Hydroxy-terminated Polydimethylsiloxane Research Articles

Effectiveness Evaluation of Silicone Oil Emulsion In Situ Polymerization for Dehydration of Waterlogged Wooden Artifacts

Organosilicon materials have shown potential as dehydration agents for waterlogged wooden artifacts. These materials can polymerize under normal conditions to form polymers with favorable mechanical strength, antibacterial properties, and aging resistance. However, the insolubility of most organosilicon hindered their penetration into waterlogged wood, which may lead to an unwanted cracking. This study aimed to evaluate the effectiveness of polydimethylsiloxane (PDMS) and hydroxy-terminated polydimethylsiloxane (PDMS-OH) with low viscosity and moderate reactivity for dehydrating waterlogged wooden artifacts from the Nanhai No.1 shipwreck. Four surfactants ((3–aminopropyl) triethoxysilane (APTES), alkyl polyoxyethylene ether (APEO), tri-methylstearylammonium chloride (STAC), and fatty alcohol polyoxyethylene ether (AEO)) and cosurfactant were employed to transform the two kinds of water-repellent silicone oils into eight groups of highly permeable oil-in-water (O/W) emulsions. Under the catalysis of a neutral catalyst, in situ polymerization occurred within the wood cells. Group P2-2 formulated with PDMS-OH and APEO showed the best efficiency in maintaining the dimensions of the wood during dehydration. The dehydrated wood exhibited a natural color and texture with a minimal volume shrinkage rate of 1.89%. The resulting polymer adhered uniformly to the cell walls, effectively reinforcing the wood cell structure. The weight percent gain of the wood was only 218%, and the pores of the cell lumen were well maintained for future retreatment. This method effectively controlled the sol–gel reaction process of the organosilicon and prevented damage to the wooden artifact during the dehydration process. Moreover, the dehydrated wood samples only experienced a low weight gain of 17% at 95% relative humidity (RH), indicating their great environmental stability.

Preparation of hydroxy-terminated polydimethylsiloxane and nano-SiO2 hydrophobic polyurethane coated urea and investigation of controlled nitrogen release

In the present study, we successfully developed hydroxy-terminated polydimethylsiloxane (PDHT) and nano-SiO2 hydrophobic polyurethane-coated urea by applying the optimal conditions for hydrophobic polyurethane preparation. The hydrophobic polyurethane membrane material undergoes a comprehensive characterization. Infrared analysis confirmed the successful grafting of PDHT onto the polyurethane membrane material. X-ray Photoelectron Spectroscopy (XPS) and Energy Dispersive X-Ray Spectroscopy (EDX) analysis verify the even distribution of silicon on the surface of the membrane material. By Scanning Electron Microscopy (SEM) comparison, we elucidate the micro-structural disparity between the unmodified and modified castor oil-based polyurethane, accounting for the micro-level performance enhancement. The resulting modified membrane exhibited a water contact angle of 133.6°, indicative of its hydrophobic nature. The optimal ratios for PDHT and nano-SiO2 were determined to be 16 % and 2 %, respectively. Notably, hydrophobic polyurethane-coated urea demonstrated an extended-release period of 98 days (5 % coating amount), a 40 % improvement over its unmodified counterpart. In addition, the silicone-modified coated urea reduced the amount of ammonia volatilization by about 76.32 %, which plays a significant role in enhancing fertilizer utilization efficiency and is important for ecological environment protection. This research provides a straightforward and efficient way to fabricate slow-release fertilizers, with significant implications for the advancement of coated slow-release fertilizer technology.

Enhancing flame retardancy and multi-functionalization of environmentally friendly cotton fabrics with a polydimethylsiloxane-based polyurethane

