Crystallinity index of microcrystalline cellulose particles compressed into tablets

A mini-review on the dielectric properties of cellulose and nanocellulose-based materials as electronic components

Cellulose-based materials have the advantages of renewable, non-toxic, flexible, and strong mechanical properties, so it of is great significance to study the dielectric properties of cellulose-based materials. In this paper, we summarized the factors influencing the dielectric properties of cellulose and nanocellulose-based dielectric and the ways to change the dielectric properties, mainly exploring the methods to improve the dielectric constant of cellulose-based dielectric materials. Cellulose and nanocellulose-based dielectric need to improve the hygroscopic property, increase the flexibility and reduce dielectric loss of the composite materials. This review summarizes the current state-of-art progress of new dielectric materials for green energy storage and flexible electronic devices.

Use of Atomic Force Microscopy (AFM) to monitor surface crystallization in caffeine-oxalic acid (CAFOXA) cocrystal compacts

Our objective was to monitor the surface crystallization in disordered caffeine-oxalic acid (CAFOXA) cocrystals following exposure to elevated water vapor pressure. This was accomplished using atomic force microscopy (AFM). Disorder was induced in the cocrystal particles by the common pharmaceutical unit operations of milling and compaction. The 'activated' solid, upon exposure to elevated water vapor pressure, had a high propensity to sorb water. This led to a rise in molecular mobility and the surface underwent rapid crystallization to form needle shaped crystals of CAFOXA. Using AFM height and phase imaging, we were able to directly visualize phase transformations on the compact surface. The milled compacts exhibited higher processing induced disorder than the unmilled compacts, thereby accelerating the surface recrystallization.

Wound Healing Composite Materials of Bacterial Cellulose and Zinc Oxide Nanoparticles with Immobilized Betulin Diphosphate

A design of new nanocomposites of bacterial cellulose (BC) and betulin diphosphate (BDP) pre-impregnated into the surface of zinc oxide nanoparticles (ZnO NPs) for the production of wound dressings is proposed. The sizes of crystalline BC and ZnO NPs (5-25%) corresponded to 5-6 nm and 10-18 nm, respectively (powder X-ray diffractometry (PXRD), Fourier-infrared (FTIR), ultraviolet (UV), atomic absorption (AAS) and photoluminescence (PL) spectroscopies). The biological activity of the wound dressings "BC-ZnO NPs-BDP" was investigated in rats using a burn wound model. Morpho-histological studies have shown that more intensive healing was observed during treatment with hydrophilic nanocomposites than the oleophilic standard (ZnO NPs-BDP oleogel; p < 0.001). Treatment by both hydrophilic and lipophilic agents led to increases in antioxidant enzyme activity (superoxide dismutase (SOD), catalase) in erythrocytes and decreases in the malondialdehyde (MDA) concentration by 7, 10 and 21 days (p < 0.001). The microcirculation index was restored on the 3rd day after burn under treatment with BC-ZnO NPs-BDP wound dressings. The results of effective wound healing with BC-ZnO NPs-BDP nanocomposites can be explained by the synergistic effect of all nanocomposite components, which regulate oxygenation and microcirculation, reducing hypoxia and oxidative stress in a burn wound.

Microfibrillated cellulose from Argania spinosa shells as sustainable solid particles for O/W Pickering emulsions

Microfibrillated cellulose (MFC) from Argan (Argania spinosa) shells was prepared by chemical purification of cellulose, then mechanical disintegration via high pressure homogenization was performed to isolate fibrils of cellulose. Chemical characterization of raw argan shell (AS-R), purified cellulose (AS-C), and argan shell MFC (AS-MFC) included FT-IR, XRD and NMR. Morphological characterization of AS-MFC was assessed using TEM. Next, the use of AS-MFC as oil-in-water (O/W) emulsions stabilizer was investigated. The particle concentration was observed to affect the long-term stability of the emulsions; high concentrations (0.5-1 % w/w) of AS-MFC resulted in emulsions that were thermodynamically stable during 15 days of storage, which was demonstrated by the droplet's size evolution. The suitable oil concentration for a maximum volume of emulsion using 1 % w/w AS-MFC was demonstrated. The results show that AS-MFC is able to stabilize 70 % w/w MCT oil without visual phase separation. Finally, CLSM shows the adsorption of AS-MFC at the oil-water interface and the formation of a 3D network surrounding oil droplets, confirming Pickering emulsion formation and stabilization.

