Special Topics Review

Research progress on toughening modification technologies of epoxy resin

Fu Yuqi

[The Patent Examination Coorperation (Beijing) Center of The Patent Office, CNIPA, Beijing  100160, China]

【Abstract】To address the defects of epoxy resin such as high crosslinking density, high brittleness, and weak resistance to crack initiation and propagation, the research progress on toughening modification technologies of epoxy resin in recent years was systematically summarized in this paper, providing reference for material design that balanced high toughness and comprehensive properties. Starting from molecular structure design and energy dissipation mechanisms, the existing toughening technologies were categorized into nine types: liquid rubber toughening, core-shell particle toughening, thermotropic liquid-crystalline polymer toughening, thermoplastic resin toughening, interpenetrating/semi-interpenetrating polymer network structure toughening, hyperbranched polymer toughening, chemical structure modification toughening, flexible-chain curing agent toughening, and dynamic coordination bond toughening. Their action mechanisms, process characteristics, and effects on material properties were elaborated for each category. The core of epoxy resin toughening modification lay in constructing multiple energy dissipation pathways. Future efforts needed to rely on molecular simulation to achieve structural customization of toughening agents, integrate multi-technology synergistic strategies, and develop green toughening systems with simplified processes and bio-based materials, in order to break through the industrialization bottleneck where toughening effects, mechanical properties, and processing costs were difficult to optimize synergistically.

【Keywords】epoxy resin; toughening; liquid rubber; core-shell particle; thermotropic liquid crystal; interpenetrating polymer network; hyperbranched polymer; dynamic coordination bond

Recent developments in functional protein adhesive

Chen Shan, Ouyang Guanghua, Shi Liang, Wan Ruyi, Zhang Yu, Zhong Xueqin, Zheng Baochang, Chen Hailong

(Kosen New Materials Co., Ltd., Changsha  410131, Hunan, China)

【Abstract】The excessive exploitation of non-renewable resources and aggravated environmental pollution highlight the growing health and environmental hazards of synthetic resin adhesive, and protein adhesive has emerged as a research hotspot owing to their green, renewable nature and versatile functionalities. The latest research progress on functional protein adhesive was systematically summarized in this paper, and the protein sources were classified into plant proteins (soybean, wheat, zein, etc.), animal proteins (gelatin, collagen, spider silk protein, etc.), and waste protein resources. The modification strategies and performance mechanisms of protein adhesive with water resistance, high toughness, mold resistance, flame retardancy, conductivity/electromagnetic-shielding, fluorescence, biocompatibility, and other special functions (thermal conductivity, self-healing, and intelligent response) were elaborated, which covered covalent and multiple crosslinking, nano-enhancement, and genetically engineered fusion-protein approaches. Finally, it was pointed out that the current industrialization was facing difficulties such as limited types of raw materials, high costs, lack of specialized equipment, and fluctuations in batch performance. It was proposed that artificial intelligence could assist in protein structure screening, formula prediction, modification control, and process optimization, providing theoretical reference for the innovative development of functional protein adhesive.

【Keywords】protein adhesive; functional; research status; artificial intelligence

Research and application progress of high-strength glass fiber and its composites

Li Yafeng, Zhang Dujuan, Lu Haijun

(1. Composite Technology Center, AVIC Manufacturing Technology Institute, Beijing  101300, China; 2. National Key Laboratory of Science and Technology on Advanced Composites, AECC Beijing Institute of Aeronautical Materials, Beijing 100095, China)

【Abstract】High-strength glass fiber is an important specialty reinforcing fiber for advanced resin-matrix composites and is widely applied in aviation, aerospace, ordnance, warships, and electronics. To systematically reflect its latest research progress, the development and application status of high-strength glass fibers, fabrics, and their composites at home and abroad were reviewed. At present, series of high-strength glass fibers including American S-2, French R, Japanese T, Russian BMΠ, and Chinese HS, had all achieved large-scale production. The tensile strength of fiber-impregnated roving generally exceeded 3 000 MPa, and the tensile modulus reached 84-96 GPa. High-strength glass fiber fabrics significantly improved the interfacial bonding performance with resin matrices through sizing agent modification and post-treatment processes. High-strength glass fiber reinforced thermosetting resin/thermoplastic resin-matrix composites combined excellent mechanical properties, impact resistance, fatigue resistance, and wave-transmitting capability, and were successfully applied in ballistic armor, helicopter rotor blades, radomes, and other critical components. In the future, the development of high-strength glass fibers and their composites was projected to move toward high performance, high modulus, fabric post-treatment processes, and recycling of thermoplastic composites.

