The study on the mechanical properties of PU/MF double shell selfhealing microcapsules

The self-healing microcapsules can be buried in the coating to improve the anticorrosive ability. In this paper,self-healing microcapsules of polyurea(PU)/melamine resin(MF) double shell were prepared by in-situ polymerization and interfacial polymerization with isocyanate as the core material. Scanning electron microscope was used to observe the microcapsule morphology. The structures of microcapsules prepared with different chain extenders were characterized by Fourier transform infrared spectroscopy. The micromanipulation system was used to loading–holding, loading–unloading and loading to rupture individual microcapsules, so as to explore the mechanical properties of microcapsules. The Young's modulus corresponding to microcapsules was calculated by mathematical model fitting. The self-healing properties of microcapsule coating were characterized by optical microscope. The experimental results showed that the microcapsule shell prepared under optimized conditions had a complete morphology and good mechanical properties. The microcapsule was in the elastic deformation stage under small deformation, and the plastic deformation stage under large deformation. The Young's modulus range of microcapsules was 9.29–14.51 MPa, and the corresponding Young's modulus could be prepared by adjusting the process. The surface crack of the coating containing microcapsule could heal itself after48 h in a humid environment.     

Fabrication and Properties of Ti3SiC2/SiC Composites

Ti3SiC2/SiC composites were fabricated by reactive hot pressing method. Effects of hot pressing temperature, the content and particle size of SiC on phase composition, densification, mechanical properties and behavior of stress-strain of the composites were investigated. The results showed that ： （ 1 ） Hot-pressing temperature influenced the phase composition of Ti3SiC2/SiC composites. The flexural strength and fracture toughness of composites increased with hot pressing temperature. （2） It became more difficult for the composites to densify when the content of SiC in composites increased. It need be sintered at higher temperature to get denser composite. The flexural strength and fracture toughness of composites increased when the content of SiC added in composites increased. However, when the content of SiC reached 50 wt%, the flexural strength and fracture toughness of composites decreased due to high content of pore in composites. （3） When the content of SiC was same, Ti3SiC2/SiC composites were denser while the particle size of SiC added in composites is 12. 8 μm compared with the composites that the particle size of SiC added is 3 μm. The flexural strength and fracture toughness of composites increased with the increase of particle size of SiC added in composites. （4） Ti3SiC2/SiC composites were non-brittle fracture at room temperature.     

新型环氧大豆油增韧酚醛树脂的合成与性质

A novel epoxidized soybean oil-toughened-phenolic resin（ESO-T-PR）has been synthesized by etheri- fication graft and multi-amine curing ESO.Fourier transform infrared spectroscopy（FTIR）was adopted to investi- gate its molecular structure and scan electron microscope（SEM）was used to observe the micro morphology of its impact fracture surface.This ESO-T-PR was adopted as the matrix resin to prepare paper copper clad laminate （P-CCL）and the properties of resulting P-CCL are found superior to the related Chinese National Standard.The toughing mechanism was investigated by comparing the impact strength,solderleaching resistance,flexural strength, peeling strength and morphology of this ESO-T-PR with those of other two ESO modified phenolic resins.It is demonstrated that during the synthesizing process of ESO-T-PR,the phenol hydroxyl is etherified by ESO or ESO epoxy resin prepolymer（ESO chain extension polymer）and the long ESO epoxy resin chain segments enhance the crosslink density of ESO-T-PR and consequently improve the impact toughness and solderleaching resistance of P-CCL made of ESO-T-PR.The ESO-T-PR is a cheap matrix resin with excellent properties to make P-CCL（elec- tric guide board）.     

Characterization of the Mechanical Properties of Urea-Formaldehyde Microcapsules

The mechanical properties of urea-formaldehyde (U-F) microcapsules were determined using a micromanipulation technique and a theoretical model. Loading-unloading, compressing and holding, and compressing to bursting tests at different speeds between two parallel plates for single microcapsules were carried out. It was found that the U-F microcapsules were visco-elastic (mainly elastic) at small compressive deformation, and plastic under large deformation. The transition point from elastic to plastic occurred at about (14±0.2)% compressive deformation. All the microcapsules would disrupt when compressed to about (17±0.2)% deformation, and the burst force increased linearly with their diameter. Compressing speed had no remarkable effect on both burst force and burst deformation. Liquid filled non-permeable and linear elastic spherical membrane model was used to simulate the uniaxial compression of single microcapsule, and its membrane modulus Eh was determined by fitting model prediction to experimental data. The average value of Eh was estimated to be (478±8) N/m.     

