Showing papers in "Polymers & Polymer Composites in 2002"
TL;DR: Ti or Zr coupling agents chemically bridge two dissimilar species such as an inorganic filler/particulate and organic polymer via proton coordination on non-silane reactive substrates such as CaCO3.
Abstract: Ti or Zr coupling agents chemically bridge two dissimilar species such as an inorganic filler/particulate and organic polymer via proton coordination on non-silane reactive substrates such as CaCO3...
32 citations
TL;DR: A method for the synthesis of 3,4-dihydro-3-pentafluorophenyl-2H-1,3-benzoxazine in a high yield derived from pentafluoroaniline is described in this paper.
Abstract: A method for the synthesis of 3,4-dihydro-3-pentafluorophenyl-2H-1,3-benzoxazine in a high yield derived from pentafluoroaniline is described. This fluorinated benzoxazine monomer has been developed as a potential precursor for a polybenzoxazine in electronic applications as well as others taking advantage of the low dielectric constant, low flammability, low refractive index, low coefficient of friction, and high glass transition temperature of fluorinated compounds. The traditional benzoxazine synthesis conditions are inappropriate for the synthesis of fluorinated benzoxazines when the fluorination is on the primary amine component. It is found that the pH value of the reaction medium is the controlling factor in the yield of the compound from weak amines. A strongly acidic condition is necessary for the synthesis of similar compounds from other very weak amines having a pK a lower than 3. A dramatic increase in the yield of benzoxazine ring has been observed when benzoxazines with very weak amines are synthesized in an acidic medium. The effects of solvent and pK a of phenol are also discussed. The synthesized compounds have been characterized by 1 H NMR, FTIR, GPC and HPLC.
24 citations
TL;DR: In this article, the water absorption behavior of sisal and its epoxy based composites and the mechanical properties of composites that have been aged in water were discussed and a series of fibre pretreatment techniques, including mercerization, acetylation, cyanoethylation, coupling agent treatment and thermal treatment, were evaluated.
Abstract: The authors discuss the water absorption behaviour of sisal and its epoxy based composites and the mechanical properties of composites that have been aged in water. In addition, a series of fibre pretreatment techniques, including mercerization, acetylation, cyanoethylation, coupling agent treatment and thermal treatment, which are believed to be able to improve the water resistance of sisal and its composites, have been evaluated. It was found that the water absorption behaviour of sisal composites is controlled mainly by the fibre and the fibre/matrix interfacial characteristics. As a result, appropriate fibre modification to retard water diffusion and enhance interfacial adhesion is necessary if the natural fibre composites are to be used in practical applications.
22 citations
TL;DR: In this paper, low density polyethylene (LDPE)/Styrene-Butadiene-Styrene (SBS) blends prepared under high shear stress were used as asphalt modifiers.
Abstract: In this paper, Low Density Polyethylene (LDPE) / Styrene-Butadiene-Styrene (SBS) blends prepared under high shear stress were used as asphalt modifiers. Compared to the asphalts modified by LDPE and SBS added directly, the blend modified asphalts showed much better storage stability in the presence of sulfur at high temperature. No visible phase separation was observed under an optical microscope at high temperature and the morphology analysis indicated that the phase structure of the LDPE/SBS blend modified asphalts was unchanged with time at high temperature. After storage at 163°E for 48h, the LDPE/SBS blend modified asphalts had no evidence of coalescence of polymer particles. The rheological properties of the asphalts were also improved by the addition of polymers in all cases.
18 citations
TL;DR: In this article, various physicochemical analysis methods were used to determine the extent of the changes to the prepregs during storage, including infrared spectroscopy (IR), thermal analysis (TA), and other chemical methods to measure the volatile and insoluble components content.
