Special Topics Review

Research progress on encapsulation materials and 0BB encapsulation technology for high-efficiency photovoltaic cells

Ye Ancheng¹, Li Weijing², Shi Hongtao³, Wang Weimin⁴, Pei Kemei¹

(1.School of Chemistry and Chemical Engineering, Zhejiang Sci-Tech University, Hangzhou  310018, Zhejiang, China; 2.Guangdong COSCO Shipping Heavy Industry Co., Ltd., Dongguan  523146, Guangdong, China; 3.Zhejiang SINOPOLY Materials Co., Ltd., Jiaxing  314011, Zhejiang, China; 4.School of Materials Science and Chemical Engineering, Ningbo University, Ningbo  315211, Zhejiang, China)

【Abstract】To support the development of high-efficiency photovoltaic cells such as HJT, TOPCon, and perovskite/crystalline silicon tandem cells towards high power, low loss, and long lifetime, the research progress and classification characteristics of photovoltaic module encapsulation materials were summarized in this paper. Four types of encapsulation films were analyzed in details, namely ethylene-vinyl acetate copolymer (EVA), organosilicon, polyolefin elastomer (POE), and emerging light-conversion co-extruded integrated film (EPE) materials. The physical properties, advantages, disadvantages, and application scenarios of mainstream encapsulation materials were deeply discussed. The mainstream process routes, advantages, and technical bottlenecks of three kinds of busbar-free (0BB) encapsulation technologies, such as SWCT, dispensing, and welding-dispensing were compared, and the development status of encapsulation films adapted to 0BB technology (skin film+conventional adhesive film, integrated film, etc.) was elucidated. 0BB technology could reduce silver paste consumption, decrease shading area, improve module power, and enhance anti-microcrack capability by eliminating busbars. It was one of the core directions for high-efficiency cell encapsulation, but still faced challenges such as high process complexity, rising material costs, and insufficient film adaptability. Future encapsulation technology development would focus on material formulation optimization, 0BB process simplification, and cost control, promoting the deep integration of encapsulation technology with high-efficiency cells, and providing support for cost reduction and efficiency improvement in the photovoltaic industry.

【Keywords】photovoltaic module; encapsulation material; 0BB encapsulation technology; material failure and protection

Effect of adhesive layer on the bulletproof performance of ceramic composite armor

Yao Yibin, Zhang Hong, Sun Zhihao, Lin Wensong

(Zhejiang Light-Tough Composite Materials Co., Ltd., Huzhou  313219, Zhejiang, China)

【Abstract】Composite armor fabricated by bonding and curing ceramic panels to metal or fiber composite backplate is a mainstream form of contemporary lightweight bulletproof armor. Its bulletproof performance depends not only on the ceramic panel and backplate, but also on the adhesive layer which plays a critical role. Based on the elucidation of the bulletproof mechanism of multilayer composite armor, the effects of bonding strength, mechanical properties, acoustic impedance, and thickness of adhesive layer on the bulletproof armor were systematically reviewed in this study. Through systematic analysis, it was found that improving the bonding strength could effectively suppress interfacial delamination and enhance the multi-hit resistance; increasing the elastic modulus helped improve single-hit bulletproof effectiveness but reduced the material toughness; reducing the acoustic impedance mismatch between the adhesive and ceramic could delay the early failure of ceramics; the thickness of adhesive layer exhibited a nonlinear effect on protective performance, with an optimal range. This study provided theoretical reference for adhesive selection and interface structure optimization of ceramic composite armor.

【Keywords】ceramic composite armor; bulletproof mechanism; adhesive; epoxy resin; polyurethane

Research Report

Preparation and performance study of low-odor high-strength two-component acrylic structural adhesive: Based on self-synthesized polyacrylate elastomers

Su Kaiyu, Huang He

(College of Chemistry, Chemical Engineering and Materials Science of Soochow University, State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, Suzhou  215123, Jiangsu, China)

【Abstract】Two-component acrylate structural adhesive is widely used due to its excellent comprehensive properties and broad applicability, but traditional products generally suffer from problems of strong odor and high costs. To achieve both low odor and high strength while reducing raw material costs, low-cost and readily available low-odor 2-hydroxyethyl methacrylate (HEMA) was employed as the diluent monomer in this study, and based on the principle of similar compatibility, two types of polyacrylate elastomers that could dissolve well in HEMA were independently designed and synthesized: one was the Type I elastomer without double bonds in the molecular chain, and the other was the Type II elastomer with double bonds introduced into the molecular chain, and the first-generation (FGA) and second-generation (SGA) low-odor two-component acrylate structural adhesive were prepared, respectively. Through solubility tests, single-factor experiments, and orthogonal experiments, the effects of elastomer composition, monomer type, and formulation ratio on adhesive properties were systematically investigated. The research results showed that the solubility of both types of self-made elastomers in HEMA exceeded 50%, which was significantly superior to conventional elastomers such as polychloroprene rubber, nitrile rubber, and MBS. The tensile shear strength of FGA adhesive reached up to 20.40 MPa, which was basically equivalent to that of SGA adhesive (21-23 MPa). After optimizing the ratio of Type II elastomer to HEMA, the tensile shear strength of SGA adhesive was further improved to 23.70 MPa, which was superior to the benchmarking reference product (22 MPa), and the odor level was low with significantly reduced raw material costs. This study confirmed that the use of low-odor HEMA combined with self-made polyacrylate elastomers could successfully prepare low-odor high-strength two-component acrylate structural adhesive with excellent comprehensive properties, providing new ideas for the low-cost and environmentally friendly development of such products.

