Adhesion between polymers and evaporated gold and nickel films

To obtain information on the adhesion between metal films and polymeric solids, the adhesion force was measured by means of a tensile pull test. It was found that the adhesion strengths between polymeric solids and gold films evaporated on polymer substrates were (1.11 + or - 0.53) multiplied by 10(6) N/M(2) on PTFE, about 5.49 multiplied by 10(6) N/m(2) on UHMWPE, and 6.54x10(6) on 6/6 nylon. The adhesion strengths for nickel films evaporated on PTFE, UHMWPE, and 6/6 nylon were found to be a factor of 1.7 higher than those for the gold coated PTFE, UHMWPE, and 6/6 nylon. To confirm quantitatively the effect of electron irradiation on the adhesion strength between a PTFE solid and metal films, a tensile pull test was performed on the irradiated PTFE specimens, which were prepared by evaporating nickel or gold on PTFE surfaces irradiated by 2-keV electrons for various times. After irradiation, the adhesion strength increased to (4.92 + or - 0.92)x10(6) N/m(2) for nickel coated PTFE and (1.82 + or - 0.48)x10(6) N/m(2) for gold coated PTFE. The improvement in adhesion for nickel is higher than that for gold

Determinação da aderência entre resinas epoxídicas e argamassas hidráulicas

A determinação da aderência entre polímeros e argamassas coloca alguns problemas. A utilização de ensaios tradicionais como tracção directa, flexão ou corte, normalmente não permite a determinação do valor numérico da aderência. Quando o ligante é bom e a colagem é bem executada, a rotura ocorre na argamassa. Este tipo de roturas permite concluir que a aderência é superior ao valor da tensão de rotura obtida, não sendo possível dizer qual o valor numérico da aderência. Utilizando um ensaio baseado na mecânica da fractura é mais fácil a determinação da aderência. Os provetes com entalhe permitem a concentração de tensões na junta polímero/argamassa. Assim, as roturas adesivas são mais frequentes, permitindo a determinação do valor numérico da aderência. O provete escolhido para este estudo foi o DCB (“double cantilever beam”). Os materiais utilizados foram uma resina epoxídica e uma argamassa normal. Os ensaios de tracção directa das colagens entre estes dois materiais conduziram a roturas na argamassa. No entanto, nos ensaios com provetes DCB obtiveram-se sempre roturas mistas. Para a determinação da energia de fractura (Gf) é necessário conhecer o comprimento da fissura. Este parâmetro altera-se durante o ensaio, não sendo fácil a sua determinação em cada instante. Para esta determinação, utilizaram-se três métodos: emissão acústica, colocação de um deflectómetro no meio do caminho de fissura e complacência. O método da complacência revelou-se mais adequado. Outro problema é o desvio das fissuras para fora do seu caminho esperado. Para evitar estes desvios, reforçaram-se os provetes exteriormente, colando placas de aço. Assim, conseguiu-se que as roturas seguissem o caminho de propagação esperado. Por último, para evitar o reforço exterior, utilizaram-se provetes DCB com secção variável. Estes provetes comportaram-se bem durante os ensaios

Friction and Adhesion in Rigid Surface Indentation of Nitrile Rubber

When a rigid body in the form of a plane strain indentor is forced into an elastomer, the asperities on the surface of the indentor are filled by the softer material. As depth of ingress increases, the rubber displaced into the indentor asperities exhibits stick-slip behaviour. The rubber adheres to the rigid body and if the depth of ingress is held at a maximum, the level of adhesion remains constant despite short-term load relaxation occurring in the rubber. This text describes the influence of a range of factors on indentation forces and adhesion in rigid indentation of hydrogenated nitrile rubbers. Blocks of rubber in four hardness grades were subjected to plane strain indentation using mild steel plate indentors. The edges forced into the elastomers were radiused to produce ingress of a semi-circular profile into the blocks and this allowed subsequent finite element modelling of the indentor as a continuum. During physical testing, indentation rates and indentor surface finish were varied and load/displacement characteristics, adhesion and short-term load relaxation were measured. The correlation between indentation loads at the common maximum depth of ingress and the adhesion theory of friction for different surface finishes was examined. Nonlinear finite element stress analyses, employing adaptive meshing, alternative friction algorithms and competing strain energy density functions were used to model the indentation process and comparisons of surface profiles with test results are included

Optimization of thermoplastic blend matrix HDPE/PLA with different types and levels of coupling agents

High-density polyethylene (HDPE) and poly(lactic) acid (PLA) blends with different ratios of both polymers, namely, 30:70, 50:50, and 70:30, were produced. Polyethylene-grafted maleic anhydride and a random copolymer of ethylene and glycidyl methacrylate were also considered as compatibilizers to modify HDPE/PLA optimal blends and were added in the amounts of 1, 3, and 5 wt.%. Different properties of the blends were evaluated by performing tensile tests and scanning electron microscopy to analyze blend and interfaces morphology. Moreover, thermomechanical analysis through differential scanning calorimetry, thermo-gravimetric analysis, and infrared spectroscopy were also performed. The blend containing equal amounts of HDPE and PLA seemed to present a good balance between amount of bio-derived charge and acceptable mechanical properties. This suggests that these blends have a good potential for the production of composites with lingo-cellulosic fillers

