高温相变材料胶囊化及应用研究进展

高温相变材料因具有较高的相变温度，且单位体积的潜热值较大，将其胶囊化用于高温领域（＞120℃）具有较大的应用前景。本文介绍了高温相变材料的种类及其胶囊化技术，对不同类型的高温相变胶囊制备方法进行了阐述。指出了目前高温相变胶囊制备过程中存在的问题，如金属大胶囊的芯材与壁材的相容性、微/纳胶囊易破碎等。重点论述了溶胶-凝胶法、水热法制备高温相变微/纳胶囊过程中囊壁材料、热处理温度等对胶囊性能的影响。针对上述因素引起的胶囊热循环性能差、过冷大等问题，提出了解决方案。最后阐述了高温相变胶囊的相关应用情况，并提出未来在寻找与芯材相容性好的壁材、优化微/纳胶囊制备方式、抑制胶囊过冷等方面需要进一步探索。     

Efficient preparation and characterization of paraffin-based microcapsules by emulsion polymerization

Microencapsulated phase-change materials (MEPCMs) with paraffin as the core and poly(methyl methacrylate) (PMMA) and PMMA copolymers as the shell were prepared by emulsion polymerization using redox initiators at low temperatures. Fourier transform infrared spectroscopy was used to characterize the chemical composition of MEPCMs. The thermal properties and thermal stabilities of MEPCMs were tested by differential scanning calorimetry and thermogravimetric analysis. The morphologies and sizes of the microcapsules were investigated by scanning electron microscopy and particle size distribution analysis. The results indicated that the yield of microcapsules is as high as 96.2%, and the encapsulation efficiency of paraffin is nearly 100% when the paraffin content in MEPCM is 70%. The MEPCMs have good stability: the leakage ratios of MEPCMs can be less than 1% after 50 heating–cooling cycles. Therefore, the microencapsulation of paraffin using redox initiators has good production and application prospects. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47552.     

Preparation and characterization of paraffin microcapsules for energy-saving applications

A series of microencapsulated phase-change materials (PCMs) with styrene–divinyl benzene shells composed of an n-octadecane (OD or C₁₈)–n-hexadecane (HD or C₁₆) mixture as the core were synthesized by an emulsion polymerization method. The effects of the core/shell ratio (C/S) and surfactant concentration (C_surf) on the thermal properties and encapsulation ratios of the PCMs were investigated. The chemical structures and morphological properties of the microcapsules were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy analysis, respectively. The characteristic peaks of the paraffin mixtures and shell material located in the FTIR spectrum of the microencapsulated PCMs proved that the encapsulation of the PCM mixture was performed successfully. The thermal properties of the paraffin microcapsules were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis. DSC analysis demonstrated that the microcapsules containing the maximum amount of paraffin mixture (C/S = 2:1) and the minimum C_surf (45 mmol/L) had the highest latent heat value of 88 kJ/kg and a latent heat of temperature of 21.06°C. Moreover, the maximum encapsulation ratio of the paraffin mixture was found to be 56.77%. With respect to the analysis results, the encapsulated binary mixture, which consisted of OD–HD with a poly(styrene-co-divinyl benzene) shell, is a promising material for thermal energy storage applications operating at low temperatures, such as in the thermal control of indoor temperatures and air-conditioning applications in buildings for desirable thermal comfort and energy conservation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47874.     

Biphasic,tough composite core/shell PCL/PVA-GEL nanofibers for biomedical application

Emulsion electrospinning using natural and synthetic polymers, including two dissimilar materials is a promising technique for nanofibers fabrication in a core/shell configuration for tissue engineering, controlled or sustained drug delivery and dressing applications. In this study, we designed and fabricated core/shell nanofibers based on polycaprolactone (PCL) as core material and poly(vinyl alcohol) (PVA)-gelatin (GEL) blend as shell materials (PCL/PVA-GEL) to achieve high mechanical properties, good cell growth, and proliferation via emulsion electrospinning. The effect of water to acetic acid ratio in the solvent system (8:2, 7:3, 6:4, 5:5) and also type and concentration (3, 5, 7 w/v %) of surfactant on emulsion stability and nanofibers morphology were investigated. The emulsion containing 2% Tween80 and 1% Span60 as surfactants were selected by considering the stability of emulsion and uniform fiber morphology. In the tensile strength and elongation at break, 53 and 8% increase in the crosslinked wet state of the PCL/PVA-GEL nanofibers compared with PVA-GEL nanofibers were observed respectively. The cell culture results indicated that the PCL/PVA-GEL nanofibers surface has presented suitable interaction with fibroblast cells and cells attached and proliferated well on the fabricated substrate within 24 and 48 hours and also would be a good candidate for biomedical applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48713.     