Abstract: This paper reports the characterisation methods used in evaluating the chemical changes in glass fibre/epoxy prepregs during storage in an environment chamber. The specimens were exposed to an environment with a relative humidity of 50% at 25°C for up to 196 days. Various physicochemical analysis methods were used to determine the extent of the changes to the prepregs during storage. These methods include infrared spectroscopy (IR), thermal analysis (TA) and other chemical methods to measure the volatile and insoluble components content. During storage, the chemical reaction occurs between some epoxide groups, which is known as precuring. Results indicate that precuring in the epoxy resin system consumed a considerable number of epoxide groups during the exposure. The epoxide index obtained from IR analysis gives a straight measure of the number of epoxide groups remaining in the prepregs at different stages of the storage. A parameter known as the precured degree, defined from the epoxide index, can be used to measure the prepregs' quality. A set of laminates made from prepregs that had been degraded to different degrees were subjected to flexural and tensile testing. The flexural and tensile properties were significantly reduced as a consequence of the increase in the precured degree for the prepregs. The results show that it is important to control the precuring reaction in epoxy-based prepregs during storage before they are transferred into composite products.
18 citations
TL;DR: In this article, the authors studied the re-use of these wastes as blends with virgin and recycled polymers, which can be used to make: porous pipes intended for irrigation or fertilization, tiles or flooring in the building industry, road safety and traffic control equipment, sound absorbing screens along motorways, packing in biological wastewater treatment, biodegradable flower pots, buckets, fence elements and similar profiles.
Abstract: Voluminous post-life waste and production waste pose the paramount environmental problem of our times. One major problem is how to reuse post-life waste: spent plastics, rubber scrap, worn-out automobile tyres, waste paper and production waste; wood pulp or powder and particularly the waste arising in the production of fertiliser, phosphogypsum. We have been studying the re-use of these wastes as blends with virgin and recycled polymers. These novel polymer compositions can be used to make: ○ porous pipes intended for irrigation or fertilization. ○ vehicle parts in the automobile industry ○ tiles or flooring in the building industry ○ road safety and traffic control equipment ○ sound-absorbing screens along motorways ○ packing in biological wastewater treatment ○ biodegradable flower pots, buckets, fence elements and similar profiles.
16 citations
TL;DR: In this paper, the SiC surface was pre-treated with a silane coupling agent, followed by radical grafting polymerization of acrylamide and styrene, respectively.
Abstract: For the purpose of preparing polymer composites filled with SiC nanoparticles to be used in tribological applications, grafting polymerization onto the particles was carried out as a way of surface modification. It is believed that the interfacial interaction in the composites can be tailored in this way. The SiC surface was pre-treated with a silane coupling agent, followed by radical grafting polymerization of acrylamide and styrene, respectively. Infrared spectroscopy and measurement of dispersiveness in solvent demonstrate that the desired polymer chains have been covalently bonded to the surface of the nanoparticles. In addition, the polymerization conditions were investigated and the controlling factors were established accordingly.
14 citations
TL;DR: In this article, the permanent antistatic effect depends upon a complete dispersion of the combined organometallics and thus works differently than conventional surface blooming hygroscopic antistats that rely on polymer incompatibilization and resultant surface bloomoming to attract ESD atmospheric moisture to the thermoplastic surface in environments having humidity greater than 25%.
Abstract: Minor amounts of thermally and hydrolytically stable combined dissimilar polarity type neoalkoxy titanates and/or zirconates can be added directly into the polymer during the thermoplastic or thermoset compounding phase at temperatures in excess of 200°C to form bipolar layers that provide a transparent, non-blooming organometallic transfer circuit resulting in a volume as well as surface antistatic effect. The permanent antistatic effect depends upon a complete dispersion of the combined organometallics and thus works differently than conventional surface blooming hygroscopic antistats that rely on polymer incompatibilization and resultant surface blooming to attract ESD atmospheric moisture to the thermoplastic surface in environments having humidity greater than 25%. A transparent film results since the combined organometallics are of good color and solubilize into the polymer, and are not made of insoluble conductive particulate or cobalt-based metallocenes. Specifically, it will be shown that when using a combined trineoalkoxy dodecylbenzene sulfonyl zirconate/trineoalkoxy aliphatic amino zirconate antistatic agent, transparent olefin films remain clear after long-term aging tests. Atomic dispersion of the antistat will be shown to be critical. For example, data will show that when 1% of the new and novel antistat is added to polypropylene in an intensive mixer (Banbury) operating in the range of 160 to 190°C - and the mixer compounding conditions are changed (to increase specific energy input) from 30-second drop after flux occurs @ 50 rpm to 2-3 minutes drop after flux occurs at 100-125 rpm - the resistivity will be lowered from 10 13 to 10 11 Ω/sq. for 30 mil compression molded slabs. Differences in ESD effects in HDPE using a 2-roll mill vs. a twinscrew extruder will be discussed. In addition to PP and HDPE, ESD effects will be shown in various other polymer disciplines such as LLDPE, PVC, PVC/Nitrile, PETG, Nylon, PES, Acrylic, ABS, Ethyl Acetate (Nail Polish), Natural Rubber Latex, Acrylic Latex and Polyurethane. For example, a clear thermoplastic polyurethane having a surface resistivity and a volume resistivity of 1.3 x 10 16 Ω/sq. and 1.7 x 10 15 Ω-cm respectively will exhibit ESD properties of 7.4 X 10 12 Ω/sq. and 4.6 x 10 11 Ω-cm when 2% by weight of PU of a 60% active combined trineoalkoxy zirconate on silica powder masterbatch is used.
