Increasing Compression Pressure Research Articles

One-Dimensional Compression of Air-Foam Treated Lightweight Geo-Material in Microscopic Point of View

Air-foam treated lightweight geo-material (LGM), which is a mixture of dredged clay, cement, and air-foam, has been developed and utilized for various coastal structures, in order to reduce both overburden stress acting on an underground structure (tunnel, buried pipe, etc.) and lateral earth pressure acting on a retaining structure (quay wall, seawall, shore protection, etc.). In this study, one-dimensional compression behavior of the LGM was investigated in microscopic point of view with scanning electron microscope, optical CCD digital microscope, color laser 3-D profile microscope and mercury intrusion porosimetry (MIP). Though air-foam bubbles with diameters in a range of 200-500 11m are observed in the microscopic images, these sizes are not well reflected in the pore entrance size distribution by MIP because of the very small pore entrances. In MIP, there are in total three pore groups for LGM as in ranges of greater than 10 μm, 0.5-10 μm, and less than 0.5 μm. The group of the largest size corresponds to the air-foam bubbles, the one of the smallest size corresponds to the intra-pores in aggregates, and the one of the middle size corresponds to the inter-pores between the particle aggregates. When compression pressure increases, the observable airfoam bubbles primarily decreases; then the inter-pores between aggregates slightly decreases under a large compression pressure, but the intra-pores in aggregates do not decrease so much.

Pressure dependence of human fibrinogen correlated to the conformational alpha-helix to beta-sheet transition: an Fourier transform infrared study microspectroscopic study.

We used Fourier transform infrared (FTIR) microspectroscopy to investigate pressure-induced conformational changes in secondary structure of fibrinogen (FBG). Solid state FBG was compressed on a KBr pellet (1KBr method) or between two KBr pellets (2KBr method). The peak positions of the original and second-derivative ir spectra of compressed FBG samples prepared by the 1KBr method were similar to FBG sample without pressure. When FBG was prepared by the 2KBr method and pressure was increased up to 400 kg/cm(2), peaks at 1625 (intermolecular beta-sheet) and 1611 (beta-sheet aggregates structure and/or the side-chain absorption of the tyrosine residues) cm(-1) were enhanced. The peaks near 1661 (beta-sheet) and 1652 (alpha-helix) cm(-1) also exhibited a marked change with pressure. A linear correlation was found between the peak intensity ratio of 1611/1652 cm(-1) (r = 0.9879) or 1625/1652 cm(-1) (r = 0.9752) and applied pressure. The curve-fitted compositional changes in secondary structure of FBG also indicate that the composition of the alpha-helix structure (1657-1659 cm(-1)) was gradually reduced with the increase in compression pressure, but the composition of the beta-sheet structure (1681, 1629, and 1609 cm(-1)) gradually increased. This indicates that pressure-induced conformational changes in FBG include not only transformations from alpha-helix to beta-sheet structure, but also unfolding and denaturation of FBG and the formation of aggregates.

Effects of ankle-to-knee external pressures on skin blood perfusion under and distal to compression.

To compare the effects of select leg compression pressures on blood perfusion in the skin overlying bone and the skin distal to the leg compression. Blood perfusion of skin overlying the tibia and the foot dorsum was simultaneously measured in 12 healthy subjects using laser Doppler. Each subject's calf was compressed from ankle to knee with an air cast that applied external pressure, ranging from 0 to 40 mm Hg in 10 mm Hg increments. All measurements were initiated after a 20-minute rest interval and were recorded with each subject in a supine position. University research center. The main findings show that compression causes a significant decrease in skin blood perfusion (SBF) at both sites, with greater reductions in SBF occurring with increased compression pressure. Greater SBF reductions occurred at the foot than at the directly compressed tibia site. Thus, at the highest pressure (40 mm Hg), the foot SBF reduction (61.6% +/- 13.7%) was greater than at the directly compressed tibial site (33.3% +/- 0.3%), both of which were significantly less than baseline (P <.01). The present findings and considerable related evidence indicate that lower extremity external compression, within the range of commonly used therapeutic levels, reduces SBF by an amount that depends on the magnitude of the compression pressures. The quantitative difference between the effect of compression on SBF within the compression area, and distal to it, is likely a result of the way that the compression affects arteriolar and venous resistance to blood flow at the 2 sites. From a clinical perspective, it would seem prudent to anticipate that sub-bandage and distal SBF would be negatively affected by compression, with greater effects likely in tissue distal to compression.

