Epoxy Silane Research Articles

Experimental and quantitative assessment of flame retardancy by the shielding effect in layered silicate epoxy nanocomposites

A quantitative experimental assessment of flame retardancy by the heat shielding in epoxy layered silicate nanocomposite (EP/TPPMMT) is presented. Online heat flux measurements and temperature monitoring within the specimen are performed during the burning in the cone calorimeter. For EP the surface layer equals a pyrolysis front. The reradiation by the hot surface corresponds to the fourth power of the pyrolysis temperature. The surface reradiation (around 10kWm−2) is thus fairly invariable over burning time and different external heat fluxes. Further, the thermal feedback of the flame is approximated to 20kWm−2 for both EP and EP/TPPMMT and invariable over different irradiations. Thus the net heat fluxes transformed to the fuel release rate within the pyrolysis front of EP are increased to 45–80kWm−2 when irradiations of 35–70kWm−2 are applied. For a residue-forming EP/TPPMMT the surface temperature and thus the reradiation (42–68kWm−2) crucially increases compared to EP and with increasing irradiation. The net heat fluxes are reduced to 13–22kWm−2 accordingly. This quantitative assessment of the heat shielding in EP/TPPMMT goes along with proportional and consistent improvement in the fire performance, such as the pyrolysis front velocity, the heat release rate (HRR) characteristics such as averaged and quasi-steady-state HRR and the peak HRR (PHRR). The heat shielding is proven to be the only major flame retardancy effect occurring in nanocomposites based on non-charring polymers.

Effect of NH2-MWCNTs on crosslink density of epoxy matrix and ILSS properties of e-glass/epoxy composites

Crosslink density is one of the important parameters that govern the physical properties of fiber reinforced polymer (FRP) composites. Enhancement of crosslink density by effective matrix modification through nanoparticle incorporation is the most prominent way to improve mechanical and thermo-mechanical properties of FRP composites. In this study, at first, 0.1–0.4wt.% amino-functionalized multi-walled carbon nanotubes (NH2-MWCNTs) were incorporated in SC-15 epoxy system and the variation in crosslink density was investigated using rubber elasticity theory. Subsequently, the effect of these MWCNTs on interlaminar shear strength (ILSS) of e-glass/epoxy composites was studied. Result obtained from the tests showed a linearly increasing trend in crosslink density and ILSS properties from 0 to 0.3wt.% MWCNTs loading. Better dispersion of MWCNTs facilitated more crosslinking sites, whereas, the three-way reaction between amine functional groups of MWCNTs with epoxide groups of resin and epoxy silanes of fiber surfaces improved the crosslinking and thereby ILSS properties of e-glass/epoxy composites.

Biphenyl liquid crystalline epoxy resin as a low-shrinkage resin-based dental restorative nanocomposite

Low-shrinkage resin-based photocurable liquid crystalline epoxy nanocomposite has been investigated with regard to its application as a dental restoration material. The nanocomposite consists of an organic matrix and an inorganic reinforcing filler. The organic matrix is made of liquid crystalline biphenyl epoxy resin (BP), an epoxy resin consisting of cyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (ECH), the photoinitiator 4-octylphenyl phenyliodonium hexafluoroantimonate and the photosensitizer champhorquinone. The inorganic filler is silica nanoparticles (∼70–100nm). The nanoparticles were modified by an epoxy silane of γ-glycidoxypropyltrimethoxysilane to be compatible with the organic matrix and to chemically bond with the organic matrix after photo curing. By incorporating the BP liquid crystalline (LC) epoxy resin into conventional ECH epoxy resin, the nanocomposite has improved hardness, flexural modulus, water absorption and coefficient of thermal expansion. Although the incorporation of silica filler may dilute the reinforcing effect of crystalline BP, a high silica filler content (∼42vol.%) was found to increase the physical and chemical properties of the nanocomposite due to the formation of unique microstructures. The microstructure of nanoparticle embedded layers was observed in the nanocomposite using scanning and transmission electron microscopy. This unique microstructure indicates that the crystalline BP and nanoparticles support each other and result in outstanding mechanical properties. The crystalline BP in the LC epoxy resin-based nanocomposite was partially melted during exothermic photopolymerization, and the resin expanded via an order-to-disorder transition. Thus, the post-gelation shrinkage of the LC epoxy resin-based nanocomposite is greatly reduced, ∼50.6% less than in commercialized methacrylate resin-based composites. This LC epoxy nanocomposite demonstrates good physical and chemical properties and good biocompatibility, comparable to commercialized composites. The results indicate that this novel LC nanocomposite is worthy of development and has potential for further applications in clinical dentistry.

