1,721,016 research outputs found
Poly(ethylene glycol)/Polyvinyl chloride Composite Form‐Stable Phase‐Change Materials by the Azide‐Alkyne Click Reaction
No full textThermal energy storage has become a key area in modern technology. Polyethylene glycol (PEG) is known to be an extremely effective solid-liquid phase change material (PCM). For efficient energy storage, alternative liquid-solid PCMs without encapsulation were designed. In particular, a series of PCMs, comprising PEG-stearate and PEG-stearate-Polyvinyl chloride (PVC), were prepared by the azide-alkyne cycloaddition click reaction. The click reactions of azido-PEG, azido-PVC, and alkynyl stearate were carried out. The prepared polymers, PEG-stearate and PEG-stearate-PVC PCMs were characterized by Fourier-transform infrared spectroscopy (FTIR) spectroscopy. The latent heat and thermal stability of PCMs were investigated by Differential Scanning Calorimetry (DSC) and Thermogravimetric analyzer (TGA). DSC results revealed that PCMs exhibit latent heat values ranging from 80 to 104 J/g at -2 and 46 degrees C. In addition, PCMs exhibited high thermal stability with the increase in the content of PVC
DOPO tethered Diels Alder clickable reactive silica nanoparticles for bismaleimide containing flame retardant thiol-ene nanocomposite coatings
No full textThe modification of nanoparticles (NPs) with functional groups that render them much more compatible with the polymeric matrices to prepare organic-inorganic hybrid materials is an active area of research. In this work, flame retardant and reactive nanosilica particles were prepared. First, nanosilica particles were coated with aminosilane and then reacted with furfural to introduce Diels Alder clickable sites. Finally, these reactive NPs were phosphorylated by reacting them with 9,10-dihydro-9-oxy-10-phosphaphenanthrene-10-oxide (DOPO). Different amounts of DOPO tethered Diels Alder clickable nanosilica particles (DDAS) were added to a bismaleimide resin containing thiol-ene based liquid pho-tocurable mixture. Bismaleimide acted as a crosslinker between the organic matrix and DDAS NPs. The effects of DDAS on the thermal and mechanical properties and the curing kinetics of the photocured coatings were investigated. The addition of BMI increased the Tg of the coatings from 40 to 78 degrees C with respect to the base formulation. The presence of BMI improved the distribution of DDAS NPs in the organic matrix. Moreover, the thermal and the flame retardancy of the hybrid coatings were improved. While the LOI of the base formulation was found as 21.6%, with the introduction of DDAS NPs the LOI of the hybrid coatings was increased up to 24.1%. (C) 2017 Elsevier Ltd. All rights reserved
Biodegradable Polyurethane Solid-Solid Phase Change Materials
No full textPolyurethane based phase change material (PCM) was prepared using polyethylene glycol (PEG), isophoronediisocyanate and octadecanol via a two-step process. PEG and octadecanol served as phase change components. The structural characterization of PCM was performed by ATR-FTIR and H-1-NMR spectroscopies. The latent heat, phase change temperature and thermal stability of PCM were characterized by differential scanning calorimetry and thermogravimetric analysis. The results show that PCM has an excellent energy storage capacity, suitable phase transition temperatures and great thermal stability at 100 degrees C without leakage. PEG/octadecanol polyurethane PCM reached 126 and 95 J/g enthalpy values. To investigate the efficiency of the PCM in a biodegradable polymeric support, blend films were prepared by mixing PEG/octadecanol polyurethane with the PLA. Films exhibited high light transmission. Elongation at break increased compared with pure PLA from 6 % to 87 %. In addition, tensile strength and modules of PLA/PEG-octadecanol PCM decreased. Water contact angle values of the films increased to 66 and 70 degrees with adding polyurethane PCM. In conclusion, PLA/PCMs exhibited high thermal energy storage property and suitable phase change temperature as good as the PEG/octadecanol polyurethane PCM. Therefore, PLA/PCMs can be used in ranges between 10 and 55 degrees C
Polydimethylsiloxane (PDMS)-based antibacterial organic-inorganic hybrid coatings
