1,720,964 research outputs found
Effect of fibre surface treatment on kenaf filled recycled polypropylene composite
Get PDFLignocelluloses based natural fibre is being used as an alternative to traditional glass and carbon fibre in the composite materials due to its low density and higher specific properties.Furthermore,these fibres are available at a very low cost.Current work is focused on kenaf fibre based reinforced recycled polypropylene composites.In this project,initially the raw kenaf fibre was grinded to a small size (2 to 5 mm) and then mixed with recycled polypropylene (RPP) followed by extrusion through a twinscrew extruder.Fibre loading in the composite was 10, 20, 30 40 and 50% by weight.After that test specimens for tensile, flexural and impact testing were prepared through an injection moulding machine.Melt flow indexer was used to evaluate theflow property of the extruded materials.To improve the interfacial property between fibreand matrix maleic anhydride grafted polypropylene (MAPP)was used as a coupling agent with ratio of 10:1.Mechanical tests showed that significant improvement achieved due to coupling agent.Fibre surface modifications for better adhesion between fibre and matrix were carried out by three ways including alkali,ultrasound and laccase enzyme treatment.Treated fibre was then blended with recycled polypropylene with 40%fibre loading in the presence of MAPP,as 40% loading found the optimum regarding tensile performances with untreated fibre based composites. For alkali treatment,both concentration of the solution and soaking time were considered as treatmentvariables for the fibre.Mechanical tests were carried out to evaluate the optimum treatment condition for the best strength.For ultrasound,normal water was used as media for the treatment.Both temperature and sonication power was considered as treatment variables.Mechanical tests were carried out to evaluate the best strength at optimum condition of fibre treatment.Enzymatic treatment was carried out for an alternative way of fibre treatment.The composites strength was increased by 18% for fibre loading whereas coupling agent improves it by 37%. Ultrasound and alkali treatment of fibre improved the tensile strength of the composites almost by 57%. Weathering and water uptake were carried out for the composites. After that mechanical tests were performed to evaluate the properties of the composites.Thermal test like thermogravimetric analysis (TGA) was carried out to evaluate the thermal stability of the composites.It was found that,RPP degrade at one stage while composites degrade at two stages.Activation energies of the composites were calculated from the TGA analysis.Crystallinity and melting point were detected through differential scanning calorimetry(DSC) analysis. Incorporation of fibre increased the crystallinity of the polymer matrix.Structural morphology was carried out of the fractured samples to evaluate the bonding interface between fibre and matrix.Improved adhesion between fibre and matrix was found for the case of treated fibre based composites in the presence of MAPP.Fourier transform of infrared radiation (FTIR)spectroscopy was used to find out any structural change due to the treatment of the fibre and analysis found that treatment of fibre able to remove the non-cellulosic compound to a varying extent depending on treatment parameters.Response surface method (RSM) was used to optimize process parameters and one of the best set of treatment conditions was 99.96% sonication power at 94.46oC to achieve 28.86 MPa of TS
Preparation and characterization of palm oil based polyalkyd films and composites with multi-walled carbon nanotubes
Get PDFIn this research, polyalkyd resins were prepared from palm oil by using polycondensation reaction. A two-step method viz., alcoholysis and esterification was conducted to synthesize polyalkyd resins. Prior to alcoholysis, crude palm oil was subjected for dehydration process to increase its unsaturation. Different types of catalysts such as, sulphuric acid, para-toluene sulfonic acid, phosphoric acid, sodium hydrogen sulphate and potassium hydrogen sulphate were used for the dehydration. In alcoholysis process, the triglyceride-based dehydrated oil was reacted with glycerol to produce monoglyceride. The prepared monoglyceride was further brought into contact with acid anhydride to prepare polyalkyds. Response surface methodology was used to optimize the reaction parameters for esterification like reaction temperature, reaction time, catalyst concentration, acid anhydride to mono-glyceride ratio and agitation speed. The optimum condition was used to prepare various types of polyalkyds by using different types of acid anhydrides such as, maleic anhydride, succinic anhydride, phthalic anhydride, 3,4,5,6-tetrahydrophthalic anhydride and cis-1,2-cyclohexanedicarboxylic anhydride. A comparison was drawn among the resins prepared by using different types and percentages of acid anhydrides. The produced bioresins were characterized for physico-chemical properties such as, viscosity, density, iodine value, acid value, drying time, non-volatile materials content, specific gravity, colour, etc. The resins prepared with optimum reaction parameters were subjected for curing process by using methyl ethyl ketone peroxide and cobalt naphthanate. To enhance the resinous property, multi-walled carbon nanotubes (MWCNTs) were dispersed into the resin at different percentages of loading such as, 0.5, 1.0 and 1.5 wt.