Interfacial adhesion between embedded fibre optic sensors and epoxy matrix in composites

Fibre optic (FO) sensors are becoming increasingly popular for different applications in structural monitoring. Among their excellent properties, a strong interest for this type of sensors are represented by the possibility of embedding FOs inside composite components. In this case, one of the factors that significantly influence the efficiency of the whole Structural Health Monitoring (SHM) system is the interfacial adhesion between FO sensors and the host material. The main objective of this work is to investigate the interfacial adhesion between embedded fibre optic sensors and epoxy matrix to find the best type of optical fibre to be used in epoxy matrices to produce smart composites. Four types of optical fibres with different diameters and coatings (i.e. polyimide, polyacrylate and ormoceramic) were used. Pull-out tests were carried out and different methods were used to obtain the composite/optical fibre interfacial properties. Finally, an optical microscopy and Scanning Electron Microscopy (SEM) analysis were performed to characterize the fibre/matrix interfaces. It was found that the optical fibre that presented the highest energy required for interface rupture and, consequently, less invasiveness to the host material was the ormoceramic fibre with the smallest diameter.     

环氧乙烯基防腐地坪及制备工艺

介绍了Atlac环氧乙烯基玻璃钢防腐地坪和Atlac环氧乙烯基树脂混凝土防腐地坪的制作工艺 ,也介绍了用于防腐地坪的Atlac系列环氧乙烯基树脂的性能、玻璃纤维的选择及其它辅助材料的指标、配比等。     

Comparison of water permeation behaviour in poly(dimethylsiloxane), poly(ether ether ketone), and glass fibre reinforced composites using dielectric spectroscopy

Abstract

This paper describes the use of dielectric spectroscopy to characterise the absorption of water by three different classes of polymeric materials: an elastomer, poly(dimethylsiloxane); a thermoplastic, poly(ether ether ketone); and two composites, polyester and vinyl ester glass fibre reinforced laminates (GRP). Novel approaches have been used to assess water absorption by the elastomer and the GRP and the results are critically assessed. The data for all the materials are discussed in the context of their molecular structures. The applicability and limitations of these dielectric methods for the assessment of water absorption in polymeric materials that have considerably different physical properties is demonstrated.     

Effect of styrene on properties of vinyl ester resins,I

The paper describes the effect of styrene on the properties of bis(methacryloxy) derivatives of epoxy resins (vinyl ester resins). The styrene concentration in the resin was systematically varied between 20–60 wt.-%. The curing characteristics of vinyl ester resins changed only marginally on dilution with styrene. Dilution with styrene resulted in a decrease in tensile modulus and increase in elongation of neat resin castings and glass fibre reinforced laminates. The glass transition temperature of laminates was determined by dynamic mechanical analysis and was found to decrease with increasing styrene content.     

Degradation of fatigue resistance of filament wound glass fibre reinforced/vinyl ester pipes exposed to aqueous environments

Abstract

In this contribution, the author reports the effect of salt spray and oxygenated salt water immersion and 100% relative humidity conditions on the fatigue resistance of filament wound glass fibre reinforced/vinyl ester thermoset pipes. Exposure to salt spray and oxygenated sea water immersion for periods of up to 10?000 h produced varying degrees of degradation in the fatigue resistance of glass fibre reinforced plastic pipes. The most severe degradation in fatigue resistance was observed at an exposure of 300 h under salt water spray condition and at 10?000 h of exposure under oxygenated salt water immersion condition.     

