Viscosity Grade Research Articles

Release Kinetics of Hydroxypropyl Methylcellulose Governing Drug Release and Hydrodynamic Changes of Matrix Tablet.

Hydrophilic Hydroxypropyl Methylcellulose (HPMC) matrix tablets are the standard role model of the oral controlled-release formulation. Nevertheless, the HPMC kinetics for the mechanistic understanding of drug release and hydrodynamic behaviors are rarely investigated. This study aims to investigate the release behaviors of both HPMC and paracetamol (model drug) from the hydrophilic matrix tablet. Two different viscosity grades of HPMC were used (Low viscosity: 6 cps, High viscosity: 4,000 cps). Three different ratios of drug/HPMC (H:38.08%, M:22.85%, and L:15.23% (w/w) of HPMC amounts in total weight) matrix tablets were prepared by wet granulation technique. The release profiles of the drug and HPMC in a matrix tablet were quantitatively analyzed by HPLC and 1H-Nuclear Magnetic Resonance (NMR) spectroscopy. The hydrodynamic changes of HPMC were determined by the gravimetric behaviors such as swelling and erosion rates, gel layer thickness, front movement data,and distributive Near-Infrared (NIR) chemical imaging of HPMC in a matrix tablet during the dissolution process. High viscosity HPMC tablets showed slower release of HPMC than the release rate of drug, suggesting that drug release preceded polymer release.Different hydration phenomenon was qualitatively identified and corresponded to the release profiles. The release behaviors of HPMC and drug in the tablet could be distinguished with the significant difference with fitted dissolution kinetics model (Low viscosity HPMC 6cps; Korsmeyer-Peppas model, High viscosity HPMC 4000cps; Hopfenberg model, Paracetamol; Weibull model) according to the weight of ingredients and types of HPMC. The determination of HPMC polymer release correlating with drug release, hydrodynamic behavior, and NIR chemical imaging of HPMC can provide new insights into the drug release- modulating mechanism in the hydrophilic matrix system.

Superpave performance graded asphalt binder selection for asphalt mixture design in Ghana

The Superior Performing Asphalt Pavements (Superpave) system – comprising asphalt binder grading, mixture design and mixture performance evaluation – has been in existence for nearly 30 years and has been implemented or evaluated for possible adoption in several countries to help address fatigue cracking, rutting and thermal cracking. These asphalt pavement distresses minimize pavement integrity to cause significant increase in maintenance cost, safety risks and roughness. Premature fatigue cracking and rutting failures are common in Ghana. Currently, only the mixture design component of the Superpave system is an option in the country's standard construction specification; asphalt binder selection is based on viscosity grading. Recently, very few projects have utilized Superpave-graded binders, and some of the binder grade selections were problematic. The use of Superpave-graded binders on high-volume roads is anticipated to become a common practice in the foreseeable future. However, there is no road agency guidance document on Superpave binder grade selection in Ghana currently, and this study sought to fill the gap. Such a guidance document will facilitate binder grade selection and streamline binder grade selection practices. This study utilized 42 years (1979–2020) of air temperature data collected from 24 weather stations across the country and measured asphalt pavement temperature to evaluate four existing Superpave binder grade prediction models. The model derived from the Long-Term Pavement Performance program better represented Ghana's climatic conditions and suggested the country may be partitioned into two Superpave binder grade selection zones: the Northern Savannah zone and the Transition/Forest/Coastal zone. At 98% reliability level, a binder grade of PG 70–10 was determined for the northern sector and PG 64–10 for the rest of the country. These are base binder grades (based on weather only) which must be adjusted for traffic conditions at the project site. Research should focus on local model formulation for refined Superpave binder grade selection and, during construction, selected binder grades must be verified through laboratory testing. Proper binder grade selection must be supplemented with effective pavement design, construction, axle load control and maintenance for good pavement performance and longevity.

