Mechanical properties of a self-healing fibre reinforced epoxy composites

Inspired by biological systems in which damage triggers an autonomic healing response, a polymer composite material that can heal itself when cracked has been developed. In this work, compression and tensile properties of a self-healed fibre reinforced epoxy composites were investigated. Microencapsulated epoxy and mercaptan healing agents were incorporated into a glass fibre reinforced epoxy matrix to produce a polymer composite capable of self-healing. The self-repair microcapsules in the epoxy resin would break as a result of microcrack expansion in the matrix, and letting out the strong repair agent to recover the mechanical strength with a relative healing efficiency of up to 140% which is a ratio of healed property value to initial property value or healing efficiency up to 119% if using the healed strength with the damaged strength.     

Review of the mechanical properties of carbon nanofiber/polymer composites

In this paper, the mechanical properties of vapor grown carbon nanofiber (VGCNF)/polymer composites are reviewed. The paper starts with the structural and intrinsic mechanical properties of VGCNFs. Then the major factors (filler dispersion and distribution, filler aspect ratio, adhesion and interface between filler and polymer matrix) affecting the mechanical properties of VGCNF/polymer composites are presented. After that, VGCNF/polymer composite mechanical properties are discussed in terms of nanofibers dispersion and alignment, adhesion between the nanofiber and polymer matrix, and other factors. The influence of processing methods and processing conditions on the properties of VGCNF/polymer composite is also considered. At the end, the possible future challenges for VGCNF and VGCNF/polymer composites are highlighted.     

The effect of carbon nanofibres on self-healing epoxy/poly(ε-caprolactone) blends

The effects of carbon nanofibres (CNFs) on the mechanical performance and healing efficiency of self-healing epoxy/poly(ε-caprolactone) (PCL) blends were examined. Through a simple polymer blending process, phase-separated epoxy/PCL blends were prepared, which showed self-healing capability upon thermal activation. The introduction of CNFs into a co-continuous phase-structured epoxy/PCL system, at the content of as low as 0.2 wt.%, has been found to yield combinational improvements in the flexural strength, tensile strength, toughness and hardness with no adverse effect on the self-healing performance. Significantly enhanced mechanical performance by low content of CNFs enables the development of epoxies and advanced polymer composites with longer service life and less maintenance.     

Carbon Dots as Fillers Inducing Healing/Self‐Healing and Anticorrosion Properties in Polymers

Self‐healing is the way by which nature repairs damage and prolongs the life of bio entities. A variety of practical applications require self‐healing materials in general and self‐healing polymers in particular. Different (complex) methods provide the rebonding of broken bonds, suppressing crack, or local damage propagation. Here, a simple, versatile, and cost‐effective methodology is reported for initiating healing in bulk polymers and self‐healing and anticorrosion properties in polymer coatings: introduction of carbon dots (CDs), 5 nm sized carbon nanocrystallites, into the polymer matrix forming a composite. The CDs are blended into polymethacrylate, polyurethane, and other common polymers. The healing/self‐healing process is initiated by interfacial bonding (covalent, hydrogen, and van der Waals bonding) between the CDs and the polymer matrix and can be optimized by modifying the functional groups which terminate the CDs. The healing properties of the bulk polymer–CD composites are evaluated by comparing the tensile strength of pristine (bulk and coatings) composites to those of fractured composites that are healed and by following the self‐healing of scratches intentionally introduced to polymer–CD composite coatings. The composite coatings not only possess self‐healing properties but also have superior anticorrosion properties compared to those of the pure polymer coatings.     

自修复微胶囊复合材料的制备及力学性能研究

为了提高树脂基复合材料的使用寿命,以脲醛树脂为壁材,双环戊二烯为囊芯,通过原位聚合法制备了内含修复液的微胶囊,探讨了反应过程中脲醛量比及乳化剂用量等对微胶囊表面形貌和结构的影响.通过优化工艺条件制备出表面致密的微胶囊,并将微胶囊埋植在环氧树脂基体中制备复合材料.采用扫描电镜对胶囊进行形貌表征,运用快速傅里叶变换红外光谱...     

Review of current strategies to induce self-healing behaviour in fibre reinforced polymer based composites

Abstract

This paper addresses the various strategies to induce self-healing behaviour in fibre reinforced polymer based composites. A distinction is made between the extrinsic and intrinsic healing strategies. These strategies can be applied at the level of the fibre, the fibre/matrix interface or at the level of the matrix. It is shown that the degree of healing depends on the type of damage and the testing mode used and examples are given both for extrinsic and for intrinsic healing systems. The conclusion is drawn that self-healing in fibre reinforced composites is possible yet unlikely to become a commercial reality in the near future.     

