Humidity Aging Research Articles

Degradation of physicomechanical properties of epoxy nanocomposites with carbon nanotubes upon heat and humidity aging

The dependence of the physicomechanical properties of epoxy nanocomposites subjected to heat and humidity aging on the type of covalently functionalized carbon nanotubes and on the uniformity of their distribution in the epoxy matrix was studied. Two types of carbon nanotubes were used: those modified with carboxy and amide groups. The elastic modulus, bending deflection, and ultimate bending strength for the initial epoxy nanocomposites with carbon nanotubes and for those subjected to heat and humidity aging were determined. The epoxy binders modified with carboxylated carbon nanotubes are more resistant to the action of aging factors. The presence of aggregates of carboxylated carbon nanotubes in the epoxy matrix positively influences the preservation of physicomechanical properties of the composite subjected to heat and humidity aging. Microscopic examination revealed structural features of the epoxy nanocomposite and their effect on the resistance of the composite to the heat and humidity aging.

On characterizing microscopically the adhesion interphase for the adhesion between metal and rubber compound Part III. Effect of brass-plating amount for brass-plated steel cord

Three kinds of brass-plated steel cords with different brass-plating amounts from 2.62 to 5.01 g/kg were prepared and their adhesion properties to rubber compounds were studied. Adhesion properties decreased with the increase in the brass-plating amount from 2.62 to 3.88 g/kg. Furthermore as the increase of brass-plating amount over 3.88%, adhesion property increased. The strong adhesion of brass-plated steel cord with low brass-plating amount to the rubber was shown not only after curing but also after hostile aging treatments. The good adhesion stability against humidity aging of adhesion property for brass-plated steel cord with low brass-plating amount to rubber compound was discussed in terms of the formation and growth of adhesion interphase determined by AES depth profile. The good adhesion stability of brass-plated cord with low brass-plating amount can be resulted from the suppression of the excessive growth of copper sulfide and the inhibition of dezincification due to the low brass-plating amount.

Humidity Aging Effect on Adhesive Strength of Composite Single-lap Joint

Because adhesively bonded joints are used in many structural systems, it is important to predict accurate adhesive strengths. Composite aircraft with many joints are easily exposed to low temperatures and high relative humidity. This paper presents a humidity aging effect on the adhesive strength of a composite single-lap joint (SLJ). The adhesive strength of the SLJ is predicted using a finite element analysis with a cohesive zone model (CZM) technique. The humidity aging effect is evaluated based on the adhesive strength and CZM parameters. A lap joint test is carried out on the composite SLJ specimens, which are exposed for four months of 100% R.H. at 25°C. The predicted strengths are in good agreement with experimental data, and the actual crack propagation is satisfactorily simulated using the local CZM technique.

Effect of mechanical states on water diffusion based on the free volume theory: Numerical study of polymers and laminates used in marine application

Abstract The humid aging of composite materials is often interpreted assuming a constant diffusivity and most particularly independent on the mechanical fields. However, some experimental investigations highlight a coupling between the mechanical fields and the water diffusion in polymer based materials. In this work, this hygro-mechanical coupling is implemented through the semi-empirical free volume theory. The transient coupled problem is numerically studied using the classical finite element method. The problem is solved with the commercial code Abaqus©. Three numerical examples, emphasizing the interest of using such models in the investigation of the aging of composites, are presented. In the two first cases, the aging of pure resin specimen, under mechanical loading, is analyzed. In the last instance, the impact of the stiff reinforcements, assumed hydrophobic, on the water absorption behavior of an uni-directional laminate is studied.