Nanoencapsulation of n-Octadecane Phase Change Material in Self-Assembled Polyelectrolyte by Soft Solution Technique

Nanoencapsulation of n-octadecane phase change material was performed by facile soft solution technique. An emulsion of n-octadecane and sodium dodecyl sulfate was prepared by high intensity sonication and then mixed with 1–6 mM of poly(diallyldimethylammonium chloride) (PDDA) solution. The capsules with globular core-shell structure were obtained via self-assembly of PDDA molecules coated on the primary emulsion droplets, described as PDDA encapsulated n-octadecane (PDDA-en-Oc). Average particle size and ζ-potential of PDDA-en-Oc increased with increasing of PDDA concentration due to the different PDDA conformation and thickness of capsules' shell. The smaller diameter of PDDA-en-Oc, the faster heat releasing and absorption were obtained. However, the increasing of PDDA concentration could improve the encapsulation efficiency, resulting in an increment of latent heat quantity. The PDDA-en-Oc capsules prepared from 4 mM PDDA with ～166 nm in size possessed the maximum latent heat and encapsulation efficiency (i.e., 124.4 J/g and 58%, respectively).     

Fabrication and characterization of nanoencapsulated epoxy resin/crosslinked PMMA shells with in situ polymerization via phase inversion emulsion (PIE) method

Encapsulated epoxy resin healing agents with poly(methyl methacrylate (PMMA) as a thermoplastic polymeric shell are suffered from leakage of the core after a while. This problem leads to loss of their performance and its ability in self-healing systems. One way to stop or reduce the leakage of the core is crosslinking the PMMA shell. In this study, nanoencapsulation of epoxy healing agent with crosslinked PMMA as shell was carried out by in situ polymerization via phase inversion emulsion method. Ethylene glycol dimethacrylate was employed as crosslinking agent. Nonionic (SPAN 60) and ionic (sodium dodecyl sulfate) surfactants were used for competitive adsorption and phase inversion in emulsion system. Chemical structures, morphologies, and thermal properties of nanocapsules were characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analysis, respectively. SEM investigations showed that nanocapsules had a particle size of less than 100 nm with a narrow particle size distribution. Efficiency of nanoencapsulation was equal to 83.5%. And synthesized nanocapsules had at least 37% core contents. Nanocapsules with crosslinked shell were able to maintain liquid core up to 18 weeks, while, noncrosslinked shell lost core content after 14 weeks. It seems that low crosslink density has no effect on capsule durability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48793.     

Preparation of poly(methyl methacrylate)‐Silica nanoparticles via differential microemulsion polymerization and physical properties of NR/PMMA‐SiO2 hybrid membranes

Poly(methy methacrylate) (PMMA)‐SiO₂ nanoparticles were prepared via differential microemulsion polymerization. The effects of silica loading, surfactant concentration, and initiator concentration on monomer conversion, particle size, particle size distribution, grafting efficiency, and silica encapsulation efficiency were investigated. A high monomer conversion of 99.9% and PMMA‐SiO₂ nanoparticles with a size range of 30 to 50 nm were obtained at a low surfactant concentration of 5.34 wt% based on monomer. PMMA‐SiO₂ nanoparticles showed spherical particles with a core‐shell morphology by TEM micrographs. A nanocomposite membrane from natural rubber (NR) and PMMA‐SiO₂ emulsion was studied for mechanical and thermal properties and pervaporation of water‐ethanol mixtures. PMMA‐SiO₂ nanoparticles which were uniformly dispersed in NR matrix, significantly enhanced mechanical properties and showed high water selectivity in permeate flux. Thus, the NR/PMMA‐SiO₂ hybrid membranes have great potential for pervaporation process in membrane applications. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers     

