Strength and adhesion characteristics of elementary flax fibres with different surface treatments

It is known that the best flax fibres can compete in terms of mechanical properties with glass fibres. However, during the manufacturing process flax fibres are often damaged, and hence, the properties can be lowered. Furthermore, these properties change from batch to batch (depending on the time and place of harvest), which means that they are somewhat unpredictable. The most affected fibre property is strength, which can vary in very wide interval due to defects introduced by the manufacturing process. Therefore, there is a need for a simple but reliable testing procedure that allows the estimation of the strength of flax fibres, so called quality control. Regarding the final goal, that is the development of natural fibre composites, another crucial property is the fibre/matrix adhesion. The objective of this study is to investigate the possibility to use the single fibre fragmentation test to characterize strength distribution of flax fibres and to evaluate the adhesion. Untreated flax fibres and fibres coated by a special surface treatment are used. Fragmentation tests are performed on flax fibres embedded in thermoset, vinylester and polyester, resins. Results show that there is a definite improvement in interfacial strength when a fibre surface treatment is applied. Fibre strength distribution is obtained from SFFT and compared with limited results available from single flax fibre tests.     

Influence of visco-elastic binder properties on ram extrusion of a hardmetal paste

The influence of the viscous and elastic components of a visco-elastic binder phase on the extrusion behaviour of a tungsten carbide–cobalt hardmetal paste was investigated by studying the paste over a range of temperatures, 30–42 °C, where the binder changed from a semi-solid gel to a viscous liquid. The extrusion behaviour of the paste was studied by ram extrusion and quantified by the Benbow–Bridgwater (BB) method. The elastic and viscous components of the binder were studied separately by means of oscillatory and steady shear techniques in a controlled stress rheometer using rough parallel plates. The paste behaviour fitted the four parameter BB model well: the initial bulk yield stress parameter, σ₀, increased linearly with the binder elastic modulus, G′, while both the velocity dependence parameters α and β were linearly related to the binder steady shear viscosity. Analysis of paste-wall slip parameters gave estimated slip layer thicknesses of 2–5 particle diameters.     

Effect of binder type and content on physical and mechanical properties of geopolymers

In this study, the physical and mechanical behaviors of geopolymers prepared by using different amounts of silica fume and calcium hydroxide as binding materials, acidic pumice as fine aggregate and waste aluminium particles as air-entraining agent were investigated. Test results showed that binder types, amount of binders and alkali activator (sodium hydroxide) significantly affected the physical and mechanical behavior of geopolymer specimens. Bulk density, compressive and flexural strength decreased with the higher alkali activator content. Addition of waste aluminium particles led to decrease in bulk density and strength due to the some extent of entrained air. In the case of same alkali activator content, compressive and flexural strength increased with increase in silica fume and calcium hydroxide up to a certain level.     

Design of green concrete made of plant-derived aggregates and a pumice-lime binder

The use of particles from agricultural lignocellulosic resources in concrete gives it desirable environmental and multiphysics qualities. In this study, parallels are drawn between particles derived from hemp and sunflower stems, in terms of their morphological and physical properties. A pumice-lime binder is proposed as an alternative to the traditional cement or lime based solutions for both environmentally friendly and mechanical qualities. Compaction is applied during casting and its effects on mechanical properties are analysed. A principal finding of this study is that the hemp and sunflower materials show large similarities in terms of morphology and mechanical performance of the resulting concrete. The pumice-lime binder provides desirable properties even with raw pumice sand, which represent 90% of the binder mass proportion. Compaction level during casting induces an orthotropy, even with low plant content, and increases the compressive strength. A simple analytical model using Powers’ equation is proposed to predict plant concrete compressive strength with low plant quantities.     

Computational mineral physics and the physical properties of perovskite

The inherent uncertainties in modern first-principles calculations are reviewed using geophysically relevant examples. The elastic constants of perovskite at lower-mantle temperatures and pressures are calculated using ab initio molecular dynamics. These are used in conjunction with seismic tomographic models to estimate that the lateral temperature contrasts in the Earth's lower mantle are 800 K at a depth of 1000 km, and 1500 K at a depth of 2000 km. The effect of Al(3+) on the compressibility of MgSiO(3) perovskite is calculated using three different pseudopotentials. The results confirm earlier work and show that the compressibility of perovskites with Al(3+) substituted for both Si(4+) and Mg(2+) is very similar to the compressibility of Al(3+)-free perovskite. Even when 100% of the Si(4+) and Mg(2+) ions are replaced with Al(3+), the bulk modulus is only 7% less than that for Al(3+)-free perovskite. In contrast, perovskites where Al(3+) substitutes for Si(4+) only and that are charge balanced by oxygen vacancies do show higher compressibilities. When corrected to similar concentrations of Al(3+), the calculated compressibilities of the oxygen-vacancy-rich perovskites are in agreement with experimental results.     