Preparation,characterization, and improvement of hollow epoxy particle‐toughened vinyl ester composites for high‐end applications

Spherical hollow epoxy particles (HEPs) that can serve as advanced reinforcing fillers for vinyl ester thermosets were prepared using the water‐based emulsion method. The HEP fillers were incorporated into the vinyl ester matrices at different loading amounts, ranging from 0 to 9 wt %, to reinforce and toughen the vinyl ester composite. The optimum mechanical properties of the HEP‐toughened epoxy composite can be achieved by the addition of 5 wt % HEP filler into the vinyl ester matrices. The toughening and strengthening of the epoxy composites involved the interlocking of vinyl ester resins into the pore regions on the HEP fillers. The toughening and interlocking mechanisms of HEP‐toughened vinyl ester composites were also proposed and discussed. The addition of HEP fillers into vinyl ester matrices increased the glass transition temperature (T_g) and thermal stability of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Fatigue of marine laminates in aqueous environments

Abstract

The effect of pre-exposure in sea water on the fatigue of glass fibre composites has been investigated in fully reversed bending at constant amplitude. Stiffness monitoring during fatigue showed the usual gradual decline caused by increasing microcrack density, followed by a rapid fall due to the onset of delamination. This transition has been characterised for three resin systems and both wet and dry. Glass–polyester was the only system adversely affected by pre-exposure, which significantly reduced the number of cycles to the transition point, presumably by affecting the fibre/matrix interface. In contrast, both glass–vinyl ester and glass–phenolic resin were largely unaffected by pre-exposure. This was attributed to a superior hydrolysis resistant interface in the vinyl ester case and to a relatively poor initial interface in the case of the phenolic resin. When exposed to water over time, glass–phenolic resin and glass–polyester display rather similar fatigue performances. For polyester there was a significantly higher level of acoustic emission events in the wet samples, especially at higher numbers of cycles, indicating a greater level of ongoing damage.     

Short‐term and long‐term performance of thermosets exposed to water at elevated temperatures

The water‐transport, mechanical, and chemical‐structure changes in various vinyl ester, novolac, and urethane‐modified vinyl ester thermosets exposed to water at 50 to 95°C for times up to 1000 days have been studied within the framework of a larger study of osmotic blistering in fiber reinforced plastics (FRP) process components. The water sorption saturation concentration did not reach a steady‐state value but gradually increased in many cases upon long‐term exposure. The diffusion coefficient was not significantly affected. Infrared spectroscopy and gas chromatography‐mass spectrometry indicated that the net mass loss from the thermosets on immersion in water was due to the leaching of non‐reacted styrene, monomer, and additives. It is suggested that this, together with polymer relaxation processes (as measured on specimens under tension in water at 80°C), is the primary reason for the time‐dependent increase in the water saturation concentration. Infrared spectroscopy indicated that, even at the highest temperatures, hydrolysis of the polymer ester groups was small. Correlations were found between the styrene content in the uncured thermosets, the estimated solubility parameters, and the sorption and diffusion coefficients. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Water‐induced degradations in MWCNT embedded glass fiber/epoxy composites: An emphasis on aging temperature

This article is focused to elucidate the critical influence of diffusion temperature on the water uptake and subsequent degradation behavior of multi‐walled carbon nanotube embedded glass fiber/epoxy (MWCNT‐GE) composite. Presence of MWCNT in the glass fiber/epoxy (GE) composite significantly suppressed its water absorption propensity at lower aging temperature (25 °C). However, MWCNT reinforcement in GE composite adversely affected its high temperature water resistance due to generation of unfavorable thermal and hygroscopic stresses at the MWCNT/polymer interfaces. Effect of MWCNT and water diffusion temperature on the glass transition temperature and chemical bonding characteristics of GE composite have been verified by differential scanning calorimetry and Fourier transformed infrared spectroscopy. Flexural testing of the water saturated samples revealed that diffused water exerts more detrimental effect on mechanical performance of MWCNT‐GE composite than that of control GE composite. The extent of recovery in mechanical performance of the composites has also been evaluated after complete desorption of the water saturated samples. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45987.     

