Mercerization of sisal fibers: Effect of tension on mechanical properties of sisal fiber and fiber-reinforced composites

Sisal fibers were mercerized, under tension and no tension, to improve their tensile properties and interfacial adhesion with soy protein resin. Mercerization of fibers under tension is known to minimize fiber shrinkage and to lower the microfibrillar angle by aligning them along the fiber axis. Mercerization improved the fracture stress and Young’s modulus of the sisal fibers while their fracture strain and toughness decreased. Mercerized sisal fiber-reinforced composites with soy protein resin showed improvement in both fracture stress and stiffness by 12.2% and 36.2%, respectively, compared to the unmercerized fiber-reinforced composites. Scanning electron microscope (SEM) photomicrographs of the composite fracture surfaces showed shorter fibrils protruding in the mercerized fiber-reinforced composites resulting in better sisal fiber/soy adhesion. Changed fiber surface properties were also responsible for better adhesion.     

Investigation on mechanical properties of woven alovera/sisal/kenaf fibres and their hybrid composites

The go-green concept results in multipoint focus towards materials made from nature; easily decomposable and recyclable polymeric materials and their composites along with natural fibres ignited the manufacturing sectors to go for higher altitudes in engineering industries. This is due to the health hazard and environmental problems faced in manufacturing and disposal of synthetic fibres. This study was undertaken to analyse the suitability of new natural fibre as an alternative reinforcement for composite materials. In this paper, tensile, flexural and impact test is made for the woven alovera and kenaf (AK), sisal and kenaf (SK), alovera, sisal and kenaf fibre hybrid epoxy composites (ASK). The composite laminates are made through a hand-layup process. The surface analysis is studied through scanning electron microscopy. From the investigation the SK hybrid composite shows good tensile property, AK hybrid composite shows better flexural property and the best impact strength is observed for ASK hybrid composite. The natural fibres slowly replace the synthetic fibres from its environmental impact, marching towards a revolution in engineering materials.     

Thermal and mechanical behaviour of sisal/phenolic composites

This research proposes the development of polymeric composites reinforced with natural fibres to become stronger the damaged timber structures and proposes thermal and mechanical characterization of these composites. Fibres with larger structural applications are glass and carbon fibres but the use of natural fibres is an economical alternative and possesses many advantages such as biodegradability, low cost and is a renewable source. Woven sisal fabric was submitted to heat treatment before moulding and the influence of moisture content of fibres on the composites behaviour was observed. The paper presents mechanical characterization by tensile and flexural strength of woven sisal fabric composites, with and without thermal treatment (at 60 °C for 72 h) on the fabric, thermal characterization by TGA and the manufacturing process by compression moulding. Experimental results show to sisal/phenolic composites a tensile strength and a flexural strength value of 25.0 MPa and 11.0 MPa, respectively, independent to the use of sisal fibres with or without thermal treatment.     

Mechanical properties of sisal fibre at elevated temperatures

Sisal fibres extracted from the leaves of Agava sisalana plants 3, 5, 7 and 9 years old were tested at different temperatures for tensile strength, elongation, toughness and modulus. The tensile strength, modulus and toughness values of sisal fibre decreased with increase in temperature. The effect of plant age on tensile strength, tensile modulus and toughness of sisal fibre became very much less at 100 °C as compared to 30 °C. Fractured fibres were observed by using a scanning electron microscope. The ends of fibres fractured at elevated temperature showed a failure similar to that of inorganic fibres. Elongation values at all temperatures increased with age. Elongated capillaries were observed in fibres fractured at 80 and 100 °C, due to the removal of moisture and volatiles originally present in the fibres. The fibrils are clearly observed in the form of hollow cylinders. Fractured surfaces are composed of brittle as well as ductile phases. The ductile portion increased with the increase of temperature.     

Optimization of mechanical properties of non-woven short sisal fibre-reinforced vinyl ester composite using factorial design and GA method

This work presents a systematic approach to evaluate and study the effect of process parameters on tensile, flexural and impact strength of untreated short sisal fibre-reinforced vinyl ester polymer-based composites and predicts the optimum properties of random natural fibre-reinforced composites. The natural fibre of sisal at lengths of 10, 30 and 50 mm and vinyl ester resin at loadings of 15, 30 and 45 (wt%) were prepared. The composite panel was then fabricated using hand lay method in cold process of size 180×160 mm². Samples were then cut from the panel and subjected to mechanical properties testing such as tensile, flexural and impact strengths. The average tensile strength ranges between 27·1 and 43·9 MPa. The flexural strength ranged between 26·9 and 49·5 MPa and the impact strength ranged between 16 and 93 J/m. The strength values were optimized using factorial design and genetic algorithm (GA) method. The predicted optimum process parameter values are in good agreement with the experimental results.     

