Dispersed Silica Research Articles

Polycarbonate-based hybrid ternary blend with regulated silica dispersion and distribution towards high environmental stress crack resistance, high strength and high toughness

Polycarbonate (PC) has a very low environmental stress crack resistance (ESCR). This work aims at increasing its ESCR as well as its tensile strength and toughness via a hybrid ternary blend (HTB) which is composed of PC, hydroxyl-rich polyvinyl butyral (PVB) and hydroxyl-rich silica (SiO2). Selective distribution and fine dispersion of SiO2 in the dispersed phase (PVB) through hydrogen bonding between the PVB and SiO2 endows the HTB with high ESCR, tensile strength and toughness. Two processes are compared to develop the HTB. One is composed of two steps: the SiO2 is dispersed in the PVB dissolved in anhydrous ethanol; after the removal of the ethanol, the resulting (PVB/SiO2) is then blended with the PC in the molten state. The other process is composed of a single step: PVB, SiO2 and PC are directly blended in the molten state. The two-step process yields better properties: The PC/(PVB-10/SiO2-2) containing 10 wt% of PVB and 2 wt% of SiO2 shows higher melt flow index, tensile strength and toughness. More importantly, its ESCR in carbon tetrachloride is 5 times that of the PC. We envision that this work provides a new perspective to the theory of HTB, and opens a promising route to prepare high-performance PC with excellent practicality.

Utilization of biosilica for energy-saving tire compounds: Enhancing performance and efficiency

Abstract Energy-saving tires have been developed by researchers in the industry in order to minimize hysteresis loss. In general, this is achieved by combining precipitated silica sourced from silica sand with a silane coupling agent. This strategic reaction serves to elevate the performance characteristics of tread tire, effectively enhancing their properties. Therefore, this research is aimed to investigate the utilization of commercially available biosilica compared to high dispersed (HD) silica, examining their potential as reinforcing agents in the composition of passenger tread tire compound. This compound was formulated using a blend of solution styrene-butadiene rubber (SSBR) and butadiene rubber (BR). A comprehensive analysis was conducted to assess the impact of varying ratios between biosilica and HD silica on the mechanical and dynamic properties of tread tire compound composed of SSBR and BR blend. The results showed that the incorporation of biosilica could effectively reduce the filler network resulting in better dispersion of biosilica in the SSBR/BR blend matrix. As a result, it improved wet grip (44%) and rolling resistance (26%) while maintaining abrasion resistance compared with HD silica in passenger tread tire compound. The application of biosilica as an eco-friendly reinforcement material exhibited its potential for elevating the performance of energy-efficient tread tire.

Ultrasound‐assisted freeze‐drying strategy to enhance nanoparticle dispersion in aerogels: A case study on polyimide/silica nanocomposite aerogel

AbstractThermal protection materials should possess light weight, excellent thermal insulation, flame retardant and hydrophobic properties. Aerogel are considered a promising thermal protection material due to its high porosity and low density. Among them, nano‐silica/polyimide composite aerogel has been intensively studied as they can solve the problem of fragility of nano‐silica aerogel while ensuring thermal insulation and flame retardant performance. However, the problems of nanoparticle agglomeration and the tedious preparation process remain unsolved. The ultrasound‐assisted freeze‐drying (UAFD) strategy presented in this paper avoids the tedious silica solution preparation process by hydrolyzing silica precursors to achieve good dispersion of silica. This strategy replaces the traditional approach of functionalized modification of silica nanoparticles to inhibit their agglomeration with a new method of nanoparticle dispersion by ultrasound and rapid freezing to lock the dispersed state. The UAFD strategy enables the rapid and efficient preparation of well‐dispersed nano‐silica/polyimide composite aerogels, and the hierarchical pore structure of the composite aerogels is imparted by this facile preparation strategy that cooperates with the co‐regulation capability of the tert‐butanol on the morphology of the ice template. The aerogels have substantially improved thermal insulation, flame retardant, and hydrophobic properties when compared with those prepared by conventional freeze‐drying methods.Highlights Ultrasound‐assisted freeze‐drying (UAFD) enhances nanoparticles dispersion. UAFD and tert‐butanol synergistically prepared hierarchically pore structure. Thermal protection performance of aerogels prepared by UAFD is improved.