14 citations
TL;DR: In this paper, the rheological properties of polycarbonate/high density polyethylene/glass fiber composites have been studied, along with fiber-resin interface behavior.
Abstract: The rheological behaviour and mechanical properties of the polycarbonate/high density polyethylene/glass fiber (PC/HDPE/GF) composites have been studied, along with fiber-resin interface behaviour....
13 citations
TL;DR: In this article, the steady-state rate of post-induction oxygen consumption during the model reaction of initiated cumene oxidation was investigated in order to determine antioxidants of the HAS type derived from 2.6,6-tetramethylpiperidine.
Abstract: The effective stabilisation of polypropylene (PP) plastics for durable applications is often achieved by compounding with a combination of hindered phenolic (SHPh) and amine (HAS) antioxidants. Hence, to assess the lifetime of these materials it is useful and often necessary to test the status of each type of stabiliser used during or after exposure. In this paper, we discuss the measurement of the steady-state rate of post-induction oxygen consumption during the model reaction of initiated cumene oxidation. This is in order to determine antioxidants of the HAS type derived from 2,2.6,6-tetramethylpiperidine. As already published, the measurement of the induction period can be used for the simultaneous determination of the SHPh content. The rate of the post-induction oxidation reaction depends linearly on the reciprocal square root of the concentration of this HAS-antioxidant type, for a sufficiently wide concentration range. The presence of sterically hindered phenolic stabilizers (SHPh) and organophosphites usually of the kind used has no influence on this post-induction phase. Thus the dependence established offers a remarkable possibility of determining simultaneously the effective stabiliser concentrations of the HAS and SHPh antioxidants by means of one model reaction. We present the results of the successful determination of a HAS and an SHPh antioxidant in PP granules. They have to be ground down to particles with mean dimensions smaller than 250 μm. We found perfect coincidence with the data given by the granule producer. Thus the model reaction of initiated cumene oxidation is a useful method forthe simultaneous quantitative study of SHPh and 2,2.6,6-tetramethylpiperidine derived HAS-antioxidants, even in the presence of organophospites in PP, and possibly other plastics.
13 citations
TL;DR: The physicochemical and kinetic properties of resols prepared with different catalysts (NaCH, LiOH and Ba(OH)(2)) and variable formaldehyde/phenol ratios (2.5 pound R pound 3.5) were followed to determine their effects on the mechanisms and reaction products at a fixed pH and temperature as mentioned in this paper.
Abstract: The physicochemical and kinetic properties of resols prepared with different catalysts (NaCH, LiOH and Ba(OH)(2)) and variable formaldehyde/phenol ratios (2.5 pound R pound 3.5) were followed to determine their effects on the mechanisms and reaction products at a fixed pH and temperature. Kinetic monitoring and quantification of residual monomers were carried out by liquid chromatography coupled with mass spectrometry (LC/UV/MS), by C-13 nuclear magnetic resonance (NMR) and by chemical assay for formaldehyde. Oligomer formation (n : 2) was determined by LC/LTV/MS, size exclusion chromatography (SEC) and C-13 NMR. It was found that minor compounds form during syntheses (phenol methanol hemiacetals, hemiacetals of phenol and of oligomers...) and that the ratio R affects primarily the kinetics of formation of monomers and oligomers, in contrast to the catalysts that modify reaction mechanisms. The understanding of the structure of the resols was an important step for the determination of the final properties of the material
TL;DR: In this paper, the impact of conductive carbon blacks (high structure, low and high surface area) on plastics performance, and especially on electrical properties, is discussed and some guidelines for compounding are also covered.
