J. C. del Real

Epoxy Composite Reinforced with Nano and Micro SiC Particles: Curing Kinetics and Mechanical Properties

Epoxy-based composite materials reinforced with hard particles can be used as anti-wear coatings. In this study, a commercial bicomponent resin was used, with 6 and 12% SiC particles in two different particle sizes (nano and 10 µm). The epoxy curing process was studied by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and confocal microscopy. Dynamic mechanical thermal analysis (DMTA) tests evaluated the influence of particle additions on the glass transition temperature (T g ). In addition, mechanical properties (hardness and bending strength) and wear resistance were evaluated. The addition of nanometric particles reduced the reaction order. A higher amount of particles decreased T g due to the lower number of crosslinking points. The agglomeration of nano particles led to non-uniform mechanical properties. 6% nano particle addition dramatically improved wear resistance and decreased the friction coefficient.

Adhesive bonding of aluminium with structural acrylic adhesives: durability in wet environments

The durability of EN AW 6082-T651 aluminium alloy joints bonded with a toughened acrylic adhesive was investigated upon exposure to wet environments (humidity, water immersion and salt water immersion). Environmentally-friendly surface treatments were used to avoid hexavalent chromium. Single lap shear tests were used to determine the durability of the adhesively bonded joints. Specimens were exposed to 31% and 95% relative humidity and submerged in deionized water and 3 wt% sodium chloride solution at 25°C and 50°C, for 10, 30 and 90 days. The data collected in the experiments showed that the durability was higher for surfaces treated with γ-methacryloxypropyltrimethoxysilane (γ-MPS) and sulfo-ferric etchant (P2 etch) than other surface treatments. Both these treatments improved considerably the durability in all environments tested. The results indicate that specimens even without surface treatment maintained a significant residual strength after exposure to low humidity environment (room temperature at 31% RH). The joints exposed to a high humidity environment showed a higher reduction in adhesive strength than those immersed in deionized water and saline solution.

Influence of the Size and Amount of Cork Particles on the Impact Toughness of a Structural Adhesive

The inclusion of particles (nano or micro) is a method to improve the mechanical properties, such as toughness, of structural adhesives. Structural adhesives are known for their high strength and stiffness but also for their low ductility and toughness. There are many processes described in the literature to increase the toughness, one of the most common being the use of rubber particles. In the present study, natural micro particles of cork were used with the objective to increase the impact resistance of a brittle epoxy adhesive. The idea is for the cork particles to act like crack stoppers and absorb impact leading to higher absorption of energy. The influence of the cork particle size and amount were studied. Particles of cork ranging from 38 to 250 µm were mixed in the epoxy adhesive Araldite® 2020 from Huntsman. The amount of cork in the adhesive was varied between 1 and 5% by weight. Surface treatment (low pressure plasma) was applied to the cork powder to assess the effect of the interaction adhesive-cork with several degrees of adhesion. This evaluation was made using impact tests and it was evident that impact absorption was related to the size and amount of cork particles in the resin, considering a uniform particle distribution.

Effect of Moisture and Temperature on the Mechanical Properties of an Epoxy Reinforced with Boron Carbide

The degree of degradation in a polymer composite is directly related to the amount of moisture it absorbs. Plasticization and swelling are among the undesirable consequences of absorbed water. This effect is rather important in materials under severe requirements. The use of these composites as coatings requires studying changes in their properties. For this reason, the aim of this work was to study the effect of moisture and temperature on the mechanical properties of an epoxy reinforced with boron carbide. Different B4C particle sizes (7 and 23 μm) were studied, and the carbide used was 6 wt%. The specimens were exposed to two moisture environments (50 and 95% RH) at 60°C to quantify composite degradation level. Shore D hardness, three-point bending, and pin-on-disk wear tests were used to determine the effect of humid environments. Mechanical properties were determined at several exposure time intervals. Besides, the degradation process was analysed with differential scanning calorimetry (DSC) and infrared spectroscopy (FTIR–ATR). A general loss of properties was observed after water absorption. However, most cases showed recovery after the drying process, depending on the amount of water remaining in the material, which acts as a plasticiser, particularly improving strength.

Influence of Surface Preparation on the Fracture Behavior of Acrylic Adhesive/CFRP Composite Joints

The surface modification and adhesive bonding of a carbon fiber reinforced plastic (CFRP) composite has been investigated. Wettability studies showed that plasma-treated specimens provide a significant increment in the surface energy, relative to untreated material. The surface modification resulted in significantly improved adhesion between the composite and an applied toughened acrylic adhesive; a considerable increase in fracture energy was observed following grit blasting and grit blasting plus silane treatments. Specimens treated with atmospheric plasma showed a slight increment in fracture energy, usually failing adhesively. The durability was tested using a wedge test. Specimens degreased and treated with atmospheric plasma showed the greatest crack growth and failed in an adhesive mode.

