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

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

High‐temperature Bending Strength of Self‐Healing Ni/Al2O3 Nanocomposites

Bending strength of 5 vol.% Ni/Al₂O₃ composites as a function of testing temperature is investigated at temperatures ranging from room temperature to 1200°C. Self‐healing performance at high temperatures of the composites is evaluated by conducting high‐temperature bending tests for as‐sintered, as‐cracked, and as‐healed specimens. Bending strength of as‐sintered specimens dramatically decreases from 995 MPa at room temperature to 205 MPa at 1200°C. Additionally, the plastic deformation of the as‐sintered specimens occurs when the testing temperature reaches to 1200°C. The values of high‐temperature bending strength of as‐healed specimens are comparable with those of as‐sintered specimens. Similar to that of as‐sintered specimens, bending strength of as‐healed specimens degrades when the testing temperature increases. Results of the present study indicate that the recovery of bending strength by the self‐healing function is able to achieve at temperatures as high as 1200°C. Unlike the mechanical behaviors at high temperatures of as‐sintered and as‐healed specimens, the bending strength of as‐cracked specimens slightly increases with the increase of testing temperature. This phenomenon is attributed to the effect of the self‐healing mechanism during high‐temperature bending tests.     

Frequency Dependence of Fatigue Life and Internal Heating of a Fiber-Reinforced/Ceramic-Matrix Composite

The influence of loading frequency on the fatigue life and internal (frictional) heating of unidirectional SiC-fiber/ calcium aluminosilicate-matrix composites was investigated at room temperature. Specimens were subjected to tension–tension fatigue at sinusoidal loading frequencies from 25 to 350 Hz and maximum fatigue stresses of 180 to 240 MPa. The key findings of the study were that (1) fatigue life decreased sharply as the loading frequency was increased, (2) for all loading frequencies, fatigue failures occurred at stress levels that were significantly below the monotonic proportional limit stress of ∼285 MPa, and (3) pronounced internal heating occurred during fatigue, with the surface temperature of the fatigue specimens increasing by 160 K during 350-Hz fatigue at a peak stress of 240 MPa.     

Surface grafting of carbon fibers with artificial silver‐nanoparticle‐decorated graphene oxide for high‐speed electrical actuation of shape‐memory polymers

Poor heat conduction in the interface between the carbon fiber and polymer matrix is a problem in the actuation of shape‐memory polymer (SMP) composites by Joule heating. In this study, we investigated the effectiveness of grafting silver‐nanoparticle‐decorated graphene oxide (GO) onto carbon fibers to improve the electrothermal properties and Joule‐heating‐activated shape recovery of SMP composites. Self‐assembled GO was grafted onto carbon fibers to enhance the bonding of the carbon fibers with the polymeric matrix via van der Waal's forces and covalent crosslinking, respectively. Silver nanoparticles were further self‐assembled and deposited to decorate the GO assembly, which was used to decrease the thermal dissimilarity and facilitate heat transfer from the carbon fiber to the polymer matrix. The carbon fiber was incorporated with SMP to achieve the shape recovery induced by Joule heating. We found that the silver‐nanoparticle‐decorated GO helped us achieve a more uniform temperature distribution in the SMP composites compared to those without decoration. Furthermore, the shape‐recovery behavior and temperature profile during the Joule heating of the SMP composites were characterized and compared. A unique synergistic effect of the carbon fibers and silver‐nanoparticle‐decorated GO was achieved to enhance the heat transfer and a higher speed of actuation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41673.     

Investigating the acoustical properties of carbon fiber‐, glass fiber‐, and hemp fiber‐reinforced polyester composites

Wood is one of the main materials used for making musical instruments due to its outstanding acoustical properties. Despite such unique properties, its inferior mechanical properties, moisture sensitivity, and time‐ and cost‐consuming procedure for making instruments in comparison with other materials (e.g., composites) are always considered as its disadvantages in making musical instruments. In this study, the acoustic parameters of three different polyester composites separately reinforced by carbon fiber, glass fiber, and hemp fiber are investigated and are also compared with those obtained for three different types of wood specimens called poplar, walnut, and beech wood, which have been extensively used in making Iranian traditional musical instruments. The acoustical properties such as acoustic coefficient, sound quality factor, and acoustic conversion factor were examined using some non‐destructive tests based on longitudinal and flexural free vibration and also forced vibration methods. Furthermore, the water absorption of these polymeric composites was compared with that of the wood samples. The results reveal that the glass fiber‐reinforced composites could be used as a suitable alternative for some types of wood in musical applications while the carbon fiber‐reinforced composites are high performance materials to be substituted with wood in making musical instruments showing exceptional acoustical properties. POLYM. COMPOS., 35:2103–2111, 2014. © 2014 Society of Plastics Engineers     

Polystyrene/calcium phosphate nanocomposites: Morphology,mechanical, and dielectric properties