阿司匹林壳聚糖-明胶载药微胶囊的制备及性能研究

以阿司匹林为囊芯,壳聚糖和明胶为壁材,采用乳化交联法制备了明胶-壳聚糖微胶囊,考察了芯壁比、水油体积比、乳化剂用量、交联时间等因素对微胶囊性能的影响.采用高效液相色谱法来测定微胶囊的载药量、包封率和释放性能.研究发现,当芯壁比为1∶1,水油体积比为1∶3,乳化剂Span-80用量为5％,交联时间为2h的条件下制备的微胶囊形状规整,载药量为47.99％,包封率为83.18％,且在人工肠液中具有明显的缓释效果.     

Investigation on enhancement of weld strength between PMMA and PBT in laser transmission welding—Using intermediate material

Poly(methyl methacrylate) (PMMA) and poly(butylene terephthalate) (PBT) are widely used in industry; however, poor compatibility between two materials lead to poor weld strength. Polycarbonate (PC) has good compatibility with PMMA and PBT. Therefore, the welding method was that PC film as intermediate material was used to enhance weld strength in laser transmission welding (LTW) of PMMA and PBT. Through the LTW experiment, the weld strength was tested by mechanical testing and it was found that the best weld strength was improved more than four times than the weld strength without intermediate material. By observing the micro morphology of the weld zone, one reason was founded that the bubbles can be used to form micro‐mechanical riveting to enhance the weld strength. The reptation time for PMMA, PC, and PBT were investigated to analyze the establishment of the weld strength. When the reptation time is much shorter than time in molten state, the higher weld strength is feasible. It can be concluded that the weld strength of PC/PBT was higher than the weld strength of PMMA/PC. The equilibrium interfacial width was calculated through Helfand's theory to analyze the compatibility of dissimilar materials. The equilibrium interfacial width for PMMA/PC and PC/PBT were similar to tube diameter. That is the reason for weld strength enhancement. And then, the response surface methodology was designed to predict the weld strength.© 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44167.     

Tunable mechanical properties of core‐shell polymers of poly(hexyl methacrylate) and poly(methyl methacrylate) by semicontinuous heterophase polymerization

The synthesis of core/shell polymers with tunable mechanical properties made of poly(hexyl methacrylate) (PHeMA) and poly(methyl methacrylate) (PMMA) by a two‐stage semicontinuous heterophase polymerization, is presented here. This polymerization technique is characterized by employing low surfactant concentrations to produce large polymer‐to‐surfactant ratios. In this process, monomer is added in a continuous low rate to achieve monomer starved conditions, allowing to control particle size (usually smaller than 50 nm). To modulate the mechanical properties, the weight ratio of core/shell polymers are varied from 10/90 to 90/10 for direct and reverse compositions, respectively. Conversion was followed gravimetrically; nanoparticles were characterized with quasi‐elastic light scattering, IR spectroscopy, differential scanning calorimetry, transmission electron microscopy, and mechanical tests (tensile and hardness). Highly stable latex formed of nanoparticles, with high conversions are obtained. Tensile tests show that the mechanical properties can be tuned according to core/shell composition, mainly in the system formed by PMMA/PHeMA. These results are explained in terms of core‐and‐shell polymers location, composition and hardness. As expected, an increment in concentration of PMMA produces a more rigid material independently of its position. POLYM. ENG. SCI., 59:365–371, 2019. © 2018 Society of Plastics Engineers     

ACR中壳层PMMA相对分子质量对PVC／ACR共混物性能的影响

采用种子乳液法制备了核壳型聚丙烯酸酯(ACR),并分别采用十二烷基硫醇和正辛基硫醇作为链转移剂对 ACR壳层的聚甲基丙烯酸甲酯(PMMA)进行相对分子质量调节,并用于PVC共混改性。黏度法对PMMA的相对分子质量测定表明,正辛基硫醇的相对分子质量调节能力较强。采用差示扫描量热分析测定PMMA的玻璃化转变温度(Tg),并对共混树脂进行动态力学性能测试。当ACR壳层PMMA平均相对分子质量低于12×104时,PVC/ACR 共混树脂的缺口冲击强度大大提高。与纯PVC相比,共混树脂的Tg均略有提高,其增量随ACR壳层PMMA平均相对分子质量的降低而减小。动态力学性能测试结果表明,ACR壳层聚合物平均相对分子质量越低,共混物分子链段运动活化能提高越少。     