%. The loading was optimized based on the tensile strength of the film. Finally, in-situ polymerization with carbon nanotubes during esterification was performed by adding optimum percentage of loading. The films produced from different formulations were characterized by different testing such as, adhesion, chemical resistivity, thermogravimetric analysis, differential scanning calorimetry, field-emission scanning electron microscopy, x-ray diffraction analysis, contact-angle measurement, tensile testing, pencil hardness, gloss, etc. In addition, the curing kinetics of the resin was analysed to evaluate the kinetic parameters such as, reaction rate, activation energy and degree of conversion in terms of time and temperature. Result analyses through RSM revealed a desirability of 0.985 for the reaction time of 88.64 min. Moreover, 91.5% fractional conversion was achieved actually, which is close to the predicted value. Analysis revealed that 3,4,5,6-tetrahydophthalic anhydride-based resin showed improved resinous property than others due to high degree of crosslinking. It was also found that higher amount of aliphatic acid anhydrides are responsible for high degree of crosslinking density, whereas higher thermal stability was ensured by the inclusion of aromatic acid anhydride. Finally, incorporation of MWCNTs into the alkyd resin enhanced the overall film properties, which was further improved through in-situ reaction. The physical bonding and mechanical entanglement were the possible reason for showing improved properties, as revealed from the analysis
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dispersion characteristics of hydroxyl and carboxyl-functionalized multi-walled carbon nanotubes in polyester nanocomposites
Get PDFMulti-walled carbon nanotube (MWCNT) reinforced polyester-based composites were prepared by mixed blending in a solvent. Orthophthalic unsaturated polyester was blended individually with different types of non-functionalized and functionalized MWCNTs. Two types of functional groups: hydroxyl (-OH) and carboxyl (-COOH) were introduced with MWCNTs for the nanocomposites. The mechanical properties of the composites, like tensile, three-point bending and impact energy were evaluated. Fourier transform infrared spectroscopy was used for the functional group analysis. The dispersion characteristics of the samples were observed by transmission electron microscopy and field-emission electron microscopy. In addition, the thermal decomposition and melting behavior of the samples was assessed by differential scanning calorimetry and thermogravimetric analysis. The properties were varied due to the variation of the functional groups. The result analysis showed that the entangled agglomerations of hydroxyl-functionalized MWCNTs were destroyed to relatively smaller clusters. The hydroxyl-functionalized MWCNTs were more effective for homogeneous dispersion and contributed for better mechanical properties of the composites, compared to non-functionalized and carboxyl group-functionalized MWCNTs
Dispersion characteristics of hydroxyl and carboxyl-functionalized multi-walled carbon nanotubes in polyester nanocomposites
No full textAbstract
Multi-walled carbon nanotube (MWCNT) reinforced polyester-based composites were prepared by mixed blending in a solvent. Orthophthalic unsaturated polyester was blended individually with different types of non-functionalized and functionalized MWCNTs. Two types of functional groups: hydroxyl (-OH) and carboxyl (-COOH) were introduced with MWCNTs for the nanocomposites. The mechanical properties of the composites, like tensile, three-point bending and impact energy were evaluated. Fourier transform infrared spectroscopy was used for the functional group analysis. The dispersion characteristics of the samples were observed by transmission electron microscopy and field-emission electron microscopy. In addition, the thermal decomposition and melting behavior of the samples was assessed by differential scanning calorimetry and thermogravimetric analysis. The properties were varied due to the variation of the functional groups. The result analysis showed that the entangled agglomerations of hydroxyl-functionalized MWCNTs were destroyed to relatively smaller clusters. The hydroxyl-functionalized MWCNTs were more effective for homogeneous dispersion and contributed for better mechanical properties of the composites, compared to non-functionalized and carboxyl group-functionalized MWCNTs.</jats:p
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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