The effect of nesting on the in‐plane permeability of unidirectional fabrics in resin transfer molding

The nesting of layers has great effect on the permeability, which is a key parameter in resin transfer molding. In this article, two mathematical models were developed to predict the in‐plane permeability of unidirectional fabrics with minimum and maximum nesting, respectively. For different zones of characteristic yarn arrangement in the unit cell, the local permeability was modeled as a function of geometrical yarn parameters. The global permeability was then modeled as a mixture of permeabilities of different zones with the electrical resistance analogy. A reasonably good agreement was found between the model predictions and experimental results. We also found that at the same fiber volume fraction, the results for Ky were two times larger with minimum nesting than with maximum nesting, whereas the results for Kx were a little lower with minimum nesting than maximum nesting. In addition, the differences between minimum and maximum nesting decreased with increasing fiber volume fraction. POLYM. COMPOS., 37:1695–1704, 2016. © 2014 Society of Plastics Engineers     

Statistical characteristics of out‐of‐plane permeability for plain‐woven structure

Since out‐of‐plane permeability of fiber preforms is a function of the number and arrangement of stacked layers, either many layers of preforms or numerous experiments are required to obtain an exact out‐of‐plane permeability experimentally. The reason is that there exist nesting and phase shifting when the preforms are laid up. From a statistical viewpoint, the effect of the number of preform layers on the out‐of‐plane permeability was analyzed by adopting an analytical model proposed in this study. Numerical simulation for a unit‐cell constructed based on geometry of the preform was carried out to validate the analytical model as well as experimental measurements of the permeability. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Morphological development during injection molding of self‐reinforcing composites. I: Experimental results

The correlation between structure development during injection molding and the modulus of injection molded PET/LCP blends were studied. Process parameters such as injection speed and mold and melt temperatures were varied to determine the effect of these parameters on the tensile modulus and structure development of the blends. The skin/core structure in the cross section of injection molded samples was observed with both optical and scanning electron microscopy techniques. Injection molding experiments show that the thickness of the skin layer increases with decreasing injection speed and decreasing melt and mold temperatures. The trends in morphological developments in the injection molded specimens correlate with the measured tensile moduli.     

Experimental characterization of woven jute‐fabric‐reinforced isothalic polyester composites

In this article, mechanical performance of isothalic polyester‐based untreated woven jute‐fabric composites subjected to various types of loading has been experimentally investigated. The laminates were prepared by hand lay‐up technique in a mold. Specimens for tests were fabricated as per ASTM standards. All the tests (except impact) were conducted on closed loop servo hydraulic MTS 810 material test system using data acquisition software Test Works‐II. From the results obtained, it was found that the tensile strength and tensile modulus of jute‐fabric composite are 83.96% and 118.97% greater than the tensile strength and modulus of unreinforced resin, respectively. The results of other properties, such as flexural, in‐plane shear, interlaminar shear, impact, etc., also revealed that the isothalic‐polyester‐based jute‐fabric composite have good mechanical properties and can be a potential material for use in medium load‐bearing applications. The failure mechanism and fiber‐matrix adhesion were analyzed by scanning electron microscope. Effects of long‐term immersion in water on mechanical properties are also presented. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2650–2662, 2007     

Atmospheric plasma‐aided biocidal finishes for nonwoven polypropylene fabrics. I. Synthesis and characterization

Novel biocidal fabrics were synthesized by the graft copolymerization of glycidyl methacrylate (GMA) onto plasma‐treated nonwoven polypropylene (PP) to produce PP/GMA grafts. Atmospheric oxygenated helium plasma was used to enhance the PP fabrics' initiation before GMA grafting. The grafted PP/GMA epoxide group was reacted with β‐cyclodextrin, monochlorotrizynyl‐β‐cyclodextrins, or a quaternary ammonium chitosan derivative [N‐(2 hydroxy propyl) 3‐trimethylammonium chitosan chloride]. Some interesting biocidal agents were complexed into the cyclodextrin (CD) cavity of PP/GMA/CD grafted fabrics. Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and optical and scanning electron microscopies were used to characterize the grafted complexed fabrics. These synthesized biocidal fabrics proved to be antistatic, antimicrobial, and insect‐repelling (see part II of this study). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1900–1910, 2007     