Novel microporous MgO-based high-temperature thermal insulator

This paper addresses the development of a novel microporous MgO-based (MPMB) thermal insulator whose temperature-resistant microporous structure was engineered for the introduction of controlled packing flaws amongst their highly asymmetric and porous particles during compacting by uniaxial pressing. Hard-burnt MgO, dolomite, and TiO2 particles were dry-mixed with expanded aluminum phyllosilicate and fibers before being sprayed with a colloidal silica dispersion. The mixture was uniaxially pressed as 400 × 100 × 20 mm boards and dried at 120 °C. Samples were thermally treated at different temperatures (120-1100 °C) for the evaluation of their physical properties (compression strength, rigidity, permanent dimensional thermal variation, solid density, total porosity, pore diameter distribution, and thermal conductivity), crystalline phases, and microstructure. The microporous microstructure generated during pressing was not significantly affected by thermal treatments up to 1100 °C and the samples’ thermal conductivity, total porosity, and compression strength varied between 0.20 and 0.14 W (m K)−1, 54–56%, and 29-15 MPa in the 200-1000 °C temperature range.

Influence of dispersion liquid and silica concentration on rheological properties of shear thickening fluids (STFs)

Influence of dispersion liquid and silica concentration on rheological properties of shear thickening fluids (STFs)

GLYCIDYL METHACRYLATE AS A NON-SILANE MODIFIER IN RUBBER/SILICA COMPOSITES

ABSTRACT Glycidyl methacrylate (GMA) was grafted onto styrene butadiene rubber (SBR) and silica by a solution grafting process. Successful grafting onto rubber and silica was confirmed by Fourier-transform infrared (FTIR) spectrometry, with the peaks at 1149, 842, and 1729 cm−1 attributed to the C–O stretching, the epoxy group, and the C=O stretching vibration of the GMA monomer, respectively. After grafting onto the silica surface, the peak at 842 cm−1 in the spectra disappeared, confirming the grafting reaction through the epoxy group. Grafting onto SBR was also confirmed by proton nuclear magnetic resonance (1H NMR) spectroscopy, and the SBR-GMA interaction was shown using two-dimensional 1H NMR spectroscopy. The grafted products were further characterized by thermogravimetric analysis (TGA) and differencial scanning calorimetry. Grafting density and grafting weight percentage of GMA-grafted silica were calculated using TGA: 10 and 20% GMA-grafted SBR and 20% GMA-grafted silica compounds and their vulcanizates were prepared. Rubber–silica interaction through grafted GMA was shown using FTIR spectroscopy for both types of vulcanizates. Dispersion of pristine and GMA-modified silica onto the SBR matrix was quantified using scanning electron microscopy and atomic force microscopy. Mechanical and dynamic mechanical properties of these GMA-modified vulcanizates were studied and compared with those of previously reported 3-octanoylthio-1-propyltriethoxysilane–modified vulcanizates. The effect of the state of dispersion of silica onto the physico-mechanical properties of the vulcanizates was investigated. The properties of the non-silane–modified systems were comparable with, and in some cases superior to, that of the new mercapto silane-modified systems in the energy-efficient tire application.

Novel colloidal silica technology for MgO-containing refractories – Part 1: Anti-hydroxylation binder

Refractory castables play major roles in high-temperature applications and two important types are MgO-containing and colloidal silica-bonded castables. Whereas the former shows high refractoriness and resistance to slag corrosion, the latter offers straightforward mixing, curing, and drying processes. However, their association in a same system has not been synergistic. During mixing, MgO particles release Mg2+ ions that trigger the gelling of colloidal silica. Therefore, small MgO additions gradually hard high-alumina colloidal silica-bonded castables; conversely, larger amounts instantly set the system, hindering homogenization and casting. Despite the challenges, there is potential for making these systems compatible towards technological application. This study successfully combined fine MgO sinter with a novel aqueous dispersion of epoxysilane-modified colloidal silica, creating self-flowing suspensions of good workability. Cured samples exhibited no signs of damage by MgO hydroxylation, sufficient strength for demolding and safer drying. Thermal treatments resulted in a dense microstructure with MgO grains surrounded by Mg2SiO4.

