Special Topics Review

Research progress on bonding of low surface energy materials

Wu Wenxiao¹, Zhang Chengyu¹, Yang Zhihui¹, Shi Haobo², Tian Weizhi², Sun Fanghao¹, Wu Lianfeng³, Lu Haifeng¹

(1.School of Chemistry and Chemical Engineering, Shandong University, Ji'nan  250100, Shandong, China; 2.Beijing Xinghang Mechanical-Electric Equipment Co., Ltd., Beijing  100074, China; 3.State Key Laboratory of Marine Coatings, Marine Chemical Research Institute Co., Ltd., Qingdao  266071, Shangdong, China)

【Abstract】Low surface energy materials endow significant application values while also bringing about the problem of difficult bonding. Starting from the principle of difficulty in bonding low surface energy materials, the research progress in improving the bonding performance of low surface energy materials at home and abroad in recent years was summarized in this paper, covering surface physical treatment methods for low surface energy materials (such as mechanical physical treatment, plasma treatment, corona treatment, and irradiation treatment), surface chemical treatment methods (such as flame treatment, chemical etching treatment, grafting treatment, primer treatment), combined treatment of physical and chemical methods, as well as research and exploration of adhesive types for direct bonding without surface treatment. Finally, future development prospects for related research were proposed.

【Keywords】low surface energy materials; surface modification; adhesive

Research Report

Effect of vinyl acetate on the performance of polyacrylate pressure-sensitive adhesive

Zhang Xin, 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】Vinyl acetate is a kind of intermediate monomer between traditional soft and hard acrylate monomers, and is often used in the preparation of polyacrylate pressure-sensitive adhesive. However, there is no systematic study report on adjusting the performance of polyacrylate pressure-sensitive adhesive by changing the amount of vinyl acetate. Therefore, in this paper, polyacrylate pressure-sensitive adhesive was prepared by solution copolymerization of intermediate monomer vinyl acetate with traditional soft and hard acrylate monomers. The effect of intermediate monomer vinyl acetate on the performance of polyacrylate  pressure-sensitive adhesive was studied in details and it was compared with that of the traditional hard monomer methyl methacrylate. The research results showed that, ⑴ As the amount of vinyl acetate increased, the cohesion of pressure-sensitive adhesive increased, and the adhesion to the substrate decreased. When the amount of vinyl acetate reached 9.5%, interface failure occurred, and the peel strength could reach 18.78 N/25 mm. At this time, the holding power and initial tack were 1.10 h and 4# ball, respectively. ⑵ Compared to traditional hard monomer methyl methacrylate, the use of intermediate monomer vinyl acetate had no advantage in contributing to the initial tack and holding power of pressure-sensitive adhesive, but could increase the peel strength by about 20%.

【Keywords】solution polymerization; polyacrylate; pressure-sensitive adhesive; vinyl acetate

Study on storage stability of lignin-based phenolic resin adhesive by adding kaolin

Zhuang Junping, Huang Rui, Liu Yuqi

(School of Light Industry and Engineering, South China University of Technology, Guangzhou  510640, Guangdong, China)