Matrix mediated synthesis of nanoparticles was utilized to prepare calcium phosphate nanoparticles with a size of 10 nm. The particles were characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Nanocomposites of polystyrene and nano‐calcium phosphate were prepared by the melt‐mixing technique. The composites were characterized by TEM to assess the dispersion of the nanoparticles. SAXS measurements of the composites and the fit with Beaucage model described the fractal dimensions of the particles. Mechanical properties of the composites significantly improved with the addition of nanofillers. Dielectric behavior of the nanocomposites was measured with respect to the filler content, temperature, and frequency. The dielectric constant increases with increase in temperature and decreases with increase in frequencies. Dielectric constant increased with filler content in all frequencies; however, lower frequencies showed marked effect. α‐Relaxation of the composites from the dissipation factor of the composites showed higher values for the lower frequencies. Electrical conductivity increased with respect to the filler content and volume resistivity showed the reverse trend. The theoretical prediction of the dielectric constant showed close agreement with the experimental value. POLYM. ENG. SCI. 2012. © 2011 Society of Plastics Engineers     

Numerical and experimental analysis of vibration damping performance of polyurethane adhesive in machine operations

Machining operations inherently cause structural vibrations of the work piece and machine involved, especially during roughening operations. This clearly adversely affects the surface roughness, tolerances and tooling lifetime. These effects are even more prominent in case the stiffness of the work piece to be machined is low and machining vibration excitation frequency range strongly overlaps the range of structural resonance frequencies of the work piece. This is typically the case for lightweight (sheet) metal structures. Additional fixation is costly, time-consuming and moreover it may induce structural loading and deformation which, after finishing, causes an out-of-tolerance work piece.This work presents an alternative approach which applies Polyurethane foam adhesive bonding as a temporary measure to reduce structural vibrations during milling operations of a large welded sheet metal construction.The first part of this work analyses the actual structural vibrations that occur during milling operations. Experimental and numerical modal analysis is carried out in order to determine the excitation and resonant vibration behaviour of the sheet metal structure. A dedicated Finite Element Model (FE – model) is set up which enables the necessary insights in where and how critical vibration levels may be reduced and how the work piece supports can be optimized. The second part of the work discusses the development and application of suitable vibration dampening supports applying Polyurethane foam adhesive. For this purpose, experiments are carried out to determine the vibration dampening performance of different foam layer thicknesses. These involve hammer excitation of dedicated small-scale adhesively bonded samples. FE modelling is applied to optimize the mounting of bonded Polyurethane dampers and to predict the effect on structural vibrations during milling operations. This part extensively outlines the specific experiments involved and the strategy for modelling the viscoelastic foam dampeners in the structural numerical model in a robust but effective way. The third part describes the validation measurement campaign and extensively compares structural vibration levels before and after providing the foam dampening measures. It concludes by showing that critical vibration levels may be reduced by over 58% with the method applied.     

A simplified model for predicting the ignition of FRP composites with validation using intermediate‐scale fire experiment data

This study presents a simplified theoretical model to predict the ignition of FRP composites of general thermal thickness (GTT) subjected to one‐sided heating. A simplified GTT heat transfer model to predict the surface temperature of GTT composite panels was developed, and the exposed surface temperature was used as ignition criterion. To validate the GTT model, intermediate scale calorimeter fire tests of E‐glass fiber reinforced polyester composite panels at three heat flux levels were performed to obtain intermediate‐scale fire testing data in a controlled condition with well‐defined thermal boundary conditions. The GTT model was also verified by using results from finite element modeling predictions. This model can be used to estimate the surface temperature increase, time‐to‐ignition, and mass loss of FRP composites for fire safety design and analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Electric self‐heating behavior of acetylene carbon black filled high‐density polyethylene composites

The electric self‐heating behavior of carbon black (CB) filled high‐density polyethylene (HDPE) was studied in relation to the time‐dependent current and surface temperature under various voltages and to the voltage‐dependent surface temperature at electric–thermal equilibrium. The resistance increase due to self‐heating restricts the current flow through the sample and thus stabilizes the electric power and the self‐heating temperature to their saturation values, which vary with the voltage. A simple phenomenological model shows that self‐heating at electric‐thermal equilibrium is involved in the initial resistance, the electric field induced positive temperature coefficient (PTC) transition and the heat dissipation. The influences of annealing and irradiation crosslinking on the self‐heating behavior are discussed. Copyright © 2004 Society of Chemical Industry     

Pressure‐crystallized piezoelectric structures in binary fullerene C70/poly(vinylidene fluoride) based composites

