Impregnation Stage Research Articles

Some Aspects of Manufacturing the Prepregs for Long-Length Products from Composite Materials with a Thermoplastic Binder

The technology for producing products from composite materials with a thermoplastic binder differs from the traditional method, which uses thermosetting resins as a binder, and requires new design and technological solutions. This article proposes a two-stage method for manufacturing a long-length carbon strand of high-voltage cables: in the first stage, a thermoplastic layer of the polyetheretherketone (PEEK) melt is applied to the carbon filament; in the second stage, a strand is formed from the filaments and crimped by hydrodynamic drawing. Using the finite-element method, a numerical model of the process of applying a thermoplastic layer to a carbon filament in an axisymmetric die is constructed. To describe the rheological properties of the PEEK melt, a generalized Carreau model was selected and the material constants included in it are determined. The velocity, pressure, and temperature fields are calculated, and the effects of the applied pressure and strand drawing speed on the thickness of the applied layer are estimated. For the stage of formation and impregnation of the strand composed of carbon filaments covered with a thermoplastic layer, a dimensionless equation for the position of the impregnation front of the porous carbon filament influenced by an external pressure that is linearly distributed along the channel is obtained on the basis of the analytical solution of the flat-radial filtration problem under the assumption that each filament in the strand is under the same conditions in the process of crimping. The developed mathematical model allows one to calculate the pressure and temperature fields and flow kinematics, to evaluate the influence of technological parameters on the thickness of the thermoplastic layer applied to the filament, and to predict the degree of uniformity of the finished product.

Investigation on process parameters of 3D printed continuous carbon fiber-reinforced thermosetting epoxy composites

Continuous fiber-reinforced thermosetting polymer composites (CFRTPCs) were prepared via three-dimensional (3D) printing in this study. The entire process was divided into impregnation, printing, and curing stages. The impregnation stage ensured a tightly bonded interface and uniform distribution of fibers and resin. The printing stage solved the great conveying resistance and poor adhesion caused by the addition of continuous fibers. The curing stage aimed to preserve the shapes of the pre-formed samples and completed the polymerization and crosslinking reactions. An investigation into the experimental design focused on optimizing the parameters of the manufacturing process, wherein printing speed, printing space, printing thickness, curing pressure, and curing temperature were selected as target variables. Finally, 3D printed CFRTPC samples with 58 wt.% fiber content exhibited maximum flexural strength and modulus of 952.89 MPa and 74.05 GPa, respectively. Moreover, complex CFRTPC components were fabricated to demonstrate the feasibility and generality of the proposed technique. These results may broaden the potential use of 3D printed CFRTPCs in aerospace, defense, and automotive applications.

Initial Stage of Impregnation and Extraction in Modeling a Porous Medium by a Two-Continua Model

Initial Stage of Impregnation and Extraction in Modeling a Porous Medium by a Two-Continua Model

Nanocomposites based on the SBA-15 mesoporous silica highly loaded with various iron oxides

Nanocomposites highly loaded with various iron oxides were obtained by thermal treatment of SBA-15 mesoporous silica soaked in concentrated freshly prepared ferric oxalate aqueous solution. Ultradispersed iron oxide particles appeared to cover external surface of the matrix as well as to be embedded into the depth of silica. We showed that CO evolving during the thermal decomposition of ferric oxalate added at the second impregnation stage is able to reduce the iron(III) oxide preliminary formed by oxidative thermolysis of the salt having been initially loaded.

Plastination-A scientific method for teaching and research.

Over the last four decades, plastination has been one of the best processes of preservation for organic tissue. In this process, water and lipids in biological tissues are replaced by polymers (silicone, epoxy, polyester) which are hardened, resulting in dry, odourless and durable specimens. Nowadays, after more than 40years of its development, plastination is applied in more than 400 departments of anatomy, pathology, forensic sciences and biology all over the world. The most known polymers used in plastination are silicone (S10), epoxy (E12) and polyester (P40). The key element in plastination is the impregnation stage, and therefore depending on the polymer that is used, the optical quality of specimens differs. The S10 silicone technique is the most common technique used in plastination. Specimens can be used, especially in teaching, as they are easy to handle and display a realistic topography. Plastinated silicone specimens are used for displaying whole bodies, or body parts for exhibition. Transparent tissue sections, with a thickness between 1 and 4mm, are usually produced by using epoxy (E12) or polyester (P40) polymer. These sections can be used to study both macroscopic and microscopic structures. Compared with the usual methods of dissection or corrosion, plastinated slices have the advantage of not destroying or altering the spatial relationships of structures. Plastination can be used as a teaching and research tool. Besides the teaching and scientific sector, plastination becomes a common resource for exhibitions, as worldwide more and more exhibitions use plastinated specimens.