核壳结构纳米TiO_2/PU/PMMA复合材料制备及其光催化性能研究

采用纳米TiO2有机化改性、加成及原位乳液聚合,制备了纳米TiO2、聚氨酯(PU)、聚丙烯酸酯(PMMA)的复合材料。透射电镜形貌表明:合成了以纳米TiO2为核,PU与PMMA为壳的核壳结构的复合材料。研究了该复合材料的光催化性能。     

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.     

原位聚合法制备高透光率韧性PMMA复合树脂的研究

采用原位聚合法制备PMMA/P(BA-St)/PMMA三层韧性有机玻璃复合树脂,分子设计方法的使用,保持了材料的透明性。考察了韧性粒子粒径、橡胶相组成以及橡胶含量对材料力学和光学性能的影响。借助透射电镜、扫描电镜和动态光散射方法对复合胶乳粒子以及所制材料的形态结构进行了表征。结果表明:橡胶相的折光指数对材料的透光率有明显影响,橡胶相玻璃化温度越低,越有利于增韧。     

Effect of particle size on the mechanical properties of polystyrene and poly(butyl acrylate) core/shell polymers

The effects of particle size and polymer location (core or shell) on the mechanical properties of core/shell materials composed of polystyrene (PST) and poly(butyl acrylate) (PBA) made by a two-stage emulsion or microemulsion polymerization process are reported. Low-seed content (LSC) latexes were made by batch polymerization in microemulsions stabilized with DTAB in the presence of an organic salt (dibutyl phosphite). High-seed content (HSC) latexes were produced by microemulsion or emulsion polymerization in semi-continuous process. These latexes were subsequently used to form core/shell particles of PST/PBA or PBA/PST and their mechanical properties were examined and compared. Our results indicate that core/shell particle size and the location of the polymers have important effects on the mechanical properties.     

Effects of preparation methods on the property of PMMA/SBA-15 mesoporous silica composites

In the paper, poly(methyl methacrylate)(PMMA)/SBA-15 composite materials were prepared by four different methods, that is, in-situ batch emulsion polymerization in the presence of mesoporous SBA-15, PMMA emulsion mixed with SBA-15 powder or dispersion in water, PMMA powder mixed with SBA-15 powder, and the properties of the composite materials were determined and compared. The composites were characterized by infrared spectroscopy (IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanics analysis (DMA) and scanning electron microscope (SEM). The results showed that the glass transition temperatures (Tg), the storage modulus and tensile strength of the PMMA/SBA-15 composites were all improved obviously, while the thermal decomposition temperature did not influenced apparently. The composite made by in-situ batch polymerization exhibited the most improvement in the mechanical properties and Tg while the composite prepared by mixing PMMA emulsion and SBA-15 dispersion gave rise to the least improvement in the mechanical properties and Tg. These results were contributed to introducing different amount of voids into polymer matrix which were demonstrated by dielectric constant measurement and SEM morphology observation.     

A facile strategy to fabricate microencapsulated expandable graphite as a flame‐retardant for rigid polyurethane foams

A facile strategy is reported for one‐step preparation of reactive microencapsulated expandable graphite (EG) for flame‐retardant rigid polyurethane foams (RPUF), which is based on in situ emulsion polymerization and the use of poly(glycidyl methacrylate) (PGMA) as reactive polymer shell. FTIR and SEM observations well demonstrate the formation of PGMA microencapsulated EG (EG@PGMA) particles. The encapsulation of PGMA shell significantly improves the expandability of EG particles from 42 to 70 mL g^?1. RPUF/EG@PGMA composite with only 10 wt % EG@PGMA loading reaches the UL‐94 V‐0 rating. The limiting oxygen indexes increase remarkably from 21.0 to 27.5 vol %. Additionally, the improved chemical and physical interaction enhance the interfacial bonding between EG and matrix, thus resulting in improved mechanical properties of RPUF/EG@PGMA. These attractive features suggest that the strategy proposed here can serve as a promising means to prepare highly efficient, reactive microencapsulated EG and corresponding good flame‐retarding RPUF with high mechanical properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42364.     