【Keywords】low odor; high strength; acrylate structural adhesive; elastomer

Preparation and properties of bio-based epoxy thermally conductive structural adhesive

Li Ziqi, Wu Zibang, Ai Jiaoyan, Song Lina, Liu Baohua

(School of Materials and Energy, Guangdong University of Technology, Guangzhou  510006, Guangdong, China)

【Abstract】To address the problems of low thermal conductivity of conventional petroleum-based epoxy resin and insufficient research on bio-based epoxy resin thermally conductive composites, self-synthesized itaconic acid-based epoxy resin was used as the matrix and polyamide 650 as the curing agent, spherical alumina (single particle size/dual particle size) and modified chopped carbon fiber (CF) were introduced, a series of bio-based epoxy thermally conductive structural adhesive were prepared. The effects of filler particle size, filler content, dual particle size grading, and CF/Al₂O₃ hybrid ratio on thermal conductivity, mechanical, and thermomechanical properties were systematically investigated. The research results showed that in the single particle size filling system, spherical Al₂O₃ with 10 μm diameter achieved the highest thermal conductivity [1.06 W/(m·K)] at the filling ratio of 75%, but exhibited relatively low toughness. In the dual particle size grading system, the combination of 5 and 10 μm achieved a relatively optimal balance between thermal conductivity [1.09 W/(m·K)] and impact strength (12.32 kJ/m²), while the shear strength (15.14 MPa) was at a moderate level, demonstrating excellent comprehensive performance. The combination of 5 and 20 μm exhibited the highest thermal conductivity [1.11 W/(m·K)], which was 504.55% of the matrix epoxy resin [0.22 W/(m·K)]. In the carbon fiber/alumina hybrid filler system, the formula with 5% CF added maintained high thermal conductivity [1.02 W/(m·K)] while increasing the shear strength to 17.28 MPa, impact strength to 14.83 kJ/m², glass transition temperature to the highest (87.3 ℃), and curing network integrity was the best. This study revealed the synergistic thermal conductivity/toughening mechanism of multi-scale filler packing and fiber reinforcement, providing theoretical basis for the development of high-performance and environmentally friendly bio-based thermally conductive structural adhesive.

【Keywords】itaconic acid; bio-based; epoxy resin; thermally conductive adhesive

Development and performance study of TGTHEIC multifunctional epoxy-BMI adhesive

Yang Hong, Yu Xinhai

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

【Abstract】In order to improve the toughness, heat resistance, and comprehensive dielectric properties of epoxy resin and broaden its application in electronic packaging, aerospace, and other fields, the multifunctional nitrogen-containing heterocyclic epoxy resin triglycidyl tris(2-hydroxyethyl) isocyanurate (TGTHEIC) was used as the matrix in this study, combined with epoxy resin, carboxyl-terminated liquid nitrile rubber, and 4,4'-diaminodiphenyl sulfone, and introducing four kinds of bismaleimide (BMI) resin with different molecular structures (BAPP-BMI, DDM-BMI, DETDA-BMI, and ODA-BMI), a series of multifunctional epoxy-BMI adhesive (JTH-1~JTH-4) were prepared, and their properties were tested and analyzed. The research results showed that, curing kinetic analysis revealed that the apparent activation energy (E_a) of JTH-1 epoxy adhesive containing 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane (BAPP-BMI) was 63.74 kJ/mol, and the curing reaction order (n) was 0.9. JTH-4 containing 4,4'-bismaleimidodiphenyl ether (ODA-BMI) showed advantages in bonding performance, with tensile shear strength exceeding that of other three formulations at most temperatures. At -20 ℃, the tensile shear strength reached 19.244 MPa.  JTH-1 was superior to other three formulations in terms of impact strength and tensile strength, with values of 14.413 kJ/m² and 53.337 MPa, respectively. Four formulations had good overall dielectric stability, with capacitance fluctuations ≤0.2 pF, exhibiting capacitance stability, excellent dielectric performance, and good hydrophobicity. This study provided experimental basis and data support for the molecular structure design and engineering application of high-performance epoxy-BMI adhesive.