In‐line monitoring of the injection molding process by dielectric spectroscopy

In recent years, electrical techniques like microdielectrometry have increasingly been utilized for their ability to continuously monitor, in a nondestructive way, the advancement of the reaction of thermoset resins under cure. This paper discusses an extension of this technique for the “in‐situ” monitoring of the crystallization of thermoplastics applied during an injection molding process. Electric sensors were positioned at the walls of the mold cavity so that an analysis of the volume dielectric properties of material during the filling, the post‐filling, and the cooling steps could be carried out. Poly(vinylidene fluoride) was chosen for this study. A correlation between the evolution of the dielectric parameters and the succession of the steps in this process was undertaken. The dielectric response was sufficiently sensitive to identify the steps of the closing of the mold, filling, post‐filling, cooling, and ejection of the part. In addition, information concerning the crystallization phenomenon near the wall or in the middle of the sample was collected. The gradual filling of the cavity of the mold was also identified by dielectric measurements. The temperature dependence of dielectric properties of the sample was beneficial in evaluating the increase of the temperature of the mold with the succession of injection cycles. The influence of the packing pressure has been clearly identified and confirms the usefulness of the dielectric method as a probe for detecting the shrinkage of the part during the optimization phase of the machine parameters. The dielectric method detailed herein provides a new non‐invasive technique and could be applied to a closed‐loop control of the injection molding process.     

Numerical prediction of residual stresses and birefringence in injection/compression molded center‐gated disk. Part I: Basic modeling and results for injection molding

The present study attempted to numerically predict both the flow‐induced and thermally‐induced residual stresses and birefringence in injection or injection/compression molded center‐gated disks. A numerical analysis system has been developed to simulate the entire process based on a physical modeling including a nonlinear viscoelastic fluid model, stress‐optical law, a linear viscoelastic solid model, free volume theory for density relaxation phenomena and a photoviscoelasticity and so on. Part I presents physical modeling and typical numerical analysis results of residual stresses and birefringence in the injection molded center‐gated disk. Typical distribution of thermal residual stresses indicates a tensile stress in the core and a compressive stress near the surface. However, depending on the processing condition and material properties, the residual stress sometimes becomes tensile on the surface, especially when fast cooling takes place near the mold surface, preventing the shrinkage from occurring. The birefringence distribution shows a double‐hump profile across the thickness with nonzero value at the center: the nonzero birefringence is found to be thermally induced, the outer peak due to the shear flow and subsequent stress relaxation during the filling stage and the inner peak due to the additional shear flow and stress relaxation during the packing stage. The combination of the flow‐induced and thermally‐induced birefringence makes the shape of predicted birefringence distribution quite similar to the experimental one.     

On the characterization of tensile creep resistance of polyamide 66 nanocomposites. Part I. Experimental results and general discussions

Relatively poor creep resistance is considered as a deficiency of thermoplastics in general. Our previous study [1] on the enhanced creep resistance of polyamide 66 by a very low filler content of spherical nanoparticles explored an exciting phenomenon, which is expected to be able to promote the engineering applications of these materials. In order to comprehensively and deeply understand the effect of nanoparticles, here we provide a systematic investigation on various kinds of nanofillers, i.e. spherical particles and nanoclay, modified polyamide 66 under different stress levels (20, 30 and 40 MPa) at room and elevated temperatures (23, 50 and 80 °C), respectively. Static tensile tests are also performed at corresponding temperatures. Creep was characterized by considering the isochronous stress-strain curves, creep rate, and creep compliance with influence of temperature and stress, respectively. It was found that the creep resistance of nanocomposites was significantly enhanced by nanoparticles without sacrificing the tensile properties. The orientational hardening, as well as the thermal and stress activated process are briefly introduced in order to understand the mechanisms of viscoelasticity of these nanocomposites.     

