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Measurement and prediction of thermal conductivity for hemp fiber reinforced composites

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Abstract

The thermal conductivity of hemp fiber reinforced polymer composites were studied from the steady state temperature drop across samples exposed to a known heat flux. The transverse and in-plane thermal conductivities for oriented and randomly oriented composites for different volume fractions of fiber were investigated. Experimental results showed that the orientation of fibers has a significant effect on the thermal conductivity of composites. To validate the experimental results, the heating tests for the thermal conductivity measurements were simulated by a finite element model using the thermal conductivity values obtained from the experiments. Predicted temperatures show close agreement with measured temperatures. Moreover, the experimental results of thermal conductivities of composites at different directions were compared with two theoretical models and illustrated good agreement between the obtained results and models. POLYM. ENG. SCI. 47:977–983, 2007. © 2007 Society of Plastics Engineers

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... In addition, natural fiber composites exhibit anisotropic thermal properties that enable efficient thermal dissipations along certain directionalities [7], and thus providing flexible alternative options for thermal insulators. In order to test the TCs in either direction, numerous experiments were conducted by focusing on microstructural details for various natural fibers, such as bamboos [8]; flax and hemp fibrous materials [9,10], banana-jute hybrid composites [11], kenaf fiber composites [12], Aleppo Pine wood and black agglomerated cork [13], and even biomimetic leaf composites [14], just to name a few. A brief review of the functional thermal properties of natural fiber composites is referred to Takagi [15]. ...
... Fig. 7 compares the present technique in simulating the manila hemp fiber composites against the FE results and experimental measurement. The constituent thermal conductivities of hollow fibers and polymer matrix are k hf = 0.185W/(mK) [20,21,43] and k m = 0.42W/(mK) [9,21], respectively. According to the literature, the thermal conductivity coefficient of hollow fibers is inversely determined through the experimental measurement of composite specimen and theoretical conductivity formulae between the composite and its constituents [43]; while the polymer matrix is an environmentally friendly thermoset water-based acrylic polymer that is an aqueous solution of a polycarboxylic acid and a polyhydric alcohol as a crosslinking agent in water (52% water) [9]. ...
... The constituent thermal conductivities of hollow fibers and polymer matrix are k hf = 0.185W/(mK) [20,21,43] and k m = 0.42W/(mK) [9,21], respectively. According to the literature, the thermal conductivity coefficient of hollow fibers is inversely determined through the experimental measurement of composite specimen and theoretical conductivity formulae between the composite and its constituents [43]; while the polymer matrix is an environmentally friendly thermoset water-based acrylic polymer that is an aqueous solution of a polycarboxylic acid and a polyhydric alcohol as a crosslinking agent in water (52% water) [9]. A portion of lumens are filled within the fiber bundles and α = 0.565. ...
Article
The effective transverse thermal conductivity and localized thermal fields of unidirectional natural fiber composites is investigated through the proposed progressive micro-modeling technique. Different from the classical models, the present model starts from recovering the actual natural fibrous microstructures with fiber bundles filled with lumens and surrounded with matrix phase. Based on the concept of hierarchical microstructures, the fiber bundles with lumen and hollow fibers are treated as the lower-level composite unit cells while the composites with reinforced fiber bundles and matrix as the higher-level unit cells. The information transfer between two levels is guaranteed by a progressive homogenization technique-local exact homogenization theory that is presently extended with thermal conductivity for composites with nano-surface effects. The predicted effective transverse thermal conductivity coefficients of nano-/micro-composites are validated against the analytical and numerical simulations, as well as experimental data, where good agreement is generally obtained. An optimization procedure is also connected to the present micromechanics to search for the optimal microstructural parameter for the designed effective thermal coefficients at various fiber volume fractions. Finally, the local hierarchical thermal fields are also recovered to get insights into the microstructural concentrations. We have also encapsulated our progressive model into a black-box program with inputs/outputs, facilitating its application by other researchers.
... 14 Improvement of the thermal insulation is happening due to the presence of thermal insulatingair in the lumen of the hollow structure of natural cellulosic fibre. [36][37][38][39][40][41] Apart from the above-mentioned reason, the void content also plays a vital role for enhancement in the thermal insulation values. Along with the addition of filler loading the void content proportionally increase. ...
... 38 Therefore, it can be inferred that a very low amount of moisture is present in the fabricated composites. 37 Several investigations show that the enthalpy change in this zone is significantly larger than what would be predicted if moisture were the only factor involved. As a result, the peak in this location may be regarded as comparable to the samples T g. 43 The FA dispersed composites show a small rise in T g as well. ...
Article
The present investigation is carried out to study the swelling and thermal behaviours of alkali treated cellulosic fibre (sisal and jute) with fly ash dispersed unsaturated polyester composites. These composites are fabricated by compression moulding with a filler loading of 5, 15, 25, 35 and 45 wt. %. The electronic thermal insulation tester, differential scanning calorimeter, and thermogravimetric analyzer are used for thermal analyses of the synthesized composites. It was observed that the thermal stability and degradation temperature of the composites improved significantly with addition of the filler within the unsaturated polyester resin.The swelling behaviours are determined by immersing the synthesized samples in the different pH content of water. In case of swelling behaviours, the changes in water absorption are quite acceptable as compared to the treatment time and the atmospheric condition. The fabricated composites displayed optimum results for filler content with 35 wt. % followed by saturation in properties with the dispersion above the same.
... It should be mentioned that, the thermal conductivities ( Fig. 9(a)) at about 24°C are 0.0568, 0.0512, 0.0499, and 0.0493 W/mK corresponding to samples number 1, 2, 3, and 4 respectively. These values of thermal conductivities shown in Fig. 9 (a) for the four samples are lower than the corresponding insulating materials extracted from date palm leaf base (petiole) (0.083 W/mK) [10], sisal (0.070 W/mK) [30], hemp (0.115 W/mK) [31], and banana (0.117 W/mK) [32] which motivates the potential of using them as insulation materials. Fig. 9(b) shows the corresponding thermal resistance in terms of R-values for the same samples used in Fig. 9(a). ...
... It worth mentioning that the thermal conductivity at 24°C (typical temperature for building insulation material in the field) for the samples 5, 6, 7, and 8 are 0.0418, 0.0420, 0.0454, and 0.0515 W/m K respectively. These values of thermal conductivities shown in Fig. 10(a) for the four samples are lower than similar insulating materials extracted from other natural fibers as mentioned earlier compared to references [10,[30][31][32] which ensures the importance of using hybrid insulating materials. Fig. 10(b) presents the thermal resistance (R-value) for the samples 5, 6, 7, and 8. ...
Article
Hybrid new insulating materials are proposed using different binders such as cornstarch, glue (wood adhesive) and white cement. Five hybrid samples were produced from date palm trees surface fibers (PTSF) and Apple of Sodom fibers (AOSF) for different ratio of mass and densities. One hybrid sample was produced from AOSF and agave fiber (AF) using glue (wood adhesive) as a binder. Thermal conductivity measurements were conducted for all samples at temperature ranging from 10 °C to 50 °C which resulted in average values of 0.04234–0.05291 W/m K. Microstructure analysis was conducted for AF using the scanning electron microscope (SEM) which resulted in an average diameter range of 170–259 μm. Infrared (FT- IR) Fourier transformation spectra of AF showed ranges of wavenumber functional groups. Thermogravimetric analysis (TGA and DTGA) was obtained for AF and showed that the fibers start to degrade and decompose at about 221 °C where the fiber loses 5% of its original mass. The Differential Scanning Calorimetry (DSC) analysis is also reported for AF and shows a broad endothermic transition range of 292–357 °C with a peak at 353 °C. Sound absorption coefficients were obtained for the hybrid samples and indicate the potential of using these samples for sound absorption. The current tests indicate the feasibility of using such hybrid samples as insulating materials for heat as well as sound absorption. The proposed tested hybrid samples are all natural, safe for human beings, utilize the wasted material and biodegradable therefore, it is good for saving our environment.