Selected mechanical properties of gold,silver, aluminium and germanium coatings

Selected mechanical properties such as tensile properties, internal friction, internal stress, adhesion and crack formation of metallic coatings were investigated in the as-deposited and annealed conditions. In addition, the density, elastic constants and thermal expansion coefficient of the metallic coatings were measured on self-supported coatings and they agree well with tabulated values. The experimental procedures are presented and those characteristics peculiar to coatings are discussed.     

Effect of flame retardants on flame retardant,mechanical, and thermal properties of sisal fiber/polypropylene composites

A flame retardant efficiency of flame retardants; ammonium polyphosphate (APP), magnesium hydroxide (Mg(OH)₂), zinc borate (Zb), and combination of APP with Mg(OH)₂ and Zb in sisal fiber/polypropylene (PP) composites was investigated using a horizontal burning test and a vertical burning test. In addition, maleic anhydride grafted polypropylene (MAPP) was used as a compatibilizer to enhance the compatibility in the system; i.e. PP-fiber and PP-flame retardants. Thermal, mechanical, and morphological properties of the PP composites were also studied. Adding the flame retardants resulted in improved flame retardancy and thermal stability of the PP composites without deterioration of their mechanical properties. APP and combination of APP with Zb effectively enhanced flame retardancy of the PP composites. No synergistic effect was observed when APP was used in combination with Mg(OH)₂. SEM micrographs of PP composites revealed good distribution of flame retardants in PP matrix and good adhesion between sisal fiber and PP matrix.     

Toward the link between structural and mechanical properties of fiber aggregates in paper materials

Journal of Materials Science - Mechanical properties of fiber-based materials, such as paper, are governed by the heterogeneous microstructure induced by the formation process. For example, in...     

The mechanical properties of (SN)X single crystals

The compression stress-strain behaviour of single crystals of sulphur nitride, (SN)_x, a metallic polymer, was measured in the ambient environment. Measurements were made both parallel and perpendicular to the chain axis on crystals which were about 1 mm in size. The plastic stress-strain behaviour resembled that of a highly anisotropic metal. Deformation to large strains produced a fibrilated structure which graphically exhibits the polymeric nature of (SN)_x. Young's moduli parallel and perpendicular to the chain were 21 and 1.4 GPa respectively. An analysis of the possible slip systems in (SN)_x indicated that there is only one easy glide system, (1 0 0) [0 0 1].Supported by the National Science Foundation MRL Program under Grant No. DMR 76-80994.     

High-temperature mechanical properties of WC-Co hard metals (Review)

Experimental results are discussed of the laboratory investigations into high-temperature mechanical properties of WC-Co hard metals as functions of the microstructure parameters (cobalt content, average sizes of carbide grains and cobalt interlayers), binder composition (carbon and cubic carbide contents) and the thermal and force action found in the literature. The effect of high temperatures on deformation characteristics in bending, tension and compression has been analyzed. The problems of short-and long-time strengths (high-temperature strength) and thermomechanical fatigue are discussed. The revealed mechanisms of the high-temperature deformation are considered.     

Preparation and properties of sisal microfibril/gelatin biomass composites

In this work, the natural sisal fibers were fibrillated by enzyme hydrolysis or mechanical disintegration into microfibrils with a width of 5-10 μm and different aspect ratios. The sisal microfibrils or microfibril mats were added into the gelatin to prepare biomass composites, by solvent-casting or solution impregnation techniques, respectively. The morphology, mechanical properties, biodegradation property, and water adsorption behaviors of the composites were investigated. It was found that the tensile strength of the composites was dramatically increased with the addition of sisal microfibrils. The degradation ratio of the composites decreased continuously with increasing the sisal fibril content. The addition of sisal microfibrils decreased the water uptake at equilibrium and the water diffusion coefficient. Scanning electron microscopy characterization showed that the sisal microfibrils were very well embedded in the gelatin matrix, showing a good interfacial adhesion.     

