, transition behaviors, and particle size. AFM images revealed that, as the amount of these ionic co-monomers increases, more ordered films are obtained, while the particle inter-diffusion is greatly retarded. A dimensionless parameter indicating relative roughness of the films further supported the aforementioned findings. (C) 2014 Elsevier B.V. All rights reserved

Sulfonate-functionalized polyacrylonitrile-based nanoparticles; synthesis, and conversion to pH-sensitive nanogels

The present paper reports the synthesis of polyacrylonitrile (PAN)-based nanoparticles through soap-free emulsion polymerization (SFEP). Employing different types of co-solvent, as well as ionic commoners, synthesis of pure PAN nanoparticles was unsuccessful. However, when vinyl acetate,or methyl (meth) acrylate was introduced (conc. > 10\ua0mol%), crystallization of PAN was decreased and consequently stable nanoparticles in the size range of 80–250\ua0nm were achieved. Such a co-polymerization not only produced clean and functionalized nanoparticles but also allowed addition of a cross-linker without sacrificing colloidal stability. As a model, the cross-linked poly(acrylonitrile-co-vinyl acetate) nanoparticles were hydrolyzed in alkaline media, which yielded poly(acrylic acid-co-vinyl alcohol) nanogels. The swelling measurement exhibited that the prepared nanogels have a pH-sensitive behavior

Intumescent flame retardant polyurethane/starch composites: thermal, mechanical, and rheological properties

Intumescent flame retardant polyurethane/starch (IFRPU/starch) composites were prepared by means of melt blending. Microencapsulated ammonium polyphosphate (MCAPP) was added to improve its compatibility with matrix, retardation of reaction between acid and carbon source, and its water resistancy. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of hydrogen bonding and entangled network between IFR system and PU matrix. Further, scanning electron microscopy (SEM) illustrated homogeneity of starch in matrix. By addition of 10 wt % of starch and 20 wt % of IFR, limiting oxygen index (LOI) increased from 22.0 to 40.0 and UL94 V0 rating was achieved. Differential scanning calorimetry (DSC) detected three endothermic transitions and one glass transition (T-g). The temperature of transition III and T-g increased with starch due to crosslinking between PU and starch. The improved thermal stability in the presence of starch was confirmed by thermogravimetric analysis (TGA). Beside the fact that starch was used as a carbonization agent to improve flame retardancy, it also effectively led to enhanced mechanical and viscoelastic properties. (C) 2014 Wiley Periodicals, Inc

High sensitivity ammonia detection using metal nanoparticles decorated on graphene macroporous frameworks/polyaniline hybrid

In this paper, we presented the fabrication and properties of new ammonia (NH) sensors with sensitive layer of nickel nanoparticles decorated on three-dimensional nitrogen-doped graphene-based frameworks/polyaniline (NiNPs@3D-(N)GFs/PANI) hybrid. The hybrid are synthesized through in-situ oxidative polymerization on flexible thin substrate. Synergetic behavior between both components manifested outstanding sensitivity (750.2 at 1000 ppm NH) and quick response (95 s) and recovery (25 s) times and a lower limit of detection (~ 45 ppb) at room temperature. The sensitivity of NiNPs@3D-(N)GFs/PANI hybrid sensor was shown to be about 14 times more than its of pure PANI sensor at 1000 ppm of NH. The excellent sensitivity of the as-prepared hybrid is mainly originated from the substantial rise of hole-like carriers by NiNPs@3D-(N)GFs as well as improved inter-molecule interactions via π- π electron networks. The obtained results revealed significant advantages for the synthesized hybrid sensor, making it a suitable choice for real-world applications of NH detection

Anti-bacterial poly(vinyl alcohol) nanocomposite hydrogels reinforced with in situ synthesized silver nanoparticles

This work describes fabrication and properties of anti-bacterial poly(vinyl alcohol)/silver nanoparticles (PVA/AgNPs) nanocomposite hydrogels prepared via cyclic freeze-thaw. The AgNPs, at different concentrations, were synthesized in situ in PVA solution, without employing either capping or reducing agent. Stable AgNPs with the average diameter of 16 nm uniformly dispersed in PVA was obtained. The presence of 2 wt% of AgNPs enhanced tensile strength and elongation at break by 40 and 31%, respectively due to extended network formation between AgNPs and PVA. AgNPs also provided the hydrogels with anti-bacterial capability, while did not change water uptake markedly. Furthermore, the electrical conductivity of 1.5 x 10(5) S cm(-1) was achieved by the addition of as low as 2 wt% of AgNPs. POLYM. COMPOS., 40:1322-1328, 2019. (c) 2018 Society of Plastics Engineer