Investigation into powder tribo-charging of pharmaceuticals. Part I: Process-induced charge via twin-screw feeding

Powder feeding is a crucial unit operation in continuous manufacturing (CM) of pharmaceutical products. Twin-screw feeders are typically employed to ensure the accurate mass flow of pharmaceutical materials throughout the production process. Here, contact and separation of particles can give rise to electrostatic charges, affecting feeder performance and final product quality. The knowledge of the material charging tendency would therefore be beneficial for both formulation and process design. At the early stage of product development, only a limited amount of material is available and the propensity of the powders to charge needs to be assessed on lab test equipment, which not necessarily represent the material state during processing. In this study, the tribo-charging behaviour of a set of common pharmaceutical materials (i.e., microcrystalline cellulose, D-mannitol, paracetamol and magnesium stearate) was experimentally evaluated. To this end, powder materials were let to flow over the stainless-steel pipes of the GranuCharge™ instrument. The resulting charge was compared to the one acquired during twin-screw feeding. In both cases, paracetamol exhibited the highest charging tendency followed by D-mannitol and microcrystalline cellulose and last by magnesium stearate. A good correlation was found for charge values obtained for both methods, despite the different tribo-charging mechanisms involved in the two set-ups. However, these differences in experimental set-ups led to diverse magnitudes and, in one case, polarity of charge. Additionally, an extensive material characterization was performed on the selected powders and results were statistically analyzed to identify critical material attributes (CMAs) affecting powder tribo-charging. A strong correlation was obtained between the measured charge and inter-particle friction. This indicated the latter as one of the most influencing material characteristic impacting the powder tribo-charging phenomenon of the selected materials.

A New Perspective of Multiple Roller Compaction of Microcrystalline Cellulose for Overcoming Re-Compression Drawbacks in Tableting Processing

In this paper, new scientific insights in relation to the re-compaction of microcrystalline cellulose (MCC; Avicel®® PH-101) under specific compaction conditions are reported. MCC was subjected to multiple compaction cycles (1st, 2nd, and 3rd) under high compaction pressures, up to 20,000 kPa, using a roller compactor of 100 kg/h capacity. Initially, granules from the 1st and 2nd compaction cycles produced tablets with lower crushing strength compared to those made from the original non-compacted MCC. Tablet weakness was found to be correlated to the generation of a higher intra-granular pore size (diameter) and hence higher tablet porosity compared to that of the original MCC particles. Using Kawakita and Heckel compression analyses, it is suggested that such behavior is attributed to the formation of harder granules of re-compressed powder with a larger diameter than non-compacted MCC particles. Moreover, these granules resulted in a reduction in powder bed volume after the powders were subjected to the 1st and 2nd compaction cycles. Surprisingly, granules resulting from the 3rd compaction cycle produced tablets displaying a higher crushing force than non-compacted MCC. Results from compression analysis indicated a reduction in both the intra-granular pore size (diameter) and in tablet porosity of Avicel PH-101-3rd compaction cycle compared to that of the original non-compacted MCC. It is concluded that intense compression causes shedding of one or more layer from MCC fibers exposing new surfaces with strong binding ability. The foregoing results infer that intensified roller compaction can be employed to improve MCC powder compactibility without any deleterious effects on compact strength.