Study on Synthesis and Chloramphenicol Release of Poly（2-hydroxyethylmethacrylate-co-acrylamide） Hydrogels

In this article, poly（2-hydroxyethylmethacrylate-co-acrylamide） hydrogels were synthesized by bulk free-radical copolymerization of 2-hydroxyethylmethacrylate （HEMA） and acrylamide （AAm） for soft contact lens（SCL）-based ophthalmic drug delivery system. The copolymer was characterized with FT-IR and SEM, the swelling property of the hydrogels were studied by gravimetrical method, and chloramphenicol was used as a model drug to investigate drug release profile of the hydrogels. The results showed that poly（2-hydroxyethylmethacrylateco-acrylamide） hydrogels were transparent and useful SCL biomaterial, the water content increased as AAm content increase and pH decrease, and in the same way, hydrogel composition affected chloramphenicol release process too. Migration rate of chloramphenicol increased as the AAm content in the hydrogels increased in the first stage of diffusion process, whereas there was no significant difference thereafter.     

Preparation and Processing Properties of Nozzle Plate for Aluminum Continuous Strip Casting

The currently used ceramic nozzles for aluminum deep processing continuous hot rolled strips are featured with good integrity,high strength,good processing property,but non-uniform structure caused by the migration of silica sol. In this work,nozzle materials were prepared with aluminum silicate ceramic fiber,kaolin,and aluminum tripolyphosphate as starting materials,silica sol or silica sol- epoxy resin as the binder. After pulping,casting,curing at different temperatures and hot treatment,the prepared materials were analyzed in terms of migration layer thickness,cold modulus of rupture,and microstructure morphology. The results show that( 1) with the same curing temperature,the migration layer thickness of specimens bonded by different binders all decreases with the curing time prolonging; with the same curing time,the migration thickness declines first and climbs then as the curing temperature increases; overall,the specimen cured at 40 ℃ for 120 min has the thinnest migration layer; from the comparison,it is found that the silica sol- epoxy resin bonded specimen has slightly thinner migration layer than the specimen bonded by silica sol only;( 2) the specimen bonded by silica sol and epoxy resin has thinner migration layer,lower cold modulus of rupture and obvious lower bulk density than the silica sol bonded specimen;( 3) the material introduced with epoxy resin has better processing property but slightly lower strength than the material bonded by silica sol.     

Experimental Study Refining on Composition Slag Containing Optimization for BaO

Laboratory study; was carried out on deep desulfurization of molten steel by CaO-Al2O3 based refining slag containing BaO at 1873K to achieve lower sulphur level in steel. A mathematical model of desulfurization was established with the methodology of quadratic orthogohal regression. According to the modle, the influence of AlO3/CaO, MgO, CaF2, BaO in slag on desulfurization rate was analyzed. The results showed that the desulfurization rate almost linearly decreased with the increase of Al2O3/CaO and it increased firstly then decreased when MgO and BaO content increased respectixely, yet the trend is on the contrary as CaF2 content increased. Based on the comprehensive analysis, the optimum composition of the refining slag was achieved under the experimental conditions.     

纤维蛋白原在微胶囊表面的吸附行为

Alginate-chitosan-alginate (ACA) microcapsules have been widely studied as devices for the immuno-isolation and transplantation of living cells.However, long-term survival of the micro-encapsulated cell grafts and thus their potential clinical applications are hampered by the pericapsular fibrotic overgrowth induced by adsorbed protein.In this study, the adsorption behavior of plasma fibrinogen (Fgn) onto ACA microcapsules was studied by using the batch technique.The results showed that the equilibrium time for the adsorption was 24 h.The adsorption of Fgn onto ACA microcapsules fitted very well with Freundlich isotherm, which was indicative of multilayer adsorption.The kinetic experimental data correlated well with the second-order kinetic model,indicating that chemical sorption was the rate-limiting step.The effects of pH and ionic strength on the adsorption were also studied to interpret the mechanism of adsorption.It was found that the amount of adsorbed Fgn decreased with increasing pH in the range of 4.9—7.4.At pH 7.4, the amount of adsorbed Fgn increased with increasing NaCl concentration, and then decreased with further increase in NaCl concentration.At pH 6.0, the amount of adsorbed Fgn decreased with increasing NaCl concentration, indicating that electrostatic interaction was one of the main interactions between Fgn and ACA microcapsules and the positively charged chitosans which was not sufficiently neutralized on the surface of microcapsules induced the adsorption.     

