Silicone resin synthesized by tetraethoxysilane and chlorotrimethylsilane through hydrolysis–condensation reaction

Silicone pressure‐sensitive adhesives compositions contain a polydimethylsiloxane and a silicone resin, which can enhance the instant bonding ability and bonding strength of the adhesive. In this study, silicone resin was designed to have a low molecular weight and a highly nonpolar chemical structure. The silicone resin was applied to silicone pressure‐sensitive adhesives. The molecular structure of silicone resin was characterized by FT‐IR, GPC, ¹H‐NMR, and ²⁹Si‐NMR spectroscopic techniques. Properties such as thermal stability, solubility, hydrophobic, and transparent properties were researched and compared. When the chlorotrimethylsilane increased, it appeared that the amount of silanol groups, molecular weight and thermal stability decreased, while the hydrophobic and transparent properties increased. The silicone resin was completely soluble in toluene and xylene. It was also applied to silicone pressure‐sensitive adhesives, resulting in good peel adhesion. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40317.     

Structural,dielectric and mechanical behaviors of (La,Nb) Co-doped TiO2/Silicone rubber composites

Ceramic/polymer composites have great potential to achieve the concomitant enhancement of both dielectric constant and breakdown field while maintaining other superior properties of the polymer matrix, ideal for elastomer sensors, actuators, capacitive energy storage, and many other applications. However, material incompatibility between the ceramic filler and the polymer matrix often leads to void formation, particle aggregation and phase separation, with significantly degraded performance. Herein, through surface modification, co-doped TiO₂ particles were uniformly dispersed and bridged onto the silicone rubber matrix via a silane coupling agent for fabricating composites via mechanical mixing and hot-pressing. The synthesized composites exhibit enhanced dielectric constant, increased from 2.78 to 5.06 when 50 wt% co-doped TiO₂ particles are incorporated. Their dielectric loss is less than 0.001 in a broad frequency range. Theoretical modelling and experimental results reveal that the morphology and dispersion state of co-doped TiO₂ particles were crucial to the dielectric properties of the silicone rubber-based composites. Besides, the composites are thermally stable up to 400 °C. Significantly increased tensile strength (612 kPa) and elongation at break (330%) were obtained for the composite incorporated with 30 wt% co-doped TiO₂ particles, accompanied by a moderate increased elastic module (540 kPa). Such composites have the potential for different applications.     

Steel-Epoxy Composite Joints Bonded with Nano-TiO2 Reinforced Structural Acrylic Adhesive

This article reports a study on the effect of TiO₂ nanoparticles on the adhesion strength of steel–glass/epoxy composite joints bonded with two-part structural acrylic adhesives. The introduction of nano-TiO₂ in the two-part acrylic adhesive led to a remarkable enhancement in the shear and tensile strength of the composite joints. The shear and tensile strengths of the adhesive joints increased with adding the filler content up to 3 wt.%, after which it decreased with adding more filler content. Also, addition of nanoparticles caused a reduction in the peel strength of the joints. Differential scanning calorimeter analysis revealed that glass transition temperature (T_g) values of the adhesives rose with increasing the nano-filler content. The equilibrium water contact angle decreased for adhesives containing nanoparticles. Scanning electron microscope micrographs revealed that addition of nanoparticles altered the fracture morphology from smooth to rough fracture surfaces.     

Viscoelastic and adhesive properties of polystyrene-hydrogenated (3,4-polyisoprene and 1,4-polyisoprene)-polystyrene and polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate-based HMPSA

In the current study, hot melt pressure sensitive adhesives (HMPSA) were prepared by blending polystyrene-hydrogenated (3,4-polyisoprene and 1,4-polyisoprene)-polystyrene (HYBRAR7311), polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (LA2250), tackifier, and other additives in an internal mixer. The compatibility of LA2250, HYBRAR7311, and glycerol rosin ester was investigated on the basis of transparency, differential scanning calorimeter, and scanning electron microscope. The results indicated that glycerol rosin ester was compatible with HYBRAR7311 and LA2250, while HYBRAR7311 was only partly compatible with LA2250. Besides, styrene-ethylene-butene-styrene block copolymers grafted MALEIC ANLYDRIDE was used as compatibilizer added into HMPSA. Although it increased the compatibility and shear strength yet the tack and peel strength were sharply decreased. Simple variable method was used to study the effect of main components on the tack, peel strength, and shear strength of HMPSA. The relationship between adhesive properties and viscoelastic properties of HMPSA was studied via dynamic mechanical analysis. The investigation showed that the smaller storage modulus at low frequency (0.01–0.1?1/s), the larger the tack. Peel strength was found proportional to G′′(f₁)/G′(f₂)(f₁?=?32.03?1/s, f₂?=?0.07?1/s). Similarly, the effect of this blend on damping performance and substrate on peel strength of HMPSA was investigated which was found excellent in this case. The peel strength of polypropylene was larger when HYBRAR7311 content was more than LA2250. However, the peel strength of polycarbonate and polyethylene glycol terephthalate was larger when LA2250 content was more than HYBRAR7311. Furthermore, the mechanical properties of HYBRAR7311/LA2250 HMPSA were found to be superior to the one-polymer HMPSA.     

