Journal of Thermoplastic Composite Materials recent issues

Magnetic and Dielectric Properties of Composites Consisting of Oriented, Iron Flake Filler within a Thermoplastic Host: Part I. Material Fabrication and Electromagnetic Characterization

Golt, M.C., Yarlagadda, S., Gillespie, J.W. — Wed, 21 Oct 2009 19:24:25 PDT

Materials that contain both electric permittivity and magnetic permeability greater than unity (magneto-dielectrics) are currently being investigated for microwave applications. An experimental procedure for fabricating magneto-dielectric composite materials based upon flake-like iron inclusions was developed. Samples consisting of iron flakes oriented within a low loss thermoplastic host were produced by extrusion film forming, to minimize loss and maximize permeability. The electrical and magnetic properties of the magneto-dielectric samples were measured as a function of the filler’s aspect ratio, surface characteristics and volume fraction. It was found that forming iron powder into flakes increases the permeability by reducing the demagnetization factor of the shape of the particle. The change to higher aspect ratio filler also increased the dielectric constant and the dielectric loss due to greater instances of inter-particle conduction. Insulating the flakes with a low dielectric greatly significantly mitigated this effect.

Magnetic and Dielectric Properties of Materials Consisting of Oriented, Iron Flake Filler within a Thermoplastic Host: Part II Transport Model Review and Evaluation

Golt, M.C., Yarlagadda, S., Gillespie, J.W. — Wed, 21 Oct 2009 19:24:25 PDT

Materials that contain both an electric permittivity and magnetic permeability greater than unity (magneto-dielectrics) are currently being investigated for microwave applications. Magneto-dielectric composite materials based upon flake-like iron inclusions were fabricated and the iron flakes oriented within a low loss thermoplastic host. The electrical and magnetic properties of the magneto-dielectric composites were predicted using mean field and effective medium approximations, as well as the Wu—McCullough generalized transport model. Predicted values were compared to measured properties as a function of the filler’s aspect ratio, surface characteristics and volume fraction. The Wu—McCullough model was found to be the most accurate in predicting the transport properties, but required an accurate description of the microstructure (flake aspect ratio and alignment).

On the Thermal Expansion Behavior of Polystyrene/Polyethyleneterephthalate Blend Systems: Experimental Study

Alsewailem, F. D. — Wed, 21 Oct 2009 19:24:25 PDT

Thermal expansion behavior defined as the percentage of dimensional change upon heating for the blend systems of polystyrene/polyethyleneterephthalate has been investigated in this study. General purpose polystyrene (PS) and high impact polystyrene (HIPS) were blended with polyethyleneterephthalate (PET) at a weight ratio of (15/85). The dimensional change of the neat and blended polymers versus temperature is measured by a thermomechanical analyzer using an expansion probe. The study investigates thermal expansion behavior of the PS/PET and HIPS/ PET blend systems under various conditions of heating rate, load, and heating regime. Higher thermal expansion values for the neat polymers and the blends were observed at lower heating rate, i.e., 5°C/min, while increasing load did not seem to affect thermal expansion behavior of the materials except for neat PET and HIPS/ PET blend system at higher temperature range, i.e., beyond T_g of PET and near softening temp of HIPS, where thermal expansion values decreased as load increased. Neat polystyrenes exhibited noticeable thermal expansion and contraction behavior when tested isothermally. The blend systems formulated and tested in this study, which consisted 15/85 wt% of both PS/PET and HIPS/PET, have proven to be more thermally stable and have better thermal expansion behaviors in both heating regimes used, i.e., nonisothermal and isothermal, than those behaviors observed for the neat polymers especially the minor phase, i.e., the polystyrenes.

Effect of Die Pressure on Mechanical Properties of Wood--Plastic Composite in Extrusion Process

Shakouri, E., Behravesh, A.H., Zolfaghari, A., Golzar, M. — Wed, 21 Oct 2009 19:24:25 PDT

This article presents an experimental study on the effect of die pressure on mechanical properties of a woodplastic composite (WPC) in an extrusion process. The strength-pressure relationship could govern the selection process of the equipment (size), especially for the load bearing applications of WPCs. A modular die was designed and manufactured to produce rod shaped products of various diameters. The induced pressure was also recorded. Tests on tensile and flexural strengths were carried out and bulk densities were measured. The results illustrate that an increase in die pressure significantly increases the strength of the product accompanied with a decrease in porosity and an increase in bulk density. When the pressure increased to 5-folds, for smaller product size, the tensile and flexural strengths increased to 3-folds and 2-folds, respectively.