Consequences in a softwood kraft pulp mill of initial high alkali concentration in the impregnation stage

Abstract Impregnation with high initial concentration is fast and efficient, leading to a homogeneous delignification in the subsequent cook, resulting in improved screened pulp yield. To obtain high initial alkali concentration, the white liquor flow needs to be significantly increased. The moisture content of the wood chips and the alkali concentration of the white liquor limit the initial alkali concentration of the impregnation liquor that can be reached. It is therefore of interest to evaluate the possibility to implement high alkali impregnation (HAI) industrially and the consequences this would have on the mill system. The effect of HAI on mass and energy balances in a kraft pulp mill has been studied using mill model simulations. The sensitivity to disturbances in important parameters for process control has been compared to impregnation scenarios used industrially. It was shown that high initial alkali concentration can be achieved on industrial scale by increased white liquor flow. HAI has a positive effect on recovery flows and reduces the need for make-up chemicals. The HAI concept is less sensitive to variations in process parameters, such as chip moisture and white liquor concentration, thus diminishing the risk of alkali depletion in chip cores.

Regeneration of wastewater contaminated by cationic dye by nanoporous activated carbon produced from agriculture waste shells.

The discharge of organic dye into environment is the threat to hydrosphere and biosphere. On the other hands, the agriculture solid wastes such walnut and almond shells pose serious pollutions in lithosphere and atmosphere when burned. The aim of present investigation is to fabricate microporous activated carbon from agriculture waste shells by microwave irradiation as efficient adsorbent to overcome these problems. Firstly, zinc chloride was impregnated into milled shell particles, 300μm, by conventional and microwave-assisted techniques and then the dry precursors were heated in the closed and open ceramic vessels in air and nitrogen atmospheres. The experimental investigation was carried out to understand the roles of different fabrication factors such as shell particle size, catalyst impregnation ratio, microwave power, carbonization temperature, and atmosphere on cationic dye removal from wastewater. The mentioned factors efficiently affect the dye removal onto obtained activated carbon. The increase in the microwave power up to 600W could effectively increase the dye removal. However, the higher powers inversely affect the removal efficiency. The equilibrium data were well fitted by Langmuir equation with high linear regression coefficients in which the maximum adsorption capacities of activated carbon produced by walnut and almond shells were determined to be 98 and 114mg/g, respectively. The most prominent advantage of activated carbon produced from almond shell is lower content of catalyst employed in impregnation stage. Although the larger particles of solid waste were applied, the spongy nature with average pore diameter of 2.4nm is the unique characteristic of activated carbon fabricated from almond shell which improves the performance of adsorbent in wastewater treatment.

The system of indicators of the quality of the carbon-carbon composite materials and technologies of their production

The system of indicators of quality of carbon-carbon composite material and technological operations of its production is proved in the work. As a result of the experimental studies, with respect to the existing laboratory equipment, the optimal number of cycles of saturation of the reinforcing frame with a carbon matrix is determined. It was found that to obtain a carbon-carbon composite material with a low cost and the required quality indicators, it is necessary to introduce additional parameters of the pitch melt at the impregnation stage.

How does phosphoric acid interact with cherry stones? A discussion on overlooked aspects of chemical activation

The fabrication of activated carbon (AC) is widely carried out by the so-called chemical activation method, in which the biomass substratum is put in touch with an impregnating chemical agent prior to the carbonization stage. Even though this methodology is known for a long time, there are many features that are still poorly understood, particularly those regarding the details of the underlying mechanisms involved during the interaction of the activating agent with the precursor, eventually leading to the development of AC. Previous research conducted in the laboratories dealt with the use of cherry stones (CS) and phosphoric acid, toward ACs with tailored porous structures, finding out that the experimental variables of the impregnation stage were crucial for their eventual characteristics. Thus, the results obtained at that time deserved further discussion, with the aim at unraveling the true nature of those findings. With such purpose, the authors comment further on the CS and H3PO4 in non-conventional impregnation methodologies, performed in the previous works. Four series of H3PO4-impregnated products were prepared in a previous research, using a wide range of impregnation strategies, aiming at controlling the loading of H3PO4 on the lignocellulosic substratum. Herein, with the mass uptake as the main, it was possible to link the uptake with the chemical changes of H3PO4 in agreement with essential chemistry knowledge. Mass gain is strongly dependent on the impregnation method, and interesting insights arise on the basis of the mass changes of CS after impregnation.