Characterization of monoclinic crystals in tablets by pattern-fitting procedure using X-ray powder diffraction data

The purpose of this study is to characterize the monoclinic crystals in tablets by using X-ray powder diffraction data and to evaluate the deformation feature of crystals during compression. The monoclinic crystals of acetaminophen and benzoic acid were used as the samples. The observed X-ray diffraction intensities were fitted to the analytic expression, and the fitting parameters, such as the lattice parameters, the peak-width parameters, the preferred orientation parameter and peak asymmetric parameter were optimized by a non-linear least-squares procedure. The Gauss and March distribution functions were used to correct the preferred orientation of crystallites in the tablet. The March function performed better in correcting the modification of diffraction intensity by preferred orientation of crystallites, suggesting that the crystallites in the tablets had fiber texture with axial orientation. Although a broadening of diffraction peaks was observed in acetaminophen tablets with an increase of compression pressure, little broadening was observed in the benzoic tablets. These results suggest that “acetaminophen is a material consolidating by fragmentation of crystalline particles and benzoic acid is a material consolidating by plastic deformation then occurred rearrangement of molecules during compression”. A pattern-fitting procedure is the superior method for characterizing the crystalline drugs of monoclinic crystals in the tablets, as well as orthorhombic isoniazid and mannitol crystals reported in the previous paper.

Natural gas storage in activated carbon pellets without a binder

Activated carbon pellets without a binder from cellulose microcrystals as a raw material were investigated. After compression of the raw materials, the thus obtained raw material pellets were slowly carbonized to 1073 K under nitrogen. To activate them, the carbon pellets were heated to 1173 K under carbon dioxide. The activated carbon pellet shape, after heat treatment, was columnar by using the previous employed compression of the raw material. The total surface area, pore volume, and average pore diameter for all the samples were evaluated from the analysis of N 2 adsorption isotherm data. The total surface area and the pore volume were decreased with an increase in compression pressure under the same heat treatment conditions. On the contrary, the bulk densities of the activated carbon pellets were increased. However, these properties can be easily controlled by changing the sintering temperature and time. The bulk density of sample pellet was 0.56 g/cm 3. It is 2.3 times higher than activated carbon powder, which was made without the compression process. The total methane storage capacity at 298 K reached 164 cm 3 in 1 cm 3 volume of activated carbon pellets at 3.5 MPa.

Preparation of Activated Carbon Pellets without Binder and Their Methane Adsorption Propertie

Activated carbon pellets were prepared from cellulose microcrystals without binder. The column form of activated carbon pellets was maintained after heat treatment by use of compressed cellulose microcrystals. The bulk density of the activated carbon pellets increased with increasing compression pressure of the raw materials. On the other hand the total pore volume decreased.The bulk density of the activated carbon pellets is 2.5 times greater than that of activated carbon powder under the same sintering conditions. The amount of methane adsorption at 30°C is 82 mg/g at 0.86MPa. The total methane storage efficiency of adsorbed gas is 280 cm3 in 1 cm3 volume of the activated carbon pellet prepared in this work, being 1.7 times higher than that of the methane compressed at 13.0 MPa.