... Multiscale modeling of the electrical conductivity of composite materials is a complex topic, particularly if microstructural features lead to a size effect in electronic conduction and create an anisotropy [21][22][23]. as large as the one of (i) due to the effect of grain boundaries. In analogy to 45 scattering at the surface in an infinite long fiber with a small diameter, the size effect was experimentally confirmed and can be modeled [27][28][29][30][31][32][33]. ...
... posites can be separated into two types: mean-field analytical methods [34][35][36][37] 55 and full-field ones [23,38]. Among the mean-field models, the Generalized Self-Consistent scheme (denoted GSC hereafter) was initially developed to study the elastic behavior of multi-coated fiber-reinforced composites [39]. ...
Article
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Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (> 90T) as they combine both high electrical conductivity and high strength. Multi-scaled Cu-Nb wires can be fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured and nanostructured microstructure providing a unique set of properties. This work presents a comprehensive multiscale study to predict the anisotropic effective electrical conductivity based on material nanostructure and architecture. Two homogenization methods are applied: a mean-field theory and a full-field approach. The size effect associated with the microstructure refinement is taken into account in the definition of the conductivity of each component in the composites. The multiscale character of the material is then accounted for through an iterative process. Both methods show excellent agreement with each other. The results are further compared, for the first time, with experimental data obtained by the four-point probe technique, and also show excellent agreement. Finally, the qualitative and quantitative understanding provided by these models demonstrates that the microstructure of Cu-Nb wires has a significant effect on the electrical conductivity.
... Multiscale modeling of the electrical conductivity of composite materials is a complex topic, particularly if microstructural features lead to a size effect in electronic conduction and create an anisotropy (Heringhaus et al., 2003;Mallick, 2007;Behzad and Sain, 2007). ...
... In order to predict the anisotropic effective conductivity with considering the particular morphology of fiber-reinforced composites (such as Cu-Nb wires at different scales in Fig. 3.1), several homogenization models have been proposed. The homogenization models for composites can be separated into two types: mean-field analytical methods (Schulgasser, 1976a;Hasselman and Johnson, 1987;Tavman and Akinci, 2000;Hervé-Luanco and Joannès, 2016) and full-field ones (Islam and Pramila, 1999;Behzad and Sain, 2007). Among the analytical mean-field models, the Generalized Self-Consistent scheme (denoted GSC hereafter) has been found to be very efficient to estimate the electrical conductivity of Cu-Nb wires . ...
Thesis
Les fils composites nanostructurés et architecturés cuivre-niobium sont de candidats excellents pour la génération de champs magnétiques intenses (>90T); en effet, ces fils allient une limite élastique élevée et une excellente conductivité électrique. Les fils Cu-Nb multi-échelles sont fabriqués par étirage et empaquetage cumulatif (une technique de déformation plastique sévère), conduisant à une microstructure multi-échelle, architecturée et nanostructurée présentant une texture cristallographique de fibres forte et des formes de grains allongées le long de l'axe du fil. Cette thèse présente une étude compréhensive du comportement électrique et élasto-plastique de ce matériau composite, elle est divisée en trois parties: modélisation multi-échelle électrique, élastique et élasto-plastique. Afin d'étudier le lien entre le comportement effective et la microstructure du fil, plusieurs méthodes d'homogénéisation sont appliquées, qui peuvent être séparées en deux types principaux: la méthode en champs moyens et en champs complets. Comme les spécimens présentent plusieurs échelles caractéristiques, plusieurs étapes de transition d'échelle sont effectuées itérativement de l'échelle de grain à la macro-échelle. L'accord général parmi les réponses de modèle permet de suggérer la meilleure stratégie pour estimer de manière fiable le comportement électrique et élasto-plastique des fils Cu-Nb et économiser le temps de calcul. Enfin, les modèles électriques prouvent bien prédire les données expérimentales anisotopique. De plus, les modèles mécaniques sont aussi validés par les données expérimentales ex-situ et in-situ de diffraction des rayons X/neutrons avec un bon accord.
... La conductivité thermique du bois de palmier dattier est de λ = 0,083 W/m.K rapportée par Agoudjil et al. 2011b. En effet, le bois de palmier dattier présente une faible conductivité thermique qui le place comme un bon candidat pour le développement d'isolant thermique au regard aux autres matériaux de même nature à l'image du sisal (λ = 0,070 W/m.K) (Kalaprasad et al. 2000), du chanvre (λ = 0,115 W/m.K) (Behzad et al. 2007) et des fibres du bananier (λ = 0,117 W/m. K) (Paul et al. 2008). ...
Article
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This work reports the results of an experimental study on the incorporation of wood waste date palm reduced in particles for the manufacture of wood – cement composites. These materials are chipper than the conventional insulator material and environmental friendly. Five types of wood – cement composites with various concentrations of the wood particles, ie. 2, 4, 6, 8 and 10% of total volume, were made according to defined protocol and mix design. Their thermal and mechanical properties were measured and compared to other conventional materials. The obtained results show that the thermal conductivity is positively correlated to the content of particles in the mixture. The compressive strength of composites decreases where the content of particles increase. However, taking account of the ASTM C 109 / C109‐95 standard, the wood – cement composite contained 10% of wood particles, considered as lightweight concrete, could be used as non‐structural material in construction.
... Despite the number of reprocessing cycles, the mechanical properties of recycled hemp fiber/PP biocomposites remain well preserved. Thermal conductivity for hemp fiber reinforced PP [89], mechanical performance of hemp fiber reinforced PP biocomposites at different operating temperatures [90], and rheological properties of hemp fiber/PP composites [91] were also evaluated. ...
Chapter
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Natural fiber reinforced polypropylene (PP) biocomposites and nanobiocomposites are gaining more attraction in research and industrial applications because of their advantages, including low cost, low density, high specific mechanical properties, and less abrasion for processing machineries. These biocomposites can be processed by various conventional plastic processing methods like extrusion, thermoform- ing, and injection molding. Because of incompatibility between polypropylene and natural fibers, various physical and chemical methods are applied on natural fibers for improving interfacial adhesion between polymer and fiber, and, consequently, mechanical properties of final product. At present, natural fiber reinforced PP bio- composites are used in automobile, packaging, and construction sectors. © 2018 by World Scientific Publishing Europe Ltd. All rights reserved.
... The mean value of the thermal conductivity of pure date palm samples studied by Agoudjil et al. [32] was 0.083 W/ m K at atmospheric pressure. The thermal conductivity of the prepared DPPpolystyrene composite materials is very promising when it is compared with the other proposed composites containing date palm fibers (0.075-0.6 W/ m K ) [18], hemp fibers (0.115 W/ m K ) [33], and banana fibers (0.117 W/ m K ) [34]. On the other hand, the thermal conductivity of composites reported here is much less than the thermal conductivity of hemp, jute, and glass fiber-reinforced polyester composites studied by Subba Raju et al. [35], as the thermal conductivity of their composites varied between 0.207 and 0.190 W/ m K at 30°C for filler contents ranging between 18 and 36 vol.%. ...
Article
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This study is aimed at developing a thermoplastic composite based on date pit powder waste for use as a thermal insulator in building industries. Date pits are the by-product of date stoning, either for the production of pitted dates or for the manufacture of date paste. The date pit powder (DPP) used in this study was obtained from the UAE University farm in Al Foah, UAE. DPP waste contents ranging from 0 wt.% to 50 wt.% were used to prepare the DPP-polystyrene composite. Date pit powder was mixed with polystyrene using a melt extruder, and then the mixture was transferred to the hot press to produce the final sample. The thermal and physical characteristics of the produced composites were measured experimentally and analyzed theoretically in terms of date pit and polystyrene properties. The characterized properties of the DPP-polystyrene composites, namely, density, thermal conductivity, water retention, thermal stability, and microstructure, showed that a stable composite material with insulation and construction capacity can be formed by the addition of date pit powder to the polystyrene matrix. The theoretical modeling of the measured thermal conductivity and the scanning electron microscope (SEM) monographs supported the hypothesis of date pit agglomeration in the composite matrix. The prepared composites showed low thermal conductivity (0.0515-0.0562 W/m K at 25°C) and very low density (457-630 kg/m3 ), thus demonstrating their potential for use as a thermal insulator for building materials. In addition, replacing one-third of the classical construction wall content with DPP-polystyrene composite showed promise for constructive applications as a thermal insulator with 85% reduction in the overall thermal conductivity. Indeed, these properties are similar to those of other conventional insulating materials. This will lead to produce an inexpensive insulation material that exploits a common waste product in date fruit-producing countries.
