Improved dispersion of carbon nanotubes in poly(vinylidene fluoride) composites by hybrids with core–shell structure

Core–shell structure hybrids of carbon nanotubes (CNTs)/BaTiO₃ (H‐CNT‐BT) and commercial multi‐wall CNTs are respectively incorporated into poly(vinylidene fluoride) (PVDF) for preparing the composites near the percolation thresholds. A comprehensive investigation for CNT's dispersion and composite's conductivity is conducted between H‐CNT‐BT/PVDF and CNT/PVDF at different depths vertical to the injection's direction. Gradual increases of the conductivity in two composites are observed from the out‐layer to the core part which infers an inhomogeneous CNT's dispersion in the interior of composites due to their migration under flow during the injection. However, the use of H‐CNT‐BT fillers with core–shell structure enables to reduce this inhomogeneous dispersion in the composite. Furthermore, the conductive network of CNTs in H‐CNT‐BT/PVDF is less sensitive to the thermal treatment than the one in CNT/PVDF composite, which infers the core–shell structure of hybrids can ameliorate the sensitivity of the conductive network. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45693.     

Comparative performance of carbon nanotube and nanoclay on thermal properties and flammability behavior of amorphous polyamide/SEBS blend

Multiwall carbon nanotubes (CNT) or montmorillonite clay (MMT-30B) were added to a poly(hexamethylene isophthalamide-co-terephthalamine) (an amorphous polyamide - aPA) and styrene-ethylene/butylene-styrene graphitized with maleic anhydride (SEBS) blend, in different concentrations, in order to investigate the morphology, thermal properties and flammability behavior. Different nanoparticle localizations in the phase blend were observed through transmission electronic microscopy. CNT nanoparticles are localized in SEBS phase, and MMT-30B nanoparticles in aPA phase. No significant changes were observed on transition temperatures and thermal stability with both nanoparticle additions. However, a slight increase on storage modulus for clay nanocomposites and a slight reduction for carbon nanotube nanocomposites were observed, due to their different phase localizations. Regarding flammability, CNT nanocomposites showed better performance as a flame retardant when compared to samples with MMT-30B. Although the MMT-30B nanocomposites could not be classified according to the UL-94 criteria, no dripped flaming particles were observed, due to the a char barrier formation on the polymer surface. The CNT nanocomposites were classified according to the UL-94 criteria as V-2. The CNT's selective localization on the SEBS phase decreases its heat-release rate, but no interconnected network structure was formed in the matrix to suppress the dripping flaming particles.     

Carbon nanotube agglomeration effect on piezoresistivity of polymer nanocomposites

Carbon nanotube (CNT) agglomeration exists inevitably in all CNT-polymer composites. This paper quantified the effect of CNT agglomeration on the piezoresistivity of CNT-polymer composites. A new multiscale model of 3-dimensional deformable CNT percolating networks has been developed, where the CNT agglomerates were modeled as second phases embedded randomly in the polymer matrix. The newly developed model agrees quantitatively with experimental data. The study found that the CNT agglomeration is responsible for the reduced electrical conductivity and nonlinearity of piezoresistivity with respect to the zero strain. Its effect can be quantified by the newly developed model. Parametric analyses were conducted to show the effects of morphology and electrical properties of CNTs, the Poisson's ratio of CNT-polymer composites and the extent, internal density and size of CNT agglomeration on the electrical conductivity and piezoresistivity. The current work provides a useful analysis tool for designing smart sensing and multifunctional polymer composites.     

Electrical conductivity of interphase zone in polymer nanocomposites by carbon nanotubes properties and interphase depth

In this work, carbon nanotubes (CNT) properties and interphase depth define the interphase conductivity in polymer CNT nanocomposites (PCNT). In addition, the operative CNT length and volume portion are linked to the conductivity transportation between CNT and insulated polymer medium to propose a simple model for conductivity. The significances of various terms on the interphase conductivity and conductivity of PCNT are justified and the model's predictions are examined using the experimental outputs of certain examples. Thin CNT and dense interphase obtain the extraordinary conductivity transportation, while CNT length and conductivity are ineffective. Moreover, thin, small, and high-conductive CNT as well as dense interphase introduce the high interphase conductivity. The estimations of conductivity appropriately follow the experimental data authorizing the established model. This model is capable to substitute the conventional models owing to the assumption of innovative nanocomposite's terms.     