Dielectric and AC Electrical Conductivity of Polycarbonate Kaolinite Composites

Al-Ramadin, Y., Zihlif, A.M., Elimat, Z.M., Ragosta, G. — Wed, 21 Oct 2009 19:24:25 PDT

The dielectric and AC conductivity of polycarbonate/kaolinite composites were studied using the impedance measurements technique. The study was carried out as a function of frequency in the range from 20 kHz to 1 MHz, temperature in the range from 20°C to 100°C and kaolinite concentrations 0, 5, 10, and 15 wt%. It was observed that the AC conductivity and dielectric constant are increased by increasing the kaolinite content in the composite. The calculated activation energy varied with the filler content, temperature, and applied frequency. The observed electrical results fit approximately the reported empirical equations concerning the AC conductivity and dielectric behavior of polymer composites. However, the results were explained on the basis of the interfacial (space charge) polarization, dipolar polarization, and decrease of the hindrance produced by the polymer matrix.

Effect of Variables on the Mechanical Properties and Maximization of Polyethylene--Aspen Composites by Statistical Experimental Design

Gu, R., Kokta, B. V., Chalupova, G. — Wed, 21 Oct 2009 19:24:25 PDT

Systemic studies of the effects of the concentrations of maleated polyethylene (MAPE) loading, the content and addition sequence of dicumyl peroxide, the content and type of nanoclay (NC), and aspen fiber loading on the mechanical properties of PE—aspen composites were undertaken with the objective to increase the impact strength as well as the tensile properties. In this article, the formation of an optimal compatibilizing system for the hybrid composite PE—aspen—NC by combining basic principles for compatibilization was investigated. Statistical approach experimentation using Statgraphics Centurion^® with the objective to maximize both the tensile strength as well as the impact properties of natural fiber and nanoclay filled PE was applied to reach values well above that of virgin PE.

The Study on Poly (Vinylidene Fluoride)/Silica Hybrid Composites Made by Sol--gel Process

Huang, S.-I., Chen, H. — Wed, 21 Oct 2009 19:24:25 PDT

In this study, the PVDF (Poly (vinylidene fluoride))/silica hybrid composites are prepared by mixing PVDF and silica, which was synthesized by sol—gel process. We changed R (the molar ratio of water/TEOS) during the sol—gel process, and made a film. The crystallinity of PVDF in the hybrid is measured by DSC (Differential scanning calorimetry), and the morphologies are observed with SEM pictures. We found that the silica particles could be well dispersed in PVDF, and R-value influenced the particle size and the crystallinity of PVDF. The concentration of TEOS also influenced the particle size and shape of silica. Higher concentration of TEOS made the silica particles have round shape and also lowered the crystallinity of PVDF.

Accelerated Ultraviolet Weathering of Recycled Polypropylene--Sawdust Composites

Adhikary, K. B., Pang, S., Staiger, M. P. — Wed, 21 Oct 2009 19:24:25 PDT

Accelerated ultraviolet (UV) weathering of hot-press molded recycled polypropylene (rPP)—sawdust composites was investigated with combinative UV radiation and water spray testing to assess the durability performance. The water absorption and thickness swelling of the composites were increased after accelerated weathering. The surface of the composites underwent significant color changes (E) and lightening (L*) after weathering. The Young’s modulus and flexural strength were decreased after weathering. Microstructural observations revealed a decrease in interfacial bonding between the wood flour and polymer matrix with increased exposure to weathering. The crystallinity and melting temperature of the PP—wood flour composites were decreased while neat rPP showed a 6% increase in the crystallinity after weathering. The crystallinity of rPP in the control composites without maleic anhydride polypropylene (MAPP) was slightly lower than for neat rPP, while MAPP-containing composites showed an increase in the crystallinity of rPP.