【Abstract】Lignin, as an economical, easily accessible, and renewable bio-resource, can partially replace phenol in the production of lignin-based phenolic resin (LPF).However, the macromolecular structure of the product from the reaction between substituted phenol and formaldehyde is more complex compared to pure phenolic resin (PF), leading to easy agglomeration and low storage stability of LPF.In order to address this challenge, kaolin was added during the preparation of LPF to develop kaolin-lignin-based phenolic resin (K-LPF). Using storage time and bonding properties as main evaluation indicators, the orthogonal design method was employed to optimize the main factors affecting the storage stability of K-LPF. The research results showed that, ⑴ The addition of kaolin as a stabilizer of adhesive effectively enhanced the storage stability. The optimal process conditions determined by orthogonal design method were: lignin substitution rate of 60%, alkali dosage of 25%, and addition of 6% kaolin during the third batch of feeding. The bonding strength of the adhesive obtained was 1.33 MPa, and the storage time could reach 98 days, with all indicators meeting the requirements of GB/T 14732—2017 standard. The range analysis revealed that the main factors affecting storage stability followed the order: alkali dosage > lignin substitution rate > kaolin addition amount > kaolin feeding batch. ⑵ Infrared spectroscopy (FT-IR) and thermogravimetric (TG) analysis indicated that the K-LPF prepared by adding kaolin had similar structures to LPF and PF in infrared spectra, suggesting that kaolin and lignin participated in the reaction with phenol and formaldehyde through copolymerization. It reduced the precipitation of organic macromolecules caused by self-polymerization, thereby improving its storage stability. ⑶ The verification experiment showed that the actual experimental results conformed to the prediction of orthogonal design method, further proving the effectiveness and reliability of the optimized process conditions obtained above, providing theoretical and practical basis for the preparation of K-LPF with high storage stability.

【Keywords】lignin-based phenolic resin; kaolin; orthogonal design; bonding strength; storage stability

Effect of boron nitride dosage on the properties of acrylate adhesive-based boron nitride/pine wood powder composite panels

Liu Mei¹, Ge Bingjie¹, Qi Anjie¹, Yu Zhuqing¹, Xiang Shanglin^1,2

(1.School of Materials Science and Engineering, Nanjing Tech University, Nanjing  211816, Jiangsu, China; 2.Shandong Lihe New Material Technology Co., Ltd., Jining  272200, Shandong, China)

【Abstract】Boron nitride (BN), due to its excellent thermal conductivity and chemical stability, has become an ideal filler for enhancing the thermal conductivity of composite materials. Although acrylate adhesive has many advantages, it has relatively poor thermal conductivity and is not resistant to high temperature, which restricts its application in high-temperature environment. In this paper, the thermally conductive filler boron nitride was introduced into the acrylate adhesive, and the acrylate adhesive-based boron nitride/pine wood powder composite panels (BN/SMF composite panels) were prepared by the simple preparation process, namely the direct hot pressing method. The effects of the amount of boron nitride on the thermal conductivity, hardness, impact resistance, and flame retardancy of BN/SMF composite panels were studied. The research results showed that, ⑴Fourier transform infrared spectroscopy testing indicated that the curing reaction of acrylate adhesive was complete. ⑵ With the increase in the amount of boron nitride, the thermal conductivity coefficient of BN/SMF composite panels also increased accordingly. ⑶ The inorganic component boron nitride was not easy to decompose at high temperature and could play an excellent physical barrier role, thus increasing the decomposition temperature of BN/SMF composite panels. ⑷ As the amount of boron nitride increased, the impact strength and hardness of BN/SMF composite panels increased. However, when the amount of boron nitride reached a certain value, due to the agglomeration of particles, the continuity of the composite matrix was disrupted, and both the impact strength and hardness decreased. ⑸ With the increase in the amount of boron nitride, both the thermal conductivity and flame retardancy of BN/SMF composite panels were improved.

【Keywords】boron nitride; acrylate adhesive; composite panel; thermal conductivity

Preparation and properties of infrared and laser compatible coating with high lubricating oil resistance

Lyu Dandan¹, Yang Cong¹, Zhang Weigang¹, Qiao Zhi², Kong Xiangbing²

(1. Chuzhou University, Chuzhou  239000, Anhui, China; 2. Anhui Huibang Paint Industry Co., Ltd., Tianchang  239311, Anhui, China)

【Abstract】Infrared and laser compatible coating with outstanding lubricating oil resistance has been widely applied in multi-spectral compatible stealth fields for various aircrafts, demonstrating broad application prospects and currently constituting a research hotspot in stealth materials. Using the sericite modification method, a kind of composite coating [(PU)/Al-Sm₂O₃] with outstanding lubricating oil resistance was prepared in this paper, and the changes in the physical and chemical properties of the coating were studied systematically. The research results showed that, the microstructure of the coating surface modified with sericite was still very regular, and the PU resin still tightly wraped the pigment/filler in the coating, maintaining a stable microstructure. Modification of sericite could significantly improve the regularity, density, and arrangement of flake aluminum powder in the coating, leading to a significant decrease in coating emissivity and a significant improvement in the stability of coating against lubricating oil corrosion. Modification of sericite could significantly improve the impact strength of the coating, allowing it to remain in its optimal state even during prolonged lubricating oil corrosion process.