碳纤维树脂基复合板料的铺层方式对低速冲击性能的影响

为研究碳纤维增强树脂基复合材料(CFRP)板铺层方式对低速冲击性能的影响,设计了一系列CFRP板的冲击试验.对CFRP板的铺层方式、冲击能量的形式进行调节和改变,获取CFRP板在各种条件下的低速冲击行为;再通过冲击实验和超声波扫描的方法研究冲击过程中CFRP板的铺层方式和冲头质量对碳纤维树脂基复合材料板冲击性能的影响....     

Measurements of Kinetic Energy Loss for Particles Impacting Surfaces

Incoming and rebounding particle velocities were measured to within several particle diameters of the impaction surface using laser Doppler velocimetry. Impacts occurred normal to the surface and ranged from 1 m/s, near the threshold for particle bounce, to 100 m/s, well into the plastic damage regime. Monodisperse ammonium fluorescein spheres, 2.6–6.9 μm in diameter, impacted target surfaces including polished molybdenum and silicon, cleaved mica, and a fluorocarbon polymer. The incident kinetic energy recovered on rebound depended on particle size and target composition at low velocity (< 20 m/s), where the adhesion surface energy is important. No dependence on target composition was found at higher velocities where up to half of the impact energy was lost to plastic deformation. Plastic deformation was a significant component of energy loss even at impact velocities near critical velocity. Critical velocities for the onset of bounce decreased with a stronger power-law dependence on particle diameter than expected from classical adhesion theory or the elastic flattening model proposed by Dahneke. This is consistent with kinetic energy loss contributions from both plastic deformation and surface forces. Auxiliary experiments conducted with and without continuous discharge of the impact surface indicated the absence of a significant electrostatic contribution to particle adhesion.     

On the mechanism of piezoresistivity of carbon nanotube polymer composites

Carbon nanotube (CNT) polymer composites exhibit strong nonlinear and asymmetric piezoresistivity about zero strain in tensile and compressive strain states. The existing models explain the characteristic qualitatively but not quantitatively. This paper attempts to understand the mechanisms of this piezoresistivity by developing a new 3-dimensional percolation CNT network model, where the effect of CNT deformation (wall indentation and tube bending) is considered for the first time. The predicted electrical conductivity and piezoresistivity agree with experiments quantitatively, which reveals that the CNT deformation is a dominant mechanism for the nonlinearity and asymmetry of piezoresistivity of CNT-polymer composites. Parametric studies have been conducted to show the effects of morphology and electrical properties of CNTs, work functions and Poisson's ratio of polymer on the piezoresistivity of CNT-polymer composites for future application in nanosensing composites.     

Mechanical properties of defective carbon nanotube/polyethylene nanocomposites: A molecular dynamics simulation study

Because of their remarkable performance properties and technological promise, polymer nanocomposites reinforced with single‐walled carbon nanotubes (SWCNTs) have attracted considerable attention in the engineering, applied physics, and materials science communities. Recent experimental and computational investigations have shown that the presence of nanoscale defects in CNTs can significantly impact their electrical, mechanical, and thermal properties. In this article, for the first time, we examine the effect of defective CNTs on the interfacial characteristics and mechanical properties of CNT/polyethylene (PE) nanocomposites. Our molecular dynamics simulations show that as few as five vacancy defects in each CNT in a high‐volume‐fraction CNT/PE nanocomposite can decrease the longitudinal Young's modulus of the nanocomposite by as much as 18%, and the shear stress at the CNT/polymer interface by as much as 38%. By accounting for nanoscale defects and their effect on the CNT/polymer interfacial mechanics, our findings provide a practical guide for designing nanocomposites that are capable of attaining a desired set of elastic performance properties. POLYM. COMPOS., 305–314, 2016. © 2014 Society of Plastics Engineers     

Molecular dynamics simulation of mechanical properties and interaction energy of polythiophene/polyethylene/poly(p‐phenylenevinylene) and CNTs composites

Carbon nanotubes (CNTs) have very important applications in ultrastrong lightweight materials. CNTs can improve mechanical properties of polymer matrix such as breaking stress and Young's modulus. In this article, we studied the interaction between polythiophene (PT)/polyethylene (PE)/poly(p‐phenylenevinylene) (PPV) and CNTs by molecular dynamics (MD) simulation based on a reactive force field (ReaxFF). We studied the influence of CNT diameter, polymer type, and temperature on interaction energy. We found that a large radius CNT at low temperature shows the strongest interaction energy with PT. In addition, we computed the mechanical properties of CNTs‐polymer composites such as the breaking stress, breaking strain, and Young's modulus. Our results show that there is a direct relation between mechanical properties and interaction energy. We found that the mechanical properties of CNTs‐PT composite are better than CNTs‐PPV and CNTs‐PE and it is a good candidate for ultrastrong lightweight materials. We studied the influence of temperature on the mechanical properties. Our results show that CNTs‐polymer composites show stronger mechanical properties at low temperature. We found that ReaxFF can reproduce the other force fields results and it is a very powerful force field to study the various properties of CNTs‐polymer composites. POLYM. COMPOS., 35:2261–2268, 2014. © 2014 Society of Plastics Engineers     