Changes in the Key Physicochemical Parameters and Selected Trace Elements of Oil Due to Its Use in Hydraulic System of Woodworking Equipment

Abstract The research presented supported a comprehensive assessment of the condition of real oil samples of the HM quality class and VG 46 viscosity grade as functions of oil usage time in the hydraulic system of two round timber sorting and transport carriages (RSTWI and RSTWII) Baljer & Zembrod intended for handling wood logs by following the degradation and concentration of abrasive metals in the oil. The oil data were collected every Δ = 500 operating hours during one year by off-line monitoring of hydraulic oil. Measured values were compared to the acceptability limits. Multivariate associations were analysed using a principal component analysis (PCA; Statistica 12.0) to describe the patterns of co-variation among the examined traits. Based on the data obtained, it was observed that the oil in RSTWI was more oxidatively stressed in contrast to the oil in RSTWII despite it being subjected to an excessive wear mode.

Gastroretentive Sustained-Release Tablets Combined with a Solid Self-Micro-Emulsifying Drug Delivery System Adsorbed onto Fujicalin®.

Gastroretentive drug delivery systems (GRDDS) get retained in the stomach for a long time, thus facilitating the absorption of drugs in the upper gastrointestinal tract. However, drugs that are difficult to dissolve or unstable in an acidic environment are not suitable for GRDDS. The current study designs GRDDS combined with a self-micro-emulsifying drug delivery system (SMEDDS) for drugs with solubility or stability problems in the stomach. The model drug fenofibrate was formulated into the optimized liquid SMEDDS composed of 50 w/w% Capryol® PGMC, 40 w/w% Kolliphor® RH40, and 10 w/w% Transcutol® HP and solidified through adsorption on several porous adsorbents. In a dissolution medium at pH 1.2, the powdered SMEDDS using Fujicalin® dissolved quickly and achieved higher drug dissolution than other adsorbents. Based on these results, a gastroretentive bilayer tablet consisting of a drug release layer and a swelling layer was designed. The drug release layer was formulated with the powdered SMEDDS and hydroxypropyl methylcellulose (HPMC) as a release modifier. HPMC was also added to the swelling layer as a water-swellable polymer. The dissolution rate depended on the viscosity of the HPMC in the drug release layer. The time for 90% drug release was extended from 3.7 to 12.0h by increasing the viscosity grade of HPMC from 0.1 to 100K. Moreover, the tablet swelled and maintained a size comparable to a human pylorus diameter or more for at least 24h. This GRDDS could apply to a broader range of drug candidates.

EVALUATION OF DIFFERENT GRADES OF GUAR GUM, ACACIA GUM, AND POLYVINYL PYRROLIDONE AS CROSS-LINKERS IN PRODUCING SUBMICRON PARTICLES

Objective: The main goal of this research is to evaluate using of guar gum (GG), Arabic gum, and poly-vinylpyrrolidone, each of two viscosity grades, as crosslinking agents in producing nanoparticles and submicron particles. Methods: The method used is the preparation of nanoparticles of carbamazepine using two viscosity grades of polymers (GG, acacia gum, and polyvinyl pyrrolidine) by emulsification/solvent evaporation technique. Based on a statistical design composed of mixed 32-levels factors and 13-levels factor was selected for screening and preliminary optimization purposes. The collected nanoparticles from the first portion of all 24 runs were subjected to the following qualifications, particle diameter, polydispersity index (PDI%), zeta potential, entrapment efficiency (EE%), and drug loading. Results: The study revealed that based on the obtained findings and the associated statistical analysis, influences of stirring rate, polymer type, polymer grade, and polymer loading in different formulation runs resulted in produced particles with different characteristics such as particle size of different formulation series are in sub-micron (0.13–91.83 μm) with EE% (max 52.28%), reduced EE observed in this study can be attributed to lower polymer load in the dispersed phase (1% and 10%) and zeta potential values were small (range 35.69–41.68), all preparation factors have no significant effect on zeta potential, PDI values (close to zero) showed that all the samples formed monodispersions in water and its due to steric hindrance than a surface charge. Conclusion: The study recommends that different polymers need special techniques for producing cross-linked particles with sub-micron particles, no universal technique can be applied. Keywords: Polymer, Guar gum, Acacia gum, Polyvinyl pyrrolidine, Carbamazepine, Emulsification/solvent evaporation technique, Stirring rate.