... The theoretical prediction using ROM is not restricted to mechanical properties, but it can also be applied to predict the physical and thermal properties of composite materials. Behzad and Sain (2007) employed ROM to predict the thermal properties of unidirectional hemp fiber-reinforced composites. The predicted thermal properties obtained from ROM model showed a strong correlation with the experimental findings. ...
Chapter
The contemporary trend has attested that fiber-reinforced composites have been utilized to replace steel and other metal alloys in a broad range of engineering applications, particularly in the transportation sectors to improve energy efficiency without compromising safety performance. The intensive research works toward the excellent mechanical performance of composite materials without compromising the environmental friendliness have stimulated the growth of hybrid composites. The hybrid composites refer to the materials which are composed of multiple types of synthetic or natural fibers within a single polymer matrix. Over the years, it has been proven that hybrid composites have shown innumerable benefits over non-hybrid composite materials in terms of mechanical performance and ecological concerns. Nevertheless, the challenging issues which affect the miscellaneous properties of hybrid composite materials still exist and have not been fully resolved. This chapter aims at providing brief overview of the factors influencing the miscellaneous properties of composite materials. Furthermore, the miscellaneous properties of various types of hybrid composites are briefly discussed and demonstrated.
... The numerical and experimental analyses of thermal properties of date palm fibre-reinforced composites have been studied by using guarded-hot-plate method and three-dimensional (3D) finite element modelling (Haddadi et al. 2015). The in-plane and transverse thermal conductivities of hemp FRPCs for different volume fractions of fibre have been evaluated (Behzad and Sain 2007). The experimental results were compared with finite element model and two theoretical models and found a good agreement between the models and the obtained results. ...
... The heat change with environment in x-y plane for horizontal composite is less effective than that with heat sink. Since graphene consists of polycrystalline lattices that are parallel arranged in its plane, graphene is highly anisotropic, which gives less thermal resistance along its plane compared with across its plane [45]. For vertical composite, both graphene film and interface planes are along the heat transfer plane, so the heat engendered by LED can easily transfer from composite plate to heat sink. ...
Article
Efficient removal of heat has become one of the most critical challenges in the development of modern microelectronic devices. However, it is hard to dramatically improve thermal conductivity of composite materials even with highly loaded thermally conductive fillers due to the lack of efficient heat transfer paths. In this article, both horizontal and vertical graphene film/epoxy (GF/E) composites were designed and fabricated and their thermal and mechanical properties were studied. Vertically aligned structure constructed of continuous graphene films forms channels for heat removal. The thermal conductivity of vertical GF/E composites reaches 384.9 W m À1 K À1 at 44 vol% graphene, i.e. a dramatic enhancement of 3570% per vol% compared to the pure epoxy, and representing the highest value of all epoxy based composites. The cooling performance of light-emitting diode (LED) package with the application of GF/ E composites is enhanced by reducing the temperature of LED lamp about 20.7 °C compared with the application of pure epoxy. The vertical GF/E composite proved to be a potential material for heat management of LED or other electronic devices.
... It is a bast fibre and due to the porous structure of bast fibers, hemp fibers are also suitable for thermal insulations [9]. Existing literature mainly focused on investigating thermal insulation of hemp composites [10][11][12]. ...
Article
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In the present research, the thermal properties of the traditional fabric of the Rize city (Turkey) were investigated. A Feretiko, which is a fabric produced from hemp fibers at handlooms, were chosen and the thermal properties were evaluated via thermal manikin as well as the Alambeta tester and Air permeability tester. The thermal manikin tests were performed at 23 °C ± 1 constant ambient temperature and 75 ± 5% relative humidity regarding to the past annual average temperature and relative humidity data of Rize city were considered. The thermal resistance of Feretiko was measured 0.011 m²K/W by Alambeta tester and the total clothing insulation of the shirt manufactured from Feretiko was measured as 0.032 m²K/W by thermal manikin. Moreover, in ASHRAE Standard 55-2013, the clothing insulation of a long-sleeve shirt ensemble stated as 0.25 clo. The clothing insulation of the shirt manufactured from Feretiko was 0.20 clo, which is close to the value stated in the standard.
... The circular disc-shaped sample of about 45 mm diameter and 10 mm thick was prepared for the test. The thermal conductivity of each sample was determined according to the methods of [18,19]. The thermal conductivity experimental set-up (Plate 2) consists of heating element a b ...
Article
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The specific heat capacity and thermal conductivity of the ground dika (Irvingia wombolu Vermoesen) kernel were measured using the thermal probe method. Bulk density was determined using the graduated cylinder and the value obtained was used to calculate thermal diffusivity. The effects of temperature (Room temperature – 90� ) and moisture content (5.17 – 20% wet basis) on the thermo physical properties of the ground and hydrated dika kernel were studied. Linear, quadratic and cubic regressions were modelled at each temperature as a function of the corresponding moisture contents, and the best model was selected based on the coefficient of determination (R2) values. The results of the specific heat capacity ranged between 0.951 and 3.089 kJ/kg�, thermal conductivity (4.36 and 31.87 W/m �*105), bulk density (0.492 and 0.680 g/cm3) and the thermal diffusivity values between 6.313 and 43.065 m2/s*105. All the values are within literature range. The result of the investigation revealed that thermo physical properties were moisture content and temperature dependent, and quadratic equation fitted all the models than linear equation for all the properties investigated. The data obtained from the study can be used in the process design of the ground kernel or the soup on a commercial scale.
... where m 1 and m 2 are the masses of the empty brick and of the hemp fibres used to fill the holes of the hollow brick, respectively. The specific heat of the hemp fibres (c ph ) is referred to literature data [23] and for T = 20 • C, it is 2200 J kg −1 K −1 . ...
Article
The analysis of the thermal dynamic behaviour of buildings is an important tool for reducing inefficiencies and then wasted energy. In this field, European Standards specify the procedures to obtain information about the thermal behaviour of building in terms of decrement factor and time lag. However, these procedures are based on a theoretical approach that does not take into account the real factors involved in the heat exchange phenomena such as the correct knowledge of thermo-physical parameters and the presence of non-homogeneous materials or defects in the investigated walls.
... Conductivity is influenced by their densities, the fiber surface treatment and the used coupling agent (Kim et al., 2006;Takagi et al., 2007;Ramamoorthy et al., 2015C). Thermal conductivity of natural fiber and thermoset acrylic resins has been studied (Behzad and Sain, 2007). The conductivity of hemp fiber was messured to 1.48 W/mK. ...
Chapter
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This chapter focuses on physicochemical and mechanical characterization of composites made from renewable materials. Most common renewable materials used in composites are natural fibers and polymers based on starch or vegetable oil. The extent of using renewable materials in biocomposites has increased during the past decade due to extensive research on cellulosic fibers and biobased polymers. Earlier, the research was focused on using the natural fibers as reinforcement in crude oil-based polymers such as polypropylene. Later, the emphasis shifted to increase the amount of renewable components in the biocomposites which led to the introduction of biobased resins in the composites. The properties of some biocomposites are today comparable to the properties for commercially available nonrenewable composites. Several plant biofibers have been used as reinforcement in biobased thermoplastics or thermosets to manufacture biocomposites. Material characterization is important to understand the performance of these composites under specific environment. Detailed discussion about the mechanical and physicochemical characterization is provided in this chapter. Physicochemical characterization includes chemical composition, density, viscosity, molecular weight, melting temperature, crystallinity, morphology, wettability, surface tension, water binding capacity, electrical conductivity, flammability, thermal stability, and swelling. Mechanical characterization includes tensile, flexural, impact, compressive, shear, toughness, hardness, brittleness, ductility, creep, fatigue, and dynamic mechanical analysis.