Design of experiments for optimization a biodegrable adhesive based on ramon starch (Brosimum alicastrum Sw.)

In this work, a Central Composite Design (CCD) and Response Surface Methodology (RSM) were used to study the effect of starch content, hydrolyzing agent (NaOH) content, temperature and cooking period on peel strength and shear strength of biodegradable adhesives based on Ramon (Brosimum alicastrum Sw.) and Corn (Zea mays L.) starch. Scribe® paper was used as substrate or adherent. The CCD consisted of 36 experiments (including 12 central points). The second-order regression models of the response surface method, used to predict the response variables, exhibited a high correlation between the data obtained and the predicted data, and were thus considered reliable to optimize the mechanical properties for peel strength and shear strength of the Ramon starch adhesives. Starch content, hydrolyzing agent content and the cooking temperature of the adhesives proved to be the most significant factors affecting peel strength and shear strength of the adhesives of both the Ramon and corn starch. Moreover, the interactions of Starch-NaOH and Starch-Temperature were found to be the most significant in the adhesive properties in both adhesives. The mechanical properties (peel strength and shear strength) of both adhesives increased until reaching approximately their temperatures of gelatinization (T _{RAMON GEL} = 83 °C, T _{GEL CORN} = 72 °C). At higher temperatures, the mechanical properties of the adhesives diminished. The results of this study show that the adhesive prepared with the Ramon starch presents adhesive properties similar to those of an adhesive prepared with corn starch. This would imply that the Ramon starch is a viable alternative to substitute corn starch in industrial applications not relating to food production.     

Synthesis and characterization of carboxymethyl cellulose powder and films from Mimosa pigra

Mimosa pigra peel was sun‐dried for 2 days and then ground before being boiled with 30%w/v sodium hydroxide (NaOH) at 100°C for 3 h, washed and then dried at 55°C to constant weight. The cellulose was then synthesized using different NaOH concentrations and monochloroacetic acid (MCA) in isopropyl alcohol (IPA). Effects of various NaOH concentrations on degree of substitution (DS), viscosity and thermal of carboxymethyl cellulose from Mimosa pigra peel (CMC_m) were investigated. The increasing of NaOH concentration resulted in increasing DS and viscosity. However, viscosity of CMC_m decreased as temperature increased. Thermal properties were studied using differential scanning calorimetry (DSC). The melting point of the samples decreased as %NaOH increased. The effects of various NaOH concentrations in CMC_m synthesis on the mechanical properties and water vapor permeability (WVP) of the CMC_m films were investigated as well. With increasing NaOH concentrations (30–50%) were also found to result in improved mechanical properties. However, when the level of NaOH concentration was 60%, the mechanical properties of the CMC films decreased. This result indicates that the highest mechanical properties were found for 50% NaOH‐synthesized CMC_m films. The WVP of the CMC_m films increased as %NaOH increased. In addition, the CMC_m films were tested to determine the effect of glycerol as a plasticizer on the mechanical properties. Increasing the amount of glycerol showed an increase in elongation at break but also led to a decrease in tensile strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Nanotailoring of polyurethane adhesive by polyhedral oligomeric silsesquioxane (POSS)

