In‐plane anisotropic permeability characterization of deformed woven fabrics by unidirectional injection. Part I: Experimental results

Because of the increasing use of polymer composites in a wide variety of industrial applications, the manufacturing of complex composite parts has become an important research topic. When a part is manufactured by liquid composite molding (LCM), the reinforcement undergoes a certain amount of deformation after closure and sealing of the mold. In the case of bidirectional woven fabrics, this deformation may significantly affect the resin flow and mold filling because of changes in the values of permeability. Among other considerations that govern the accuracy of numerical simulations of mold filling, it is important to predict the changes of permeability as a function of the local shearing angle of the preform. The resin flow through a fibrous reinforcement is governed by Darcy's law, which states that the fluid flow rate is proportional to the pressure gradient. The shape of the flow front in a point‐wise injection through an anisotropic preform is an ellipse. Part I of this article describes a new methodology based on the ellipse equation to derive the in‐plane permeability tensor from unidirectional injection experiments in deformed woven fabrics. Part II presents a mathematical model that predicts the principal permeabilities and their orientation for sheared fabrics from the permeability characterization of unsheared fabrics. Unidirectional flow experiments were conducted for a nonstitched, balanced, woven fabric for different shearing angles and fiber volume fractions. This article presents experimental results for deformed and undeformed fabrics obtained by unidirectional flow measurements. A comparison of the proposed characterization methodology with radial flow experiments is also included. POLYM. COMPOS. 28:797–811, 2007. © 2007 Society of Plastics Engineers.     

Accurate permeability characterization of preforms used in polymer matrix composite fabrication processes

The permeabilities of fabrics composed of carbon and glass fibers have been determined by utilizing both simple 1-dimensional and 2-dimensional radial flow measurements using silicone oil and motor oil as permeants. The carbon fabric is typical of that used in fabrication of aerospace grade polymer matrix composites, while the glass fabric is a 3-dimensional woven fabric that has been proposed as a standard reference material for permeability characterization. Our results indicate that reliable permeability data for fiber preforms with varying architectural complexity can be obtained provided that the experiments are performed with utmost care and that appropriate equations are used to analyze the data. In-plane permeabilities for the carbon fiber preforms from transient unidirectional constant flow rate and constant pressure experiments agreed within 5%, regardless of the preform orientation to the flow direction. Steady-state results on the same preforms showed agreement within 2% between constant flow rate and constant pressure experiments. The capillary pressure effect was shown to be negligible for the transient experiments. The maximum difference between the transient and steady state permeability values was 3%. The maximum difference between a permeability measured with unidirectional flow and the same permeability measured with radial flow is less than 10%.     

Characterization of the draping behavior of jute woven fabrics for applications of natural‐fiber/epoxy composites

In this study, we investigated the draping behavior of jute woven fabric to study the feasibility of using natural fabrics in place of synthetic glass‐fiber fabrics. Draping behavior describes the in‐mold deformation of fabrics, which is vital for the end appearance and performance of polymer composites. The draping coefficient was determined with a common drapemeter for fabrics with densities of 228–765 g/m² and thread counts under different humidity and static dynamic conditions. The results were compared to glass‐fiber fabrics with close areal densities. Characterization of the jute fabrics was carried out to fill the knowledge gap about natural‐fiber fabrics and to ease their modeling. The tensile and bending stiffnesses and the shear coupling were also characterized for a plain woven jute fabric with a tensile machine, Shirley bending tester, and picture frame, respectively. As a case study, the draping and resin‐transfer molding of the jute fabric over a complex asymmetric form was performed to measure the geometrical conformance. The adoption of natural fibers as a substitute for synthetic fibers, where the strength requirements are satisfied, would thus require no special considerations for tool design or common practices. However, the use of natural fibers would lead to weight and cost reductions. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1453–1465, 2013     

防电磁辐射混纺织物的设计与开发

20μm的不锈钢长丝与25 tex的竹浆/丝光羊毛(50/50)股线经过并线加捻设计开发出5种不锈钢长丝含量不同的纱线,设计并试织了不锈钢长丝质量分数分别为11%、15%、17%、22%、26%的5种2/2斜纹组织织物。测试和分析了这5种织物的防辐射性能、厚度、面密度、透气性、悬垂性、刺痒感、汽蒸收缩性、折皱回复性。结果表明:开发的5种织物均具有良好的防电磁辐射性能,且随着不锈钢长丝含量增加,织物的防辐射性能提高,厚度、面密度、刺痒分值逐渐增大,透气性、悬垂性、折皱回复性降低,汽蒸收缩性先降低后保持不变。     