Abstract: New developments in knowledge of conductive carbon blacks and their conduction mechanisms have led to new plastics compounds. Conductive carbon blacks enable us to make polymers conductive at a 'low' or 'very low' loading, leading to better mechanical property retention. The 'in-mixture' dispersion and the resulting ultimate dispersion quality also influence the final properties. This study shows the impact of conductive carbon blacks (high structure, low and high surface area) on plastics performance, and especially on electrical properties. Some guidelines for compounding are also covered. This understanding gives rise to new applications and provides the tool to select the most appropriate carbon black to fit the application demand.
TL;DR: In this article, some white natural fillers (kaolin and talc) and synthetic mineral ones (precipitated silica, sodium-aluminium silicate, zinc silicates, calcium silicate) together with waste materials (cement dusts and post-fluor silicas) were subjected to surface modification and characterised.
Abstract: Some white natural fillers (kaolin and talc) and synthetic mineral ones (precipitated silica, sodium-aluminium silicate, zinc silicate, calcium silicate) together with waste materials (cement dusts and post-fluor silicas) were subjected to surface modification and characterised. Various types of silane coupling agents (amino-, mercapto-, methacryloxy- and ureidosilanes) were used for surface modification. The modified fillers were mixed with butadiene-styrene rubber, polyurethane and PVC. Good physico-mechanical properties were obtained for PVC containing talcs and kaolins modified with methacryloxy- and ureidosilanes. The strength of polyurethanes was increased most by modification of the fillers with mercapto- and aminosilanes.
TL;DR: In this paper, a new averaging scheme is proposed to predict the effective average permeability of the multi-layered preform, which accounts for the transverse flow effect, and the predicted flow front is compared with the experimental results and shows a good agreement.
Abstract: In resin transfer molding, mold filling is governed by the flow of resin through a preform which is considered as an anisotropic porous media. The resin flow is usually described by Darcy's law and the permeability tensor must be obtained for filling analysis. When the preform is composed of more than two layers with different in-plane permeability, effective average permeability should be determined for the flow analysis in the mold. The most frequently used averaging scheme is the weighted averaging scheme, but it does not account for the transverse flow between adjacent layers. A new averaging scheme is suggested to predict the effective average permeability of the multi-layered preform, which accounts for the transverse flow effect. When the flow in the mold is unsaturated, the effective average permeability is predicted by using the predicted mold filling time and transverse permeability. The new scheme is verified by measuring the effective permeability of the multi-layered preforms which consist of glass fiber random mats, carbon fiber woven fabrics, aramid fiber woven fabrics. Fluid flow through the preform composed of more than two layers with different in-plane permeability shows different flow fronts between layers. The difference in the flow front advancement is observed with a digital camcorder. The predicted flow front is compared with the experimental results and shows a good agreement. It is expected that the effective average permeability can be used for modeling the resin flow through the multi-layered preform.
TL;DR: In this paper, the authors studied the dielectric properties of composite materials based on both thermoplastic and thermoset resins filled with nickel or copper, with various particle sizes and shapes.
