Preparation of microencapsulated ammonium polyphosphate with montmorillonite‐melamine formaldehyde resin and its flame retardancy in EVM

Microencapsulated ammonium polyphosphate (MMT‐MF‐APP) with a montmorillonite‐melamine formaldehyde resin coating layer was successfully prepared by in situ polymerization. The product was characterized by Fourier‐transform infrared, X‐ray photoelectron spectroscopy, and scanning electron microscopy. Water absorption analysis showed that the microencapsulation of APP with the MMT‐MF resin leads to a decrease in the particle's water solubility. The microcapsules also exhibited better mechanical properties and higher flame retardancy in the ethylene–vinyl acetate copolymer with high vinyl acetate content (EVM) rubber compared with the common ammonium polyphosphate. Moreover, thermogravimetric analysis results showed that the EVM composites with MMT‐MF‐APP and dipentaerythritol (DPER) as flame retardants possess higher thermal stability than those with common APP and DPER as flame retardants. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and characterization of microencapsulated dicyclopentadiene with melamine–formaldehyde resins

Microcapsules containing healing agents have been used to develop the self-healing polymeric composites. These microcapsules must possess special properties such as appropriate strength and stability in surrounding medium. A new series of microcapsules containing dicyclopentadiene (DCPD) with melamine–formaldehyde (MF) resin as shell material were synthesized by in situ polymerization technology. These microcapsules may satisfy the requirements for self-healing polymeric composites. The chemical structure of microcapsule was identified by using Fourier transform infrared (FTIR) spectrometer. The morphology of microcapsule was observed by using optical microscope (OM) and scanning electron microscope. Size distribution and mean diameter of microcapsules were determined with OM. The thermal properties of microcapsules were investigated by using thermogravimetric analysis and differential scanning calorimetry. Additionally, the self-healing efficiency was evaluated. The results indicate that the poly(melamine–formaldehyde) (PMF) microcapsules containing DCPD have been synthesized successfully, and their mean diameters fall in the range of 65.2∼202.0 μm when the adjusting agitation rate varies from 150 to 500 rpm. Increasing the surfactant concentration can decrease the diameters of microcapsules. The prepared microcapsules are thermally stable up to 69 °C. The PMF microcapsules containing DCPD can be applied to polymeric composites to fabricate the self-healing composites.     

Effects of ammonium chloride and heat treatment on residual formaldehyde contents of melamine-formaldehyde microcapsules

Microencapsulated n-octadecane with melamine–formaldehyde resin (MF) shell was synthesized by in situ polymerization. Ammonium chloride was used to reduce the residual formaldehyde content of microencapsulated phase change materials (microPCMs) caused by the inherent characteristics of MF. Moreover, microPCMs were heat-treated at 160 °C for 30 min. The surface morphology of the microPCMs fabricated at various microencapsulation periods was examined, and the shell thickness was measured. The effects of heat treatment on the surface morphology, residual formaldehyde content, phase change properties, and thermal stability of the microcapsules were systematically investigated. The globular surface of microcapsules fabricated at microencapsulation period of 120 min was smooth and compact with an average diameter about 2.2 μm, and the shell thickness was ranged from 30 to 70 nm. The thermal stability of heat-treated microcapsules enhanced significantly as microencapsulation period increased; in addition, the residual formaldehyde content of microcapsules decreased from 125 ± 1 mg/kg to 19 ± 1 mg/kg.     