Experimental process pressure analysis for model-based manufacturing of composites by resin transfer moulding

An experimental study of the process pressure characteristics prevailing in an RTM mould during the preform impregnation stage is presented. The pressure data is analysed with respect to a superposition of preform compaction and hydraulic fluid pressure. A methodology is proposed to isolate the hydraulic fluid pressure from the preform compaction pressure involving knowledge about the compressibility behaviour of the reinforcing material. For this purpose, the preform compressibility and relaxation behavior was studied by means of transverse compaction tests on both, unsaturated as well as the saturated sample stacks. The resulting isolated hydraulic fluid pressure is finally compared with numerical predictions derived from flow simulations, revealing good overall agreement. The findings of this work will contribute to realize the concept of model-based processing of fibre-reinforced polymer composites by means of the RTM process.

Frequency-Domain Diagnosis Methods for Quality Assessment of Nb3Sn Coil Insulation Systems and Impedance Measurement

In recent years, the superconducting Nb3Sn cable material became the privileged mature candidate for the high-field magnets in new projects like high-luminosity LHC (HL-LHC) accelerator at CERN, Geneva, Switzerland. The technology in 2017–2021 needs to be deployed through an unprecedented magnet series production with dedicated online quality control. The key fabrication stage of the vacuum pressure impregnation (VPI) after the heat treatment reaction of Nb3Sn coils, as on the new 11-T dispersion region dipole, enhances both the structural integrity and the dielectric strength of the winding packs. The global vacuum impregnation pressure method exhibits various merits in insulation performance and high dielectric strength reliability, which is strongly dependent on the success of the resin filling cycle. This online capacitive measurement method enables one to derive comparative master trend curves of various impregnated coils and possibly optimize the curing cycle. Ultimately, a combination of the above methods with a dielectric frequency response can bring insights on the impregnation process, the impacts from the resin choice and insulation material quality on the degree of curing, and the coil assembly geometry. The frequency impedance measurement of the first short dipole models DP101-102 provides the distributed lumped circuit fitting electrical parameters for the transient characterization of produced magnets.

From mantle peridotites to hybrid troctolites: Textural and chemical evolution during melt-rock interaction history (Mt. Maggiore, Corsica, France)

Recent studies investigate the replacive formation of hybrid troctolites from mantle peridotites after multiple stages of melt-rock reaction. However, these studies are not conducted in a field-controlled geological setting displaying the clear evolution from the protolith to the end-product of the reactions. The Mt. Maggiore peridotitic body exposes a clear evolution from spinel lherzolite to plagioclase-bearing lithotypes (plagioclase peridotites, olivine-rich troctolites and troctolites) during two continuous episodes of melt-rock interaction. In the spinel facies, the reactive percolation of a LREE-depleted melt leads to the dissolution of mantle pyroxenes and the growth of olivine crystals, forming replacive spinel dunites. The progressive evolution from spinel lherzolite to harzburgite to replacive dunite is accompanied by a change of olivine Crystallographic Preferred Orientation (CPO), from axial-[100] in the lherzolite to axial-[010] olivine CPO in the dunites, indicative of deformation in presence of melt. The initial percolating melt composition is consistent with single melt increments after 6% partial melting of a depleted mantle source. Reactive melt percolation leads to a progressive enrichment in the melt M-HREE absolute concentrations, while preserving its LREE depletion, consistent with the enriched analyzed HREE composition of olivine in the spinel dunite.In the shallower plagioclase facies, the melts modified by reactive melt percolation impregnate the spinel-facies lithotypes, leading to the dissolution of olivine and crystallization of plagioclase and orthopyroxene in the peridotites. This impregnation stage is also observed in the spinel dunites, forming hybrid olivine-rich troctolites and troctolites. The dissolution-precipitation reactions forming hybrid troctolites cause a progressive textural evolution of the olivine matrix, with the disruption of deformed coarse grains into undeformed small rounded grains. This textural evolution is not accompanied by clear changes in the olivine CPO, indicating low instantaneous melt/rock ratios during the impregnation process. Olivine, plagioclase and clinopyroxene REE compositions analyzed in troctolite fit a process of impregnation with a progressive closure of the porosity (at decreasing melt mass), leading to the crystallization of trapped melt and REE enrichments during the last crystallization increments.

