Poly(1,3,4-oxadiazoles). Effect of structure on polymer properties

Poly(1,3,4-oxadiazole-2,5-diylvinylene) and poly(1,4-phenylene-1,3,4-oxadiazole-2,5-diylvinylene) were prepared by polymerizing different quantities of terephthalic acid (T), maleic acid (M), and hydrazine sulfate (HS) in the presence of fuming sulfuric acid. Homopolymers of M and T and various copolymers of M:T were prepared. The polymers were characterized by viscosity, IR, UV, and elemental analysis. Their solubility in different solvents was investigated. The relative thermal stability of the polymers was evaluated by TGA and DTA.     

Preliminary<Emphasis Type="Italic">in vitro</Emphasis> and<Emphasis Type="Italic">in vivo</Emphasis> characterizations of a sol-gel derived bioactive glass-ceramic system

This study investigates quantitatively and qualitatively the sol-gel derived bioactive glass-ceramic system (BGS)—apatite-wollastonite (AW) type granules in the size range of 0.5–1 mm, as an effective graft material for bone augmentation and restoration. Scanning electron micrographs (SEM) of the sintered granules revealed the rough material surface with micropores in the range 10–30 μm. X-ray diffraction (XRD) pattern of the granules revealed the presence of crystalline phases of the hydroxyapatite and wollastonite, and the functional groups of the silicate and phosphates were identified by Fourier transform infrared spectroscopy (FT-IR). Thein vitro cell culture studies with L929 mouse fibroblast cell line showed very few cells adhered on the BGS disc after 24 h. This could be due to the highly reactive surface of the disc concomitant with the crystallization but not due to the cytotoxicity of the material, since the cellular viability (MTT assay) with the material was 80‰ Cytotoxicity and cytocompatibility studies proved that the material was non-toxic and biocompatible. After 12 weeks of implantation of the BGS granules in the tibia bone of New Zealand white rabbits, the granules were found to be well osteointegrated, as observed in the radiographs. Angiogram with barium sulphate and Indian ink after 12 weeks showed the presence of microcapillaries in the vicinity of the implant site implicating high vascularity. Gross observation of the implant site did not show any inflammation or necrosis. SEM of the implanted site after 24 weeks revealed good osteointegration of the material with the newly formed bone and host bone. New bone was also observed within the material, which was degrading. Histological evaluation of the bone healing with the BGS granules in the tibial defect at all time intervals was without inflammation or fibrous tissue encapsulation. After 2 weeks the new bone was observed as a trabeculae network around the granules, and by 6 weeks the defect was completely closed with immature woven bone. By 12 weeks mature woven bone was observed, and new immature woven bone was seen within the cracks of the granules. After 24 weeks the defect was completely healed with lamellar bone and the size of the granules decreased. Histomorphometrically the area percentage of new bone formed was 67.77% after 12 weeks and 63.37% after 24 weeks. Less bone formation after 24 weeks was due to an increased implant surface area contributed by the material degradation and active bone remodeling. The osteostimulative and osteoconductive potential of the BGS granules was established by tetracycline labelling of the mineralizing areas by 2 and 6 weeks. This sol-gel derived BGS granules proved to be bioactive and resorbable which in turn encouraged active bone formation.     

Isothermal diffusion—reaction in a slab catalyst with bimolecular Langmuir-Hinshelwood kinetics: Connections with negative first-order kinetics

The problem of isothermal diffusion-reaction in a slab catalyst with bimolecular Langmuir—Hinshelwood kinetics is studied. Analytic solutions for the concentration profile and the catalytic effectiveness factor are reported for the full range of Thiele modulus values, in the limit of large adsorption inhibition constant. In this limit, connections with negative first-order kinetics are shown, and rather good explicit estimates of the region of multiple steady states are provided. Comparisons with numerical calculations are also made.     

Thermal behavior of aryl-aliphatic polyamides

Low molecular weight poly(p-phenylene sebacamides) and (m-phenylene sebacamides) were prepared by interfacial polycondensation by varying the concentration of p-and m-phenylenediamine in the initial feed. The polymers were characterized by intrinsic viscosity measurement and IR spectra. The relative thermal stability was evaluated by differential thermal analysis and dynamic thermogravimetry in air and nitrogen atmospheres. A systematic dependence of stability on intrinsic viscosity of poly(m-phenylene sebacamide) was observed indicating an endgroup initiation of degradation. No such dependence was observed in poly(p-phenylene sebacamide). A probable mechanism for the thermal degradation has been proposed.     

Modification of poly(vinyl alcohol) fibers by hexamethylene diisocyanate

Poly(vinyl alcohol) multifilament yarn was modified by reaction with hexamethylene diisocyanate. The effects of reaction variables such as time, temperature, concentration of reagents, solvent, and atomosphere were studied. The role of solvent appears to be very important in the reaction. Dimethylformamide, on account of its swelling power, proved better than the solvents benzene, toluene, and dioxane. Physical properties of modified fibers were compared with those of the parent. Moisture regain of the modified samples decreased with increasing add-on percent. The elastic recovery was not improved, and there was little effect of the HMDI treatment on mechanical properties. The thermal stability of poly(vinyl alcohol) modified with diisocyanate with small add-on was slightly improved.     

The application of low temperature infra-red spectroscopy to studies of iron substitution in tricalcium aluminate (C3A)

Low temperature IR spectroscopy has been used to study the extent of solid solution of Fe in C₃A. The intensity of the bands in the IR spectra obtained in sufficient to permit peak ratios to be used (for the first time) as an aid to determining the extent and nature of the solid solution.     

Pressure drop,solids concentration and mean holding time in multistage fluidisation

Correlations for the pressure drop, solids concentration and mean holding time of the solids in multistage fluidisation have been presented based on the experimental data of the present study and that available in literature covering a wide range in process variables.     

The high field enhancement of photoemission in multi-alkali photocathodes

The enhancement of photoemission by the application of a high electric field to the surface was measured for high sensitivity multi-alkali photocathodes. Alarge increase in photoemission was observed near the threshold region. The enhancement of photoemission decreased towards shorter wavelengths; at wavelengths of about 5000 Å and below there was almost no increase. The increase is assumed to arise from Schottky lowering of the surface potential barrier for the electrons. The variations of the field enhancement with wavelength are due to the energy distribution of the photoelectrons; this was verified by photoelectron spectroscopy.