Journal of Thermoplastic Composite Materials current issue

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.