Comparison of two varieties of microcrystalline cellulose as filler-binders I. Perdnisone tablets

A comparative study of two varieties of microcrystalline cellulose (Avicel PH 101 and Avicel PH 102) as excipients in direct compression prednisone tablets has been carried out. The effects of compression force, proportion of drug/excipient and variety of cellulose (defined by means of mean particle size) on the structural, mechanical and release properties of the tablets were studied. Differences were observed in the behaviour of the two varieties of cellulose affecting all the properties analyzed. These differences diminished, and disappeared in some cases, when 10% prednisone was present. The different degrees of interparticle association and the relations between the structural, mechanical and drug release properties of the tablets explain the differences observed.     

Adsorption of an amine drug onto microcrystalline cellulose and silicified microcrystalline cellulose samples

The adsorption of a model amine drug (tacrine hydrochloride) from aqueous solution onto 21 microcrystalline cellulose (MCC) based samples has been investigated. The MCC source (manufacturer) affected adsorption. The adsorption appeared to be fully reversible. Adsorption was reduced by the use of high-density grade MCC, high-energy milling, and silicification. Adsorption of the model drug was not affected by the particle size of the MCC. Significant variations of the adsorption characteristics between batches of certain MCC products were found. The primary mode of adsorption was by ion exchange.     

Low frequency dielectric properties of human blood

Nano- and microparticles in human blood affect drastically the charge transfer CT through the viable fluid. Low-frequency dielectric properties of the blood, characterized by CT of β - dispersion type, are widely investigated with special stress on physical mechanisms. However, no publication in the literature deals with the presence of α - dispersion in human blood. In the present study, a mechanism associated with α-, β-, and γ- dispersions is presented. The dielectric losses (electrical conduction) phenomenon is also discussed with special emphasis on the distribution of relaxation times. These losses cause problems with low-frequency dielectric measurements, thus, they are correlated with the famous empirical Col-Cole factor, (1-α). A Gaussian distribution of relaxation times is suggested and found to be exponentially related with (1-α). The results suggest new diagnostic and therapeutic methods for blood disorders.     

Functional performance of silicified microcrystalline cellulose versus microcrystalline cellulose: a case study

Background: During the development of a tablet dosage form of an investigational compound, R411, several aspects were identified as critical quality attributes that required optimization. The use of nonsolvent processing prevented the moisture-induced physical changes in the drug product but presented manufacturing challenges related to sticking during compression and slowdown in dissolution after storage at stress conditions. Aim: The aim of this study was to evaluate silicified microcrystalline cellulose (SMCC), microcrystalline cellulose (MCC), and physical mixture of MCC–colloidal silicon dioxide (MCC/CSD at 98:2 ratio) as extragranular compression aids to address the processing and dissolution stability issues of this formulation. Methods: The compactibility and stickiness upon compression over extended period of time as well as the dissolution of R411 formulations incorporating the aforementioned compression aids were investigated. In addition, the water sorption/desorption properties of these compression aids were determined. Results: All formulations showed comparable compactibility irrespective of the compression aid used. Nevertheless, MCC alone or in a physical mixture with CSD showed sticking of the lower punches, whereas SMCC resulted in clean punch surface during extended compression runs. Furthermore, the three compression aids were compared for their effect on dissolution stability after storage at stress conditions. The formulations containing SMCC provided superior dissolution stability over the other compression aids evaluated in the study. Conclusions: Novel functionalities of SMCC are presented in terms of sticking prevention while having the most beneficial effect on dissolution stability in R411 formulation.     