Laser-induced birefringence of methyl red in a polymeric nanocomposite prepared by sol–gel method

Non-linear optical (NLO) dyes used as guests in polymeric films have recently attracted interests in optical applications. In this regard, dye-grafted polymeric systems can outperform conventional guest–host dye-containing films because they have lower loading limitations and aggregation problems. These give rise to enhanced molecular orientation. The work presented here is an attempt to study the laser-induced birefringence for a novel sol–gel based polymeric nanocomposite prepared by reacting an NLO dye (methyl red) and an epoxy silane coupling agent at different concentrations of dye. 3-Glycidoxy propyltrimethoxysilane was hydrolyzed and condensed to prepare a siloxane structure from which a dye-containing hybrid was obtained. The structural and morphological properties of the resulting nanocomposites were studied by FTIR spectroscopy, differential scanning calorimetry and transmission electron microscopy. Results showed that the dye was chemically attached to the siloxane structure built through sol–gel processing. This chemical modification leads to nanostructured morphology in which inorganic phase was entangled to the organic phase. The size of clusters formed was 60–80 nm in dimension. The optical responses of nanocomposites were investigated at different process parameters, including dye concentration, film thickness and curing regimes. These were then discussed based on the photochemical and photothermal properties of the dye molecules, the rotation dynamic of which was shown to strongly depend on the physical and chemical properties of the host. The samples with 8 wt% of dye revealed the maximum birefringence, while the sample with 10 wt% showed the best memory effect. The best condition for curing was found to be 24 h. By increasing the film thickness, there was an increase in the amount of induced birefringence.

Effect of plasma pretreatment on adhesion and mechanical properties of sol-gel nanocomposite coatings on polycarbonate

Adhesion of the coatings to the substrate plays a vital role in improving mechanical properties of sol-gel coatings especially when deposited on plastics. In the present study, an attempt was made to study the effect of atmospheric air plasma surface activation on the adhesion of sol-gel nanocomposite coatings on polycarbonate substrate. The sol was synthesized by the hydrolysis and condensation of an epoxy silane (3-Glycidoxypropyl trimethoxy silane) along with titanium tetraisopropoxide. Coatings were deposited on 100 × 100 mm substrates by spray coating and subsequently subjected to UV curing followed by thermal curing at 130 °C for 1 h. One set of the substrates was subjected to atmospheric air plasma surface pretreatment prior to coating deposition. Coating thickness, adhesion as well as mechanical properties like pencil hardness, scratch resistance and taber abrasion resistance were evaluated for coatings deposited over plasma-treated and -untreated surfaces. It was found that plasma surface pretreatment has improved the pencil hardness from H to 2H and adhesion of coatings from 2B to 4B. Results obtained from the above experiments were discussed on the basis of surface modification using plasma pretreatment.

SEM/EDX: Advanced investigation of structured fire residues and residue formation

Heterogeneous, gradual or structured morphology of fire residues plays an important role in fire retardancy of polymers. A scanning electron microscope with an attached energy dispersive X-ray spectrometer (SEM/EDX) is highlighted as a powerful tool for the advanced characterization of such complex fire residues, since it offers high resolution in combination with both good depth of field and analysis of chemical composition. Two examples are presented: First, comprehensive SEM/EDX investigation on a complex structured fire residue of glass fibre reinforced polyamide 6,6 (PA 66-GF) flame retarded by diethylaluminium phosphinate, melamine polyphosphate and some zinc borate. A multilayered surface crust (thickness ∼ 24 μm) covers a rather hollow area stabilized by GF glued together. The resulting efficient thermal insulation results in self-extinguishing before pyrolysis is completed, even under forced-flaming combustion. Second, sophisticated, quasi online SEM/EDX imaging of the formation of residual protection layer in layered silicate epoxy resin nanocomposites (LSEC). Burning specimens were quenched in liquid nitrogen for subsequent analyses. Different zones were distinguished in the condensed phase characterized by distinct processes such as melting and ablation of organic material, as well as agglomeration, depletion, exfoliation and reorientation of the LS.