Influence of nickel during the thermal degradation of pine cone shell. Study of the environmental implications

Abstract Thermal valorization of heavy metal impregnated biomass has grown up as a researching field during the last few years; however the use of these contaminated wastes as fuel still presents several economic and technical drawbacks. Specially, insertion of nickel metal into the biomass during an impregnation stage with aqueous solutions of nickel salts, promotes wide dispersion of the precursor inside the lignocellulosic matrix and impacts on good results with respect to the reduction of tars. Therefore, the catalytic effect of the nickel during the thermal decomposition of an impregnated pine cone shell is investigated in this work. The effects of the heating rate and the atmosphere on the thermal decomposition of the natural solid show that an increase in heating rate produces a shifting of the curves at higher temperatures without significant change of its shape. Three distinct stages of mass loss are presented during degradation process for the different reaction atmospheres; however, the temperature ranges in which the stages are performed are different. Moreover, an increase in the thermal stability of nickel-loaded pine cone shell in the early stages is observed. The results obtained by mean method of Coasts-Redfern show that the function that could represent the thermal degradation mechanism associated with the major step of degradation of the pine cone shell is the reaction of nth order, being the third, fourth or fifth order the most regular order. About the environmental implications, the residual waste is lower for nickel-loaded biomass. Moreover, the nickel remains mainly in the ashes, therefore, the nickel content in these ashes may be recovered, or ashes distribute to any subsequent application.

The balance between alkali diffusion and alkali consuming reactions during impregnation of softwood. Impregnation for kraft pulping revisited

AbstractThe purpose of the impregnation stage is to ensure that cooking chemicals reach all parts of the chips. However, as alkali comes into contact with wood, reactions take place, which alter the paths available for ionic transport and dissolve wood components. The aim of the present study is to establish the most favorable impregnation conditions, which result in an even alkali concentration profile through the chip at a sufficiently high level without extensive yield losses due to peeling. Softwood chips were subjected to different impregnation conditions. The progress of impregnation was assessed by analyzing the concentration of hydroxide ions in the bound liquor inside wood chips and the release of acetic acid. The extent of undesired reactions was measured as the amount of carbohydrate degradation products formed and amount of wood dissolved. Increased temperature and time lead to more degradation of the carbohydrates during impregnation. At high temperature, the concentration of alkali in the bound liquor was lower due to higher alkali consumption in degradation reactions. The most favorable process is to perform impregnation at an elevated initial effective alkali (EA) for a short time. This resulted in an increased alkali concentration in the bound liquor within the chip without extensive carbohydrate degradation.

Hydrotreating of Middle-Distillate Fraction on Sulfide Catalysts Containing Crystalline Porous Aluminosilicates

The effect of the impregnation stage on the synthesis of NiW sulfide catalysts supported on the ZSM-5 zeolite has been studied. The hydrodearomatization (HDA) of light cycle oil (LCO) in the presence of a catalyst containing nickel and tungsten sulfides as an active phase impregnated onto a micro/mesoporous ZSM-5/SBA-15 support has been conducted. The catalyst has been compared with a commercial AGKD-400 diesel hydrotreating catalyst. It has been found that the impregnation of the supports with a solution containing an oxalic acid additive leads to an improvement in the morphology and composition of the active phase. The deepest hydrogenation is observed at 360°C, 6 MPa H2, and a LHSV = 0.5 h–1. The amount of diaromatic hydrocarbons decreases 12-fold, and the sulfur content decreases by 90%.

Technical-environmental optimisation of the activated carbon production of an agroindustrial waste by means response surface and life cycle assessment.