Effect of high temperature high humidity and thermal shock test on interfacial intermetallic compounds (IMCs) growth of low alpha solders

In this study, the effects of high temperature high humidity aging conditions and thermal shock tests on the growth of intermetallic compounds (IMCs) in low alpha Sn–1.0Ag–0.5Cu (LA-SAC105) solder and low alpha Sn (LA-Sn) solder have been investigated. The aging has been performed at 50, 85 and 150 °C for 30, 70 and 120 h at a relative humidity (R.H.) of 40 and 85%. The thermal shock tests of LA solders has been performed from −65 to 150 °C for 100, 200, 400, 600, 800 and 1000 thermal cycles, and the results are compared with the normal SAC105 and Sn solders. It is observed that the evolution of Cu–Sn IMCs with aging time and temperature is diffusion controlled and the IMC thickness increases linearly with square root of aging time. The thickness of IMCs of LA-SAC105 and LA-Sn is smaller than that of SAC105 and Sn solders. It is also observed that as the number of thermal cycles increased, the IMC grain coarsening occurs in case of LA-SAC105 and as well as LA-Sn solders. In addition, whisker growth is noticed in LA-Sn and Sn solders. However, the LA-Sn has the lower sensitivity towards the whisker growth. On the contrary, a rapid growth and cracking of the IMCs formed at the interface of the normal SAC105/Cu system causes the solder sample to detach from the joint after 600 cycles, as compared to the LA-SAC105/Cu which resists the fracture up to 1000 cycles. The LA-SAC105 and LA-Sn can reduce the growth of IMCs when compared with the normal SAC105 and Sn as reference solders and may improve the solder joint reliability.

Investigation on stability and moisture absorption of superhydrophobic wood under alternating humidity and temperature conditions

The application of superhydrophobic wood is majorly limited by its durability when subjected to natural conditions. Herein, the stability of two representative superhydrophobic woods (i.e., Poplar (Populus tomentosa) and Chinese fir (Cunninghamia lanceolata)), were prepared via a one-step hydrothermal process using tetrabutyltitanate (Ti(OC4H9)4, TBOT) and vinyltriethoxysilane (CH2CHSi(OC2H5)3, VTES) as a co-precursor and sequentially tested under different humidity and temperature conditions. The variables including morphology, water contact angle (WCA), color parameter, chemical components of the surface, and moisture absorption property were characterized using a scanning electron microscope (SEM), WCA measurement, a colorimeter, a Fourier transform infrared (FTIR) spectroscopy, and a moisture absorption test, respectively. It was found that initial static WCAs of superhydrophobic wood were larger than 150°. Micron-sized cracks were formed on the coatings after the alternating humidity and temperature aging cycles. This lowered the water repellency, but the WCA was still greater than 140°. There was nearly no chemical change of wood after the aging test; the color change between the same species of untreated and superhydrophobic wood was very small, only with a difference of 0.42 and 4.05 in overall color change ΔE∗ values for Chinese fir and poplar, respectively. The superhydrophobic coatings had a trivial influence on wood moisture absorption property, which only lowered 3% in poplar and 2% in Chinese fir, respectively.

Solvent-Free and Highly Transparent SiO2 Nanoparticle–Polymer Composite with an Enhanced Moisture Barrier Property

Solvent-free SiO2–poly(trimethylolpropane triacrylate) (SiO2–PTPT) nanocomposites are successfully fabricated for an encapsulation layer by surface modification of a SiO2 nanoparticle. In order to lead surface-initiated polymerization and introduce structural similarity between a SiO2 surface and polymer, the surface of the SiO2 nanoparticles are modified with [3-(methacryloyloxy)propyl]trimethoxysilane. The modified SiO2 nanoparticle dispersed in trimethylolpropane triacrylate (TPT) is converted to a SiO2–PTPT nanocomposite under UV irradiation. Because SiO2 incorporated in a polymer generates a tortuous path and absorbs a water molecule, the SiO2–PTPT nanocomposite shows a considerably lower water vapor transmission rate than PTPT. All of the nanocomposite films are highly transparent (over 98%) in the visible region before and after humidity aging tests. Furthermore, a light-emitting diode encapsulated by a 20 wt % SiO2–PTPT nanocomposite exhibits a considerably longer lifetime in the accelerated aging...