Headgroup Effect on Silane Structures at Buried Polymer/Silane and Polymer/Polymer Interfaces and Their Relations to Adhesion

Sum frequency generation (SFG) vibrational spectroscopy was used to study the effect of silane headgroups on the molecular interactions that occur between poly(ethylene terephthalate) (PET) and various epoxy silanes at the PET/silane and PET/silicone interfaces. Three different silanes were investigated: (3-glycidoxypropyl) trimethoxysilane (γ-GPS), (3-glycidoxypropyl) methyl-dimethoxysilane (γ-GPMS), and (3-glycidoxypropyl) dimethyl-methoxysilane (γ-GPDMS). These silanes share the same backbone and epoxy end group but have different headgroups. SFG was used to examine the interfaces between PET and each of these silanes, as well as silanes mixed with methylvinylsiloxanol (MVS). We also examined the interfaces between PET and uncured or cured silicone with silanes or silane-MVS mixtures. Silanes with different headgroups were found to exhibit a variety of methoxy group interfacial segregation and ordering behaviors at various interfaces. The effect of MVS was also dependent upon silane headgroup choice, and the interfacial molecular structures of silane methoxy headgroups were found to differ at PET/silane and PET/silicone interfaces. Epoxy silanes have been widely used as adhesion promoters for polymer adhesives; therefore, the molecular structures probed using SFG were correlated to adhesion testing results to understand the molecular mechanisms of silicone-polymer adhesion. Our results demonstrated that silane methoxy headgroups play important roles in adhesion at the PET/silicone interfaces. The presence of MVS can change interfacial methoxy segregation and ordering, leading to different adhesion strengths.

Effect of stearic acid and epoxy silane on the structure and flame‐retardant properties of magnesium hydroxide/ethylene vinyl acetate copolymer/very low density polyethylene composites

AbstractEthylene vinyl acetate copolymer (EVA) and very low density polyethylene (VLDPE) blends filled with magnesium hydroxide (MH) were compounded by melt blending. Two kinds of surface treatments were used in this research, including stearic acid and epoxy silane. The composites were analyzed by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, limiting oxygen index (LOI), and cone calorimeter testing to study the effects of stearic acid and epoxy silane on the structure and flame‐retardant properties of the MH/EVA/VLDPE composites. The results indicate that stearic acid and epoxy silane had different effects on the interfacial interaction of the MH/EVA/VLDPE composites; this made a difference in the condensed phase of the physical process. Thus, the composites with different surface treatments had different flammability characteristics, thermal degradation processes, char yields, and LOIs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The effect of SiO2 filler content and its organic compatibility on thermal stability of epoxy resin

Thermal properties of the organic–inorganic bicontinuous nanocomposites prepared via in situ two-stage polymerization of various silanes, epoxy, and amine monomers are investigated, and the impact of filler content and its organic compatibility on thermal stability of these nanocomposites is studied. Two series of epoxy–silica nanocomposites, namely, EpSi-A and EpSi-B containing 0–20 wt% silica, are synthesized. An epoxy–silane coupling agent is employed to improve the organic compatibility of silica in EpSi–B nanocomposites. The composites synthesized via two-stage polymerization are characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric (TG) analysis. DSC and TG/differential thermogravimetric results reveal substantially high glass transition (T g) and excellent thermal stability of the bicontinuous nanocomposites as compared with pristine epoxy polymer. Both T g and thermal properties, however, considerably vary depending on the organic compatibility of the nanocomposites. Significantly higher decomposition temperatures are recorded in case of EpSi-B nanocomposites owing to the chemical links between the epoxy and silica phases. Kinetic studies also show relatively higher activation energies of pyrolysis for EpSi-B nanocomposites.