Influence of surface treatment on adhesion of polyethylene fibres

Abstract

A detailed examination has been undertaken of the influence of surface treatment on the adhesion of polyethylene fibres to epoxy resin. The pull-out adhesion has been determined for untreated, chromic acid treated, and plasma etched monofilaments with different draw ratios and thermal annealing treatments. In a few cases, additional chemical treatments were applied to plasma treated fibres before the pull-out test. The polyethylene surface energy also has been determined by measurement of contact angle. The results, taken together, suggest that the adhesion depends on three factors: (i) the wettability (or physicochemical interactions), which is affected by the extent and nature of the surface treatment as well as the fibre draw ratio; (ii) the surface roughness, after plasma etching only, where a honeycomb structure of pits permits mechanical keying between the fibre and the resin (this structure has been examined by scanning electron microscopy); and (iii) the number of chemical bonds per unit area between the fibre and the resin. It is concluded that these three factors can be regarded as additive and that optimum results are obtained when their respective pull-out strengths reach their maximum values, ~2, ~3, and ~1·7 MN m^?2.

MST/640     

Improvement of adhesion of fucoidan on polyethylene terephthalate surface using gas plasma treatments

Attachment of polysaccharide fucoidan to the polyethylene terephthalate (PET) polymer surface was studied by X-ray photoelectron spectroscopy (XPS). Fucoidan has antithrombogenic and anticoagulant properties and is therefore a promising coating for vascular graft implants for improving their hemocompatibility. Samples of PET polymer were first modified by nitrogen plasma treatment in order to change the surface wettability and to introduce amino groups to the surface, which act as a linker for further binding of fucoidan. Plasma treated samples were then incubated for 30 min in fucoidan solution. The presence of fucoidan layer on the polymer surface was demonstrated by appearance of S2p signal in the XPS spectra of the coated PET samples. The procedure for immobilization of fucoidan on PET surface was optimized by varying pH value of fucoidan solution from 5 to 7.4. The best results were obtained when using lower pH value pH = 5. At these conditions the thickness of the fucoidan coating was estimated to about 7 nm.     

Influence of atmospheric pressure plasma treatment on various fibrous materials: Performance properties and surface adhesion analysis

Atmospheric pressure plasma treatment using oxygen gas was applied to wool fibrous materials. The plasma-treated fibrous materials were characterised using advanced instrumental techniques including scanning electron microscopy and X-ray photoelectron spectroscopy. They were also tested for performance properties including tensile and tearing strength as well as change in yellowness using international standard testing methods. Wettability analysis was conducted to study the surface area and surface energy of the plasma-treated fibrous materials. Surface modification regarding the enhancement of their adhesion to other substance, i.e. microcapsule treatment, was investigated.     

Influence of atmospheric pressure plasma treatment on various fibrous materials: Performance properties and surface adhesion analysis

Atmospheric pressure plasma treatment using oxygen gas was applied to wool fibrous materials. The plasma-treated fibrous materials were characterised using advanced instrumental techniques including scanning electron microscopy and X-ray photoelectron spectroscopy. They were also tested for performance properties including tensile and tearing strength as well as change in yellowness using international standard testing methods. Wettability analysis was conducted to study the surface area and surface energy of the plasma-treated fibrous materials. Surface modification regarding the enhancement of their adhesion to other substance, i.e. microcapsule treatment, was investigated.     

Influence of the binder on the properties of catalysts based on titanium-vanadium oxides

The influence of the nature of the binder and its concentration in V₂O₅/TiO₂ catalysts on their mechanical and catalytic properties has been studied. The characterization analysis showed that the agglomeration mechanism is different when an inorganic acid, such as H₃PO₄, or a natural silicate, such as sepiolite, were used. Two different patterns are proposed, which explain the effect of these binders on the performance of this type of catalyst in the selective catalytic reduction of NO _x with NH₃.     

Influence of industrially produced recycled aggregates on flow properties of concrete

This research aims at evaluating the main risks for the durability of concrete made of industrially produced recycled aggregates called Recycled Aggregate Concrete (RAC). A characterisation of recycled aggregates is performed and their peculiarities are highlighted. A comparison between the behaviour of RAC and that of ordinary natural aggregate concrete is carried out. The influence of both the composition and the curing conditions is discussed. The durability study is focused on the assessment of parameters representing the porous structure and concrete characteristics. Because of the high total water/cement ratio of RAC, their flow properties control their durability. It is established that RAC are characterised by significantly higher water absorption and air permeability. The diffusion of the carbon dioxide is faster, too. That leads to a weaker resistance of RAC to environmental attacks. Since the main durability problems are caused by the fine recycled fraction, its use needs to be restricted. Another way to increase RAC durability seems to be the extended curing in wet environment.     