Thermoreversible and remendable glass-polymer interface for fiber-reinforced composites

Adhesion of the reinforcement to the polymer matrix is essential for load transfer from the polymer matrix to the reinforcement material in fiber-reinforced composites. The reversible Diels-Alder reaction between a furan-functionalized epoxy-amine thermosetting matrix with a maleimide-functionalized glass fiber was used to impart remendability at the polymer-glass interface for potential application in glass fiber-reinforced composites. At room temperature the Diels-Alder adduct is formed spontaneously and above 90 °C the adduct breaks apart to reform the original furan and maleimide moieties. Healing of the interface was investigated with single fiber microdroplet pull-out testing. Following complete failure of this interface, significant healing was observed, with some specimens recovering over 100% of the initial properties. Healing efficiency was not affected by the distance of displacement, with an overall average of 41% healing efficiency. Up to five healing cycles were successfully achieved. It is expected that a glass fiber-reinforced composite of maleimide-sized glass within a furan-functionalized network will demonstrate extension of fatigue life.     

Improving the through-thickness thermal and electrical conductivity of carbon fibre/epoxy laminates by exploiting synergy between graphene and silver nano-inclusions

Fibre-reinforced polymer composites typically feature low functional (e.g., electric and thermal conductivity) and structural (e.g. mechanical strength and fracture toughness) properties in the laminate’s thickness direction. In the event of lightning strikes, overheating, and impact by foreign objects, composite laminates may suffer wide spread structural damage. This research explores the synergistic physical interaction between two-dimensional nanostructured (graphene nano-platelets) and, zero- or one-dimensional conductive fillers (silver nanoparticles or silver nanowires, respectively) when both are dispersed in fibre–polymer laminates. The results reveal a synergistic improvement in the through-thickness thermal conductivity that is more than the additive improvements by each constituent. Specifically, the simultaneous inclusion of graphene nano-platelets and silver nanoparticles/nanowires at a combined loading of 1 vol% resulted in approximately 40% enhancement in the through-thickness thermal conductivity while the inclusion of graphene nano-platelets alone at the same loading resulted only in 9% improvement. Similarly, the through-thickness electrical conductivity of carbon fibre/epoxy laminates incorporating graphene nano-platelets together with silver nanoparticles/nanowires was notably higher (⩾70%) than can be achieved by graphene nano-platelets alone (∼55%). These results demonstrate that the presence of nano-reinforcements exhibiting varied phonon transport and electron transfer pathways, and geometric aspect ratios promote synergistic physical interactions. Small improvements were found in the mechanical properties, including tensile, flexural or compressive properties of the carbon fibre-reinforced laminates, due to the relatively low concentrations of the nano-fillers.     

Thermomechanical modelling the fire properties of fibre–polymer composites

Simple-to-use models are presented in this paper for determining the residual tension, compression and flexural properties of burnt fibre reinforced polymer composite materials following a fire. The post-fire mechanical properties are calculated using analytical equations that combine the properties of the fire-damaged (i.e. char) and undamaged regions of a composite. Fire tests were performed on composites containing carbon, glass or Kevlar fibres with an epoxy, polyester, vinyl ester or phenolic resin matrix to assess the accuracy of the models. The composites were tested to a wide range of fire conditions with temperatures from 525 to 850 °C for times up to 30 min. It is found that the post-fire properties drop rapidly with increasing heat flux and duration of a fire due to the thermal degradation of the polymer matrix. It is shown that the reduction to the post-fire properties of the burnt composites can be accurately determined using the models. In almost all test cases, the agreement between the calculated and measured residual mechanical properties is within 10%.     

Micromechanical deformations in PP/lignocellulosic filler composites: Effect of matrix properties

Polypropylene composites were prepared from three different PP matrices, a homopolymer, a random and a heterophase copolymer, and corn cob to study the effect of matrix characteristics on deformation and failure. The components were homogenized in an internal mixer and compression molded to 1 mm thick plates. Mechanical properties were characterized by tensile testing, while micromechanical deformations by acoustic emission measurements and fractography. The results proved that the dominating micromechanical deformation process may change with matrix properties. Yield stress determined from the stress vs. strain traces may cover widely differing processes. Debonding is the dominating process when the adhesion of the components is poor, while matrix yielding and/or filler fracture dominate when adhesion is improved by the introduction of a functionalized polymer. The dominating deformation mechanism is determined by component properties and adhesion. Interfacial adhesion, matrix yield stress and the inherent strength of the reinforcement can be limiting factors in the improvement of composite strength. The properties of polymer composites reinforced with lignocellulosic fillers are determined by micromechanical deformation processes, but they are independent of the mechanism of these processes.     