The effective fabrication of polar crystalline structures of poly (vinylidene fluoride) (PVDF), such as beta and gamma, is crucial to the development of piezoelectric polymer devices. In this study, we report the effect of pressure on binary fullerene C70/PVDF‐based composite with an overall good C70 dispersion, which was prepared by an easy physical and mechanical route. The C70/PVDF composites were crystallized in a piston‐cylinder high‐pressure apparatus, and the polymeric crystalline structures totally with extended‐chain piezoelectric beta‐ or gamma‐form lamellae were successfully achieved in the composite samples by varying temperature, pressure, crystallization time, and composite composition. The c‐axis thickness of the extended‐chain beta‐form lamellae of PVDF in the composites increased and decreased with the increase of the applied temperature and pressure, respectively, and it increased with the increase of crystallization time. Although C70 was found to be negative for the rapid formation of beta‐form PVDF crystals, it played an important role in the growth of a beta‐form PVDF nanowire with extended‐chain crystalline substructures. The template‐free formation of such piezoelectric nanowires was attributed to a C70‐induced self‐assembly of the polymer, driven by physical interactions at high pressure. The pressure‐crystallized C70/PVDF composites, self‐reinforced with unique one‐dimensional piezoelectric structures, may diversify niche applications in advanced functional polymeric devices. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1823–1833, 2013     

Experimental study on the flow and deposition of powder particles in rotational molding

The nature of powder flow and its effect on particle deposition in rotationally molded parts were considered in this work. Experiments were carried out to observe the effects of various parameters, such as particle characteristics and operating conditions, on the deposition patterns of polyethylene powders and micropellets. The results indicate that the polymeric powders were cohesive enough to prevent size segregation at ambient temperature; however, segregation occurred when particles that had a smooth surface and regular shape were used. During processing, however, a new phenomenon of reverse cohesive segregation was observed. The results showed that the final deposition patterns are controlled primarily by the initial segregation patterns, as well as by the heating rate and rotation speed, which affect the evolution of adhesive forces between particles during heating and melt deposition process. An order‐of‐magnitude analysis was conducted to evaluate the development of cohesive forces between particles, and to estimate their effects on the movement of particles. This study provides a better understanding of the flow characteristics of polymer particles during the rotational molding process, which is very important in the development of techniques for fabricating composites and multilayered products. Polym. Eng. Sci. 45:62–73, 2005. © 2004 Society of Plastics Engineers.     

Temperature‐dependent tensile strength model for 2D woven fiber reinforced ceramic matrix composites

This paper presents a temperature‐dependent model for predicting the tensile strength of 2D woven fiber reinforced ceramic matrix composites. The model takes into account the combined effects of temperature, temperature‐dependent residual thermal stress, temperature‐dependent matrix strength, and fibers strength on the tensile strength of composites. To verify the model, the tensile strengths of 2D woven fiber reinforced ceramic matrix composites available are predicted at different temperatures. The model predictions agree well with the experimental data. This work could provide a practical technical means for predicting the temperature‐dependent tensile strength of 2D woven fiber reinforced ceramic matrix composites and uncovering the dominated mechanisms leading to the change of tensile strength and their evolution with temperature.     

Mechanical and open hole tensile properties of self‐reinforced PET composites with recycled PET fiber reinforcement

The tensile strength of notched composites is an important factor for composite structural design. However, no literature is available on the notch sensitivity of self‐reinforced polymer composites. In this study, self‐reinforced recycled poly (ethylene terephthalate) (srrPET) composites were produced by film stacking from fabrics composed of double covered uncommingled yarns (DCUY). Composite specimens were subjected to uniaxial tensile, flexural, and Izod impact tests and the related results compared with earlier ones achieved on srPET composites reinforced with nonrecycled technical PET fibers. Effects of open circular holes on the tensile strength of srrPETs were studied at various width‐to‐hole diameter (W/D) ratios of the specimens. In the open hole tensile (OHT) measurements bilinear (yielding followed by post‐yield hardening) stress–strain curves were recorded. The srrPET composites had extremely high yield strength retention (up to 142%) and high breaking strength retention (up to 81%) due to the superior ductile nature of the srrPETs, which induces plastic yielding near the hole thereby reducing the stress concentration effect. The results proved that srrPET composites are tough, ductile notch‐insensitive materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43682.     

Kinetics modeling of carbon‐fiber‐reinforced bismaleimide composites under microwave and thermal curing

This article focuses on the analysis of the curing kinetics of carbon‐fiber‐reinforced bismaleimide (BMI) composites during microwave (MW) curing. A nonisothermal differential scanning calorimetry (DSC) method was used to obtain an accurate kinetic model. The degree of curing, chemical characterization, and glass‐transition temperature of the resin and composites cured by thermal and MW heating were analyzed with DSC, Fourier transform infrared spectroscopy, and dynamic mechanical analysis. The experimental results indicate that MW accelerated the crosslinking reaction of the BMI resin and had different effects on the reaction processes, especially for the glass‐transition temperature and chemical bonds. However, the curing reaction rate of the BMI resin decreased when the carbon fibers were added to the BMI resin during thermal and MW curing. According to the experimental results, the curing kinetic model of the BMI composite was used to provide a theoretical foundation for MW curing analysis. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43770.     