The development and commercialization of nanoparticles such as nanoclays (NCs), carbon nanotubes (CNTs) and polyhedral oligomeric silsesquioxanes (POSS) offers new possibilities to tailor adhesives at the nanoscale. Four types of POSS, with reactive mono-functional groups of isocyanatopropyl, glycidoxypropyl, aminoethyl and non-reactive octaphenyl, were incorporated in concentrations of 1, 3 and 5 wt% into a polyurethane (PU)-based adhesive. Thermo-mechanical bulk properties were studied using dynamic mechanical analysis (DMA). Adhesive properties were characterized in shear and peel modes. Atomic force microscopy (AFM) was used to study the nanoscale morphology. DMA measurements indicated that the neat PU possessed a glass transition temperature (T _g) of ≈ 30°C. The T _g of PU/POSS-glycidoxypropyl nanocomposite adhesive increased gradually with POSS concentration to 50°C for 5 wt%. PU/POSS-octaphenyl nanocomposite adhesive exhibited an increased T _g by 10°C for 5 wt%. The incorporation of POSS-isocyanatopropyl in the PU had no effect on the T _g. With respect to shear properties of POSS-octaphenyl-, POSS-isocyanatopropyl- and POSS-glycidoxypropyl-based PU nanocomposite adhesives, shear strength improved by 230, 178 and 137%, respectively, compared to neat PU. POSS-aminoethyl exhibited lower shear and peel strengths, while POSS-isocyanatopropyl provided the best balance of both higher shear and peel strengths compared to neat PU. It was concluded that the grafted functional group on the POSS and its reactivity with the PU network components were the decisive factors with respect to the thermo-mechanical, morphological and adhesive properties of the resulting nanocomposite adhesives. Consequently, the POSS/polyurethane based nanocomposite adhesives could be tailored for a large range of applications.     

Preparation of highly stable superhydrophobic TiO2 surfaces with completely suppressed photocatalytic activity

TiO₂ nanoparticles with a mean size of 20–30 nm were covered by ultrathin polydimethylsiloxane (PDMS) film, which shows hydrophobic properties. Surfaces consisting of the PDMS-coated TiO₂ particles showed water contact angles close to 170°. In contrast to the hydrophobic films consisting of organic molecules, which can be photocatalytically decomposed on TiO₂ in the presence of UV light, PDMS-coating on TiO₂ was highly stable. The PDMS-coating completely suppressed the photocatalytic activity of TiO₂. The unique properties of PDMS-coating can be exploited for UV protection layer and self-cleaning surfaces.     

Plasticity in peeling

Contrary to classical theory, a high proportion of bond failures by peeling involve progressive plastic adherend flexural yield. Such yield occurs with adherend thicknesses below a critical value, T_c, which is shown calculable by combining elastic peel mechanics with plastic bending criteria. The geometry of such “peel with yield,” and thence the moment-controlled peel forces, can be accounted for only if the adhesive is also recognized as behaving essentially plastically. Subsequent plastic adherend unbending is important with highly extensible adhesives. The geometry of “legging” peel in such cases is best described by fully plastic mechanics. These are derived and shown to account for literature data on dependencies of peel force upon peel rate and adhesive thickness. “Stick-slip” peel phenomena are indicated to be controlled by recurring interacting plastic–elastic transitions, in both adhesive and adherend: adhesive strain rate is critical in such phenomena. Four regimes of peel behavior can therefore apply as adherend thickness (T) increases, with peel forces proportional respectively to T⁰, T^2/3, T^3/2 (above T_c) and finally controlled by moment limitations due to joint configurational constraints (“cleavage”).     

Preparation of TiO2-loaded nanocapsules and their sun protection behaviors

Titanium dioxide (TiO₂) sol (TS) or TiO₂ nanoparticles with chitosan shell were encapsulated to enhance their sun protection abilities. Nanocapsules loaded with TiO₂ were evaluated for their ultraviolet (UV) absorption and UV protection rate. The effect of eicosapentaenoic acid (EPA) incorporation into the nanocapsules was examined in relation to UV absorption. The particle size of TiO₂ crystallites in TS was below 30 nm, which was considerably smaller than that of a commercial TiO₂ (P25 TiO₂) particles. In the encapsulation of TiO₂ with chitosan, the loading efficiencies of TS were higher than those of P25 TiO₂. The sizes of the nanocapsules loaded with TiO₂ particles ranged from 30 to 80 nm. The absorption range of irradiation wavelength was enlarged by the incorporation of EPA into the nanocapsules. The TS-loaded nanocapsules exhibited a high UV protection rate of up to 95% to both UV-A and UV-B.     

Silicone functionalized pigment to enhance coating performance

The present study reports chemical treatment of pigment titanium dioxide (TiO₂) with silicone to give surface functionalized TiO₂. The surface functionalization was confirmed by Fourier Transform Infra Red Spectroscopy, Scanning Electron Microscopy, Transition Electron Microscopy and Dynamic Light Scattering analysis. Coatings were formulated by incorporation of these functionalized TiO₂ into the epoxy polymer matrix and compared for coating properties with untreated TiO₂. The effect of the functionalized TiO₂ on various coating properties with respect to physico-mechanical properties, anticorrosion efficiencies, UV resistance and chemical resistance was studied in detail. The results revealed remarkable enhancement of coating properties with functionalized TiO₂ when compared with the coatings formulated with untreated TiO₂.     