The study of rapid curing crease‐resistant processing on cotton fabrics. Part I. The effect of chitosan on the physical properties of processed fabrics

The principal aim of this study is to explore the effect of chitosan on the physical properties of cotton fabrics in rapid curing crease‐resistant processing. It was determined that compared with the traditional three‐stage processing, the addition of chitosan is beneficial to the absorbency of processed fabrics, dry‐wet wrinkle recovery angle, and tensile strength retention. In addition, the dry‐wet wrinkle recovery angle of processed fabrics increases with the increase of curing temperature and curing treatment time, but absorbency and tensile strength retention both decrease. Also, the dry‐wet wrinkle recovery angle and tensile strength retention of processed fabrics increase with higher chitosan concentrations, but the fabric's absorbency is reduced. In general, use of 0.5%≈︁0.75% chitosan with DMEU curing treatment conditions of 8%, 200°C for 30 s will provide optimum physical property balance for processed fabrics. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 35–40, 2000     

In‐plane functionalizing graphene nanolayers with polystyrene by atom transfer radical polymerization: Grafting from hydroxyl groups

Graphene oxide (GO) was prepared from the oxidation of graphite and then it was functionalized with (3‐aminopropyl)triethoxysilane (APTES) from hydroxyl groups by a coupling reaction. Subsequently, alpha‐bromoisobutyryl bromide (BiBB) was attached to the APTES groups to yield initiator anchored graphene nanolayers (GOHBr). Then, GOHBr was used in different amounts as the precursor for atom transfer radical polymerization of styrene to evaluate the effect of graphene loading along with the graft density on the properties of final product. Successful in‐plain attachment of APTES, BiBB, and polystyrene to GO was evaluated by Fourier transform infrared spectroscopy. Graphene interlayers expansion by oxidation and functionalization processes was evaluated using X‐ray diffraction. The ordered and disordered crystal structures of carbon were evaluated by Raman spectroscopy. Morphology of graphene nanolayers was studied by scanning electron microscopy and also transmission electron microscopy. POLYM. COMPOS., 35:386–395, 2014. © 2013 Society of Plastics Engineers     

Primary and secondary gas penetration during gas‐assisted injection molding. Part I: Formulation and modeling

A theoretical study has been carried out on the transient gas‐liquid interface development and gas penetration behavior during the cavity filling and gas packing stage in the gas‐assisted injection molding (GAIM) of a tube cavity. A mathematical formulation describing the evolution of the gas/melt interface and the distribution of the residual wall thickness of skin melt along with the advancement of gas/melt front is presented. The physical model is put forward on the basis of Hele‐Shaw approximation and interface kinematics and dynamics. Numerical simulation is implemented on a fixed mesh covering the entire cavity. The model and simulation can deal with both primary and secondary gas penetrations. The predicted and measuredresults are compared in Part II of this study to validate the theoretical model. Polym. Eng. Sci. 44:983–991, 2004. © 2004 Society of Plastics Engineers.     

Color inhibition of phenolic antioxidants in Ziegler‐Natta polyethylene. I. In‐situ polymer studies

Although the level of transition‐metal catalyst residues in polyethylene (PE) has been drastically reduced over the years, they can still give rise to discoloration, particularly when associated with other additives such as antioxidants. This first of this series of papers screens a variety of candidate color suppressants featuring a range of functional groups, including alcohols, amine/sulfur compounds, and acid‐containing species. These candidate color suppressants were melt‐blended into a Ziegler‐Natta linear low‐density PE in combination with 2,2′‐isobutylidenebis(4,6‐dimethylphenol) (a highly discoloring hindered bisphenol antioxidant) and zinc stearate antacid. Yellowness index measurements made after multiple extruder passes indicated that dipentaerythritol (DPE) and triisopropylamine (TIPA) gave good color inhibition and, in some cases, outperformed established phosphites. The DPE and TIPA were found (via melt flow rate measurement) not to affect melt stability, and hydroperoxide determination revealed that DPE had no peroxide decomposition activity. The latter results indicate that the color‐suppression mechanism of DPE and TIPA is different from that associated with phosphites. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

In‐situ characterization of deposits in ceramic hollow fiber membranes by compressed sensing RARE‐MRI