Abstract: The authors have studied the dielectric properties of composite materials based on both thermoplastic and thermoset resins filled with nickel or copper, with various particle sizes and shapes. In addition, two types of particle distribution, random and segregated, were produced for composites filled with nickel. The main objective was to study the effect of the above factors on the dielectric properties of the composites. The concentration dependence of the dielectric parameters (i.e. the real, e', and the imaginary, e, parts of the complex dielectric permittivity and the dielectric loss tangent, tanδ), calculated for all the systems studied, demonstrates a critical behaviour in the percolation threshold region, with maximum values reached at a volume fraction φ=φ c . The dependence of the dielectric parameters on concentration follows power-law behaviour in the φ < φ c region. The critical exponent value for e' is q = 0.75, in agreement with the theoretical one. The dielectric characteristics of the filled composites are more sensitive to the spatial filler distribution. For the segregated PVC-Ni system with an ordered filler distribution, the value of φ c is much lower than for ER-Ni composites with a random filler distribution. Besides, for the segregated PVC-Ni system, the value of q is not constant, as it depends on the filler concentration. A model for the structure, which explains this behaviour, is proposed.
TL;DR: In this paper, the authors investigated the tensile properties of Functionally Graded Materials (FGM) made from tubular braided composites and found out the relationship between tensile property of the FGM and that of the corresponding non-FGM.
Abstract: The primary objective of this research work was to investigate experimentally the tensile behaviour of Functionally Graded Materials (FGM) made from tubular braided composites and to find out the relationship between the tensile property of the FGM and that of the corresponding non-FGM. Composites were made using tubular braided carbon fibre fabrics and an epoxy resin. The FGM specimens had varying braiding angles and the non-FGM specimens had constant braiding angles. The effect of braiding angle on the composite properties was established from the test results for the non-FGM specimens. It was shown that both the tensile strength and modulus decreased as the braiding angle increased. The tensile behaviour of the FGM specimens was demonstrated to be related to that of the non-FGM specimens. The tensile modulus of an FGM specimen could be estimated from the tensile moduli of a series of non-FGM specimens. The tensile strength of an FGM specimen was a function of its largest braiding angle, and was higher than that of a non-FGM specimen with a braiding angle equal to this largest braiding angle.
TL;DR: In this paper, a brief description of bumper components and a critical review of polymer-based bumper systems with specific methodology are provided, and the authors also discuss bumper components from the standpoint of the materials and their manufacturing processes.
Abstract: An automobile bumper is a structural component, which contributes to vehicle crashworthiness or occupant protection during front or rear collisions. The bumper systems also protect the hood, trunk, fuel, exhaust and cooling system as well as safety related equipments. A brief description of bumper components and a critical review of polymer-based bumper systems with specific methodology are provided. This article advocates proper bumper design and material selection. The authors also discuss bumper components from the standpoint of the materials and their manufacturing processes.
TL;DR: In this article, the impact strength of composites initially decreased due to the addition of discontinuous glass fiber, but increased when the content of continuous glass fiber further increased, and the authors found that the modification of the interfacial adhesion between reinforcements and matrix resin by using functionalized polypropylene played a significant role in improving the mechanical properties of the composites.
Abstract: The mechanical properties of discontinuous glass fiber/continuous glass fiber mat/ polypropylene composites were investigated. The mechanical properties increased with increasing areal weight of the continuous glass mat, whereas the suitable content of discontinuous fiber was also depended on the mat areal weight. The impact strength of composites initially decreased due to the addition of discontinuous glass fiber, but increased when the content of discontinuous glass fiber further increased. Comparisons between the 4 mm discontinuous fiber length and the 12 mm fiber showed that the longer discontinuous glass fiber was advantageous to the mechanical properties of composite system. The modification of the interfacial adhesion between reinforcements and matrix resin by using functionalized polypropylene played a significant role in improving the mechanical properties of the composites. But the impact strength decreased above 5% of MA-g-PP level (with respect to matrix resin). It was also found that using a matrix resin with a high melt index was beneficial impregnation with the mechanical properties improving accordingly.
TL;DR: In this article, the authors evaluated the performance of various polypropylenic compounds containing representatives of organomodified siloxanes and found that a positive influence on surface properties could be obtained by selecting favorable additives from this class of products.
Abstract: Organomodified siloxanes combine the high efficiency of silicone oils with good compatibility with polymeric resins. The synthesis of organic siloxanes reveals a high degree of freedom, giving access to a variety of different representatives. Depending on the nature of the organic moiety and the overall molecular weight, organomodified siloxanes can be adapted to special applications within polymers. Thus their performance covers the range from performance additives, as lubricant or dispersing agent, as in filled compounds, to surface modifying additives, helping to improve surface characteristics, such as scratch resistance. Various polypropylenic compounds containing representatives of such organomodified siloxanes were evaluated. Process parameters such as energy consumption, pressure build up and out-put rate on a twin screw extrusion line could be increased. A positive influence on surface properties could be obtained by selecting favourable additives from this class of products.
TL;DR: In this paper, the impact performance of E-glass/Dyneema® hybrid laminates was investigated in a series of falling weight impact tests and it was shown that the influence of Dyneema® fibres on the impact behavior of hybrid composite laminate is rather small because damage processes are the result of local contact stresses in the vicinity of the impact body.
Abstract: This paper describes the results of falling weight impact tests (FWITs) on glass-fibre-reinforced (GRP) laminates and E-glass/Dyneema® hybrid laminates. The test programme consisted of (i) falling weight impact tests to determine the penetration energy and (ii) experiments to determine the influence of hybrid construction on damage development and impact fatigue lifetime under repeated impact conditions at sub-penetration energy levels. The objective of this work was to investigate the effect of hybridisation on the impact behaviour of GRP laminates as well as to find optimal conditions for hybridisation. It was shown that in the case of a rigid test set-up - and hence small deflections - the influence of the Dyneema® on the impact behaviour of hybrid laminates is rather small because damage processes are the result of local contact stresses in the vicinity of the impact body, whereas in the case of a compliant test set-up and large deflections the high energy storage capacity of the ductile Dyneema® fibres is used far more effectively for the protection of hybrid composite laminates. Therefore, it was concluded that in order to fully utilise the potential of high-performance polyethylene fibres it is essential that these fibres are located on the (non-impacted) tensile side of an impacted laminate and that the geometrical test conditions are such that large (bending) deformations are allowed.
Abstract: Highly filled polypropylene composites have been prepared with filler contents up to 43.8 vol.% (70 wt.%) after surface treatment of the fillers with titanate or silicone. The fillers used were cal...
TL;DR: In this article, the effect of different amounts of EVA waste on the tensile strength, elongation at break, hardness, tear strength and dynamic mechanical properties was studied, and a combination of optimum tensile properties, resistance to solvent penetration and dynamic properties, such as storage modulus and loss tangent, was achieved by introducing 50 phr of EVAW in the NBR matrix.
Abstract: Rubber blends containing nitrile rubber (NBR) and ground ethylene-vinyl acetate copolymer waste (EVAW) from the footwear industry have been prepared over a wide range of composition (up to 90 phr of waste component). The ground EVAW had particle size in the range of 100-350 mm and a gel content of 60±5%. The effect of different amounts of EVA waste on the tensile strength, elongation at break, hardness, tear strength and dynamic mechanical properties was studied. EVAW had a good reinforcing effect on the NBR matrix. A combination of optimum tensile properties, resistance to solvent penetration and dynamic mechanical properties, such as storage modulus and loss tangent was achieved by introducing 50 phr of EVAW in the NBR matrix. This composition also presents a more uniform morphology, as indicated by scanning electron microscopy.
TL;DR: In this paper, the authors verify and apply an analytical model developed previously for the calculation of mode-I stress intensity factor of a pre-existing crack in an orthotropic composite structure due to the phase transition of trapped moisture.
Abstract: SUMMARY Verifications and applications of an analytical model developed previously for the calculation of mode-I stress intensity factor of a pre-existing crack in an orthotropic composite structure due to the phase transition of trapped moisture are presented in this paper. The verifications are based on comparisons of the stresses in an elliptic elastic inclusion and the stress intensity factor with a special case of isotropy (for which there exists an analytical solution) and with finite element analysis for the case of orthotropy. The results indicate that the stress state in a slender elliptic elastic inclusion can be used to approximate the stress field at the crack face, which could subsequently be adopted to determine the stress intensity factor. Analyses of the delamination and fatigue life prediction for freeze-thaw cycling are provided as specific applications of the model. becomes negligible when the distance between them is larger than about four times the characteristic length of inhomogeneity. In other words, results from the analysis of a single inhomogeneity remain valid for numerous defects if the distance between any two defects is larger than four times the characteristic length of the defect.