Study on Thermal Decomposition of Intumescent Fire-Retardant Polypropylene by TG/Fourier Transform Infrared

Zhang, F., Zhang, J., Sun, D. — Wed, 21 Oct 2009 19:24:25 PDT

The thermal decomposition processes of polypropylene formulations containing intumescent flame-retardant additives as well as the individual components in the composites have been studied using thermogravimetric analysis and real time Fourier transform infrared in both air and nitrogen atmospheres. The results show that the thermal decomposition processes of pure polypropylene (PP), polyamide, pentaerythritol, and intumecent flame-retarded PP (IFR-PP) composites in air are significantly different from that in nitrogen atmosphere. The existence of oxygen promotes the decomposition of the above materials. However, oxygen has little influence on the thermal decomposition of ammonium polyphosphate and zinc borate both in air and nitrogen atmospheres. All IFR-PP composites show an earlier onset of decomposition in comparison with pure PP both in nitrogen and air atmospheres. Accordingly, the initial release gases such as NH₃ or H₂O help to swell the melted PP polymer and improve the flame retardancy of IFR-PP composite. At temperature higher than 290°C in air and 440°C in nitrogen, the IFR-PP composites are more thermally stable than PP because of the incorporation of intumescent flame additives. The decomposition mechanisms of these materials are discussed based on the analysis of the results of TG/FTIR.

Improving Erosion Resistance of Polymer Reinforced Composites

Ahmed, T.J., Nino, G.F., Bersee, H.E.N., Beukers, A. — Wed, 21 Oct 2009 19:24:25 PDT

This article reports on solid particle erosion tests performed on glass fiber reinforced polyphenylene sulphide (PPS) for use on an all-composite ice-protection system for aircraft structures. The idea was introduced to use a metal mesh as a convenient way of toughening the surface layer thereby increasing erosion resistance. The erosion rates of the composites were evaluated at different impingement angles and with different erodent particle size. An aircraft-grade aluminium sheet was also used to provide a comparison for the composites. It was found that the erosion rate of the composites drastically reduced upon the introduction of an impregnated mesh onto the surface of the baseline glass/PPS laminate, to values similar to that of the aluminium sheet. In addition, the erosion rate was found to be dependent not only on the volume fraction of the matrix on the surface, but also the properties of the metal used for the mesh. The solution to use a metal mesh was shown to have multifunctional uses for composite based ice-protection system.

A Self-contained Module for Predicting Micro-scale Material Properties during Fiber-reinforced Polymer Processing

Brennan, K. P., Walrath, D. E. — Wed, 21 Oct 2009 19:24:25 PDT

A finite element-based approach was created to generate fiber scale permeability and thermal conductivity tensors for unidirectional fiber-reinforced composites. This model used fiber radius, volume fraction, and symmetry angle in addition to an assigned temperature and pressure gradient as inputs. Results and comparisons are presented for both Newtonian and non-Newtonian fluids. Permeability and conductivity values generated by the model agreed strongly with experimental and numerical data obtained by other research. The model was also able to capture the dependence of these tensors on fiber structure and fluid properties. This was accomplished within the confines of a small computational domain.

Flow and Mechanical Properties of Carbon Black Filled Acrylonitrile-Butadiene-Styrene (ABS)

Shenavar, A., Abbasi, F., Aghjeh, M.K. R., Zamani, A. — Wed, 21 Oct 2009 19:24:25 PDT

Thermal stability of acrylonitrile—butadiene—styrene (ABS) polymers is one of the most essential necessities for color and glossy durability of their surfaces. On the other hand, mechanical properties of ABS are significantly affected by its thermal degradation. One way to protect ABS against degradation is the addition of carbon black (CB) that can act as a stabilizer. In this work, CB was compounded with ABS via melt mixing and the effect of CB structures on the melt and final ABS/CB composites behavior were examined. Flow behavior of ABS/CB compounds was investigated by measurement of melt flow index (MFI). The variation of the MFI of the composites with CB content, particle size and the applied load was also investigated. The results showed that the effect of smaller particles in decreasing the MFI was pronounced than larger particles. The fracture surfaces of the impact tests were studied by scanning electron microscopy, and showed that a semi-brittle fracture surface appeared when CB was added to the ABS. The Young’s modulus of ABS increased and the yield stress decreased by increasing the CB loading.

