Intumescent flame retardant polyurethane/reduced graphene oxide composites with improved mechanical, thermal, and barrier properties

Intumescent flame retardant polyurethane (IFRPU) composites were prepared in the presence of reduced graphene oxide (rGO) as synergism, melamine, and microencapsulated ammonium polyphosphate. The composites were examined in terms of thermal stability (both under nitrogen and air), electrical conductivity, gas barrier, flammability, mechanical, and rheological properties. Wide-angle X-ray scattering and scanning electron microscopy indicated that rGO are well-dispersed and exfoliated in the IFRPU composites. The limiting oxygen index values increased from 22.0 to 34.0 with the addition of 18wt% IFR along with 2wt% rGO. Moreover, the incorporation of rGO into IFRPU composites exhibited excellent antidripping properties as well as UL-94 V0 rating. The thermal stability of the composites enhanced. This was attributed to high surface area and good dispersion of rGO sheets induced by strong interactions between PU and rGO. The oxygen permeability, electrical, and viscoelasticity measurements, respectively, demonstrated that rGO lead to much more reduction in the gas permeability (by ~90%), high electrical conductivity, and higher storage modulus of IFRPU composites. The tensile strength, modulus, and shore A remarkably improved by the incorporation of 2.0wt% of rGO as well

Soap-free emulsion polymerization of poly (methyl methacrylate-co-butyl acrylate): effects of anionic comonomers and methanol on the different characteristics of the latexes

Soap-free emulsion polymerization (SFEP) of methyl methacrylate, butyl acrylate was conducted in water/methanol media with sodium salts of four different acidic comonomers, namely styrene sulfonic acid (NaSS), 2-acrylamide-2-methyl-1-propane sulfonic acid (NaAmps), acrylic acid (NaAA), and itaconic acid (Na(2)ita). It was found that the introduction of methanol as co-solvent (35 wt%) to the medium greatly decreases the amount of water-soluble polyelectrolyte in the cases NaAA and Na(2)ita while it does not make difference for NaSS and NaAmps. Having employed the concept of conductance dependency to the ion mobility, the onset concentration in which soluble chains were formed was detected. The addition of sulfonic-based comonomers (NaSS and NaAmps), first decreased particle size and then led to predomination of solution polymerization over SFEP. On the contrary, the incorporation of carboxylic-based comonomers (NaAA and Na(2)ita) led to increase in particle size. Moreover, the particle size results were in good qualitative agreement with the classical Smith–Ewart theory

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

Synthesis of monodisperse anionic submicron polystyrene particles by stabilizer-free dispersion polymerization in alcoholic media

In this work, monodisperse polystyrene (PS) particles were synthesized in ethanol/water medium using sodium salt of styrene sulfonic acid and 2,2'-azobis(isobutyronitrile) as ionic comonomer and nonionic initiator, respectively. The polymerization was carried out at low agitation speed, and no stabilizer (or surfactant) was added to the polymerization medium. This polymerization system (stabilizer-free dispersion polymerization) was initiated as a homogeneous solution of monomer, comonomer, medium, and initiator. With the production of free radicals, polymerization developed into a heterogeneous system. The effect of various polymerization conditions on the size and size distribution of the obtained particles was evaluated. The experimental results showed that with an increase in ethanol content, the size of the particles increased while no significant change was observed in particle size distribution. Furthermore, with increasing ionic comonomer content, the size of the particles decreased and their size distribution became broader. Moreover, it was observed that addition of an electrolyte to the polymerization medium also increased the particles' size and broadened their size distribution. It is noteworthy to point out that the coagulation occurred in higher amounts of electrolyte. Finally, it is concluded that the polar component of Hansen solubility parameter of the polymerization medium affects the particle size and particle size distribution greatly

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

Gas permeability and permselectivity properties of ethylene vinyl acetate/sepiolite mixed matrix membranes

Ethylene vinyl acetate (EVA) mixed matrix membranes (MMMs) were prepared by incorporating fibrous sepiolite modified by 3-aminopropyltrimethoxysilane (3-APTMS). Gas transport through the prepared MMMs was investigated in detail. Permeabilities of O2, CO2, CH4, and N2, gases were significantly increased by the addition of 3 wt.% of sepiolite. At the same sepiolite loading, the CO2/CH4 and CO2/N2 selectivity of the MMMs at 5 bar were respectively enhanced by 9% and 28.2%, while the O2/N2 selectivity did not notably change and their values remained nearly constant around 2.5-3. The enhanced permeation was attributed to the decreased crystallinity percentage, confirmed by X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). Moreover, XRD results and microscopic images demonstrated that sepiolite fibers were uniformly dispersed in the EVA matrix due to the presence of hydrogen bonding between amino groups of modified sepiolite and carbonyl groups of EVA. Also, upon the incorporation of 3 wt.% sepiolite, the tensile strength and elongation at break were simultaneously enhanced by 46% and 76%, respectivel

Preparation and characterization of ethylene-vinyl acetate/halloysite nanotube nanocomposites

Ethylene-vinyl acetate (EVA) nanocomposites based on halloysite nanotubes (HNT) were prepared by solution casting method. The thermal, mechanical, water uptake, as well as oxygen permeability properties of the nanocomposites were examined. X-ray diffraction (XRD) and field emission scanning electron microscopy showed that HNTs were dispersed well into the EVA matrix. XRD data also suggested that HNT frustrates chain ordering and reduced total crystallinity percentage. The thermal and mechanical properties of the nanocomposites were improved with HNT loading, up to 3 wt%. Both ductility and toughness were enhanced by incorporation of up to 3 wt% of HNT, implicitly confirming that HNT has been dispersed in EVA homogeneously. The addition of HNT also enhanced the water resistance and oxygen permeability of the prepared nanocomposites

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

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