【Keywords】high-strength glass fiber; resin-matrix composite; application progress; development trend

Research Report

Reliability research of conductive adhesive at different bonding interfaces

Cui Zhiyuan, Liu Zhao, Zhu Shuyan, Jin Zezhu, Liu Hao, Zhao Dingwei

(Beijing Santel Technology & Trading Corp., Beijing  100854, China)

【Abstract】Conductive adhesive plays an important role in the field of electronic packaging, and its performance directly affects the reliability and service life of devices. To address the reliability evaluation requirement for conductive adhesive interconnection at heterogeneous interfaces in electronic packaging, and to reveal the influence of environmental stress and interface material compatibility on the service performance of conductive adhesive, HD-908 low-stress epoxy conductive adhesive was selected as the research object in this study. Three typical interface combinations, namely silicon chip/Kovar alloy substrate, ceramic chip/aluminum alloy, and ceramic capacitor/ceramic substrate were selected. High-temperature aging tests at 150 ℃ for 1 000 h and 200-cycle temperature shock tests were conducted according to GJB 548C—2021 standard. The chip shear strength and volume resistivity of conductive adhesive were tested, and the microstructure and thermal behavior were characterized by SEM and DSC. The research results showed that after high-temperature aging, the volume resistivity decreased from 2.0×10^-4 Ω·cm to 0.4×10^-4 Ω·cm. The chip shear strength of silicon chip and ceramic chip increased by 5.49% and 13.28%, respectively, while that of caramic capacitor decreased by 19.18%. During the temperature shock tests, the volume resistivity first decreased sharply and then increased slightly. The change in chip shear strength was related to the difference in coefficient of thermal expansion between the interconnected materials. The greater the coefficients of thermal expansion mismatch between the interconnected materials, the more severe the attenuation of chip shear strength. The attenuation magnitude increased in the following order: silicon chip/Kovar alloy substrate < ceramic capacitor/ceramic substrate < ceramic chip/aluminum alloy. This study systematically analyzed the performance change of conductive adhesive under different interface combinations and revealed the influence of environmental and material factors on the reliability of conductive adhesive. These findings provided certain guidance for the process optimization and the selection of interconnection materials in the field of electronic packaging.

    【Keywords】conductive adhesive; high-temperature aging; temperature shock; reliability

Reliability and application research of high-temperature resistant paste adhesive in aerospace field

Jing Junyi¹, Mu Xuefeng¹, Sun Mingming², Xing Wenxu², Liu Caizhao²

（1.AVIC Chengdu Aircraft Design and Research Institute, Chengdu  610041, Sichuan, China; 2. Institute of Petrochemistry, Heilongjiang Academy of Sciences, Harbin  150040, Heilongjiang, China）

【Abstract】With the rapid development of aerospace technology, the performance requirements for structural adhesive increase continuously. To meet the stringent demands of the service environment of aerospace vehicles for high-temperature resistance and process adaptability of structural adhesive, the reliability and application research on the domestically produced 80 ℃ curing high-temperature resistant paste epoxy adhesive was conducted in this study, providing data support for its engineering promotion. First, the curing behavior and thermal stability of high-performance paste epoxy adhesive were analyzed. The effects of process parameters (including storage time, adhesive layer thickness, and surface treatment method) on its bonding performance were investigated. Its bonding compatibility with different composite materials was evaluated, and its environmental aging resistance (damp heat, medium, salt spray) and thermal aging performance were thoroughly investigated. The research results showed that, the initial curing temperature of adhesive was 74 ℃, the 5% weight-loss temperature reached 325 ℃ under nitrogen atmosphere, the shear strength still remained at 16.3 MPa at 230 ℃. The adhesive exhibited a certain degree of process tolerance to room-temperature storage time. However, increased adhesive layer thickness led to increased internal stress and more defects, resulting in decreased strength. Moreover, the quality of surface treatment played a decisive role in interfacial performance. The adhesive achieved substrate failure with both ZT9H/2401 and ZT9H/1316 composite materials. The high-temperature shear strength retention rate reached over 82.6% after damp heat resistance testing (immersion in water at 70 ℃ for 14 d). The resistance to aeronautical kerosene and salt spray was excellent. In conclusion, this adhesive possessed excellent high-temperature resistance, process adaptability, and environmental reliability, and had the potential for engineering application in the structures of new-generation aeronautical equipment in China. This study also provided certain data support and theoretical basis for the engineering application of high-performance paste adhesive in aircraft structures.