Effect of natural and synthetic tackifiers on viscosities,adhesion properties and thermal stability of SNR and DPNR solution adhesives

Styrene-grafted natural rubber (SNR) and deproteinized natural rubber (DPNR) latexes were formulated with coumarone-indene (CI), gum rosin and petro resin (PR) tackifiers into solution adhesives with toluene as a solvent. The solution viscosities were evaluated by a Brookfield viscometer DV-II Plus with spindle No. 3. Pressure sensitive adhesives (PSAs) films were made and the adhesion properties were evaluated with loop tack, peel strength and shear strength tests. Thermal stability of the film was evaluated via Perkin-Elmer Pyris 6^TM thermogravimetric analysis at temperatures ranging from 30 to 600?°C at a heating rate of 10?°C per minute in nitrogen environment. Results indicate that as the tackifiers content increased, the solution viscosities increased with SNR/PR and DPNR/PR formulations showing the highest viscosities. Adhesion test also indicates that loop tack and peel strength of the adhesive solution increased but their shear strength decreased; increase of CI tackifier loadings conferred the highest peel strength for both SNR- and DPNR-based PSAs. Thermal analyses show that the addition of 40 phr CI tackifiers improved thermal stability of SNR adhesives based on their higher T_max and integral procedural decomposition temperature properties.     

Impact of porosity and thickness of nano‐TiO2 films on the corrosion protection performance of C‐steel in H2SO4

The current study investigates the improvement in the corrosion protection performance of C‐steel after being dip‐coated with nano films from both pure TiO₂ and poly ethylene glycol (PEG) modified TiO₂. Characterization of the deposited TiO₂ films was performed by different techniques. Effect of morphology, porosity, and thickness of the deposited TiO₂ layers were also studied. Results revealed an increased corrosion protection of both coated TiO₂ films as compared to uncoated samples, with pure TiO₂ (without PEG) samples showing higher protection. Moreover, increasing the layer thickness of both types of TiO₂ coated films improved the protective properties.     

Effects of water density on acid-catalytic properties of TiO2 and WO3/TiO2 in supercritical water

The effects of water density on the acid-catalytic properties of TiO₂ and WO₃/TiO₂ catalysts in supercritical water at 400 °C were investigated by using the kinetic analysis of the dehydration reaction of glycerol. The reaction selectivity of TiO₂ and WO₃/TiO₂ catalysts and the apparent-reaction orders for water indicated that the acid-catalytic properties of these two catalysts show different dependence on water density. In the reaction using TiO₂, the contribution of Lewis acid sites in TiO₂ was large at a low water density, while the contribution of Brönsted acid sites in TiO₂ increased with increasing water density. On the other hand, the reaction using WO₃/TiO₂ was mainly catalyzed by Brönsted acid sites in WO₃/TiO₂ even at a low water density, and the nature of Lewis/Brönsted acid sites in WO₃/TiO₂ was not influenced by the water density.     

Enhancement in electrical and thermal performance of high-temperature vulcanized silicone rubber composites for outdoor insulating applications

High-temperature vulcanized silicone rubber composites are highly desirable as outdoor insulating materials due to their immense thermal and electrical performance. The aim of this work is to study the role of co-combined fillers (modified fumed silica [MFS], titanium dioxide [TiO₂], with graphene [G]) on electrical and thermal properties of silicone rubber (S) composites. The dielectric response of S/MFS_10 phr and S/TiO₂_20 composites tailored with 2 phr G was characterized by broadband dielectric spectroscopy. The hybrid filler/composites were found to show higher thermal stability when 2 phr G was added. In addition, a low quantity of G filler was found to slightly increase the AC dielectric breakdown strength of the S/MFS_10 and S/TiO₂_20, where an improvement of 3 and 5% was found, respectively. Several steps were observed in the thermal decomposition of the S rubber composites by thermogravimetric analysis-Fourier-transform infrared spectroscopy. Our findings revealed great potentials for fabricating hybrid-filler/silicone rubber composites with enhanced electrical and thermal properties for outdoor insulating applications.     

Effect of SiO2 and TiO2 nanoparticle on the properties of phenyl silicone rubber

Two types of nanoparticles TiO₂ and SiO₂ treated with silane coupling agents were incorporated into phenyl silicone rubber at a low concentration (≤1.0%) and cured by the room temperature vulcanized method. The results showed that treated TiO₂ or SiO₂ nanoparticles improved the ultraviolet (UV)‐shielding ability and enhanced the visible transmittance of the phenyl silicone rubber, compared with their respective untreated particles. Moreover, when comparing treated nanoparticles, TiO₂ was more responsible for augmenting the UV‐shielding ability of the phenyl silicone rubber, while SiO₂ played a more important role in increasing the transmittance of visible light. Low levels of nanoparticles reduced the dielectric constant of the nanocomposite; however, on reaching a critical concentration, increasing the nanoparticle content had the opposite effect. The thermal conductivity of nanocomposites increased linearly with the amount of treated nanoparticles, while SiO₂ nanocomposites exhibited better thermal conductivity than those of TiO₂. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42806.     