Evaluation of fatigue characteristics of asphalt mixtures using Cracking Tolerance index (CTIndex)

Evaluation of the cracking potential of asphalt mix during the design phase can considerably limit the fatigue cracking and increase the service life of the flexible pavement. Thus, attention needs to be paid to employing a simple yet reliable performance test indicator. Indirect Tension Asphalt Cracking Test (IDEAL-CT) is one such emerging test method and is widely used in research across the world. The present study examines the potential of using the cracking tolerance index (CTIndex) as an appropriate parameter to explain the fatigue resistance of mixtures with both unmodified and modified binders. This test can be conducted using a Marshall testing machine or multispeed tester, routinely used for asphalt mixture design in India and many other countries. To evaluate the effectiveness of this parameter, fatigue resistance indicators for different binders, i.e., recovery at 3.2 kPa stress level (R3.2) from multiple stress creep and recovery (MSCR) test, fatigue life (TNf3.5) from the time sweep (TS) test at 3.5% strain, fatigue life at 2.5% (LNf2.5), and 5% (LNf5) strain from linear amplitude sweep (LAS) test, as well as for different mixtures, i.e., fatigue life from Indirect tensile fatigue test (ITFT) at 150 microstrain were considered. Two unmodified (viscosity grade 30, viscosity grade 40) and three modified (polymer, crumb rubber, sasobit) binders were evaluated for their fatigue parameters which were further correlated with CTIndex. The CTIndex exhibited good to excellent correlations (R2 ∼ 0.85 to 0.92) with the fatigue lives of the binders and the mixtures. To examine the effect of rheology and chemistry of the binder on the CTIndex, correlations of complex shear viscosity using Dynamic Shear Rheometer (DSR) at 60 °C and asphaltenes content from Thin-layer chromatography with flame ionization detector (TLC-FID) with CTIndex were explored. Viscosity, asphaltenes content, and elastic recovery of the binders depicted good correlations (R2 ∼ 0.88) with CTIndex, indicating higher cracking tolerance of stiffer yet elastic binders. Further, the sensitivity of CTIndex to binder type, binder content, aggregate gradation, and test temperature was examined. Overall, the values of the CTIndex displayed less variability (coefficient of variation < 10%) in this study.The observed sensitivity of CTIndex to asphalt mix parameters and the correlations of the CTIndex with fatigue resistance indicating parameters suggested that the CTIndex is an effective parameter for evaluating the fatigue characteristics of asphalt mixes.

Hydraulic Performance of Geosynthetic Clay Liners Comprising Anionic Polymer–Enhanced Bentonites

The hydraulic performance of geosynthetic clay liners (GCLs) comprising anionic polymer–enhanced bentonites (EBs), or EB-GCLs, based on permeation with 500 mM NaCl and 167 mM CaCl2 at an average effective stress of 27 kPa and hydraulic gradients of ∼300 was evaluated. The EBs included powdered sodium bentonite (NaB) enhanced with one of seven anionic polymers, including linear, noncrosslinked poly(acrylic acid) (PA) with low, medium, and high molecular weights, sodium carboxymethylcellulose (CMC) with either low viscosity or high viscosity, a covalently crosslinked sodium polyacrylate, and an in situ polymerized bentonite polymer composite. The NaB was enhanced with polymer at mass loadings of 5%, 8%, or 10% using dry-sprinkling, dry-mixing, and/or wet-mixing methods. Hydraulic conductivity tests at a low hydraulic gradient (∼35) also were conducted to determine the effect of seepage forces. Overall, the hydraulic performance of the EB-GCLs to the NaCl solution was better than that to the CaCl2 solution. Dry sprinkling (DS) with PA generally provided the best hydraulic performance, with hydraulic conductivity values based on permeation with 500 mM NaCl and 167 mM CaCl2 of 1.3×10−11 and 4.0×10−11 m/s, respectively, for the high-molecular-weight PA added at 5% via DS and 2.9×10−11 and 4.7×10−11 m/s, respectively, for the medium-molecular-weight PA added at 8% via DS. The CMC viscosity grade did not affect the hydraulic conductivity of the EB-GCLs. All EB-GCLs eluted polymer during permeation, regardless of mixing method or polymer type. Polymer elution was correlated with preferential interaggregate flow paths in multiple EB-GCL specimens, indicating the importance of polymer retention in maintaining low hydraulic conductivity of EB-GCLs. Because standard termination criteria for the measurement of the hydraulic conductivity of conventional unenhanced GCLs (e.g., as per current ASTM standards) do not address the potential impact of polymer elution from EB-GCLs, caution should be exercised when adapting these criteria to measure the hydraulic conductivity of EB-GCLs such as those evaluated in this study.