Ultrafiltration with ceramic hollow fiber membranes was investigated by compressed sensing rapid acquisition relaxation enhancement (CS‐RARE) magnetic resonance imaging (MRI) to characterize filtration mechanisms. Sodium alginate was used as a model substance for extracellular polymeric substances. Dependent on the concentration of divalent ions like Ca²⁺ in an aqueous alginate solution, the characteristics of the filtration change from concentration polarization to a gel layer. The fouling inside the membrane lumen could be measured by MRI with a CS‐RARE pulse sequence. Contrast agents have been used to get an appropriate contrast between deposit and feed. The lumen was analyzed quantitatively by exploring the membrane's radial symmetry, and the resulting intensity could be modeled. Thus, different fouling mechanisms could be distinguished. CS‐RARE‐MRI was proven to be an appropriate in situ tool to quantitatively characterize the deposit formation during in‐out filtration processes. The results were underlined by flux interruption experiments and length dependent studies, which make it possible to differentiate between gel layer or cake filtration and concentration polarization filtration processes. © 2018 American Institute of Chemical Engineers AIChE J, 64: 4039–4046, 2018     

Optimization of the procedure to burn textile fabrics by cone calorimeter: Part I. Combustion behavior of polyester

The aim of this study was the optimization of cone calorimeter to determine the burning behavior of textile fabrics. In particular, the combustion behavior of commercial polyester textile fabrics with varying densities was studied in terms of time to ignition (TTI), heat release rate (HRR), and relative peak (pkHRR) were monitored. Reproducibility and repeatability of the data have been verified by the influence of instrument variable including incident heat flux, the temperature of ceramic backing pads and retaining grid used during sample mounting as well as sample weight (as the number of fabric layers), the density of textiles, and the relative humidity. A low reproducibility has been obtained when a wire grid was not used to stabilize samples during the tests. The effects of these variables on TTI and pkHRR were observed. Copyright © 2010 John Wiley & Sons, Ltd.     

Automatic detection of layout of color yarns of yarn‐dyed fabric. Part 1: Single‐system‐mélange color fabrics

To recognize the layout of color yarns of single‐system‐mélange color fabric automatically, a novel FCM‐based stepwise classification method is proposed in this article. This method consists of three main steps: (1) warp yarn segmentation, (2) weft color recognition, and (3) the layout of color warps recognition. In the first step, the yarn segmentation method based on mathematical statistics of subimages is adopted to localize warp yarns preliminarily; and then the segmentation results of warp yarn are corrected by misrecognized‐boundary remove and missing‐boundary interpolation. In the second step, the weft color is extracted based on RGB color histograms of whole fabric image. In the third step, the pixels in each warp yarn are classified into two clusters by fuzzy C‐means clustering (FCM) algorithm in CIELAB color model separately, and the preliminary recognized layout of color warps is obtained. All warp colors are clustered by FCM algorithm in CIELAB color model again and the precise layout of color warps is output. The experimental and theoretical analysis proved that the proposed method can recognize the layout of color yarns of single‐system‐ mélange color fabrics with satisfactory accuracy and good robustness. © 2015 Wiley Periodicals, Inc. Col Res Appl, 40, 626–636, 2015     

Automatic detection of layout of color yarns of yarn‐dyed fabric. Part 3: Double‐system‐Mélange color fabrics

Automat layout detection of color yarns is necessary for weaving and producing processes of yarn‐dyed fabrics. This study presents a novel approach to inspect the layout of color yarns of double‐system‐mélange color fabrics automatically, which is Part III of the series of studies to develop a computer vision‐based system for automatic inspection of color yarn layout for yarn‐dyed fabrics. The inspection of single‐system‐mélange color fabrics has been realized in Part I of the series of studies. Integrating the projection‐based region segmentation method proposed in Part I and the FCM‐based stepwise classification method proposed in Part II, the proposed approach is composed of three steps: (1) fabric region segmentation, (2) fabric region selection, and (3) layout of color yarns recognition. In the first step, the fabric regions are segmented by the projection‐based region segmentation method. In the second step, the reasonable fabric regions are selected by analyzing their color histograms and comparing their weft color's frequency. In the third step, the layout of color yarn is recognized by the FCM‐based stepwise classification method, and the precise layouts of color warps and wefts are produced. The experimental analysis proved that the proposed method can recognize the layout of color yarns of double‐system‐mélange color fabrics correctly by testing four different color fabrics and three pieces of same yarn‐dyed fabrics. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 250–260, 2017     