... The potential for hemp crop farming has for example been investigated by Cochran et al. (2000) with intentions of application in the state of Arkansas, USA. In fact, the initial hemp fibers' length which has been reported around 2-3 m depending on its type and the region in which it is farmed is a clear gain as compared to wood fibers which are only a few centimeters long; however, they are often shortened by post-harvesting operations (Eichhorn et al. 2001;Behzad & Sain 2007). Hemp plants are also high-yield crops with about three farming cycles per year (Holmes 2000;West 2002), depending on the geographical area. ...
Chapter
This chapter covers the outcome of processing polyethylene terephthalate (PET) with hemp fibers as a case study for the reinforcement of high-melting matrices (Tm 200 °C) with plant fibers. Such products have been emerging as important engineering materials in various sectors; however, their melt processing is hindered by the fibers’ limited thermostability. Moreover, their optimal application requires a judicious combination of different critical factors including the material’s properties and the processing parameters. The variations of those critical factors with the fiber concentration are investigated in this work, and the implications for their potential applications are examined, while giving a special consideration to those based on large deformations. The observed results are potentially transferrable to pave the way for the valorization of similar kinds of matrices and reinforcements.
... Existen trabajos sobre las propiedades aislantes de residuos vegetales: cáscara de coco [1], residuos de fabricación de papel y médula de maíz [2], fibras de kenaf [3], fibras de tallo de algodón [4,5], cáscara de coco y bagazo [6], fibras de cáñamo [7,8], fibras de palmera datilera y yeso [9], lino [10], lino y cáñamo [11], tallo de arroz [12], sisal [13], bagazo de caña de azúcar [14], caña común [15,16], palmera canaria [17] y palmera washingtonia [18]. ...
... However, as a fiber reinforced composite, the thermal conductivity of the CMC material is anisotropic [7,8] due to the significant differences between the thermal conductivities in the fiber's axial direction and the radial direction and the differences between the thermal conductivities of the fibers and the matrix. Lebel et al. [9] investigated the thermal and mechanical performances of the CMC materials under the cyclic thermal stresses of a gas turbine combustion chamber. ...
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The thickness of the hot component in a turbine engine is usually small. Therefore, the traditional prediction model of anisotropic thermal conductivity (ATC) based on the periodic hypothesis may be improper for use in the thermal analysis of ceramic matrix composite (CMC) components with a thin-wall structure. Thus, the prediction model for the ATC of a 2.5-D braided CMC was investigated, taking into account the actual thickness of the CMC thin-wall structure. An RVE (Representative Volume Element) model with a periodic boundary and a full-size model with the actual thickness were built to study the temperature field, the heat flux field, and the effective thermal conductivity of the CMC. A validation experiment was carried out to verify the accuracy of the two prediction models. The effect of the composite’s thickness on the ATC and the critical thickness suitable for the RVE model were also studied. The results showed that in the thermal analysis of the thin-wall structure, the RVE model had a large deviation in the estimation of the effective thermal conductivity in the thickness direction. The relative error between the numerical data based on the RVE model and the experimental data reached 10.93%, while the relative error was only 3.53% for the full-size model. Additionally, with increasing thickness, the effective thermal conductivities, based on the RVE model and the full-size model, were close to each other. For the critical thickness for the RVE model, which would be suitable for the prediction of the ATC, if the material’s thermal properties such as the absolute value ratio and the level of anisotropy changed, the corresponding critical thickness was also different. For the ATC of the SiC/SiC composites used in this study, the critical thickness was found to be 18.4 mm, nearly 31 times larger than the RVE model’s thickness.
... De ce fait, le diamètre de ce dernier est réduit [70] [74], et la surface de contact efficace des fibres avec la matrice est augmentée ; ce qui améliore davantage l'adhérence avec la matrice [31], [75], [74]. Cette amélioration affecte les propriétés thermo-physiques des composites et contribue à une conductivité thermique plus élevée [76]. ...
Thesis
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Dans l’optique de répondre à la demande du marché des matériaux biosourcés en France pour le secteur du bâtiment, les travaux présentés dans cette thèse avaient pour objectif de formuler un nouveau matériau biosourcé en exploitant des nouvelles ressources végétales, telle que la plante de Diss. Ce matériau sera destiné pour la production des panneaux de bardage pour la réhabilitation énergétique des bâtiments. Dans un premier lieu, une étude sur l’extraction, le traitement et la caractérisation des fibres de Diss a été menée. Elle a été suivie dans un deuxième temps par une application de ces fibres comme renfort à une matrice thermoplastique, le polypropylène. La caractérisation mécanique et hydrothermique, l’étude de durabilité et l’évaluation environnementale de la phase de production de ces biocomposites ont été abordées. Les résultats montrés sont prometteurs, notamment pour une telle application où les fibres de Diss ont présenté des propriétés mécaniques et hydro/hygrothermiques intéressantes. De plus, l’incorporation de ces fibres a amené à une amélioration des propriétés mécaniques de la matrice. D’autre part, l’étude de durabilité a mis en évidence l’effet du vieillissement hydrothermique sur leurs propriétés mécaniques. Il a été conclu également que l’utilisation des fibres de Diss avait un effet nettement positif sur la réduction des impacts relatifs au réchauffement climatique, grâce à la séquestration biogénique du CO2. Ces résultats aident à mieux anticiper une future industrialisation de ces fibres et mettre en amont leur effet bénéfique sur l’environnement.
... Thermal conductance of composite material containing hemp as the reinforcement and polymer matrix was studied by Behzad and Sain (2007) and Sayyidmousavi et al (2019). They compared the thermal conductance of the composite material measured experimentally. ...
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Use of lightweight composite materials in automobile applications such as doors, bonnets, and bumpers and also the utilization of composite materials in building insulations require superior mechanical and thermal properties. This study attempts to determine the thermal conductivity, linear thermal expansion coefficient, heat deflection temperature and thermo gravimetric analysis of hybrid composite containing reinforcement fibers stacked in seven different combinations in an epoxy matrix as per ASTM standards. Each composite contained two different fibre materials, i.e., Kevlar and basalt. The study revealed that the stacked layers of basalt fibers had more influence on the thermal properties. It was observed that the hybrid composite made of least quantity layers of Kevlar and most of basalt exhibited the maximum thermal conductance of 0.219W/mK, while with vice versa laminate developed 0.191W/mK which was least thermal conductance. The composition prepared by made Kevlar as core layer and basalt as its outer layers exhibited coefficient of linear thermal expansion above 11.5x10-6/oC. Maximum decomposition weight loss of 76.92% occurred in the composition prepared by keeping basalt as core and Kevlar as outer layer. The differential thermal graph showed that the said hybrid composite exhibited the peak decomposition rate of 1wt.%/oC. The thermal properties of the laminate prepared by keeping two layers of Kevlar sandwiched between the basalt were excellent when compared to other six hybrid composites investigated in this study.
... W/m.K, showing increasing values, depending on the density of the straw bale [39]. Regarding hemp, the thermal conductivity values that were found in the experimental analyses varied from 0.039 to 0.123 W/m.K [28,40], depending on fibres direction, with lower λ values for fibres positioned in perpendicular direction with respect to the heat flux, and higher ones for fibres in the parallel direction [41]. A further consideration concerns the fire resistance of these two materials, which is very low (category E) due to their organic origin [34]; however, it should be emphasized that the presence of natural origin binders, which are necessary for the realization of the panels, generates an increase in the fire resistance approximately around +30% [42]. ...
