Carbon fiber/epoxy composite materials cured thermally and with microwave irradiation

In this paper, composite materials of short carbon fibers (CFs) and a thermosetting epoxy were prepared in three different ways: without curing, thermal curing, and thermal curing followed by microwave irradiation. Mechanical properties of the three kinds of CF reinforced plastic (CFRP) composites were studied to explore the effect of microwave irradiation. Microscopic study with the aid of a scanning electron microscope (SEM) was performed on fractured composite surfaces to identify the principle features of failure. Degree of polymerization of the epoxy resin in the three CFRP composites was evaluated by infrared (IR) spectroscopy. The microwave irradiated CFRP exhibited mechanically ductile behavior even though its highest degree of polymerization. Use of microwaves and resultant stronger physico-chemical linkage at the interface between CF and epoxy resin are the main feature of this study.     

Effect of sonication on nitroxide-controlled free radical polymerization of styrene

Effect of sonication on the autopolymerization of styrene in the presence of 2,2,6,6-tetramethylpiperidinyl-1-oxy as the mediating radical was investigated at 110-135 degrees C. The thermal polymerization under sonication proceeded in the manner of a "living" radical polymerization to afford well-defined polystyrene. The sonication was found to decrease the induction period and increase the polymerization rate.     

Photothermal monitoring of curing in multilayered systems

In this work the process of a curing layer buried inside two external layers is monitored in real time using photothermal radiometry. The curing materials studied are two adhesives and a UV curing resin. It is shown that the curing process can be observed in all the cases as an increase in the thermal diffusion coefficient of the buried sample. It is shown that the kinetic behavior of the adhe- sives is very similar, probably due to the fact that evaporation is the main mechanism that generates the curing contrary to what happens in the UV curing resin where the light flux is the determining factor that induces the polymerization.     

Effect of ultrasonic frequency on polymerization of styrene under sonication

The effect of ultrasonic frequency on polymerization of styrene under sonication at 50 degrees C was studied at the frequencies of 23.4, 45.7, 92, 518 kHz and 1 MHz. Polymerization under sonication was carried out at the ultrasonic intensity that gives the same reaction rate of decomposition of porphyrin. The magnitude of the polymerization rate increases in the order of 92, 45.7 and 23.4 kHz. At the high frequencies of 518 kHz and 1 MHz, no polymerization was observed. These facts mean that there is an optimum frequency in the range from 92 to 518 kHz for effective polymerization. The average-number molecular weights at the sonication time of 3 h are 5.5 x 10(4), 8.0 x 10(4) and 11.5 x 10(4) for the irradiated frequencies of 92, 45.7 and 23.4 kHz, respectively. Sonication for 3 h at 92 kHz gives polystyrene with very high polydispersity, about 5.0, in comparison with the results obtained at 23.4 and 45.7 kHz. These observations indicate that polymerization under sonication is influenced by the irradiated frequency.     

Kinetic parameters and monomeric conversion of different dental composites using standard and soft-start photoactivation modes

This paper evaluates the photopolymerization kinetics and degree of conversion of different commercial dental composites when photoactivated by a LED curing unit using two different modes (standard and soft-start mode). The investigation was performed on with RelyX ARC (dual-cured), Filtek Z-350 (Nanocomposite), Filtek Z-250 (Hybrid), and Filtek Z-350flow (Flowable) resin composites. The analysis used was attenuated total reflection with a Fourier transform infrared (ATR-FTIR). The RelyX ARC resin demonstrated the highest degree of conversion with both LED photoactivation modes. For this resin a 28% decrease in maximum rate was observed and the time to reach its highest rate was almost 2.3 times higher than when the soft-start photoactivation light curing was used. Z-350flow resin recorder a higher maximum rate using the soft-start mode rather than the standard mode. In contrast, the Z-250 showed a higher value using the standard mode. Although Z-250 and Z-350 showed a higher total degree of conversion effectiveness using the soft-start mode, RelyX and Z-350flow achieved a higher value using the standard mode.     

Improvement in properties of coal water slurry by combined use of new additive and ultrasonic irradiation

Coal water slurry (CWS) was prepared with a newly developed additive from naphthalene oil. The effects of ultrasonic irradiation on coal particle size distribution (PSD), adsorption behavior of additive in coal particles and the characteristics of CWS were investigated. Results showed that ultrasonic irradiation led to a higher proportion of fine coal in CWS and increased the saturated adsorption amount of additive in coal particles. In addition, the rheological behavior and static stability of CWS irradiated by ultrasonic wave were remarkably improved. The changes on viscosity of CWS containing 1% and 2% additive are qualitatively different with the increasing sonication time studied. The reason for the different effect of sonication time on CWS viscosity is presented in this study.     

