Ihab Kamel

Argon plasma treatment of glass surfaces

The effect of argon plasma treatment of glass surfaces is studied by FTIR and SEM. The argon plasma on cleaned glass surfaces resulted in increased surface area due to microetching and surface rearrangement of the silicate network as indicated by the observed changes in the Si-O stretching infrared absorption. The result was a relative increase in surface hydrophilicity which could be optimized by the plasma reaction conditions. The etching action of the argon plasma on the substrate surfaces facilitated the removal of the micrometre thick sizing from the commercial fibres accompanied by little loss in tensile strength. Plasma was also used to graft selected monomers to the surface of glass fibres for enhancement of bond compatibility in a composite system. This grafting treatment was followed by an argon etching step. The argon plasma action on the coated surfaces improved the wettability further and increased the sur face area. Changes in surface chemistry that accompanied the argon etching treatment were very subtle in the case of the plasma polymer of allylamine, but proved significant in the case of the plasma polymer of hexamethyldisiloxane. On the latter surfaces, rearrangement of the siloxane (Si-O-Si) bonds to silylmethylene (Si-(CH2)n-Si) groups is suggested.

Effect of radiation on the structure of ultrahigh molecular weight polyethylene

Abstract Radiation sterilization of ultrahigh molecular weight polyethylene (UHMW-PE) was recently found to cause changes in crystallinity, contradicting earlier observations on linear polyethylene of lower molecular weight. In this study, UHMW-PE (Hercules 1900) was gamma-irradiated up to 21 Mrad. Changes in melting and crystallization temperatures, enthalpies of melting and of crystallization, determined by differential scanning calorimetry, are reported. In particular, the temperature at the onset of crystallization provided a clearer view of the radiation damage to the polymer chains. A mechanism based on chain scission is proposed to explain the observed increase in crystallinity in agreement with recent findings. The crystallization temperature may be useful as an indicator of radiation and/or other damage to the UHMW-PE.

The Development of a Novel Tooth-root Implant Material

Polyacrylic acid-alumina composites have been developed in this laboratory and were found to be biocompatible and resistant to biodegradation. These composites can be designed to apply a predetermined pressure on the bone interface which was found beneficial for stimulation of new bone formation and increased bone densification at the implant interface. Optimization of the physical and mechanical properties is presented, and a brief summary of the subcutaneous and oral implantation is reported.

Radiation modified filler for dental restorative composites

Abstract γ-Radiation was utilized to graft acrylic acid in the vapor phase to the surface of glass fibers and quartz particles. This treatment improved the wettability of the filler with the polymeric matrix and enhanced the mechanical properties of the composite. Samples were prepared from the unfilled dental resin, and from composites containing untreated, silane treated and polyacrylic acid-grafted fillers. These composites contained 30, 45 and 69 vol.% filler in each category. The composites containing grafted filler were superior in hardness and compressive strength, and equivalent in abrasion resistance to those with silane treated fillers. However, both treatments showed at least a 50% improvement in compressive strength and a 300% reduction in wear over composites with untreated filler. This improvement was even more substantial when glass fibers were used as the filler material.

Radiation processed PAA composites for endosseous implants

Abstract A new porous polymer-ceramic composite has been developed in this laboratory for use in bone restoration. The alumina-poly (acrylic acid) composite was developed by the polymerization of an aqueous acrylic acid solution in the presence of 0.3μ alumina powder. The polymerization was initiated by exposing the above mixture to gamma radiation at a dose rate of 0.24 Mrad/hr for a total dose of one Mrad. The radiation step was followed by a heat treatment step to drive the excess water out of the system and create the interconnecting porosity necessary for bone ingrowth. The porosity of the PAA-alumina composites was varied from 30–60 vol. % by adjusting the monomer concentration. Mechanical testing indicated ductile behavior with compressive yield strengths of 69 MPa and 125 MPa at 60 and 30 vol. % porosity respectively. The degree of cross-linking of the PAA matrix can be varied to induce different levels of water solubility thereby allowing the equilibrium water absorption to be easily controlled. When the polymer matrix was crosslinked to 60, 80 and 95%, composite swelling in water was 50, 25 and 15 vol. % respectively. Corresponding changes in mechanical properties as a function of crosslink density will also be presented. The ability to control the composites properties allows a variety of implant applications such as endosseous root implants and ridge augmentation. Preliminary results for endosseous implants in dogs showed material biocompatibility and ease of body fluid diffusion. In addition, a distinct advantage of this material is its ease of fabrication and adaptation to various socket geometries. Implantation experiments are now in progress to determine the long term behavior of the material.

UHMW-PE fiber as reinforcing materials in EPDM rubber vulcanized by E-beam radiation

Ethylene-propylene-diene terpolymer (EPDM) was reinforced with different concentrations of Ultra high molecular weight polyethylene chopped fiber (Spectra?m 1000). The reinforced samples were vulcanized using different doses of E-Beam radiation. It was found that E-Beam radiation improves the interfacial adhesion between UHMW-PE fiber and EPDM matrix which was detected by scanning electron microscopy (SEM). In addition the Youngs modulus of the composites increases as irradiation dose increases. Increasing the concentration of the fibers up to 40 phr leads to an enhancement in mechanical properties and swelling resistance of obtained composites, especially in the absence of carbon black. In contrast, the tensile strength of EPDM loaded with carbon black decreased as fiber concentration increased even though the other mechanical properties were improved. Although the tensile strength decreased with increasing fiber concentrations, the absolute value of the tensile strength increased by at least three fold with the addition of carbon black.

Submicron pyrogenic silica and its use in polymer and coating systems

We describe briefly the manufacturing process and commercial grades of pyrogenic silica. We discuss their unique chemical and physical properties. We illustrate the physical and mechanical properties which they impart as fillers in polymer systems and to suggest explanations for these properties in relation to silica surface-polymer interactions

Potential Use of One-Phase Poly(methyl methacrylate) in Dental Implants

Through compounding and molding techniques, variation of porosity and the resulting effect on the mechanical properties of one-phase poly(methyl methacrylate) (PMMA) were studied. Characterization of the composites developed was pursued by correlating the microstructure with the physical and mechanical behavior of the material. From the three compounding techniques studied, NaCl-filled PMMA proved to have the best overall mechanical properties and control of porosity compared to a wide range of filler content.

Effect of Ionizing Radiation on the Properties of Ultrahigh Molecular Weight Polyethylene Fibers

Ultrahigh molecular weight polyethylene UHMW-PE fibers intended to be used as reinforcing fillers in elastomers were subjected to ionizing radiation vulcanization to avoid the deleterious effect of conventional sulfur vulcanization conditions, i.e., vulcanization temperature on the properties of polyethylene fibers. Thus, UHMW-PE fibers (Spectra™ 1000) were subjected to both gamma as well as electron beam radiation in absence of air and up to 250 kGy. Changes in melting (Tm) and crystallization temperature (Tc) enthalpy of melting and crystallization depending on the type and dose of radiation were followed up using differential scanning calorimetry (DSC). In addition to the observed decrease in tensile strength, decrease in fiber diameter and increase in modulus depending on radiation dose were correlated with the changes in fiber morphology.