A simplified chemorheological model of viscosity evolution for solvent containing resol resin in RTM process

The solvent content‐dependent chemorheology of the solvent containing resol resin for resin transfer molding (RTM) was investigated. The curing behavior of the resol resin was studied by in situ Fourier transform infrared spectroscopy together with rheology tests. The chemorheological behavior of resol resins with a series of solvent contents was measured under isothermal conditions. The four parameters of empirical dual‐Arrhenius equation regarding isothermal resin viscosity and reaction rate constant were found to be functions of the solvent content. A simplified chemorheological model involving only three parameters of curing temperature, time, and solvent content was first established to facilely describe the viscosity during precuring process. The simulated viscosity results during isothermal curing process agreed well with the experimental data which shows the simplified chemorheological model can be utilized to describe the viscosity evolution and offer guidance for optimizing the injection process and improving the design flexibility of RTM process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45282.     

Optimization method to reduce three-dimensional thermal gradients in resin transfer molding

Presently, the mold and resin are heated to promote resin flow and shorten curing period in order to improve manufacturing efficiency of resin transfer molding (RTM). This nonisothermal manufacturing process easily generates three-dimensional thermal gradients in the direction of resin flow and thickness of composite part. However, the existing heating systems only consider the thermal gradients along thickness direction. The thermal gradients in direction of resin flow cannot be reduced which will lead to residual stress even deformation and cracking in composite part. This article aims at reducing the three-dimensional thermal gradients in the direction of resin flow and thickness of composite part. Based on the theory of energy and fluid flow, an optimization method of heating system design by using numerical simulation is proposed. The results show this method reduces the three-dimensional thermal gradients effectively in composite part manufactured by RTM process. This study can provide powerful tools for heating system design to manufacture composites products in polymer industry. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48948.     

Development of a pressure–volume–temperature measurement method for thermoplastic materials based on compression injection molding

The pressure–volume–temperature (pvT) relationship of polymers is vitally important information in designing and manufacturing polymers. Because of the special behavior of polymers, however, it is extremely difficult to accurately measure the data in a way that matches the thermal conditions of injection molding, which is one of the most widely used processing methods. As neither widely used, commercially available measuring devices, nor special equipment mentioned in the literature can fully satisfy this need, it was decided to build a new device able to determine the pvT relationship during injection molding of the polymer. The new device consists of a special mold that can be used on an injection molding machine and a data collection system connected to it. With the help of this device, pvT data can be measured during processing according to the thermal conditions of injection molding, and also considerably faster, and even in an industrial setting. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41140.     

Thermosetting resin system based on novolak and bismaleimide for resin‐transfer molding

A thermosetting resin system for resin‐transfer molding based on novolak and bismaleimide (BMI) was developed. The novolak resin was allylated and BMI was used as the curing agent, and allyl phenyl ether, as the diluent. The viscosity–temperature curve and the viscosity–time curve were used to characterize the processing property of the resin system. The resin system had a long pot life at the injection temperature. Based on the DSC data, a regime for the curing and postcuring cycles was established. The cured resin showed outstanding heat resistance and good flexural properties. Composites based on the resin system and woven glass fabric were fabricated using RTM technology. The composites showed very good flexural properties at room temperature and high retention rates at 200 and 300°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1651–1657, 2002     

New melamine–formaldehyde–ketone resins. VI. Preparation of filled molding compositions and compression‐molding materials from reactive solvents based on cyclohexanone

The conditions and a method of preparing new molding compositions and filled compression‐molding materials from melamine–formaldehyde–cyclohexanone resins are described. The resins were obtained from melamine solutions in a reactive solvent prepared by the reaction of 1 mol of cyclohexanone with 7 mol of formaldehyde. The fillers were wood powder and sulfite cellulose. The thermal properties of the samples prepared from the compositions were studied with dynamic thermal analysis, thermogravimetry, and differential scanning calorimetry analysis. Selected mechanical properties [Brinell hardness, unnotched impact strength (Charpy method), and bending strength] of the cured resins were also measured. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The compressive property of a fiber-reinforced resin beetle elytron plate and its influence mechanism

To develop composite material beetle elytron plates (BEPs), short basalt fiber-reinforced epoxy resin BEPs with hollow trabeculae and honeycomb walls were fabricated exploratively. Through comparison with honeycomb plates (HPs) with the same wall thickness, the basic mechanical performance, failure mode and influence mechanism were studied via out-of-plane compression tests. The results show that compared with HPs, the specific strength and energy consumption per volume of BEPs can be at least 18% and 112% higher, respectively; however, the increase is less than half that of BEPs made of ductile materials. The former is due to the synergistic mechanism of the trabecular-honeycomb structure in the BEP core layer, which endows the composite BEPs with better ductility than HPs, while the latter is caused by the prominent brittleness of the composite material used in this study. Additionally, the height-to-thickness ratio of the plate honeycomb wall in this article is not large enough. Thus, the core has great rigidity and fails to buckle in experiments; instead, shear failure of the core material occurs. This study reveals for the first time the mechanical compression properties and failure mechanism of brittle material BEPs and shows a direction for developing BEPs in similar material types.     