Effect of pre-heating resin composite and light-curing units on monomer conversion

The purpose of this study was to evaluate the effect of pre-heating resin composite photo-cured with light-curing units (LCU) by FT-IR. Twenty specimens were made in a metallic mold (4 mm diameter × 2 mm thick) from composite resin—Tetric Ceram® (Ivoclar/Vivadent) at room temperature (25°C) and pre-heated to 37, 54, and 60°C. The specimens were cured with halogen curing light (QTH) and light emitted by diodes (LED) during 40 s. Then, the specimens were pulverized, pressed with KBr and analyzed with FT-IR. The data were submitted to statistical analysis of variance and Kruskal-Wallis test. Study data showed no statistically significant difference to the degree of conversion for the different light curing units (QTH and LED) (p > 0.05). With the increase of temperature there was significant increase in the degree of conversion (p < 0.05). In this study were not found evidence that the light curing unit and temperature influenced the degree of conversion.     

Preparation of conducting polyaniline colloids under ultrasonication

The effects of ultrasonication on the chemical polymerization of aniline leading to the formation of conducting polyaniline colloids were examined. The formation rate of the colloids was significantly increased under ultrasonication. Furthermore, it was also observed that the morphological structure of the colloids thus prepared was greatly affected by the sonication. The polyaniline colloids were further characterized by a range of techniques including electric resistance meter, gel permeation chromatography, FT-IR and cyclic voltammetry. It is noteworthy that the application of ultrasound to the polymerization resulted in a marked increase in the doping level, which reflected to the high electroconductivity of polyaniline colloids.     

Changes in the temperature of a dental light-cured composite resin by different light-curing units

The purpose of this study was to evaluate the temperature increase during the polymerization process through the use of three different light-curing units with different irradiation times. One argon laser (Innova, Coherent), one halogen (Optilight 501, Demetron), and one blue LED (LEC 1000, MM Optics) LCU with 500 mW/cm² during 5, 10, 20, 30, 40, 50, and 60 s of irradiation times were used in this study. The composite resin used was a microhybrid Filtek Z-250 (3M/ESPE) at color A₂. The samples were made in a metallic mold 2 mm in thickness and 4 mm in diameter and previously light-cured during 40 s. A thermocouple (Model 120–202 EAJ, Fenwal Electronic, Milford, MA, USA) was introduced in the composite resin to measure the temperature increase during the curing process. The highest temperature increase was recorded with a Curing Light 2500 halogen LCU (5 and 31°C after 5 and 60 s, respectively), while the lowest temperature increase was recorded for the Innova LCU based on an argon laser (2 and 11°C after 5 and 60 s, respectively). The temperature recorded for LCU based on a blue LED was 3 and 22°C after 5 and 60 s, respectively. There was a quantifiable amount of heat generated during the visible light curing of a composite resin. The amount of heat generated was influenced by the characteristics of the light-curing units used and the irradiation times.     

用布喇格光纤光栅传感器测定口腔复合树脂材料光固化收缩与温度演化特性

复合树脂材料已成为重要的牙齿美容修复材料.本文利用两种布喇格光纤光栅传感器测定了口腔复合树脂材料在光固化过程中的收缩与温度演化特性.一种为普通的光纤布喇格光栅,另一种为经过了化学镀镍的光纤布喇格光栅,同时埋入复合树脂样品中,用光照射使其固化,测得光纤布喇格光栅在固化过程中温度和应力随时间的演化曲线.实验结果表明,在光固化过程中,因为聚合反应,树脂产生了强烈的收缩应力和温度变化.掌握复合树脂的光固化收缩特性和温度变化特性对不断改良材料性能以及优化口腔材料的治疗效果具有实际意义.     