Measurement and modelling of hollow rubber spheres: surface-normal impacts

Abstract

The performance of natural rubber sports balls under impact conditions is dominated by the material's behaviour under high strain rate conditions dictated by the impact velocity and ball dimensions. To design improved products, sports ball manufacturers need to better understand the physical phenomena associated with ball impact against both rigid and deformable surfaces. This understanding will provide the foundation for performance prediction and optimisation design tools as well as more appropriate product and ultimately material testing techniques. Rebound characteristics of pressurised and pressureless tennis balls and their respective rubber cores subject to normal impacts are presented for a range of incident velocities. High-speed video analysis has been used to measure coefficient of restitution, impact duration and 'whole ball' deformation to validate a surface-normal impact finite element method based predictive model as the first step towards a more comprehensive oblique impact model. Accounting for strain rate dependent stiffness and damping material properties has achieved close correlations between model predictions and observed impact behaviour. The propagation of dominant bending and hoop-strain waves through the ball during the impact is revealed to illustrate the methodology's effectiveness in predicting ball performance associated with difficult to observe impact phenomena.     

Toughening of unmodified polyvinylchloride through the addition of nanoparticulate calcium carbonate and titanate coupling agent

PVC/CaCO₃ polymer nanocomposites of differing compositions were produced using a two‐roll mill and compression molding. In all formulations, 0.6 phr of titanate was incorporated to assist dispersion during processing. The morphology was observed using transmission electron microscopy, and the static and dynamic mechanical and fracture properties were determined. Fracture toughness examination was performed according to strain energy release test method. The presence of nanometer‐sized CaCO₃ particles led to a slight decrease in the tensile strength but improved the impact energy absorption, storage modulus, and fracture toughness. The use of titanate coupling agent softened the polymer matrix and reduced the matrix's modulus. Fracture surface examinations by scanning electron microscopy showed that the coupling agent improved particle–matrix bonding and inhibited void formation around the particles. Finite element analysis suggested that the improved particle–matrix bonding reduced the matrix's plasticity around the particles, which decreased the toughening efficiency of the composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Toward mechanistic understanding the effect of aspect ratio of carbon nanotubes upon different properties of polyurethane/carbon nanotube nanocomposite foam

This study investigated the carbon nanotube's aspect ratio's influence on the nanocomposite foams' cellular structure and mechanical, acoustic absorption characteristics. The free-rising foaming process has been used for producing different flexible polyurethane (PU) foams embedded with other multi-walled carbon nanotubes (MWCNT's). Dynamic mechanical and thermal analysis, flow resistivity, and compressive mechanical measurements were achieved on the prepared samples. The acoustic absorption coefficient in a wide range of frequencies was estimated for the prepared PU/CNT foamed nanocomposite samples. Results indicated that by increasing the aspect ratio of MWCNT, the absorption coefficient's peak shifts toward the lower frequencies and improved sound absorption characteristics of PU foam in the low-frequency region. Moreover, the Young modulus of nanocomposite samples increases by increasing the aspect ratio of MWCNT's, whereas the stored strain energy or area under the stress–strain curve increases. Based on the obtained results, it is observed that the acoustic absorption coefficient of produced nanocomposite foams at the frequency of 800 Hz has been reported to have a 70% improvement in 2 cm samples and a 40% improvement in 3 cm samples compared to obtained results from pure PU foam.     

Role of paper sludge particle size and extrusion temperature on performance of paper sludge–thermoplastic polymer composites

The effect of paper sludge's particle size and extrusion temperature on the physical and mechanical properties of paper sludge–thermoplastic polymer composites was investigated. In the experiment three levels of particle sizes for the paper sludge and four extrusion temperatures were designed to examine the physical and mechanical properties of these composites. The ash contents of the paper sludge were about 73.7, 46.2, and 38.1% with particle sizes of below 0.15, 0.18–0.25, and 0.42–0.84 mm, respectively, which meant lower ash content and higher cellulose fiber content, in the larger particle size of paper sludge. As the particle size of the paper sludge decreased, the swelling thickness, water absorption, and tensile and flexural strengths of the composite improved; but the particle size of the paper sludge had no effect on its unnotched impact strength. With the increase of the extrusion temperature the thickness swelling and water absorption of the composites were slightly improved but not statistically different. A rise of the extrusion temperature generally had a positive effect on the tensile and flexural properties of the composite. The notched and unnotched impact strengths of the composite increased with the increase of the extrusion temperature from 190 to 230°C, but they decreased slightly at an extrusion temperature of 250°C. This low impact energy at an extrusion temperature of 250°C may be attributed to the excessively brittle fibers from thermal decomposition. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2709–2718, 2001     

Failure and fragmentation of ceramic target with varying geometric configuration under ballistic impact

The failure and fragmentation of monolithic bare alumina 99.5% ceramic target and energy dissipation of steel 4340 projectile have been studied in a series of ballistic experiments carried out, with the incidence velocities in a range, 122–290 m/s. The velocity drop and energy dissipation increased with incidence velocity for 10 mm thick target with damage zone extended upon the whole area of rear face at higher velocities. The ballistic results obtained with the 10 mm thick target have been compared with the ballistic performance of the 5 mm thick target used in a previous study to explore the effects of target thickness on the failure mechanism. A model for the residual velocity of projectile after perforation of the single layered ceramic target has been developed based on the Lambert Jonas model by using the experimental data available for 5 mm and 10 mm thick alumina 99.5% target against 10.9 mm projectile. The residual velocities and damage patterns were reproduced with a reasonable amount of accuracy by a three-dimensional finite element model developed on commercial ABAQUS/CAE. The effect of obliquity and projectile diameter to target thickness ratio (D/T) on ballistic performance has been determined by the numerical simulation model with impact velocity in a range of 300–500 m/s. A spatial variation of ejected fragments velocity at different time steps was plotted to develop a velocity profile for the ceramic fragments coming out of the target. A semi-empirical model has been proposed for residual velocity after perforation of a monolithic ceramic target, relating to the incidence velocity and projectile diameter to target thickness ratio. The monolithic ceramic targets have been investigated for a comparative assessment of energy dissipation by the ceramic layer to eventually design an efficient front layer of a ceramic based composite armour in future studies.     

Experimental characterization and computational simulations of the low‐velocity impact behaviour of polypropylene

The objective of this work is to validate predictive models for the simulation of the mechanical response of polypropylene undergoing impact situations. The transferability of material parameters deduced from a particular loading scenario (uniaxial loading) to a different loading situation (multiaxial loading) was studied. The material was modelled with a modified viscoplastic phenomenological model based on the G'Sell–Jonas equation. To perform the numerical simulations, a user‐material subroutine (VUMAT) was implemented in the ABAQUS/explicit finite element code. Constitutive parameters for the model were determined from isostrain rate uniaxial tensile impact test data using an inverse calibration technique. In addition, falling‐weight low‐energy impact tests were performed on disc‐shaped specimens at velocities in the range 0.7 to 3.13 m s^?1. The model predictions were evaluated by comparison of the experimental and finite element response of the falling‐weight impact tests. The G'Sell–Jonas model showed much better predictability than classical elastoplasticity models. It also showed excellent agreement with experimental curves, provided stress‐whitening damage observed experimentally was accounted for in the model using an element failure criterion. © 2013 Society of Chemical Industry     

Prediction of the effective thermal conductivity of carbon nanotube‐reinforced polymer systems

A study dealing with the effect of the carbon nanotubes (CNTs), at various weight fractions, on the effective thermal conductivity of a CNT‐reinforced polymer by associating it with the Kapitza resistance (R_Kap) phenomena is presented. The finite element method was utilized as a tool for the models' solution by using the principles of the representative volume element. An intermediate continuum layer between polymer matrix and CNTs was considered for the representation of the R_Kap phenomena. The influence of the intensity of R_Kap phenomena at various CNT contents was investigated through the parametric study of the R_Kap value and the thickness of the intermediate layer. The predicted results were compared against experimental measurements derived from an equivalent CNT–epoxy resin system. The discrepancy between calculated and measured values is diminished when the R_Kap phenomena are taken into account, thus confirming the existence of thermal resistance between the CNTs and the polymer matrix. The R_Kap rise as the % CNT weight content is increased. This behavior is correlated to the higher CNT agglomeration at higher CNT contents, which is proven by the scanning electron microscopy and thus providing a first indication of the effect of the CNT agglomeration on the effective thermal conductivity at various CNT contents. POLYM. COMPOS., 35:1997–2009, 2014. © 2014 Society of Plastics Engineers     

Impact characterization of a carbon fiber‐epoxy laminate using a nonconservative model