挤压AM50(-Ca)镁合金的显微组织与力学性能研究

研究了挤压AM50(-Ca)镁合金的微观组织和力学性能.研究发现添加钙在AM50合金中生成新的Al2Ca相,并细化合金的晶粒尺寸.大于2wt.%的钙使铸态AMS0的晶粒尺寸从200 μm减小到40 μm,使挤压态AM50的晶粒尺寸从15 μm减小到7.5 μm.含钙量较少时,晶粒内仍含有少量的Mg17Al12相,Al2Ca相主要分布在晶界;含钙量多于2wt.%时,合金中的Mg17Al12完全消失,除晶界处的Al2Ca相外,在晶粒内部出现大量的针状Al2Ca相.加钙提高了AM50合金的低温抗拉强度,同时在所有试验温度下合金的屈服强度得到提升.     

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.     

Orientation dependent mechanical properties of commercially pure (cp) titanium

The present investigation is an attempt at correlating the crystallographic orientation and mechanical properties of hexagonal commercially pure titanium (cp-titanium). Annealed cp-titanium sheets are subjected to tensile deformation along the rolling direction, along 45° to the rolling direction and along 90° to the rolling direction respectively. Crystallographic textures and mechanical properties of these cp-titanium samples are investigated in the present study. The hardness of different grains/orientations is estimated through nanoindentation, grain average misorientation, orientation estimated elastic stiffness and Taylor factor measurements. It is observed that the hardness of the grains close to basal orientation is higher compared to non-basal orientations. It is further observed that the estimated bulk mechanical properties of cp-titanium have a direct relationship with the volume fraction of basal grains/orientations.     

Thermal and dynamic mechanical analysis of polystyrene composites reinforced with short sisal fibres

The thermal behaviour of polystyrene composites reinforced with short sisal fibres was studied by means of thermogravimetric and dynamic mechanical thermal analysis. The thermal stability of the composites was found to be higher than that of sisal fibre and the PS matrix. The effects of fibre loading, fibre length, fibre orientation and fibre modification on the dynamic mechanical properties of the composites were evaluated. Fibre modifications were carried out by benzoylation, polystyrene maleic anhydride coating and acetylation of the fibre and the treatments improved the fibre-matrix adhesion. PS/sisal composites are thermally more stable than unreinforced PS and sisal fibre. The addition of 10% fibre considerably increases the modulus but the increase is found to level off at higher fibre loadings. The T_g values of the composites are lower than that of unreinforced PS and may be attributed to the presence of some residual solvents in the composites entrapped during the composite preparation. The treated-fibre composites show better properties than those of untreated-fibre composites. The Arrhenius relationship has been used to calculate the activation energy of the glass transition of the composites. A master curve is constructed based on time-temperature superposition principle.     

The mechanical properties of lithium tetraborate (100), (011) and (112) faces

The mechanical properties of lithium tetraborate (LTB) were studied using micro- and nanoindentation on (100), (011) and (112) oriented plates. The lowest values of the hardness obtained for the LTB (100) face are caused by relatively easy cleavage parallel to the {100} planes. The hardness values decrease at the maximal load increasing for the LTB faces studied, however the indentation size effect is less pronounced for the LTB (011) face. The residual stresses of the indent area were detected using a micro-Raman spectroscopy of indents. It was found that the LTB does not exhibit irreversible phase transitions at an applied load range up to 113-130 mN.     

Investigation of the electrical and mechanical properties of short sisal fiber-reinforced epoxy composite in correlation with structural parameters of the reinforced fiber

Chemical modification of the sisal fiber is done through dewaxing. Increment in the degree of crystallinity, crystallite size, and bulk density are observed in case of the dewaxed sisal fiber. The partial removal of wax, hemicellulose, and lignin content is confirmed from the FTIR spectra. Better flexural strength and tensile strength are observed in case of dewaxed sisal fiber-reinforced epoxy composite (DSFREC) in comparison to the raw sisal fiber-reinforced epoxy composite (RSFREC). This may be due to the improvement in the adhesion between the fiber and matrix. Lower values of dielectric constant (ε_r) and dielectric loss (tanδ) are also observed in case of DSFREC. The shifting of M″_max toward higher frequency side with rise in temperature ascribing a correlation between motions of mobile ions and suggests a spread of relaxation times. Moreover, the structural parameters of the fiber are correlated with the mechanical and electrical properties of the composite.     

Non-destructive evaluation of mechanical properties of poly (vinyl) alcohol-hydroxyapatite nanocomposites

Hydroxyapatite-poly (vinyl) alcohol nanocomposite powder was synthesized using varying poly (vinyl) alcohol concentrations. The dried powder was compacted into micro-porous disks at a load of 4 tons. The disks were sintered at 1200°C to evolve porous nanocomposites. Size and shape of the pores observed in the scanning electron micrographs were quantified by using image processing software. Ultrasound velocity measurements were done to evaluate mechanical properties non-destructively.