Strength and Durability of Epoxy-Aluminum Joints

The adhesive strength and durability of adhesively-bonded aluminum joints in wet environments was analyzed. A2024-T4 alloy was subjected to two different surface treatments based on etching with chromic-sulfuric acid (FPL) and with sulfuric acid-ferric sulfate (P2). Small differences were observed in the lap shear strength as a function of the applied surface treatment. However, durability in humid environments was higher for the joints whose adherends were treated with P2.

Although the amount of water absorbed by the epoxy adhesive is lower in saline environments, the effects on the glass transition temperature of the epoxy adhesive and on the lap shear strength of the joints are more marked than the effects caused by aging with distilled water.

Finally, a new epoxy adhesive with a siloxanic hardener was tested, obtaining good mechanical properties, high glass transition temperature, moderate values of lap shear strength, and high durability in wet environments.     

Polystyrene recycling processes by dissolution in ethyl acetate

This study evaluated the thermal, morphological, chemical, and mechanical properties of virgin and recycled polystyrene. The recycling process was carried out by dissolution of polystyrene (extruded and crystal) in ethyl acetate, followed by two processes for solvent removal: vaporization by direct contact with water at 85 °C in a tubular evaporator and vaporization during the extrusion process. For the samples produced by solvent evaporation in the tubular evaporator, there was practically no degradation on polymer chain, neither reduction in glass transition temperature. For the samples produced by solvent evaporation during the extrusion, a polymer chain degradation was noted by reduction in molar weight and in glass transition temperature. The FTIR evaluation suggests that polymer oxidative degradation, in both samples, was more pronounced in the extruded sample. The removal of plasticizing additives could be evidenced by the glass transition temperature increase in the recycled samples produced in the tubular evaporator. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46208.     

Dynamic mechanical response of adhesively bonded beams: Effect of environmental exposure and interfacial zone properties

The dynamic mechanical response of adhesively bonded metal beams has been examined over a broad temperature range using a dynamic mechanical thermal analyzer (DMTA). The measured dynamic mechanical response of the bonded beam contains rich information about the viscoelastic properties of the adhesive resin such as glass transition temperatures. The measured storage moduli and loss factors of the bonded beams are very sensitive to changes in the properties of adhesive induced by exposing the beam specimens to environmental attack. Dynamic mechanical responses associated with dry adhesive resin, water plasticized resin, and aggregated water were observed for an electro-galvanized steel/epoxy beam exposed to water. The effect of the presence of an interfacial accommodation zone (IAZ) between adhesive resin and metal substrate was also examined; measured properties were very sensitive to the presence of a low modulus IAZ. It was successfully demonstrated in this study that the DMTA testing of bonded beams is a potentially useful tool for studying dynamic performance and durability of automotive adhesive joints.     

Chemical and electrical properties of the surface layers of some glass electrodes

Some sodium— and lithium—silicate pH responsive glasses exhibited a stepwise alkali ion profile with distance inwards towards the glass as a result of attack by aqueous solutions, ie, the average alkali ion concentration of the gel layer was low but increased rapidly within a transition region between the gel layer and the glass bulk. The electrical resistivity of the gel layer was a factor at least five times lower than that of the original glass. An extremely high electrical resistance in the transition region was found to be proportional to the chemical durability of the glass independent of hydration time. The smaller size of the lithium ion which favours stronger binding, compared with the sodium ion, as well as the action of the calcium ion in the sodium silicate network to block the sodium ion/hydrogen ion exchange were among the factors that increased the chemical durability by orders of magnitude. Equilibrium conditions were not reached for the deeper parts of the gel layers. The chemical durability of the glass increased in the same order as found for the ideal function of the glass electrode. The size of the electrical resistance of the transition region was thus useful for deducing glass compositions suitable for electrode purposes.     

Hygrothermal ageing of an epoxy adhesive used in FRP strengthening of concrete

The efficiency of strengthening of deteriorating concrete through the external bonding of prefabricated fiber reinforced composite strips to the concrete substrate depends on the durability of the adhesive. In this application, adhesives can be exposed to water and salt water, as well as alkali solution resulting from the permeation of water through concrete. This paper presents the results of a durability program designed to study the effects of ageing and environment on the durability of a typical adhesive used in external bonding, through characterization of moisture uptake and cure and investigation by dynamic thermal mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, and tensile testing. It is seen that the adhesive shows two‐stage diffusion with primary deterioration taking place in the first phase. Exposure to moisture is seen to cause plasticization and decreases in performance characteristics. The decrease in glass transition temperature due to hygrothermal ageing is such that the level is very close to the Federal Aviation Authority (FAA) recommended value of the wet glass transition temperature being at least 30°F higher than the maximum operation temperature. Overall, the effect of salt solution exposure is seen to have the least effect, whereas exposure to concrete based alkali solution has the greatest deteriorative effect. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Biodegradable extruded starch blends