Optimization of injection molding design. Part I: Gate location optimization

The placement of a gate in an injection mold is one of the most important variables of the total mold design. The quality of the molded part is greatly affected by the gate location, because it influences the manner in which the plastic flows into the mold cavity. Some defects, such as weldline and overpack, can be effectively controlled only by the gate location. Therefore, the product quality can be greatly improved by determining the optimum gate location. In this paper, we develop a general methodology for gate location optimization. We first quantify quality in terms of flow simulation outputs. We can thus assess detrimental effects such as warpage and dimensional instability as a function of the independent variable, which is in this case the gate location. Next we develop methods to search for the optimum gate location. The search method introduced in this paper is a method that combines a deterministic hill climbing search with a stochastic annealing search method. The method is appropriately called simulated annealing and hill climbing (SANHIL). The criteria used for evaluation during the search process are a function of the flow simulation outputs. We demonstrate the success of the method for a complex industrial mold. The approach is applicable to any complex mold geometry and any plastic.     

Temperature control of injection molding. Part I: Modeling and identification

This paper develops a mathematical model for the dynamics of a plastic injection molding machine (IMM) that may be used for the design of a temperature‐control system. The research in this paper is novel in comparison to others since the derived models explicitly include the effects of zone interaction and backpressure, and do not lump these into an arbitrary disturbance signal. A series of experiments were conducted on a 150‐tonne IMM to identify the parameters of the proposed model using measurements of zone temperatures, percentage heater input, backpressure and screw speed. The identified model was validated using a series of blind tests that compared the model output with the measured barrel temperatures of the IMM. Polym. Eng. Sci. 44:2308–2317, 2004. © 2004 Society of Plastics Engineers.     

Kinetics of CO2/Char gasification at elevated temperatures: Part I: Experimental results

The gasification kinetics of char has so far been mainly studied based on data measured at low temperatures and low heating rates with a thermo-gravimetric analyzer. The results cannot be directly applied to high temperature gasifiers such as entrained flow gasifiers. In this work, gasification of seven types of chars in CO₂ at elevated temperatures and high heating rates was investigated with a uniquely made fluidized bed. It was found that the reaction rates for various chars were very different in low and high temperature ranges, and two orders of magnitude more pronounced in the lower temperature range. From 1273 K to 1673 K, all chars demonstrated a strong tendency to increase reaction rate with temperature. However, at a high temperature range (1773 to 1873 K), different chars demonstrated different temperature dependences. The seven types of chars studied can be roughly separated into three groups based on ash fusion temperature. Each group demonstrated a different temperature dependence at a high temperature range. For chars with low ash fusion temperatures, the reaction rate leveled off, or even decreased a little as temperature increased, which was presumed to be because of the ash fusion at elevated temperatures. These results suggest that a high temperature does not necessarily raise the gasification rate.     

Experimental characterization and morphology investigation of composites based on high‐density and low‐density polyethylene reinforced with non‐crimp‐stitched glass fabrics

In this study, the effects of matrix material on mechanical properties were investigated in glass fiber reinforced high‐density and low‐density polyethylene composites. Also, in order to compare the fiber configuration effect on anisotropic behavior, unidirectional and biaxial glass fabrics were used as reinforcement material. Composite laminates were manufactured via the compression molding technique. Tensile and three‐point bending flexural tests were conducted up to failure on specimens cut out in different directions. Extensive fracture photomicrographs were presented for observing the failure modes (e.g. delamination) of the composites resulting from a variety of loading conditions. In addition, Scanning electron micrographs of postfractured surfaces of composites were interpreted in an attempt to explain the failure mechanisms (adhesive or cohesive failure) of the composites. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers