Fiber Polymer Composites Research Articles

Hybrid and hierarchical nanoreinforced polymer composites: Computational modelling of structure–properties relationships

Hybrid and hierarchical polymer composites represent a promising group of materials for engineering applications. In this paper, computational studies of the strength and damage resistance of hybrid and hierarchical composites are reviewed. The reserves of the composite improvement are explored by using computational micromechanical models. It is shown that while glass/carbon fibers hybrid composites clearly demonstrate higher stiffness and lower weight with increasing the carbon content, they can have lower strength as compared with usual glass fiber polymer composites. Secondary nanoreinforcement can drastically increase the fatigue lifetime of composites. Especially, composites with the nanoplatelets localized in the fiber/matrix interface layer (fiber sizing) ensure much higher fatigue lifetime than those with the nanoplatelets in the matrix.

Using in-situ polymerization of conductive polymers to enhance the electrical properties of solution-processed carbon nanotube films and fibers.

Single-walled carbon nanotubes/polymer composites typically have limited conductivity due to a low concentration of nanotubes and the insulating nature of the polymers used. Here we combined a method to align carbon nanotubes with in-situ polymerization of conductive polymer to form composite films and fibers. Use of the conducting polymer raised the conductivity of the films by 2 orders of magnitude. On the other hand, CNT fiber formation was made possible with in-situ polymerization to provide more mechanical support to the CNTs from the formed conducting polymer. The carbon nanotube/conductive polymer composite films and fibers had conductivities of 3300 and 170 S/cm, respectively. The relatively high conductivities were attributed to the polymerization process, which doped both the SWNTs and the polymer. In-situ polymerization can be a promising solution-processable method to enhance the conductivity of carbon nanotube films and fibers.

Thermoplastic Matrix Material Selection Using Multi Criteria Decision Making Method for Hybrid Polymer Composites

Multi criteria decision making (MDCM) methods are amongst the approaches available in aiding composite designers to make the final decision especially during the material selection process where multiple solutions are present and various requirements are required to be satisfied simultaneously. Thus, in this paper, material selection process of thermoplastic matrix using MDCM methods for hybrid natural fiber/glass fiber polymer composites is presented. The aim is to identify the most suitable type of thermoplastic matrix to be used in the hybrid polymer composites formulation. The Weighted Sum Method (WSM) is applied in the selection process of seven candidate thermoplastic matrix materials based on the product design specifications. The overall analysis highlights that low density polyethylene (LDPE) is the preferred matrix for the intended application based on the highest scores obtained compared to other candidate materials. A signal-to-noise (S/N) ratio analysis was further performed to validate the initial selection results where LDPE once again outperformed other candidate materials with highest S/N ratio score in the non-compensatory approach.

Luminescent composite polymer fibers: In situ synthesis of silver nanoclusters in electrospun polymer fibers and application

The purpose of this study is to prepare multifunctional polymer fibers. We report a simple and controllable method for in situ synthesis of Ag nanoclusters (NCs) in electrospun polymer fibers via a photochemical reaction. The prepared composite polymer fibers emit pink luminescence and the luminescence property can be optimized by pH and Ag(I) precursor concentration. The as-prepared Ag NCs in electrospun polymer fibers were mainly Ag2–5 with a quantum yield of 6.81% and a lifetime of 2.29ns. The in situ growth of Ag NCs avoids excessive surface modifications which may cause the aggregation of Ag NCs in many ex situ assembly methods. The combination of Ag NCs with polymer fibers greatly improves the stability of Ag NCs and broadens their applications. The storage of Ag NCs becomes facilitative due to the formation of bulky mat. Furthermore, these luminescence composite polymer fibers show strong antibacterial activity against Staphylococcus aureus (S. aureus).

Thermal conductivity of high performance carbon nanotube yarn-like fibers

In the present paper, we present results of thermal conductivity measurements in free standing carbon nanotube (CNT) yarn-like fibers. The measurements are made using a T-type experimental configuration utilizing a Wollaston-wire hot probe inside a scanning electron microscope. In this technique, a suspended platinum wire is used both as a heater and a thermal sensor. A low frequency alternating current source is used to heat the probe wire while the third harmonic voltage across the wire is measured by a lock-in amplifier. The conductivity is deduced from an analytical model that relates the drop in the spatially averaged temperature of the wire to that of the sample. The average thermal conductivity of the neat CNT fibers and the CNT –polymer composite fibers is found to be 448 W/m-K and 225 W/m-K, respectively. These values for conductivity are amongst the highest measured for CNT yarn-like fibers fabricated using a dry spinning process from vertically aligned CNT arrays. The enhancement in thermal conductivity is understood to be due to an increase in the CNT fiber elastic stiffness during the draw and twist operations, lower CNT thermal contact resistance due to increase in CNT contact area, and better alignment of the CNT fibrils along the length of the fiber.

Application of mechanical model for natural fibre reinforced polymer composites

Mechanical models were often used to describe and predict synthetic fibre reinforced thermosetting polymers. However, natural fibre reinforced thermoplastic polymers were less mentioned. In this paper, the application of mathematical methods in natural fibre–polymer composite was reviewed. Typical mechanical models, such as the rule of mixtures, inverse rule of mixtures and Hirsch models, were presented. The advantages and disadvantages of each model were pointed out. Finally, a flax–wood–polypropylene composite was taken as an example. Some models were compared to describe this composite.

Low temperature growth of carbon nanotubes on carbon fibre to create a highly networked fuzzy fibre reinforced composite with superior electrical conductivity

We report a method for the growth of carbon nanotubes on carbon fibre using a low temperature growth technique which is infused using a standard industrial process, to create a fuzzy fibre composite with enhanced electrical characteristics. Conductivity tests reveal improvements of 510% in the out-of-plane and 330% in the in-plane direction for the nanocomposite compared to the reference composite. Further analysis of current–voltage (I–V) curves confirm a transformation in the electron transport mechanism from charge – hopping in the conventional material, to an Ohmic diffusive mechanism for the carbon nanotube modified composite. Single fibre tensile tests reveal a tensile performance decrease of only 9.7% after subjecting it to our low temperature carbon nanotube growth process, which is significantly smaller than previous reports. Our low-temperature growth process uses substrate water-cooling to maintain the bulk of the fibre material at lower temperatures, whilst the catalyst on the surface of the carbon fibre is at optimally higher temperatures required for carbon nanotube growth. The process is large-area production compatible with bulk-manufacturing of carbon fibre polymer composites.

Effects of moisture on glass fiber-reinforced polymer composites

Glass fiber polymer composites are used in wind turbine blades because of their high-specific strength and stiffness, good fatigue properties, and low cost. The wind industry is moving offshore to satisfy economies of scale with larger turbines. High humidity in this environment degrades mechanical performance of wind turbine blades over their lifetime. Here, environmental moisture conditions were simulated by immersing glass fiber-reinforced polymer specimens in salt water for a period of up to 8 years. The mechanical properties of specimens were analyzed before and after immersion to evaluate the degradation mechanisms. Single-fiber tensile testing was also performed at different moisture conditions. The water-diffusion mechanism was studied to quantify the diffusion coefficients as a function of salt concentration, sample geometry, and fiber direction. Three degradation mechanisms were observed: polymer plasticization, fiber stress corrosion, and interface degradation, where the latter was found to be the most detrimental for wind-industry applications.

Tensile properties of kenaf fiber due to various conditions of chemical fiber surface modifications

Nowadays, due to environmental concerns and financial problems of synthetic fibers, natural fibers or bio-fibers are interesting to be used as reinforcement fibers in polymer composites for structural elements and construction materials. Chemical surface modification method is a well-known method to increase the interfacial bonding strength between fibers and polymer matrix. The alkaline treatment of kenaf fiber may affect not only the surface but also the texture of fiber resulting in the variation of the mechanical and physical properties. This study was conducted to find out the effects of different conditions of alkaline treatment in terms of the concentration of alkali solution and immersion time on the fiber properties. For this study, 360 fiber specimens were tested for 24 various conditions of initial treatment and alkaline surface modifications. Then, the results were analyzed and reported by using of three methods including regression method, averaging the data and system compliance method. Besides, the scanning electron microscopy was employed to observe the specimens’ appearance, fracture area and fibers’ diameter. Result from the study found that the average diameter of untreated kenaf fiber was 67.6μm, the density was 1.2g/cm3 and the tensile strength was 780MPa. Moreover, the 5% alkali solution was the best for kenaf fiber treatment because of causing no tension on the fiber texture and structure as compared to 10% and 15% alkali solution.

An empirical equation for predicting mechanical property of chemically treated natural fibre using a statistically designed experiment

An empirical equation was developed for single fibre tensile strength for industrial hemp fibres which were subjected to a combination of chemical treatment conditions varying two sets of four different treatment variables (sodium hydroxide (NaOH) concentration, sodium sulphite (Na2SO3) concentration, treatment temperature, and digestion time) using partial factorial design. Estimation of tensile strength (TS) for untested combination of treatment factors, prediction of the combination of factors for a target value of fibre TS and sensitivity analysis and tolerance design confirms the validity of the derived empirical model. Such an approach of deriving empirical equation to predict fibre TS would obviously save money, time and use of chemicals and hence would be a very important land mark for industries related to natural fibre polymer composites.

The effect of hybridization on mechanical properties of woven kenaf fiber reinforced polyoxymethylene composite

The challenges of using natural fibers in polymer composites include high moisture uptake and poor interfacial bonding with thermoplastic matrix. In this study, the effect of hybridization was investigated to address the challenges of high moisture uptake and balanced mechanical properties in natural fiber reinforced polymer composites. Polyethylene terephthalate fiber (PET) was used in woven kenaf reinforced POM due to its hydrophobic characteristics. The results of tensile test showed that the tensile strength of the interwoven POM/kenaf/PET hybrid composite when tested along kenaf fiber direction, increased from 72 to 85 MPa due to increase in fiber content. Similarly, the tensile strength of the interwoven POM/kenaf/PET hybrid composite increased from 67 to 75 MPa. However, the flexural strength of the interwoven POM/kenaf/PET hybrid composite dropped from 160.1 to 104.9 MPa while that of woven POM/kenaf composite dropped from 191.4 to 90.3 MPa. The interwoven hybrid composite also showed significant improvement in impact strength compared to the woven POM/kenaf composite. The water absorption of the woven POM/kenaf composite dropped by approximately 30% due to hybridization with PET fiber. The results confirmed that hybridization with PET fiber significantly improved the tensile and impact properties of the woven composite and increased its resistance to moisture uptake. POLYM. COMPOS., 35:1900–1910, 2014. © 2014 Society of Plastics Engineers

Is there really no need to be able to predict matrix failures in fibre-polymer composite structures? Part 1: Explanation of fatal flaws in existing theories

A logic-based case is presented that it is necessary to be able to predict matrix failures in fibre-polymer composites, even though some 50 years after the introduction of the advanced fibre-polymer composites there is still no widely accepted theory capable of actually doing so. This lack is due to the widespread malpractice of artificially homogenising distinct fibre and matrix constituents into an “equivalent” anisotropic solid, to simplify the mathematics. The enormous residual thermal stresses in the matrix, even when the lamina is stress-free, are not widely recognised; these detract appreciably from the ability of the matrix to withstand applied mechanical loads. The extreme thermal mismatch between the fibres and the polymer causes the resin to try to shrink during cool-down after cure at high temperature, but the strong stiff fibres prevent this from happening. Such internal residual stresses cannot possibly exist in truly homogeneous materials, so the consequences are overlooked whenever homogenised material models are used in analyses when they should not have been. The case is made that it is impossible to predict matrix failures using any theory in which the fibre and resin constituents have been artificially homogenised, despite the myriad of theories claiming to do so that cannot.