Biocomposites Produced from Hardwood Particles by Equal Channel Angular Pressing Without Additives

Equal channel angular pressing (ECAP) has been shown to be a promising method for producing biocomposites from wood particles. However, severe plastic deformation during ECAP would cause considerable cracking when consolidation is carried out without a binder. In this study, the processing conditions were investigated for ECAP of hardwood particles into bulk biocomposites without any additives. Crack formation and wood cell deformation were examined in conjunction with thermal stability and crystallinity of the biocomposites. In comparison with hot pressing without severe shearing, a decrease in crystallinity and severe deformation of wood cells occurred during ECAP. Improved processability and homogeneous deformation would occur at high ECAP temperature (e.g., 210 °C) or low ECAP speed (e.g., 10 mm/min), leading to reduced crack formation in the ECAP-produced biocomposites. Despite its tendency to cause periodic cracking, effective plastic deformation in the regions between cracks was shown to improve interparticle binding. Ongoing research points to the potential achievement of crack-free hardwood (HW) consolidated without a binder, leading to significantly enhanced strength.

A Study of the Physical and Mechanical Properties of Aerogels Obtained from Bacterial Cellulose

Aerogels with a density of 4.2-22.8 kg/m³ were obtained from bacterial cellulose synthesized under static and dynamic cultivation conditions on a molasses medium. The strength properties and porous structure of the aerogels strongly depended on their density. With an aerogel density of 22.8 kg/m³, the modulus of elasticity at 80% compression of the sample was 0.1 MPa. The decrease in the density of aerogels led to an increase in the pore sizes ranging from 20 to 1000 μm and a decrease in the modulus of elasticity. These characteristics were more pronounced in aerogels obtained from bacterial cellulose under static cultivation conditions. The aerogels had a low coefficient of thermal conductivity (0.0257 W m^-1 °C^-1), which is comparable to the thermal conductivity of air, and moderate thermal stability because the degradation processes of the aerogels began at 237 °C. The aerogels obtained from bacterial cellulose had high sound absorption coefficients in the frequency range of 200-5000 Hz, which makes it possible to use the aerogels as heat- and sound-insulating materials.

Transport Properties of Commercial Cellulose Nanocrystals in Aqueous Suspension Prepared from Chemical Pulp via Sulfuric Acid Hydrolysis

A cellulose nanocrystal (CNC) sample prepared from chemical pulp via sulfuric acid hydrolysis procedures has been supplied by InnoTech Alberta Inc. in the shape of white dry powder as a prototype product. Some transport coefficients were precisely investigated for the CNC sample in aqueous suspensions at the room temperature of 25 °C such as the average rotational and translational diffusion coefficients (D _r and D _t) and viscoelastic relaxation times (τ_v) at dilute conditions. The determined values, D _r ≈ 2.3 × 10³ s^-1 and D _t ≈ 1.0 × 10^-11 m² s^-1, using depolarized and usual dynamic light scattering (DLS) techniques, respectively, proposed the consistent length and width of L ≈ 170 nm and W ≈ 7.6 nm via a theoretical model for monodisperse rigid rods dispersed in pure water. The viscoelastic behavior for aqueous CNC suspensions containing spherical probe particles was examined using DLS rheological techniques. The obtained value of τ_v = 1.0 × 10^-4 s fairly agrees with that of (6D _r)^-1 ≈ 7.4 × 10^-5 s. Because the theoretical model for monodisperse rods denotes the relationship τ_v = (6D _r)^-1, this observation strongly confirms that the CNC sample behaves as approximately monodisperse rigid rodlike particles. Transmission electron microscopy (TEM) images clearly demonstrated a bimodal distribution in rod length with major and small minor peaks at ca. 150 and 240 nm, respectively. Then, the reason for the observed disagreement between the L values resulted from the transport coefficients and the major peak in TEM images is the presence of the small minor component with L ≈ 240 nm. Consequently, individual nanosize rodlike crystalline particles in the CNC sample well disperse without forming large aggregations because of strong interactions and behave as isolated individual rods in dilute aqueous suspensions.