Influence of Yb_2O_3-MgO on Mechanical Properties and Thermal Conductivity of Silicon Nitride Ceramics via Gas Pressure Sintering

In this work,Yb2O3 and Mg O were used as sintering aids in preparing silicon nitride ceramics by gas pressure sintering( 0. 6 MPa N2atmosphere) to investigate how the amounts of Yb2O3- Mg O influence the mechanical properties and thermal conductivity of silicon nitride ceramics. The total contents of Yb2O3- Mg O added were 1 mol%,2 mol%,4 mol%,6 mol%,8 mol%,10 mol%,12 mol%,14 mol%,keeping the Yb2O3-Mg O molar ratio of 1 ∶ 1 steadily. Curves of the relative density,thermal conductivity and bending strength plotted against the aids content present a ‘mountain'shape with a maximum at nearly 10 mol% aids. The fracture toughness increased with the amounts of additives up to10 mol% and decreased slightly thereafter. The mechanical properties and thermal conductivity were almost proportional to the amount of the additives before10 mol%. When the content of aids exceeded 10 mol%,it would weaken the mechanical properties and thermal conductivity of the ceramics. The optimum content of Yb2O3- Mg O was 10 mol% by gas pressure sintering( 0. 6MPa) at 1 850 ℃ for 4 h,which led to a relative density of 98. 9%,a flexural strength of( 966 ± 38)MPa as well as a fracture toughness of( 6. 29 ± 0. 29)MPa·m1 /2and thermal conductivity of 82 W /( m·K).     

悬浮态乳液聚合条件对聚氯乙烯树脂颗粒特性的影响

Suspended emulsion polymerization of vinyl chloride was carried out in a 5 L autoclave. The influence of agitation, polymerization conversion, dispersant and surfactant on the average particle size (PS) and particle size distribution (PSD), particle morphology and porosity of polyvinyl chloride (PVC) resin was investigated. It showed that the agitator had great influence on the smooth operation of polymerization, PS and PSD. The PS increased and PSD became narrow as polymerization conversion became high. The porosity decreased with the increase of conversion. A convenient choice of additives, both dispersants and non-ionic surfactants, allows one to adjust PS and PSD. The PS decreased with the addition of polyvinyl alcohol or hydroxypropyl methylcellulose dispersants,and increased with the addition of Span surfactants. The addition of dispersants or surfactants also affected the morphology and porosity of resin, and PVC resin with looser agglomeration and homogeneous distribution of primary particles was prepared.     

Influence of microcapsule shell material on the mechanical behavior of epoxy composites for self‐healing applications

In this article, we have studied the effect of microcapsule shell material on the mechanical behavior of self‐healing epoxy composites. Liquid epoxy healant was encapsulated in melamine‐formaldehyde (MF) and urea‐formaldehyde (UF), using emulsion polymerization technique to prepare microcapsules of different shell walls. The core content of the microcapsules, as determined by solvent extraction technique was found to be 65 ± 4%, irrespective of the shell wall of microcapsule. Morphological investigations reveal a rough texture of the spherical microcapsules, which was attributed to the presence of protruding polymer nanoparticles on the surface. Epoxy composites containing UF and MF microcapsules (3–15% w/w) were prepared by room temperature curing and their mechanical behaviour was studied under both quasi‐static and dynamic loadings. The tensile strength, modulus, and impact resistance of the matrix was found to decrease with increasing amount of microcapsule in the formulation, irrespective of the shell wall material used for encapsulation. Interestingly, substantial improvement in the fracture toughness of the base resin was observed. Morphological investigations on the cracked surface revealed features like crack pinning, crack bowing, microcracking and crack path deflection, which were used to explain the toughened nature of microcapsule containing epoxy composites. Our studies clearly indicate that the microcapsule shell wall material does not play any significant role in defining the mechanical properties of the composites. In addition, presence of secondary amine functionalities in UF and MF shell wall do not interfere with the reaction of epoxy with triethylene tetramine hardener during the curing process. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40572.     