No full textUV-curable antibacterial organic-inorganic hybrid coatings were prepared by sol-gel method. Triethoxysilane-terminated poly(dimethylsiloxane) (TESi-PDMS) as a new coupling agent to improve the compatibility between organic and inorganic phases was synthesized. PDMS-based urethane methacrylate oligomer was obtained by reacting isophorone diisocyanate with hydroxyethyl methacrylate and hydroxyl-terminated PDMS. The formulations were applied onto polycarbonate panels and then cured by UV radiation. Physical properties of UV-cured free films such as gel content, stress-strain, and conversion of acrylate double bond were examined. In addition, the antibacterial effects of the coatings were investigated. Nanosilver-containing formulations exhibited high antibacterial effect against Escherichia coli and Staphylococcus aureus. Thermogravimetric analysis indicated that thermal stability of the hybrids was significantly higher than the organic polymer. Contact angle measurement showed that addition of silane precursor increased the contact angle from 95 degrees to 110 degrees
Maleimide Containing UV-Cured Hybrid Coatings
No full textIn this work, new organic-inorganic hybrid coatings were prepared by the sol-gel method. N-p-hydroxyphenyl maleimide was synthesized and then modified with 3-isocyanato propyltriethoxysilane to obtain a new alkoxysilane monomer. Poly(dimethyl siloxane (PDMS) based on the urethane acrylate oligomer was synthesized using hydroxyl-terminated PDMS, isophorone diisocyanate, and 2-hydroxyethyl methacrylate. This oligomer was synthesized to increase the hydrophobicity of coatings. Hybrid formulations were applied onto polycarbonate plates and irradiated with UV light. Coatings' performance was investigated with thermal, mechanical, morphologic, and antibacterial analyses. It is observed that the thermal stability of UV-cured films is improved with the incorporation of the sol-gel precursor. It is shown that the nanosilver addition to hybrid coatings leads to significant enhancements in antibacterial property in vitro. (C) 2013 Wiley Periodicals, Inc
Dual-crosslinked thiol-ene/sol gel hybrid electrospun nanowires: preparation and characterization
No full textIn this report, we describe the preparation and characterization of cross-linked electrospun membranes by using a reactive electrospinning. A novel methacrylate functional poly(vinyl alcohol) (M-PVA) was synthesized by reacting PVA and isocyanatoethyl methacrylate (2-ICEMA). The crosslinked membranes were achieved in a simple process at a single step using thiol-ene reaction between M-PVA and 3-mercaptopropyl trimethoxysilane (MPTMS) during the electrospinning process. In order to improve theirs the stability, the crosslinked membranes were also thermally treated. The morphology was characterized by scanning electron microscopy (SEM). The structure of M-PVA was characterized by attenuated total reflectance FT-IR. Morphological investigations show that the resulting membranes have nanowires morphology. The thermal analysis of the electrospun membranes was also investigated. Thermal stability of the membranes was improved with the incorporation of the sol gel precursor. The described method provides novel route for organic-inorganic hybrid membranes
Methacrylate Functionalized MWCNTs/PDMS-Polyurethane Methacrylate UV-Curable Nanocomposites
No full textPolyurethane (PU)-carbon nanotube composites have gained interest in the area of aerospace, automobiles, fuel cells electrical appliances and communication related applications. However, there is still insufficient information on PU-carbon nanotube composites. In this study, hydrophobic and high performance UV-curable nanocomposites were prepared by using surface functionalized multi-walled carbon nanotubes (MWCNT). First, MWCNT were treated with acid solution (HNO3/H2SO4) and then grafted with poly(ethylene glycol) methacrylate (PEGMA) to introduce UV-photopolymerization sites. Different amounts of methacrylate tethered MWCNT and sol-gel precursor or hydrophobic nanosilica were added to PDMS-polyurethane methacrylate based UV-curable formulation and cured by UV irradiation. The composites were also thermally treated (post-cure). The effects of the carbon nanotube, the sol-gel precursor and the hydrophobic nanosilica content on thermal, mechanical and morphological properties of the nanocomposite films were investigated. The addition of the sol-gel precursor and hydrophobic nanosilica increased thermal stability with regard to the base formulation. The addition of MWCNT and silica increased the modulus of the composite from 245 to 318 MPa with regard to the base formulation. Moreover, the thermal decomposition range was increased with addition of the modified MWCNTs. The morphology of the composite films was also carried out by using scanning electron microscopy (SEM). Morphological investigations showed that better dispersion of nanoparticles and performance were achieved when the surface functionalized MWCNTs and hydrophobic silica nanoparticles used together in nanocomposite preparation