Induction Heated Joining of Aluminum and Carbon Fiber Reinforced Nylon 66

Mitschang, P., Velthuis, R., Emrich, S., Kopnarski, M. — Wed, 21 Oct 2009 19:24:25 PDT

Joining different material types, like metal and thermoplastic fiber reinforced polymer composites (TP-FRPC), offers a large potential for innovative light weight applications. This kind of bonding depends on mechanical, physical, and chemical interactions and is, therefore influenced by joining partner surface treatments. This study describes adhesion models and the effect of surface treatments of AlMg3-CF/PA66-joints. Joining by means of induction heating is an appropriate joining technology for the bonding of metal/TP-FRPC as it is utilized by a rapid heat generation. The characterization of the bonding mechanisms and the influence of the surface treatments are presented by single-lap joints and by microscopic analyses.

Large-scale Experimental Study on Combustion Behavior of Thermoplastics with Different Thickness

Qiyuan Xie, , Heping Zhang, , Liang Xu, — Thu, 27 Aug 2009 08:01:44 PDT

Mutual-enhancing loop mechanism generally occurs between vertical thermoplastic sheet combustion and the melt induced pool fire. The objective of this study is to investigate the effects of thickness of thermoplastics on their combustion behavior. A corresponding experimental rig is designed based on the ISO 9705 fire test room. Commercially available typical thermoplastics, i.e., polypropylene (PP) and polystyrene (PS) with a thickness of 3 and 5 mm are used in the large-scale experiments. The experimental results show that the thickness of PP and PS sheets plays an important role in increasing the heat release rate and the peak values. The pool fires of a thinner sheet develop faster than those of a thicker one. Relatively smaller peak heat release rate is attained earlier during the experimental tests for a thinner thermoplastic sheet. The peak heat release rate of the 5 mm thick PP sheet is about 9 times that of the PP sheet with a thickness of 3 mm. The peak heat release rate of the 5 mm PS sheet is about 2.5 times that of the 3 mm one. In addition, for PP material, the burning flow induced pool fire area is not as large as that of the corresponding pool area. However, for PS sheets, the melt formed pool fire area is nearly equal to the pool area during the development of pool fires.

Polypropylene Nanocomposites with Thermally Stable Imidazolium Modified Clay: Mechanical Modeling and Effect of Compatibilizer

Mittal, V. — Thu, 27 Aug 2009 08:01:44 PDT

Thermally stable imidazolium modification as compared to the conventional ammonium modification is chosen to prepare polypropylene nanocomposites. Different volume fractions of organo-montmorillonite are used to generate polymer nanocomposites and the effect of the modified clay on mechanical properties is studied. The mechanical properties are also compared with Halpin—Tsai models and its modified versions to achieve better insight into the system. Addition of small amount of compatibilizer enhanced the extent of delamination of the filler. Compatibilizers are selected on the basis of their chemical nature, molecular weight, amount of grafting, and location of the polar groups. Incompatibility of the surface modification with the compatibilizer is suspected to counterbalance the delamination effect thus resulting in no change or deterioration of the oxygen permeation through the composite films. However, the tensile modulus is enhanced on addition of comaptibilizer owing to increased exfoliation, which exceeded the amount of matrix plasticization caused by the addition of the low-molecular weight compatibilizer. The compatibilizers neither affected the crystallization behavior of polymer nor the thermal behavior of the resulting composite.

Synthesis and Assembly of Nano-copper/PMMA-b-PSt by ATRP

Guo Cai Xu, , Hong Long Xing, , Xiao Li Ji, , Jan Jun Shi, , Xiao Mei Zhang, — Thu, 27 Aug 2009 08:01:44 PDT

The poly(methyl methacrylate) with single-caped halogen (PMMA-Br) was synthesized by atom transfer radical polymerization (ATRP) method under ultrasonic irradiation, with ethyl -bromopropionate as the initiator and CuBr/2, 2-bipyridine (BPy) as the catalyst. Then the block copolymer poly(methyl methacrylate)-b-polystyrene was synthesized in cyclohexanone solution containing styrene as comonomer and PMMA-Br as the macromolecular initiator as same as the above synthesis condition. Nano-copper/poly(methyl methacrylate)-b-polystyrene composites was successfully prepared by NaBH₄ as reductant in the polymerization system. The homopolymer, copolymers, and nanocomposites were characterized by means of FT-IR, ¹H NMR, GPC, XRD, XPS, and TEM, and the results showed that the molecular weight of the block copolymer was controlled, and there existed interaction between copper particles and PMMA chain, and that ordered-assembly behaviors of block copolymer, induced by the nano-copper, were investigated by HTEM.