自修复聚脲甲醛微胶囊的制备及成囊机理研究

采用原位聚合法制备了自修复聚脲甲醛包覆环氧树脂微胶囊。考察了原料用量、反应温度、酸化值和固化时间等对微胶囊粒径分布和表面形态的影响,确定了微胶囊的最佳制备工艺。借助显微镜实时监测微胶囊化过程,探讨了微胶囊的成囊机理,并将微胶囊填充到脲醛树脂中。结果表明:采用最佳制备工艺制得的微胶囊包覆率较高、结构紧密、粒度均匀,室温下保存一周后没有出现团聚和破裂;将9%微胶囊添加到脲醛树脂中,微胶囊分散均匀,脲醛树脂复合材料的韧性得到提高。     

环氧树脂微胶囊与潜伏性固化剂自修复体系断裂韧性的研究

微胶囊二元自修复系统对聚合物基复合材料在使用中产生的微小裂纹具有修复作用,但微胶囊和固化剂的加入会对基体材料的断裂韧性产生影响。本文研究了环氧树脂微胶囊和咪唑类潜伏性固化剂对聚合物基复合材料基体材料的断裂韧性的影响。采用环氧树脂E-51作为基体材料,三乙烯四胺为常温固化剂,咪唑类衍生物2MZ-Azine和实验室自制的包含环氧树脂芯材的微胶囊为材料制作断裂韧性拉伸试样。实验结果表明,当微胶囊的含量达到一定比例之前,基体材料的断裂韧性随着微胶囊含量的增加而增强,当微胶囊含量超过此比例后,基体材料的断裂韧性随着微胶囊含量的增加而减小,潜伏性固化剂的加入会增大基体材料的断裂韧性。这与环氧树脂材料增韧理论相符合。     

Preparation and assessment of a self‐healing material based on microcapsules filled with ethyl phenylacetate

A self‐healing material was developed on the basis of a biological system. The self‐healing epoxy resin, which incorporated microcapsules filled with ethyl phenylacetate (EPA), was investigated. The microcapsules were prepared by an in situ polymerization method. The microcapsule‐formation process was monitored by optical microscopy, and the surface morphology was observed by scanning electron microscopy (SEM). The self‐healing performance of the epoxy resin was assessed by manual and in situ healing experiments. We investigated the effects of the healing time, amount of EPA, and degree of curing of matrix on the healing performance by manually injecting EPA into the crack plane. The maximum healing efficiency was obtained within 24 h. The swelling curve was overlaid onto the healed load plot; this indicated that crack healing was achieved as a result of solvent diffusion. The healing load reached the maximum value when the amount of EPA was 0.5 μL and was capable of filling the crack volume. Moreover, the healing performance was related to the degree of swelling. The in situ healing efficiency was dependent on the microcapsule concentration. The fracture toughness could be fully restored when the microcapsule concentration was 10%. Finally, the crack interface was analyzed with SEM. The results show that the fracture line was difficult to detect, and this suggested complete crack healing by EPA. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43430.     

Preparation and curing behavior of latent 2-PhIm-PS microcapsule curing agent for epoxy resin

A core–shell microcapsule latent epoxy curing agent (2-PhIm-PS) is obtained by solvent evaporation method with 2-phenyl imidazole (2-PhIm) as the core material and polystyrene (PS) as the wall material. The microcapsule parameters, morphology, structure, curing behavior, and the mechanic properties of cured epoxy resin with this microcapsule latent curing agent were characterized through comparing with 2-PhIm. The particle size distribution of the microcapsule is narrow, the average particle size is about 10.56 μm, and the core material content is 23%. The prepared 2-PhIm-PS microcapsule curing agent has excellent latent curing properties. It can completely cure epoxy resin E-51 within 10 min at 130°C, and its latent period can be more than 40 days at room temperature. In addition, the curing kinetics of one-component epoxy resin curing system (E-51/2-PhIm-PS) composed of 2-PhIm-PS microcapsules and epoxy resin E-51 is also studied by using Kissinger equation, Flynn–Wall–Ozawa and Crane formula. The results provide an outline for the evaluation on the applicability of the microcapsule curing agent of 2-PhIm-PS for epoxy resin.     

Autonomous self-healing based on epoxy resin–imidazole chemistry in carbon fiber-reinforced polymer composites

Epoxy resin–imidazole chemistry is used as a new autonomous self-healing system for unidirectional fiber-reinforced polymers and tested for its efficiency in recovery of fracture properties in laminated carbon fiber-reinforced polymers. The dual microcapsule approach is utilized to store and distribute the reactive chemistries in the structure. Microcapsules were located in possible damage regions using polymeric interleaves. Microcapsules containing separately the epoxy resin (EPIDIAN 52–ethyl phenylacetate) and imidazole hardener (1-benzyl-2-methylimidazole) are prepared with poly(urea-formaldehyde) and PMMA shell wall, respectively. Mode I fracture toughness tests are used to evaluate the recovery of the material mechanical properties. At optimized conditions, 117.5% of the interlaminar fracture toughness (G_IC) was recovered after heat treatment at 100 °C for 24 h. Furthermore, it is demonstrated that the self-healing efficiency is strongly dependent on the load of microcapsules with the imidazole hardener and that the microcapsules’ presence in the laminate has a detrimental effect on the material's mechanical performance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46938.     