The influence of curing and surface preparation on the adhesion of protective coatings on concrete

In cases where concrete has to be repaired or protected due to exposure to an aggressive environment, a protective coating is often used. The guidelines referenced on the subject of repairs and coatings of concrete require the substrate must be clean, dry and free from loose material but no mention is made of a preferred method of surface preparation. This research report presents details of an investigation in which concrete was subjected to different curing regimes in order to induce different qualities of surface concrete. The different surface qualities were prepared using four alternative surface preparation methods prior to coating. After an initial investigation, five different coatings were chosen in order to cover a broad spectrum of coatings available to the construction industry. Once the applied coatings had cured they were tested using a pull-off testing device to determine the adhesion properties. The mode of failure was determined by visual examination. In addition, surface characteristics were determined using an optical microscope and the water sorptivity test. Results indicate that preparing the surface before application of coatings does improve adhesion. The preparation that was easiest to carry out, and which also gave the best adhesion results, was the wire brushing technique. Considering the practicality for site application, the mechanical method would be most appropriate. From the findings, aliphatic coating exhibited the best adhesion properties, while epoxy resin and cementitious-based materials also gave satisfactory results. B T Benn 7231599 iii Elastomeric coating with lower adhesion strengths at early ages may be suited to surfaces that are expected to crack, as the elastic nature of the material will bridge the gap. Masonry paint, which was only used for comparative purpose did not perform as well as expected and had the lowest bond strengths. Where the removal of defective concrete is likely to result in a rough surface the cementitious material may be preferable

Waste and recycling materials used in concrete

Materials with higher strength and high performanceprovide excellent benefits. But after a very short useful-life become waste and contribute to environmental degradation. Some investigations are focused on recycling by using innovative and clean technologies. In this work, waste and recycled materials as well as gamma radiation are proposed as tools for improving mechanical properties of concrete; polyethylene terephthalate of bottles, automotive tire rubber as well as cellulose of Tetra Pak packages are studied as materials.Autonomous University of the State of Mexico (UAEM), Grant 3886/2015F

Mixed matrix membranes

In recent decades, mixed matrix membranes (MMMs) have attracted considerable interest in research laboratories worldwide, motivated by the gap between the growing interest in developing novel mixed matrix membranes by various research groups and the lack of large-scale implementation. This Special Issue contains six publications dealing with the current opportunities and challenges of mixed matrix membranes development and applications as solutions for the environmental and health challenges of 21st century society.Financial support by the Spanish Ministry for Science and Universities under project grant no. CTQ2016-76231-C2-1-R at the Universidad de Cantabria is gratefully acknowledged

Synthesis and Characterization of Electrically Conducting Polyaniline Doped with Glacial Acetic Acid (CH3COOH) at Room Temperature

Polyaniline (PANI) has been prepared by chemical oxidation method at room temperature and the effect of concentration of dopant Glacial Acetic Acid (CH3COOH) on the structure of the polymer was investigated. Polymers prepared in absence and in the presence of varying concentrations of CH3COOH were characterized using UV-visible, FTIR spectroscopy and conductivity measurements. In UV-visible spectra of PANIs recorded in DMSO revealed that absorption bands increases with increasing concentration of CH3COOH. The FTIR spectra shows the absorption bands related to quinoid and benzenoid rings for the undoped and doped PANI in CH3COOH indicating that the polymer is composed of amine and imine units. Highest conductivity value was obtained in presence of 1.0 M CH3COOH indicating that the more preferable doping of PANI will be at this concentration of CH3COOH. The effect of the temperature upon the conductivity of PANI synthesized with different concentrations of CH3COOH has been studied

Durability of high-performance concrete with fly ash

High-performance concrete (HPC) is usually produced using high quality materials. These high quality constituents drastically increase the initial cost of HPC, hence hindering its more widespread use. Therefore, the main goal of this research project was to produce a low cost enhanced performance concrete or even a low cost HPC, using low quality fly ash and locally available crushed aggregates. In this way, a significant reduction in the use of Portland cement, as well as that of scarce natural resources, would be obtained. The effect of high percentages of fly ash and crushed aggregates on concrete performance was studied by comparing the mechanical and durability performances of such concretes with nominally similar types of concrete with no fly ash incorporated. The results obtained indicate that it is possible to produce concrete in the low range of HPC with up to 65 MPa at 56 days by replacing up to 40% of cement with as received fly ash using crushed granite aggregates. Furthermore, it was observed that workability and durability both increased significantly when fly ash partially replaced Portland cement

In Vitro Study of Release of Metronidazole Tablets Prepared from Okra Gum, Gelatin Gum and their Admixture

The aim of this study is to evaluate the ability of okra gum to release it\'s medicament in bioadhesive polymer-based drug delivery system. Bioadhesive studies using the tensiometer were done to evaluate its bioadhesivenes. Conventional tablets were made with okra gum as binder and in-vitro release studies carried out using gelatin as a standard reference. Okra gum was seen to have a comparable result with gelatin in term of the bioadhesive property the amount of drug released. Keywords: Bioadhesive, Okra gum, Gelatin gum, Metronidazole, Release studiesBio-Research Vol. 6 (1) 2008: pp. 339-34