【Keywords】epoxy resin; bismaleimide; adhesive; development; performance study

Process and Application

Research on the bonding performance and application process of high-performance epoxy structural adhesive

Jing Junyi¹, Li Li¹, Pan Jiandong¹, Xue Gang²,

Yuan Zhigang², Xue Shuangle², Sun Mingming², Zhang Bin²

(1.AVIC Chengdu Aircraft Design and Research Institute, Chengdu  610091, Sichuan, China; 2.Institute of Petrochemistry, Heilongjiang Academy of Sciences, Harbin  150040, Heilongjiang, China)

【Abstract】To address the synergistic demand for “high strength-high toughness-process reliability” of room-temperature curing epoxy adhesive in aerospace structural bonding, the self-made high-performance two-component epoxy structural adhesive was employed as the research object in this study, the effects of curing process, substrate adaptability, and construction process on adhesion properties were systematically investigated. Through DSC, mechanical testing, and wedge tests, the structure-property relationships between curing degree and mechanical properties in the temperature range of 25-70 ℃ were analyzed, and the bonding durability and failure mechanisms of aluminum alloy, titanium alloys, and composite material systems were evaluated. The research results showed that this adhesive exhibited excellent comprehensive performance under three processes: 25 ℃/7 d, 50 ℃/5 h, and 70 ℃/3 h. The room temperature shear strength was over 30 MPa, and it still maintained over 10 MPa at 100 ℃, meeting the requirements of aviation structures for wide temperature range performance. This adhesive exhibited excellent adhesion performance to aluminum alloy, various titanium alloys, and composite materials. The failure modes were mostly mixed failure or interlayer cohesive failure of composite materials, proving that the wettability and adhesion strength of this adhesive to heterogeneous material interfaces had reached a high level. After being treated in a humid and hot environment, the crack propagation length of the sample was only 0.1 cm, confirming that the adhesive had excellent resistance to humid and hot aging and had long-term structural stability. To address bubble defects during construction, a bubble-free adhesive application process based on the combination of two-component static mixing and “center pile-up” was innovatively proposed in this study, and “I-shaped” and “asterisk-shaped” pile-up strategies were optimized according to the geometric characteristics of the bonded parts, and significantly improved the density and process controllability of the adhesive layer. This study provided important process parameters and theoretical support for the engineering application of aerospace structural adhesive.

【Keywords】epoxy structural adhesive; room-temperature curing; shear strength; application process; durability

Preparation of vegetable oil-based polyurethane elastomer for reactive polyurethane hot-melt adhesive used in automotive central control screen

Liang Haozhong^1,2, Huang Xitong², Song Jun², Chen Jianjun^2,3, Huang Hengchao², Zhu Kelong¹

(1. School of Chemistry, Sun Yat-sen University, Guangzhou  510275, Guangdong, China; 2. Guangzhou Baiyun Technology Co., Ltd., Guangzhou  510540, Guangdong, China; 3. Guangdong Baiyun Technology Co., Ltd., Foshan  528143, Guangdong, China)

【Abstract】To address the environmental pressure faced by conventional petroleum-based reactive polyurethane (PUR) hot-melt adhesive in the bonding application of automotive central control screen, as well as the problems of poor compatibility, low cohesive strength, unsatisfactory thermoplastic properties, and low reactivity associated with the direct use of vegetable oil-based polyols, the synthesis of castor oil-based thermoplastic polyurethane elastomer (TPU-CO) was proposed in this study with castor oil as raw material via the stepwise polymerization strategy, and then it was introduced into the PUR system as a functional additive. The structure and thermomechanical properties of the product were characterized by FT-IR, TMA, and other analytical techniques. The effects of polyol blending ratio, R value, and TPU-CO content on the melt viscosity, open time, initial adhesion strength, and final adhesion strength of PUR were systematically investigated. The research results showed that the synthesized TPU-CO20 exhibited good compatibility with the polyol system and could significantly enhance the mechanical properties and weather resistance of PUR. The R value of 1.9 was selected, together with the ratio m(Dynacoll 7380):m(Dynacoll 7360):m(PN-110):m(PPG-2000)=25:40:17:13, and the TPU-CO20 content of 20%, the optimized PUR formulation (PUR-12) for automotive central control screen was obtained. Performance tests indicated that PUR-12 had the melt viscosity of 11,200 mPa·s at 110 ℃, the open time of 130 s, the initial adhesion strength of 1.78 MPa, and the final adhesion strength of 10.04 MPa. After subjecting to moisture resistance, water resistance, heat resistance, and cold resistance tests, all performance degradation remained within 15%. The comprehensive performance of PUR-12 was superior to similar domestic products and comparable to imported competitors. It could meet the technical requirements of PUR hot-melt adhesive for automotive central control screen, providing theoretical basis and technical support for the localization replacement of high-performance bio-based PUR hot-melt adhesive.