Phosphorus-containing flame retardants are prone to result in the buildup of biotoxins, while halogen flame retardants easily lead to hazardous gases. Therefore, it is crucial to develop a multifunctional flame-retardant cotton fabric without phosphorus and halogen. Herein, single-ended hydroxy-terminated polydimethylsiloxane (PDMS-ID) was synthesized through single-ended hydrosilicone oil and 1,4-butanediol, followed by the preparation of a waterborne polyurethane (RWPU) containing side chain polydimethylsiloxane through the reaction of PDMS-ID with isocyanate prepolymer. Characterization data shows that its particle size distribution is relatively dispersed while maintaining good emulsification performance. Based on this, a halogen-free and phosphorus-free multifunctional flame retardant cotton fabric (COF-BBN@RWPU) was successfully prepared through treatment with boric acid/borax/3-aminopropyltriethoxysilane solution and subsequent RWPU encapsulation. In vertical flammability test (VFT), COF-BBN@RWPU has a char length of 57 mm and a limiting oxygen index (LOI) of 42.3 % with a 11 % weight gain while pure cotton was burned through with a LOI of 18.0 %. In addition, the total heat release and total smoke release of COF-BBN@RWPU decreased by 80.0 % and 47.2 %, compared with pure cotton. Additionally, COF-BBN@RWPU can achieve a maximum contact angle of 140.1° with an oil-water separation rate of 98.4 %. This study presents an eco-friendly approach to achieving the multifunctionality of cellulose fabrics.

Synthesis and properties of silicone-modified polyurethane acrylate for magnetically driven blue light photocurable superhydrophobic coatings

A low surface energy silicone-modified polyurethane acrylate (Si-PUA) has been synthesized and employed as the primary constituent for the magnetically driven photocurable coatings. By integrating magnetically driven assembly technology with blue light photocuring technology, a superhydrophobic coating featuring low surface energy and micro/nano rough structures was successfully fabricated. The influences of hydroxy-terminated polydimethylsiloxane (PDMS) content and the R-value (-NCO/-OH) on the performance of PUA and coating systems were investigated using Photo-DSC, TGA, rheology, tensile testing machine, and SEM-EDS. The molecular structure of Si-PUA was characterized using FT-IR and 1HNMR. The result revealed that the composite coating exhibited a minimum surface energy when the PDMS content was 5 wt% and the R-value was 1.6, resulting in a surface free energy of 24 mJ/m2. When the coating formulation consists of a Si-PUA:HEA ratio of 7:3, an initiator dosage of 2% (with CQ/EDB at a 1:1 ratio), and a carbonyl iron powder (CIP) content of 100 wt%, the resulting photocured film exhibits a surface contact angle of 157.6° and a rolling angle of 5°, thereby satisfying the superhydrophobicity standard.

PDMS/TiO2 and PDMS/SiO2 Nanocomposites: Mechanical Properties' Evaluation for Improved Insulating Coatings.

The use of nanoparticles (NPs) as reinforcements in polymeric coatings allows for direct interaction with the polymeric chains of the matrix, resulting in a synergistic process through physical (electrostatic forces) and chemical interactions (bond formation) for the improvement of the mechanical properties with relatively low weight concentrations of the NPs. In this investigation, different nanocomposite polymers were synthesized from the crosslinking reaction of the hydroxy-terminated polydimethylsiloxane elastomer. Different concentrations (0, 2, 4, 8, and 10 wt%) of TiO2 and SiO2 nanoparticles synthesized by the sol-gel method were added as reinforcing structures. The crystalline and morphological properties of the nanoparticles were determined through X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The molecular structure of coatings was through infrared spectroscopy (IR). The crosslinking, efficiency, hydrophobicity, and adhesion degree of the study groups were evaluated with gravimetric crosslinking tests, contact angle, and adhesion tests. It was observed that the crosslinking efficiency and surface adhesion properties of the different nanocomposites obtained were maintained. A slight increase in the contact angle was observed for the nanocomposites with 8 wt% compared to the polymer without reinforcements. The mechanical tests of indentation hardness and tensile strength following the ASTM E-384 and ISO 527 standards, respectively, were performed. As the nanoparticle concentration increased, a maximum increase of 157% in Vickers hardness, 71.4% in elastic modulus, and 80% in tensile strength was observed. However, the maximum elongation remained between 60 and 75%, ensuring that the composites did not become brittle.