Optical properties of a dispersion of randomly oriented identical aggregates of spheres deposited on a plane surface

Our previous theory for calculating the scattering pattern from a single aggregate of spheres deposited on a dielectric substrate is extended to deal with a dispersion of identical aggregates onto the substrate with a random distribution of their orientations. To this end the definition of the transition matrix of an aggregate is generalized to take account of the presence of the substrate; then the transformation properties under rotation of the newly defined transition matrix are used to perform analytically the required orientational averages. When the patterns calculated with this theory are compared with the calculations for a single aggregate, it can easily be seen that the features that reveal the anisotropy of the scatterers are not canceled by the averaging procedure.     

Manufacturing of lightweight aggregates with carbon fiber and mineral wastes

The use of carbon fiber wastes (FC) as a component to manufacture lightweight aggregates (LWAs) for concrete has been studied. Amounts of 0, 2.5, 5 and 10% (w/w) of powdered FC were added into a mineral matrix composed by 90% of granite-marble sludge (COR) plus 10% of sepiolite rejection (SEP). The mixtures were milled, kneaded with water, extruded, shaped into pellets, oven-dried and finally fired at 1100, 1125 and 1150 °C for 4, 8 and 16 min in a rotary kiln. The main technological properties of the sintered aggregates were measured. The addition of FC promoted bloating and the formation of an internal structure in which both pores and unburnt carbon fibers were present. Improvements in lightness and mechanical properties were also observed. This is the first time that carbon fibers have been embedded within aggregates, opening the way to the development of a new type of LWAs for concrete.     

The influence of implant surface properties on cell adhesion and proliferation

Interactions of the foreign material of implant and the living tissue on the cell level can cause prolonged healing or, worse, loss of the implant. The cell response to the presence of some implant materials was studied under in vitro conditions. The influence of physicochemical surface parameters on the response of the cells in the immediate vicinity of implants, namely on adhesion, proliferation and synthetic activity of fibroblasts, and on the blood coagulation were compared. The direct contact of tested materials (titanium and Ti6Al4V alloy with various surface treatments, Cr Co Mo alloy, hydroxyapatite-coated titanium, zirconium oxide ceramics, polyethylene and carbon composite) on cell spreading was monitored and the presence of TNF-α and IL-8 was evaluated in the cultivation medium. The formation of blood clots was investigated on samples immersed in a well with freshly drawn whole rabbit blood using a scanning electron microscope. The surface free energy was estimated using the measurement of static contact angle. Both the advancing and receding contact angles were measured by the dynamic Wilhemy plate method. Two main groups with extremes in cell viability were established. In the first group the increased polar component of surface free energy, the highest cell density, the lowest inflammatory cytokine production, but no fibres in the clotting blood were found. On the contrary, the second group of materials with a very low polar component of the surface free energy showed distinctly higher expression of inflammatory mediators, low cell proliferation, but faster formation of fibres in the blood coagulum.     

Influence of preform surface treatments on the strength of fluorozirconate fibres

Zirconium fluoride (ZrF₄)-based glass preforms made by the rotational casting process were treated prior to fibre drawing to eliminate pre-existing defects. Emphasis was given to the removal of external defects by different surface preparation methods which include mechanical polishing, and chemical etching in 0.2m H₃BO₃ solution as well as microwave-assisted plasma fluorination. The strength of the fibres was measured using both bending and dynamic loading tests. Fluorine exposure increased the median tensile strength by an additional 20%. As expected, the Weibull distribution for bending tests was shifted to the higher strength range, and was generally a factor of two more than in the dynamic tensile measurements.     

Influence of extreme dilutions on the magnetic properties of single-domain particle aggregates

Various magnetic properties of samples of single-domain particles dispersed in a nonmagnetic matrix are examined as functions of the packing fractionp. The range of variability ofpis from 0.0003 to 0.20. The squareness ratio and the rotational and alternating hysteresis integrals change withp, while the coercive field, the initial anhysteretic susceptibility, and the areas between the remanence curves are not dependent onp. These results are interpretated as a consequence of the formation of agglomerates interacting with each other, rather than as a consequence of analogous interactions among the single-domain particles which are in the aggregate.     