TL;DR: In this paper, the authors established a theoretical framework for the calculation of the stress intensity factor (K I ) of a pre-existing crack in a composite structure due to the phase transition of trapped moisture.
Abstract: SUMMARY With the increasing use of fibre composites in applications such as cryogenic liquid hydrogen tanks and repair/retrofitting of bridges, the diffusion and freezing of moisture to form ice is an issue of growing importance. The volumetric expansion of water when it freezes to form ice results in stress concentrations at the inclusion tip that may synergistically interact with the residual tensile stresses in a laminate at low temperatures to initiate a crack. In addition, understanding the long-term effect of daily and/or seasonal freeze-thaw cycling on crack growth in a laminate is of vital importance for structural durability. The objective of this paper is to establish a theoretical framework for the calculation of the stress intensity factor (K I ) of a pre-existing crack in a composite structure due to the phase transition of trapped moisture. The constrained volume expansion of trapped moisture due to freezing is postulated to be the crack driving force. The principle of minimum strain energy is employed to calculate the elastic field within an orthotropic laminate containing an idealized elliptical elastic inclusion in the form of ice. It is postulated that a slender elliptical elastic inclusion can be used to approximate the stress field at the crack face, which can subsequently be used to calculate the stress intensity factor, K I , for the crack. The verification of the analytical model predictions and some potential applications will be published in a separate paper.
TL;DR: In this paper, a pre-irradiation method was used to introduce functional moieties into Tefzel® film, a copolymer of tetrafluoroethylene and ethylene.
Abstract: To introduce functional moieties into Tefzel® film, a copolymer of tetrafluoroethylene and ethylene, graft copolymerization of vinyl monomers such as methyl acrylate (MA) and ethyl acrylate (EA) was attempted by a pre-irradiation method in aqueous medium. Optimum conditions for obtaining the maximum grafting was evaluated for both monomers. Maximum grafting of MA (306.0%) and EA (462.1%) was obtained at a total dose of 25.4 and 31.9kGy respectively, using [MA] = 2.20 mol/L and [EA] 0.032 moles. The effect of aliphatic alcohols of varying chain length, such as methanol, ethanol, n-butanol, 1-Pentanol and cyclohexanol on the percentage grafting of MA & EA was also studied. Characterization of Tefzel® and grafted Tefzel® films was carried out by IR spectroscopy and thermogravimetric analysis. Grafted Tefzel® film was found to have improved thermal resistance.
TL;DR: In this article, surface modified silver nanoparticles with various sizes, synthesized by water-in-oil micro-emulsion, were incorporated into polystyrene (PS) to form transparent nanocomposite films through solution-mixing and static-casting.
Abstract: Surface-modified silver nanoparticles with various sizes, synthesized by water-in-oil micro-emulsion, were incorporated into polystyrene (PS) to form transparent nanocomposite films through solution-mixing and static-casting. It was found that the Ag nanoparticles could be re-dispersed well in the polymer matrix by using chloroform as a solvent due to a strong interaction between Ag and chloroform. XPS analysis suggested that there is no obvious interaction between nanosilver and the polystyrene matrix. The third-order nonlinear optical susceptibility of Ag/PS nanocomposite films is around 10 esu and increases with increasing particle size, as measured by the time-resolved femtosecond optical Kerr effect experiment at a wavelength of 830nm. The results demonstrate that the present fabrication approach can effectively tailor the structure and properties of the nanocomposites.
TL;DR: In this paper, the effect of fiber aspect ratio (a r ) on the stiffness of composite rods reinforced with rigid spheroidal inclusions has been investigated, where the reinforcing spheroids are randomly placed within the containing rod and are also perfectly aligned with the tensile axis.