Studies on Enhancement of Mechanical Properties and Interfacial Adhesion of Flax Reinforced Polypropylene Composites

Erasmus, E., Anandjiwala, R. — Thu, 27 Aug 2009 08:01:44 PDT

Natural fibre is often used as reinforcement in polymer composites. The main problem of using these natural fibres is their poor compatibility and hydrophilic nature. Therefore, chemical modification of constituents becomes necessary to enhance adhesion between hydrophilic fibre and hydrophobic polymer matrix. The aim of this work is to improve the interfacial adhesion between the polypropylene matrix and the nonwoven flax batting. Chemical treatments with acrylic acid, 4-pentanoic acid, 2,4-pentadienoic acid, and 2-methyl-4-pentanoic acid were investigated. The composites were processed by compression molding using a film stack method. The mechanical properties of these modified composites, such as tensile, flexural, and impact strength were analyzed and compared. It was found that these properties were dependent on the kind and amount of chemical treatment. SEM and thermal studies were also conducted.

Reinforcement of Dynamically Vulcanized EPDM/PP Elastomers Using Organoclay Fillers: Dynamic Properties of Rubber Vibration Isolators and Antivibration Performance

Wu, J.-H., Li, C.-H., Chiu, H.-T., Shong, Z.-J., Tsai, P.-A. — Thu, 27 Aug 2009 08:01:45 PDT

Dynamically vulcanized ethylene—propylene—diene/polypropylene (EPDM/PP) elastomers that were reinforced with various amounts of organoclay were prepared using octylphenol—formaldehyde resin and stannous chloride dehydrate as vulcanizing agents. The effects of organoclay on X-ray, mechanical properties, dynamic mechanical analysis, hysteresis, and dynamic properties were studied. X-ray analysis revealed that these organoclay-filled thermoplastic vulcanizates (TPVs) were intercalated. The organoclay improved the mechanical properties of TPVs. Dynamic mechanism analysis indicated that organoclay can increase the damping (tan ) and storage modulus of EPDM/PP TPVs at ambient temperature. The hysteresis behavior revealed that when the organoclay content exceeded 6 phr, the antivibration performance of these TPVs increased with the organoclay content. The dynamic ratio does not vary greatly as tan of EPDM/PP TPVs is increased.

Effect of Poly (Propylene-g-maleic Anhydride) on the Morphological, Rheological, and Mechanical Properties of PP/HDPE Blend

Ahmad Ramazani, S.A., Abdi Valami, M., Khak, M. — Thu, 27 Aug 2009 08:01:45 PDT

In this study, the morphological, rheological, and mechanical properties of PP/HDPE blend compatibilized with poly (propylene-g-maleic anhydride) were studied. Necessary blends were prepared using a counter current twin-screw extruder. The blend composition ranged from 10 to 50 wt% of dispersed phase (HDPE) and compatibilizer (MAPP) with two Concentration ranges 10, 20 wt% were used for PP/HDPE (80/20) blend with respect to the dispersed phase (HDPE). The results of morphological studies shows a droplet dispersion morphology in the composition to 50wt% HDPE content, which indicates that HDPE forms a dispersed phase and PP forms a continuous phase in these composition region. Addition of the MAPP compatibilizer decreases the dispersed phase diameter. Rheological studies show that addition of the MAPP compatibilizer increases the melt viscosity, complex viscosity, storage, and loss modulus of the blends. Mechanical studies show that with increasing of HDPE concentration the tensile and impact strength first increase, and then decrease. The elongation at break decreases with increasing of HDPE concentration. Addition of the MAPP compatibilizer increases the elongation at break, tensile, and impact strength.

Effect of Multiwalled Carbon Nanotubes on Crystallization Behavior of Poly(e-caprolactone)diol

Jana, R.N., Im, C., Bhunia, H. — Thu, 27 Aug 2009 08:01:45 PDT

Multiwalled carbon nanotubes (MWNTs) were found to be well dispersed in poly(-caprolactone)diol (PCL) matrix after grafting to the surface of MWNTs by grafting to approach. Afterward, the effect of MWNTs on nonisothermal crystallization of PCL was investigated by differential scanning calorimetry (DSC), X-ray diffraction spectroscopy, and polarized optical microscopy (POM). From the DSC observation, the onset and peak crystallization temperatures of the composites were found to be always higher than those for neat PCL, indicating high nucleation ability of MWNTs in PCL. However, the crystallization rate, characterized by inversed half-crystallization time of the composite was lower than that of the neat PCL. The experimental data were analyzed using modified Avrami equation, and the activation energy for crystallization for PCL was found to reduce in the presence of MWNTs. POM showed a direct evidence for nucleating action of MWNTs in the crystallization process.