화염 플라즈마 및 실란 표면처리가 실리카 강화 고무복합재료의 기계적 특성에 미치는 영향

ABSTRACT The effect of surface treatments with the atmospheric pressure flame plasma (APFP) and epoxy silane (ES) is experimentally investigated to yield the best mechanical properties of silica (    ) reinforced elastomeric composites. The tensile strength of the composites is increased significantly with decrease the mean diameter. When the diameter is 2.2㎛, that of the composite is increased about 1.4 times compared to the matrix (2.52㎫). Also, the tensile strength of silica reinforced composites with APFP and ES treated is increased 8.8∼13.3%, 9.9~12.5%, respectively. When the diameter is 26.6㎛, the tensile modulus of the composite is increased about 2 times compared to the matrix (0.88㎫), and the tensile modulus of silica reinforced composites with APFP and ES treated is increased 15.6∼22.8%, 21.1~25.8%, respectively. Conventional silane coupling agent treatment have a few disadvantages because of using organic solvents. However APFP treatment is a fast, economic and eco-friendly method to improve the mechanical properties.

Flammability of layered silicate epoxy nanocomposites combined with low‐melting inorganic ceepree glass

AbstractTetraphenylphosphonium modified layered silicate epoxy nanocomposite (EP/TPPMMT) combined with low‐melting silicate glass, Ceepree (CP) is investigated by thermal analysis, flammability tests and cone calorimeter at different heat fluxes. Adding CP and TPPMMT does not change the pyrolysis apart from increasing inorganic residue. The total heat evolved (THE) is changed insignificantly, as neither relevant additional carbonaceous charring nor flame inhibition occurs. However, flame retardancy is clearly observed due to an inorganic‐carbonaceous surface protection layer. The peak heat released rate (PHRR) is reduced by around 32–42% when 5 wt% TPPMMT is added, and 51–63% when 10 wt% CP is added. PHRR reduction less than expected is observed when both additives are combined. The reduction is greater than that achieved by using TPPMMT but less than when only CP is used. The morphology of fire residue is investigated by scanning electron microscope on different length scales and turns out to be the key to understanding the efficiency of flame retardancy. The fire residue of EP/CP shows a layered structure, whereas separated columns limit the barrier properties for EP/5%TPPMMT on the micrometer scale. Columns dominating the fire residue structure of EP/5%TPPMMT/10%CP deteriorate the fire retardancy, whereas a more integral structure at the top of the residue causes the improvement over EP/5%TPPMMT. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Improving the corrosion protection properties of organically modified silicate–epoxy coatings by incorporation of organic and inorganic inhibitors

Organically modified silicate (ORMOSIL)–epoxy coatings were formed on aluminium alloy 2024-T3 in order to protect the substrates from corrosion. Organic and inorganic compounds, all known for their corrosion inhibition ability, were incorporated into the polymer matrix for the improvement of the corrosion resistance. The ORMOSIL–epoxy coatings were deposited via the dip-coating process. The properties of the coatings were investigated after 24h of curing at 90°C. The morphology of the coatings was examined by scanning electron microscopy (SEM). Their composition and structure were investigated by Fourier transform infrared spectroscopy (FT-IR) and energy dispersive X-ray analysis (EDX). The corrosion resistance of these coatings was investigated using electrochemical impedance spectroscopy (EIS). The results showed that the most effective corrosion protection ability was provided by the inorganic inhibitors and that an important role can be attributed to the cation in the nitrate salt.

Peptide-tags for enhanced DNA microarray performance

DNA microarrays are powerful tools for gene expression analysis and genotyping studies in research and diagnostic applications. A high sensitivity and short time-to-result are prerequisites for their practical application in the clinic. The hybridization efficiency of DNA microarrays depends on the probe density and the probe orientation and thus their accessibility for target molecules. In order to find an optimal probe immobilization procedure a set of different oligonucleotide modifications was tested on epoxy silane functionalized glass slides. It was found that histidine-tagged oligonucleotides resulted in the highest amount of bound probe and by far the best hybridization efficiencies. The detection limit obtained with histidine-tagged probes was up to two orders of magnitude lower compared to commonly used probe modifications. In order to further investigate the binding mechanism of histidine-tags towards functionalized glass substrates a set of different peptide-tags with and without free terminal amino-groups and with different amino acid compositions was tested. The results indicate an impact of the terminal amino group on the covalent surface binding and of aromatic amino acid residues on the enhanced hybridisation efficiency.