Forced in-plane flow through complex deformable structures: Influence of an imposed curve

Forced in-plane flow of liquids through contiguous flat and curved regions of confined fabrics has been studied both as a general phenomenon and for predicting the flow of polymers during injection molding of monolithic composite structures with complex configurations. A controlled pressure difference is applied to drive the flow, while the mass flow rate is measured gravimetrically by Liquid/Air Displacement Analysis (LADA). Measurements have been carried out along fabric paths that are first vertical, then curved, and finally horizontal. Fluid flow equations have been adapted for analyzing flow in the flat sections, leading to the evaluation of permeability constants and capillary pressures. A saturated flow rate measured at constant hydrodynamic pressure is used to evaluate the overall permeability coefficient of the encapsulated fabric. Data are presented showing that permeability can be reduced as a consequence of flow through the curved region.     

Water vapor permeability and mechanical properties of fabrics coated with shape‐memory polyurethane

Water vapor permeable fabrics were prepared by coating shape‐memory polyurethane (PU), which was synthesized from poly(tetramethylene glycol), 4,4′‐methylene bis(phenylisocyanate), and 1,4‐butanediol, onto polyester woven fabrics. Water vapor permeability and mechanical properties were investigated as a function of PU hard‐segment content or polymer concentration of the coating solution. Water vapor permeability of PU‐coated fabrics decreased dramatically with increased concentration of coating solution, whereas only a slight change was observed with the control of PU hard‐segment content. The coated fabric showed the clear appearance of a nonporous PU surface according to SEM measurements. Attainment of high water permeability in PU‐coated fabrics is considered to arise from the smart permeability characteristics of PU. Mechanical properties of coated fabrics, although there was some variation depending on the concentration of coating solution, were primarily affected by PU hard‐segment content. Fabrics coated with PU hard‐segment content of 40% showed the lowest breaking stress and modulus as well as the highest breaking elongation, which could be interpreted in terms of the dependency of mechanical properties of coated fabrics on PU hard‐segment content and the yarn mobility arising from a difference in penetrating degree of coating solution into the fabric. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2812–2816, 2004     

Surface and adhesion properties of poly(ethylene glycol) on polyester(polyethylene terephthalate) fabric surface: Effect of air‐atmospheric plasma treatment

The surface and adhesion properties of different molecular weight poly(ethylene glycol) (PEG) (400, 1500, and 3000 g/mol) on untreated and air‐atmospheric plasma‐treated PET woven fabrics were studied, with the aim of developing durable hydrophilic PET fibrous structures. PEG application was carried out by padding of the PET fabric in aqueous solution of PEG followed by curing and drying. The surface properties of the PEG‐coated PET fabrics were then characterized using wicking test to measure the water contact angle (θ°) and capillary weight (W_c), and using atomic force microscopy (AFM) images in the tapping mode. Results showed that without a prior air‐atmospheric plasma treatment of the PET fabric, the water contact angle decreased and capillary weight increased with the three PEGs, implying an increase in the hydrophilicity of both inner and outer PET fabric fiber surface. Air‐plasma treatment of the PET fabrics before PEG coating increases further the hydrophilicity of the inner fabric fiber surface: the capillary weight was almost doubled in the case of the three PEGs. Best results were obtained with PEG 1500: water contact angle decreasing from 82° to 51°, and the capillary weight increasing from 11 mg to 134 mg. Moreover, wash fastness test at room temperature and at 80°C confirms improved adhesion of PEG‐1500 to the plasma‐treated PET woven fabric surface, while under the same conditions the plasma‐treated PET without PEG loses completely its hydrophilic character. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Through air drying of paper—the effect of dryer fabric