Experimental data and model predictions of aluminium agglomeration in ammonium perchlorate-based composite propellants including plateau-burning formulations

Sixteen propellant formulations based on ammonium perchlorate (AP), hydroxyl-terminated polybutadiene, and aluminium particles have been tested for size distribution of aluminium agglomerates emerging from their burning surface. The formulations are based on a bimodal size distribution of AP particles. Ten of the formulations exhibit one or two plateaus/mesa in their burning rate variation with pressure (zero/negative pressure exponent of burning rate). The relevant formulation variables, namely, coarse and fine AP sizes and coarse-to-fine ratio, aluminium size and content, and two different curing agents, have been varied. Tests are performed in the 1–10 MPa pressure range. A direct correlation between burning rate and agglomerate size exists for propellants with normal burning rate trends but a neutral or inverse correlation is observed for those exhibiting plateau burning behaviour. Larger the parent aluminium size, lesser the agglomeration, as expected; but the effect of aluminium content is non-monotonic. The coarse AP size influences the aluminium agglomerate size as expected from the pocket model regardless of plateau burning effects. The agglomerate size decreases with increase in fine AP size, however. A computer model developed earlier at this laboratory for prediction of aluminium agglomerates based on three-dimensional packing of particles and deduction of AP particles with attached leading edge diffusion flames is applied to the present formulations. The model under-predicts the agglomerate size, only marginally for propellants that do not exhibit plateau burning rate trends, but substantially, otherwise. This is because it does not take into account effects of binder melt flow and is independent of the curing agent of the binder.     

基于XRD和SEM的含碳微细粒金矿氧化焙烧机理研究

含碳微细粒金矿是世界难处理金矿主要类型,且储量巨大,矿石中的有机碳、石墨碳能吸附溶液中的金氰络合物,因而含碳金矿在浸出之前需进行预处理。氧化焙烧是应用时间最长、可靠性和适应性最好的预处理工艺,已经成功的用于生产实践。针对传统氧化焙烧法存在生产成本高,收尘系统复杂等不足,近年来国内外学者在焙烧工艺和设备方面进行了大量的研究工作,取得了丰硕的研究成果,为氧化焙烧技术的发展注入了新的活力。但关于焙烧理论方面的研究较少,研究方法也比较单一,尤其是对于焙烧过程的相关理论研究比较薄弱,这在一定程度上影响了氧化焙烧技术的发展。焙烧时间是影响焙烧效果的关键因素,决定化学反应进度及物相变化程度。在不同时间条件下(焙烧温度650 ℃),对含碳微细粒金矿石进行焙烧-浸出试验,首次采用X射线衍射(XRD)、扫描电镜(SEM)、能谱分析(EDS)和孔结构分析等手段对含碳金矿及焙砂进行分析表征,进而揭示氧化焙烧过程中碳质物的氧化、矿石晶体结构变化、物相变化等对金浸出效果的影响机理。工艺矿物学研究表明： 矿石中主要矿物有石英、白云石、方解石、绢云母、高岭石、黄铁矿和石墨等;矿石中自然金粒度微细,以5～10 μm粒级为主,部分微粒自然金被石英、碳质组成的碎屑包裹;碳质(有机碳和石墨碳)含量高、粒度细,且与脉石矿物紧密共生。焙烧-浸出试验结果表明： 原矿直接浸出时,金浸出率仅为12.50%,碳质的“劫金”作用显著;随着焙烧时间的增加,金的浸出率先逐渐增大后变化平稳,焙烧时间为2 h时,金浸出率最高;当焙烧时间为1 h 时,绢云母发生了脱羟基变化,高岭石分解生成蒙脱石,黄铁矿氧化为赤铁矿,碳质(有机碳和石墨碳)氧化且产生CO₂,但未完全氧化,此时焙砂中石英的d₁₀₀和d₁₀₁值以及平均孔径较小,不利于浸出剂的扩散,导致金浸出率仅为58.09%;当焙烧时间为1.5 h 时,白云石开始分解,碳质已完全燃烧,产生的CO₂使微孔数量增多,有利于浸出剂的扩散,此时金浸出率增加到73.34%;当焙烧时间为2 h时,白云石分解较完全,焙砂中有MgO生成,此时焙砂中石英的d₁₀₁值达到最大值(4.255 03 nm),焙砂松散密度变大且孔容和平均孔径达到最大值,分别为0.009 954 cm3·g-1和6.640 80 nm,焙砂中产生的微孔最多,增加了浸出剂的扩散通道,有利于金的浸出,金浸出率也达到了最大值(91.28%);当焙烧时间为3 h时,焙砂表面生成Ca₂SiO₄和CaSO₄等在高温时易形成低熔点物质,发生微弱的烧结现象,导致颗粒内部的微孔被填充、闭合,微孔减少,孔容和平均孔径降低,内部结构变得致密,不利于浸出剂的扩散,同时造成金的浸出率下降。     

Changes on degree of conversion of dual-cure luting light-cured with blue LED

The indirect adhesive procedures constitute recently a substantial portion of contemporary esthetic restorative treatments. The resin cements have been used to bond tooth substrate and restorative materials. Due to recently introduction of the self-bonding resin luting cement based on a new monomer, filler and initiation technology has become important to study the degree of conversion of these new materials. In the present work the polymerization reaction and the filler content of dual-cured dental resin cements were studied by means of infra-red spectroscopy (FT-IR) and thermogravimetry (TG). Twenty specimens were made in a metallic mold (8 mm diameter × 1 mm thick) from each of 2 cements, Panavia® F2.0 (Kuraray) and RelyX? Unicem Applicap (3M/ESPE). Each specimen was cured with blue LED with power density of 500 mW/cm² for 30 s. Immediately after curing, 24 and 48 h, and 7 days DC was determined. For each time interval 5 specimens were pulverized, pressed with KBr and analyzed with FT-IR. The TG measurements were performed in Netzsch TG 209 under oxygen atmosphere and heating rate of 10°C/min from 25 to 700°C. A two-way ANOVA showed DC (%) mean values statistically significance differences between two cements (p < 0.05). The Tukey’s test showed no significant difference only for the 24 and 48 h after light irradiation for both resin cements (p > 0.05). The Relx-Y? Unicem mean values were significantly higher than Panavia® F 2.0. The degree of conversion means values increasing with the storage time and the filler content showed similar for both resin cements.     

Ultrasound assisted lipase catalyzed synthesis of poly-6-hydroxyhexanoate

Ultrasonic irradiation greatly improved the Candida antarctica lipase B mediated ring opening polymerization of ε-caprolactone to poly-6-hydroxyhexanoate in the ionic liquid 1-ethyl-3-methylimidazolium tetraflouroborate. Compared to the conventional nonsonicated reaction, sonication improved the monomer conversion by 63% and afforded a polymer product of a narrower molecular weight distribution and a higher degree of crystallinity. Under sonication, the polydispersity index of the product was ∼1.44 compared to a value of ∼2.55 for the product of the conventional reaction. With sonication, nearly 75% of the monomer was converted to product, but the conversion was only ∼16% for the reaction carried out conventionally. Compared to conventional operation, sonication enhanced the rate of polymer propagation by >2-fold and the turnover number of the lipase by >3-fold.     

Sonolysis of synthetic sediment particles: particle characteristics affecting particle dissolution and size reduction

The effect of ultrasound on particle shape and surface structure was explored to understand particle characteristics affecting contaminant desorption and destruction from sediment particles. Compared to only hydrodynamic mixing, in the presence of an ultrasonic probe, operating at 20 kHz with a power density of 460 Wl-1, sonication decreased the particle size of alumina and silica particles following a first-order regime. In addition, the dissolution of particles during sonication is 7-20 times higher than that of non-sonicated solutions. However, the decrease of particle size was not totally explained by dissolution. Scanning electron microscopy studies showed that the surface of particles both became smoothed and pitted as a result of sonication. Therefore, it seems that multiple mechanisms are occurring simultaneously; microstreaming acts to smooth particle surfaces and dissolve particles and shockwaves and microjets imploding on the particle surfaces both shear and pit the surface of the particles. The sonication of humic acid laden particles resulted in a similar decreasing trend. However, the existence of humic acid increased the complexity of the system.     

Combined ultrasound and germination treatment on the fine structure of highland barley starch

Highland barley is a grain crop grown in Tibet, China. This study investigated the structure of highland barley starch using ultrasound (40 kHz, 40 min, 165.5 W) and germination treatments (30℃ with 80% relative humidity). The macroscopic morphology and the barley's fine and molecular structure were evaluated. After sequential ultrasound pretreatment and germination, a significant difference in moisture content and surface roughness was noted between highland barley and the other groups. All test groups showed an increased particle size distribution range with increasing germination time. FTIR results also indicated that after sequential ultrasound pretreatment and germination, the absorption intensity of the intramolecular hydroxyl (–OH) group of starch increased, and hydrogen bonding was stronger compared to the untreated germinated sample. In addition, XRD analysis revealed that starch crystallinity increased following sequential ultrasound treatment and germination, but a-type of crystallinity remained after sonication. Further, the Mw of sequential ultrasound pretreatment and germination at any time is higher than that of sequential germination and ultrasound. As a result of sequential ultrasound pretreatment and germination, changes in the content of chain length of barley starch were consistent with germination alone. At the same time, the average degree of polymerisation (DP) fluctuated slightly. Lastly, the starch was modified during the sonication process, either prior to or following sonication. Pretreatment with ultrasound illustrated a more profound effect on barley starch than sequential germination and ultrasound treatment. In conclusion, these results indicate that sequential ultrasound pretreatment and germination improve the fine structure of highland barley starch.     

An Insight into the Diffusion of Unsaturated Polyester (UP) Resin into Expanded Graphite (EG) to Improve the Mechanical Properties of the UP/EG Composites

Abstract

Polymer/expanded graphite (EG) nanocomposites have great importance in many industrial applications mainly due to their high electrical/thermal conductivity or flame retardancy. However, to fully employ the benefits of polymer/EG nanocomposites one must consider the high degree of porosity of EG. The high degree of porosity of EG can deteriorate the composites’ mechanical properties if the polymer chains cannot diffuse completely into the EG pores. In this article, an insight is given into the diffusion of unsaturated isophthalic polyester (UP) resin, consisting of a combination of maleic anhydride and isophthalic anhydride in the resin backbone, with two viscosities, into the pores of the EG particles of various degrees of porosity. The diffusion experiments were carried out on compressed EG tablets with the same density but different porosity due to the different porosity of the EG particles. The results showed that the diffusion rate of the UP resin with higher viscosity slightly decreased when the EG porosity decreased but, in the opposite way, it strongly increased for the low viscosity UP resin. The EG nanocomposites samples were molded at varying pressures. The micrographs of the fractured surfaces of the EG nanocomposites showed that the EG pores were not filled with resin, thus the EG nanocomposites had residual pores. It was found that composites containing EGs with higher expansion ratio and larger particles and pores showed larger residual pores. Furthermore, the composites prepared with the more viscous UP resin showed more residual pores. By applying a pressure of 10?bar instead of 1?bar, a reduction of 7–20% in the residual pores of the nanocomposites was observed which led to improved mechanical properties by up to 20% in flexural strength for the EG with the highest expansion ratio.     

Degradation of azo dye direct sky blue 5B by sonication combined with zero-valent iron

The degradation of azo dye direct sky blue 5B by sonication combined with zero-valent iron (US-Fe(0))was investigated and an evident synergistic effect was observed. The synergetic effect is mainly due to the increase of ()OH radical concentration from Fenton's reaction. The ()OH radical concentrations in sole sonication and US-Fe(0) process were detected by using terephthalic acid as a fluorescent probe and found that ()OH radicals were generated continuously during sonication and the production of ()OH radicals in US-Fe(0) process was much higher than that in sole sonication. The degradation of direct sky blue 5B followed a pseudo-first-order kinetics and the degradation rate constants were found to be 0.0206 and 0.169 min(-1) with sole sonication and US-Fe(0) process respectively. It was also found that the degradation ratio of direct sky blue 5B increased with the increase of zero-valent iron dosage and decrease of pH value of the dye aqueous solution. The degradation mechanism of direct sky blue 5B with US-Fe(0) process was discussed by the changes of UV-Vis spectrogram of the dye during degradation. The dramatic changes of UV spectra showed a disappearance of both azo and aromatic groups during the degradation.     

Electrostatic powder spraying process for the fabrication of stable superhydrophobic surfaces

Nano-sized Al₂O₃ particles were modified by heptadecafluorodecyl trimethoxysilane and 2,3-epoxy propoxy propyl trimethoxysilicane to make it both hydrophobic and reactive. The reactive nano-particles were mixed with polyester resin containing curing agents and electrostatic sprayed on stainless steel substrates to obtain stable superhydrophobic coatings after curing. The water contact angle (WCA) on the hybrid coating is influenced by the content of Al₂O₃ particles in the coating. As the Al₂O₃ concentration in the coating was increased from 0% to 8%, WCA increased from 68° to 165°. Surface topography of the coatings was examined using scanning electron microscopy (SEM). Nano-particles covered on the coating surface formed continuous film with greatly enhanced roughness, which was found to be responsible for the superhydrophobicity. The method is simple and cost effective and can be used for preparing self-cleaning superhydrophobic coating on large areas.     

NMR study of liquid crystalline polymer curing in magnetic field

Effect of magnetic field on curing a cross-linked polymer based on diglycidyl ester of terephthaloyl-bis (4-hydroxy benzoic acid) in liquid crystalline (LC) state was studied using NMR. The magnetic field was shown to inhibit anionic polymerization. In the course of spontaneous curing the order degree decreased to 0.5 whereas at anionic polymerization the complete disordering was attained. The ordering of the liquid crystalline polymer can be conserved in anionic polymerization if it is performed under controlled temperature conditions.