Lamellar Structure of a Reactive Blend of 1,2-Polybutadiene and Nylon 11

Soeda, Y., Xiaomin Zhang, , Matsuda, Y., Tasaka, S. — Tue, 28 Jul 2009 01:39:22 PDT

Reactive blending of syndiotactic 1,2-polybutadine (SPB) and nylon 11 was carried out with a twin-screw extruder to obtain a thermoplastic vulcanizate (TPV) with good mechanical properties. A lamellar structure formed by continuous nylon 11 phase and long filamentous ligaments of SPB was observed for the TPV sample with a transmission electron microscope. Infrared spectra of nylon 11 films casted on SPB films show that chemical bonds between nylon 11 and SPB were formed after the curing of the films. Good mechanical properties of the TPV, which were owed to its morphology and strong adhesion at the interface, were investigated by peel tests and tensile tests.

Physico-mechanical Properties of Maleic Acid Post Treated Jute Fiber Reinforced Polypropylene Composites

Rahman, R., Hasan, M., Huque, M., Islam, N. — Tue, 28 Jul 2009 01:39:22 PDT

During the past decade, increasing environmental awareness has renewed the interest in natural fiber reinforced thermoplastics. In current work, injection-molding method was utilized in manufacturing polypropylene (PP) composites reinforced with 20, 25, 30, and 35 wt% jute fibers. In order to increase the adhesion between the jute fiber and PP matrix, manufactured composites were post treated with maleic acid. Microstructural analysis and mechanical testing were subsequently carried out. Post treated specimens yielded better mechanical properties compared to the raw ones, while 30% fiber reinforced composites had the optimum set of mechanical properties. According to the authors, chemical modification of the PP matrix may improve mechanical properties at higher fiber content by having better interfacial bonding between the PP matrix and maleic acid post treated jute fiber.

Numerical Analysis of Interlaminar Stresses of Angle-ply AS4/PEEK Laminate with a Central Hole

Zhao, G.H., Tong, J.W., Shen, M., Aymerich, F., Priolo, P. — Tue, 28 Jul 2009 01:39:22 PDT

This article addresses the distributions of interlaminar stresses of centrally notched angle-ply AS4/PEEK laminates by finite element method (FEM). The calculation results indicate: interlaminar stress concentration always occurs in the vicinity of free edges (including two free sides and hole edge), which is the so-called free edge effect; when two adjacent plies have the same layup angles, the free edge interlaminar normal stress dominates; when two adjacent plies have the opposite layup angles, interlaminar shear stress dominates. For both conditions, the highest interlaminar stresses generally occur at the hole edge. The results of digital speckle correlation measurement test indicate that the result predicted by FEM is reliable.

Reinforcing of Biologically Derived Apatite with Commercial Inert Glass

Gunduz, O., Ahmad, Z., Ekren, N., Agathopoulos, S., Salman, S., Oktar, F.N. — Tue, 28 Jul 2009 01:39:22 PDT

Apatite-based ceramics, derived from fine powder of calcinated bovine—bone (BHA), were successfully reinforced with 5 and 10 wt% commercial inert glass (CIG), which contained biocompatible elements, via sintering at different temperatures between 1000 and 1300°C. The products were subjected to mechanical testing and microstructural and crystallographic analyses. Comparison of the experimental results with those from earlier similar studies shows that CIG is superior for reinforcing of BHA ceramics compared with other bioactive glasses. Provided that the CIG addition does not exceed a certain limit, optimally being approximately 5 wt%, the resultant BHA-CIG materials can exhibit high strength after sintering and remarkable resistance toward over-firing at 1300°C. The influence of the amount of CIG on the developed microstructure and crystalline structure after sintering at different temperatures is discussed.