Polymerization of ε‐caprolactone on calcium alkoxide‐functionalized silica substrates

AbstractBiodegradable composite materials free from toxic initiator residues have been prepared using calcium alkoxides bound to silica. Polycaprolactone with low polydispersity was synthesized by ring‐opening polymerization of ε‐caprolactone at 100 °C on a calcium alkoxide‐functionalized silica substrate prepared by the grafting of a hydrolysed epoxy silane onto silica gel, followed by reaction with calcium hydride. The polymerization was also initiated by the product of the direct reaction of calcium hydride with unfunctionalized silanol groups. Characterization of the reaction products and the real‐time reaction kinetics using Raman spectroscopy suggests a living coordination–insertion mechanism. There is a difference in reactivity of a factor of ca 7 between the calcium alkoxide formed on the silanized and unsilanized silica surface, resulting in a monomer conversion of 90% in 100 h for the silanized silica compared to only 30% for the unsilanized silica. The degree of grafting ranges from a maximum of 30% for the silanized surface to 10% for the unsilanized silica alone. There is evidence for cyclic transesterification products, and release of the polymer from the silica occurs in this way and also by adventitious hydrolysis. Copyright © 2010 Society of Chemical Industry

Temperature inside burning polymer specimens: Pyrolysis zone and shielding

AbstractOn the basis of two examples, temperature measurements are proposed within burning polymer specimen during the cone calorimeter test; especially to gain deeper insight into the actual pyrolysis conditions and flame retardancy mechanism. The heating and pyrolysis within a poly(methyl methacrylate) specimen were characterized, discussing the characteristic maximum heating rates (165−90°Cmin−1 decreasing with depth within the specimen and >275°Cmin−1 at the initial surface), pyrolysis temperature (454−432°C decreasing in accordance with decreasing heating rates), thickness of the pyrolysis zone (0.5–1.3 mm) and its velocity (1.2−2.1 mm min−1) as a function of sample depth and burning time. Thermally thick behaviour corresponds to a pyrolysis zone thickness of 0.74 mm and a velocity of 1.51 mm min−1 and occurs until the remaining specimen thickness is less than 8 mm. The shielding effect against radiation occurring in a layered silicate epoxy resin nanocomposite was investigated. It is the main flame retardancy effect of the silicate‐carbon surface layer formed under fire. The reradiation from the hot surface is increased by a factor of around 4–5 when an irradiance of 70kWm−2 is applied. The energy impact into the pyrolysis zone is crucially reduced, resulting in a reduction of fuel production and thus heat release rate. Copyright © 2009 John Wiley & Sons, Ltd.

Flame retarded epoxy resins by adding layered silicate in combination with the conventional protection‐layer‐building flame retardants melamine borate and ammonium polyphosphate

AbstractThe pyrolysis and flammability of phosphonium‐modified layered silicate epoxy resin nanocomposites (EP/LS) were evaluated when LS was combined with two flame retardants, melamine borate (MB) and ammonium polyphosphate (APP), that also act via a surface protection layer. Thermogravimetry (TG), TG coupled with Fourier Transform Spectroscopy (TG‐FTIR), oxygen index (LOI), UL 94 burning chamber (UL 94) and cone calorimeter were used. The glassy coating because of 10 wt % MB during combustion showed effects in the cone calorimeter test similar to nanodispersed LS, and somewhat better flame retardancy in flammability tests, such as LOI and UL 94. Adding APP to EP resulted in intumescent systems. The fire retardancy was particularly convincing when 15 wt % APP was used, especially for low external heat flux, and thus, also in flammability tests like LOI and UL 94. V0 classification is achieved when 15 wt % APP is used in EP. The flame retardancy efficiency of the protection layers formed does not increase linearly with the MB and APP concentrations used. The combination of LS with MB or APP shows antagonism; thus the performance of the combination of LS with MB or APP, respectively, was disappointing. No optimization of the carbonaceous‐inorganic surface layer occurred for LS‐MB. Combining LS with APP inhibited the intumescence, most probably through an increase in viscosity clearly above the value needed for intumescent behavior. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Rheology of SiO2/(acrylic polymer/epoxy) suspensions. I. Linear viscoelasticity

