Mechanical characteristics of tire/clay modified epoxy used in fabrication of medical prostheses and artificial human parts
Epoxy is used in many dental and medical applications such as manufacturing prostheses. This polymer is not toxic and is a good candidate for easily forming of artificial hand, leg, etc. In recent years, the recycled waste tire has been concerned as inexpensive modifier for improving the toughness characteristics of many thermoset resins such as epoxy. Herein, the influence of addition of nanoclay on mechanical characteristics of waste tire-modified epoxy was investigated. Mechanical properties i.e. compressive and flexural characteristics, fracture toughness and impact strength of the samples were investigated. The fracture surfaces of the specimens were examined using scanning electron microscope (SEM). Moreover the glass transition temperature (T ) of the samples were measured. Results reveal that nanoclay can improve the g mechanical characteristics of waste tire-modified epoxies.
Synthesis and Study on Effect of Various Chemical Conditions on the Swelling Property of Collagen- g -poly(AA- co -IA) Superabsorbent Hydrogel
In this work, a novel family of salt-responsive polymeric hydrogel based on collagen was prepared via simultaneously graft copolymerization of acrylic monomers, acrylic acid (AA) and itaconic acid (IA) onto collagen backbones by a free radical polymerization technique using ammonium persulfate (APS) as initiator and methylene bisacrylamide (MBA) as a crosslinker. The effect of grafting variables, i.e. AA/IA weight ratio and concentration of MBA and APS, was systematically optimized to achieve a hydrogel with swelling capacity as high as possible. The water absorbency increased with increasing the AA/IA amount in the monomer feed due to formation of polyelectrolyte and then become constant. The swelling of the hydrogel samples in town water and saline solution (0.15 mol/L LiCl,NaCl,KCl, CaCl 2 and AlCl 3 ) was examined. Results indicated that the swelling capacity decreased with an increase charge of cation. This behavior can be attributed to charge screening effect for monovalent cations, as well as ionic crosslinking for multivalent cations.finally,a mechanism for hydrogel formation was proposed and the structure of the product was established using Fourier transform infrared (FTIR) and Scanning Electron Microscopy (SEM) spectroscopies. Also, thermogravimetric analysis showed the thermal stabilities of the hydrogels.
Microstructure of the solder-casting zone in bridges of dental gold alloys.
The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.