Laboratory evaluation of use of areca fibres in SMA mixes

ABSTRACT One of the problems associated with Stone Matrix Asphalt (SMA) mixes is the drain down of binder mortar during production, transportation and placement of the mixes. A commonly adopted method to control the drain down is to add a stabilising additive such as natural, synthetic or mineral fibres to the mixture, which is also known to improve the mechanical and volumetric properties of SMA. The present study evaluates the feasibility of using areca fibres extracted from areca husk in SMA as a stabilising additive. Three SMA mixtures were prepared with Viscosity Grade VG 30 bitumen using areca fibre (SMA-AF), coconut fibre (SMA-CF) and cellulose fibre in pelletised form (SMA-PF) and their performance was compared with a control SMA mixture prepared using Polymer Modified Bitumen (SMA-PMB). The prepared SMA specimens were evaluated for volumetric and Marshall properties, workability characteristics, Indirect Tensile Strength (ITS), fatigue, rutting and moisture susceptibility. The drain down test results indicated that the fibres controlled the drain down, and the optimum fibre content was 0.3% for the mixes with fibres. All the mixtures satisfied the requirements of SMA per IRC:SP 79-2008. The statistical analysis conducted revealed that the fibre type had a significant effect on the properties of SMA mixes. The SMA-PMB and SMA-CF mixes required the least and the highest energy for compaction. Among the mixes with natural fibres, SMA-AF performed better than SMA-CF.

Numerical Study of the Optimum Fiber Content of Sealing Grease Using Discrete Element Method.

A sealing grease plays a crucial role in the sealing of shield tails. Its pumpability and pressure sealing resistant sealing performance are greatly affected by the fiber content. In this study, discrete element method models were used to simulate the pressure-resistant tests of sealing grease in order to investigate the influence of viscosity grade and fiber’s aspect ratio on the optimum fiber content of sealing grease. Meanwhile, the rationality of the optimum fiber number determined based on the sealing performance was verified with the unbalanced force and fiber area proportion obtained in the simulation, of which the variation curves with the increasing fiber number were practically identical. The simulation results elucidated that the viscosity of grease had little effect on the optimum fiber content for sealing grease. However, the increase in viscosity can improve the sealing effect, and increasing the fiber’s aspect ratio can reduce the fiber number to reach a specific seal state. Based on the analysis of the total number of fiber spheres for the models with different fiber’s respect ratios, it can be concluded that the sealing grease sample made of the same fiber material and quality can reach the same seal state and seal effect, independent on fiber’s aspect ratio.

Laboratory data integration and grading viscosity assessment for polymer flooding by simulation