Covalent “Bridge-crosslinking” strategy constructs facilitated transport mixed matrix membranes for highly-efficient CO2 separation

Facilitated transport mixed matrix membranes (FTMMMs) separation technology has shown advantages in improving CO2 recycling efficiency and reducing the environmental impacts associated with carbon emission. The design of FTMMMs is highly dependent on the selection of a compatible combination of polymer and filler. Herein, a novel grafted nanoparticles (GNPs) filler UiO-66-NM@PEG with multiple groups prone to hydrogen bond was designed to alleviate the phase separation and performance degradation caused by filler/polymer poor compatibility. In the GNPs configuration, by employing the coexistence strategy of coupling reaction and covalent bonds, maleic anhydride (MAH) was coupled with the amino group on UiO-66-NH2 without clogging or cracking, and the generated carboxyl groups can be cross-linked with the hydroxyl groups on the poly (ethylene glycol) (PEG) by covalent bonds. The UiO-66-NM@PEG demonstrated excellent interface compatibility between the filler and matrix phase of UiO-66-NM@PEG/PVDF, which was further convinced by molecular modelling. The resultant UiO-66-NM@PEG/PVDF achieved a simultaneous enhancement of gas permeability (537.6 Barrer) and ideal CO2/N2 selectivity (47.8), which surpassed Robenson upper bound. Moreover, the UiO-66-NM@PEG/PVDF has a lasting sustainability over 960 h (40 days), and a valid anti-acid/alkali corrosion resistance in harsh environments. More importantly, UiO-66-NM@PEG can also be well mixed with other mixture matrices such as hydroxy-terminated polydimethylsiloxane (PDMS) and polyether-block-polyamide copolymer (PEBAX) to promote permeability/ideal selectivity up to (724.1 Barrer/21.1) and (307.4 Barrer/31.4). We thus concluded that this rational-design GNPs approach provides a general toolbox for controllable engineering in GNPs whereby enhanced favorable filler/matrix compatibility in FTMMMs with optimized CO2/N2 separation properties.

Controlled Orientation of Silicon-Containing Diblock Copolymer Thin Films by Substrate Functionalization Under Vacuum

This work demonstrates a simple approach to control the orientation of the self-assembled nanostructured block copolymer thin films of polystyrene-block-polydimethylsiloxane (PS-b-PDMS) by functionalization of the oxide layer (SiO2) on the Si substrate followed by thermal annealing under low-pressure environmental conditions. The substrate can be functionalized through two-step grafting of hydroxy-terminated polystyrene brush (PS–OH brush) followed by hydroxy-terminated polydimethylsiloxane brush (PDMS–OH brush) onto the wafer substrate. By controlling the grafting ratio of PS–OH and PDMS–OH brushes, the affinities of the PS and PDMS blocks with the substrates can be fine-tuned to provide a neutral substrate in order to form perpendicular cylinders from the bottom after thermal annealing. Owing to the vacuum-driven orientation [i.e., thermal annealing under low-pressure environment conditions (∼10–4 Pa)], the orientation of the cylinders can be controlled at the air/polymer interface. Interestingly, by combining the vacuum-driven approach with substrate functionalization, perpendicular cylinders from the air/polymer interface and substrate/polymer interface can be generated, respectively. Consequently, well-aligned perpendicular cylinders with long-range ordering can be fabricated by the self-alignment process.

Effect of Synergistic Modification of Building Materials Based on α-Hemihydrate Phosphogypsum by Portland Cement/H-PDMS on Water Resistance.

Alpha-hemihydrate phosphogypsum (α-HPG) is a cementitious material obtained by dehydration of phosphogypsum (PG), a byproduct of phosphoric acid production. Poor water resistance of α-HPG has usually restricted its application in construction materials. In this study, hydroxy-terminated polydimethylsiloxane (H-PDMS) and Portland cement (PC) were used for the hydrophobic modification of α-HPG. The fluidity, setting times, compressive strength, flexural strength, ratio of compressive to flexural strength, water absorption rate, softening coefficient, pore structure, chemical information, and microstructure of the samples were measured to evaluate the modification effect of H-PDMS and PC. The results showed that H-PDMS and PC significantly improved waterproof properties of α-HPG and reduced its porosity, total pore area, and pore diameter. Specifically, PC provided the reactive group -OH that reacted with H-PDMS. Also, due to the coverage of hydrophobic -CH3 groups, PG was given an overall hydrophobicity with a contact angle of 134° (1.5% H-PDMS). H-HPG (H-PDMS- and PC-modified α-HPG) hydrophobic material can be used in building materials with waterproof requirements and achieve the comprehensive utilization of solid waste PG.