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... However, a precise information about material properties is required for obtaining desired materials that are to be implemented for developing hybrid composite. Thermal conductivity is the material property which describes capability to transfer heat and also helps to encourage the temperature deviation inside the composite materials during specific operations [8]. Enhancing the thermal property of this epoxy-based polymer at present is considered to be challenging. ...
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... Unlike porous materials, plant fillers also provide strong mechanical resistance to the biocomposite. Several studies have shown good thermal insulating properties as well as strong mechanical properties, especially at higher filler percentages (Behzad and Sain 2007;Agoua et al. 2013;Li et al. 2008;Qi et al. 2013). Furthermore, filler treatment, additives and coupling agents also affect the thermal properties of biocomposites (Gardner et al. 2018;Kairytė et al. 2019;Ahmad et al. 2019). ...
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Plant fiber biocomposites have the potential of being thermal insulating materials with strong mechanical resistance. However, they are vulnerable to defects due to the incompatibility of the materials. In that prospect, this study focuses on the determination of thermal properties of wood particles reinforced HDPE composites (WPC) using experimental, theoretical, and computational modeling approaches. From the laser flash analysis in the experimental setup, the results show that the addition of 30 and 60 wt\% of wood particles leads to a reduction of 20 and 44% in thermal conductivity, respectively, as compared to the neat HDPE. This demonstrates the thermal insulation capabilities of the wood particles. The use of several theoretical models to determine the WPC’s effective thermal conductivity shows good consistency with the experimental results, with a maximum discrepancy error of 4%. However, a noticeable divergence is observed as the wood content increases. Further study on the effective properties is carried out using the pixel-based computational homogenization analysis. This computational method carries out finite element calculations on representative 2D images of the WPC. The computational results are also consistent with the experimental results, but similar divergence like the theoretical models is still observed. The divergence is suspected to originate from the presence of porosity in the experimental specimens. The percentage of porosity is estimated using theoretical models and is integrated into the computational homogenization technique by introducing another phase in a different color code. This leads to the convergence of computational and experimental results. The pixel-based homogenization method has shown great flexibility and is able to integrate defects like porosity to yield precise results of the effective thermal conductivity of WPC which can then be used in structural engineering analysis.
... The greatest challenge when working with plant fibers is the considerable variation in their thermal properties and characteristics, which depend on their complex structural geometric architectures [2]. Numerous studies have been carried out on the insulating properties of plant waste: Coconut fiber [3], paper manufacturing waste and corn peel [4], kenaf fibers [5], cotton stalk fibers [6,7], coconut husk and bagasse [8], hemp fibers [9,10], date palm fibers and gypsum [11], flax [12], flax and hemp [13], rice straw [14], sisal [15], sugarcane bagasse [16], giant reed [17][18][19], Canary Islands palms [20], and Washingtonia palms [21]. ...
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... conform to a general relationship between material density and thermal conductivity. Application of hydrophobic agents could reduce the rate of degradation of the thermal insulation properties. Zach et al. (J. Zach, 2013) found that the hydrophobic treatments considerably affected the absorbability of thermal-insulating mats based on hemp fibres. Behzad et al. (T. Behzad, 2007)studied the thermal conductivity of hemp fiber reinforced polymer composites. Hemp fibers were formed on a perforated screen and the acrylic resin solution was circulated to impregnate the fibers with the solution. Experimental results showed that the orientation of fibers has a significant effect on the thermal conductivity of composite ...
Conference Paper
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Artificial neural networks (ANN) have been used for characterization of 7 rubber blend mixtures ageing and for prediction of mechanical properties according 8 to chemical composition. Strength R m and modulus M100 have been evaluated. 9 The ANN application was tested by statistical function RMSE (root mean square 10 error) and R 2 (coefficient of determination) which value for all predictions was 11 higher than 0.93. 12
Article
Date palm trees surface fibers (DPSF) are one of the most common environmental waste in the Middle East. Thermal and microstructure of date palm tree surface fibers (DPSF) reveal that they could be used as a new building insulation material. Cornstarch is used as a resin to bind the fibers, which makes the insulation material totally natural. Thermal conductivity of the proposed insulation material is measured for four different densities and the results show that the minimum and maximum values are 0.0475 and 0.0697 W/m-K, respectively. The Scanning Electron Microscopy (SEM) analysis of the fiber diameter shows the average range of the diameter is 12–580 µm. Fourier Transformation-Infra Red (FT-IR) spectra of the fibers is obtained and shows that there are strong stretching peaks at 2918.45 and 2850.6 cm⁻¹ which may be due to the presence of Alkane (C-H) functional group. Thermogravimetric Analysis (TGA and DTGA) indicates that the degradation and decomposition of the fibers starts at 232 °C where the sample loses only about 8.5% of its original mass. The Differential Scanning Calorimetry (DSC) analysis is performed and shows that the endothermic transition starts at around 243–382 °C with a peak at 369 °C. Three points bending test is used to determine the maximum flexural strength σ and the Young’s Modulus E for some specimens of bounded fibers and relationships between load-deflection and flexural strength-deflection are obtained. The proposed natural material is comparable to conventional insulation material with the advantages of being safe to human beings as well as utilizes waste material.
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This work aims to develop a new composite material to improve the thermophysical properties and the lightness of gypsum plaster made with date palm fibers for the purpose of reducing the building energy consumption. This composite material is intended to be used in walls or false ceilings. Date palm fibers- gypsum boards could be used instead of plaster boards as thermal insulators in buildings. By varying the mass fraction of date palm fibers (from 0 to 20%), an experimental investigation of the thermo physical proprieties of gypsum reinforced with date palm fibers was mainly performed using the periodical and flash methods which were coupled to an inverse technique. The experimental results of thermal conductivity showed a good agreement with the theoretical model developed by Woodside and Mesmer for the determination of equivalent thermal conductivity.
Chapter
This chapter begins by describing the thermal decomposition of constituents (polymer and natural fibre reinforcement) of natural fibre composites (NFCs). It then investigates the fire performance of NFCs, including reaction to fire testing, heat transfer of NFC building materials, thermal decomposition and fire resistance of NFCs. The chapter also includes a review of the modelling fire performance of NFCs, its residual mechanical properties and its thermoroperties.
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The finite element analysis is used to investigate the sensitivity of the effective transverse thermal conductivity of polymeric composites reinforced with Manila hemp fibers in terms of their degree of saturation. It is predicted that the hierarchical structure of the fiber bundle will highly magnify the rate of water absorption and in consequence, the effective transverse thermal conductivity of the composite is altered. This influence is quantized in terms of the volume fraction of the fiber bundle and the lumen to produce a homogenized representative continuum. It was found that increasing the fiber volume fraction in a dry medium results in a decrease in the thermal conductivity whereas an increase of conductivity will be evident in a wet condition. Furthermore, the increase in the volume fraction of the lumen enhances the thermal conductivity by retaining more water during saturation which supports the developed hypothesis.
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The anisotropic micro-structure of fiber will lead to the macroscopic anisotropic properties of fiber reinforced composites in both heat transfer and mechanical strength. However, few experimental studies have be made on the anisotropic heat transfer properties of fiber reinforced composites. In this study, the anisotropic thermal conductivities of two-dimensional (2D) plain woven and twill woven carbon-fiber/epoxy composites are measured at different temperature with the one-dimensional (1D) steady-state method, transient plane source (TPS) method and transient hot wire method, respectively. The out-of-plane thermal conductivity and in-plane thermal conductivity at the temperature ranging from -45 ℃ to 160 ℃ are obtained and comparisons are made among the three methods. The results show that all the three methods can be used to measure the anisotropic thermal conductivity of fiber/epoxy woven composites. Both the out-of-plane thermal conductivity and in-plane thermal conductivity of carbon-fiber/epoxy woven composites increase with temperature, and the in-plane thermal conductivity is approximately four times as high as the out-of-plane thermal conductivity for the plain woven composites. Compared with the results of 1D steady-state method, the max deviations of TPS method and hot wire method are 18.1% and 17.1%, respectively. The sources of error that leading to the deviations are also discussed.