A custom experimental apparatus is designed to perform through air drying under well-controlled drying conditions such as air temperature and mass-flowrate. Using a novel optical measurement technique, the spatial distribution of moisture content in paper during through air drying is quantified as a function of time. The technique is capable of measuring the moisture content distribution with high spatiotemporal resolution while air flows through a paper mat sitting on a permeable dryer fabric. Four commercially available fabrics with different structural design and properties are used in the investigations. The effect of the fabrics’ structural properties, which are characterized using optical coherence tomography (OCT), is studied under various drying conditions. It is shown that the geometry of the contact spots of the fabrics has a significant impact on the drying time at high drying intensities. However, at low rates of drying (i.e., low air temperature and flowrate), no correlation between drying time and fabric properties is observed. After a cycle of through air drying, the permeability of paper increases irreversibly. This increased permeability is observed to be a function of the fabric structure. It is shown that the increase in permeability is larger for coarse fabric structures although no monotonic correlation with the fabric permeability can be observed. Comparing the spatial maps of moisture content with the paper grammage distribution reveals that there is a correlation between the local grammage and the spatial pattern of drying in a paper sheet.     

A note on permeability simulation of multifilament woven fabrics

A conventional approach for modeling permeability of multifilament fabrics is to consider their warps and wefts to be individual thick filament made of homogeneous porous media and solve the flow equations for such monofilament fabrics. In this work, for the first time, the full 3-D geometry of an idealized multifilament woven fabric, wherein the filaments are packed in hexagonal arrangement, is generated to compute its permeability and compare with the homogeneous anisotropic lumped model of Gebart (1992. Permeability of unidirectional reinforcements for RTM. Journal of Composite Materials 26(8), 1100-1133). While a relatively good agreement is obtained, our results indicate that Gebart's model slightly underestimate the permeability of multifilament fabrics even at high yarn's solid volume fractions.     

Measurement and Simulation of Axial Velocity in a Filter Bag

The axial velocity in two different tests with pulse‐jet bag filters made of needle felts on a pilot‐scale test facility separating limestone dust from air under ambient conditions is measured and simulated at different cake area loads. Results reveal that the axial velocity profiles are not truly linear along the whole length of the bag. A nonuniform gas flow prevails when the bags are differently dust‐loaded. The same behaviors are observed even at the end of filtration cycles at different upper pressure drop limits. At the higher upper limit, the nonuniformity is stronger. Radial velocity profiles are nearly symmetric along the length of the bag.     

聚乙烯瞬时释压纺丝法无纺布制备及其性能研究

以不同熔体流动速率的高密度聚乙烯为原料,二氟一氯甲烷和四氟二氯乙烷混合物为溶剂,通过瞬时释压纺丝法制备加工成无纺布,制备得到聚乙烯无纺布材料。通过扫描电子显微镜、动态接触角测量仪、自动比表面积和孔径分析测试仪、差示扫描量热仪、热失重分析仪、电子强度仪和数字透气度仪对所制备的无纺布的形貌、接触角、比表面积、断裂强度和断裂伸长率、热性能、透气性和耐水性依次进行表征和分析。结果表明,基于瞬时释压纺丝法的聚乙烯无纺布由平均单丝直径为4 μm的超细纤维构成,最大拉伸断裂强度为220 N/5 cm;无纺布表现出良好的透气性、防水性和油墨润湿性,可应用于制备新型鞋面材料。     

基于闪蒸法制备再生聚乙烯无纺布及其性能研究

以2种熔体流动速率（MFR）不同的再生聚乙烯为原料,二氟一氯甲烷和四氟二氯乙烷混合物为溶剂,采用闪蒸法制备了2种再生聚乙烯无纺布,并通过扫描电子显微镜（SEM）、差示扫描量热仪（DSC）、电子强力机和数字透气度仪等对其表观形貌、热性能、力学性能、透气性和抗水压性等进行了表征和测试。结果表明,基于闪蒸法制备的再生聚乙烯无纺布由超细纤维黏连堆叠而成,其最大拉伸断裂强力为233 N/5 cm,最大断裂伸长率为77 %,且具有良好的透气性、抗静水压性、印染性和阻隔性;制备的再生聚乙烯无纺布具有良好的综合性能,实现了再生聚乙烯赋能增值的目标,符合可持续发展理念,具有广阔的市场前景。     

Comparison of mechanical and ballistic performance of composite laminates produced from single‐layer and double‐layer interlocked woven structures