We prepared biodegradable extruded starch blends by first mixing starch with additives and then processing the mixture in an extruder. The mechanical properties, including tensile strength and elongation at break, solubility, biodegradability, rheological properties, molecular weight, and glass‐transition temperature of the extruded blends were studied. Glycerol and urea, to some extent, could both decrease the tensile strength and increase the percentage elongation at break because the former acts as a plasticizer and the latter can break down interactions among starch macromolecules. The extruded starch blends showed thermoplasticity, and their melts behaved as pseudoplastic liquids at a comparatively low shear rate. The biodegradability of the extruded starch was slightly higher than that of native starch. The molecular weight of starch displayed a decreasing tendency after extruding modification. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 627–635, 2003     

Effects of processing conditions on the fiber length distribution and mechanical properties of glass fiber reinforced nylon‐6

The effects of processing conditions on fiber length degradation were investigated in order to produce composites with higher performance. Nylon‐6 was compounded with glass fibers in a twin‐screw extruder for various combinations of screw speed and feed rate. Collected samples were injection molded and Izod impact and tensile tests were performed in order to observe the effect of fiber length on the mechanical properties. Also, by using the extruded and injection molded smaples, fiber length distribution curves were obtained for all the experimental runs. Results show that when the shear rate is increased through the alteration of the screw speed and/or the feed rate, the average fiber length decreases. Impact strength, tensile modulus and tensile strength increase, whereas elongation at break decreases with the average fiber length.     

Effect of network connectivity on behavior of synthetic Broborg hillfort glasses

There is wide industrial interest in developing robust models of long-term (>100 years) glass durability. Archeological glass analogs, glasses of similar composition, and alteration conditions to those being tested for durability can be used to evaluate and inform such models. Two such analog glasses from a 1500-year-old vitrified hillfort near Uppsala, Sweden have previously been identified as potential analogs for low concentration Fe-bearing aluminosilicate nuclear waste glasses. However, open questions remain regarding the melting environment from which these historic glasses were formed and the effect of these conditions on their chemical durability. A key factor to answering the previous melting and durability questions is the redox state of Fe in the starting and final materials. Past work has shown that the melting conditions of a glass-forming melt may influence the redox ratio value (Fe⁺³/∑Fe), a measure of a glass's redox state, and both melting conditions and the redox ratio may influence the glass alteration behavior. Synthetic analogs of the hillfort glasses have been produced using either fully oxidized or reduced Fe precursors to address this question. In this study, the melting behavior, glass transition temperature, oxidation state, network structure, and chemical durability of these synthesized glass analogs is presented. Resulting data suggests that the degree of network connectivity as impacted by the oxidation state of iron impacted the behavior of the glass-forming melt but in this case does not affect the chemical durability of the final glass. Glasses with a lower degree of melt connectivity were found to have a lower viscosity, resulting in a lower glass transition temperature and softening temperature, as well as in a lower temperature of foam onset and temperature of foam maximum. This lower degree of network connectivity most likely played a more significant role in accelerating the conversion of batch chemicals into glass than the presence of water vapor in the furnace's atmosphere. Future work will focus on using the results from this work with outcomes from other aspects of this project to evaluate long-term glass alteration models.     

Extrusion foaming of polystyrene/carbon particles using carbon dioxide and water as co-blowing agents

Carbon particles such as platelet-like graphite (GR), spherically shaped activated carbon (AC), and tubular carbon nanofiber (CNF) were used as additives in extruded polystyrene (PS) foams with carbon dioxide (CO₂) and water as co-blowing agents. It was found that GR is the best additive for improving the thermal insulation performance of CO₂ based foam samples because of GR’s good absorption and reflectivity of infrared (IR) radiation. However, when the GR concentration was higher than 0.5 wt.%, the extruded foams exhibited large bubbles in the center of the foam and the extrusion line became unstable. By adding water carried by AC as a co-blowing agent, it was able to decrease the temperature in the center of the extruded foam, which successfully eliminated the bubble problem and achieved stable foam extrusion with good control of the foam density and cell morphology. Moreover, water carried by AC could also improve the mechanical performance of extruded foams containing CNF or GR. Water was not found in the extruded foams and the presence of water during extrusion did not affect the molecular weight and glass transition temperature of PS. Our results showed that a combination of AC as a water carrier and GR as an absorber and reflector of IR radiation can produce CO₂ based PS foams with good thermal insulation and mechanical properties, particularly with the presence of a small amount of CNF nanoparticles.     