Effect of Porosity on Strength Distribution of Microcrystalline Cellulose

Fracture strength of pharmaceutical compacts varies even for nominally identical samples, which directly affects compaction, comminution, and tablet dosage forms. However, the relationships between porosity and mechanical behavior of compacts are not clear. Here, the effects of porosity on fracture strength and fracture statistics of microcrystalline cellulose compacts were investigated through diametral compression tests. Weibull modulus, a key parameter in Weibull statistics, was observed to decrease with increasing porosity from 17 to 56 vol.%, based on eight sets of compacts at different porosity levels, each set containing ∼ 50 samples, a total of 407 tests. Normal distribution fits better to fracture data for porosity less than 20 vol.%, whereas Weibull distribution is a better fit in the limit of highest porosity. Weibull moduli from 840 unique finite element simulations of isotropic porous materials were compared to experimental Weibull moduli from this research and results on various pharmaceutical materials. Deviations from Weibull statistics are observed. The effect of porosity on fracture strength can be described by a recently proposed micromechanics-based formula.

Solid-, solution-, and gas-state NMR monitoring of ¹³C-cellulose degradation in an anaerobic microbial ecosystem

Anaerobic digestion of biomacromolecules in various microbial ecosystems is influenced by the variations in types, qualities, and quantities of chemical components. Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for characterizing the degradation of solids to gases in anaerobic digestion processes. Here we describe a characterization strategy using NMR spectroscopy for targeting the input solid insoluble biomass, catabolized soluble metabolites, and produced gases. ¹³C-labeled cellulose produced by Gluconacetobacter xylinus was added as a substrate to stirred tank reactors and gradually degraded for 120 h. The time-course variations in structural heterogeneity of cellulose catabolism were determined using solid-state NMR, and soluble metabolites produced by cellulose degradation were monitored using solution-state NMR. In particular, cooperative changes between the solid NMR signal and ¹³C-¹³C/¹³C-¹²C isotopomers in the microbial degradation of ¹³C-cellulose were revealed by a correlation heat map. The triple phase NMR measurements demonstrated that cellulose was anaerobically degraded, fermented, and converted to methane gas from organic acids such as acetic acid and butyric acid.

Crystalline and amorphous cellulose in the secondary walls of Arabidopsis

In the cell walls of higher plants, cellulose chains are present in crystalline microfibril, with an amorphous part at the surface, or present as amorphous material. To assess the distribution and relative occurrence of the two forms of cellulose in the inflorescence stem of Arabidopsis, we used two carbohydrate-binding modules, CBM3a and CBM28, specific for crystalline and amorphous cellulose, respectively, with immunogold detection in TEM. The binding of the two CBMs displayed specific patterns suggesting that the synthesis of cellulose leads to variable nanodomains of cellulose structures according to cell type. In developing cell walls, only CBM3a bound significantly to the incipient primary walls, indicating that at the onset of its deposition cellulose is in a crystalline structure. As the secondary wall develops, the labeling with both CBMs becomes more intense. The variation of the labeling pattern by CBM3a between transverse and longitudinal sections appeared related to microfibril orientation and differed between fibers and vessels. Although the two CBMs do not allow the description of the complete status of cellulose microstructures, they revealed the dynamics of the deposition of crystalline and amorphous forms of cellulose during wall formation and between cell types adapting cellulose microstructures to the cell function.