Effects of ultrasonic vibration on the rheological behavior of high‐density polyethylene composites filled with flash aluminum flake pigments

The metallic effect of polymer composites was produced through the loading of flash aluminum flake pigments (FAFPs) into polymers. This production method could eliminate postprocessing techniques, such as spray coating, painting, or metallization. We used a self‐improved, ultrasound‐assisted capillary rheometer to explore the rheological behavior of high‐density polyethylene composites filled with FAFPs in the absence and presence of ultrasound treatment. The effects of the ultrasound intensity, experimental temperature, filler content, and particle size on the composite viscosity were studied. The results show that the composite viscosity not only decreased as the ultrasound intensity, experimental temperature, and particle size increased but also decreased as the filler content decreased. A viscosity model of the polymer melts was proposed to illustrate the relationship between the viscosity and ultrasonic intensity. The viscosity obeyed the equations under ultrasonic vibration. The predicted results for the composite viscosity complied greatly with the experimental values. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44906.     

Modeling of coat‐hanger die under vibrational extrusion

The distributions of the pulsatile pressure field, the pulsatile velocity field, and the pulsatile resident time of the polymeric melt in the coat‐hanger die are derived by using the pulsation of volumetric flow rate and pressure. Subsequently, formulae of the manifold radius and the slope of the manifold are deduced via volumetric flow rate pulsation. Polypropylene (PP) was employed for the experiments of the vibrational extrusion. The results indicate that the average extrusion pressure declines with frequency or amplitude decreasing; the distribution of residence time along the width of the coat‐hanger die performs uniformly during the vibrational extrusion process; the theoretical extrusion pressure well agrees with the experimental pressure; the experiments of tensile test, impact test implicate that vibration improves the mechanical properties of products; differential scanning calorimetry testing demonstrates that the melting point of PP is moved to a higher temperature value, and the endothermic enthalpy and the crystallinity are improved as well when superimposing the vibrational force field. Accordingly, the model of the coat‐hanger die under vibrational extrusion is well consistent with the experiments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of irradiation crosslinking on time dependences of conduction and self‐heating in acetylene carbon black filled high‐density polyethylene composites

The time dependences of electrical conduction and self‐heating in high‐density polyethylene/acetylene carbon black composites crosslinked with electron beam irradiation at three different dosages are studied in relation to voltage and ambient temperature. The characteristic decay current constant (τ_i) and the exponential growth time constant for self‐heating (τ_g) are determined for the samples under voltages (U) above the onset voltage (U_c) of self‐heating. The influence of crosslinking on the current decay dynamics, self‐heating process, and amplitude of the resistance switching under field action are discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4418–4422, 2006     

Fundamental study on the development of a surgical device for polymer‐tissue adhesion using vibration damping of polymeric materials

To develop a surgical handheld device that can be used to promote polymer‐tissue or tissue‐tissue adhesion, we designed a polymeric clamp material (PCM) that self‐heats as a result of vibration. By using the PCM, heat can be applied to the target biomaterial and the tissue simultaneously. The optimal temperature is high enough to promote adhesion but low enough to retain the native tissue's integrity. Furthermore, the PCM should not adhere to the target polymer or the native tissue. We found that the temperatures of fluorinated polymers, such as poly(tetrafluoroethylene) (PTFE) and perfluoroalkoxy (PFA), increased within 60 s to 150°C and maintained a stable temperature thereafter. The heat that was transferred to the saucer attached to the potential PCM was slightly above 100°C, a temperature that promotes adhesion but does not damage the native tissue. No deformation or melting was observed during the experiment, indicating that PTFE or PFA possess desirable PCM characteristics for use as a surgical heating device. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2532–2537, 2013     

Sintering behavior of SiO2 aerogel composites reinforced by mullite fibers via in-situ rapid heating TEM observations

The direct in situ TEM imaging method is adopted to investigate the sintering behavior of SiO₂ aerogels during the rapid heating process. The structural evolution of SiO₂ aerogels and composites at different times during the heat treatment process are further investigated via SEM, FT-IR, BET and XRD. The results indicate that the shrinkage of the SiO₂ aerogels and composites primarily occurs during the initial stage of the heating process (within 20 min) with the shrinkage primarily linked to the fusion of small aerogel particles at high temperatures. The aerogel structure then stabilizes with no further shrinkage observed as the heating process continues. The heat treatment process only promotes the space rearrangement and fusion of small aerogel particles with no observed changes to the amorphous structure of the aerogels, and the small-sized particles fusion was the main causes for the structural evolution of SiO₂ aerogels and composites under rapid heating condition.