The effect of morphology on the corrosion inhibition and mechanical properties of hybrid polymer coatings

The durability and mechanical properties of epoxy ester coatings and films has been improved by blending with rigid aromatic polyurea (PU). The interaction of PU and epoxy ester was enhanced by coupling the polymers with polymethylhydrosiloxane. The reactions between various entities are analyzed by Fourier transform infrared spectroscopy and the change in physical and mechanical properties are studied by a dynamic mechanical analyzer. The corrosion resistance of the hybrid coatings was measured by direct current polarization method, direct current polarization (DCP). The addition of polymethylhydrosiloxane enhances the corrosion properties in the hybrid coatings. The surface morphology was analyzed by scanning electron microscopy. The glass transition temperature of the films increases with increasing PU concentration and a wide glass rubber transition range for hybrid coatings was achieved which confirms the higher impact strength of the hybrid coatings and films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fabrication and characterization of poly(1,4-cyclohexanedimthylene terephthalate-co-1,4-cyclohxylenedimethylene 2,6-naphthalenedicarboxylate) (PCTN) copolyester film: A novel copolyester film with exceptional performances for next generation flexible electronic devices

A novel, semi-crystalline poly(1,4-cyclohexylenedimethylene terephthalate-co-1,4-cyclohexylene dimethylene 2,6-naphthalenedicarboxylate) (PCTN) copolyester was synthesized and successfully extruded using an extruder attached with T-die. The extruded sheet was uniaxially cold-drawn into film at 150°C, a temperature between glass transition temperature and melting temperature. The mechanical, thermal, thermo-mechanical, water barrier, and optical properties of developed film were characterized. Orientation of different phases was analyzed by X-ray diffraction. The actual chemical composition of PCTN copolyester was analyzed by nuclear magnetic resonance spectroscopy. Our results clearly indicated the thermal, dimensional stability, mechanical, and water barrier properties of PCTN films increased in a linear trend with draw ratio. It was also found that PCTN film has better water barrier property compared to conventional poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) films. Based on the exceptional performance properties, novel PCTN film may find a strong position as a substrate for next generation flexible electronics among various performance materials.     

Experimental assessment of the improved properties during aging of flax/glass hybrid composite laminates for marine applications

The investigation for natural fibers composites in terms of performance, durability, and environmental impact for structural applications in marine environments is a relevant challenge in scientific and industrial field. On this context, the aim of this work is to assess the durability and mechanical stability in severe environment of epoxy/glass–flax hybrid composites. For the sake of comparison, also full flax and glass epoxy composites were investigated. All samples were exposed to salt–fog environmental conditions up to 60 aging days. Wettability behavior during time was compared with water uptake evolution to assess water sensitivity of hybrid composite configurations. Moreover, quasi-static flexural and dynamic mechanical analysis were carried to evaluate as aging conditions, laminate configuration influence the surface and mechanical performances stability of the hybrid composites. The addition of glass fibers on flax laminate allows to enhance both flexural strength by 90%, and modulus by 128%, even if these properties are lower than those of full glass laminates. The results evidenced that the hybridization of flax fibers with glass ones is a practical approach to enhance the aging durability of epoxy/flax composite laminates in marine environmental conditions, obtaining a suitable compromise among environmental impact, mechanical properties, aging resistance, and costs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47203.     

Pull-off adhesion of hybrid glass-steel adhesive joints in salt fog environment

The aim of this paper was to evaluate the durability behaviour of glass/steel adhesive joints exposed to salt fog environmental conditions for ten weeks, according to ASTM B117 standard. To this scope, pull-off mechanical tests were carried out in order to evaluate the performances evolution and damage phenomena of the adhesive joints during the ageing exposition. Two different types of adhesives were compared (i.e. epoxy and polyurethane ones). Moreover, the effects of the glass surface condition and the presence of a basalt mat layer within the adhesive thickness were evaluated. The mechanical performances were related with the occurred failure mechanisms. Epoxy-based joints showed higher strength and durability than the polyurethane based ones. Furthermore, frosted glass surface condition and basalt interlayer addition enhanced mechanical durability in salt fog environment of glass–metal dissimilar joints.     

复合材料加固混凝土结构耐久性研究

本文在国内外相关文献研究的基础上。先后分析了复合材料加固混凝土结构耐久性问题的由来，机理以及问题的解决途径。在初步的加速试验结果分析的基础上，研究了酸碱环境对一种高强复合纤维材料力学性能随时间的变化规律。最后，本文提出了延长复合材料加固混凝土结构耐久性的设计与施工建议。     

Mechanical oil expression from extruded soybean samples

Soybean is generally recognized as a source of edible and industrial oil, and the deoiled meal is seen as a source of protein in animal feed. In recent years, however, more interest has been directed toward using soy meal as a protein source for human consumption. Extrusion-expelling of soybean provides an opportunity in this direction. The main focus of this study was to maximize the oil recovery from extruded soybean processed using three different kinds of extruders and processing conditions. These extruded samples were later pressed uniaxially in a specifically designed test-cell and the oil recovery was recorded over time. The effects of process variables, including applied pressure, pressing temperature and sample height, were investigated. Results indicated that over 90% of the available oil could be recovered from pressing of extruded soy samples. The information generated is likely to be useful in interpreting the effect of process variables and extruding equipment for pretreatment of soybean for subsequent mechanical oil expression.     