Manufacturing strategies for microvascular polymeric composites: A review

A microvascular network within a composite structure can significantly boost its performance. However, properties of microvascular network and host structure largely depend on the manufacturing method, used for vascularization. This paper presents a review on various manufacturing strategies that have been implemented so far to produce vascularized polymer composites. The ways by which polymer composites can be vascularized with isolated or interconnected networks are based on either by incorporating pre-made channels or removing pre-loaded solid performs from the cured laminates. Majority of the techniques were developed for healing and recovery of structural integrity after quasi-static fracture, but microvascular networks also showed promise for enhanced-damage visualization, self-cooling, and damage sensing applications. Each technique has its own merits and demerits but the manufacturing techniques that are not only compatible with current composite manufacturing, but also give the freedom to embed complex channels which can execute multi-functions synchronously still remains the main challenge.     

Structural assessment of microvascular self-healing laminates using progressive damage finite element analysis

This paper presents a progressive damage analysis methodology to numerically analyse the effect of microvascular open channels on the structural properties of self-healing fibre–polymer laminates. The tensile and compression properties of self-healing carbon–epoxy laminates containing microvascular systems are analysed using finite element models which consider progressive in-plane ply damage and intra-ply damage (matrix and delamination cracking). The models predict with good accuracy (often within 5%) the stiffness and strength of laminates containing circular or elliptical microvascular channels of different sizes and orientations. The model calculates a progressive reduction in structural properties with increasing size of microvascular channels due to increased ply waviness, which was confirmed using experimental property data. The model also predicts the location and progression of damage under increasing tensile or compression loading to final failure. The model has application as a tool for the design of microvascular systems in self-healing composites used for structural applications.     

Polymer matrix,polymer ribbon-reinforced transparent composite materials

Composites of a polymer–matrix reinforced by polymer ribbon monofilaments are investigated as mechanically robust, transparent composite materials. Transparent nylon monofilaments are mechanically worked to form flattened nylon ribbons, which are then combined with index-matched epoxy resin to create transparent composites. A range of optical and mechanical experiments are performed on composites and surrogate systems in order to quantify properties and guide system design. The results show that these polymer–polymer composites provide good transparency over a wide temperature range, and superior ballistic penetration resistance compared to monolithic transparent polymers.     

Rheokinetic evaluation of self-healing agents polymerized by Grubbs catalyst embedded in various thermosetting systems

In self-healing polymers and composites, the activity of the embedded chemical catalyst within the thermosetting matrix is critical to healing efficiency. Rheological behavior of ring-opening metathesis polymerization (ROMP)-based healing agents, triggered by 1st or 2nd generation Grubbs catalyst suspended in various thermosetting resins, was investigated using an oscillatory parallel plate rheometer. Gel times for various healing agents were determined from the crossover of storage and loss moduli vs. time curves to indicate the activity of the ROMP reaction. Gelation of healing agents initiated by 1st generation Grubbs catalyst occurred faster than those triggered by 2nd generation catalyst. It is suggested that the dissolution rate of the catalyst by the healing agent is an important factor in determining the overall ROMP reaction rate in situ. Optical and scanning electron microscopic observations showed that the finer, rod-like solid particles of the 1st generation catalyst were distributed more homogeneously throughout the cured matrix. The effects of different healing agents and thermosetting matrix systems on the ROMP reaction are discussed in detail.     

Gradient of nanomechanical properties in the interphase of cellulose nanocrystal composites

The nanoscale transitional zone between a nanofiber and surrounding matrix (interphase) defines the ultimate mechanical characteristics in nanocomposite systems. In spite of this importance, one can hardly find quantitative data on the mechanical properties of this transitional zone in the cellulose–nanofiber composites. In addition, most of the theoretical models to predict the mechanical properties of interphase are developed with the assumption that this transitional zone is independent of the nanofiber size. In the current study, we show that the mechanical properties of interphase in cellulose nanocrystal (CNC) composites can be quantitatively characterized and the correlation with the size of CNCs can be mapped. The peak force tapping mode in atomic force microscope (AFM) was used to characterize deformation, adhesion, and modulus gradient of the interphase region in poly(vinyl alcohol) (PVA)–poly(acrylic acid) (PAA)–cellulose nanocrystal (CNC) composites. In comparison to the polymer matrix, the adhesion force of CNC was lower. The average elastic modulus in the interphase varied from 12.8 GPa at the interface of CNC to 9.9 GPa in PVA–PAA matrix. It was observed that the existence of PAA increased the gradient of mechanical and adhesion properties of the interphase zone. This occurs due to the variation in the ester linkage density from the CNC interface to the polymer matrix. Finally, it is shown that interphase thickness is higher for CNCs with larger diameter.     