Investigating the viscoelastic and hysteresis behavior of nano silica/carbon black hybrid reinforced styrene‐butadiene rubber vulcanizates via surface silanization

AbstractWith the thought of green tires and the need of replacing carbon reinforcing fillers with noncarbon silica filler, the effectiveness of silane surface modification on dispersion state, dynamic viscoelastic, hysteresis, and abrasion resistance of SBR vulcanizates filled with a hybrid of carbon black (CB)/nano SiO2 is investigated. In situ surface modification of nano SiO2 is carried out using bis‐(γ‐triethoxysilylpropyl)‐tetrasulfide (TESPT), and various compounds with different ratios of CB/SiO2 are prepared via a melt mixing process in an internal bath mixer. Scanning electron microscopy (SEM) and FT‐IR spectroscopy revealed improved dispersion of silica and CB clusters with enhanced molecular interactions using in situ surface modification with 5 phr of TESPT is performed. Evidence for enhanced molecular interactions included lower dynamic loss (tanδ) and less hysteresis measured via dynamic mechanical thermal analysis (DMTA). Our results indicate that appropriate modification of silica allows partial replacement of carbon black with silica for production of eco‐friendly rubber products.

Optimized End Functionality of Silane-Terminated Liquid Butadiene Rubber for Silica-Filled Rubber Compounds.

As the world is shifting from internal combustion engine vehicles to electric vehicles in response to environmental pollution, the tire industry has been conducting research on tire performance to meet the requirements of electric vehicles. In this experiment, functionalized liquid butadiene rubber (F-LqBR) with triethoxysilyl groups at both ends was introduced into a silica-filled rubber compound as a substitute for treated distillate aromatic extract (TDAE) oil, and comparative evaluation was conducted according to the number of triethoxysilyl groups. The results showed that F-LqBRs improved silica dispersion in the rubber matrix through the formation of chemical bonds between silanol groups and the base rubber, and reduced rolling resistance by limiting chain end mobility and improving filler-rubber interaction. However, when the number of triethoxysilyl groups in F-LqBR was increased from two to four, self-condensation increased, the reactivity of the silanol groups decreased, and the improvement of properties was reduced. As a result, the optimized end functionality of triethoxysilyl groups for F-LqBR in silica-filled rubber compound was two. The 2-Azo-LqBR with the optimized functionality showed an improvement of 10% in rolling resistance, 16% in snow traction, and 17% in abrasion resistance when 10 phr of TDAE oil was substituted.

Self‐flocculation and its mechanism of natural rubber latex by accelerant‐modified silica

AbstractIn this paper, an accelerant with vulcanization‐promoting and silanization‐promoting effects, 1,3‐diphenylguanidine (DPG), is loaded on green filler silica by high‐energy ball milling technology. Meanwhile, DPG breaks the ionization equilibrium of latex and realizes the self‐flocculation. The DPG‐induced self‐flocculation technology promotes the dispersion of silica and the silanization reaction, forming more complete filler‐rubber network and three‐dimensional crosslinking network. X‐ray diffraction, Fourier‐transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and thermogravimetric analysis results show that the ball milling technology makes DPG strongly adsorbed on the surface of silica, and the loading rate is 14.4%. Compared with dry mixing, the ball milling‐self‐flocculation technology increase the silanization index, tensile strength and aging coefficient by 8%, 31%, and 19%, respectively. The curing rate is improved, and the rolling resistance is the lowest. This research provides a green flocculation technology of the raw materials in formula without other flocculants and acidic wastewater discharge, avoiding the serious dust pollution and high energy consumption in the dry mixing process, as well as the poor aging resistance of rubber in the acid flocculation process of latex.

Enhancing silica dispersion and interfacial interaction in styrene butadiene/silica rubber composites by using epoxidized styrene butadiene rubber as interfacial compatibilizer

AbstractIt is usually desired but often challenging to improve the wet traction, and reduce the abrasion and rolling resistance simultaneously in tread rubber, which is referred to as “magic triangle” in tire industry. To fulfill this goal, the filler dispersion and interfacial interaction required to be improved, as they are two essential factors to concurrently govern the ultimate properties of rubber composites. Herein, we synthesized the epoxidized solution polymerized styrene butadiene rubber (ESSBR) with different epoxy level, and used them as interfacial compatibilizer to promote the silica dispersion and silica/rubber interfacial interaction. The epoxy of ESSBR would react with silanol on silica surface and co‐crosslink with SSBR simultaneously, therefore build a strong bridge between rubber matrix and filler. By incorporation of 20 phr of ESSBR‐15% (15% of double bonds on main chain was epoxidized), the wet grip was improved by 40%, and DIN abrasion and rolling resistance were reduced by 38% and 21%, respectively with hardly sacrifice the mechanical properties. We envisage that this study provides an approach for the fabrication of rubber composites with improved silica dispersion and strengthened interfacial interaction.

