Application of Dual Silane Coupling Agent-Assisted Surface-Modified Quartz Powder in Epoxy Matrix for Performance Enhancement

Quartz powder (QP) is an inorganic filler that is expected to significantly enhance the dielectric and mechanical properties of epoxy (EP)-based composites applied in copper clad laminates and epoxy molding compounds for 5G applications. As is well-known, the performance of the QP–EP composites is directly correlated with the dispersion effect and the compatibility of QP with an EP matrix. Herein, we propose the surface modification method of QP by mixing SCAs of different alkyl chain lengths that contain amino and carbonyl groups. Different characterization methods (FTIR, TGA, XPS, SEM, contact angle measurement, viscosity, and mechanical properties) and molecular dynamics simulation were adopted to study its effect and mechanism. Through dual SCA modification, the viscosity of QP–EP composites was reduced by 11.70%, and the flexural and tensile strengths increased by 16.89% and 30.01%, respectively. In addition, it was revealed that the superiority of dual SCAs originated from the synergistic effect between APTES and SPIS, it was the electrostatic repulsion force between the amino groups of the two SCAs that caused a steric hindrance that activated the steric stabilization effect of SPIS, thus resulting in better dispersion and excellent compatibility. Meanwhile, the amino and carbonyl groups of the SCA interacted with the EP matrix via chemical bonds and hydrogen bonds, thus strengthening the interfacial adhesion between the QP and EP matrix and improving the mechanical performance of QP–EP composites. These results are evidence of the potential of the proposed approach, which is based on the synergistic compounding of SCA with different molecular structures, in powder industrial applications.

Enhancement of Mechanical and Bond Properties of Epoxy Adhesives Modified by SiO2 Nanoparticles with Active Groups

In order to improve the mechanical and bond properties of epoxy adhesives for their wide scope of applications, modified epoxy adhesives were produced in this study with SiO₂ nanoparticles of 20 nm in size, including inactive groups, NH₂ active groups, and C₄H₈ active groups. The mechanical properties of specimens were examined, and an investigation was conducted into the effects of epoxy adhesive modified by three kinds of SiO₂ nanoparticles on the bond properties of carbon fiber reinforced polymer and steel (CFRP/steel) double lap joints. According to scanning electron microscopy (SEM), the distribution effect in epoxy adhesive of SiO₂ nanoparticles modified by active groups was better than that of inactive groups. When the mass fraction of SiO₂-C₄H₈ nanoparticles was 0.05%, the tensile strength, tensile modulus, elongation at break, bending strength, flexural modulus, and impact strength of the epoxy adhesives reached their maximum, which were 47.63%, 44.81%, 57.31%, 62.17%, 33.72%, 78.89%, and 68.86% higher than that of the EP, respectively, and 8.45%, 9.52%, 9.24%, 20.22%, 17.76%, 20.18%, and 12.65% higher than that of the inactive groups of SiO₂ nanoparticles, respectively. The SiO₂ nanoparticles modified with NH₂ or C₄H₈ active groups were effective in improving the ultimate load-bearing capacity and bond properties of epoxy adhesives glued to CFRP/steel double lap joints, thus increasing the strain and interface shear stress peak value of the CFRP surface.

Emerging Applications of Silica Nanoparticles as Multifunctional Modifiers for High Performance Polyester Composites

Nano-modification of polyester has become a research hotspot due to the growing demand for high-performance polyester. As a functional carrier, silica nanoparticles show large potential in improving crystalline properties, enhancing strength of polyester, and fabricating fluorescent polyester. Herein, we briefly traced the latest literature on synthesis of silica modifiers and the resultant polyester nanocomposites and presented a review. Firstly, we investigated synthesis approaches of silica nanoparticles for modifying polyester including sol-gel and reverse microemulsion technology, and their surface modification methods such as grafting silane coupling agent or polymer. Then, we summarized processing technics of silica-polyester nanocomposites, like physical blending, sol-gel processes, and in situ polymerization. Finally, we explored the application of silica nanoparticles in improving crystalline, mechanical, and fluorescent properties of composite materials. We hope the work provides a guideline for the readers working in the fields of silica nanoparticles as well as modifying polyester.

A Review of the Polymer for Cryogenic Application: Methods, Mechanisms and Perspectives

Recently, the application of polymer-based composites at cryogenic conditions has become a hot topic, especially in aerospace fields. At cryogenic temperature, the polymer becomes more brittle, and the adverse effect of thermal stress induced by temperature is more remarkable. In this paper, the research development of thermoset and thermoplastic polymers for cryogenic applications are all reviewed. This review considers the literature concerning: (a) the cryogenic performance of modified thermoset polymers and the improving mechanisms of the reported modification methods; (b) the cryogenic application potential of some commercial thermoplastic polymers and the cryogenic performance of modified thermoplastic polymers; (c) the recent advance in the use of polymer for special cryogenic environment-liquid oxygen. This paper provides a comprehensive overview of the research development of the polymer for cryogenic application. Moreover, future research directions have been proposed to facilitate its practical applications in aerospace.