微晶纤维素的制备及性质研究

分别用HCl和H2SO4处理从棉纤维和稻秆中提取的纤维素，制备得到微晶纤维素。研究了酸处理对微晶纤维素的聚合度、结晶度、体积密度和热稳定性的影响．X射线衍射结果表明，纤维素微晶化后仍保持原来的晶型和晶区和非晶区两相共存的微细结构。扫描电子显微镜测试结果表明，不同原料，酸处理后所得产物的形态不同．     

Weight and weight uniformity of hard gelatin capsules filled with microcrystalline cellulose and silicified microcrystalline cellulose

The objective of this study was to investigate the weight and weight uniformity of hard gelatin capsules filled with microcrystalline cellulose (MCC) and silicified microcrystalline cellulose (SMCC) powdered formulations. A tamping-type encapsulation apparatus was used to fill the capsules. The four formulations that were tested included MCC alone, MCC blended with fumed silica, SMCC, and high-density SMCC (SMCC-HD). The mean capsule weight and the average variation in mean capsule weight of each formulation were determined. Both SMCC products exhibited better flow than the MCC alone, with SMCC-HD being the freest flowing of the powders investigated. Capsules filled with the SMCC products had higher fill weights than those containing the MCC powders. The SMCC-containing capsules exhibited the lowest variation in weight, although these findings were not significantly different from either of the MCC-containing capsules. Significantly higher weight variations were found in capsules filled with SMCC-HD. A relationship between Carr's compressibility index and capsule weight variation was found, with more compressible materials producing more uniformly filled capsules. No relationship could be established between powder flow and capsule weight uniformity. These findings suggest that powder flow may not be a critical parameter in ensuring capsule weight uniformity when the encapsulation equipment utilizes a tamping-type filling system.     

Inkjet printed surface enhanced Raman spectroscopy array on cellulose paper

A novel, ultra low-cost surface enhanced Raman spectroscopy (SERS) substrate has been developed by modifying the surface chemistry of cellulose paper and patterning nanoparticle arrays, all with a consumer inkjet printer. Micro/nanofabrication of SERS substrates for on-chip chemical and biomolecular analysis has been under intense investigation. However, the high cost of producing these substrates and the limited shelf life severely limit their use, especially for routine laboratory analysis and for point-of-sample analysis in the field. Paper-based microfluidic biosensing systems have shown great potential as low-cost disposable analysis tools. In this work, this concept is extended to SERS-based detection. Using an inexpensive consumer inkjet printer, cellulose paper substrates are modified to be hydrophobic in the sensing regions. Synthesized silver nanoparticles are printed onto this hydrophobic paper substrate with microscale precision to form sensing arrays. The hydrophobic surface prevents the aqueous sample from spreading throughout the paper and thus concentrates the analyte within the sensing region. A SERS fingerprint signal for Rhodamine 6G dye was observed for samples with as low as 10 femtomoles of analyte in a total sample volume of 1 μL. This extraordinarily simple technique can be used to construct SERS microarrays immediately before sample analysis, enabling ultra low-cost chemical and biomolecular detection in the lab as well as in the field at the point of sample collection.     

A study on water adsorption onto microcrystalline cellulose by near-infrared spectroscopy with two-dimensional correlation spectroscopy and principal component analysis

Water adsorption onto microcrystalline cellulose (MCC) in the moisture content (M(c)) range of 0.2-13.4 wt % was investigated by near-infrared (NIR) spectroscopy. In order to distinguish heavily overlapping O-H stretching bands in the NIR region due to MCC and water, principal component analysis (PCA) and generalized two-dimensional correlation spectroscopy (2DCOS) were applied to the obtained spectra. The NIR spectra in four adsorption stages separated by PCA were analyzed by 2DCOS. For the low M(c) range of 0.2-3.1 wt %, a decrease in the free or weakly hydrogen-bonded (H-bonded) MCC OH band, increases in the H-bonded MCC OH bands, and increases in the adsorbed water OH bands are observed. These results suggest that the inter- and intrachain H-bonds of MCC are formed by monomeric water molecule adsorption. In the M(c) range of 3.8-7.1 wt %, spectral changes in the NIR spectra reveal that the aggregation of water molecules starts at the surface of MCC. For the high M(c) range of 8.1-13.4 wt %, the NIR results suggest that the formation of bulk water occurs. It is revealed from the present study that approximately 3-7 wt % of adsorbed water is responsible for the stabilization of the H-bond network in MCC at the cellulose-water surface.     

Applications of low frequency dielectric spectroscopy to the pharmaceutical sciences

Low frequency dielectric spectroscopy (LFDS) is an analytical technique which has found considerable application in the study of pharmaceutical systems. In this article, an outline of the theoretical and practical aspects of the method will be given, as well as a discussion of the advantages and disadvantages of the technique. Examples will be given of how LFDS may be used in the analysis of pharmaceutical systems, including studies on solid dispersions, inter-batch variation, liposome suspensions and cyclodextrins.     