A method based on the time–temperature superposition principle to predict pressurization time in compression molding

The quality of epoxy composites reinforced by glass fibers and manufactured by compression molding is affected by the pressurization time. Traditional methods, including differential scanning calorimetry and dynamic thermomechanical analysis, cannot be reliably used to predict pressurization time in the scenario of continuous production and inconstant circumstances seen in industry. In this paper, the rheological behaviors of epoxy under constant temperature were investigated and analyzed to verify if the time–temperature superposition (TTS) principle, which defines the relation between time and temperature in the deformation and relaxation response of a viscoelastic material, could be suitably applied to describe them. The results show that the TTS principle could indeed be used to predict resin viscosity by the horizontal shift factor. A new method based on the TTS principle and written into a program to forecast pressurization time in compression molding is proposed. The uniform surface color and the qualified thickness of the composite components using the program indicate that the program works well and that this method is feasible for predicting pressurization time during compression molding. The results of tensile and short‐beam shear strength tests show that pressurization time affects the mechanical properties of the final product. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45308.     

Long jute fiber‐reinforced polypropylene composite: Effects of jute fiber bundle and glass fiber hybridization

Two types of long jute fiber pellet consisting of twisted‐jute yarn (LFT‐JF/PP) and untwisted‐jute yarn (UT‐JF/PP) pellets are used to prepare jute fiber–reinforced polypropylene (JF/PP) composites. The mechanical properties of both long fiber composites are compared with that of re‐pelletized pellet (RP‐JF/PP) of LFT‐JF/PP pellet, which is re‐compounded by extrusion compounding. High stiffness and high impact strength of JF/PP composites are as a result of using long fiber. However, the longer fiber bundle consequently affects the distribution of jute fiber. The incorporation of 10 wt % glass fibers is found to improve mechanical properties of JF/PP composites. Increasing mechanical properties of hybrid composites is dependent on the type of JF/PP pellets, which directly affect the fiber length and fiber orientation of glass fiber within hybrid composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41819.     

CE/nano-SiO_2复合材料的RTM工艺条件

以CE(氰酸酯)树脂为基体,以硅烷偶联剂(KH-560)表面处理过的纳米二氧化硅(nano-SiO2)为改性剂,采用高速均质剪切法制备CE/nano-SiO2复合材料;然后以该复合材料体系的黏度、凝胶化时间、弯曲强度和玻璃化转变温度(Tg)为考核指标,采用单因素试验法优选出满足树脂传递模塑(RTM)工艺用复合材料体系的最佳工艺条件。结果表明:当w(nano-SiO2)=3%、工作温度为(90±10)℃、工作时间≤10 h、固化温度为110～200℃和后处理工艺条件为220℃/4 h时,复合材料在低温时具有良好的稳定性,在高温时具有良好的反应性,完全满足RTM工艺的基本要求。     

Measurement and numerical prediction of fiber‐reinforced thermoplastics' thermal conductivity in injection molded parts

Recent improvements in injection molding numerical simulation software have led to the possibility of computing fiber orientation in fiber reinforced materials during and at the end of the injection molding process. However, mechanical, thermal, and electrical properties of fiber reinforced materials are still largely measured experimentally. While theoretical models that consider fiber orientation for the prediction of those properties exist, estimating them numerically has not yet been practical. In the present study, two different models are used to estimate the thermal conductivity of fiber reinforced thermoplastics (FRT) using fiber orientation obtained by injection molding numerical simulation software. Experimental data were obtained by measuring fiber orientation in injection molded samples' micrographs by image processing methods. The results were then compared with the numerically obtained prediction and good agreement between numerical and experimental fiber orientation was found. Thermal conductivity for the same samples was computed by applying two different FRT thermal conductivity models using numerically obtained fiber orientation. In the case of thermal conductivity, predicted results were consistent with experimental data measurements, showing the validity of the models. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39811.     