Epoxy resin/cyanate ester composites containing DOPO and wollastonite with simultaneously improved flame retardancy and thermal resistance

Flame-retardant epoxy (EP) resin/cyanate ester (CE) composites were prepared with 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and wollastonite (Wo). The combustion behavior of the flame-retardant EP/CE composites was investigated by limiting oxygen index (LOI), UL-94, and cone calorimeter tests. It is found that the EP/CE composite containing 7 wt% DOPO and 3 wt% Wo (sample 7DO/3Wo/EP/CE) exerts the best flame retardancy (LOI 35.5% and UL-94 V-0 rating). The peak heat release rate and total heat release of sample 7DO/3Wo/EP/CE increase slightly, while total smoke release decreases about 14% compared with the EP/CE composite containing 10 wt% DOPO (sample 10DO/EP/CE). Thermal studies indicate that the glass transition temperature and temperature at 5% mass loss of sample 7DO/3Wo/EP/CE are higher than that of sample 10DO/EP/CE. Moreover, the mechanical properties of EP/CE composites were investigated.

A new way synthesis of expanded graphite as a thermal filler to enhance the thermal conductivity of DGEBA resin as thermal interface material

In this work, a facile two-step method for the synthesis of highly thermal conductive expanded graphite (EG) was proposed. A binary component system of ammonium persulfate and concentrated sulfuric acid was prepared for the synthesis of EG from natural graphite flakes in which the former one acted as an oxidizing agent and the latter one used as an intercalating agent. Further, the silane functionalization of EG (mEG) was purposefully completed, as confirmed from the X-ray diffraction and Fourier transform infrared spectroscopy analysis. Epoxy-based thermal interface materials (TIMs) were fabricated with reinforcing EG and mEG by stir-casting method at different filler fraction. The guarded heat flow meter method indicated that the enhancement in thermal conductivity (TC) was 12.12-fold at 10 wt% loading of mEG (mEG10-Ep) than neat epoxy. The binding strength of mEG10-Ep composite tuned to 6.18 ± 0.8 MPa and determined by a single lap shear test, which confirms better reinforcing effect of silane functionalized EG than neat EG counterpart. The same was also corroborated from porosity evaluation of the composite system. At 50% weight loss in nitrogen atmosphere, thermogravimetric analysis revealed that the composite was stable up to 430°C. Dynamic mechanical analysis was engaged to estimate the glass transition temperature ( T g) of the epoxy composite system, which validates its prospective application as preferred TIMs in the electroactive device. The electrical conductivity of composite was deteriorated due to the encapsulation of EG with nonconductive silane functional groups. The uniform dispersion was achieved by mEG-filled composite as compared to its EG counterpart, which was visualized from fracture surface through scanning electron microscopy.

Multifunctional Hybrid Composites with Enhanced Mechanical and Thermal Properties Based on Polybenzoxazine and Chopped Kevlar/Carbon Hybrid Fibers

This work studied the structural, morphological, mechanical, and thermal properties of newly designed polymeric materials using high-performance hybrid fibers to reinforce the polybenzoxazine resins. To achieve this goal, hybrid fibers consisting of chopped Kevlar and carbon fibers were subjected to a silane surface treatment, incorporated into the resin matrix in various combinations, and then isothermally cured using the compression molding technique. The mechanical performances of the prepared composites were scrutinized in terms of bending and tensile tests. By way of illustration, the composites holding 20 wt % Kevlar fibers and 20 wt % carbon fibers accomplished a bending strength and modulus of 237.35 MPa and 7.80 GPa, respectively. Additionally, the same composites recorded a tensile stress and toughness of 77 MPa and 0.27 MPa, respectively, indicating an increase of about 234% and 32.8% when compared to the pristine resin's properties. The thermogravimetric analysis denoted an excellent thermal resistance of the reinforced hybrid composites. Fourier transform infrared spectroscopy proved that the functional groups of the as-used coupling agent were effectively grafted on the external surfaces of the reinforcing systems, and further confirmed that the chemical reaction took place between the treated fibers and the polybenzoxazine matrix, although the scanning electron microscope showed a uniform dispersion and interfacial adhesion of the fibers within the resin matrix. In fact, the incorporation of treated fibers along with their good dispersion/adhesion could explain the progressive enhancement in terms of thermal and mechanical properties that were observed in the hybrid composites.

High-performance polymer composites with enhanced mechanical and thermal properties from cyanate ester/benzoxazine resin and short Kevlar/glass hybrid fibers

The investigation and design of new polymeric materials with an astonishing combination of properties are nowadays of great importance to facilitate the manufacturing process of high-quality products intended to be utilized in different applications and technical fields. For this intent, novel high-performance blend composites composed of the cyanate ester/benzoxazine resin blend reinforced by different proportions of silane-surface modified Kevlar and glass fibers were successfully fabricated by a compression molding technique and characterized by different experimental tests. The mechanical test results revealed that the bending and impact strength properties were considerably improved when increasing the amount of the hybrid fibers. The studied materials also presented excellent thermal stabilities as compared to the unfilled blend’s properties. With respect to the properties of the reinforcing systems, these improvements seen in either the mechanical or thermal properties could be due to the good dispersion as well as excellent adhesion of the reinforcing fibers inside the resin matrix, which were further evidenced by the Fourier transform infrared spectroscopy and scanning electron microscopy results. Consequently, the improved mechanical and thermal properties promote the use of the fabricated hybrid composites in domestic and industrial applications requiring functional materials with advanced properties for aerospace and military applications.