Microencapsulation of imidazole curing agents by spray‐drying method

An epoxy resin–imidazole system was used to form the adhesives for the anisotropic conducting film (ACF), and a latent curing system was necessary for the ACF. In this study, imidazoles were microencapsulated for the latent curing system. Polycaprolactone (PCL) was used as the wall material, and the spray‐drying method was used to form the microcapsule. The imidazoles used in this study were imidazole, 2‐methylimidazole, and 2‐phenylimidazole. The effect of the ratio of PCL to imidazoles, and the effect of PCL molecular weight were investigated during the microcapsule formation. The amount of imidazoles in the microcapsule was measured using thermogravimetric analyzer and elemental analysis. The permeability of the microcapsules was measured in ethanol, and the shelf life of the microcapsules was studied for the epoxy resin. The curing behavior of these microcapsules to epoxy resin was examined using differential scanning calorimeter. In the curing reaction, the microcapsule of imidazoles exhibited delayed kinetic behaviors compared to pure imidazoles. And the curing times were estimated at 150 and 180°C using an indentation method. These microcapsules of imidazoles exhibited a long shelf life, and the curing did not occur in some of the microcapsule–epoxy resin systems at 20°C for 15 days. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Microencapsulation of imidazole curing agent by solvent evaporation method using W/O/W emulsion

The epoxy–imidazole resin system is used to form the anisotropic conducting film. The latent character of the system is very significant. In this study, imidazole (Im) or 2‐methylimidazole (2MI) was encapsulated for the latent curing system to use in the reaction of epoxy resin. Polycaprolactone was used as a wall material, and the solvent evaporation method was used to form the microcapsule using W/O/W emulsion. The shelf life of the microcapsules was studied for the epoxy resin, and the curing behavior of the microcapsules for epoxy resin was examined using a differential scanning calorimeter. The curing times at 150 and 180°C were estimated using an indentation method. The microcapsules of Im or 2MI exhibited a long shelf life for epoxy resin. When comparing the results of the previous methods with the results of this study using the W/O/W emulsion, finer microcapsules were formed and the microcapsule has longer shelf life. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

醇酸树脂微胶囊的制备及环氧涂层自修复性能

采用三聚氰胺-脲醛树脂（MUF）为壁材、合成的花椒籽油醇酸树脂为芯材,原位聚合法制备自修复微胶囊,探讨了微胶囊的制备工艺。并采用扫描电子显微镜（SEM）、红外光谱仪（FTIR）、热重分析仪（TGA）和粒径分析仪对微胶囊的表面形貌、化学结构、热稳定性及其粒径分布进行了测试表征。将醇酸树脂微胶囊分散到环氧基体中,研究了环氧涂层的力学性能和自修复性能。实验结果表明,当乳化剂浓度为2.0g/L、芯壁比为2∶1、终点pH为3.5时,微胶囊呈球形结构,无明显的缺陷和损伤,平均粒径为97.44μm,热稳定性良好。当添加质量分数5%的微胶囊时,与未添加微胶囊的自修复涂层相比,其弯曲强度、拉伸强度、黏结强度及其冲击强度分别提高了50.4%、50.0%、40.0%及25.2%,且涂层的自修复性能良好。     

Microencapsulation of imidazole curing agent for epoxy resin

An epoxy resin–imidazole system was used to form the adhesives for the anisotropic conducting film (ACF), and a latent curing system was necessary for the ACF. In this study, 2-phenylimidazole (2PhI) was encapsulated for the latent curing system. Polycaprolactone (PCL) was used as the wall material, and the solvent evaporation method was used to form the microcapsule. The effects of the ratio of 2PhI and PCL, and the effects of the molecular weight of PCL were investigated during the microcapsule formation. The amount of 2PhI in the microcapsule was measured using TGA. The permeability of the microcapsules was measured in ethanol, and the shelf life of the microcapsules was also studied for the epoxy resin. The curing behavior was examined using DSC. In the curing reaction of the epoxy resin, the microcapsule of 2PhI exhibited a delayed kinetic behavior compared to pure 2PhI. This microcapsule of 2PhI exhibited a long shelf life, and the curing did not occur in this microcapsule–epoxy resin system at 20 °C for more than 30 days.