Environmental effects on deformation,strength, and degradation of unidirectional glass-fiber reinforced plastics. II. Experimental study

Glass-fiber reinforced epoxy (GRP) and unfilled epoxy specimens were exposed to different environmental conditions consisting of hot- and cold-water absorption and subsequent drying. Effects of the environmental history on deformational and strength characteristics of the composite material were investigated. GRP specimens exposed to hot water undergo pronounced degradation, which sets in shortly after exposure and is associated with a significant irrecoverable weight loss. Degraded specimens are characterized by higher void content and lower strength compared with their cold-water and reference counterparts. The degradation process is attributed to penetration of water into the matrix-fiber interfaces and is followed by an attack, at high temperatures, on the glass-fibers surface and coupling agent. As a result, glass constituents are leached out and then removed from the system by diffusion. The degradation effect was also confirmed by micro-observation of the fractured surfaces and by infra-red spectroscopy. A simple and effective testing method is recommended, permitting detection of degradation onset and its progress by simultaneous measurement of weight and dimensional changes with time.     

Sorption and diffusion of water,salt water,and concrete pore solution in composite matrices

In recent years, the use of fiber‐reinforced polymer composites in civil infrastructure has been promoted as a solution to the deterioration of bridges, buildings, and other structures composed of traditional materials, such as steel, concrete, and wood. Any application of a polymer composite in an outdoor environment invariably involves exposure to moisture. There is also potential for exposure to saline conditions in waterfront or offshore structures, and alkaline environments, as would be encountered by a reinforcing bar in a cementitious material. This study characterizes the sorption and transport of distilled water, salt solution, and a simulated concrete pore solution in free films of vinyl ester, isophthalic polyester (isopolyester) and epoxy resins, all commercially important materials for use in structural composites. Diffusion of all three liquids in each of the three materials was observed to follow a Fickian process. Mass loss was observed for the isopolyester in salt water and concrete pore solution at 60°C, suggesting hydrolysis that was accelerated by the high temperature exposure. Both the rate of uptake, as well as the equilibrium uptake, were greater at 60°C, compared with ambient conditions. Diffusion coefficients calculated from the mass uptake data revealed that, although the epoxy resin had the highest equilibrium uptake, it had the lowest diffusion coefficient. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 483–492, 1999     

Effects of water,salt solution and simulated concrete pore solution on the properties of composite matrix resins used in civil engineering applications

One of the obstacles hindering the acceptance of polymer composites in civil engineering applications is the susceptibility of the polymeric matrix to degradation that is initiated by moisture, temperature, and corrosive chemical environments. The objective of this study was to characterize chemical and physical changes in polymer matrix resins following exposure to these environments. Resin systems studied were vinyl ester and isophthalic polyester, both of which are proposed for use in construction applications. Unreinforced free films were exposed to water, alkaline and saline environments at ambient and elevated temperatures for extended periods of time. Changes in strength and thermophysical properties were evaluated through tensile testing, dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). Chemical degradation of the polymers was characterized using Fourier transform infrared (FTIR) spectroscopy. Energy dispersive X‐ray (EDX) analysis of specimens following exposure was carried out to determine if ion diffusion into the bulk polymer occurred. Only minor changes in the glass transition temperatures of the polymers were observed after prolonged exposure at elevated temperature, but more substantial changes were noted in tensile strength, particularly in the case of the isophthalic polyester. Examination of the polymers following immersion in salt solution and alkaline solution showed essentially no ionic penetration into the bulk, with the exception of specimens that were visibly degraded. Spectroscopic analysis of chemical structure prior to and following exposure revealed varying degrees of ester hydrolysis.     

Assessment of morphological,thermal, and viscoelastic properties of epoxy vinyl ester coating composites: Role of glass flake and mixing method

In this work, glass flake (GF)/epoxy vinyl ester resin composites were fabricated with various compositions and mixing methods. The effect of GF on thermal and mechanical behavior of these composites was investigated using different techniques such as differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and thermogravimetric analysis (TGA). The results showed that the presence of GF in epoxy vinyl ester formulation could obviously affect the cure temperature, reaction enthalpy value, and degradation temperature. DMTA results also exhibited that the tan δ peak area decreased and storage modulus increased with increasing GF content and this effect seemed to be different depending on the initial epoxy vinyl ester compositions. The scanning electron microscopy (SEM) images showed that mixing method had a strong effect on the surface morphology, size, and distribution of glass flake. The effect of mixing method on properties of produced composite was also studied.     