Ultra-broadband electromagnetic wave absorbent: In-situ generated silica modified conductive carbon fiber aerogels

The research and development of dielectric microwave absorbing materials with broad electromagnetic (EM) response is a significant project in EM wave absorption field. To achieve high-performance absorption and strong interfacial bonding at the same time, thermal-assisted in-situ bonding technology was applied to fabricating the dielectric composite absorbing materials. Thanks to the combination of vacuum filtration and in-situ hydrothermal reaction, the as-prepared binary composite aerogel shows both strong interface contacting and good mechanical stability. In addition, the carbon nanofibers/silica composite aerogel (CSA) exhibits ultra-broad effective bandwidth covering from S to Ku band, originated from the uniform dispersed silica aerogel in conductive carbon fiber network. In details, for CSA1 sample, the maximum reflection loss (RL) values and effective absorption bandwidth reach −46.2 dB (1.8 mm) and 5.2 GHz (1.5 mm). Meanwhile, the optimum RCS reduction values reaches 16.2 dB m2 when the detection theta was set as 0°. For CSA2 sample, the effective absorption bandwidth reaches 8.64 GHz at 1.5 mm, and tends to possess lower frequency EM response covering the S-band. This work exhibits a kind of broad-bandwidth aerogel absorbers at low thickness, which shows huge potential in large-scale production of microwave absorbing devices.

An animal glycerol potassium salt without volatile organic compounds emission combined with plasma‐atomization technology and its application in green tires

AbstractIn this study, a VOC‐free animal glycerol potassium salt is introduced to replace the silane coupling agent, and the plasma is used to treat the modifier and silica. The impact of high‐energy electrons in the plasma increases the contact area between the modifier and silica. Combined with the atomization technology, the velocity difference realizes the microscopic dispersion of silica, the instantaneous thin‐layer drying reduces the oxidation of the rubber chains. XPS and SEM show that the plasma promotes the silanization reaction of silica. FTIR demonstrates that the existence of chemical bonds and hydrogen bonds between potassium oleate (PO) and silica, and there is a crosslinking between PO and sulfur. The PO/Si69‐silica/NR composites prepared by plasma‐atomization technology have better processing fluidity, mechanical properties and lower rolling resistance. The plasma‐atomization technology promotes the silanization reaction of silica, saves energy consumption and reduces dust pollution, meanwhile, the replacement of Si69 by PO reduces VOC emissions and the rolling resistance of the rubber, which provides an innovative idea for the development of green tires.

EPOXY RESIN, VINYL COPOLYMER, AND RICE HUSK SILICA BASED TERNARY NANOCOMPOSITES: FABRICATION, MECHANICAL CHARACTERISTICS, AND THERMAL AGING

In this research, the bio-composites based on epoxy resin filled with nano-silica and vinyl copolymer were fabricated using diethylene triamine as a curing agent and casting method. The vinyl copolymer was synthesized from Hydroxyethyl Acrylate and Methacrylic acid using ammonium persulfate as an initiator. The bio-silica was extracted from rice husk via a simple technique of acid treatment and calcination. The chemical structure of poly(HEA-Co-MAA), silica was confirmed with help of the FTIR, and NMR-1H. The high-speed mechanical stirrer was used to obtain the good dispersion of silica and poly(HEA-Co-MAA) in epoxy resin before mixing and curing with Diethylenetriamine (DETA) hardener. The thermal stability of cured epoxy resin was enhanced with the presence of rice husk silica and poly(HEA-Co-MAA). The composite sample with 1 wt.% of bio-silica and 3 wt.% of poly(HEA-Co-MAA) showed the best mechanical properties with an improvement of up to 28.82%; and 35.36% of impact strength and tensile strength, respectively when compared with a pristine sample. The aging testing was also performed to investigate the effect of additive added on the thermal resistance of epoxy resin.