Textile structures have become quite popular as reinforcement materials in composite laminates due to their high impact‐damage tolerance and energy absorption ability. The impact performance of textile composites is not only affected by the type of fiber/matrix but also by the fabric structure used as reinforcement. The aim of this study was to compare the mechanical and ballistic performance of composite laminates reinforced with single‐layer and double‐layer interlocked woven fabrics. Kevlar^®−29 multifilament yarn was used for preparation of all the fabric structures and epoxy resin was used as the matrix system. The composites were produced using a hand lay‐up method, followed by compression molding. The mechanical and ballistic performance of composites reinforced with single‐layer and double‐layer interlocked woven fabrics was investigated in this study. The energy absorption and mechanical failure behavior of composites during the impact event were found to be strongly affected by the weave design of the reinforcement. The composites reinforced with double‐layer interlocked woven fabrics were found to perform better than those comprising single‐layer fabrics in terms of impact energy absorption and mechanical failure. POLYM. COMPOS., 35:1583–1591, 2014. © 2013 Society of Plastics Engineers     

Atmospheric continuous cold plasma treatment: Thermal and hydrodynamical diagnostics of a plasma jet pilot unit

An atmospheric pressure plasma jet (APPJ) for continuous treatment of polymeric films and textile materials was investigated to characterize its thermal, hydrodynamic and chemical features. The operative variables of the plasma jet equipment are: gas flow rate and composition, electrical power to the plasma generator and fabric velocity. A diagnostic evaluation of the equipment was carried out to improve the treatment homogeneity and generate an effective feedback for scale-up. The cross profile of gas temperature and velocity, the fabric temperature and concentration transitory in the gas system generated by a reverse step of oxygen were determined. These measurements showed that the original prototype configuration required a better gas distribution to fully demonstrate its potentiality to functionalize textiles. The surface modifications induced by plasma were detected by processing wool fabrics and by evaluating the treatment benefit on dyeing.     

Permeability characterization. Part 1: A proposed standard reference fabric for permeability

A three-dimensionally woven fabric is proposed as a standard reference material for permeability characterization. The 3-D woven fabric requires care in cutting and handling, although it is more robust than 2-D woven or braided fabrics. If prepared carefully, the permeability of the 3-D woven fabric can be measured reproducibly within 15% in either radial flow or saturated 1-D flow geometries. The material was characterized for permeability in radial, unsaturated and saturated 1-D, and through-thickness flow geometries. The transient results demonstrated the importance of structural heterogeneity on the unsaturated flow behavior, and agree qualitatively with a simplistic model of flow in heterogeneous unsaturated porous media. The effects of heterogeneity were manifested in the proposed SRM by an increasing trend in the “unsaturated permeability.” Experiments were also conducted with a random mat that displayed transient flows dominated by wicking. The effects of wicking on the macroscopic flow behavior were manifested by transients in the “unsaturated permeability” in which a decreasing trend was observed.     

Use of a predictive colour model for managing the colour appearance of two‐colour woven fabrics

The aim of this study was to implement a two‐dimensional colour appearance model for prediction of the colour values of weft threads when the optical mixing of a two‐colour woven structure had to match the colour appearance of a single‐colour reference woven fabric. Five single‐colour woven fabrics were woven from five threads of similar hue. One of the samples was chosen as a reference, for which the colour appearance was the goal to be achieved in the two‐colour woven fabrics prepared with the other available warp threads and newly dyed weft threads. The colour values of dyed weft threads were predicted by a two‐dimensional colour appearance model. With dyed weft threads, managing the colour appearance of the two‐colour woven fabric was enabled to achieve the colour values of the reference. In the results, colour deviations between the predicted and measured colour values of weft threads revealed some limitations to the colour appearance model and performance of the dyeing process. After the production of the two‐colour woven fabric, the colour appearance matched the appearance of the reference, resulting in deviations of ΔE_CMC(2:1) = 1.2‐7.8. Moreover, the differences between theoretically predicted and measured colour values of the two‐colour woven fabric were evaluated as small, ranging from ΔE_CMC(2:1) = 1.5‐1.9. The results demonstrated the efficiency of implementing the colour appearance model and the dyeing process of weft threads as an approach to achieve the defined colour appearance of two‐colour woven fabrics, which with small colour deviations matches the colour of a single‐colour reference.     