Novel polyphenylene oxide microcapsules filled with epoxy resins

Novel polyphenylene oxide (PPO) microcapsules filled with epoxy resins (PPOMCs) were synthesized by in situ polymerization technology with 2, 6‐dimethy phenol as shell materials and diglycidyl ether of bisphenol A epoxy resins as core materials. The structures and morphologies of PPOMCs were characterized using Fourier‐transform infrared spectroscopy, micro‐confocal Raman microscope, laser scanning confocal microscopy, scanning electron microscopy and optical microscopy, respectively. The thermal properties of PPOMCs were investigated using differential scanning calorimetry and thermogravimetric analysis. The influences of different processing parameters such as the weight ratio of shell material to core material, kind of surfactant and reaction temperature on the morphologies and sizes of PPOMCs were investigated. Preliminary investigation on application of PPOMCs to thermosetting resins 4,4′‐bismaleimidodiphenylmethane/O,O′‐diallylbisphenol A (BMI/BA) system was conducted. Results indicate that PPOMCs can be synthesized successfully. The sizes and surface morphologies of PPOMCs may be significantly affected by different processing parameters. PPOMCs can be well prepared at about 30°C, and they depend strongly on the kind of surfactant and the weight ratio of shell material to core material. PPOMCs basically exhibit high thermal stability when the temperature is below 258°C. The addition of PPOMCs can improve the mechanical properties and maintain the thermal properties of BMI/BA system. The released core materials from PPOMCs may repair the matrix cracks through the polymerization of epoxy resins initiated by curing agent. Copyright © 2012 John Wiley & Sons, Ltd.     

Thermal behavior and flammability of epoxy/glass fiber composites containing clay and decabromodiphenyl oxide

Epoxy/glass fiber hybrid composites with organo-montmorillonite (OMMT) and decabromodiphenyl oxide (DBDPO) flame retardants were prepared by vacuum-assisted resin infusion technique. The effects of OMMT and DBDPO on the flammability properties of epoxy/glass fiber hybrid composites were evaluated through UL-94 vertical flammability test and limiting oxygen index (LOI). Thermal decomposition was studied by means of thermogravimetric analyzer (TG). Field emission scanning electron microscopy (FESEM) was used to study the char morphology of the epoxy hybrid composites after being subjected to UL-94 vertical flammability test. Epoxy/glass fiber/OMMT hybrid composites with DBDPO loading of 40 wt% showed V-1 rating, whereas an increase to 50 wt% loading showed V-0 rating. The LOI values increased from 22.7 to 39.9 % as the loading of DBDPO increased. The obtained TG results showed that the thermal stability of epoxy hybrid composites decreased as the DBDPO loading increased. DBDPO decomposed at a lower temperature to form bromine radicals, which reacted with the combustible gases to form hydrogen bromide to inhibit the flame spread in the gas phase. The condensed phase activity was shown in FESEM, in which a layer of compact and continuous char was formed in epoxy/glass fiber/OMMT/DBDPO hybrid composites.     

Thermal stability of microencapsulated epoxy resins with poly(urea-formaldehyde)

A series of microcapsules filled with epoxy resins with poly(urea-formaldehyde) (PUF) shell were synthesized by in situ polymerization, and they were heat-treated for 2 h at 100 °C, 120 °C, 140 °C, 160 °C, 180 °C and 200 °C. The effects of surface morphology, wall shell thickness and diameter on the thermal stability of microcapsules were investigated. The chemical structure and surface morphology of microcapsules were investigated using Fourier-transform infrared spectroscope (FTIR) and scanning electron microscope (SEM), respectively. The thermal properties of microcapsules were investigated by thermogravimetric analysis (TGA and DTA) and by differential scanning calorimetry (DSC). The thermal damage mechanisms of microcapsules at lower temperature (<251 °C) are the diffusion of the core material out of the wall shell or the breakage of the wall shell owing to the mismatch of the thermal expansion of core and shell materials of microcapsules. The thermal damage mechanisms of microcapsules at higher temperature (>251 °C) are the decomposition of shell material and core materials. Increasing the wall shell thickness and surface compactness can enhance significantly the weight loss temperatures (T_d) of microcapsules. The microcapsules with mean wall shell thickness of 30 ± 5 μm and smoother surface exhibit higher thermal stability and can maintain quite intact up to approximately 180 °C.     