The Effect of Adherends on the Curing of an Epoxy Adhesive

The effect of E-glass, cured vinyl ester resin, and silica gel on the curing of an epoxy-anhydride adhesive was examined. The techniques used were calorimetry in both isothermal and scanning modes and Fourier transform infrared spectroscopy in the attenuated total reflectance (ATR-FTIR) mode. Isothermal calorimetry was used to obtain the exotherm, conversion rate, and curing kinetic parameters, and scanning calorimetry was used to obtain the glass transition temperature. ATR-FTIR was used to study the curing kinetics and chemistry of the adhesive. The results suggest either the immobilization of a layer of the epoxy adhesive adjacent to inert solid surfaces or selective adsorption of the accelerator or both, each of which suppresses the cure reaction. This was reversed by the presence of adsorbed water. At least for this epoxy-anhydride system, adsorbed water seems to have had the beneficial effect of increasing the crosslink density in the interfacial region between the adhesive and adherend. Water seems also to change the overall cure reaction, causing more ether formation and less ester formation than without water. An additional finding was that the cured vinyl ester surface appeared to have a catalytic effect on the reaction, perhaps in conjunction with the accelerator, benzyldimethylamine.     

Experimental characterization of interfacial adhesion of an optical fiber embedded in a composite material

The efficiency of an optical sensor embedded in a composite structure strongly depends on the interfacial adhesion between the optical fiber coating and the surrounding solid material. The present paper reports on the study of the interfacial adhesion of an optical fiber embedded in a composite material. A simple system composed of optical fibers embedded in an epoxy vinylester resin was first studied to evaluate the influence of embedded length, curing temperature and curing time. Pull-out tests on optical fibers bonded in epoxy vinylester/glass fiber composite material were carried out to measure the effect of glass concentration on the fiber bonding. The pull-out results showed no effect of both embedded length and curing temperature. However, an increase of the interfacial debonding stress is reported with increased curing time. For the optical fiber/composite system, a linear evolution of interfacial debonding stress with increasing glass fiber concentration is reported.     

Cure monitoring of the liquid composite molding process using fiber optic sensors

Fluorescence has been demonstrated to be an accurate tool for monitoring resin cure. It is measured using an evanescent wave fiber-optic sensor. An economical optical fiber sensor has been developed with a refractive index greater than 1.6, permitting evanescent wave monitoring of epoxy resins. The fluorescence wave-length-shift, which has been correlated with monomer conversion, is monitored during the liquid molding process. Unidirectional glass fabrics with volume fractions from 40% to 60% were injected with epoxy resin at a variety of driving pressures and cured at several temperatures. Several composite parts were fabricated to test the effects of vacuum pressure, injection rate, cure temperature, and fiber fraction on the performance of the sensor. The sensitivity of the evanescent wave fluorescence sensor to the condition of the resin system was also examined. The sets of resin/hardener samples were subjected to rigorous chemical analysis to determine the extent of their differences.     

Mechanical and barrier properties of epoxy resin filled with multi-walled carbon nanotubes

Different multi-walled carbon nanotube (MWCNT) concentrations were incorporated in an epoxy resin and both the epoxy precursor and the composite were cured at 110 °C with a tertiary amine. Infrared spectroscopy was used to follow the curing progress by determining the decrease of the band due to the epoxy group. It was shown that the presence of MWCNTs accelerates the process, halving the time for the disappearance of the epoxy band. Atomic force microscopy demonstrated that the carbon nanotubes are well embedded in the epoxy matrix and singularly dispersed or in bundles, depending on their concentration. As a consequence of the good dispersion and interpenetration of the carbon nanotubes in the epoxy matrix, the glass transition temperature increased with increasing MWCNT concentration. Dynamic-mechanical analysis indicated a higher elastic modulus, particularly at high temperatures. The study of the transport properties, sorption and diffusion of water vapour at different activities, showed improved barrier properties on increasing the CNT concentration.     