Polymer flooding improves the mobility ratio by mainly increasing the injected water viscosity. Typically, these projects minimize the volume of polymer due to economic aspects since the polymer cost significantly affects operation expenditures. However, the injection of a single slug sometimes produces an abrupt viscosity transition at the slug tail, and the chase water forms fingers that can bypass the slug, destroying its integrity. Injecting gradually more dilute slugs mitigates viscous fingering and reduces polymer mass. The scarce field applications, scarce testing at laboratory scale, and the absence of simulations discussion drove the interest in the subject. This study implements and evaluates a numerical simulation by integrating laboratory scale data – bulk rheology, single- and two-phase core floodings – and then history matching graded viscosity core flooding. The results were compared using performance indicators and validated with three laboratory experiments from the literature. The experiments consist of one continuous injection core flood and two core floods using grading viscosity with similar polymer injected mass, one with two slugs and another with three polymer slugs. Experimental and simulated history data for oil recovery and cumulative water matched with less than 5% of normalized error. Events such as water and polymer breakthroughs were well represented. The performance indicators revealed the three slugs test showed the best polymer utility factor for oil/water and best injectivity. On the other hand, the two slugs test reached higher final incremental oil recovery. This work contributes to data integration and extended discussions necessary to enable tailoring and motivating applications of polymer viscosity grading, to save polymer mass and reduce the produced water.

Numerical Assessment of Tribological Performance of Different Low Viscosity Engine Oils in a 4-Stroke CI Light-Duty ICE

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Decreasing fuel consumption in Internal Combustion Engines (ICE) is a key target for engine developers in order to achieve the CO&lt;sub&gt;2&lt;/sub&gt; emissions limits during a standard cycle. In this context, reduction of engine friction could help meet those targets. The use of Low Viscosity Engine Oils (LVEOs), which is currently one of the avenues to achieve such reductions, was studied in this manuscript through a validated numerical simulation model that predicts the friction of the engine’s piston-cylinder unit, journal bearings and camshaft. These frictional power losses were obtained for four different lubricant formulations which differ in their viscosity grades and design. Results showed a maximum friction variation of up to 6% depending on the engine operating condition, where the major reductions came from hydrodynamic-dominated components such as journal bearings, despite an increase in friction in boundary-dominated components such as the piston-ring assembly. Also, an evaluation of the potential fuel reduction that can be obtained by low viscosity oils during a WLTC approval cycle was performed. Overall, a fuel saving of 1% was obtained. In general terms, the majority of the engine map showed potential for mechanical loss reduction through LVEOs, that is, a better engine efficiency and consequently a decrease in the fuel consumption and CO&lt;sub&gt;2&lt;/sub&gt; emitted to the atmosphere. The present work also exemplifies the trade-offs encountered when reducing the engine friction through LVEOs and highlights the need to co-engineer the hardware and lubricant in order to utilize the full friction reduction potential of LVEOs.&lt;/div&gt;&lt;/div&gt;

Observation of curcumin-loaded hydroxypropyl methylcellulose (HPMC) oleogels under in vitro lipid digestion and in situ intestinal absorption in rats

Curcumin-loaded nanostructured lipid carriers (Cur-NLCs)-based hydroxypropyl methylcellulose (HPMC) oleogels (Cur-NLCs-HPMC-OGs) were fabricated using a cryogel template. The effect of the HPMC viscosity grade on the oleogel characteristics and in situ intestinal absorption were examined. Highly stable Cur-NLCs were prepared with a mean particle size of 314 nm and polydispersity index of 0.275. Cur-NLCs affected the creamy texture of self-standing Cur-NLCs-HPMC-OGs. The Cur-NLCs were tightly packed as oil droplets in the network of HPMC. However, a high viscosity of HPMC-4000 led to a greater ability to entrap and prevent droplet coalescence compared to a low viscosity of HPMC-400. NLCs promoted the release of free fatty acids during in vitro lipid digestion, whereas HPMC-4000 maintained the strength and durability of oleogels against mechanical and enzymatic breakdown. The in situ loop results revealed higher curcumin absorption by Cur-NLCs-HPMC-OGs than by Cur-HPMC-OGs. HMPC-4000 showed slightly higher curcumin absorption compared to HPMC-400.