The study of polymer and composite behavior under high strain rates is of fundamental relevance to determine the material suitability for a selected application. However, the impact phenomenon is a very complicated event, mainly due to the short duration, large deformation, and high stresses developed in the sample. In this work, we have performed impact tests over a carbon fiber reinforced epoxy using low‐energy in the striker. A nonconservative and nonlineal spring‐dashpot series model has been proposed to reproduce the material behavior. The model considers simultaneously both flexural and indentation phenomena accounting for energy losses by means of the restitution coefficient. Using this model, an excellent fit between the predicted and the experimental force‐time trace has been obtained below the composite failure point, which was recognized by a separation of both mentioned curves. As the epoxy‐fiber laminate has a very low viscoelasticity, the high strain rate Young's modulus obtained from the model was compared with that extracted from a conventional three point bending test, finding a very good match between the values. The study of the dashpot coefficients allows concluding that the dominant mechanism is the composite flexion, while the indentation effects contribution takes on importance at low impact velocities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2256–2263, 2005     

Using supercritical carbon dioxide in preparing carbon nanotube nanocomposite: Improved dispersion and mechanical properties

Improvements in carbon nanotube (CNT) dispersion and subsequent mechanical properties of CNT/poly(phenylsulfone) (PPSF) composites were obtained by applying the supercritical CO₂ (scCO₂)‐aided melt‐blending technique that has been used in our laboratory for nanoclay/polymer composite preparation. The preparation process relied on rapid expansion of the CNTs followed by melt blending using a single‐screw extruder. Scanning electronic microscopy results revealed that the CNTs exposed to scCO₂ at certain pressures, temperatures, exposure time, and depressurization rates have a more dispersed structure. Microscopy results showed improved CNT dispersion in the polymer matrix and more uniform networks formed with the use of scCO₂, which indicated that CO₂‐expanded CNTs are easier to disperse into the polymer matrix during the blending procedure. The CNT/PPSF composites prepared with scCO₂‐aided melt blending and conventional melt blending showed similar tensile strength and elongation at break. The Young's modulus of the composite prepared by means of conventional direct melt blending failed to increase beyond the addition of 1 wt% CNT, but the scCO₂‐aided melt‐blending method provided continuous improvements in Young's modulus up to the addition of 7 wt% CNT. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Synthesis and properties of porous ion-exchange membranes,I. Polymer-polymer-filler system

A method of preparation of porous ion-exchange membranes (PIEM's) with sulfonic groups is presented. One of the four studied polymer blends is recommended for PIEM's preparation. It is the ternary blend of polyethylene with poly(styrene-co-divinylbenzene), isotactic polypropylene, and calcium carbonate. The effect of blend composition on membrane properties is also discussed. Both blend components, PP and CaCO₃, affected the membrane porosity while only PP governed the pore diameter. A model of PIEM's creation is suggested. The antifouling behaviour of PIEM's was evaluated by means of ultrafiltration of bovine serum albumine or poly(ethylene glycol) solutions as well as skimmed-milk and an active sludge designated for bioconversion of aldehydes. It was found that membranes with ion-exchange capacity higher than 1 mmol/g offer antifouling effect. PIEM's have also higher solute rejection parameter and are easier to regenerate than membranes without sulfonic groups.     

Modelling the impaction of a micron particle with a powdery layer

The interaction of an incoming micron particle with already deposited particles is an important factor in particulate fouling of heat exchangers. A numerical model was developed based on the discrete element method to simulate this interaction. The contact forces between the colliding particles are based on the concept of contact mechanics, which takes plastic deformation of particles into consideration. The numerical model predicts the critical sticking and removal velocities, which are important parameters in determining the fouling rate of heat exchangers. Very detailed information of the bed dynamics can be extracted from the numerical model. It appears that the time required for a particle to be ejected out of a bed of particles due to an incident particle impact is proportional to the interacting particles diameter and to the square root of the number of bed layers. The maximum indentation in an incident particle hitting a bed of particles is proven theoretically and numerically to be directly proportional to the velocity and diameter of the incident particle if plastic deformation occurs. Experiments were carried out in a vacuumed column to validate the numerical model. In the experiments, incident particles dropped onto a bed of particles and the sticking, bouncing and removal behaviour were measured as a function of the incident particle impact speed. Both the numerics and the experiments showed that there are velocity regimes at which the incident particle sticks, bounces off or removes particles from the bed of particles. The regimes overlap due to the impact angle effect. The numerical model predictions regarding the critical sticking and removal velocities are in agreement with the measured values.