Simultaneously improving the thermal conductive and flame retardant performance for epoxy resins thermosets by constructing core‐shell‐brush structure and distributing of MWCNTs in brush intervals

Fire safety and thermal dissipation performance of epoxy resins thermosets were critical for its application in key fields such as electronic devices. The simultaneous improvement of flame retardant and thermal conductivity properties were still a challenge. Herein, ammonium polyphosphate (APP) was firstly encapsulated with 5‐wt% epoxy resins based on APP and then surface grafted with polyurethane polymer chain, and the resulting APP with core‐shell‐brush structure was constructed. Finally, the multiwalled carbon nanotube (MWCNT) was assembled in the intervals of polymer brush on APP surface, and the prepared filler was defined as MF‐APP. Its chemical structure and morphologies were characterized and confirmed. The wettability of MF‐APP was evaluated by water contact angles tests (WCA) and MF‐APP exhibited hydrophobic property with the WCA of 138°. When 9‐wt% MF‐APP was incorporated into EP thermosets, the thermal conductive value of EP/MF‐APP achieved 1.02 Wm^?1 K^?1, and the MWCNTs concentration was only 1.8 wt% in thermosets. Compared with the previous work, the prepared EP/MF‐APP thermosets exhibited outstanding thermal conductive efficiency because of the homogeneously distribution of MWCNTs. Moreover, the samples fulfilled UL‐94 V‐0 grade during vertical burning tests with the limiting oxygen index of 30.8%. As a result, the thermal conductivity and flame retardancy of EP thermosets were simultaneously enhanced with a relatively low addition amount of MF‐APP, which would bring more chance for wider application of EP thermosets in key fields.     

Thermal degradation of lignin–phenol–formaldehyde and phenol–formaldehyde resol resins

Resol resins are used in many industrial applications as adhesives and coatings, but few studies have examined their thermal degradation. In this work, the thermal stability and thermal degradation kinetics of phenol–formaldehyde (PF) and lignin–phenol–formaldehyde (LPF) resol resins were studied using thermogravimetric analysis (TG) in air and nitrogen atmospheres in order to understand the steps of degradation and to improve their stabilities in industrial applications. The thermal stability of samples was estimated by measuring the degradation temperature (T _d), which was calculated according to the maximum reaction rate criterion. In addition, the ash content was determined at 800 °C in order to compare the thermal stability of the resol resin samples. The results indicate that 30 wt% ammonium lignin sulfonate (lignin derivative) as filler in the formulation of LPF resin improves the thermal stability in comparison with PF commercial resin. The activation energies of degradation of two resol resins show a difference in dependence on mass loss, which allows these resins to be distinguished. In addition, the structural changes of both resins during thermal degradation were studied by Fourier transform infrared spectroscopy (FTIR), with the results indicating that PF resin collapses at 300 °C whereas the LPF resin collapses at 500 °C.     

Preparation and characterization of 2,4–D butyl ester capsule suspension for mitigation of its drift risk

A novel capsule suspension (CS) formulation was prepared by in situ polymerization of melamine formaldehyde (MF) resin which was the first time to be used to encapsulate 2,4–D butyl ester. The prepared 2,4–D butyl ester capsule suspensions were studied by ultraviolet spectrophotometer (UV), laser particle size analyzer, Optical microscopy (OM), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Results showed that the encapsulation efficiency reached 93.23%, and the mean particle size (D₅₀) could be reduced to 13.80 µm by adding 4% Tween80. OM and SEM images illustrated that the core-shell structure related largely to the stability of emulsion. The spherical microcapsules possessed with rougher outer surface and the shell was about 1.5-2.0 µm thick with good methanol tolerance. Then, the formation of pre-polymer, shell material and microcapsules were revealed by FT-IR. Finally, experiments showed that the 2,4–D butyl ester CS exhibited a sustained releasing behavior in water, which could reach to 14 days.     