Effects of Hydrophilic Excipients and Compression Pressure on Physical Properties and Release Behavior of Aspirin-Tableted Microcapsules

Aspirin ethylcellulose microcapsules were tableted by compression with or without excipients (lactose or polyvinylpyrrolidone [PVP]). The effects of the amount of the excipients and microcapsule size on the crushing strength and release rate of aspirin from tableted microcapsules were investigated. Tablets without excipients had a crushing strength that was independent of the applied pressure and microcapsule size. An increase in compression pressure from 15 to 60 MPa resulted in an increase in the crushing strength of tablets containing 20% or 40% w/w lactose, but the reverse results were obtained for the tableted microcapsules containing 20% or 40% w/w PVP. Results showed that the release rate of aspirin from microcapsules containing lactose or PVP was independent of the compression pressure with the exception of tablets containing 40% w/w lactose. In vitro release profiles of aspirin from tableted microcapsules containing lactose or PVP showed that increasing the concentration of the excipients resulted in an increase in the release rate of aspirin. Values of n were changed by the compression pressure and the added excipients.

Effect of compressional force on the crystallinity of directly compressible cellulose excipients

The effect of compressional force on the crystallinity of low crystallinity cellulose (LCPC), microcrystalline celluloses (Avicel ® PH-101, PH-102 and PH-302 grades) and powdered cellulose (Solka Floc BW-100) has been investigated using an X-ray diffraction method. Microcrystalline and powdered celluloses showed an increase of about 10% in their crystallinities, compared to the values for the corresponding powders, at a compression pressure of 5–10 MPa. The increase in the crystallinity of LCPC was gradual and reached the maximum value of 5% at a compression pressure of 15 MPa. Further increase in compression pressure (to 77 MPa) had no effect on the crystallinity of LCPC, Avicel ® PH-101, Avicel ® PH-302 and Solka Floc BW-100. Avicel ® PH-102, on the other hand, showed a decrease in crystallinity at 15 MPa. Beyond 15 MPa, however, no statistically significant change in the crystallinity of the product was noted.

Formulation Factors Affecting Drug Release from Poly(Lactic Acid) (PLA) Microcapsule Tablets

A sustained-release (SR) formulation of phenobarbital (PB) microcapsule tablet was prepared using low molecular weight (MW) DL- and high MW L-poly(lactic acid) (PLA) polymer. Microencapsulation of PB showed a unimodal size distribution (375 to 550 μm) of the microcapsules with high loading capacity (>84%). Drug release from the microcapsule was influenced by the polymer ratios and increased with an increase in L-PLA amount. Microcapsules and physical mixtures of PB and the PLA were directly compressed independently to form microcapsule and matrix tablets, respectively. Drug release from the microcapsule tablets was significantly lowered (p <. 001) compared to matrix tablets or free microcapsule (free microcapsule > matrices > microcapsule tablets). We also investigated the effect of tablet adjuvants, compression pressures, and microcapsule loading on the tablet performance in terms of friability, hardness, porosity, tensile strength, and the release kinetics of PB. The drug release rate increased with increasing compression pressure in the case of Emcompress or lactose, but not Avicel. The drug release rate was three- to fivefold increased with sodium starch glycolate compared to tablets without a disintegrant. With an increase in microcapsule loading, a decrease in the drug release rate was observed; however, the tablet performance remained satisfactory. The morphology of the microcapsules was monitored microscopically after the dissolution and the disintegration of tablets. The drug release accelerated with compression pressures and microcapsule loading from the tablets due to mechanical destruction of the microcapsule wall, which was more clearly seen after disintegration and dissolution of the tablets. Our data suggest that the PLA microcapsule can be tableted to make a SR product without significantly affecting its release kinetics.

Effect of tableting conditions on the sticking of tablet using ibuprofen

Influence of tableting conditions on sticking was investigated using two formulations, the one formulation containing ibuprofen (formulation A) and the other being the standard formulation (formulation B). Sticking was observed on formulation A, and was not observed on formulation B. The degree of sticking was decreased with increase in compression pressure, and increased with compression speed. The shape of punch face was influenced the degree of sticking (sugar concave < bebel < flat). It was thought that sticking was observed when the adhesion between tablet and punch was larger than that among tableting granules. We investigated the pressure placed on a scraper (SCR), the adhesion between granules and metal, and boring hardness of tablet. The results showed that sticking was not observed when the SCR and/or the adhesion were small enough or boring hardness of tablet was high enough. Furthermore, it was suggested that boring hardness distribution would influence sticking.

Effect of Water Content on Sticking during Compression.

A rotary type tablet machine (Correct 12 HUK-AW, Kikusui, Co., Ltd.) fitted with flat-faced punches 8 mm in diameter was used to measure the scraper pressure (SCR), a kind of shear stress, as a direct means of evaluating sticking. The shear stress between the tablet and lower punch surface was determined using a system of SCR detection (strain gauge type, Okada Seiko Co., Ltd.).SCR increased with increasing compression pressure for samples at all water contents teste. The SCR had a tendency to increase up to a water content of 3%, then showed a decrease at a high water content. This suggests that the adhesive force between particles increases with increasing water content, but for high water content, shear stress decreased due to the effect of water as a lubricant. It is assumed that the sticking ratio increases proportionally with water content until about 3%.Mean surface roughness (Ra) of tablets due to sticking showed the same relationship between SCR and water content. The SCR increased with an increasing value of Ra. Thus, it was suggested that the adhesive force between particles and the punch surface plays an important role in sticking.

Effect of plastic deformation on ionic conduction in pure AgI and AgIAl 2O 3 composite solid electrolytes

The ionic conductivities of pure silver iodide and silver iodide-(10–40 mol%) alumina composites used as solid electrolytes are determined at room temperature by a.c. impedance spectroscopy as a function of compression pressure and annealing temperature. The ionic conductivities of both the pure and the composite silver iodide specimens increase with increasing compression pressure. This suggests that structural defects acting as conduction paths are generated in abundance by the plastic deformation. The mechanical strength of the as-deformed pure silver iodide specimen is decreased drastically by annealing at 413 K, whereas that of the as-deformed composite specimens remains virtually, unchanged. This indicates that the deformation-induced defects are present largely as dislocations. The ionic conductivity of the as-deformed pure silver iodide specimen determined during annealing at 323 K decreases with annealing time, whereas the conductivities of the as-deformed composite specimens are practically unchanged. It is concluded that the removal of the deformation-induced dislocations during annealing is impeded by dispersed alumina particles.

Effects of grinding and tableting on physicochemical stability of an anticancer drug, TAT-59.

The effects of grinding and tableting on the physicochemical stability of TAT-59, (E)-4-[1-[4-[2-(dimethylamino)ethoxy]phenyl]-2-(4-isopropyl) phenyl]-1-butenyl]phenyl monophosphate, were studied. The crystallinity of TAT-59 ground in a planetary ball mill for 0-120 min or compressed at 0-4500 kg/cm2 was evaluated by X-ray diffraction analysis and differential scanning calorimetry (DSC). The surface of TAT-59 was measured under a scanning electron microscope (SEM). The physicochemical stability of TAT-59, ground or compressed, was determined by measurements of water content, crystallinity and the amount of hydrolysis product, DP-TAT-59, formed. The crystallinity of ground TAT-59 decreased with increasing grinding time, and the amount of DP-TAT-59 increased with decrease in the crystallinity. Similar to ground TAT-59, the crystallinity of TAT-59 tablet gradually decreased with increasing compression pressure, and the amount of DP-TAT-59 tended to increase with decreasing crystallinity. These findings suggested that the decrease of the crystallinity of TAT-59 by mechanical force, such as grinding and tableting, raised the drug's reactivity and affected its stability.

Compression behavior and tensile strength of heat-treated polyethylene glycols

The compression behavior and tensile strength of five heat-treated polyethylene glycol (PEG) powders of different average molecular weights were determined. Compacts were prepared at various compression pressures using three different size fractions. The compression behavior of the compacts was analyzed according to the Kawakita, Cooper-Eaton and Heckel methods, respectively, and their compression parameters were calculated. Compared to the other polymers, PEG 4000 underwent greater densification during compression. The yield pressure from the slope of the Cooper-Eaton plot was lowest for PEG 4000. The yield pressure determined via the Heckel method was found to be proportional to the molecular weight of the PEG. These polymers obey a Heckel relationship at lower pressures (not exceeding 80 MN/m 2) and exhibit a behavior similar to those of fatty acid powders. The specific surface area of the compacts decreased with increasing compression pressure. The change in specific surface area of compacts compressed at pressures greater than 80 MN/m 2 was only very slight. This indicates that the surface of the compacts melts at such pressures. At pressures above 26.53 MN/m 2, PEG 10 000 compacts had superior tensile strength compared to the other polymers.

Deformation of the Stokes B2 Rotary Tablet Press: Quantitation and Influence on Tablet Compaction

Deformations that affect the vertical punch displacement of a Stokes B2 rotary tablet press were characterized with a cathetometer. The press deformation was found to be elastic for both the upper and lower compression roller assemblies. However, the upper and lower compression roller assemblies have different Hookian spring constants: 8.58×104and 5.18×104kN/m for the upper and lower assemblies, respectively. Using two‐way analysis of variance, the Hookian spring constants were shown to be independent of compaction phases and lower punch penetration setting. To study the influence of press deformation on tablet compaction, the Hookian spring constants were factored into the calculation of the incremental work of compaction for dibasic calcium phosphate dihydrate and microcrystalline cellulose. As the peak compression pressure increases, the force‐displacement work done on the tablet during the loading phase decreases relative to calculations that neglect press deformation. This decrease in force‐displacement work was attributed to elastic press deformation, which absorbs energy during the loading phase and then releases this energy later in the compaction cycle, altering the punch‐displacement profile. The rate at which the press stores and releases elastic energy depends in part upon the viscoelastic properties of the tablet. Based upon these results, the coupling between press elasticity and a tablet. Based upon these results, the coupling between press elasticity and a tablet's viscoelastic properties should be accounted for when analyzing tablet compaction or trying to simulate the punch‐displacement profile of a tablet press that deforms during compaction.

Effect of Some Excipjents and Compression Pressure on the Adhesion of Aqueous-Based Hydroxypropyl Methylcellulose Film Coatings to Tablet Surface

AbstractThe adhesion between aqueous-based hydroxypropyl methylcellulose (HPMC) films and tablet surface was evaluated using a Lloyd LRX materials testing machine. Special attention was paid to the effects of compression pressure and the excipients (microcrystalline cellulose, lactose and a commercial combination of lactose and cellulose (CellactoseR)) on the adhesion properties of the film.The adhesion of HPMC films was the lowest for the tablets containing lactose as a diluent and the highest for the tablets containing microcrystalline cellulose. The adhesion to CellactoseR-based tablets increased with increasing compression pressure. With microcrystalline cellulose (MCC) and lactose, the effect of compression pressure on film adhesion was not so clear. The increase in concentration of a hydrophopic lubricant, magnesium stearate, decreased the adhesion between the films and tablets cores. The greatest decrease was observed with the MCC tablets.Furthermore the results showed that, the film coating increa...

Study of the packing behavior of radial compression columns for preparative chromatography

The behavior of the packing of radial compression preparative columns (17.5 × 7.5 cm) was studied using C 18 silica IMPAQ as the stationary phase and water—methanol solutions as the mobile phase. The retention volumes of phenol and cresol and the efficiency of their peaks were repeatedly measured on three different columns, over several hundred hours, during which repeated water—methanol gradient runs were conducted. No significant changes in the retention factors and the column efficiency were observed during the testing period. The effects of the mobile phase temperature and of the radial compression pressure on the column efficiency were also studied. The external porosity and the permeability of the packing were found to decrease slowly with increasing compression pressure. Finally, a set of experiments were performed to trigger the formation of channels and to show their possible repair by applying elevated radial compression pressures.

Effects of compression pressure on physical and chemical stability of tablets containing an anticancer drug TAT-59.

(E)-4-[1-[4-[2-(Dimethylamino)ethoxy]phenyl]-2-(4-isopropyl) phenyl]-1-butenyl]phenyl monophosphate (TAT-59) is a new drug for the treatment of breast cancer. Physical and chemical stability of mixtures of TAT-59 and microcrystalline cellulose (1:9) compressed at 0, 300, 600 and 1400 kg/cm2 was evaluated by determination of water content, porosity and the amount of hydrolysis product, DP-TAT-59, formed. The water contents and porosity of these tablets scarcely changed during 57 d at 25-60 degrees C under 50% relative humidity (RH). The degradation rate of TAT-59 increased with increasing compression pressure as well as temperature. The apparent activation energy and frequency factor were determined from an Arrhenius plot of the degradation rate. Activation energy of these tablets was almost the same, while the frequency factor tended to increase with increasing compression pressure. The porosity and pore sizes in TAT-59-containing tablets decreased with increasing compressive force. We speculated from these observations that the increase in compression pressure decreased the distance and increased the contact area between TAT-59 and microcrystalline cellulose. The proximity between TAT-59 and moisture presented at the surface of microcrystalline cellulose by compression was considered to enhance the degradation of TAT-59.

Development and evaluation of controlled-release diclofenac microspheres and tabletted microspheres.

Diclofenac wax microspheres were prepared using the congealable dispersephase encapsulation method. Emulsifiers, glyceryl monostearate (GMS) and stearic acid, were added to improve the efficiency of emulsification. Microspheres containing either of the emulsifiers or both showed a high drug content (80-90%) and the particle size distribution was log-normal compared with microspheres without the emulsifiers. Increase in GMS concentration decreased the drug release and, in contrast, stearic acid appeared to channel the drug from the wax matrix. The addition of both emulsifiers at different concentrations modified drug release. Increase in dispersant (PVP) concentration, and decrease in microsphere size accelerated the rate of drug release. Higuchi/Baker Londsdale spherical matrix dissolution kinetics was followed. Disintegrating tableted microspheres were prepared with Avicel and Explotab. With the increase in compression pressure the crushing force and disintegrating time increased, but the thickness decreased, and the dissolution profile did not appear to be affected. Slightly faster release was noticed with tableted microspheres compared with that of uncompressed microspheres. Tablets containing 40 and 60% microsphere loadings had disintegration times of 5.12 +/- 0.63 and 57.73 +/- 3.53 min, respectively. In contrast, tablet formulation containing 80% microsphere load had a significant increase in disintegration time (130.83 +/- 4.26 min). The dissolution from this formulation also showed a lag time of 30 min in contrast with the other two formulations, which showed no lag time. Increased microsphere size from 215 to 630 microns had no effect on tableting properties (such as hardness and thickness); and only very little effect on dissolution. The microspheres appeared deformed but intact irrespective of compression pressures on scanning electron micrographs.

Pattern Fitting Procedure for the Characterization of Crystals and/or Crystallites in Tablets.

A pattern fitting procedure for the characterization of crystals and/or crystallites in tablets using X-ray powder diffraction data has been described. Observed X-ray diffraction intensities were fitted to the analytic expression, and the fitting parameters, such as the lattice parameters, the peak-width parameters and the preferred orientation parameter(s), were optimized by a non-linear least-squares procedure. Orthorhombic crystals of isoniazid and D-mannitol were used for the samples.Lattice parameters were found to increase slightly with an increase in compression pressure. In isoniazid, the peak-width broadened with an increase of compression pressure, and a marked broadening at a relatively high scattering angle was observed. It is indicated that both a decrease of the crystallite size and the lattice disorder occurred simultaneously with compression. In D-mannitol, the peak-width broadened with compression and the broadening was independent of the scattering angle. It is indicated that although the crystallite size decreased, the lattice disorder did not increase with compression. The strength of the preferred orientation of the crystallites increased with compression in both crystals.