Preparation and Properties of Fluorosilicone Fouling-Release Coatings.

To improve the antifouling performance of silicone fouling-release coatings, some fluorosilicone and silicone fouling-release coatings were prepared and cured at room temperature with hydroxyl-terminated fluoropolysiloxane (FPS) or hydroxy-terminated polydimethylsiloxane (PDMS) as a film-forming resin, tetraethyl orthosilicate (TEOS) as a crosslinking agent, and dibutyltin dilaurate (DBTDL) as a catalyst. The chemical structure, surface morphology and roughness, tensile properties, and antifouling properties of the coating were studied by infrared spectroscopy, a laser confocal scanning microscope, contact angle measurement, tensile tests, and marine bacteria and benthic diatom attachment tests. The results showed that the FPS coatings were not only hydrophobic but also oleophobic, and the contact angles of the FPS coatings were larger than those of the PDMS coatings. The surface free energies of the FPS coatings were much lower than those of the PDMS coatings. Generally, the fluorine groups can improve the antifouling performance of the coating. Introducing nonreactive silicone oil into PDMS or FPS coatings can improve the antifouling performance of the coating to a certain extent. The prepared fluorosilicone fouling-release coatings showed good application prospects.

Modified cardanol based colorless, transparent, hydrophobic and anti-corrosive polyurethane coating

Despite having unique functional properties, renewable resourced cardanol based polymers have limited usage in industrial coatings because of its dark brown or red color after polymerization. The current work reports the development of colorless, transparent, hydrophobic and corrosion resistant coating derived from cardanol 2,3-dihydroxy propyl ether (CPE) and modified with hydroxy-terminated polydimethylsiloxane (HTPDMS). CPE was synthesized to be used as a reactive aliphatic diol in forming polyurethane (CPU) and characterized. HTPDMS-CPU copolymers with multifunctional properties were prepared through copolymerization of 5, 10, 15, 20 wt% HTPDMS and CPE. HTPDMS-CPU coatings showed improved adhesion and hydrophobicity (>100°), enhanced transparency with easy readability underneath and a reasonable UV transmittance (92–96%). One distinct Tg and single phase surface morphology of HTPDMS10CPU and HTPDMS15CPU confirmed the good miscibility and compatibility of the system. Electrochemical Impedance Spectra (EIS), salt water immersion and salt spray studies revealed the anti-corrosive property of the copolymers with best performance at 10–15 wt% HTPDMS content. Thermogravimetric study showed almost no interference in thermal stability after the incorporation of HTPDMS into the system. The development of HTPDMS-CPU co-polymeric multifunctional coatings represents a more effective pathway to achieve multi-functional coatings with desirable hydrophobic, anti-corrosive and improved thermal stability.

Fabrication of silicone modified polyurethane matrix superhydrophobic coating with hydroxy-terminated polydimethylsiloxane modified SiO2 nanoparticles

ABSTRACT Superhydrophobic coatings have been widely used in anti-icing, anti-fouling, self-cleaning, etc., but the production and application of superhydrophobic coatings have been restricted due to the large amount of fluorine-containing substances. Therefore, the development of an environmentally friendly preparing technology is still a severe challenge. In this article, the hydroxy-terminated polydimethylsiloxane (PDMS) was used as a modifier to replace the general fluorine-containing substance as a modifier to hydrophobically modify the SiO2 nanoparticles. Meanwhile, silicone modified polyurethane (SIPU) was used as an adhesive to prepare a new type of superhydrophobic coating by spraying. The results showed that the hydrophilic SiO2 nanoparticles were converted into hydrophobic SiO2 nanoparticles successfully by grafting PDMS onto the surface of SiO2 nanoparticles. By controlling the content of PDMS@SiO2 nanoparticles, the water contact angle (WCA) and water sliding angle (WSA) of PDMS@SiO2/SIPU composite coating could reach 156.29 ± 1° and 3 ± 1°. Simultaneously, the coating exhibited excellent roughness, wear resistance and special self-cleaning ability. Furthermore, the motion state of the water droplets impacting on the superhydrophobic surface was discussed in detail. The bounce state, splash shape and movement direction of the sub-droplets were closely related to the impact speed, which simulated the outdoor actual raindrop impact.