Drape behavior of 3D woven glass‐epoxy composites

This article deals with the drapability of 3D woven glass fabrics for composite applications. The study focuses on forming a 3D fabric over the mold, the result is a preform, which generally is then injected with a polymer matrix by so called Liquid Composite Molding (LCM) technique. When draping pre–impregnated composites, the fabric is embedded in the epoxy resin as matrix material. Various drape models for dry and pre‐impregnated fabrics have been proposed in the work. Solidworks and ANSYS are the software used for modeling and simulation of 3D woven fabric composites. Given the linear density (tex) and density of E‐glass fiber, the radius of the yarn was calculated. So far the cross section of yarn is assumed to be perfectly circular in shape, keeping the perimeter of yarn constant the circular cross section was deformed into a race track shape which is a much more practical and realistic shape of a yarn cross section. After calculating all the required dimensions, all the three 3D woven structures namely angle interlock, warp interlock and orthogonal were developed in solidworks. All the parameters like total number of warp and weft yarn per unit distance and thickness of the fabric were kept constant in all three structures. The analysis is based on first principles and the parameters of yarn and fabric construction. Results obtained through simulation are reported. These are validated with experimental composite samples. The model used to predict drapability of 3D woven glass‐epoxy composite gives good results. Orthogonal structure proves to be the best as far as resistance to deformation is concerned. However, if a relatively more flexible and formable prepreg is desired, it is advisable to use angle interlock or warp interlock structures. Warp interlock 3D structure proves most beneficial for draping on a mold. POLYM. COMPOS., 37:472–480, 2016. © 2014 Society of Plastics Engineers     

丙纶机织物防水涂层整理加工

采用自主研发的防水剂对丙纶机织物进行防水整理,结合丙纶的性能得出最佳工艺配方,并与市场上常用防水剂进行性能对比。筛选并配制了适合丙纶用的PA涂层胶,对防水后的织物进行涂层整理,并在工厂进行放样。测试结果显示:经涂层后的丙纶织物的耐水压为6 972.5 Pa,防水等级90分。     

Assessment of uniformity of fibre coloration in Tencel woven fabrics dyed using reactive dyes

Weave structure and fabric density has an influence on dye penetration. The uniformity of dyeing, expressed as the uniformity of fibre coloration, of Tencel woven fabrics comprised of different weave structures, was assessed. The fabrics were dyed by exhaust and continuous dyeing methods using selected reactive dyes. Cross‐sectional images were captured and then given a rating 1–5 with respect to the depth of the fibre filaments of the yarn of the woven fabric. The images were assessed both subjectively and objectively. The uniformity of fibre coloration was expressed in terms of the standard deviation, mean value and histogram analysis such as dispersion and bandwidth. Objective assessment of uniformity of fibre coloration is a more accurate and quicker method than visual assessment and can be used to assess the uniformity of fibre coloration of woven and knitted fabrics dyed by any class of dyes. Improvement of the uniformity of fibre coloration of Tencel fabrics of various weave structures by causticisation of the fabrics and by modification to the padding process was investigated.     

A facile one‐step synthesis of flame‐retardant coatings on cotton fabric via ultrasound irradiation

This article reports a facile one‐step methodology to increase fire resistance properties of cotton fabric. The flame‐retardant coating for cotton fabric was synthesized with methyltriethoxysilane and organophosphates (M102B) through an ultrasound irradiation process. The coating structure and surface morphology of uncoated and coated fabrics were investigated by Fourier transform infrared spectroscopy and scanning electron microscope, respectively. The flame‐retardant properties, bending modulus, air permeability and thermal stability were studied by vertical burning test, cantilever method, air permeability test and thermogravimetric analysis (TGA). As a result, the cotton fabric coated with 29.2% (mass increased) of flame‐retardant coating was able to balance the flame retardant property and wearing comfort of the fabrics. The TGA results showed that the residue char of cotton was greatly enhanced after treatment with the coating, which has a high char forming effect on cellulose during testing. Furthermore, flame‐retardant property of coated fabrics did not change significantly after 10 washing cycles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45114.