【Keywords】reactive polyurethane hot-melt adhesive; castor oil-based polyurethane elastomer; automotive central control screen; bio-based material; bonding performance

Material Science

Preparation of phenolic resin adhesive by synergistic modification of lignin with deep eutectic solvent-laccase

Zhuang Junping, Wang Zishuai

(School of Light Industry and Engineering, South China University of Technology, Guangzhou  510641, Guangdong, China)

【Abstract】To overcome the obstruction of lignin dense structure on enzymatic hydrolysis reactions, and to solve the problems of low efficiency of laccase modification alone and poor enzyme stability in solvents, a new strategy for preparing phenolic resin adhesive by synergistic modification of lignin with deep eutectic solvent (DES)-laccase was constructed in this study. Mixed acid of acetic acid/formic acid was used as the hydrogen bond donor, and choline chloride was used as the hydrogen bond acceptor, a series of DES were prepared by regulating the type of polyols and the molar ratio. The influence mechanism of DES composition and concentration on laccase activity and thermal stability was systematically investigated, and DES-laccase synergistic activation of lignin and preparation of lignin-based phenolic resin (CMLPF) adhesive were achieved by the one-step method. The research results showed that, ⑴ The addition of an appropriate amount of DES exhibited a certain promoting effect on the laccase enzymatic reaction. The activity was maintained best at a concentration of 10% and began to decrease significantly at 20%. When the optimal molar ratio of DES components (mixed acid, choline chloride, polyol) was 1∶1∶3, the laccase activity was the highest. ⑵ As the DES content in the system increased to 30%, the presence of DES severely destroyed the enzyme structure and caused its inactivation. Therefore, a 10% DES aqueous solution was most favorable for maintaining enzyme activity and thermal stability. ⑶ The bonding strength of CMLPF prepared from DES-laccase synergistically modified lignin by the one-step method was 2.10 MPa. The scanning electron microscopy of the cross-section and fracture surface of the plywood indicated that the prepared lignin-based phenolic resin adhesive exhibited good bonding properties. ⑷As a novel green and environmentally friendly solvent, DES could break through the dense structure of lignin, enhance enzyme activity and stability, and strengthen the synergistic catalytic effect of the enzyme through DES component regulation. This study provided research directions and technical pathways for DES-enzyme synergistic modification of lignin to prepare adhesive.

【Keywords】lignin; deep eutectic solvent (DES); laccase; thermal stability; synergistic modification; phenolic resin adhesive

Study on additive formulation optimization and performance regulation of waterproof PUmaterial

Wang Wei

(CCCC-SHB Fourth Engineering Co., Ltd., Luoyang  471013, Henan, China)

【Abstract】To address the core demand for “high density and high mechanical strength” of polyurethane (PU) adhesive in underground engineering waterproofing, as well as the bottleneck problems of unclear additive regulation mechanisms and lack of engineering adaptability in the formulation system, three key additives, i.e. crosslinking agent trimethylolpropane (TMP), chain extender 1,4-butanediol (BDO), and foam stabilizer were selected in this study. Through single-factor variable experiments and formulation verification experiments, the regulation laws of single additive dosage and formulation ratio on the density, flexural strength, and compressive strength of waterproof PU adhesive were systematically investigated, and the synergistic mechanism of multiple additives was revealed. The research results showed that the effects of all three additives on material properties exhibited significant threshold effects, and with increasing dosage, both density and mechanical properties showed an “initial increase followed by decrease” trend. When the TMP dosage was 4.0 phr, BDO was 8.0 phr, and foam stabilizer was 1.5 phr, the single system exhibited the optimal performance. The formulation experiments further confirmed that significant synergistic effects existed among the three, and under the optimal formulation (TMP 4.0 phr + BDO 8.0 phr + foam stabilizer 1.5 phr), the material density reached 1.28 g/cm³, the flexural strength was 4.2 MPa, the compressive strength was 12.5 MPa, and the performance variation coefficient was ≤2.1%, and the cell structure was uniform and dense (average cell diameter was 248.72 μm, porosity was 14.2%, and 200-300 μm cell diameter accounted for 89%). This study clarified the optimal additive formulation system for underground engineering requirements, revealed the micro-regulation mechanism of “crosslinking-chain extension-foam stabilization” rate matching and “network densification-molecular ordering-cell stabilization”, and provided theoretical support and technical pathways for precise formulation design and engineering application of waterproof PU adhesive.

【Keywords】additive formulation; waterproof PU material; mechanical property; density; performance regulation