Preparation mechanism and characterization of a novel,regulable hollow phenolic fiber

A novel hollow phenolic fiber was successfully prepared by the dissolution of the uncrosslinked core of the partially crosslinking spun filament derived from the melt spinning of the phenolic resin. A series of hollow phenolic fibers with various degrees of hollowness were obtained through different preparation processes. The hollow phenolic fibers were characterized with scanning electron microscopy, infrared spectrometry, and thermogravimetric analysis. The formation of the hollow core in the hollow phenolic fibers was attributed to partial crosslinking of the filaments during the curing process; the prepared hollow phenolic fibers had high crosslinkage after the second cure, their thermal stability was as excellent as that of the solid phenolic fiber, and their hollowness could be regulated from 5 to 85%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Physicomechanical and thermal properties of moldings made from liquefied wood‐based novolak PF resins under various hot‐pressing conditions

The wood powder of Cryptomeria japonica (Japanese cedar) was liquefied in phenol, with H₂SO₄ and HCl as a catalyst. The liquefied wood was used to prepare the liquefied wood‐based novolak phenol formaldehyde (PF) resins by reacting with formalin. Furthermore, novolak PF resins were mixed with wood flour, hexamethylenetetramine, zinc stearate as filler, curing agent, and lubricating agent, respectively, and hot‐pressed under 180 or 200°C for 5 or 10 min to manufacture moldings. The results showed that physicomechanical properties of moldings were influenced by the hot‐pressing condition. The molding made with hot‐pressing temperature of 200°C for 10 min had a higher curing degree, dimensional stability, and internal bonding strength. The thermal analysis indicated that using a hot‐pressing temperature of 180°C was not sufficient for the liquefied wood‐based novolak PF resins to completely cure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Research on rotary nozzle structure and flow field of the spinneret for centrifugal spinning

High-speed centrifugal spinning is a novel method of fabricating nanofibers by use of centrifugal force field. The neoteric designs and proper structural parameters of spinning nozzle will change the outlet velocity and velocity distribution uniformity of spinning solution, which could affect the quality of nanofibers. Four different spinning nozzles that can be used for high-speed centrifugal spinning are proposed. The flow of spinning solution in the different rotary nozzles is simulated based on the theoretical analysis. It can be found that the curved-tube nozzle is better for high-speed centrifugal spinning comparing with the velocity distribution of spinning solution in the four different spinning nozzles. The influence degree of the structure parameters of the curved-tube nozzle on the solution outlet-velocity is explored by orthogonal test method. The result shows that the curved-tube nozzle with an inlet diameter of 10 mm, conical transition pipe length of 3 mm, nozzle outlet diameter of 0.8 mm, curvature radius of 4 mm, and central angle of curved tube of 30°, can effectively enhance the outlet velocity of spinning solution. Finally, it is proved by centrifugal spinning experiment that the curved-tube nozzle after optimization can improve the morphology and quality of nanofibers.     

Experimental and theoretical studies on the adjustable thermal properties of epoxy composites with silver‐plated short fiberglass

This article investigates the evolution of the thermal conductivity and the coefficient of thermal expansion (CTE) of epoxy composites filled with different silver‐plated short glass fibers (Ag@GFs) treated by electroless plating. After electroless plating, the results of X‐ray diffraction and scanning electron microscopy showed that glass fibers were coated with pure silver shells whose thickness was controlled via the repetition of electroless plating cycle, and calculated by weighting method. The optical photographs showed that Ag@GFs are randomly oriented and uniformly dispersed in the composites. HotDisk thermal constant analyzer and dilatometer were used to further characterize the thermal conductivity and the CTE of the composites, respectively. The results revealed that the thermal conductivity of Ag@GF/epoxy composites increased with the increase of Ag@GF content, and was adjusted by changing the thickness of silver shell. But the CTE of the composites drops sharply as the Ag@GF content increases compared with neat epoxy. Based on Agari model with fitted factors of C_p and C_f, the calculated thermal conductivity values of Ag@GF/epoxy composites agreed well with the experimental results, and C_p kept almost unchanged, but C_f varied with the change of the thickness of silver shell, despite increasing filler content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45555.     

Manufacturing and mechanical characterization of perforated hybrid composites based on flexible polyurethane foam

This study focused on the fabrication and mechanical evaluation of nonwoven reinforced flexible polyurethane foam composites. Effects of perforation ratio, aperture size, and perforation depth on bursting and low‐velocity impact responses of perforated composite panels were investigated. The nonwoven fabric used for cover sheet was composed of flame retardant polyester, low‐melting point polyester, and recycled Kevlar staple fibers. Blending ratio of Kevlar fiber was confirmed to have relation to mechanical mechanism of cushioning layer. The highest mechanical strength value was obtained at 5 wt % of Kevlar ratio because of the highest cohesive force among recycled Kevlar, flame retardant polyester, and low‐melting point polyester fibers was provided at the blending ratio. The perforated high‐density flexible polyurethane foam composites panel was adhered with intra‐ply hybrid laminates with various areal densities on each face to form sandwich structural composites. The results revealed that perforation ratio and aperture significantly influenced the bursting and low‐velocity impact resistance behaviors of the perforated composites panel. Perforated composites with 10% perforation ratio and 4 mm aperture lead to maximum bursting strength of 437 N. Additional hybrid laminates significantly promoted the maximum bursting strength of the semiperforated hybrid composites by 212%. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42288.     