Effect of prolonged water absorption on mechanical properties in cellulose fiber reinforced vinyl‐ester composites

With the increasing of worldwide societal awareness about environmental impact, sustainability, and renewable energy sources, the polymer natural fiber composites recently have attracted the attention of researchers due to the fact that they are recyclable and biodegradable. This study conducted a new infiltration method that involved very thin sheets of recycled cellulose fibers (RCF) being fully soaked in vinyl‐ester resin for the development of natural fiber reinforced polymer composites. The effect of prolonged water absorption on the mechanical behavior of cellulose fiber (0–50 wt%) reinforced vinyl‐ester composites was investigated. The elastic modulus of these composites was measured and the data were validated with various mathematical models. The modeling results revealed that the experimental data matched the prediction data obtained by the Cox–Krenchel model. Prolonged exposure of these composites to water absorption caused a reduction in elastic modulus, strength, and toughness. POLYM. ENG. SCI., 55:2685–2697, 2015. © 2015 Society of Plastics Engineers     

Transport and adhesion properties of an unlined and a liquid‐crystalline polymer–lined vinyl ester thermoset exposed to severe environments

The application of liquid‐crystalline polymers (LCP) as lining materials for fiber‐reinforced plastics was investigated. The lining consisted of one uniaxially and one biaxially oriented LCP and, for comparison, a fluorinated ethylene propylene copolymer. The lining was attached to a glass‐fiber–reinforced vinyl ester thermoset. The laminates were examined with respect to their chemical resistance, transport/barrier properties, and lining/matrix adhesion behavior. The transport properties were determined by gravimetric desorption measurements and cup tests. It was shown that the LCP was suitable as a lining in organic solvent and nonoxidizing acid environments. Diffusivities, equilibrium concentrations, and transmission rates of water, methanol, toluene, and trichloroethylene were obtained in the LCP, the fluorinated ethylene propylene copolymer, and also, in the case of the vinyl ester, of hydrochloric acid. In general, the diffusivity and transmission rate in the LCP were one to several orders of magnitude lower than those of the fluorinated ethylene propylene copolymer and the vinyl ester. The reinforcement in the glass‐fiber–reinforced plastic led to an increase in the water and methanol diffusivities and transmission rates, which was probably attributable to liquid capillary diffusion. The lap‐shear bonding strength between the LCP and the vinyl ester was poor, but it was improved almost sixfold by a combined abrasive and oxygen plasma treatment. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 797–806, 2005     

UV‐Printable and Flexible Humidity Sensors Based on Conducting/Insulating Semi‐Interpenetrated Polymer Networks

Humidity sensors are of great interest in many fields because humidity plays a crucial role in several processes. Nevertheless, their application is often limited by the expensive fabrication and the stiffness of the substrates usually employed. In this work, novel UV‐curable and flexible humidity sensors based on semi‐interpenetrated polymer networks are fabricated. They can be prepared either as self‐standing sensors or applied on different bendable substrates. The fabrication consists of a simultaneous UV‐curing of an insulating network (acrylic or epoxy) and photopolymerization of conducting polypyrrole (PPy). The detection mechanism involves proton transfer on the PPy chains that can be macroscopically observed by electrical impedance variations. These devices show promising humidity‐sensing properties from 20 to 97% of relative humidity with a maximum response of about 180%. The dynamic sensing investigation proves that the recovery process can be tailored playing on the glass transition temperature and wettability of the films. The remarkable sensing capabilities of these sensors make them a valid alternative in many applications where printability and flexibility are required along with simple fabrication method consisting of one‐step synthesis.