Microstructure Changes in Polyester Polyurethane upon Thermal and Humid Aging.

The microstructure of compression molded Estane 5703 films exposed to 11%, 45%, and 80% relative humidity and 70 °C for 1 and 2 months has been studied by small-angle neutron scattering (SANS), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Scattering data indicated increase of the interdomain distance and domain size with a higher humidity and longer aging time. GPC data showed a progressive shortening of polyurethane chains with increasing humidity and aging time. The shortening of the polyurethane chains caused a drop of the glass transition temperature of soft segments, and promoted crystallization of the soft segments during long-time storage of the aged samples at room temperature. FTIR showed a substantial increase in the number of inter-urethane H-bonds in the aged samples. This correlates with the increase of the hard domain size and the degree of phase separation as measured by SANS. The data collected reveals that the reduced steric hindrance caused by hydrolysis of ester links in polybutylene adipate residues promotes the organization of hard segments into domains, leading to the increase of domain size and distance, as well as phase segregation in aged Estane. These findings provide insight into the effects of humidity and thermal aging on the microstructure of aged polyester urethane from molecular to nanoscale level.

Synthesis of mesoporous TiO2 structures through P123 copolymer as the structural directing agent and assessment of their performance in dye-sensitized solar cells

A novel and efficacious strategy was implemented for creation of mesoporous TiO2 films and powder through an integration of sol–gel and evaporation-induced self-assembly (EISA) processes aided by triblock Pluronic P123. A mesoporous crack-free thin film with virtual thickness of 300nm was attained under 10% relative humidity aging, for 72h at the low temperature of 5°C. Further, the TiO2 film with porous structure has been formed from conventional paste, exploiting as-prepared mesoporous titania powder. The X-ray Diffraction (XRD) of synthesized mesoporous powder disclosed formation of anatase phase as well as rutile phase, in such a manner that the latter constituted a very small minority. Moreover, Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Helenda (BJH) proved that the isotherm pertaining to synthesized powder implies a combination of types II and IV which are related to mesoporous material with average pore size of 5.8nm and BET surface area of 114m2/g. Owing to the quantum size effect, diffuse reflection spectroscopy of prepared mesoporous TiO2 powder denoted a blue shift by comparison with that of bulk TiO2. The mesoporous TiO2 film which has been prepared under optimized circumstances, possesses appropriate microstructural and optical properties so that it can be utilized for dye-sensitized solar cell (DSSC) applications. In order to delve profoundly into the effect of TiO2 thin film, two types of monolayer and doublelayer DSSCs were made. In light of the achieved results, the doublelayer cell indicated superior power conversion efficiency and short circuit current density of 8.05% and 18.27mA/cm2, respectively.

Effects of Thermal and Humidity Aging on the Interfacial Adhesion of Polyketone Fiber Reinforced Natural Rubber Composites

Polyketone fiber is considered as a reinforcement of the mechanical rubber goods (MRG) such as tires, automobile hoses, and belts because of its high strength and modulus. In order to apply it to those purposes, the high adhesion of fiber/rubber interface and good sustainability to aging conditions are very important. In this study, polyketone fiber reinforced natural rubber composites were prepared and they were subjected to thermal and humidity aging, to assess the changes of the interfacial adhesion and material properties. Also, the effect of adhesive primer treatment, based on the resorcinol formaldehyde resin and latex (RFL), of polyketone fiber for high interfacial adhesion was evaluated. Morphological and property changes of the rubber composites were analyzed by using various instrumental analyses. As a result, the rubber composite was aged largely by thermal aging at high temperature rather than humidity aging condition. Interfacial adhesion of the polyketone/NR composites was improved by the primer treatment and its effect was maintained in aging conditions.