【Keywords】coating; sericite; infrared and laser compatible; lubricating oil resistance

Process and Application

Study on the effect of supercritical CO₂ treatment on the interface properties of aramid fiber composite materials

Li Yafeng, Zhang Dujuan, Lu Haijun

(1. Composite Technology Center, AVIC Manufacturing Technology Institute, Beijing  101300, China; 2. National Key Laboratory of Advanced Composites, Beijing  100095, China)

【Abstract】Aramid fiber is a high-performance fiber that has a wide range of application in the field of composite materials. However, due to its chemically inert surface, its interface adhesion with the resin matrix is poor, and impurities often remain on the surface of fiber fabric during the fiber preparation process, which affects the bonding between the fiber and resin. The surface treatment of two kinds of aramid fibers (K49 and F-12) using supercritical CO₂ fluid was investigated in this paper, and the effect of supercritical CO₂ fluid on the surface of fiber fabrics (F-12F) was also studied. Then, using processed aramid fibers and fiber fabrics as raw materials, aramid fiber-reinforced epoxy resin composite materials were prepared, and the fexural and interlaminar shear properties of composite materials were studied. The research results showed that, ⑴ Supercritical CO₂ treatment had no significant effect on the tensile properties of K49 and F-12 fibers, but it effectively cleaned the surface of fibers and significantly reduced the content of impurity elements on the surface. ⑵ After supercritical CO₂ treatment, the surface roughness of K49 fiber increased, while the overall surface roughness of F-12 fiber decreased. After supercritical CO₂ treatment, the interfacial shear strength between K49 fiber and resin increased by 40.8%, and the bonding between fiber and resin was significantly improved, while the interfacial shear strength between F-12 fiber and resin slightly decreased. ⑶ The changes in flexural and interlaminar shear properties of aramid fiber/epoxy composites (K49/5224A and F-12/5224A) before and after supercritical CO₂ treatment were within 10% range. Supercritical treatment had no significant effect on the flexural and shear macroscopic mechanical properties of the two aramid fiber-reinforced composites. For F-12 fiber fabrics, supercritical CO₂ treatment could effectively remove impurities generated during the weaving process and improved the interfacial bonding between fiber fabric and resin.

【Keywords】aramid fiber; supercritical CO₂; surface modification

Development of polyurethane sealant with fast surface drying at low temperature

Zhao Zhaolin, Guo Meng, Wei Xinzhao, Jiang Hong

(Guangdong Pustar Adhesives and Sealants Co., Ltd., Dongguan  523646, Guangdong, China)

【Abstract】To meet the constantly accelerating production pace, the development of single-component polyurethane sealant with fast drying and fast curing at low temperature is one of the most important trends. A single-component polyurethane sealant with fast surface drying at low temperature was prepared in this paper, and the effects of the relative molecular weight of plasticizers, polyether polyols with different primary hydroxyl contents, different dosages of two catalysts, and different ratios of two prepolymers on the surface drying time and curing speed of sealant at low temperature were discussed. The research results showed that, ⑴ Plasticizers with different relative molecular weights had an impact on the curing rate of single-component polyurethane sealant, with smaller relative molecular weights resulting in faster curing rates. Considering the migration of plasticizers, a relative molecular weight between 270 and 350 was relatively suitable. ⑵ The higher the primary hydroxyl content of polyether polyols, the greater the improvement in surface drying time and curing speed of single-component polyurethane sealant at low temperature. Considering the influence of primary hydroxyl groups on resin compatibility, the polyether polyol with a primary hydroxyl content of 20% was relatively optimal. ⑶ When 0.15% of 2,2'-dimorpholinyldiethyl ether (DMDEE) and 0.05% of dibutyltin dilaurate (DBTDL) were added, the surface drying time at low temperature was relatively fast and the curing speed was also the fastest. ⑷ The combination of prepolymers prepared by using 4,4'-diphenylmethane diisocyanate (MDI) and those prepared by using toluene diisocyanate (TDI) could improve the surface drying time and curing speed of the sealant. When the addition amounts of the two were 25% and 10% respectively, it ensured fast surface drying time at low temperature without reducing the curing speed.