Experimental Investigation of Optimal Nanoparticle Inclusion for Enhanced Flexural Performance in Continuous Fiber Ceramic Nanocomposites

Gudapati, V. M., Veedu, V. P., Anyuan Cao, , Ghasemi-Nejhad, M. N. — Tue, 28 Jul 2009 01:39:22 PDT

This work reports the effects of using varying weight percentage of nanoparticle inclusions on mechanical performance of continuous fiber ceramic composites. The ceramic fiber reinforcement was Nicalon^TM, and KiON CERASET^® preceramic polymer was mixed with nanoparticle inclusions in the presence of a surfactant agent, which gave good dispersion of the particles within the matrix. Yttrium oxide nanoparticles with an average size of 29 nm was used as the inclusion with varying weight percentages of 5, 10, 15, and 20%. For comparison, samples without nanoparticles were also manufactured. Two different types of nanoparticle filled composites were manufactured. The first one followed neat preceramic polymer reinfiltration cycle, whereas the second system was manufactured with corresponding nanoparticle dispersed preceramic polymer reinfiltration. A characterization analysis of the samples using scanning electron microscopy revealed proper dispersion of nanoparticle along with good quality of the parts. In general, the weight gain percentage at each stage of reinfiltration/pyrolysis for both types of nanoparticle filled ceramic composites is consistently less than that for ceramic composites manufactured without nanoparticle. This indicates the compactness of the material and retention of shape during the B-staging. Four-point bending test was also conducted to evaluate the mechanical performance of the ceramic composite samples at room temperature. Nanoparticle filled samples consistently showed significant improvement in flexural strength compared to their counterparts without nanoparticle reinforcement.

Dielectric Relaxation of Curing DGEBA/mPDA System at 2.45 GHz

Liming Zobg, , Hawley, M. C., Rensheng Sun, , Kempel, L. C. — Wed, 15 Apr 2009 07:11:19 PDT

The dielectric behavior of a curing system of diglycidyl ether of bisphenol A and m-phenylenediamine has been studied over the temperature range of 20—100°C under 2.45 GHz microwave radiation. The dielectric constant and the dielectric loss factor of the system increase as temperature increases while they decrease as the curing reaction progresses. The epoxy resins at different extents of cure exhibit the g relaxation, which can be described by the Arrhenius rate law. The relaxation is attributed to the motions of the dipolar groups associated with the crosslinking system. The Davidson—Cole model is used to represent the temperature dependency of the dielectric properties.

Influence of Sawdust on the Mechanical Properties of Vinyl Plasticized Composites

Crespo, J.E., Sanchez, L., Parres, F., Lopez, J. — Wed, 15 Apr 2009 07:11:19 PDT

The present study develops a composite material using environmental friendly materials. The influence of lignocellulosic products, as sawdust, on the mechanical properties of compound materials elaborated using a thermoplastic matrix of PVC and plasticizer, is analyzed. The results obtained for the mechanical properties: tensile strength, elastic modulus, and hardness have been analyzed focusing on the amount of plasticizer and the grain size of sawdust used. In addition, the analysis of the fracture of obtained compound materials by scanning electronic microscopy has been done to understand the behavior of the composite material. Finally, the mechanical behavior of the materials obtained based on the relation between the matrix phase of the compound material (PVC and plasticizer) and the disperse phase of sawdust is justified.

An Investigation of the Physical Properties of Extruded Glycerol- and Formamide-Plasticized Cornstarch

Ning Wang, , Yu Jiugao, , Ma Xiaofei, , Han Chunmei, — Wed, 15 Apr 2009 07:11:19 PDT

Glycerol and formamide are used as plasticizers to prepare dry thermoplastic starch (DTPS) in a single-screw extruder. Glycerol/formamide—water plasticized starch (TPS) is also studied as a standard. Scanning electron microscopy reveals that more residual granules exist in glycerol-plasticized dry starch than in other blends. After the removal of water, DTPS becomes rigid and fragile. Increasing the formamide content results in a dramatic increase in the elongation of DTPS, and it maintains a high tensile strength. Dynamic mechanical thermal analysis demonstrates that formamide can decrease the glass transition temperature (T_g) of TPS and replace water to form formamide—starch mixtures in DTPS. Thermogravimetric analysis shows that destructurization of the polysaccharide chain is accelerated after removal of water, but it is alleviated by increasing the formamide content. It is also shown using Fourier transform infrared spectroscopy that formamide can form stronger hydrogen-bond interactions with starch than glycerol. At the same time, X-ray diffractometry shows that starch is plasticized more completely both in TPS and DTPS with a high formamide content. Finally, rheological study shows that formamide can decrease the shear viscosity and improve the fluidity of TPS and DTPS.