Detection of Inhomogeneities and Cracks in Composite Materials by the Method of Partial Discharges

Composite materials such as concrete or polymer fiber composites contain a large number of inhomogeneities. It is possible to use the method of partial discharges to detect existing inhomogeneities. Tested materials covered with metal electrodes on both sides represent a parallel plate capacitor. Partial discharges have an impact on conductivity at a high electric field and they are important sources of current noise and acoustic emission signals. The concrete samples were measured before and after mechanical loading by the method of partial discharges and the correlation between them was studied. This method may be used for the diagnosis of inhomogeneities and cracks in composite materials.

Microscale damage mechanisms and degradation of fiber-reinforced composites for wind energy applications: results of Danish–Chinese collaborative investigations

Recent research works in the area of experimental and computational analyses of microscale mechanisms of strength, damage and degradation of glass fiber polymer composites for wind energy applications, which were carried out in the framework of a series of Sino–Danish collaborative research projects, are summarized in this article. In a series of scanning electron microscopy in situ experimental studies of composite degradation under off-axis tensile, compressive and cyclic loadings as well as three-dimensional computational experiments based on micromechanics of composites and damage mechanics, typical damage mechanisms of wind turbine blade composites were clarified. It was demonstrated that the damage mechanisms in the composites strongly depend on the orientation angle of the applied loading with the fiber direction. The matrix cracking was observed to be the main damage mechanism for tensile axial (or slightly off-axis axial) loading; for all other cases (off-axis tensile, compressive and cyclic tensile loadings), the interface debonding and shear control the damage mechanisms.

Conceptual design of kenaf fiber polymer composite automotive parking brake lever using integrated TRIZ–Morphological Chart–Analytic Hierarchy Process method

This paper presents the conceptual design of kenaf fiber polymer composites automotive parking brake lever using the integration of Theory of Inventive Problem Solving (TRIZ), morphological chart and Analytic Hierarchy Process (AHP) methods. The aim is to generate and select the best concept design of the component based on the product design specifications with special attention to incorporate the use of natural fiber polymer composites into the component design. In this paper, the TRIZ contradiction matrix and 40 inventive principles solution tools were applied in the early solution generation stage. The principle solution parameters for the specific design characteristics were later refined in details using the aid of morphological chart to systematically develop conceptual designs for the component. Five (5) innovative design concepts of the component were produced and AHP method was finally utilized to perform the multi-criteria decision making process of selecting the best concept design for the polymer composite automotive parking brake lever component.

Analysis tools for fibrous nanofiller polymer composites: Macro- and nanoscale dispersion assessments correlated with mechanical and electrical composite properties

Emerging methods to study the nanofiller agglomeration state (macrodispersion) and level of individualized nanofiller (nanodispersion) within polymer nanocomposites have been used separately to characterize microstructure and relate to material properties. However, nanofiller dispersion characteristics on different scales within polymer nanocomposites may affect the composite properties in different ways and their complement has not been studied quantitatively. In this study, the dispersion of carbon nanofiber in polycarbonate, controlled by sonication conditions, was studied by the combination of macro and nanoscale style quantitative dispersion characterization tools. The quantitative dispersion results were then correlated with the electrical and mechanical properties of the nanocomposites. Key quantitative indicators of performance were identified for nanocomposite macrodispersion such as the shape of the agglomerate size distributions and number of agglomerates per volume. However, the nanodispersion style analysis demonstrated more significant differences between similarly macrodispersed systems, providing vital information required to assess nanofiller network formation potential. The results indicate the relevant use of differently scaled image analysis processes and their necessity for a comprehensive understanding of the dispersion as well as the properties of nanocomposites. POLYM. COMPOS., 35:10–18, 2014. © 2013 Society of Plastics Engineers

Improved production of laccase by Daedalea flavida: consideration of evolutionary process optimization and batch-fed culture