Preparation and evaluation of linseed oil based alkyd paints
No full textAlkyd resins are produced with reaction of oil or fatty oil, polyol and polyacid. Alkyd resins are commonly used in coating and paint industry due to ease of application in changing environmental conditions. Linseed oil based paints executed all requirements of technical properties, drying time, storage properties, simplicity in maintenance, appearance, economy, etc. In this study, linseed oil based alkyd resins having different oil contents were synthesized Paint formulations were prepared by mixing alkyd resin and various additives such as huntite, Aerosil R972, talc, titanium dioxide, dryer, wetting agent and anti-skinning agent. All formulations were applied on paper test plates and were dried at 30 degrees C. The obtained coatings were characterized by pencil hardness test, pendulum hardness test, chemical resistance test, cross-cut test, contact angle and gloss measurement. Also thermal and morphological properties were investigated by thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM) respectively. The thermal stability of the paint materials are improved with by increasing the amount of huntite and Aerosil R972 in the paint compositions. (C) 2013 Elsevier B.V. All rights reserved
Fabrication of collagen immobilized electrospun poly (vinyl alcohol) scaffolds
No full textIn the development of tissue engineering scaffolds, the interactions between material surface and cells play crucial roles. The biomimetic 3-D scaffolds absolutely provide better results for fulfilling requirements such as porosity, interconnectivity, cell attachment and proliferation. In this study, 3-D electrospun scaffolds were prepared by using an electrospinning technique. Photo cross-linkable polyvinyl alcohol was used as a polymeric matrix. During the electrospinning, the nanofibers were cross-linked with in situ ultraviolet radiation. The crosslinked polymer fibers were achieved in a simple process at a single step. Nanofiber surface was modified with collagen by a chemical approach. The chemical structures were proven by attentuated total reflectance Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. The surface morphology of the nanofibers was characterized by scanning electron microscope (SEM). Morphological investigations show that the resulting nanofibrous matrix has uniform morphology with a diameter of 220-250 nm. In vitro attachment and growth of 3T3 mouse fibroblasts and human umbilical vein endothelial cells (ECV304) cells on polyvinyl alcohol-based nanofiber mats were also investigated. Cell attachment, proliferation, and methylthiazole tetrazolium cytotoxicity assays indicated good cell viability throughout the culture time, which was also confirmed by SEM analysis. Copyright (C) 2015 John Wiley & Sons, Ltd
Immobilization of alpha-amylase onto poly(glycidyl methacrylate) grafted electrospun fibers by ATRP
No full textIn this study, novel alpha-amylase immobilized poly(vinyl alcohol) (PVA) nanofibers were prepared. The PVA nanofiber surfaces were functionalized with 2-bromoisobutyryl bromide (BiBBr) and followed by surface initiated atom transfer radical polymerization (SI-ATRP) of glycidyl methacrylate (GMA). The morphology of the poly(glycidyl methacrylate) (PGMA) grafted PVA nanofibers was characterized by scanning electron microscopy (SEM). Also PGMA brushes were confirmed by X-ray photo electron microscopy (XPS). alpha-Amylase was immobilized in a one step process onto the PGMA grafted PVA nanofiber. The characteristic properties of the immobilized and free enzymes were examined. The thermal stability of the enzyme was improved and showed maximum activity at 37 degrees C by immobilization, pH values of the maximum activity of the free and immobilized enzymes were also found at 6.0 and 6.5, respectively. Free enzyme lost its activity completely within 15 days. The immobilized enzyme lost only 23.8% of its activity within 30 days. (C) 2015 Elsevier B.V. All rights reserved
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