Applications of low frequency dielectric spectroscopy to the pharmaceutical sciences

Abstract

Low frequency dielectric spectroscopy (LFDS) is an analytical technique which has found considerable application in the study of pharmaceutical systems. In this article, an outline of the theoretical and practical aspects of the method will be given, as well as a discussion of the advantages and disadvantages of the technique. Examples will be given of how LFDS may be used in the analysis of pharmaceutical systems, including studies on solid dispersions, inter-batch variation, liposome suspensions and cyclodextrins.     

Extrudate fracture and spheronisation of microcrystalline cellulose pastes

An experimental study of the ram extrusion and subsequent spheronisation of water-based microcrystalline cellulose (MCC) pastes has been performed. The effects of extrusion velocity, die geometry, and paste water content on the integrity of the extrudate produced were investigated. The apparent severity of extrudate fracture increased with decreasing die length/diameter ratio (L/D), and increasing extrusion velocity. The spacing between the fractures was approximately constant for a given set of process conditions, and increased with increasing émph{L/D} and decreasing extrusion velocity, whilst the flare of the extrudate fracture segment increased with decreasing émph{L/D} and increasing extrusion velocity. Two types of fracture shape were identified, émph{viz}. knuckle-bones and cups, the occurrence of which is explained in terms of the relative extent of the radial and axial strain release at the surface of the extrudate upon exiting the die.The shape and size distributions of the corresponding spheronised pellets were analysed and related to the geometry of the extrudate fracture segments. Severe knuckle-bone fracture gave spherical pellets with a wide size distribution. Visibly smooth extrudates gave non-spherical pellets with an apparently narrow size distribution (as measured by sieving). Extrudates displaying the cup type of fracture generated the best quality pellets in terms of both sphericity and size distribution.     

Effect of temperature and frequency on the dielectric properties of cellulose nanofibers from cotton

The present work has been carried out to evaluate the dielectric properties and ac-electrical conductivity of cellulose nanofibers. The cellulose nanofibers (CNF) described in this work are the ones extracted from cotton via a simple acid hydrolysis method and are characterized with X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and UV–Visible diffuse reflectance spectroscopy. The optical band gap of CNF found out using the Kubelka–Munk plot is 3.30 eV. The dielectric constant, dielectric loss, and ac-electrical conductivity of the prepared CNF have been investigated in the temperature range from 30 °C to 300 °C and in the frequency range from 50 Hz to 5 MHz. The synthesized system exhibits a higher dielectric constant value for all temperatures in the low-frequency (0.1 kHz) region and a frequency-independent behavior above 10 kHz. In the high-frequency region, the dielectric constant is independent of temperature. Also, the study shows that the conductivity increases with increasing frequency and temperature. The maximum values of ac-conductivity at room temperature (30 °C) and high temperature (300 °C) are found to be 4.58?×?10^–5 S/cm and 2.26?×?10^–4 S/cm, respectively. In brief, the studies point to the application potential of CNF for future flexible electronics.

     

Low frequency dielectric spectroscopy of bitumen binders as an indicator of adhesion potential to quartz aggregates using Portland cement

The purpose of this investigation was to interpret the bitumen-aggregate adhesion based on the dielectric spectroscopic response of individual material components utilizing their dielectric constants, refractive indices and average tangent of the dielectric loss angle (average loss tangent). Dielectric spectroscopy of bitumen binders at room temperature was performed in the frequency range of 0.01–1000 Hz. Dielectric spectroscopy is an experimental method for characterizing the dielectric permittivity of a material as a function of frequency. Adhesion data has been determined using the Rolling bottle method. The results show that the magnitude of the average tangent of the dielectric loss angle (average loss tangent) depends on bitumen type. The average loss tangent in the frequency range 0.01–1 Hz is introduced as a potential indicator for predicting polarizability and, thereby, adhesion potential of bitumen binders to quartz aggregates when using Portland cement. In order to obtain acceptable adhesion of 70/100 penetration grade bitumen binders and quartz aggregates when using Portland cement, it is suggested that the binder have an average tan δ > 0.035 in the frequency range 0.01–1 Hz.     