The genetic algorithm was used effectively to find the optimal values of eight process variables for the maximum laccase production by Daedaleaflavida in a stationary culture. The algorithm was modified suitably to improve laccase production with 18 parallel experiments in 4 generations. A high enzyme titer of 65% was achieved after the optimization and compared to the titer obtained before optimization. To study the effect of the surface immobilized growth on the enzyme production, the fungus was grown on three solid carriers. When cultured on polymer composite fibers, polyurethane foam, or steel wool, at least 2.5 times more biomass was produced, compared to the biomass produced in support-free growth. On the contrary, the mycelia grown on solid support produced much less laccase than non-adhering mycelia. Four parallel runs of batch-fed cultures were done, using the cell mass of D. flavida to evaluate the influence of four different volumes of medium exchanged on laccase production. For sustainable production of the enzyme, complete exchange of medium was favorable, where the laccase activity increased continuously in six consecutive cycles, though, 50% exchange of medium produced the maximum laccase in terms of mean enzyme activity obtained in six cycles.

Scaling of Strength of Metal-Composite Joints—Part III: Numerical Simulation

The size effect in the failure of a hybrid adhesive joint of a metal with a fiber-polymer composite, which has been experimentally demonstrated and analytically formulated in preceding two papers, is here investigated numerically. Cohesive finite elements with a mixed-mode fracture criterion are adopted to model the adhesive layer in the metal-composite interface. A linear traction-separation softening law is assumed to describe the damage evolution at debonding in the adhesive layer. The results of simulations agree with the previously measured load-displacement curves of geometrically similar hybrid joints of various sizes, with the size ratio of 1:4:12. The effective size of the fracture process zone is identified from the numerically simulated cohesive stress profile at the peak load. The fracture energy previously identified analytically by fitting the experimentally observed size effect curves agrees well with the fracture energy of the cohesive crack model obtained numerically by optimal fitting of the test data.

Highly scalable nanoparticle–polymer composite fiber via wet spinning

ABSTRACTMagnetic nanoparticles have continued to gather the interest of researchers due to the unique physical properties of materials found at this size scale. Herein, the production of composite magnetic fibers composed of iron oxide nanoparticles suspended in alginate is described. These materials were produced via wet spinning of a sodium alginate solution into a bath of an aqueous solution of calcium chloride. The magnetic fibers were found to have similar mechanical properties to normal alginate fibers, and exhibited superparamagnetic behavior when subjected to an external DC magnetic field. In addition, the particle loaded fibers demonstrated the potential to produce significant amounts of heat when exposed to an AC magnetic field, suggesting these new materials could be applicable to a variety of applications including magnetic hyperthermia. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1975–1980, 2013

Electrospray ionization for deposition of ultra-thin polymer layers – principle, electrophoretic effect and applications

Nebulizing of polymer solutions, in a high-voltage field under atmospheric conditions by electrospray ionization (ESI), is a comfortable way to deposit ultra-thin layers of polar or ionic polymers onto any conductive substrate materials. The substrate is grounded and the polymer solution is sprayed through a powered capillary. The formed charged droplets shrink by solvent evaporation during their way to the grounded substrate, the charges close ranks and the droplets collapse consecutively by charge repulsion, thus forming finally charged single macromolecules. After their discharging at the grounded substrate, an ultra-thin ‘quasi-monomolecular’ polymer layer is formed. It could be shown by imaging of scratches through the polymer layer by atomic force microscopy that the deposited polymer layers are dense at a thickness of about 10 nm. Carbon fibre bundles were coated with poly(allylamine) (PAAm) or poly(acrylic acid) (PAA) as potential adhesion-promoting layers in fibre–polymer composites. The polymer deposition is self-inhibiting after formation of a continuous coverage of about 200 nm for PAAm and 30 nm for PAA as result of surface charging. Continuous deposition onto such isolating layers or polymers without charging can be achieved by using current of alternating polarity. The film formation is self-healing because of the electrophoretic effect, i.e. the ion discharging occurs preferentially at non-coated areas. This electrophoretic effect of ESI was demonstrated by completely enwrapping all the carbon fibres of the roving within a distance of about 100 μm far from its outside and also at the backside of the fibre bundle with about 80% of the topside coverage, as measured by X-ray photoelectron spectroscopy and visualized using scanning electron microscopy.