Effect of natural coarse aggregate type on the physical and mechanical properties of recycled coarse aggregates

Many environmental problems caused by the large volumes of construction and demolition waste (C&DW), the lack of adequate deposition sites and the shortage of natural resources have led to the use of C&DW as replacement of natural aggregates in the production of new concrete. As in the case of natural aggregates, when recycled aggregates are used to manufacture structural concrete, the assessment of their physical, mechanical and durable characteristics is a key issue. The different physical and mechanical properties of the recycled coarse aggregate (RCA) are evaluated. RCA was obtained by crushing conventional concretes with different strength levels (different w/c ratios) containing four different types of natural coarse aggregates (three crushed stones and a siliceous gravel), which differ in shape, composition and surface texture. There is a significant influence of the natural coarse aggregate (NCA) on the properties of RCA, which in many cases is greater than that of the w/c ratio of the source concrete.     

Effects of fiber surface treatments on mechanical properties of epoxy composites reinforced with glass fabric

In this study, effects of fiber surface treatments on mechanical behavior and fracture mechanism of glass fiber/epoxy composites were investigated experimentally. To change the composition of the glass and regenerate to the hydroxyl groups, activation pretreatment of heat cleaned woven glass fabric was performed using (v/v) HCl aqueous solution at different concentrations before silane treatment. The treatment of silanization of heat cleaned and acid activated glass fibers with γ-glycidoxypropyltrimethoxysilane were performed. In this work, short beam shear test has been conducted to determine the performance of the acid treatment and the silane treatment in terms of the interlaminar shear strength. The silane coating on the heat cleaned glass fibers increased the interlaminar shear strength of the composite. However, the silane coating on the acid activated glass fibers did not improve the interlaminar shear strength of the composite. In addition, the strengths of the glass fabric specimens in tension and flexure were investigated. When the glass fibers are first treated with HCl solution and then with silane coupling agent, the tensile strengths of the composites decreased significantly. Scanning electron photomicrographs of fractured surfaces of composites were performed to explain the failure mechanisms in the composite laminates broken in tension.     

Influence of recycled aggregates and high contents of fly ash on concrete fresh properties

This study presents the fresh properties of concrete with supplementary cementitious materials (SCM) and recycled concrete aggregates (RCA), with emphasis on the feasibility of using high volumes of fly ash (FA) in RCA concrete. For this purpose, two mix families (0% coarse RCA and 100% coarse RCA) were produced, both with and without superplasticizers (SP). The coarse natural aggregates (NA) were replaced with coarse RCA at 0% and 100%, respectively. For each of the mentioned families, three incorporation levels (0%, 50% and 100%) of fine RCA were used with 0%, 30% and 60% of FA, resulting in 28 compositions. Each mix was tested in the fresh state by means of slump, density and air content. The results of this study show that RCA decreased the slump of concrete mixes, but the required water content can be minimized by incorporation FA. Regardless of the water absorption of the aggregates, for a given fine RCA incorporation ratio and the same ratio of FA, no increase in water content is required to obtain the same target slump as in the reference concrete. On the other hand, for a given coarse RCA incorporation ratio, a five times lower FA ratio is enough to obtain the same target slump as in the reference concrete. Air voids in concrete mixes were more affected by the shape of the aggregates than by their water absorption. The air content of concrete mixes increased as the incorporation levels of FA and RCA increased. However, in comparison with the individual effects, the air content decreased by combining the incorporation of both FA and RCA. Moreover, the rate of reduction in fresh density by increasing the incorporation of RCA and FA was similar in concrete mixes with and without SP.     

Influence of mechanical surface treatments on fatigue strength of commercial purity titanium

A comparative study of two mechanical surface treatments of shot peening (SP) and cold rolling (CR) on fatigue strength of commercial purity titanium has been conducted. The treated surface was characterized by using transmission electron microscopy (TEM), X-ray diffraction (XRD), and surface roughness measurements. Experimental result shows that SP and CR increased the fatigue strength of commercial purity titanium, and moreover, the following results were obtained: (1) The improvement of fatigue strength is related to the formation of deformation twins in strengthened layer. Before or after fatigue, the samples strengthened by SP or CR not only have twin shape and number change, but also have twin interactions in the SP and twin-grain boundary interactions in the CR. (2) XRD measurement demonstrated that SP leads to surface compressive residual stress are much higher than those after CR. Surface compressive residual stress has higher relaxation in the SP than in the CR condition during cyclic loading, then the surface compressive residual stress has the same values after fatigue deformation. (3) Surface roughness resulting from SP is ten times of CR.