Mechanical properties of carbon nanotube reinforced polymer nanocomposites: A coarse-grained model

In this work, a coarse-grained (CG) model of carbon nanotube (CNT) reinforced polymer matrix composites is developed. A distinguishing feature of the CG model is the ability to capture interactions between polymer chains and nanotubes. The CG potentials for nanotubes and polymer chains are calibrated using the strain energy conservation between CG models and full atomistic systems. The applicability and efficiency of the CG model in predicting the elastic properties of CNT/polymer composites are evaluated through verification processes with molecular simulations. The simulation results reveal that the CG model is able to estimate the mechanical properties of the nanocomposites with high accuracy and low computational cost. The effect of the volume fraction of CNT reinforcements on the Young's modulus of the nanocomposites is investigated. The application of the method in the modeling of large unit cells with randomly distributed CNT reinforcements is examined. The established CG model will enable the simulation of reinforced polymer matrix composites across a wide range of length scales from nano to mesoscale.     

PEEK composites reinforced with zirconia nanofiller

The present investigation deals with the preparation and characterization of nanocomposites of polyether ether ketone (PEEK) containing nanosized zirconia filler up to 3 wt.% loading. It has been observed that presence of zirconia filler dispersed in polymer matrix enhances various basic and functional properties (e.g., mechanical properties, thermal stability & other physico-mechanical properties). The SEM studies reveal that the dispersion of zirconia nanofiller is uniform throughout the polymer matrix. The thermal stability of the nanocomposites has been studied by TGA. Thermal analysis of the composites shows an increase in the thermal stability with increase of nanofiller content. This may be attributed to strong interaction between polymer chains and filler particles. DMA studies show the significant improvement in storage modulus of the nanocomposites because of better interaction of zirconia particles in PEEK matrix.     

微胶囊型自愈合聚合物基复合材料研究进展

自愈合材料是一种可以模仿生物体自行愈合的新型智能材料,具有广泛的应用前景。微胶囊型自愈合聚合物基复合材料是近年来复合材料自愈合方法领域内的研究热点之一。本文对目前聚合物基复合材料自愈合方法进行了综述,着重介绍了微胶囊型自愈合聚合物基复合材料的自愈合概念和机制、微胶囊结构及其技术发展状况,并详细介绍了微胶囊的芯材、壁材、自愈合基体材料及微胶囊临界应力等因素对复合材料自愈合性能的影响,以及自愈合效率的评估方法。最后讨论了微胶囊型自愈合聚合物基复合材料的发展趋势和面临挑战。     

Structure evolution of conductive polymer composites revealed by solvent vapor induced time-dependent percolation

The authors of this paper synthesized a series of amphiphilic triblock copolymers of polystyrene-b-poly(ethylene glycol)-b-polystyrene (PS-PEG-PS) having different PEG/PS ratios with nearly identical molecular weights of the entire copolymers. The interfacial interactions in the composites consisting of carbon black and the copolymers can thus be tailored. When these conducting composites are exposed to certain solvent vapors, their electrical resistances greatly increase, showing the gas sensitivity. The present work indicated that this switching behavior is controlled by the structural relaxation of the composites because matrix swelling acts as the main mechanism. The response time has been correlated with absolute temperature by Arrhenius equation, and the estimated activation energy reflects mobility of the fillers involved in the solvent induced expansion of the surrounding polymer. Therefore, by using the gas sensibility of the conductive composites, the structure evolution of the composite materials in solid state and the effect of filler/matrix interfacial interaction on the relaxation property of the matrix polymer has been inspected. It was found that lower activation energy represents stronger interfacial interaction in case good solvent of the matrix was used for the test.     

Enhanced thermal and mechanical properties of carbon nanotube composites through the use of functionalized CNT-reactive polymer linkages and three-roll milling

We report enhanced thermal and mechanical properties of carbon nanotube (CNT) composites achieved through the use of functionalized CNTs-reactive polymer linkages and three-roll milling. CNTs were functionalized with carboxyl groups and dispersed in a polymer containing an epoxide group resulting in a chemical reaction. To maximize CNT dispersion for practical usage, entangled CNTs are separated and then evenly dispersed within the polymer matrix using three horizontally positioned rotating rolls that apply a strong shear force to the composite. Consequently, accompanying with thermal stability, elastic modulus and storage modulus of such functionalized CNT/polymer composites were increased by 100% and 500% that of the untreated epoxy polymer.