In this study, a simultaneous optimisation of technical and environmental parameters for activated carbon production from soybean shells is presented. A 23 factorial design was developed to explore the performance of the technical responses yield and iodine number, and the single score of ReCiPe endpoint method, which was evaluated by means the life cycle assessment. The independent factors included in the design of experiments were the impregnation ratio, temperature, and time activation. Three quadratic equations were obtained and simultaneously optimised by maximisation of the overall desirability function. The principal results of the individual responses indicate that the iodine number is practically independent of the activation temperature in a range of 450 ºC-650 ºC; the yield is inversely proportional to activation time and exhibits minimum values between 500 ºC-600 ºC; and the environmental response single score presents the lowest value at a temperature and time activation of 450 ºC and 30 min, respectively. The most polluting stage of activated carbon production from soybean shells production is the impregnation stage, mainly for the use of ZnCl2 as activating agent and the energy consumption. The simultaneous optimisation of the three responses indicates that the optimal activated carbon should be produced at 180 min, 650 ºC, and an impregnation ratio of 1 g soybean shell g ZnCl2-1.

Silica Retention by the Addition of Sodium Metaaluminate During the Impregnation Stage of Bamboo Kraft Pulping

Bamboo is the most utilized non-wood biomass in China. One of its most important applications is in the pulp and paper industry. In such an application, one of the significant challenges is decreasing the silica dissolution in the pulping process. In this study, the use of sodium metaaluminate (NaAlO2) to decrease the silica dissolution into liquor was investigated. The results showed that an alkali-resistant Si–Al coating layer was formed onto the silica particles by the addition of NaAlO2. Under the impregnation conditions, NaAlO2 reacted with Na2SiO3 and produced poly-condensated Si/Al compounds, which are insoluble under kraft pulping conditions. It was found that the silicon retention in bamboo chips was 90% with the addition of NaAlO2 under the conditions studied. This novel silica-retaining technology has a great potential for industrial applications.

Experimental characterization of the pore size distribution in fibrous reinforcements of composite materials

This study uses capillary flow porometry to investigate the porous structure of engineering fabrics used in high-performance polymer composites. This technique consists of applying air pressure to a previously wetted sample to progressively expel the liquid from the pores. A porometry testing device commonly employed to characterize filtration media was used as the principal tool for this investigation. Four types of fibrous fabrics made of glass and carbon fibers with different textile architectures have been experimentally characterized with a through-thickness setup. This allowed obtaining the pore size distribution inside the tested material. In all the cases studied, the porometry technique was able to detect in a reproducible way a bimodal pore size distribution reflecting the presence of both micropores (inside the fiber yarns) and mesopores (between the yarns). Moreover, experimental results indicate that the method can be used to study the influence of the textile pattern on the pore size distribution. Overall, the study shows that capillary flow porometry can give valuable information on the dual scale structure of fibrous reinforcements, which plays a critical role during the impregnation stage of Liquid Composite Molding processes. Because of its simplicity and speed of execution, the proposed approach appears to be a promising way to complement other sophisticated techniques already used for composites such as microscopy and X-ray microtomography.

Increased pulp yield by prolonged impregnation in softwood kraft pulping

The effect on kraft cooking proceeded by an impregnation stage performed at 130 degrees C for 30 min was compared to kraft cooking following prolonged impregnation at 105 degrees C for 60-120 min. The alkali consumed during impregnation varied depending on the temperature and time of the impregnation stage. In order to study the impact of the impregnation stage on the subsequent kraft cook, the initial concentration of effective alkali was adjusted to be initially the same in all cooks before cooking for 180-290 min. The alkali consumed in the impregnation stage affected the alkali profile of the cooking stage. The more alkali consumed in impregnation, the lower the demand in cooking. Higher alkali consumption in the impregnation stage also led to faster delignification in the cooking stage. Prolonged impregnation resulted in 1-1.5 percentage points higher yield compared to the reference case. The yield increment was due to a higher cellulose retention. Although the impregnation time was prolonged from 30 min up to 2 h, the higher delignification rate and higher yield only decreased the production rate with 11% compared to the reference.

Preparation of microplastics with polysulfone and montmorillonite by impregnating aramid and glass fibers

Microplastics have been prepared by impregnating aramid and glass fibers with of polysulfone melts of various viscosities unfilled and filled with montmorillonite. A minimum of the melt viscosity has been found at a montmorillonite content of 1 wt %. Radial-transverse impregnation of multifilament fiber by a thermoplastic melt has been studied by the gravimetric method. Introduction into the polysulfone melt up to 1% of the filler at the initial stage of impregnation have almost no effect on the rate of the process; however, a decrease in it is observed as compared subsequently to impregnation with the melt containing no filler. It has been shown that torsional rigidity of microplastics, along with weight change, characterizes the degree of fiber impregnation.