A thermosetting epoxy polymer was hybrid-modified by the addition of 9 wt.% of rubber microparticles and 10 wt.% of silica nano-particles. Glass-fiber reinforced plastic (GFRP) composite laminates employing the unmodified epoxy matrix (GFRP-neat), and the hybrid epoxy matrix (GFRP-hybrid), were produced by a resin infusion technique. The experimental fatigue lives of both GFRP composites under three different variable amplitude load sequences, namely (i) a three-step increasing block, (ii) a three-step decreasing block and, (iii) a random block load sequence derived from a three-step load block, were determined. The fatigue life of the GFRPhybrid composite was higher than that of the GFRP-neat composite under all the three load sequence blocks investigated, by about x2.6 to x4.0 times. The saturated matrix crack density and the stiffness reduction rate were both lower in the GFRP-hybrid composite compared to the GFRP-neat composite material. The suppressed matrix cracking and reduced delamination growth rates measured in the hybrid-modified epoxy matrix enhanced the fatigue life of the corresponding GFRP-hybrid composite. Using the constant amplitude fatigue data generated at various stress ratios, the fatigue lives under these variable amplitude load sequence blocks were predicted using empirical models. The predicted fatigue lives, although non-conservative, were in reasonably agreement with the experimental results.
A thermosetting epoxy polymer was hybrid-modified by incorporating 9 wt. % of CTBN rubber micro particles and 10 wt. % of silica nano-particles. The unmodified and the hybrid-modified resins were poured into steel moulds and cured to produce bulk epoxy polymer sheets from which standard compact tension test specimens were machined. Fatigue crack growth tests were conducted using a 50 kN servo-hydraulic test machine, with following test parameters: stress ratio, R = σ min /σ max = 0.1, sinusoidal waveform and frequency, ν = 3 Hz. The crack length was monitored by compliance technique. The fracture surfaces were observed in a high resolution scanning electron microscope. The fatigue crack growth rate of the hybrid epoxy polymer was observed to be significantly lower than that of the unmodified epoxy polymer. The threshold stress intensity factor range, ∆K th , of the epoxy polymer was observed to increase by the addition of micron-rubber and nano-silica particles. The energy dissipating mechanisms viz., (i) cavitation of the rubber microparticles followed by plasticdeformation and void growth of the epoxy and, (ii) silica nanoparticle debonding followed by plasticdeformation and void growth of the epoxy, were observed to be operative and contribute for the reduced crack growth rate in the hybrid epoxy polymer.
Metabolic stability of a compound is an important factor to be considered during the early stages of drug discovery. If the compound has poor metabolic stability, it never becomes a drug even though it has promising pharmacological characteristics. For example, a drug is quickly metabolized in the body; it does not have sufficient in vivo exposure levels and leads to the production of toxic, non-active or active metabolites. A drug is slowly metabolized in the body it could remain longer periods in the body and lead to unwanted adverse reactions, toxicity or may cause drug interactions. Metabolic stability assay is performed to understand the susceptibility of the compound to undergo biotransformation in the body. Intrinsic clearance of the compound is measured by metabolic stability assays. Different in vitro test systems including liver microsomes, hepatocytes, S9 fractions, cytosol, recombinant expressed enzymes, and cell lines are used to investigate the metabolic stability of drugs. Metabolite profiling is a vital part of the drug discovery process and LC–MS plays a vital role. The development of high-resolution (HR) MS technologies with improved mass accuracy, in conjunction with novel data processing techniques, has significantly improved the metabolite detection and identification process. HR-MS based data acquisition (ion intensity-dependent acquisition, accurate-mass inclusion list-dependent acquisition, isotope pattern-dependent acquisition, pseudo neutral loss-dependent acquisition, and mass defect-dependent acquisition) and data mining techniques (extracted ion chromatogram, product ion filter, mass defect filter, isotope pattern filter, neutral loss filter, background subtraction, and control sample comparison) facilitate the drug metabolite identification process.
A thermosetting epoxy polymer was hybrid-modi¯ed by incorporating 9 wt.% of CTBN rubber microparticles and 10 wt.% of silica nanoparticles. The resin was poured into steel mould and cured to produce bulk epoxy polymer sheets from which fatigue test specimens were machined. The total fatigue life of the hybrid-modi¯ed epoxy polymer was determined by conducting constant amplitude fatigue tests with dog-bone shaped test specimens, at a stress ratio, R ¼ min = max ¼ 0:1, using a sinusoidal waveform at a frequency of 3 Hz. Further, the fatigue crack growth behavior of the hybrid-modi¯ed epoxy polymer, at a stress ratio, R ¼ 0:1, was determined using a standard 50 mm wide compact tension specimen. The fatigue fracture surfaces were observed using a scanning electron microscope. The cyclic fracture toughness of the hybrid-modi¯ed epoxy polymer, estimated from the fracture surface analysis, correlated well with the reported values of the toughness; which was signi¯cantly greater than that of the neat epoxy polymer. The energy dissipating micromechanisms of, (i) rubber particle cavitation and plastic deformation of the surrounding material, and (ii) silica nanoparticle debonding followed by plastic void growth, were observed to be operative, resulting in an improved fracture toughness. The fatigue crack initiation and propagation lives were determined from the experimental data. The enhanced capability to withstand longer crack lengths, due to the improved toughness together with the retarded crack growth rate, were observed to enhance the total fatigue life of the hybrid-modi¯ed epoxy polymer.
The present focus is on the development of sustained release formulations due to its inherent boons. There are several advantages of sustained release drug delivery over conventional dosage forms like improved patient compliance, reduction in fluctuation and increased safety margin of potent drug. The present study was aimed to prepare a sustained drug delivery system to design a controlled release oral dosage form of Cefpodoxime proxetil. The sustained release matrix tablets of Cefpodoxime proxetil were prepared by wet granulation and evaluated for different parameters such as weight variation, drug content, thickness, hardness, friability and In vitro release studies. The in vitro dissolution study was carried out for 12 hours using USP (Type- II) paddle apparatus in hydrochloride (0.1N) as dissolution media for first 2 hours and phosphate buffer (pH 6.8) for next 10 hours. Based on the in vitro dissolution data, formulation F8 was selected as the best formulation from Cefpodoxime proxetil formulations (F1 – F9) as the drug release was retarded up to 12 hours with 96.29 % and followed zero order release kinetics & drug release mechanism was diffusion.
Losartan potassium is used to treat high blood pressure (hypertension). The present study was aimed to prepare a floating drug delivery system to design a controlled release oral dosage form of Losartan potassium. This helps to overcome the demerit of limited residence time of the drug in the gastrointestinal track and hence to increase the duration of release. Hence objective of the present study is to develop Losartan potassium floating tablets by direct compression method using calcium starch as release retarding polymer. The calcium starch was synthesized by gelatinizing potato starch in the presence of sodium hydroxide and cross linking by treatment with calcium chloride. The micromeritic properties studies indicated that calcium starch is a promising pharmaceutical excipient in tablets. Floating tablets of Losartan potassium was formulated by direct compression technique, using different concentration of calcium starch and compared with HPMC K-100 as release retard polymer. As the amount of calcium starch in the tablet increased, the drug release decreased. The formulation F5 containing 125 mg calcium starch showed better controlled release of 76.38% after 12 hours.
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