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Natural fibers (such as kenaf) have garnered interest recently for use in composites because of their relatively high specific properties, low cost, and low environmental impact. Their thermal property information is limited, lacking experimental data on key properties such as thermal conductivity, specific heat, and CTE of the component fiber. This paper presents, for the first time, the thermal property data on kenaf fiber reinforced composites, and an approach to obtain the composite thermal properties based on constituent properties. Individual, plant-based fibers were measured independently and were then used to inform successful predictions of the effective thermal conductivity of the fiber reinforced composites. A unit cell model has been developed to predict the thermal properties of a planar, randomly oriented kenaf fiber-reinforced composite (near 22% volume fraction loading), which includes the effect of void content on the predicted thermal conductivity. A lower-level model is also developed for individual fiber thermal properties based on its constituents (lignin, cellulose, and hemicellulose). To validate this multi-level model, experimental measurements of the thermal diffusivity, coefficient of thermal expansion, and specific heat for the composite, the matrix, and the fibers were performed in the range from 30 °C to 160 °C, based on TMA, DSC, LFA, and transient electro-thermal (TET) techniques. Model results compare favorably with the experimental data, and are consistent with FEM modelling results based on fiber properties and fiber constituent materials (lignin, cellulose, and hemicellulose). This approach provides the basis for understanding component contribution to the fiber properties, as well as a technique to obtain fiber composite thermal property based on component properties. The composite thermal property data also fills an information gap and can be directly used in component design.
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Agave (AF) and wheat straw (SF) fibers are good raw materials for thermal insulation. In this study, loose agave or wheat straw fibers and hybrid boards of agave/wheat straw with different compositions and densities are tested for their thermal insulation qualities. Three new novel hybrid specimens are considered. In all specimens, cornstarch (CS) was used as a binder for the fibers. Thermal conductivity coefficient is obtained for each specimen in the temperature range 10–60°C with the resulting average value in the range 0.04555–0.06835 W/m K. Without binding, loose fibers of agave and wheat straws have an average thermal conductivity of 0.043592 and 0.044678 W/m.K, respectively, at the same range of temperature. Micrographs of the wheat straw fibers (SF) are conducted using the scanning electron microscope (SEM) which showed an average outer diameter between 1.28 and 1.98 mm and an average diameter of the bound porous tubes (multicellular) within the straw in the range 34.5 to 75.6 μm. Fourier transformation infrared (FT-IR) analyses of the wheat straw fiber are carried out which indicated stretching wavenumbers which present different chemical functional groups. Thermogravimetric analysis of the wheat straw fiber (TGA and DTGA) showed that the straws lose less than 3% of its mass at temperatures as high as 184°. Finally, the differential scanning calorimetry (DSC) analysis test of the wheat straw fiber indicates that endothermic transition starts at 342°C with a peak value at 749°C. Three-point bending moment tests for bound specimens are made and show an increase in both flexural stress and flexural modulus of the hybrid specimens. Using these hybrid specimens, agro, renewable and environmentally friendly materials in buildings will share in energy saving when used as insulation materials for building walls.
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The raw materials used to manufacture thermal insulation in buildings consume a large amount of energy and are not generally biodegradable, which means it is necessary to increase the use of renewable, eco-friendly resources such as plant fibers in order to reduce the environmental problems this generates. The wood adhesives developed by the petrochemical industry offer excellent performance and are affordable. However, their use has an expiry date and in the future they will be rejected due to the environmental and health problems they can cause. The objective of this work was to develop a new eco-friendly biocomposite that could be used for thermal insulation in buildings. Boards were manufactured from giant reed particles with a particle size of 2 to 4 mm, using 5 and 10% by weight of citric acid as a natural binder. Experiments were then carried out to investigate the effect of board density on mechanical, physical, and thermal properties. A new type of composite was obtained with a thermal conductivity of 0.081–0.093 W/m K, which makes it suitable as an insulating material. The boards with a density of 850 kg/m3 had a modulus of rupture (MOR) of 12.5 N/mm2, a modulus of elasticity (MOE) of 2440 N/mm2, and an internal bonding strength (IB) of 0.61 N/mm2, and they could be used as insulation panels for divisions and enclosures in buildings.
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Chemical treatment of natural fibers is a well-defined means of mechanical property improvement in natural fiberreinforced composites. An understanding of mechanical and thermal properties in these media is essential for evaluating heat transfer, thermal degradation, and overall performance of these composites over their product lifetime. However, very little information is available illustrating the effect of such treatment on the thermal properties of kenaf composites. Also, no study to date has reported the thermal conductivity of individual kenaf fibers. This study reports the effects of fiber treatment (in 6 % NaOH) on thermal transport in unidirectionally oriented kenaf-epoxy composites and individual kenaf fibers. The effective thermal conductivities and thermal diffusivities of chemically treated fiber composites show a general increase over untreated fiber composites (0.210 to 0.232 W/m/K at 28 °C, 0.206 to 0.234 W/m/K at 200 °C). This improvement may be attributed to improved interfacial contact between the fibers and epoxy matrix shown in microstructural images after chemical treatment. The thermal conductivity of individual fibers was evaluated at room temperature using two techniques. Results from both techniques showed slight increases after chemical treatment (0.58±0.53 to 1.0±0.13 W/m/K and 1.2±0.54 to 1.6±0.28 W/m/K) but lacked statistical significance. Any improvement in surface crystallinity after chemical treatment does not appear to affect overall fiber thermal conductivity. A better understanding of thermal transport in kenaf fibers and composites enables better estimation of the performance of these composites in different applications. Moreover, the thermal conductivities of individual fibers are useful in understanding the fiber’s contribution to conduction in different fiber reinforcement configurations.
Chapter
A parametric finite element analysis was carried out to investigate the sensitivity of the effective thermal conductivity of fibers to orientation clustering. Randomly-positioned fibers with von Mises orientation distributions were used in different considerations and volume fractions to generate the dispersion in a partitioned representative volume element. It was found that increasing the fiber volume fraction increases the thermal conductivity; this improvement is significant specially when a preferred orientation is detected with a cluster-free state. Further reinforcement of the composite is made possible by increasing the maximum principal value of the orientation tensor provided that the principal direction is set accordingly. Furthermore, clustering index does not seems to be affected by volume fraction when an equal distribution is present in partitions.
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In this experimental investigations deals with the natural fiber composites such as Abaca and kenaf with carbon for thermal insulation performance enhancement. The square matrix used for this analysis. Volume fractions, ratio of thermal conductivity lumen were the most important considerations for this investigation with respect to the thermal conductivity of the corresponding composites. The experimental and theoretical results were compared for the performance identifications.
Article
Sisal fiber along with ZrO2 particles dispersed unsaturated polyester (UP) composites were fabricated by compression molding technique. The filler contents were varied from 5 to 45 wt% with a gradual increase of 10%. The structural investigation was done using Scanning electron microscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy. Mechanical testing was performed through microhardness tester, tensile, flexural, and Izod impact test. The optimum mechanical properties were obtained at 35 wt% of filler incorporation within UP matrix followed by a slight deterioration at 45 wt%. Fractographic images of the composites display the phenomena of fiber pull‐out, debonding and breakage. The water absorption test was performed both at room temperature and boiling water temperature conditions. The thermal insulation measurement was performed by Kawabata method. POLYM. COMPOS., 2018.
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Polymer composites are widely used in different areas such as the aircraft industry, automotive industry, electronic industry and packaging industry etc. Polymer composites should have various physical, mechanical and thermal properties, within various thermal properties thermal conductivity is an important parameter to simulate heat transfer process and mechanisms in composite materials. This paper deals with various analytical methods and models for determining the effective thermal conductivity of different polymer composite materials for various applications. There are basic models, modified models and semi-empirical models to determine thermal conductivity analytically, which are discussed in brief. After that, the comparison between different models is investigated. Finally different conductive fillers, the effect of their shape, size and volume fraction on the effective thermal conductivity of composite materials are discussed.