A silica/epoxy resin nanocomposite exhibiting high thermal stability and low thermal expansion based on the uniform dispersion of hydrophilic colloidal silica nanospheres

The present study fabricated high-performance silica/epoxy resin nanocomposites having a low coefficient of linear thermal expansion (CTE) and a high glass transition temperature ( Tg). This was accomplished by dispersing colloidal silica nanospheres having hydrophilic surfaces in epoxy resins, which limited the motion of the polymer chains. Nanocomposites were produced wherein isolated primary particles of colloidal silica without silane surface modification were dispersed uniformly. These particles were generated via the breakdown of loosely bound agglomerates of spherical silica particles during the agitation of a dispersion in an epoxy resin solution. Hydrogen bonding between hydroxyl groups on the hydrophilic surfaces of the dispersed silica nanoparticles and the cross-linked epoxy polymer network evidently limited thermally-induced motion of the polymer chains, resulting in a considerable reduction in the CTE and an increase in the Tg for the nanocomposite.

Synthesis of multifunctional rubber chemicals 2‐propanol, 1‐(2‐benzothiazolylthio)‐3‐[3‐(triethoxysilyl) propoxy] silane and its application in natural rubber/silica composites

AbstractIn order to inhibit the agglomeration of silica in the rubber matrix, a new multifunctional rubber chemicals 2‐propanol, 1‐(2‐benzothiazolylthio)‐3‐[3‐(triethoxysilyl) propoxy] silane (Si‐GM) was synthesized by (3‐glycidyloxypropyl) trimethoxysilane (A‐1871) and 2‐mercaptobenzothiazole (MBT). Natural rubber (NR)/silica composites were prepared with different Si‐GM contents and its application in silica/NR composites obtained were researched. Experimental results show that the maximum and minimum torques of silica‐filled NR decrease with increasing the content of Si‐GM. With the addition of Si‐GM, the rubber compound has excellent characteristics of both fast vulcanization rate and high processing safety. Si‐GM can effectively improve the dispersion of precipitated silica in composites and strengthen the interaction between silica particles and NR matrix. It was found that Si‐GM considerably enhanced the mechanical properties such as the tensile and tear strength, dynamic compression property, and abrasion resistance of silica/NR composites, and the enhancements reached the maximum at the 5‐phr content of Si‐GM. In addition, by adding 4‐phr Si‐GM into the system, silica/NR composites acquired the superior comprehensive dynamic performances.

Effect of Biobased SiO2 on the Morphological, Thermal, Mechanical, Rheological, and Permeability Properties of PLLA/PEG/SiO2 Biocomposites

Nowadays, companies and researchers are concerned about the negative consequences of using synthetic polymers and direct their efforts to create new alternatives such as biocomposites. This study investigated the effect of biobased SiO2 on the properties of poly(L-lactic acid)/SiO2 (PLLA/SiO2) and poly(L-lactic acid)/SiO2/poly(ethylene glycol) (PLLA/SiO2/PEG) composites. The SiO2 was obtained from rice husk incineration and mixed with PLLA at various concentrations (5, 10, and 15 wt.%) via melt extrusion before compression molding. Furthermore, PLLA/SiO2/PEG composites with various PEG concentrations (0, 3, 5, and 10 wt.%) with 10 wt.% SiO2 were produced. The sample morphology was studied by scanning electron microscopy (SEM) to analyze the dispersion/adhesion of SiO2 in the polymer matrix and differential scanning calorimetry (DSC) was used under isothermal and non-isothermal conditions to study the thermal properties of the samples, which was complemented by thermal stability study using thermogravimetric analysis (TGA). Rheological analysis was performed to investigate the viscoelastic behavior of the composites in the melt state. At the same time, tensile mechanical properties were obtained at room temperature to determine their properties in the solid state. DSC and X-ray diffraction analysis (XRD) were combined to determine the crystalline state of the samples. Finally, gas permeation measurements were performed using a variable pressure (constant volume) method to analyze the permeability of different gases (CO2, CH4, O2, and H2). The results showed that SiO2 decreased the PLLA chain mobility, slowing the crystallization process and lowering the gas permeability while increasing Young’s modulus, thermal stability, and viscosity. However, PEG addition increased the crystallization rate compared to the neat PLLA (+40%), and its elongation at break (+26%), leading to more flexible/ductile samples. Due to improved silica dispersion and PLLA chain mobility, the material’s viscosity and gas permeability (+50%) were also improved with PEG addition. This research uses material considered as waste to improve the properties of PLA, obtaining a material with the potential to be used for packaging.