Ablative properties and mechanisms of hot vulcanised silicone rubber (HVSR) composites containing different fillers

Hot vulcanised silicone rubber (HVSR) composites were prepared using silicon carbide (SiC), hafnium oxide (HfO₂), zirconium oxide (ZrO₂) and zirconium boride (ZrB₂) as fillers, respectively. The tensile properties and the ablative response of the composites were examined. Tensile tests indicated that the tensile strength of HVSR was increased by the incorporation of ZrB₂. The linear ablation rate of the composites increased in the order HVSR/ZrB₂?2?2?2 and HVSR/ZrO₂, respectively, compared to that of 333?K for the blank HVSR. Scanning electron microscopy and X-ray diffraction results showed that the dense and rigid ceramic layer was hard to peel off under the high pressure and shearing forces of ablative gases. The HVSR/ZrB₂ specimens exhibited the best ablation resistance among all the composites involved in this work.     

Anticorrosion reinforcement of waterborne polyacrylate coating with nano-TiO2 loaded graphene

Photocathodic protection coatings have been widely applied in various areas such as ship and architectural protection, or chemical industry. In this work, a composite of titanium dioxide loaded with reduced graphene oxide (RGO/TiO₂) was prepared and used as filler on waterborne polyacrylate (PA) coating to reinforce the metal protection against corrosion. Compared with the current filler of zinc phosphate used for anticorrosive coating, the photoelectrochemical properties of RGO/TiO₂-PA coating exhibit improved photocathodic protection under visible light illumination since RGO/TiO₂ composite has significant superiority in enhancing metal protection due to its dispersion, micropore blocking ability, and photoelectrochemical conversion performance. The mechanism of anticorrosion reinforcement of RGO/TiO₂-PA coating was hypothesized that graphene provides an extrabarrier layer to obstruct corrosive in dark condition and photocathodic protection under lighting. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48733.     

Stretchable photochromic hydrous TiO2-embedded glycerol-poly(dimethylsiloxane) film for rewritable information storage

Photoreversible, color-changing films have great potential in various optical applications. In this study, we developed a photochromic film by embedding droplets of metatitanic acid (hydrous TiO₂) and glycerol in commercially available poly(dimethylsiloxane) (PDMS) silicone elastomers. Benefiting from the electron–hole pair scavenging abilities of glycerol, the resulting film exhibited rapid photoresponse, high photoreversible stability, excellent antiaging capability, and remarkable stretchability. The degree of color changes upon ultraviolet (UV) irradiation was effectively controlled by adjusting both the concentration of hydrous TiO₂ (1–20 wt%) and UV irradiation time (5–30 min), thereby increasing total color-changing ability (ΔE). High-resolution patterns could be repetitively printed, erased, and rewritten (≥20 times) with no significant loss of clarity. After a 30-day exposure to ambient air, there were no significant aging effects in the photochromic ability of the films, thus demonstrating promising potential as rewritable films for information storage.     

Melt Synthesis and Characterization of Aliphatic Low-Tg Polyesters as Pressure Sensitive Adhesives

Polyesters, which are readily synthesized in the absence of solvent, are excellent candidates for a new generation of pressure sensitive adhesives (PSAs) due to their low cost and potential biodegradability. In this study, linear, all-aliphatic polyesters with low glass transition temperatures (T_g) were synthesized using a solvent-free, environmentally friendly melt polycondensation methodology. Polyesters of various compositions were synthesized from different diol and diester monomers to adjust the glass transition temperature and achieve optimum adhesive properties. Melt polycondensation of an isomeric mixture of dimethyl-1,4-cyclohexane dicarboxylate (DMCD), dimethyl adipate (DMAP), diethylene glycol (DEG), and triethylene glycol (TEG) generated a series of linear low-T_g polyesters. The synthesized polyesters were characterized using size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and ¹H NMR spectroscopy. The frequency- and temperature-dependent properties of the low-T_g polyesters were characterized using dynamic mechanical analysis (DMA). The adhesive performance of the polymers was evaluated using tack, peel, and shear strength measurements at ambient humidity and temperature. The low-T_g polyesters exhibited peel and tack properties comparable with commercial acrylic adhesives.