Abstract: We report on the results of a computational investigation of the effect of fiber aspect ratio (a r ) on the stiffness of composite rods reinforced with rigid spheroidal inclusions. The reinforcing spheroids are randomly placed within the containing rod and are also perfectly aligned with the tensile axis. Attention is focused in the interesting region of low (a r ), where the stiffness of the composite rod is known to be most sensitive on (a r ). Use of low aspect ratio fibers makes the results of this analysis suitable for a class of processed materials, such as whisker-reinforced metal-matrix composites and extruded or molded short-fiber-reinforced polymers. We consider steady-state three-dimensional deformations of composite rods containing up to 50 individual, randomly placed aligned spheroids. The equations of elasticity for the entire multi-fiber assembly are solved using the Boundary Element Method (BEM), implemented on a four-processor server and the force needed to impose a certain tensile deformation on the composite is computed. From this, an effective tensile modulus is obtained. Statistical averages of the computed effective moduli are compared to the predictions of the Mori-Tanaka model for the stiffness of short fiber composites. We find a good agreement at low values of (a r ). Additionally, we investigate the effect on stiffness of random perturbations in fiber length around a mean value.
TL;DR: In this article, differentially scanning calorimetry (DSC) was used to study the crystallization and melting of the composites compared with the pure polymers, and the surface wetting properties of the fibres and morphology of composites were studied by scanning electron microscopy (SEM) and optical microscopy.
Abstract: Composite materials have been prepared from hydrophobic and hydrophilic polypropylene with flax fibres, where the flax fibres have been used with and without silane surface treatment. Other comparable composites have been prepared from poly(lactic acid) and poly(ethylene succinate), recently developed biodegradable polymers with promising mechanical properties. The polar polymers were found to provide better wetting of the surface of the flax, regardless of the surface treatment. Differential scanning calorimetry (DSC) was used to study the crystallisation and melting of the composites compared with the pure polymers. The surface wetting of the fibres and morphology of the composites was studied by scanning electron microscopy (SEM) and optical microscopy. Mechanical properties were studied using dynamic mechanical analysis (DMA). It was found that the relatively low density flax fibres provide efficient reinforcement compared with that expected from analogous glass fibre composites. The influence of the transcrystalline interphase on the dynamic storage modulus was found to be important.
TL;DR: In this article, the transport behavior of aromatic hydrocarbons in crosslinked ethylene propylene diene terpolymer (EPDM) has been studied in the temperature interval of 28-60°C.
Abstract: The transport behaviour of aromatic hydrocarbons in crosslinked ethylene propylene diene terpolymer (EPDM) has been studied in the temperature interval of 28-60°C. EPDM rubber was vulcanized by four different systems viz, Conventional (CV), Efficient (EV), Semi-efficient (SEV) and Sulphurless (S-less). The samples were cured to the same crosslink density. EPDM vulcanized with the sulphurless system showed highest solvent uptake tendency and that vulcanized with semi-efficient system showed the lowest. The influence of penetrant size on sorption behaviour of EPDM has been examined. In all systems the mechanism of diffusion showed an anomalous behaviour. From the diffusion data, the activation energies of diffusion and penetration, enthalpy and entropy of sorption, interaction parameter etc. were evaluated. Comparison between theoretical and experimental diffusion results were carried out.
TL;DR: In this article, the effect of the proportion of epoxy resins on the structure of cured bisphenol A dicyanate-novolac epoxy resin blends was investigated by FTIR.
Abstract: The cure characteristics of bisphenol A dicyanate-novolac epoxy resin blends were investigated by gel time determination and dynamic DSC. The effects of the proportion on the structures of cured blends were investigated by FTIR. In situ FTIR was utilized to study the curing mechanism and curing kinetics. The results indicated the distinct catalytic effects of the novolac epoxy resin on the curing of bisphenol A dicyanate. Due to considerable amounts of unepoxidized phenol present in the novolac epoxy resin, the reactions between phenol and cyanate disturbed the formation of the co-reaction products. The curing reactions of the blends indicated by in situ FTIR did not follow the Bauer mechanism totally. A composite mechanism of triazine-epoxy insertion and epoxy-cyanate reaction indwells in the systems. The authors suggest that most of the oxazolidinone present in the blends is formed by isomerization of oxazoline rather than by insertion of epoxy into isocyanurate. The amount of epoxy resin in the blend did not alter the curing mechanism, but had significant effects on the kinetic behaviour.