Improving the insulating performance of epoxy resin in humid environments byHTPDMSmodification

AbstractThe rapid development of the electronic packaging industry imposes stringent requirements on epoxy resin insulation materials for lower water absorption and higher insulation properties. Here, hydroxy‐terminated polydimethylsiloxane (HTPDMS) was grafted on the molecular chain of the epoxy resin for enhanced waterproof and insulating properties of the epoxy resin. The HTPDMS‐modified epoxy resin specimens were prepared and subjected to water absorption and water absorption insulation performance tests. The experimental results indicated that the water absorption rate of the modified epoxy resin was reduced by 34.2%, resulting in a 25.2% reduction of the dielectric loss, an 11.6% increase of the breakdown strength, and a 98.3% increase of the volume resistivity. The satisfactory performance of the HTPDMS‐modified epoxy resin insulation material is attributed to the low surface energy and flexible SiO bond of the introduced HTPDMS. Simultaneously, the reduction of surface defects is also conducive to the epoxy resin insulation performance. Thus, HTPDMS‐modified epoxy resin insulation materials can maintain excellent insulation properties in humid environments, making them a promising application in the field of electronic packaging.

The Interfacial Structure and Adhesion Mechanism of N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane and Epoxy Modified Silicone Tie-Coating to Epoxy Primer.

The matching application of silicone antifouling coating and epoxy primer is a major problem in engineering. Novel epoxy-modified silicone tie-coating was prepared to tie epoxy primer and silicone antifouling coating. Firstly, N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane was mechanically mixed with bisphenol A epoxy resin to form silylated epoxy resin, then the silylated epoxy resin was uniformly mixed with hydroxy-terminated polydimethylsiloxane and a curing agent and catalyst for coating. An infrared spectrometer, differential scanning calorimeter and tensile tests were used to investigate the chemical structure, phase transition temperature and mechanical properties of the tie-coatings. The interlaminar adhesion of the matching coating system was tested and analyzed by a peel-off test and a shear test. Fracture morphology was observed by scanning using an electron microscope. The results showed that crosslinking density of the tie-coating, the elastic modulus and the tensile strength of the coating increased with an increasing epoxy content, but fracture elongation decreased. The shear strength of the matching coating system is 0.37 MPa, and it shows a good tie performance. The maximum anti-peeling rate of the tie-coating on the epoxy primer reaches 100%.

Drag reduction in internal turbulent flow by fabricating superhydrophobic Al2O3/waterborne polyurethane coatings

Nowadays, increasing the CO2 emissions are one of the inevitable challenges in the world. In addition, in many industries, fossil fuels are the main source of energy demands which worsen the problem. Since in most applications, the performance and energy loss are highly affected by the drag force, many investigations have been proposed to improve the surface properties to moving surface against the water, and consequently, increasing drag reduction. To this end, one effective way is utilizing superhydrophobic coatings. In this study, we prepare two different superhydrophobic coatings using Al2O3 nanoparticles (NPs) modified by HMDS (1,1,1,3,3,3-Hexamethyldisilazane) and PDMS (Hydroxy-terminated polydimethylsiloxane), which are named HS and PS, respectively, in a waterborne polyurethane (WBPU) resin. The coated substrates show a significant water repellency and the measured contact angles are 158.6° and 153.2° for HS and PS coatings, respectively. Furthermore, the results indicate that the drag reduction is improved up to 18.771% and 16.141% for PS and HS coatings, respectively. Besides, it is observed that the friction coefficient in the superhydrophobic pipes decreases significantly. Also, to show the durability of the resultant surfaces, immersion tests in pure water, sea-water, alkaline, and acidic solutions are used.

Intrinsically hydrophobic magnesium oxychloride cement foam for thermal insulation material

To overcome the poor water-resistance, magnesium oxychloride (MOC) cement, was hydrophobically modified with hydroxy-terminated polydimethylsiloxane (PDMS). MOC cement foam was prepared using hydrogen peroxide as the foaming agent. Scanning electron microscope (SEM) images showed that the MOC cement foams contained visible pores with sizes ranging from 150 μm to 600 μm, and the apertures increase with the increase in foaming agent. A lot of acicular phase 5 were observed in the pores, which conferred strength to the materials. Porosity analyses illustrated that the addition of the foaming agent increased the porosity and enlarged the pores, making the materials less dense. The increase in porosity and pore size significantly reduced the thermal conductivity, thereby improving the thermal insulation of the MOC cement foam. The modification of PDMS not only enhanced the water-resistance, but also achieved the superhydrophobicity of MF-1, while the sample with relatively large pores also had good hydrophobic ability. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to analyse the samples, explaining the mechanism of the water-resistance enhancement from a microscopic perspective.