Synthesis of melamine‐formaldehyde polycondensates as the thermal stabilizer of polyoxymethylene through ultrasonic irradiation

Melamine (MA), as the formaldehyde (FA) absorbent of polyoxymethylene (POM), was polymerically modified by a condensation reaction with FA to form the melamine‐formaldehyde (MF) polycondensates with high molecular weight and comparatively high processing thermal stability. Ultrasonic irradiation was used for the synthesis, and ultrafine, crosslinked, and thermally stable MF polycondensates were obtained. The synthetic technique was discussed, and the thermal stabilization and nucleation effects of MF on POM were studied by the measurements of isothermal weight loss, balance torque, analysis of the formaldehyde emission amounts (FEAs), multiple extrusions, polarized light microscopy (PLM), isothermal and non‐isothermal differential scanning calorimetry (DSC), and scanning electron microscopy (SEM), which indicated that the thermal stability and the crystallization performance of POM was greatly enhanced by using MF as a thermal stabilizer and nucleation agent. The MF prepared using ultrasonic irradiation can improve the mechanical properties of POM more effectively compared with that prepared with normal mechanical stirring. Copyright © 2008 John Wiley & Sons, Ltd.     

Characterization of Plukenetia volubilis L. fatty acid-based alkyd resins

Fatty acid-based alkyd resins prepared with different amounts of glycerol and pentaerythritol were characterized. Sacha inchi oil and linseed oil (comparative purposes) were used as fatty acids’ sources. FT-IR and ¹H NMR spectroscopy were done for alkyd structural verification. Alkyd resins were evaluated through physico-chemical (colour, density, viscosity) and thermal characterization. Film coating performance (drying, hardness, chemical resistance) was also studied. The oxidative crosslinking time tendency was corroborated by the quartz crystal microbalance (QCM) technique. Alkyd resins obtained with fatty acids from sacha inchi and linseed oils had similar properties. Results indicated that lighter resins can be obtained from sacha inchi oil, whereas pentaerythritol increases viscosity and thermal stability, and retards drying time of fatty-acid based alkyd resins.     

苯基膦酸铈与十溴二苯醚在玻璃纤维增强聚对苯二甲酸乙二酯中的协同阻燃抑烟机理

采用熔融共混法制备了玻璃纤维增强聚对苯二甲酸乙二酯(PET-GF)/十溴二苯醚(DBDPO)/苯基膦酸铈(CeHPP)复合材料, 通过锥型量热仪(Cone)对复合材料的燃烧行为进行综合分析, 采用热失重-红外联用(TG-FTIR)分析了复合材料热降解过程中气体的释放量和主要成分, 并使用扫描电子显微镜(SEM)、 能量色散X射线光谱仪(EDX)和X射线光电子能谱(XPS)对复合材料燃烧后的残炭形貌、 残炭所含元素及含量等进行表征. 实验结果表明, 当CeHPP与DBDPO两者复配使用时, PET-GF/DBDPO/CeHPP复合材料的热解过程受到抑制, 凝聚相的燃烧减缓, 材料总的热分解量降低, 烟气释放量明显减小. 这主要是由于CeHPP在燃烧过程中形成了连续致密的残炭, 分布于基材和玻璃纤维表面, 将部分DBDPO及其分解产物滞留于凝聚相, 从而实现了气相-凝聚相双重阻燃作用, 有效阻隔了挥发性气体产物的释放.     

Preparation and Performance of Dual-functional Magnetic Phase-change Microcapsules

The fabrication of desired anti-magnetic materials for irradiation shielding remains a challenge to date. In this work, a new type of dual-functional magnetic shielding phase change microcapsules with paraffin as the core, melamine-formaldehyde (MF) resin as the shell and doped with magnetic particles in the shell were successfully prepared by in situ polymerization. The magnetic particles were dispersed in the shell layer by coating a hydrophilic emulsifier on the surface. These microcapsules were specifically applied to the field of magnetic shielding by the screen printing method. The effect of magnetic particles on the performance of phase-change microcapsules was examined by differential scanning calorimetry and thermogravimetric analyses. The magnetic type and magnetic strength of the microcapsules were studied by the vibrating sample magnetometer. Moreover, the effects of different magnetic particles (Fe₃O₄, CrO₂) on the performance of phase change microcapsules and the magnetic strength of microcapsules were compared. The results showed that these two kinds of magnetic particles can greatly improve the phase change latent heat, thermal stability, and thermal conductivity of the microcapsules. Finally, the great magnetic shielding role of these microcapsules was demonstrated in both static and pulsed magnetic fields through the screen printing of magnetic shielding ink on wallpaper. Incorporating 0.5 g Fe₃O₄ inside of microcapsules, specifically, the magnetic intensity was effectively reduced by ∼250 Oe within a short distance in the static field. We expect that these magnetic microcapsules hold great potential for the shielding of irradiations via the screen printing on various substrates.     