Study on the Lubrication Mechanism of Diamond-Like Carbon Coating in Two Formulated Lubricants with Two Viscosity Grades

Study on the Lubrication Mechanism of Diamond-Like Carbon Coating in Two Formulated Lubricants with Two Viscosity Grades

The Investigation of Viscometric Properties of the Most Reputable Types of Viscosity Index Improvers in Different Lubricant Base Oils: API Groups I, II, and III

Four commercial viscosity index improvers (VII) have been used to investigate the behavioral differences of these compounds in three types of universally applicable base oils. The used VIIs are structurally three types of co-polymer: ethylene-propylene, star isoprene, and two di-block styrene-isoprene. After dissolving of different amounts of VIIs in different base oils, the kinematic viscosities at two standard temperatures were determined and the intrinsic viscosities were calculated according to Huggins method, then the effects of changes in base oil and polymer type were investigated. Intrinsic viscosities as criteria for polymer molecules sizes were found to be higher at lower temperature than at higher temperature. Dependence of intrinsic viscosity on the polymer molecular weight was observed. In the previous works, one or two types of VIIs were studied in only one type of base oil and/or solvent, not different base oils. Furthermore, different ranges of temperatures and concentrations not necessarily applied ranges were selected, but in this work, common base oils and most commercial VIIs were used and the viscometric properties were compared at two temperatures. Viscosities at these temperatures are used for determining VI and definition of lubricant’s viscosity grades. VI improvement is the main cause of VII usage.

Wound-healing and cytokine-modulating potential of medicinal oil formulation comprising leaf extract of Murraya koenigii and olive oil

The study investigated the wound healing effect of medicinal oil (MO) formulation prepared from Murraya koenigii leaves extract (methanolic) incorporated in olive oil. The MO was visually transparent, homogenous, smooth in texture, the viscosity grade was observed as 140 cP and easily spreadable. Pro-inflammatory cytokines IL-1β, IL-6, and TNF-α were significantly reduced to 82.3 ± 3.5, 156 ± 6.2, 137.3. ± 5.5 pg/ml, respectively after treatment with MO when compared to disease control animals that showed IL-1β, IL-6, and TNF-α levels of 170 ± 6, 265 ± 7, and 288.6 ± 11, pg/ml respectively. The level of pro-inflammatory cytokine in povidone iodine solution (PIS) group was 95.3 ± 3, 162 ± 6, 177.6 ± 8.9 pg/ml of IL-1β, IL-6, and TNF-α respectively. Interestingly, the wound-healing efficacy of MO was found better as compared to povidone iodine treated standard group and concluded that MO has excellent wound healing effect.

Assessing the Potential Replacement of Mineral Oil with Environmentally Acceptable Lubricants in a Stern Tube Bearing: An Experimental Analysis of Bearing Performance

Abstract This study compares the performance of a plain bearing, with a similar structure to a tail shaft stern bearing, lubricated with either mineral oil or an environmentally acceptable lubricant (EAL). The main characteristic of the bearing is its length/diameter ratio of &lt;1. Measurements are carried out with the bearing operating under loads from 0.5 to 1 MPa and seven speeds ranging from 1 to 11 rev/s. The bearing lubricated with either mineral oil with a viscosity grade of 100 or an environmentally acceptable lubricant (EAL) with a viscosity grade of 100 or 150 is investigated according to the ISO standard. Bearing wear is simulated by increasing the clearance circle by 0.1 mm. According to the results obtained, the use of an EAL in place of mineral oil does not cause significant changes in the bearing performance, regardless of the value of the clearance radius. The pressure distribution in the oil film, bearing load carrying capacity, eccentricity and friction coefficient have similar values for the entire load and speed ranges considered, and the discrepancies in the results are within the range of the measurement errors. Only an increase in EAL viscosity causes significant changes in bearing performance and these changes comply with the general theory of lubrication.