【Keywords】paste adhesive; high-temperature resistance; aeronautical material; bonding performance; processability

Preparation of polyallylarylsulfone ether ketone and its application in epoxy adhesive

Hu Siyu, Yu Xinhai, Zhang Yuhuan, Yan Yaxuan, Wang Yiran, Zhao Xinyang

(College of Chemistry and Chemical Engineering, Donghua University, Shanghai  201620, China)

【Abstract】To address the problems of insufficient toughness of epoxy adhesive and the difficulty in simultaneously improving heat resistance and dielectric properties, 4,4'-difluorobenzophenone and 3,3'-diallylbisphenol S were employed as raw materials, and polyallylarylsulfone ether ketone (PAEK) was synthesized via nucleophilic substitution polycondensation. It was then blended with bisphenol A epoxy resin and an anhydride curing system. Benzoyl peroxide was introduced to initiate allyl crosslinking, and PAEK/epoxy adhesive series (E1-E5) were finally prepared. Their structures and properties were characterized, in addition, the curing kinetics were analyzed based on the Kissinger and Crane equations. The research results showed that, ⑴ The yield of PAEK was over 99%, the glass transition temperature was 162 ℃, demonstrating it had excellent heat resistance. ⑵ The introduction of an appropriate amount of PAEK had achieved a synergistic improvement in the reinforcement and toughening of epoxy adhesive system. When the addition amount of PAEK was 10% (E-4), the comprehensive mechanical properties of the adhesive were relatively optimal: the tensile shear strength remained at 12.2 MPa at high temperature of 120 ℃, the impact strength reached 22.3 kJ/m², and the flexural strength reached 106.4 MPa. ⑶ The curing kinetics of typical formula E-3 were analyzed, and the activation energy (E_a) was calculated to be 68.31 kJ/mol, with the reaction order (n) of 0.9. ⑷ The introduction of PAEK effectively reduced the density of polar groups in the system, stabilizing the dielectric loss of the adhesive in the range of 1.04%-1.12% at a frequency of 100 kHz, with the capacitance value of 4.39~5.25 pF, exhibiting excellent dielectric stability. At the same time, the dense cross-linked network resulted in the water absorption rate of less than 0.4% for all formulations, possessing good hydrophobicity and electrical insulation properties. ⑸ This PAEK/epoxy adhesive not only maintained excellent bonding performance of epoxy system, but also simultaneously improved heat resistance, toughness, and dielectric properties. It had important application potential in high-frequency and high-speed electronic packaging, aerospace insulation structure bonding, and other fields.

【Keywords】polyallylarylsulfone ether ketone; preparation; epoxy adhesive; application

Process and Application

Research on the low-temperature vulcanization process and properties of HM301 type silicone sealant

Wang Xu, Zhang Xugang, Liu Chunmi, Zhao Yan, Zhang Fengling

（Shenyang Aircraft Corporation, Shenyang  110850, Liaoning, China）

【Abstract】To address the lack of vulcanization parameters for HM301 type room-temperature vulcanization high-temperature-resistant silicone sealant in environments below 20 ℃ and the difficulty in guiding autumn and winter aviation assembly construction, the effects of vulcanization time on Shore A hardness, tensile strength, elongation at break, and 180° peel strength under simulated conditions of 10-20 ℃ and 30%–60%RH were investigated using the controlled variable method, and three-batch repeatability verification was conducted. The research results showed that, ⑴ HM301 sealant could achieve complete vulcanization by extending the vulcanization time under low-temperature conditions of 10-20 ℃. The time required for the Shore A hardness to reach the process threshold (≥35) was negatively correlated with temperature, taking 120 hours at 20 ℃and 240 hours at 10 ℃. ⑵ The key mechanical properties of HM301 sealant, such as tensile strength, elongation at break, and 180° peel strength, could stably reach the process threshold after 48 hours of vulcanization at low temperature, and prolonging the vulcanization time did not significantly improve. ⑶ The relative humidity within 30%-60% RH had no significant effect on the vulcanization rate of HM301 sealant in this low temperature range, making it more prominent in dry and low temperature environments. ⑷ The deviation of the hardness curves for three batches was less than 2 units of Shore A hardness, indicating that the low-temperature vulcanization process parameters established in this study had good batch stability. ⑸ This study clarified the quantitative relationship between the low-temperature vulcanization time and performance of HM301 sealant at 10-20 ℃, which could provide an executable process window for low-temperature assembly in autumn and winter.