Thermal characterization of mangaba-based films

The purpose of this study was to evaluate the physical–chemical properties of starch (SF), mangaba (MF), and mangaba/starch-based films (MSF), using differential thermal analysis, thermogravimetry/derivative thermogravimetry, infrared spectroscopy, mechanical profile, and scanning electron microscopy. The films were prepared by casting process using sucrose and propyleneglycol as plasticizers. The thermal profiles of MF and MSF were similar and showed increased thermal stability. The mechanical properties of MF and MSF presented decreases of tensile strength and elastic modulus when compared with SF. The MSF showed the best thermal and mechanical characteristics.     

Preparation and characterization of poly(melamine-formaldehyde) microcapsules filled with propisochlor

A novel propisochlor microcapsules suspension (CS) was prepared via in-situ polymerization. The preparation of melamine-formaldehyde resin microcapsules containing propisochlor with different ratios of core-shell material was investigated. The synthesized microcapsules were characterized by Fourier Transform Infrared spectrometer, Scanning Electron Microscope, Ultraviolet spectrometry, Thermogravimetric analyses and particle size analyzer. As the ratio of core/shell was 1, the diameter of the prepared microcapsules was the smallest (3.55?µm), while narrowest size distribution (span: 1.19) and the melamine formaldehyde microcapsules possessed the highest encapsulation efficiency (93.26%). The surface of the microcapsules was smooth and the microcapsules had poor adhesion. These microcapsules had compact microstructures and global shapes, which had a good thermal stability and propisochlor could be preserved better in the poly(melamine-formaldehyde) (PMF) microcapsules. These results indicated that the prepared microcapsule had better performance. Additionally, the propisochlor was easily degraded through microorganisms and had a short half-life. The microcapsule suspension of propisochlor hasn’t been researched yet. Therefore, it is significant to prepare microcapsule suspension. The technology of controlled release has effectively prolonged the persistence of active ingredients. More importantly, there is no use of organic solvents in the preparation of microcapsules suspension, which avoided the pollution of solvents to the ecological environment.     

The thermal and dielectric properties of high performance cyanate ester resins/microcapsules composites

Novel high performance bisphenol A dicyanate ester (BADCy) resins/poly(urea-formaldehyde) microcapsules filled with epoxy resins (MCEs) composites have been prepared. The effects of different contents of MCEs on the thermal and dielectric properties of cured BADCy were investigated using dynamic mechanical analyzer (DMA), thermalgravimetric analyzer (TGA) and broadband dielectric analyzer. The dielectric properties of BADCy/MCEs treated in hot water and hot air were also discussed. The morphologies of BADCy/MCEs composites were characterized by scanning electron microscopy (SEM). Results indicate that the appropriate content of MCEs can improve or maintain the thermal stability, the low dielectric constant and dielectric loss of cured BADCy mainly owing to higher conversion of cyanate ester (-OCN) groups. After aged in hot water and hot air, respectively, BADCy/MCEs composites with small content of MCEs can retain the low dielectric constant and dielectric loss.     