Controlled Release Formulation of Tofacitinib Citrate Tablets Evaluated Using Quality by Design (QBD) Approach

The goal of the project is to use the quality-by-design (QbD) method to create and optimise Tofacitinib citrate matrix tablets with controlled release excipients. The drug's physicochemical parameters, reference product characterisation, QTPP (Quality Target Product Profile), and CQAs were used to start product development (Critical Quality Attributes). Hypromellose (Methocel K100 premium LV CR), Polyethylene Oxide (SentryPolyox WSR N80 LEO), and Magnesium Stearate were used as formulation variables and were optimised together. The complete factorial design of experiment (DOE) with three centre points was used to investigate traditional monolithic controlled release matrix tablets. Using Design-expert12 programme, dissolution was assessed as CQA. At acidic pH, hypromellose with a higher viscosity grade provides a regulated release pattern by retaining the integrity of the medication and preventing rapid drug release. Due to the nonionic nature of the polymer, drug release from the polymer matrices is pH independent. Present monolithic controlled release matrix system the extensive degradation of Tofacitinib Citrate in the acidic condition can be avoided with desired in-vitro drug release.

Formulation and Evaluation of Controlled Release Matrix Tablets of Cefixime Trihydrate

Abstract: The main objective of the present work was to develop sustained release matrix tablets of Cefixime Trihydrate were prepared by direct compression techniques and evaluates the effect of formulation variables such as lubricant, binder, polymer content and viscosity grades of HPMC on the behavior of Cefixime Trihydrate release. The prepared tablets were evaluated for various physico-chemical parameters. In vitro release profile was check to evaluate the sustained release matrix tablet of Cefixime Trihydrate. The drug release from the optimized formulation was found to follow zero order kinetics. Thus the phenomenon of drug release showed that the release of optimized formulation is controlled by diffusion. Administration of Cefixime Trihydrate in a sustained release dosage would be more desirable for bacterial infections effects by maintaining the plasma concentrations of the drug well above the therapeutic concentration. From In vitro dissolution profile, Formulation S3 was prepared with Hydroxypropyl methylcellulose (K15M) combination where drug release was about 99.14% at the end of 24 hrs and followed zero order with non-Fickian diffusion method. It is selected as the best formulation.

In vivo Evaluation of Theophylline Sustained Release Matrix Tablets Containing Low Viscosity Guar Gum

The present investigation was carried out to evaluate the utility of guar gum as a hydrophilic matrix carrier in the design of oral controlled drug delivery. Based on the earlier reports, the low viscosity guar gum appears to be superior to medium and high viscosity grades of guar gum in providing a sustained delivery of theophylline along the GI tract. Conducting in vivo studies on theophylline matrix tablets containing 10% of low viscosity guar gum as a representative formulation assessed the in vivo performance of the guar gum matrix tablets. The in vivo studies were carried out in dogs. The effective concentration of theophylline was sustained for a period of 16 hours. The extended tmax, reduced absorption rate constant, prolonged MRT, unchanged Cmax and unchanged bioavailability indicate a controlled release of theophylline from the guar gum matrix tablets resulting in a sustained absorption and prolonged blood levels of theophylline. The theophylline matrix tablets showed blood levels well below 15 ?g/mL indicating freedom from adverse effects. Based on the studies, guar gum appears to be a potential carrier in the design of oral controlled drug delivery systems.

Thermophysical properties of R32/advanced PVE mixture and parametric analysis on oil transport characteristic of compressor suction line

Advanced PVE was developed as the coupled lubricant oil for the alternative refrigerant R32 and R32/PVE will be a potential working pair of R32 refrigeration systems. This paper presented modeling study of physical properties of PVE lubricant oil with viscosity grade 68 and R32/PVE mixture. Thermal conductivity, specific heat and surface tension of PVE oil were measured experimentally. New calculation models for properties of pure oil were developed based on the experimental data. Moreover, the solubility, miscibility and viscosity of R32/PVE mixture were also well correlated with the new correlations. Further, a parametric analysis was performed to study oil transport and retention characteristics in compressor suction line, based on the force balance method. A new consolidated database for oil retention was amassed from six existing literatures, including 187 data points. A new correlation for oil retention was established by incorporating influence factors derived from the parametric analysis. The validation result showed that the oil retention correlation exhibits satisfactory prediction accuracy, which achieved mean absolute error of 14.43% and 87.70% of data fell within ±30% error bands. The property models and oil retention correlation could serve as tools to accurately predict oil retention amount of suction line with R32/PVE mixture.