Extended Aging of Ag/W Circuit Breaker Contacts: Influence on Surface Structure, Electrical Properties, and UL Testing Performance

Samples of 120 V, 30 A commercial circuit breakers were subjected to various aging treatments and the resulting microstructures at the surfaces of the Ag/W contacts were studied using a combination of x-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy techniques. Breakers aged naturally in a hot, humid climate were compared to those subjected to accelerated aging in dry and humid environments. The most extensive oxidation was observed for contacts from breakers subjected to accelerated humid aging; these contacts exhibited thick surface layers consisting of Ag2O, Ag2WO4, Cu(OH)2∙H2O, and WO3 phases. Far less surface degradation was observed for dry-aged contacts. Naturally aged contacts showed variations in degradation with more oxidation at the surface regions outside the physical contact area on the contact face. A correlation was found between the contact resistances measured from these samples following ASTM standard B 667-97 and the observed surface microstructures. To evaluate the effects of the surface oxides on breaker performance, humid-aged breakers were subjected to standardized UL overload/temperature-rise, endurance, and short-circuit testing following UL489. The contacts in these breakers exhibit similar microstructural and property changes to those observed previously for as-manufactured contacts after UL testing. These data illustrate the robust performance of this contact technology even after being subjected to aggressive artificial aging.

Effects of Optical Brightening Agent on the Chemical Degradation Characteristics of Paper Cellulose

ABSTRACT This study was conducted to investigate the effects of optical brightening agents (OBA) on the chemical degradation characteristics of paper cellulose during humid heating aging. Three different types of OBAs were applied to a filter paper by dipping it in OBA solutions whose concentrations were controlled to 1% and 2%. The filter papers with an OBA were artificially aged at 80℃ and 65% RH, and the changes in pH of paper and viscosity of cellulose were evaluated. Their functional groups were also analyzed by ATR-FTIR (at-tenuated total reflectance fourier transform infrared spectroscopy). It was found that OBAs influenced the chemical degradation of paper cellulose during humid heating aging. Higher concentration of OBA solutions accelerated the degradation of paper cellulose. Especially, after aging for 12 days, the paper cellulose treated with the tetra-type OBA were the most significantly aged among the three types of OBAs. It was assumed that pH of OBA solutions affected the aging characteristics. Keywords: Optical brightening agent, aging characteristics, pH, viscosity, FT-IR

Strengthening of De-waxed Paper by Methyl Cellulose (MC) and Its Preservability : Effect of Viscosity and Coating Ratio of MC

ABSTRACT This study was conducted to investigate the effect of the strengthening treatment of methyl cellulose (MC) on properties and aging characteristics of the dewaxed papers during humid heating aging. Beeswax-treated Hanji was dewaxed by the supercritical fluid extraction method, and subsequently the strengthening treatment was performed with MCs having three different viscosities. MC was first applied by dipping a dewaxed paper into a MC solution whose concentration was controlled from 0.5% to 1.5%. After the strengthened papers were artificially aged at 80℃ and 65% RH, the changes in optical and mechanical properties of the samples were evaluated. The results show that viscosity and especially pick-up of MC influenced the strengthening efficiency and aging characteristics of de-waxed paper. Strength was increased with the MC coating weight; in addition, strength-ening with MC improved preservability of the dewaxed paper. The optimum conditions for the strengthening with MC was found to be the coating ratio of 4% with 1500 cP MC.Keywords: Methyl cellulose, viscosity, coating weight, strengthening, dewaxed paper, aging characteristics

How copper corrosion can be retarded – New ways investigating a chronic problem for cellulose in paper

To better assess the stabilization effects of chemical treatments on Cu(II)-catalyzed cellulose degradation, we developed Cu(II)-containing model rag paper with typical copper corrosion characteristics using e-beam radiation. The paper can be prepared homogeneously and quickly compared to tedious pre-aging methods. Using the Cu(II)-containing model rag paper, the stabilization effects of various chemicals on Cu(II)-catalyzed degradation of cellulose were tested. Benzotriazol was highly effective in retarding the degradation of the Cu(II)-containing model rag paper under hot and humid aging condition, as well as under photo-oxidative stress. Tetrabutylammonium bromide reduced Cu(II)-catalyzed degradation of cellulose, but its efficacy was dependent on the accelerated aging conditions. The results with the alkaline treatments and gelatin treatment suggested that their roles in the degradation mechanisms of cellulose in the presence of Cu(II) differ from those of benzotriazol and tetrabutylammonium bromide.