Preliminary thermal characterization of natural resins from different botanical sources and geological environments

The preliminary studies on thermal behavior of differently aged natural resins from Russia (Khatanga), Dominican Republic (El Valle), Colombia and Poland (Jantar) were performed. Thermal stability and behavior under elevated temperature were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC), while the differences in the structure and composition by FT-IR spectroscopy. Analyzed resins show different thermal effects during heating suggesting that possible post-reactions and structural changes occurred. TG results indicated that Dominican, Russian and Colombian resins present relatively high thermal stability under air conditions in the range of 228–300 °C, whereas the mass loss of 5mass% at about 217 °C was observed for Baltic amber. During DSC experiments, the analyzed resins expose thermal events which make impossible determination of glass transition temperature in a raw sample. The results indicate that both TG and DSC cannot be considered as methods for age dating of natural resins and more advanced techniques should be applied. Careful analysis of FT-IR data in the carbonyl region may provide additional information about the composition and history of the natural resin.

     

Microencapsulation of capsaicin by solvent evaporation method and thermal stability study of microcapsules

With polylactic acid (PLA) as shell and capsaicin as core substances, microcapsules were prepared based on solvent evaporation method. The orthogonal test was used to analyze the effects of the process conditions such as polyvinyl alcohol and PLA concentrations, stirring rate, and oil/water ratio on the particle size of the microencapsulated capsaicin (MC) agents. The chemical composition, morphology and size distribution of the microcapsules prepared by the most satisfactory conditions were analyzed by Fourier transform infrared spectroscopy, laser light scattering, and scanning electron microscopy. The MC agents had a mean diameter of 3–5 μm. The thermal properties of the MC agents were measured by differential scanning calorimetry and thermogravimetric analysis, it was demonstrated that the thermal stability of the MC agents was changed or even improved by the encapsulated PLA over the surface, when compared with similar parameters of the uncovered capsaicin. The in vitro release profile suggested that the microcapsules could be a suitable material for controlled release of capsaicin.     

Preparation, Curing Reactivity and Thermal Properties of Titanium-doped Silicone Resins

Novel titanium-doped silicone resins were synthesized from low-cost silane monomers and tetrabutyl titanate as raw materials and hydrochloric acid as catalyst, with titanium element as dopant into principal chain of Si-O-Si. The resins were characterized by means of FTIR, 1 H NMR and 13 C NMR spectra, their thermal properties and curing properties were investigated and their corresponding films were determined. The results show that the thermal stability and storage stability of the resins were influenced by the types of silane monomers containing different carbon atomicities of organic group. The thermal stability of the titanium-doped silicone resin with a molar ratio of silane monomer B(n-propyl triethoxysilane) to silane monomer C(n-octyl triethoxysilane) being 1:1 is superior to that of the resin with a molar ratio of silane monomer B to silane monomer C being 1:3. However, the storage stability of the former is inferior to that of the latter.This work also showed that the synthesized titanium-doped silicone resins have the highest thermal stability up to 450―500 °C with an atomicity molar ratio of 1:4 of titanium to silicon in the reactants. But the best storage stability of the resin prepared from the reactants with an atomicity molar ratio of 1:6[n(Ti):n(Si)] was obtained. The effect of the type and content of curing agent on the curing properties of the resin was also studied. Moreover, thermal mechanism and curing mechanism were proposed in this work.     

Enhanced thermal properties and flame retardancy from a thermosetting blend of a phosphorus‐containing bismaleimide and epoxy resins

Epoxy resins modified by an organosoluble phosphorus‐containing bismaleimide (3,3′‐bis(maleimidophenyl) ­phenylphosphine oxide; BMPPPO) were prepared by simultaneously curing epoxy/diaminodiphenylmethane (DDM), and BMPPPO. The resulted epoxy resins were found to exhibit glass transition temperatures as high as 212 °C, thermal stability at temperatures over 350 °C, and excellent flame retardancy with Limited oxygen index (LOI) values around 40. Incorporation of BMPPPO into epoxy resins via the thermosetting blend was demonstrated to be an effective way to enhance the thermal properties and flame retardancy simultaneously. Copyright © 2003 John Wiley & Sons, Ltd.