【Keywords】polyurethane; sealant; fast surface drying; low temperature

Study on low-temperature storage properties of epoxy adhesive

An Donglan, Li Yongliang, Di Anle, Ma Li, He Hua, Huang Tao

(AVIC Xi’an Flight Automatic Control Research Institute, Xi’an  710065, Shaanxi, China)

【Abstract】Epoxy resin and curing agent begin the curing reaction generally after mixing, thus resulting in problems such as short storage life and storage difficulties. It is necessary to establish a rapid and reliable low-temperature storage performance evaluation method for all epoxy curing systems, enabling rapid verification while reducing testing costs under the premise of reliable results. In this study, two different epoxy curing systems were taken as the research object, and the viscosity was characterized at different temperatures. According to Arrhenius equation fitting, the relationship between gel time and storage temperature was derived. Finally, the reasonable storage temperature was designed based on the storage requirements. The research results showed that,⑴ The results of viscosity and gel time tests showed that at the storage temperature of -80 ℃, the properties of m-phenyldimethylamine curing system and imidazole curing system after reaching the storage life were similar to those of the new formulation, and were better than those of the original adhesive at the storage temperature of -20 ℃ after reaching the storage life. ⑵ The shear strength test results showed that the shear strength of the adhesive at the storage temperature of -80 ℃ under both curing systems met the requirements after reaching the storage life, also higher than that of the adhesive at the storage temperature of -20 ℃, and was basically consistent with the performance of the newly formulated adhesive. ⑶ Under the curing system of m-phenyldimethylamine, the shear strength of adhesive stored at -20 ℃ was slightly lower than the required index, which posed a risk of use. Under the curing system of imidazole, the shear strength of adhesive stored at -20 ℃ met the specified requirements.

【Keywords】epoxy adhesive; low temperature; storage life; gel time

Study on the performance of high-temperature resistant RTV-1 silicone sealant

Meng Jiahua¹, Chen Bingyao², Lin Zhipeng¹, Guo Shichuan¹, Dong Ying¹

(1. Guangdong SANVO Holdings Co., Ltd., Zhongshan  528400, Guangdong, China;2. Zhongshan Minhe Chemical Technology Co., Ltd., Zhongshan  528400, Guangdong, China)

【Abstract】Using α,ω-hydroxydimethylsiloxane (107 silicone rubber) as the main raw material in this study, adding fillers such as silicon micro powder, nano calcium carbonate and fumed silica, and adding crosslinking agents, silane coupling agents, catalysts, and heat-resistant additives, high-temperature resistant single-component silicone sealant cured at room temperature was then prepared. The effects of different viscosity ratios and contents of 107 silicone rubber in the formula, different ratios of fillers, and types of heat-resistant additives on the bonding properties and heat-resistance properties of silicone sealant were explored. The research results showed that, ⑴ In the study on the influence of different viscosity ratios of 107 silicone rubber on the performance of silicone sealant, it was found that when the mass fraction of high viscosity 107 silicone rubber was relatively high, the elongation at break of the silicone sealant produced was also high, but its tensile strength and hardness were low, and the surface drying time was slow. ⑵ When adding 107 silicone rubber with a viscosity of 80 000 mPa·s and 107 silicone rubber with a viscosity of 20 000 mPa·s in equal proportions, and the total amount added was 50 parts, the tensile strength at room temperature was 2.51 MPa, the elongation at break could reach 407%, and also its high temperature resistance was excellent. ⑶ Different ratios of calcium carbonate and silicon micro powder had a significant impact on the bonding properties and temperature resistance of silicone sealant. As the proportion of calcium carbonate increased, the bonding strength of silicone sealant to the substrate gradually increased, but the magnitude of the increase in force gradually decreased. Compared to metal substrates, silicone sealant had stronger adhesion to plastic substrates. Calcium carbonate and silicon micro powder were commonly used as fillers for silicone sealant. Compared with calcium carbonate, silicon micro powder could improve the temperature resistance of silicone sealant to a certain extent. ⑷ The metal oxides in heat-resistance additives could improve the heat resistance of silicone sealant to varying degrees.