Synthesis and curing properties of a novel curing agent based on N‐(4‐hydroxyphenyl) maleimide and dicyclopentadiene moieties

A new type of epoxy resin curing agent, containing pendant phenol functions, was synthesized by the free‐radical copolymerization of N‐(4‐hydroxyphenyl) maleimide with dicyclopentadiene (DCPD) monomer in the presence of a radical initiator. The chemical structure was characterized with Fourier transform infrared spectroscopy and nuclear magnetic resonance. The molecular weight of the new curing agent was determined by gel permeation chromatography. The activity and activation energy of this new curing agent with o‐cresol formaldehyde novolac epoxy (CNE) was investigated with a nonisothermal differential scanning calorimetry technique at different heating rates. The thermal properties of the cured polymers were evaluated with thermogravimetric analysis, and the results exhibit good thermal stability. In addition, this new curing agent with CNE showed low moisture absorption because of the hydrophobic nature of the DCPD structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Experimental and simulated investigation of temperature distribution of UHMWPE laminated composites during hot pressing process

In this article, the influence of molding temperature on the mechanical properties and ballistic impact behavior of the ultrahigh molecular weight polyethylene (UHMWPE) laminated composites has been investigated. The results demonstrate that with the temperature increasing from 80 to 120 °C, the tensile strength decreases while the interlaminar bonding strength increases. The UHMWPE laminated composites manufactured by hot pressing of 75 layers UHMWPE fabrics show excellent ballistic performance when the molding temperature reaches 120 °C, indicating that dominant failure mechanism of the UHMWPE laminated composites are delamination, the fiber tension as well as bulging. Furthermore, a numerical model has been proposed to predict the temperature distribution of the UHMWPE laminated composites for a better understanding of the effect of molding temperature on the ballistic performance. The results show that the simulated results and experimental data are in good agreement. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45874.     

Effect of temperature on the release of volatile and odorous compounds in flax fibers

The behavior of flax fibers was investigated at temperatures of 80 °C, 200 °C, 215 °C, and 230 °C for a period of 60 min. First, thermogravimetric and colorimetric analyzes were carried out to characterize the impact of the temperature on the weight loss and the color of the fibers. Then, the release of volatile and odorous compounds from flax fibers was studied using both chemical and sensory approaches. Solid phase micro extraction was done to isolate the volatile organic compounds (VOCs) from the headspace of the sample while gas chromatography‐mass spectrometry (GC‐MS) and olfactometry (O) were used to determine the volatile and odorous compounds released at each temperature. About 24 VOCs were identified in the volatile fraction of flax fibers with a high occurrence of aliphatic aldehydes, phenols, and furans. Quantification by GC‐MS and by the aroma extract dilution analysis method was implemented. The results point to a critical temperature between 215 °C and 230 °C from which the odor of flax fibers becomes more intense, more complex, and with unpleasant features. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43497.     

Thermal conductivity and electromagnetic shielding effectiveness of composites based on Ag‐plating carbon fiber and epoxy

Thermally conductive and electromagnetic interference shielding composites comprising low content of Ag‐plating carbon fiber (APCF) were fabricated as electronic packing materials. APCF as conductive filler consisting of carbon fiber (CF) employed as the structural component to reinforce the mechanical strength, and Ag enhancing electrical conductivity, was prepared by advanced electroless Ag‐plating processing on CF surfaces. Ag coating had a thickness of 450 nm without oxide phase detected. The incorporation of 4.5 wt % APCF into epoxy (EP) substrate yielded thermal conductivity of 2.33 W/m·K, which is approximately 2.6 times higher than CF–EP composite at the same loading. The APCF–EP composite performed electromagnetic shielding effectiveness of 38–35 dB at frequency ranging from 8.2 to 12.4 GHz in the X band, and electromagnetic reflection was the dominant shielding mechanism. At loading content of APCF up to 7 wt %, thermal conductivity of APCF–EP composites increased to 2.49 W/m·K. Volume resistivity and surface resistivity decreased to 9.5 × 10³ Ω·cm and 6.2 × 10² Ω, respectively, which approached a metal. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42306.     

Polyurethane foams from melamine solutions in reactive solvents based on ethyl methyl ketone

This work presents conditions and method for obtaining foamed melamine–formaldehyde–butanone (Mel‐F‐MEK) materials of improved thermal stability. They were obtained from melamine solution in reactive solvents based on ethyl methyl ketone and 4,4′‐diphenylmethane diisocyanate. Some properties of obtained polyurethane foams were examined, e.g., apparent density, water absorption, dimensional stability, thermal conductivity, flammability, as well as static and dynamic thermal stability and compressive strength. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013