The effect of processing conditions on the microstructure of embossed polyethylene films

Film embossing is a mechanical process in which a flat film is transformed into an embossed product. During the process, thermal and stress fields are applied Lo the polymer, causing changes in the microstructure and physical dimensions of the material. The engineering analysis of the process requires the study of various aspects relating to the characterization of the microstructure before and after embossing, A variety of techniques were employed to characterize the properties and microstructure of the embossed film in relation to: crystallinity, orientation, mechanical properties, and dimensions of the embossed films. The thermal treatment of the polymer film was shown to be the most significant factor in the process. By controlling the thermal treatment of the film, it is possible to manipulate the properties and dimensions of the embossed film. The important aspects: influencing thermal treatment include the radiation heater temperature, preheat roll temperature, line velocity, and film thickness. The initial film orientation and embossing pressure have a minor effect on the final properties of the embossed film. The main effect of the embossing pressure is on the bulk thickness of the embossed film.     

The effect of processing conditions on phase and microstructure of CaGeO3 ceramics

The present study illustrates the effects of processing conditions on phase and microstructure of CaGeO₃ ceramics. It is shown that the fabrication of single phase, high density and crack-free CaGeO₃ ceramics is particularly challenging using conventional sintering or spark plasma sintering. The main difficulties in achieving single phase are predominantly related to the segregation of an additional phase identified as Ca₅Ge₃O₁₁, most likely driven by the volatilization of GeO₂ during processing at high temperature. This can be mainly suppressed by adding an appropriate excess amount of GeO₂. High density can be achieved by conventional sintering and spark plasma sintering (SPS), but in the temperature ranges that lead to the formation of Ca₅Ge₃O₁₁. The presence of cracks observed in the ceramics is attributed to the development of local residual stresses caused by the anisotropy of the thermal expansion and elastic properties, and it can be avoided under certain SPS conditions.     

Characterization of microstructure and surface properties of heat-treated PAN-and rayon-based activated carbon fibers

Polyacrylonitrile- and rayon-based activated carbon fibers (ACFs), subject to heat treatment over 600–1,100°C under N₂ flow, were investigated using a number of surface analytical methods, including N₂ adsorption isotherm, elemental analysis, and X-ray photoelectron spectroscopy. The adsorption capacities of benzene, carbon tetrachloride, and water vapor on as-received and heat-treated ACFs were determined. Results show that the ACFs under study were highly microporous but heat-treated ACFs contained more mesopores in the range of 20–30 Å for PAN-based and 30–45 Å for rayon-based. It can be seen that the high-resolution α_s plot provided valuable information about structure properties. The pore size distributions of ACFs gave insight into the pore development with heat treatment temperature. Besides, phenolic groups were found to be the most abundant oxygen-containing functional groups on the surface of both ACFs. The vapor adsorptions on ACFs indicated that molecular size and polarity of vapors, as well as the microstructure and chemistry of ACFs profoundly influenced the adsorption performance.     

The effect of processing conditions on carbon nanostructures formed on an iron-based catalyst

The carbon nanostructures formed during chemical vapour deposition (CVD) of ethene and hydrogen over an iron(III) oxide catalyst precursor have been investigated. Graphitic nanofibres and carbon nanotubes were both observed during synthesis, with the structures observed depending on the temperature and gas mix (C₂H₄ and H₂) used. Mixtures ranging from 100% to 5% ethene in hydrogen were investigated at different temperatures. During the synthesis, the iron(III) oxide was transformed into iron carbide (Fe₃C). The samples were characterised using transmission electron microscopy and X-ray diffraction. Filamentous nanostructures were observed with high hydrogen content (?80%) in the gas stream, whereas no filamentous structures were observed with ?20% H₂. The temperature of synthesis was varied between 500 and 800 °C, with higher temperatures giving higher carbon deposition rates, but also affected the nanostructures observed. However, it was found that increasing the temperature during CVD did not change the type of carbon deposited but did increase the deposition rate, providing a route to increase growth yields for a desired type of carbon nanostructure.     

Influence of processing conditions on adhesion between carbon fibers and electron-beam-cured cationic matrices

Adhesion between an electron-beam-cured Diglycidyl Ether of Bisphenol A (DGEBA) epoxy matrix and AS4 carbon fibers has been evaluated with the microindentation test method and compared with similar thermally cured materials. The results indicate that the absence of amine compounds and of high temperature treatment associated with thermally cured epoxy matrices are detrimental to fiber-matrix adhesion in electron-beam-cured epoxy matrices when measured by the microindentation test. Electron beam processing was not found responsible for any adsorption and/or deactivation of the irradiated carbon fiber surface as determined by surface analysis with X-ray Photoelectron Spectroscopy (XPS). Moreover, the relationship between electron-beam processing conditions (namely, dose and dose increment) with the resulting matrix properties and the adhesion to carbon fiber have revealed a strong dependency of fiber-matrix adhesion on the bulk matrix properties independent of the electron beam processing history. Undercured electron-beam-processed matrices exhibit higher adhesion to carbon fibers that can be explained by a higher matrix shear modulus.     

酚醛基活性碳纤维

酚醛树脂属于难石墨化碳，适宜制造活性碳纤维(ACF)，其特点是碳化活化收率高，制品强度高，比表面积大，孔径分布属于单峰形，吸附容量大；细孔入口形状属于狭缝形，吸脱速度快；制品柔软，深加工性好，它除用于治理环境污染外，还可用于制作防化防毒服和制造超级电容器等。     

The effect of electro-degradation processing on microstructure of polyaniline/single-wall carbon nanotube composite films

Mesostructured polyaniline/single-wall carbon nanotube (PAni/SWCNT) composite film has been prepared through electrochemical polymerization/degradation processing. The microstructures of the films are observed before and after electro-degradation. Initial twisty SWCNT bundles are broken down and linked by the polymerization of PAni. Both crystalline and disordered PAni regions coexist in the PAni/SWCNT composite nanowires. The disordered regions are gradually dissolved while the crystalline regions are basically preserved after electro-degradation. The formation mechanism of the composite with special construction has been proposed. In addition, cyclic voltammetry measurements demonstrate that the electroactive performance of PAni/SWCNT composite is enhanced after electro-degradation. It is found that the specific capacitance of electro-degraded composite reaches up to 848.7 F/g, more than twice over the untreated film, which is ascribed to its profitable charge accessible interface and increased available crystalline PAni regions.     

Oxidative dehydrogenation of ethylbenzene on activated carbon fibers

Activated carbon fibers from different precursors and with different degrees of activation were used as catalysts for the oxidative dehydrogenation of ethylbenzene. Within each group, the fibers exhibited similar surface chemistries, so that the observed catalytic performances could be interpreted exclusively in terms of their textural properties. Analysis of the catalytic results highlighted common trends. In particular, the fibers with an average micropore width larger than 1.2 nm were found to be the best catalysts for this reaction.     

Synthesis and microstructure of iridium coatings on carbon fibers

Uniform, adherent, and non-bridging iridium coatings were applied to polyacrylonitrile-derived (ex-PAN) carbon fibers using low temperature metal organic chemical vapor deposition (MOCVD) from iridium (III) acetylacetonate. Composition, morphology, texture and topography of the iridium coated carbon fibers depending on MOCVD parameters have been studied by scanning electron microscopy/energy dispersive spectroscopy, atomic force microscopy, X-ray diffraction and extended X-ray absorption fine structure (EXAFS). For the MOCVD parameters studied, metallic iridium is the main phase of the coating. Together with iridium, a carbon-containing phase can be also present in the coating. The interatomic distances, corresponded coordination numbers and structural/microstructural parameters were established. The dependence of the microstructure of the Ir-coated carbon fibers on MOCVD parameters and possible structural models are discussed in detail. EXAFS showed that the Ir–O chemical bond on the boundary between the carbon fiber and the iridium coating is either absent or its contribution is too small to be detected by this method. Iridium appears to be bound to carbon fiber only by van der Waals forces. The data obtained by all methods are in a good agreement.     