【Keywords】silicone sealant; high-temperature resistance; 107 silicone rubber; silicon micro powder; heat-resistance additive

Material Science

Synthesis of fluorinated polyurethane prepolymer

An Jingyi¹, Zhang Tianfu², Zhang Xiaoa¹, Wang Chengzhong¹, Jiang Shengling¹, Zhang Junying¹

(1. Key Laboratory of Carbon Fiber and Functional Polymers of Ministry of Education, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing  100029, China;2. Science and Technology on Aerospace Chemical Power Laboratory, Hubei Institute of Aerospace Chemotechnology, Xiangyang  441003, Hubei, China)

【Abstract】In order to solve the problem of poor compatibility in simple blending of conventionally fluorinated polyether or polyester compounds, using azide polyether diol and fluorinated polyether diol as starting materials, based on the activity differences of isocyanate groups in isophorone diisocyanate (IPDI), a series of fluorinated polyurethane prepolymers were designed and synthesized through a stepwise pre-polymerization method. The effects of the addition method, catalyst type, reaction temperature, and reaction time of azide polyether diols on the first-step of prepolymerization reaction, as well as the effects of reaction time on the second-step of prepolymerization reaction were studied. The research results showed that, the optimal conditions for the prepolymerization reaction were to introduce azide polyether diol dropwise into the reaction system, reacted for 1 hour under the catalysis of dibutyltin dilaurate at 25 ℃, and then introduced fluorinated polyether diol (PEG-45) and reacted for 4 hours at 80 ℃. The fluorinated polyurethane prepolymer was successfully synthesized in the reaction.

【Keywords】fluorinated polyurethane; prepolymer; activity differences of isocyanate groups

Preparation and characterization of three-dimensional urchin-like TiO₂ micro-nano materials by hydrothermal method

Liu Mi¹, Lai Xian²

(1. Guangzhou Vocational and Technical University of Science and Technology, Guangzhou  510550, Guangdong, China; 2. Shaanxi University of Science and Technology, Xi'an  710021, Shaanxi, China)

【Abstract】Titanium dioxide (TiO₂) micro-nano materials with special morphology and structure have become a focus of attention and research hotspots in recent years, while how to precisely control the morphology of TiO₂ through hydrothermal method remains a major challenge. By employing a one-step hydrothermal method, using titanium tetraisopropoxide (TTIP) as an efficient titanium source, and ingeniously introducing concentrated hydrochloric acid and polyvinylpyrrolidone (PVP) as morphology-regulating agents, urchin-like TiO₂ micro-nano materials were prepared in the environment of green solvent of ethylene glycol. The effects of different reaction conditions on the structure and properties of TiO₂ were investigated, and its growth mechanism was analyzed. The research results showed that the hydrothermal method could successfully prepare three-dimensional urchin-like TiO₂ micro-nano materials, and the reaction conditions had significant impacts on the materials' morphology and performance. Furthermore, under optimized conditions, when the concentration of PVP was set at 6 mg/mL, the operating temperature was controlled at 150 ℃, and the reaction time was maintained for 24 h, the dispersion performance of the sample reached the optimal state, and the integrity of its surface morphology was significantly improved.

【Keywords】hydrothermal method; urchin-like TiO₂; micro-nano materials; preparation; characterization