Effects of compatibilizing agents in poly(n-butyl acrylate)/poly(methyl methacrylate) composite latexes

Graft copolymers with poly(n-butyl acrylate) (PBA) backbones and poly(methyl methacrylate) (PMMA) macromonomer side chains are used as compatibilizing agents for PBA/PMMA composite latexes. The composite latexes are prepared by seeded emulsion polymerization of methyl methacrylate (MMA) in the presence of PBA particles. Graft copolymers were already incorporated into the PBA particles prior to using these particles as seed via miniemulsion (co)polymerization of n-butyl acrylate (BA) in the presence of the macromonomers. Comparison between size averages of composite and seed particles indicates no secondary nucleation of MMA during seeded emulsion polymerization. Transmission electron microscopy (TEM) observations of composite particles show the dependence of particle morphologies with the amount of macromonomer (i.e., mole ratio of macromonomer to BA and molecular weight of macromonomer) in seed latex. The more uniform coverage with the higher amount of macromonomer suggests that graft copolymers decrease the interfacial tension between core and shell layers in the composite particles. Dynamic mechanical analysis of composite latex films indicates the existence of an interphase region between PBA and PMMA. The dynamic mechanical properties of these films are related to the morphology of the composite particles, the arrangement of phases in the films, and the volume of the interphase polymer. © 1997 John Wiley & Sons, Inc.     

Mechanical properties of transparent poly(methyl methacrylate) nanocomposites reinforced with core–shell polyacrylonitrile/poly(methyl methacrylate) nanofibers

Having considered the mechanical and optical properties related to microstructure, the authors of the present work did a study of the in situ interface formation between polyacrylonitrile/poly(methyl methacrylate) (PAN/PMMA) core–shell nanofibers and PMMA resin so as to prepare reinforced PMMA nanocomposites (NCs). The NCs were produced using the dip-coating method. The core–shell nanofibers were generated via phase separation of PAN/PMMA solution during the conventional electrospinning. The results of attenuated total reflection-Fourier transform infrared spectroscopy, transmission electron microscope, and energy dispersive X-ray spectrometer confirmed the formation of core–shell structure of the PAN/PMMA nanofibers. According to the findings of the study, the NCs reinforced with 1.7% volume fractions (v _f) of the core–shell nanofibers, having the composition of 50/50 (PAN/PMMA), had the highest tensile and bending properties. The obtained results showed that by increasing the v _f of nanofibers from 1.7 to 2.9%, the tensile and bending moduli increased by 29.9 and 44.2%, respectively. Increasing v _f to 5.7% decreased the just-mentioned properties. Moreover, the transparency of NCs decreased by less than 1, 10, and 18%, respectively, when the aforementioned volume fractions were applied. The theoretical values for the tensile modulus were calculated using the models proposed by Manera, Pan, and Halpin–Tsai–Nielsen. The best prediction was made when the model proposed by Halpin–Tsai–Nielsen was applied.     

Investment casting pattern material based on paraffin wax fortified with EVA and filled with PMMA

Paraffin wax-based compounds are utilized as investment casting pattern materials. This study considered the effect of composition variations on the properties of paraffin wax-poly(ethylene-co-vinyl acetate) (EVA) blends filled with poly(methyl methacrylate) (PMMA) microbeads. The EVA addition significantly improved mechanical properties while the PMMA improved the needle penetration hardness. Both polymers increased the melt viscosity of the wax composition. Thermal gravimetric analysis of the pyrolysis behavior showed that the compounds volatilize readily with virtually no residue remaining above 500 °C. The 40/20/40 wax/EVA/PMMA composition offers a balanced property profile with the bending stress approaching 6 MPa, the bending strain at break exceeding 4%, and a melt viscosity of about 12 Pa s at 90 °C. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48774.