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A recent interest in the mechanical properties of spider silk has also brought about investigations into the thermal properties of thin fibers, often with contradictory results. Because of the high length-to-diameter ratio of fibers, two key obstacles arise during their thermal characterization: the need to develop non-standard techniques to measure properties and the lack of reliable methods to confirm the validity of those measurements. This is especially important since standard reference materials are difficult or impossible to produce at these small scales. This paper presents a review on the thermal conductivity and diffusivity of spider dragline silk and how the use of a suite of measurement techniques that complement each other can bound the uncertainty of the measured property. The properties of silkworm silks are then presented as evidence of a field where complementary techniques could be applied to resolve property discrepancies. This complementary approach to validating novel techniques will increase the confidence in measured properties and will open new avenues of thermal science applications.
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Unsaturated Polyester (UP) based composites with 5, 15, 25, 35 and 45 wt% filler content have been fabricated by compression moulding technique. The NaOH treated discontinuous jute fibre has been used along with vinyl silane treated zirconia (ZrO2) particle as the dispersing phases. The structures were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The thermal stability of the UP and UP based composites were observed using electronic thermal insulation tester, thermo-gravimetric analyser, differential scanning calorimetry and limiting oxygen index analyser. The swelling behaviour has been investigated in different solutions having a range of pH values. The optimum results were obtained with 35 wt% filler content for UP/Jute/ZrO2 composites. Graphical abstract Open image in new window
Article
Problems related to the production of composite materials based on synthetic polymer matrices reinforced with natural fibers of different classes are considered. The main natural fibers of plant and animal origin used to create polymer composites are characterized, and the properties of the composites are described. The advantages and disadvantages of using natural fibers for the production of polymeric composite materials for various purposes are discussed.
Article
Banana, Pineapple and Jute fiber were mixed with different combination of volume percentage by hand layup technique. For this investigation six types of combinations used. Banana fiber has 60% in all the combination and remaining 40% of fiber only shared with Pineapple fiber and Jute fiber for six different combinations and also each combination with three different (5 mm, 10 mm and 15 mm) thicknesses. The corresponding thermal analysis such as thermal conductivity and thermal resistance of six combination fiber composites were compared for the good thermal insulator for insulation applications.
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The effective thermal conductivity of unsaturated porous media is of interest in a number of applications of heat transfer. In this paper, a novel fractal solution for effective thermal conductivity is derived based on the fractal distribution of surface roughness and pore size in unsaturated porous media with roughened surfaces. The proposed fractal model explicitly relates the effective thermal conductivity to the microstructural parameters (relative roughness, porosity and fractal dimensions). The proposed fractal model is verified by a satisfying agreement of the effective thermal conductivity predicted by our model and that reported as existing experimental data in the literature. A parametric study is also elaborated to investigate the influences of the microstructural parameters on the effective thermal conductivity. The results demonstrate that our proposed fractal model improves our understanding of the physical mechanisms of heat transport through unsaturated porous media with roughened surfaces. One advantage of our fractal analytical model is that it contains no empirical constant, while it is usually required in previous models.
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The aim of this study was to determine the acoustic and thermal properties of particleboards made from mulberry wood pruning waste using urea formaldehyde resin (UF) as a binder. The investigation focused on the evaluation of the thermal conductivity and the acoustic absorption of the boards and the assessment of their feasibility for use in the construction sector. The mean thermal conductivity values of the particleboards (0.065–0.068 W/mK) were lower than those obtained in wood and similar to those in cork panels. The samples were tested with frequencies from 50 to 6300 Hz. In all cases, the results allowed us to conclude that they were better sound absorbers than commercial wood and plywood panels of the same average density for low frequencies, and with similar values for medium and high frequencies. The mechanical results reached the minimum requirement to be considered as boards for general use and, specifically with particles from 0.25 to 1.00 mm, for furniture according to European standards. The particle size of the particleboards was the variable that influenced all the acoustic properties, but did not affect the thermal conductivity. The experimental results indicated that the thermal and acoustic properties of these particleboards were promising for their application in commercial uses.
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Two models. E-S anti R-S unit cell models, are presented based on the thermal-electrical analogy technique. The analytical expressions for transverse thermal conductivities of unidirectional composites are derived. The dimensionless effective transverse thermal conductivities k(e) are expressed as a junction of the ratio (beta) of thermal conductivities of filler to matrix. filler volume fraction (v(f)) and the geometry ratio (rho = a/b) of the filler The optimization of transverse thermal conductivities of unidirectional composites is then analyzed under different filler volume fractions v(f), thermal conductivity ratios beta and different geometric architectures. The present analysis allows for a fairly precise evaluation of configuration performance and comparisons of different arrangements. The results show that if a composite is designed,for insulation material, we should choose rho< 1, and if a composite is designed for heat dissipating purpose, we should choose ρ > 1.
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In the present study, a new environmentally friendly thermoset resin was used to manufacture hemp fiber acrylic composites by sheet molding process for automotive applications. A finite difference method was applied to predict the cure behavior and temperature variation of hemp fiber acrylic based composites during the process. Dynamic Differential Scanning Calorimetry (DSC) was employed to determine the kinetic parameters for the curing reaction at different heating rates. It was found the experimental and predicted values are in good agreement at the lower heating rate. The thermophysical properties of the resin, fiber and composite were obtained to use in the model. The temperature profile and the degree of cure of the composite with 40% resin and 60% fiber were simulated and a comparison of numerical results with known experimental data confirms the approximate validity of the model.
Conference Paper
Full-text available
In the past few years, natural fibers are finding an increased interest in polymer matrices. The natural fibers serve as reinforcement by enhancing the strength and stiffness to the resulting composite structure. In this study, a novel processing technique has been developed for water based thermoset polymers to prepare resin-impregnated mats, which can be used for sheet molding process to manufacture complex automotive semi-structural and structural parts. In order to optimize the curing conditions the mechanical properties of composites at different curing temperature and the crosslink density of the composites cured at different times were evaluated. The optimum curing cycle was obtained at 180 ºC for 10 min. Composites with one and two layers of impregnated mat with 40 % resin and 60 % fiber were manufactured and their performance were evaluated. The mechanical properties of the cured pure resin and hemp fiber acrylic based composites with two different fiber lengths were measured and the effect of fiber content and fiber length were investigated. The flexural strength was found to be around 94 MPa and the flexural modulus was 14 GPa for the composite.
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Recently the critical discussion about the preservation of natural resources and recycling has led to the renewed interest concerning biomaterials with the focus on renewable raw materials. Because of increasing environmental consciousness and demands of legislative authorities, use and removal of traditional composite structures, usually made of glass, carbon or aramid fibers being reinforced with epoxy, unsaturated polyester, or phenolics, are considered critically. Recent advances in natural fiber development, genetic engineering and composite science offer significant opportunities for improved materials from renewable resources with enhanced support for global sustainability. The important feature of composite materials is that they can be designed and tailored to meet different requirements. Since natural fibers are cheap and biodegradable, the biodegradable composites from biofibers and biodegradable polymers will render a contribution in the 21st century due to serious environmental problem. Biodegradable polymers have offered scientists a possible solution to waste‐disposal problems associated with traditional petroleum‐derived plastics. For scientists the real challenge lies in finding applications which would consume sufficiently large quantities of these materials to lead price reduction, allowing biodegradable polymers to compete economically in the market. Today's much better performance of traditional plastics are the outcome of continued R&D efforts of last several years; however the existing biodegradable polymers came to public only few years back. Prices of biodegradable polymers can be reduced on mass scale production; and such mass scale production will be feasible through constant R&D efforts of scientists to improve the performance of biodegradable plastics. Manufacture of biodegradable composites from such biodegradable plastics will enhance the demand of such materials. The structural aspects and properties of several biofibers and biodegradable polymers, recent developments of different biodegradable polymers and biocomposites are discussed in this review article. Collaborative R&D efforts among material scientists and engineers as well as intensive co‐operation and co‐ordination among industries, research institutions and government are essential to find various commercial applications of biocomposites even beyond to our imagination.