Linear viscoelastic properties of SiO2/(AP/EP) suspension with various SiO2 volume fractions (ϕ) in a blend of acrylic polymer (AP) and epoxy (EP) were investigated at various temperatures (T). The AP/EP contained 70 vol.% of EP. The SiO2 particles were treated with epoxy silane coupling agent. The effects of the SiO2 particles are more pronounced in the terminal zone: a transition from viscoelastic liquid (ϕ ≤ 30 vol.%) to viscoelastic solid (ϕ ≥ 40 vol.%) was observed which can be interpreted as a critical gelation occurring at a critical particle content and critical gel temperature. The SiO2/(AP/EP) systems exhibited a critical gel behavior at ϕ ≅ 35 vol.% and T ≅ 100°C characterized with a power–law relationship between the storage and loss moduli (G ′ and G ″) and frequency (ω); G ′ = G ″/tan(nπ/2) ∝ ω n . The critical gel exponent (n) was estimated to be about 0.45. The gelation occurred with increasing T.

Hygrothermal Aging of Silane-Laced Epoxy Coatings

The impact of silane on the hygrothermal stability of epoxy coatings was investigated by specular neutron reflectivity (NR). By comparing the hygrothermal degradation behavior of neat novolac epoxy coating and corresponding bis[3-(triethoxysilyl)propyl]tetrasulfide-laced epoxy coating, the role of silane was elucidated. Accelerated aging was achieved by exposing the samples to 80°C liquid water. For the pure epoxy coating, degradation occurs at the coating–substrate interface, which makes the coating vulnerable to adhesion failure. For epoxy–silane coating the addition of silane imparts resistance to the interfacial degradation observed in the neat epoxy coating.

Glycidoxypropylsilane-functionalized Magnetite as Precursor for Polymer-covered Core-shell Magnetic Particles

Surface-functionalized core-shell magnetic particles were obtained by reacting the hydroxyl groups on the surface of pre-prepared magnetite particles with 3-glycidoxypropyltrimethoxysilane. Fourier transform infrared spectra indicated that epoxy silane molecules were chemically bound onto the surface of magnetite particles through Fe—O—Si linkages. As proved by atomic force microscopy and environmental scanning microscopy combined with energy dispersive X-ray spectroscopy, particles with average core diameter and shell width of about 700 and 70 nm, respectively, were obtained. The covered magnetite particles showed a lower saturation magnetization (46 emu g 1) as compared to the uncoated magnetite (64 emu g 1).

One-step and high-density protein immobilization on epoxysilane-modified silica nanoparticles

Silica nanoparticles are most commonly modified with amino-silanes, followed by post-modification activation for protein immobilization. In this work, epoxy-functionalized silica nanoparticles were prepared by modification with glycidyloxypropyl trimethoxysilane (GPTMS) for direct protein immobilization. Silica nanoparticles possessed an average size of 46 nm, but increased to 63 nm after GPTMS modification. Reaction time, reaction temperature and GPTMS content had no significant effect on particle size. Zeta potential of SiO2 changed from −26mV to +38mV after modification. Fourier-transformed infrared spectroscopy revealed alkyl C-H bending and stretching bands at 2944 cm−1, 1343 cm−1 and 1465 cm−1, respectively, for the modified nanoparticles. Fluorescein cadaverine was found to bind to GPTMS-modified SiO2, but not to bare SiO2, indicating the chemical reactivity of epoxy groups on the modified nanoparticle with amines. Finally, fluorescently labeled bovine serum albumin (BSA) was used as a model protein to investigate the capacity of epoxy-SiO2 nanoparticles for protein immobilization. The results showed that more proteins were immobilized on the particle with longer reaction time, higher NaCl concentration, lower pH, and less GPTMS content. More importantly, proteins bound to epoxy-SiO2 nanoparticle were highly stable. Under optimized reaction conditions, as much as 25 mg BSA/g nanoparticle was covalently attached to the nanoparticle. The epoxy silane modification of silica nanoparticles offers a reactive surface for one-step and high-density protein immobilization.