Analysis of the moisture effect on the mechanical behaviour of an adhesively bonded joint under proportional multi-axial loads

The objective of the study is to identify the 3D behaviour of an adhesive in an assembly, and to take into account the effect of ageing in a marine environment. To that end, three different tests were employed. Gravimetric analyses were used to determine the water diffusion kinetics in the adhesive. Bulk tensile tests were performed to highlight the effects of humid ageing on the adhesive behaviour. Modified Arcan tests were performed for several ageing times to obtain the experimental database which was necessary to identify constitutive models. A Mahnken–Schlimmer type model was determined for the unaged state according to a procedure developed in a previous study. This identification used inverse techniques. It was based on the unaged modified Arcan results and on a coupling between an optimisation routine and finite-element analysis. Then, a global inverse identification procedure was developed. Its aim was to relate the unaged parameters to the moisture concentration and overcome the difficulties usually associated with ageing of bonded assemblies in a humid environment: a non-uniformity of the stress state and a gradient of mechanical properties in the adhesive. This procedure was similar to the one used in the first part but needed modified Arcan results for several ageing times. It also required an initial assumption for the evolution of the Mahnken–Schlimmer parameters with the moisture concentration.

Characterization of Low EW Ionomers in Fuel Cells

Perfluorosulfonic-acid (PFSA) ionomers play a key role in the polymer-electrolyte fuel-cell (PEFC), in which they are primarily used as the proton-exchange membrane (PEM) with their remarkable transport properties and chemical/mechanical stability, but they also function as the nanometer thick "thin" electrolyte film in the catalyst layers binding the catalytic sites and providing proton transport pathways. In the thin-film regime, an ionomer exhibits vast deviations in its properties which are controlled by its interfaces with the air and the catalytic particles, i.e., carbon and platinum. While bulk membrane is responsible mainly for the ohmic resistances, in the catalyst layers, transport resistance in the ionomer film resulting from its interfacial interactions has direct implication on the mass-transport limitations in the PEFC, especially at higher current densities. Thus, it is imperative to understand the origins of ionomer-related transport resistances in fuel-cell catalysts, and how they changes with ionomer's chemistry and equivalent weight (EW). In this talk, we present our findings on the impact of EW and hygrothermal environmental stressors the structure and properties of ionomers across the lengthscales, i.e., from bulk membrane (PEM) to catalyst ionomer film in CLs. It will be shown through X-Ray scattering studies how hygrothermal ageing induces morphological changes in the catalyst ionomer films, and subsequently alters their swelling and sorption behavior as investigated by ellipsometry and quartz crystal microbalance (QCM). From the collected data, structure-swelling-uptake correlations are generated for PFSA ionomers of various EWs, both as bulk membrane and thin films. From the grazing-incidence X-ray scattering (GIXS), changes in the size and orientation of water domains in the ionomer film are determined in response to humidity, heat-treatments and hygrothermal ageing, which result in substantial changes in these morphological features. Nanostructrual anisotropy, phase-separation and sorption kinetics are all found to be related and affected by the substrates the ionomer film is interacting with. The investigation on the impact of equivalent weights (EWs) and PFSA side-chain chemistries on ionomer’s response demonstrated a key role EW plays in controlling the structure/transport relationship of the ionomer, especially in the catalyst layers. Impact of ageing and heat-treatments on ionomer’s structure and properties are similar for both bulk and thin films, but found to be more pronounced for the latter. Our results provide new insights into the environmental and operational stressors controlling ionomer's functionalities, especially as thin-films in fuel-cell catalysts.