An environmentally friendly titania–silica core–shell nanoparticles coating for protection of tiled facade of cultural-historical buildings

The purpose of the current research was to synthesize and characterize a hydrophobic ultraviolet (UV) absorbent coating for protection of tiled facade of cultural-historical buildings. Considering the environmental and conservational issues for such applications, using toxic materials is limited. A silicone-based nanocomposite coating was prepared in which organically modified silicates (ormosil) and titania–silica core–shell nanoparticles were used as matrix and reinforcing phase, respectively. Nanocomposite coatings were prepared by sol–gel method. Hydroxy-terminated polydimethylsiloxane (PDMS-OH) and tetraethoxysilane (TEOS) were used to form the ormosil matrix. Titania nanoparticles in anatase crystalline phase were used. To control their photocatalytic activity, silica–titania core–shell nanoparticles were prepared. Nanocomposite coatings were applied on microscope slides and historic tiles by dip-coating and simple brushing. The coatings were characterized by Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), water contact angle measurements and photocatalytic activity measurements. The results revealed that a transparent hydrophobic coating of prepared ormosils could obtain by adding a maximum amount of 20 wt% of PDMS-OH to the initial sols without addition of highly toxic solvents and catalysts. The FT-IR spectra of ormosil gels exhibited Si–O–Si bond corresponding to silica gels. It also showed that PDMS formed covalent bonds to silica networks. The XRD patterns showed that titania maintained its anatase crystalline structure after core–shell treatment. TEM images of core–shell treated nanoparticles illustrated the formation of continuous silica shell with less than 4 nm thickness around titania cores. Water contact angle measurements on tiles showed an increase in contact angle from 30° to 97° after coating. The results of UV–Vis spectrophotometry confirmed that the continuous silica layer acted as a barrier between photocatalytic titania and Methylene blue. Overall, the best composition for obtaining an environmentally friendly, transparent, hydrophobic, and UV absorbing nanocomposite coating could contain 20 wt% of PDMS-OH and about 0.025 wt% of silica–titania core–shell nanoparticles.

Structuring of hydroxy-terminated polydimethylsiloxane filled by fumed silica

Abstract The term “structuring” used in silicone rubber describes a phenomenon of the increase in the viscosity of polydimethylsiloxane filled with silica during storage, which limits the applications of the room temperature vulcanized (RTV) silicone rubber in the field of aerospace and military. In this pursuit, the present study was envisaged to solve the problem of structuring of the RTV. A solvent-free method was used to hydrophobize the hydrophilic silica with hexamethyldisilazane. An RTV composition prepared using eight parts of hydrophobic silica with 2.91% C content exhibited a viscosity of less than 100 Pa s, with no significant change in 21 days. In contrast, eight parts of the hydrophilic fumed silica showed an initial viscosity of RTV to be greater than 2,000 Pa s. Silica samples with different adsorbed water content were used to prepare the RTV compositions. It was found that the viscosity of the RTV prepared using the sufficiently dried silica was 5.6 times lower than that of the wet silica. The “dissolution” model of the silica–silica hydrogen bonds in water was proposed. Furthermore, the change in the viscosity of the RTV compositions at different temperatures in the range of −15°C to 30°C was studied. The viscosity of RTV stored at –15°C for 34 days did not change significantly, whereas that stored at room temperature increased from 100 to 1,710 Pa s within 21 days.