高强度透明纳米纤维素纸的制备与性能表征

以毛竹为原料,采用高压均质法、微滤沉积法、聚乙烯醇基体抛光法制备透明的纳米纤维素纸(透明纸)。通过SEM、拉伸试验和UV-Vis测量系统分析了纳米纤维素纸的微观形貌与其力学性能和透光率的相应关系。研究结果表明,多孔网状的纳米纤维素纸(纳米纸)以及抛光处理后的透明纸与传统的A4复印纸相比有着高的拉伸强度,并且网络伸展使其断裂伸长率也有所提高。透明纸的弹性模量和拉伸强度分别为(1.31±0.35)GPa和(120.3±2.1)MPa。同时,采用聚乙烯醇高透明性基体抛光处理对纳米纸的透光性有着明显的改善,透明纸在600nm处的透光率为65%。这种高强度透明纳米纸在柔性光电材料领域有着一定的应用潜力。     

Low frequency dielectric relaxation study in PMMA/PS blends

The dielectric behaviour of solution-grown films of poly (methyl methacrylate) (PMMA)-polystyrene (PS) blends has been studied as a function of frequency and temperature. The obtained results show that the β process observed in the PMMA/PS system is associated with the PMMA fraction in the blend. From the dielectric results we found that the local conformational states of the PMMA chain are perturbed by blending with a PS content higher than 9–13%, as a result of the incompatibility of this system.     

Deformation mechanisms in cellulose fibres, paper and wood

The use of Raman spectroscopy in probing the deformation mechanisms of cellulose fibres (regenerated and natural), and two natural cellulose composite systems (wood and paper) is described. It is shown that during tensile deformation the 1095 cm^–1 Raman band, corresponding to the stretching of the cellulose ring structure, shifts towards a lower wavenumber due to molecular deformation. By analysing a number of fibres with different microstructures this shift is shown to be invaluable in understanding the micromechanisms of deformation in these materials. Moreover, the rate of Raman band shift is shown to be invariant with stress for all fibre types, consistent with a fibre microstructure based on a modified series aggregate model. In the composite systems, such as wood and paper, it is shown that the stress-induced Raman band shift in the cellulose gives an important insight into their local deformation micromechanics.     

Low frequency ac conduction and dielectric relaxation in poly(N-methyl pyrrole)

The ac conductivity and dielectric constant of poly(N-methyl pyrrole) thin films have been investigated in the temperature range 77–350 K and in the frequency range 10 ²-10² Hz. The well defined loss peaks have been observed in the temperature region where measured ac conductivity approaches dc conductivity. These loss peaks are associated with the hopping of the charge carriers. The frequency and temperature dependence of ac conductivity have been qualitatively explained by considering the contribution from two mechanisms; one giving a linear dependence of conductivity on frequency and other having distribution of relaxation times giving rise to broad dielectric loss peak. Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore.     

Non destructive evaluation of adhesively bonded composite structures using high frequency dielectric spectroscopy

Over the last ten years, the application of high frequency dielectric techniques for the assessment of adhesively bonded structures has been investigated. The technique has been used for the study of adhesively bonded aluminium structures and its application to carbon fibre reinforced plastic (CFRP) bonded structures forms the basis of this paper. The electrical conductivity of the carbon fibres in the CFRP composite materials is sufficiently high for adhesively bonded structures to exhibit the properties of a wave-guide. The non-conductive adhesive behaves as a dielectric. The time domain data allows the integrity of the structure to be explored and is sensitive to the orientation of the fibres at the adherent-adhesive interface. Furthermore, a good correlation is shown between time domain dielectric spectroscopy and gravimetric results. This study indicates that the success obtained in the application of high frequency dielectric measurements to adhesively bonded aluminium structures is also applicable to CFRP bonded structures. The dielectric studies not only indicate a new way to assess the state of such a structure but also are producing new insight into the application of dielectric time domain response (TDR) measurement to non-isotropic materials.