Titles and Abstracts from Issue 3 of 2008:
A Review –Phenolic and Related Resins and Their Nanomodification Into Phenolic Resin FRP Systems
L.A. Pilato, J.H. Koo, G.E. Wissler, and S. Lao
Abstract: As phenolic resins enter their second century of existence, they continue to be an important bonding agent for a diversity of uses encompassing the joining of metals, glass, wood, paper, rubber, and other substrates with favorable cost/performance characteristics that surpass most other polymeric resins. It is equally important as a resin matrix for fiber reinforced composites requiring fire, smoke, and toxicity (FST) characteristics in critical high performance areas such as aircraft interiors/panels, tunnel materials, offshore oilfield grating and deluge pipe, and fire safe components. Closely related phenolic materials such as benzoxazines (BZ) and cyanate esters (CE) are emerging as more desirable phenolic systems with favorable FST behavior, cure with little or no volatiles, are more versatile, but are more costly. The newly developed BZ based on a phenolic component, formaldehyde, and a primary amine, leads to a cyclic structure that ring opens on polymerization without catalyst or by-product emissions. BZ resins have properties that are not observed in phenolic resins like low water absorption, and stable, low dielectric properties and are positioned for use in electronics and in FRP components. Numerous studies of nanomodification of phenolic resin systems (phenolic, BZ, and CE) are presented along with the method used to introduce selective nanoparticles and the resulting performance characteristics of the nanomodified phenolic resins. Both surface treated and functionalized nanoparticles are discussed. Various analytical and mechanical test methods are utilized to determine nanoparticle dispersion uniformity as well as diverse multifunctional features that emerge from nanomodification. Some nanomodified phenolic resin fiber reinforced polymer matrix composites are described with the type of phenolic resin, nanoparticle, fiber, type and improved application performance for the resulting nanomodified fiber reinforced polymer matrix composite.
A Comparison Between the Behavior of Glass and Carbon Fiber Fabric Reinforced PEI Subjected to Hygrothermal Loads
L. Chacón, A. Argüelles , I. Viña, M.A. García, and J. Viña
Abstract - The behavior of specimens from two composites made of a thermoplastic matrix (PEI: polyetherimide) reinforced with glass and carbon fiber fabric was studied. The materials were exposed to accelerated aging in a climatic chamber at 70°C and a relative humidity of 95% during periods of time of 10, 30, 60 and 360 days. The specimens were subsequently subjected to isothermal tests at 50, 100 and 150°C during 250, 750 and 2000 minutes at a constant stress of 40% of the material’s tensile strength obtained for each temperature. These three temperature values were selected from the results obtained in tensile tests carried out on specimens subjected to different temperatures ranging between ambient temperature and that of glass transition. In addition, the behavior of the aged specimens was compared with the original material, using the same parameters of temperature, time and constant stress.
Carbothermic Reaction Route for SiC Nanorods Synthesis Using Simple Precursors
El-Sheikh S.M. and Ahmed Y. M.Z
Abstract - Silicon carbide nanorods having a tenth of micron length and a mean diameter of 16 nm were successfully synthesized. Xerogel produced from lactose “as carbon source” and tetraethylorthosilicate (TEOS) “as silica source” was subjected to carbothermic reaction at temperature of 1500°C for 1 hr. The greenish black silicon carbide there by produced was characterized by a transmission electron microscope, X-ray diffraction, Fourier transform infra-red (FT-IR) and FT-micro-Raman. It was found that the synthesized nanorods, interestingly, have a Y-structure configuration, which is a promising candidate to various advanced applications.
Polycarbonate/Poly (methyl methacrylate) Nanofiber Composites with Improved Impact Strength
Yi Liu, Nyle E. Hedin, and Hao Fong
Abstract - In this study, an innovative type of hybrid structure made of polycarbonate (PC) and poly (methyl methacrylate) (PMMA), called “PC/PMMA nanofiber composites”, was fabricated and evaluated. Systematic investigations were conducted on (1) the electrospinning of PC and poly (methyl methacrylate- co-butadiene-co-styrene) (MBS) nanofibers, (2) the fabrication of two types of PC/PMMA nanofiber composites, and (3) the characterization/evaluation of PC and MBS nanofibers and their composites. Results indicated that uniform PC and MBS nanofibers with diameters of approximately 500 nm could be successfully electrospun from their solutions; and the MBS nanofibers could be further molecularly crosslinked while retaining of the fiber morphology. The impregnation of 0.5% (mass fraction) PC and molecularly crosslinked MBS nanofibers into the matrices of PMMA and PC, respectively, increased the impact strength values by 26.3% and 44.2%. This suggested that PC/PMMA nanofiber composites evidenced a synergetic effect yielding significantly improved impact resistance. However, impregnation of larger mass fractions of nanofibers caused the impact strength values to decrease, probably due to the formation of voids and/or structural defects in the composites. We believe that optimization of the fabrication method/procedure could lead to the PC/PMMA nanofiber composites with superior impact strength; and the PC/PMMA nanofiber composites could be particularly useful for incorporation into the design of protection devices when transparency is a requirement.
Electrical Conductivity Enhancement by Dispersion and Functionalization of SWNT Slurries through Mechanical Pot Milling
A. Vats, J.W. Sears, and H. Hong
Abstract - Single walled carbon nanotubes (SWNTs) have promising electronic, mechanical and thermal properties due to their unique structures and bonding. In this paper, we report the attempts to disperse SWNTs into nanoscale ceramics such as Si3N4 and ZrO2 through the use of the chemical surfactant carboxymethylcellulose (CMC) and through mechanical pot milling. The results of the transmission electron microscopy (TEM) show that SWNT are dispersed and partially exfoliated after pot milling. Raman spectroscopy of the slurries do not indicate any chemical functionalization occurred on SWNTs. A decrease in the electrical resistances of these ceramic matrix composite slurries was observed, 10% for Si3N4 based slurry and 35% for ZrO2 based slurry. This work may open the new way to increase the electrical conductivity of nanotube related fluids
Characterization of Process-induced Properties in Vacuum Assisted Resin Infusion Molding of High Temperature Polymer Composites
Ahmed Khattab and A. Sherif El-Gizawy
Abstract - Vacuum Assisted Resin Infusion Molding (VARIM) is a manufacturing process for composite structures. VARIM is used with resin systems such as polyesters and vinyl esters that typically cure at room temperature. It is also a process used with both epoxy systems that cure at room temperature as well as temperatures in the 82-177°C (180-350°F) range. However, VARIM processing at temperatures above 150-177°C (300-350°F) is rather limited and this paper concentrates on this higher application range. In fact, this paper concentrates on a high temperature BMI resin (Cytec 5250-4RTM) where little processing work has been reported to date using VARIM technology. This work focuses on characterization of process-induced properties that evolve in VARIM. The effects of service environment of temperature and humidity on properties of the composite structures are in the center of this investigation.
Comparison of Various Composite Material Acceptance Criteria
Elizabeth Clarkson and Yeow Ng
Abstract - Through computer generated simulations, the effect of various changes to the acceptance criteria, the original qualification samples, and the acceptance samples was studied to determine the effect on the failure rate of the acceptance samples. Simulated samples were generated with varying sample sizes, means, and standard deviations. They were then tested according to various acceptance criteria to check the reliability of those criteria and determine the effect of changes in those variables on the failure rates of those samples. The results show substantial differences between the different criteria. Although 10 different criteria were tested, only a few had acceptable error rates for both consumers risk (the probability of accepting a bad lot) and producers risk (the probability of rejecting a good lot).