Effect of N-(2-Aminoethyl)-3-Aminopropyltrimethoxysilane on the Adhesion of the Modified Silicone Tie-Coating to Epoxy Primer

In this work, modified silicone tie-paints were prepared in a simple way for securing adhesion between the epoxy anticorrosive primer and silicone fouling release coating. Hydroxy-terminated polydimethylsiloxane (PDMS) mixture containing fillers and accessory ingredient was prepared as base component. N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane (DAMO) was mechanically mixed with other functional additives as curing component. ATR-FTIR, XPS, SEM and tensile tests were used to investigate the chemical structure, morphology and mechanical properties of the tie-coatings. It was focused on the effect of the DAMO content on the adhesion of the tie-coating to epoxy primer. Peel off and shear tests were carried out to evaluate the adhesion. The results showed that introducing DAMO can significantly improve the properties of the tie-coating. The adhesion between the tie-coating and the epoxy primer increases with the increase of DAMO content, but the excessive DAMO content will decrease the fracture strength of the tie-coating and decrease the quality of the coating. When the DAMO content in tie-coating is 1.97 wt.%, the tie-coating performs excellent in the interlaminar adhesion, shear strength and mechanical properties.

Thermal desorption sampling-gas chromatography-tandem mass spectrometry with a carbonyl-iron powder composite silica monolithic column for enrichment and determination of pyrethroid pesticide residues in tea samples

Long-term exposure to pyrethroid insecticides is detrimental to the nervous system, reproductive system, and immune system in humans. Therefore, enrichment detection of pyrethroid pesticides is imperative. In this study, a novel carbonyl-iron powder composite silica monolithic column was first prepared for the enrichment of pyrethroid pesticide residues in tea samples. Then, the target analytes were thermally desorbed and online-injected into a gas chromatography-tandem mass spectrometry (GC-MS/MS) system. In the present method, hydroxy-terminated polydimethylsiloxane (PDMS) was covalently bonded to the surface of the SiO2 network and subsequently bonded with the carbonyl-iron powder. After the target analytes were adsorbed and concentrated in the PDMS spots, high-frequency induction heating was used for GC-MS/MS sampling. Under the optimal conditions, the detection limits of the pyrethroid pesticide residues were 3.8 to 7.5 μg/kg, and the relative standard deviation was 3.2% to 6.8% (n=6). The extraction recovery ranged from 97.7% to 110.5%, and the correlation coefficient was ≥ 0.9960. In addition, the enrichment factor could reach 1000 times. PDMS materials show excellent adsorption properties for non-polar solutes. In our experiment, carbonyl iron powder-bonded monolithic columns were prepared on the basis of stir bar sorptive extraction (SBSE). Carbonyl iron powder magnetic particles were evenly implanted into the inorganic-organic hybrid cassia material for realizing rapid and uniform desorption upon electromagnetic induction heating. Under the premise of perfectly integrating the technical advantages of SBSE and solid-phase microextraction (SPME), the electromagnetic induction characteristics of carbonyl iron powder can be exploited for thermal desorption and directly combined with GC-MS to facilitate online analysis and solvent-free elution. Compared with the conventional SPME method, the proposed method has the advantages of high enrichment factor, large adsorption capacity of the column, reusability, high degree of automation, and good universality. This method has high significance for sample preparation and for the extraction of pesticide residues in complex matrices.

Diisocyanate-modified graphene oxide/hydroxyl-terminated silicone rubber composites for improved thermal conductivity

Graphene oxide (GO) treated with dicyclohexylmethane-4,4′- diisocyanate (HMDI) was first synthesized and termed FGO. Fourier transform infrared spectroscopy (FTIR), energy dispersive spectrometer(EDS), and X-ray diffractometry (XRD) were carried out to characterize the FGO structure. The results showed that the dispersibility of FGO in solvent was improved. Nuclear magnetic resonance(NMR) crosslinking density tester measuring crosslink density, room-temperature vulcanized silicone rubber was prepared with hydroxy-terminated polydimethylsiloxane (HPDMS) treated with FGO as a co-crosslinking agent, resulting in FGO/HPDMS. The FGO/HPDMS composites were proven to be successfully prepared by FTIR and XRD. The effects of the addition of different amounts of FGO on the crosslinking density, thermal conductivity, and mechanical properties before and after hot air aging of the FGO/HPDMS composites were investigated. As the amount of FGO was increased, the thermal conductivity and mechanical properties of the FGO/HPDMS composites increased. At 20% FGO addition, the corresponding thermal conductivity of the FGO/HPDMS composites was 1.24 W/mK.