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The contents of this book are: Theory of Heat Conduction and Heat-conduction Equations; Thermal Conductivity; Steady Heat Conduction; Unsteady Heat Conduction; Forced Convection in Laminar Flow; Forced Convection in Turbulent Flow; Dimensional Analysis; Forced Convection in Separated Flow; Natural Convection; Radiation of Strongly Absorbing Media; and Radiation of Weakly Absorbing Media.
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In the present study a new environmentally friendly acrylic resin was characterized to develop a high-performance biocomposite for future work. Differential scanning calorimetry measurements were used to determine onset of curing reaction as well as the degree of cure at a certain temperatures. Swelling equilibrium data for an acrylic resin were generally analyzed using the Flory–Rehner equation for a perfect network, to obtain a measurement of the molar mass between two crosslinks and the crosslink density of polymer, and to establish the effect of temperature and time on these parameters. The crosslink density of cured resin at 180°C and 10 min indicates the completion of a major part of the reaction under those conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 757–762, 2004
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The thermal conductivity and thermal diffusivity of oil-palm-fiber-reinforced untreated (Sample 1) and differently treated composites were measured with the transient plane source technique at room temperature and under normal pressure. All the composites were 40% oil-palm fiber by weight. The fibers were treated with alkali (Composite 2), silane (Composite 3), and acetic acid (Composite 4) and reinforced in a phenolformaldehyde matrix. The thermal conductivity and thermal diffusivity of the composites increased after treatment to different extents. The thermal conductivity of the treated fibers as well as of the untreated fibers was calculated theoretically. The model results show that the thermal conductivity of the untreated fiber was smaller than the thermal conductivity of the treated fibers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 916–921, 2000
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Recently the critical discussion about the preservation of natural resources and recycling has led to the renewed interest concerning biomaterials with the focus on renewable raw materials. Because of increasing environmental consciousness and demands of legislative authorities, use and removal of traditional composite structures, usually made of glass, carbon or aramid fibers being reinforced with epoxy, unsaturated polyester, or phenolics, are considered critically. Recent advances in natural fiber development, genetic engineering and composite science offer significant opportunities for improved materials from renewable resources with enhanced support for global sustainability. The important feature of composite materials is that they can be designed and tailored to meet different requirements. Since natural fibers are cheap and biodegradable, the biodegradable composites from biofibers and biodegradable polymers will render a contribution in the 21st century due to serious environmental problem. Biodegradable polymers have offered scientists a possible solution to waste-disposal problems associated with traditional petroleum-derived plastics. For scientists the real challenge lies in finding applications which would consume sufficiently large quantities of these materials to lead price reduction, allowing biodegradable polymers to compete economically in the market. Today's much better performance of traditional plastics are the outcome of continued R&D efforts of last several years; however the existing biodegradable polymers came to public only few years back. Prices of biodegradable polymers can be reduced on mass scale production; and such mass scale production will be feasible through constant R&D efforts of scientists to improve the performance of biodegradable plastics. Manufacture of biodegradable composites from such biodegradable plastics will enhance the demand of such materials. The structural aspects and properties of several biofibers and biodegradable polymers, recent developments of different biodegradable polymers and biocomposites are discussed in this review article. Collaborative R&D efforts among material scientists and engineers as well as intensive co-operation and co-ordination among industries, research institutions and government are essential to find various commercial applications of biocomposites even beyond to our imagination.
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Simultaneous measurment of effective thermal conductivity (λ) and effective thermal diffusivity (κ) of pineapple leaf fiber reinforced phenolformaldehyde (PF) composites have been studied by transient plane source (TPS) technique. The samples of different weight percentage typically (15, 20, 30, 40 and 50%) have been taken. It is found that of effective thermal conductivity and effective thermal diffusivity of the composites decrease, as compared with pure PF as the fraction of fiber loading increases. Using Y. Agari, model thermal conductivity of pure fiber is evaluated and compared with the thermal conductivity of fiber determined by extrapolated experimental value of composite. Also, we have compared the results of thermal conductivity of composites with two models (Rayleigh–Maxwell and Meredith–Tobias model). Good agreement between theoretical and experimental result has been found.
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Precise conductivity measurements on models sectioned out from a cubic lattice of spheres in a continuous medium indicate that the effective conductance of such a system deviates from the values predicted by Lord Rayleigh's analytic solution of this potential distribution problem. Deviations become particularly significant when the spheres approach close packing, and when the conductance of spheres is much greater than that of the continuum. By use of a different function for potential, and by consideration of higher terms in the series expression for the potential in the continuous phase, Rayleigh's results are modified, yielding an analytical expression that represents effective conductance satisfactorily in the concentration region approaching close packing.
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The thermal conductivity and thermal diffusivity of sisal-reinforced polyethylene (SRP), glass-reinforced polyethylene (GRP) and sisal/glass hybrid fibre-reinforced polyethylene (GSRP) has been evaluated at cryogenic to high temperature (120–350 K). It has been observed that the variation of thermal conductivity with temperature is almost the same for LDPE and SRP containing perpendicularly oriented sisal fibres. The difference between the values of thermal conductivity shown by LDPE and GRP is greater than that of SRP and LDPE. The enhanced thermal conductivity of glass fibre is due to the presence of Fe2+ ions in the glass fibres. The linear variation in thermal conductivity with fibre loading is explained with the help of a model suggested by Agari. The difference between the thermal conductivity properties in directions parallel and perpendicular to the applied flux is a maximum for SRP owing to the anisotropic nature of sisal fibre. The difference is marginal for GRP on account of its isotropic nature. The position of GSRP is found to be intermediate. It can been observed that the variation of thermal diffusivity with temperature is just opposite to that of thermal conductivity. This may be due to a reduction in the mean free path of phonons. An empirical equation is derived to explain the variation in thermal conductivity and thermal diffusivity with temperature.
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Existing micromechanical approximation formulae for predicting the transverse thermal conductivity of unidirectional CFRP laminates from the properties of the constituents provide rather different results. The analytical accuracy of such formulae is examined by comparing with finite-element calculations and yields a pre-selection of two equations. Measurements by two different methods reveal that the self-consistent formula is the most realistic one.
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A new method has been developed to determine the in-plane and through-thickness thermal conductivities of polymer matrix composites. In the method, the thermal gradient produced by an imposed one-dimensional heat flow in a given direction is measured experimentally. The recorded temperature gradient is used to calculate the thermal conductivity using an inverse numerical approach. Benchmarking was conducted using an aluminium alloy with known thermal properties, yielding excellent correlation. Testing was then performed on F593 carbon-epoxy laminates and the thermal conductivity curves for a service temperature range were determined.
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The purpose of this work was to measure the thermal conductivity of polyacrylamide (PAG) and compare it with previously reported values. Polyacrylamide phantoms play an important role in the development of hyperthermia and high-temperature thermal therapies based on electromagnetic (EM) radiation by providing a material that mimics the electrical and thermal properties of human tissue. The thermal properties of PAG have, up until now, not been thoroughly investigated and at least two significantly different values have been published. In this study, the thermal conductivity of polyacrylamide was measured from the steady state temperature drop across samples exposed to a known heat flux. The measured conductivity was 0.56 +/- 0.047 W m(-1) degrees C(-1). To validate the correct set of thermal properties for polyacrylamide, simple heating experiments were performed in a PAG phantom and then simulated using a finite element numerical model that incorporated the measured thermal conductivity along with literature values for specific heat and density. Temperature predictions from the model agreed with average temperatures measured in the phantom to within 1 SD of the measured temperatures.
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