Short Nylon Fiber-reinforced HDPE: Melt Rheology

Abraham, T. N., George, K.E. — Wed, 15 Apr 2009 07:11:19 PDT

Short fiber-reinforced thermoplastics have generated much interest these days since fibrous materials tend to increase both mechanical and thermal properties, such as tensile strength, flexural strength, flexural modulus, heat deflection temperature, and creep resistance, and some times impact strength of thermoplastics. If the matrix and reinforcement are both based on polymers the composite are recyclable. The rheological behavior of recyclable composites based on nylon fiber-reinforced high density polyethylene (HDPE) is reported in this paper. The rheological behavior is evaluated both using a capillary rheometer and a torque rheometer. The study shows that the composite becomes pseudoplastic with fiber content and hence fiber addition does not affect processing adversely at higher shear rates. The torque rheometer data resemble that obtained from the capillary rheometer. The energy of mixing and activation energy of mixing also do not show much variation from that of HDPE alone.

Approximate Method for Buckling of Symmetric Composite Laminates under Thermal Loading

Barton, O. — Wed, 15 Apr 2009 07:11:19 PDT

In this paper, an approximate closed-form solution is presented to compute the thermal buckling response of a symmetric angle-ply laminates that are clamped in one edge and free along the other edge. For this boundary condition, no exact solution is available and, in order to compute the critical buckling temperatures, numerical methods such as the Rayleigh—Ritz or finite element method must be used. Approximate closed-form solutions bridge the void between exact and approximate numerical solutions and can readily be employed in design optimization. The environment corresponds to a steady state condition providing a uniform temperature distribution for the laminate. The laminate consists of four layers [/-]_s constructed of low, moderate, and high stiffness ratio materials. Comparative results using the Rayleigh—Ritz method provides a means of assessing the accuracy of the expression. For certain laminate architectures, several modes must be computed using the approximate quadratic expression to ascertain the lowest buckling mode, and once identified, provides an excellent approximation for the mode computed using the Rayleigh—Ritz method.

Mechanical Performances of Wood Polypropylene Composite due to Extended Moisture Immersion

Qingzheng Cheng, , Jingxin Wang, , Shaler, S. M. — Wed, 15 Apr 2009 07:11:19 PDT

Mechanical properties of an extruded wood polypropylene composite that was soaked in both osmotic water and artificial seawater were tested and compared in dry, wet, and redried states. Water did influence the material's flexural, compressive, and tensile strength and chord modulus after 13 months immersion. Flexural and compressive properties of the unsaturated specimens soaked in seawater were degraded slower than those of the specimens soaked in osmotic water. There was a significant effect of water type on tensile modulus of elasticity. Both nonreversible damage and recoverable portion of the material from dry to wet and then to redried state were observed for most of the mechanical properties. Results also indicated that impact strength was not affected by water immersion and redrying.

Optoelectrical Properties of Ferroelectric PC/Ceramic Composites

Ibrahim, S.S., Ayesh, A.S., Shoaibi, A. A. — Wed, 15 Apr 2009 07:11:19 PDT

Polycarbonate (PC)/ceramic (YSiBTS) composites were prepared using the casting technique. The dependence of the absorption coefficient () on photon energy (h) was determined in the spectral range from 200 nm to 800 nm at room temperature. The variation of the absorption coefficient (), optical gap (E_opt), relative permittivity (^'), AC conductivity (_AC) with YSiBTS ceramic concentration and frequency are reported. The observed optical energy gap (E_opt) was calculated from the measured absorption spectra. It was found that optical energy gap decreases with ceramic concentration and the absorption coefficient highly increases in the UV region at concentration of 18 wt% compared with the PC host. The dielectric constant and AC conductivity was measured for PC/ceramic composites at temperature range between 25°C to 140°C and at different frequency values (120 Hz, 1 kHz, 10 kHz, and 100 kHz). The obtained results indicate that PC modifies the dielectric properties of ceramic. At the same time addition of ceramic to PC polymer enhanced both dielectric constant and the polar character of PC matrix. It is also shown that at high ceramic content, the dielectric constant is independent of temperature between 30°C and 90°C. Additionally, there is agreement between the optical energy gap and AC conductivity results. Correlation between obtained results and SEM results is presented.