The effect of molecular composition and structure on the development of porosity in pitch-based activated carbon fibers

Seven oligomeric fractions of well-defined composition and molecular weight distribution were generated via supercritical extraction from an isotropic petroleum pitch (M-50) and used as precursors for the production of activated carbon fibers. Both isotropic and mesophase-containing fractions were produced, so that the effects of molecular order and molecular weight could be separated. Carbonization weight loss was found to gradually decrease with increasing molecular weight (and oligomeric number), with mesophase content not being a significant factor. Similar behavior was observed for activation weight loss when the precursors were isotropic; however, even modest increases in molecular order significantly retarded the activation process and resulted in dramatic drops in specific pore volume. A 100% dimer precursor fraction with an average molecular weight of 480 Da produced activated carbon fibers with the highest (specific) pore volume, and the highest pore volume in the range desired for hydrogen adsorption (6–7 Å). Even for isotropic precursors, decreases in pore volume with increasing molecular weight were observed. The incremental pore size distribution generated from the nitrogen adsorption data consisted of discrete peaks, which is consistent with the formation of pores by the removal of short micrographene layers, with each layer being formed from an individual oligomeric molecule.     

Studies on the structure of activated carbon fibers activated by phosphoric acid

By solid‐state ¹³C‐ and ³¹P‐NMR, XPS, and FTIR, the chemical structure of activated carbon fiber–P (ACF‐P) and its reaction with phosphoric acid were studied. Even when activated at low temperatures, these fibers developed a graphitelike carbon structure with a certain amount of phenol groups as well as acetal (or methylenedioxy) carbon. As expected, the oxygen‐containing groups were greatly reduced at high activation temperatures. Different from the ACF‐W, metaphosphoric acid (or polyphosphates) and a small amount of phosphorus exist on ACF‐P. The original ACF‐P activated at low temperature contained a lot of phosphoric acid, so it had to be washed with water to expose the large surface area. The washing process can be omitted for ACF‐P activated at high temperature because most phosphorus compounds in fiber have volatilized. The ACF‐P activated at lower temperature possessed a large amount of oxygen‐containing surface groups and had enhanced adsorption ability for polar adsorbates. The remaining of metaphosphoric acid enhanced the adsorption of silver ion. The experimental results showed that the peaks of ³¹P‐NMR, P_2p‐XPS, and FTIR at 1620 cm^?1 shifted with the increase of activated temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2253–2261, 2003     

沥青基活性碳纤维动态吸附甲苯的性能

以通用级沥青基碳纤维为原料,采用钴盐催化活化法,通过改变活化剂用量和活化时间制备出不同的活性碳纤维。研究了活性碳纤维的动态吸附甲苯以及再生性能。结果表明,活性碳纤维是一种优秀的甲苯吸附材料,其饱和吸附量受比表面积和孔径及其分布的影响。活性碳纤维对甲苯的动态吸附量达到1250 mg/g。20次吸脱附循环再生后,吸附量仍保持在900 mg/g。     

Defluorination-enhanced hydrogen adsorptivity of activated carbon fibers

Fluorinated activated carbon fibers (F-ACFs) were prepared by direct thermal fluorination of pristine activated carbon fibers. By the pyrolysis of F-ACFs at 1073 K under nitrogen gas flow, fluorine was subsequently eliminated and the sp²-bonded ACF structures were recovered. The micropore widths were 1.1 and 0.8 nm, and the isosteric heats of adsorption of nitrogen were 11.3 and 12.8 kJ/mol for pristine and defluorinated ACFs, respectively. These results strongly suggest that changes occurred in the structural properties of micropores in defluorinated ACFs. The hydrogen adsorption isotherms showed that the defluorinated ACFs adsorbed more hydrogen gas than pristine ACFs at 77 K, suggesting that the potential for interaction between hydrogen molecules and the defluorinated slit nanospaces was increased due to the changes in the pore structural properties and/or to the induced polarization of the pore walls making up the modified π-electron systems.     

活性炭纤维用于苦卤脱色的研究

采用活性炭纤维（ACF）对海盐苦卤进行吸附脱色实验.通过动态吸附实验,探讨了活性炭用量、溶液流速、温度、浓度、pH对脱色率的影响.确定活性炭纤维对苦卤溶液脱色的最佳工艺条件为：温度20 ℃,苦卤溶液浓度（以溶液中X-计）为2 mol/L,溶液pH＝6,动态吸附流速为6 mL/min.在此条件下,苦卤脱色率大于98%.活性炭纤维对海盐苦卤的饱和吸附量比颗粒活性炭大10倍.吸附后的活性炭纤维加热到120 ℃并抽真空进行脱附,可循环使用18次以上.     