Factors affecting dynamic durability of polycarbonate under bending,torsional, and impacting fatigue and in cavitation erosion and dynamic solvent cracking conditions

To understand influences of various factors on dynamic durability of engineering plastics, effects of average molecular weights of samples, molding variables, preparing methods of specimens, and fillers on plane and rotational bending, torsional, and impacting fatigue and cavitation erosion and solvent cracking of polycarbonate were studied. From the experimental results, the following tendencies are observed as a whole in case of polycarbonate: The extent of influence of the factors on dynamic durability varies depending on the type of testing. Increase in molecular weight has a favorable effect on dynamic durabilities. Influence of molding conditions is remarkable: especially, deficient drying of resin pellets before molding decreases dynamic durability noticeably, and specimens prepared by injection molding have much better durabilities than those by machaning from extruded sheet. Polyethylene blending has an unfavorable effect on durability, except for Izod-type impact strength and solvent cracking. Reinforcement by glass fiber has a favorable effect on fatigue under constant deformation and cavitation erosion.     

Viscoelastic properties of plasticized PVC reinforced with cellulose whiskers

New nanocomposites are processed with a plasticized poly(vinyl chloride) matrix reinforced by cellulose whiskers whose characteristics are a high aspect ratio and a large interface area. Dynamic mechanical analysis performed on samples reinforced with a filler fraction of up to 12.4 vol % gives the viscoelastic properties of the composite above and below its glass transition temperature. Different theoretical predictions are proposed to describe this behavior, but none of them is found wholly satisfactory for describing the reinforcing effect of these fillers. A model based on the Halpin–Kardos equation, with the assumption of an immobilized phase around the whiskers, is developed to account for significant decrease in the modulus drop, on passing above the glass transition temperature. The small discrepancy between this model and the experimental modulus measured in the rubber plateau is discussed as a possible effect of a percolating whisker network whose crosslinks are assured by chains adsorbed onto the whisker surface. Swelling experiments support this hypothesis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1797–1808, 1999     

Role of silanes in adhesion-Part I. Dynamic mechanical properties of silane coatings on glass fibers

The dynamic mechanical properties of glass fibers impregnated with y-methacryloxypropyltrimethoxy silane and methyltrimethoxy silane were studied as a function of the concentration of the silanes in the coating solution. An increase of the concentration of the silanes increases the molecular weight of the polymeric coatings, as well as the extent of their crosslinking, glass transition, modulus, and damping. The dynamic mechanical properties of y-methacryloxypropyltriethoxy silane show a correlation with the adsorption characteristics of the silane on an inorganic filler. It is demonstrated that dynamic mechanical measurements of the glass/silane composites, when combined with other instrumental approaches such as infrared spectroscopy and gel permeation chromatography, may provide valuable information on the composition, the structure, and the mechanical properties of silane coatings on a glass surface.     

Interpretation of the dynamic mechanical response of heterogeneous polymer blends in terms of continuum models

Dynamic mechanical measurements have been widely used for characterization of polymer blends and composites. This paper discusses application of continuum models to interpretation of the dynamic mechanical response of isotropic microscopically heterogeneous polymer blends. The models typically predict shifts in apparent glass transition temperature (location of principal loss tangent maximum) for each blend constituent. Experimentally observed shifts in the apparent glass transition of heterogeneous blend constituents may thus arise at least partly for mechanical reasons rather than because of changes in the properties or glass transition temperature of the blend constituents. It is suggested that, for heterogeneous blends of well characterized phase morphology, changes in glass transition behavior of blend constituents be determined by comparison of measured and calculated loss tangent maxima. For two-component blends, the loss tangent at the temperature at which the loss tangents of the blend constituents are equal may be useful as a further diagnostic tool for changes in loss mechanisius.     

Derivation of the Structural Integrity of Residual (SIR) glass model for the enhancement of waste loading

A new model based on glass structure to allow for enhanced waste loading in nuclear waste glass while maintaining chemical durability is proposed. The model is derived by splitting the molar concentrations of the targeted starting glass composition into theoretical crystalline phases anticipated to be observed during devitrification and a residual glass. An empirically derived relationship based on maintaining the residual glass structure, determined from a calculated non-bridging oxygen content, was demonstrated to successfully screen glasses for acceptable durability. The proposed model can successfully identify durable glass compositions containing 20–35 wt% Al₂O₃, a concentration that would significantly increase the projected waste loading in glasses processed at the Hanford Tank Waste Treatment and Immobilization Plant.