The Waterborne Superamphiphobic Coatings with Antifouling, High Temperature Resistance, and Corrosion Resistance.

Water-based superamphiphobic coatings are environment-friendly, which have attracted tremendous attention recently, but the performances are severely limited by the dispersibility of hydrophobic particles. To solve the poor dispersibility of modified silica powder with hydrophobicity, silica dispersion was blended with polytetrafluoroethylene (PTFE) emulsion and modified aluminum tripolyphosphate (ATP) dispersion to successfully prepare water-based coatings. Multifunctional coatings were prepared by one-step spraying. It possessed good adhesion (grade 1), excellent antifouling, impact resistance, chemical stability (acid and alkali resistance for 96 h of immersion), and corrosion resistance (3.5 wt % NaCl solutions for 20 days). More importantly, the superamphiphobic coatings had high contact angles (CAs) and low slide angles (SAs) for ethylene glycol (CAs = 154 ± 0.8°; SAs = 13 ± 0.7°) and water (CAs = 158 ± 0.7°; SAs = 4 ± 0.3°). Furthermore, the composite coating was still hydrophobic after 35 cycles of wear with high roughness sandpaper (120 mesh) under three different loads, which maintained superamphiphobicity at 425 °C. This work is expected to provide a facile idea and method for the preparation of waterborne superamphiphobic coatings.

Microstructure and Performance of Green Tire Tread Based on Epoxidized Solution Polymerized Styrene Butadiene Rubber and Epoxidized Natural Rubber

Blending a solution of polymerized styrene–butadiene rubber (SSBR) with natural rubber (NR) as a matrix and silane coupling agent (SCA) modified silica as filler is widely used to prepare green tire tread. However, it is difficult to adjust the distribution of silica in different phases of a rubber blend by SCA. Moreover, the coupling reaction between silica and SCA emits volatile organic compounds. In this work, we use a new strategy to improve the distribution of silica in two phases without a SCA. Epoxidized SSBR (ESSBR) and epoxidized NR (ENR) are synthesized, and the performance of silica-filled ESSBR/ENR nanocomposite (S-ESSBR12/ENR) is investigated and compared with that of silica-filled SSBR/NR nanocomposite (S-Si75-SSBR/NR) using Si75 as the SCA. The S-ESSBR12/ENR nanocomposites have stronger interfacial interaction that results in better silica dispersion than the S-Si75-SSBR/NR nanocomposite. The epoxy groups can effectively adjust the phase selective distribution of silica. The S-ESSBR12/ENR18 nanocomposite shows homogeneous distribution, leading to the best performance. Compared with S-Si75-SSBR/NR nanocomposite, S-ESSBR12/ENR18 nanocomposite increases wet-skid resistance by 118%, reinforcing index by 38%, and abrasion resistance by 40% and decreases rolling resistance by 23%. Moreover, S-ESSBR12/ENR nanocomposites are eco-friendly and have potential application in the production of green tire treads.

Effects of β‐dextranase in raw natural rubber on the interface and performance of natural rubber/silica composites via simulation with an outer same protein

AbstractAs one of the non‐isoprene components in raw natural rubber (NR), proteins always act an important role to the final performance of the filled rubber composites. In this work, we involved a natural protein β‐dextranase externally to simulate the same protease in raw NR, and analyzed the effects of β‐dextranase content on the dispersion of silica particles, mechanical performance, viscoelastic loss of NR/silica composites. β‐dextranase acts with silica through an intense hydrogen bond interaction, which improves silica dispersion and strengthens the mechanical properties of NR/silica composites obviously when loading 4 wt% β‐dextranase, as well as the ameliorative UV aging resistance. As a consequence, the energy loss of the composites is decreased remarkably, showing great advantage in low rolling resistance tire. Besides, the results could offer the data reference to the breeding, deep processing and application of NR.