Electrochemically enhanced adsorption of aniline on activated carbon fibers

For adsorptive separation processes, the adsorption rate and capacity are two important factors affecting the costs. This study describes the anodic polarization of activated carbon fibers (ACFs), which can enhance the adsorption rate and capacity of aniline. The electrosorption kinetics and the affecting factors (bias potential, electrolyte, and pH) of isotherms for aniline on ACFs were investigated. The adsorption/electrosorption of aniline on ACFs follow pseudo-first-order adsorption kinetics, and the adsorption rate improves with increasing bias potential. The electrosorption isotherms, which exhibit a variety of responses depending on bias potential, electrolyte and pH, follow the two classical models of Langmuir and Freundlich. With electrosorption of aniline from aqueous solution, a two-fold enhancement of adsorption capacity is achievable. The initial and saturated ACFs were characterized using scanning electron micrograph (SEM) and Fourier transform infrared spectroscopy (FT-IR). The SEM micrographs show that the surface of ACFs is not oxidized, which is also verified by cyclic voltammetry results. The FT-IR spectroscopy suggests that the interaction between aniline and ACFs is main weak physisorption instead of chemisorption. These experimental results suggest that the electrochemical polarization of ACFs can effectively improve the adsorption rate and capacity of aniline, which may be due to the enhanced affinity between aniline and ACFs instead of the oxidation on the surface of ACFs or in the solution.     

Properties of differently shaped activated carbon fibers

Differently shaped carbon fibers (R-, I-, C-, Y-, and X-type) were prepared from melt-spinning of reformed naphtha cracking bottom oil precursors through various shaped spinnerets. These carbon fibers were activated by steam and activation properties were compared. The decrease of hydraulic radius resulted in the extending of the external surface area of carbon fibers. Activation energy and rate of differently shaped carbon fibers were affected by external surface area. Especially, the activation rate of tetralobal carbon fibers (X-type) appeared much larger than other shaped carbon fibers due to the smallest hydraulic radius. Adsorption capacity of tetralobal activated carbon fibers was also larger than other shaped activated carbon fibers.     

以纸巾为模板制备活性炭纤维

以纸巾为前驱体通过NaOH化学活化制备活性炭纤维,扫描电镜观测其微观结构为多孔纤维状。通过活性炭纤维对亚甲基蓝的吸附实验研究活性炭纤维吸附动力学,Pseudo-second-order方程比Pseudo-first-order方程更适于吸附数据模型,相关系数高达0.998,所制备活性炭纤维对亚甲基蓝最大平衡吸附量为200mg/g。     

The effect of mechanical recycling on the microstructure and properties of PA66 composites reinforced with carbon fibers

This article aims to prepare by injection molding recycled polymeric composites based on PA66 reinforced with short carbon fibers after artificial aging for applications in the automotive field. The aging cycles involves the combined action of UV radiation, moisture, and temperature in order to simulate the common outdoor conditions. The 100% recycled composites are obtained by the regranulation of the aged specimens followed by the remelting and re‐injection molding. The study is focused on the comparison between the mechanical behavior and the microstructure of the composites before and after mechanical recycling. The results of mechanical, thermal, and morphological investigations reveal that the recycling process had no significant effect on the final properties and microstructure of the recycled composites. Therefore the recycled PA66CF30 composites could be successfully used for structural or semi‐structural automotive applications guaranteeing good final performances and advantages from the environmental point of view. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42275.     

The effect of processing conditions on structure evolution in melt spun poly(ethylene terephthalate) fibers

An investigation has been made into the structural evolution in poly(ethylene terephthalate) fibers as a function of wind-up speed (WUS) and quench air temperature (QAT). Analysis of the mechanics and mechanisms of cold drawing reveals that the fiber structure is heterogeneous. Evidence from differential scanning calorimetry (DSC) and density measurements indicates the presence of crystallites which are imperfect according to wide-angle diffraction (WAXD). Increased thread-line stress (higher WUS and higher QAT) appears to induce larger and more oriented crystallites in a progressively oriented matrix. A radially layered structure is disclosed from high resolution scanning electron microscopy (SEM) micrographs.