Highly Conductive and Reliable Copper-Filled Isotropically Conductive Adhesives Using Organic Acids for Oxidation Prevention

The easy oxidation of copper is one critical obstacle to high-performance copper-filled isotropically conductive adhesives (ICAs). In this paper, a facile method to prepare highly reliable, highly conductive, and low-cost ICAs is reported. The copper fillers were treated by organic acids for oxidation prevention. Compared with ICA filled with untreated copper flakes, the ICA filled with copper flakes treated by different organic acids exhibited much lower bulk resistivity. The lowest bulk resistivity achieved was 4.5 × 10−5 Ω cm, which is comparable to that of commercially available Ag-filled ICA. After 500 h of 85°C/85% relative humidity (RH) aging, the treated ICAs showed quite stable bulk resistivity and relatively stable contact resistance. Through analyzing the results of x-ray diffraction, x-ray photoelectron spectroscopy, and thermogravimetric analysis, we found that, with the assistance of organic acids, the treated copper flakes exhibited resistance to oxidation, thus guaranteeing good performance.

Variation of physicochemical and sensory properties during the aging of yerba mate

Yerba mate infusion is widely consumed in Argentina, Brazil and Paraguay. One of the processing steps used in Argentina is aging. The following three methods were used to age yerba mate: 1) air humidity and temperature-controlled aging; 2) temperature-controlled aging and 3) no control. The aim of this research was to determine the physicochemical and sensory attribute differences when yerba mate was aged using these three methods. The concentration of caffeine, glucose, fructose, maltose and phenolic compounds and pH diminished in all three aging methods but by different percentages. The sensory attributes did not exhibit uniform behaviour. Astringency remained constant in the first method and diminished in the other two. Bitterness increased in all three methods but by different percentages. Sweetness diminished in all three methods. Notably few correlations were determined between physicochemical and sensory attributes.

Evidence of thermo-oxidation phenomena occurring during hygrothermal aging of thermosetting resins for RTM composite applications

This paper focuses on the humid aging of a high temperature thermosetting resin employed for the realization of aircraft parts manufactured by the RTM process. Accelerated humid aging at several different temperatures (40–90°C) and relative humidity values (50–100%) has been carried out by means of gravimetric tests. Anomalous behavior with respect to Fick’s diffusion law and a color gradient from the edge to the center of the samples has been observed. Drying of samples after aging and mechanical tests on aged and dried samples have shown the existence of irreversible phenomena taking place during humid ageing: uniform tensile tests revealed resin embrittlement, Ultra Micro Indentation tests allowed measuring a gradient of properties from the surface to the centre of the samples. This behavior – associated to the color changes observed on aged samples – indicates that oxidation phenomena take place during hygrothermal aging.

Polyaniline-coated nylon lycra fabrics for strain sensor and electromagnetic interference shielding applications

In this article, a conductive polyaniline-coated nylon lycra fabric has been characterized for electromagnetic interference (EMI) shielding and strain sensor application. The conductive fabric is fabricated by in-situ polymerization of polyaniline on the nylon lycra fabric at low temperature. Characterization has been carried out using scanning electron microscopy and differential scanning calorimetry. The sensitivity of the developed fabric sensor is characterized using Zwick tensile tester. EMI shielding efficiency (SE) of the developed fabrics is carried out as per ASTM D4935 standard. The stability of the developed sensor is characterized with respect to temperature and humidity using Programmable Environmental Test Chamber. The measurement of the conductivity change with strain shows that the fabrics so prepared exhibits high strain sensitivity, while its good stability is indicated by a small loss of conductivity after the thermal and humidity ageing tests and supported by the slight change in conductivity over storage of 90 days. The sensor measures flexion angle of elbow up to 120° angle. The electromagnetic shielding tests show that the developed conductive fabric has the EMI SE of 26 dB in the frequency range of 8–12 GHz.