Effect of surface treatments on natural cork: surface energy, adhesion, and acoustic insulation

Cork is one of the finest natural materials with high acoustic insulation properties due to its porous structure. In addition, cork presents high water resistance due to its hydrophobic nature. In many applications, cork panels need to be bonded to other materials for manufacturing composite materials or agglomerated cork sheets. In this case, its lack of wettability becomes an important disadvantage. This paper aims to improve the wettability of cork by silanization, atmospheric plasma treatment, and vacuum plasma treatment. The processing conditions of the three treatments were optimized. The surface characterization was performed by surface energy, roughness, and attenuated total reflectance-Fourier transform infrared spectroscopy measurements. Pull-off adherence and peel tests were carried out to evaluate the performance of the treatments with an epoxy adhesive. Plasma treatment of cork plates could be a useful tool to enhance adhesion properties in the manufacturing process of cork sandwich panels or other applications where it could be joined to any material.

The Influence of pH on the Hydrolysis Process of γ-Methacryloxypropyltrimethoxysilane, Analyzed by FT-IR, and the Silanization of Electrogalvanized Steel

Silanes are commonly used as coupling agents to enhance the adhesion between polymeric and inorganic materials. Once silane hydrolysis has taken place, the condensation of the silane on the substrate surface should follow. Optimum hydrolysis conditions will depend on the type of silane and the process conditions of the solution. The pH is particularly important as it has a significant effect on the hydrolysis process. This paper deals with the hydrolysis process of 1 vol% γ-methacryloxypropyltrimethoxysilane (MPS) in aqueous solution at different pHs (2, 4, 6, 8 and 10). Because the hydrolysis rate is a function of pH, hydrolysis times, ranging from 2 min to 48 h, were studied. Fourier transform infrared spectroscopy was used to evaluate the chemical modifications produced by changing the hydrolysis time. The disappearance of the infrared band due to the Si–O–C groups and the appearance of the bands due to the Si–OH bonds were studied. It was shown that longer times were necessary for complete hydrolysis, under almost neutral pH conditions. On the other hand, the Zn-electrocoated steel was silanized with MPS under an optimum pH and the hydrolysis time conditions and the resulting surfaces were analysed by Reflection–Absorption Infrared Reflectance Spectroscopy.

The Effect of Surface Treatment on the Behavior of Toughened Acrylic Adhesive/GRP(epoxy) Composite Joints

The surface modification and adhesive bonding of a bidirectional glass reinforced polymer (GRP) composite have been investigated. Wettability studies showed that grit-blasted and plasma-treated specimens provide a significant increment in the surface energy, relative to untreated material. The most effective treatment found was grit blasting. The surface modification resulted in significantly improved adhesion between the composite and the applied toughened acrylic adhesive; a considerable increase in failure strength and in fracture energy was observed following grit blasting and grit blasting plus silane treatment. Specimens treated with atmospheric plasma showed a reduction in mechanical properties, resulting in interfacial (adhesion) failure. The durability was tested using the wedge test. Specimens treated with atmospheric plasma showed a lower durability than the other surface treatments.

Case studies in adhesives selection

Abstract The selection of an adhesive for a particular application is not as easy as endeavour as it might originally appear. To achieve optimum performance when bonding two materials, one must carefully plan every stage of the bonding process. The selection of an adhesive is a critical factor that will influence each step. The adhesive selection will be dependent primarily on: • The type and nature of substrates to be bonded. • The method of curing that are available and practical. • The expected environments and stresses that the joint will undergo in service. The adhesive selection process is difficult because many factors must be considered, and there is no universal adhesive that will fulfil every application. It is usually necessary to compromise when selecting a practical adhesive system. Adhesive properties limit performance. We need a way of surveying properties, to get a feel for the values design-limiting properties can have. One property can be displayed as a ranked list or bar chart. But it is seldom that the performance of a component depends on just one property. Almost always it is a combination of properties, for instance, of the strength-to-shear modulus ratio. This suggests the idea of plotting one property against another, mapping out the fields in property-space occupied by each adhesive type. The resulting charts are helpful in many ways. They condense a large body of information into a compact but accessible form; they reveal correlations between adhesive properties, which aid in checking and estimating data. In this paper, we have also used the methodology from Professor Michael F. Ashby of Cambridge University in order to solve general practical cases where we had chosen adhesive bonding as a joining process.

Graphene oxide versus graphene for optimisation of PMMA bone cement for orthopaedic applications

Graphene (G) and graphene oxide (GO) nano-sized powders with loadings ranging from 0.1 to 1.0wt% were investigated as reinforced agents for polymethyl methacrylate (PMMA) bone cements. The mechanical properties (i.e. bend strength, bend modulus, compression strength, fracture toughness and fatigue performance) and the thermal properties (i.e. maximum temperature, setting time, curing heat and residual monomer) of the resultant nanocomposites were characterised. The mechanical performance of G-PMMA and GO-PMMA bone cements has been improved at low loadings (≤0.25wt%), especially the fracture toughness and fatigue performance. These improvements were attributed to the fact that the G and GO induced deviations in the crack fronts and hampered crack propagation. The high functionalisation of GO compared with G resulted in greater enhancements because it facilitated the creation of a stronger interfacial adhesion between the GO and PMMA. The use of loadings ≥0.25wt% showed a detriment in the mechanical performance as consequence of the formation of agglomerates as well as to an increase in the porosity. The increase in the residual monomer and the decrease in the curing heat, observed with the increase in the level of G and GO added, suggests that such materials retard and inhibit the curing reaction at high levels of loading by interfering in the radical reaction.