【Keywords】sealant; low-temperature vulcanization; Shore A hardness; tensile property; peel strength; process parameter

Preparation and performance of large-particle microsphere binder for battery separator

Fan Xiaojun

(Changyuan New Energy Materials Research Institute (Guangdong) Co., Ltd., Zhuhai  519085, Guangdong, China)

【Abstract】In response to the complex process and high cost problems of traditional lithium battery separator ceramic coatings that required separate coating of binders, a dispersion polymerization process was adopted and monodisperse large-particle microsphere binder was prepared by using styrene, butyl acrylate, and self-made modified acrylic monomers as co-monomers in this paper, and then it was mixed with ceramic slurry to coat the surface of polyethylene separator. The effects of monomer concentration and reaction temperature on the morphology and particle size distribution of microspheres, as well as the negative electrode with mixed coating separators on the peel strength, breathability, and cell magnification discharge performance were systematically investigated. The research results showed that, when the monomer concentration was 30% (mass fraction) and the reaction temperature was 70 ℃, spherical and regular polyacrylic copolymer microspheres with narrow particle size distribution could be prepared [particle size D₁₀=3.473 μm, D₅₀=4.647 μm, D₉₀=6.228 μm, particle size distribution width (Span)=0.592]. The glass transition temperature of the microsphere was about 50 ℃, which matched well with the 70 ℃ hot pressing process. The 180° peel strength of the mixed coating separator and negative electrode reached 6.8 N/m, and the pores were not blocked. The permeability of the separator was consistent with that of pure ceramic coating. The battery cell assembled with this separator had a capacity retention rate of over 87% in the 3 C magnification discharge test. This study confirmed that large-particle microsphere binder could achieve efficient bonding between ceramic layer and electrode, while also considering ion transport channels, meeting the application requirements of power and energy storage lithium batteries. It provided new ideas for the structural design and low-cost preparation of separator binder.

【Keywords】separator binder; large-particle microsphere binder; mixed coating; battery

Material Science

Quantitative evaluation of normal temperature asphalt-aggregate interfacial adhesion

Fan Yuanping¹, Chang Linlin², Wang Zhixiang², Deng Wenti¹, Zhang Ran³, Gong Yulei¹

(1.Guangdong Provincial Highway Construction Co., Ltd. Jiangluo Branch, Guangzhou  510699, Guangdong, China; 2.Guangdong Jiaoke Technology Research and Development Co., Ltd., Guangzhou  510420, Guangdong, China; 3.School of Civil and Transportation Engineering, Beijing University of Civil Engineering and Architecture, Beijing  102616, China)

【Abstract】To address the issue of the lack of quantitative indicators for evaluating water damage in normal temperature asphalt mixtures, establishing a rapid and accurate test method capable of evaluating the interfacial adhesion between normal temperature asphalt and aggregate can provide technical support for the design of normal temperature asphalt pavement materials and construction quality control. In this study, five types of ambient temperature asphalt, including emulsified asphalt, base asphalt, modified asphalt, polyurethane modified ambient temperature liquid asphalt, and water activated ambient temperature liquid asphalt, as well as four types of aggregate including granite, limestone, basalt, and diabase, were selected. Through improved adhesion pull-off tests, the influence of curing time, water-immersion conditions, and asphalt mastic on interfacial adhesion performance was systematically investigated. Based on the water-immersion Marshall tests of asphalt mixtures, the correlation between pull-off loss rate and water-immersion residual stability was analyzed, and a threshold for interfacial adhesion technical indicator based on pull-off tests was proposed. The research results showed that under the same test conditions, the adhesion relationship between water activated ambient temperature liquid asphalt and aggregate was that the tensile strength increase of water activated liquid asphalt and aggregate was the largest, while emulsified asphalt was the smallest. From the perspective of aggregate lithology, after 12 hours of water immersion, the adhesion between limestone and asphalt was the best. The increase of curing time and the addition of mineral powder could both increase the adhesion of asphalt-aggregate interface, while the increase of water-immersion time led to a gradual decrease in interfacial adhesion. The weight order of the influence of various factors on the adhesion of asphalt-aggregate interface was: asphalt type>water-immersion time>aggregate type>curing time>asphalt mastic. The pull-off loss rate of four systems, namely base asphalt, modified asphalt, emulsified asphalt, and polyurethane modified asphalt mixture, showed a significant correlation with the water stability index of the mixture at different immersion time (R²>0.950). The pull-off loss rate could be used as a rapid evaluation index for the water stability of asphalt mixtures. This study concluded that improving the adhesion pull-off test could serve as a quantitative evaluation method for the interfacial adhesion between normal temperature asphalt and aggregate. The proposed pull-off loss rate threshold could provide a scientific basis for the mixture design and construction quality acceptance of normal temperature asphalt mixtures.

【Keywords】normal temperature asphalt; aggregate; interface; adhesion; quantitative; pull-off loss rate