Films prepared from electrosterically stabilized nanocrystalline cellulose

Electrosterically stabilized nanocrystalline cellulose (ENCC) was modified in three ways: (1) the hydroxyl groups on C2 and C3 of glucose repeat units of ENCC were converted to aldehyde groups by periodate oxidation to various extents; (2) the carboxyl groups in the sodium form on ENCC were converted to the acid form by treating them with an acid-type ion-exchange resin; and (3) ENCC was cross-linked in two different ways by employing adipic dihydrazide as a cross-linker and water-soluble 1-ethyl-3-[3-(dimethylaminopropyl)] carbodiimide as a carboxyl-activating agent. Films were prepared from these modified ENCC suspensions by vacuum filtration. The effects of these three modifications on the properties of films were investigated by a variety of techniques, including UV-visible spectroscopy, a tensile test, thermogravimetric analysis (TGA), the water vapor transmission rate (WVTR), and contact angle (CA) studies. On the basis of the results from UV spectra, the transmittance of these films was as high as 87%, which shows them to be highly transparent. The tensile strength of these films was increased with increasing aldehyde content. From TGA and WVTR experiments, cross-linked films showed much higher thermal stability and lower water permeability. Furthermore, although the original cellulose is hydrophilic, these films also exhibited a certain hydrophobic behavior. Films treated by trichloromethylsilane become superhydrophobic. The unique characteristics of these transparent films are very promising for potential applications in flexible packaging and other high-technology products.

Charged nanoparticles as supramolecular surfactants for controlling the growth and stability of microcrystals

Microcrystals of desired sizes are important in a range of processes and materials, including controlled drug release, production of pharmaceutics and food, bio- and photocatalysis, thin-film solar cells and antibacterial fabrics. The growth of microcrystals can be controlled by a variety of agents, such as multivalent ions, charged small molecules, mixed cationic-anionic surfactants, polyelectrolytes and other polymers, micropatterned self-assembled monolayers, proteins and also biological organisms during biomineralization. However, the chief limitation of current approaches is that the growth-modifying agents are typically specific to the crystalizing material. Here, we show that oppositely charged nanoparticles can function as universal surfactants that control the growth and stability of microcrystals of monovalent or multivalent inorganic salts, and of charged organic molecules. We also show that the solubility of the microcrystals can be further tuned by varying the thickness of the nanoparticle surfactant layers and by reinforcing these layers with dithiol crosslinks.

Characterization of milled wood lignin (MWL) in Loblolly pine stem wood, residue, and bark

Milled wood lignin samples from Loblolly pine stem wood, forest residue, and bark were isolated and characterized by quantitative (13)C and (31)P nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC) for molecular weight determination. Results from (13)C NMR show the stem wood and forest residue samples have similar functional group contents. However, the bark has fewer methoxyl groups, β-O-4 structures, dibenzodioxocin, and side chains than the other two lignins. The bark lignin has the highest amounts of p-hydroxyphenyl (h) and C-5 condensed lignin, stem wood has the lowest, and the residue lies between. (31)P NMR analysis indicates that bark lignin contains more C-5 substituted phenolics and fewer aliphatic hydroxyl groups than the lignin isolated from stem wood or residue. The molecular weight distribution analysis indicates the bark lignin has higher weight-average molecular weight (M(w)) and polydispersity index than the lignin recovered from stem wood or residue.

Investigation of Metformin HCl lot-to-lot variation on flowability differences exhibited during drug product processing

The purpose of this study was to determine the cause for flowability difference observed during drug product processing when different Metformin HCl drug substance batches of varying age were used. It was found that the lead time (age) between the final step (milling) in the manufacturing process of the Metformin HCl drug substance could be a factor. The lead time had an impact on flowability of Metformin/excipient blends during drug product processing even though these batches had no apparent differences in their release specifications. To study and understand the aging effect, two batches of Metformin HCl manufactured at different periods of time were selected. The surface energy values obtained by the density functional theory (DFT) method together with X-ray diffraction patterns, thermally stimulated current measurements, and dynamic vapor sorption isotherms indicated that the freshly manufactured Metformin HCl material contains detectable amounts of surface crystal defects, but are absent in aged sample, which could be the cause of flowability differences of Metformin/excipient blends observed during the drug product processing. Having identified the cause for different flow behavior, a method to destroy these defects was designed and the issue was resolved by rapid aging of Metformin HCl under humidity at room temperature.

Analytical techniques for quantification of amorphous/crystalline phases in pharmaceutical solids

The existence of different solid-state forms such as polymorphs, solvates, hydrates, and amorphous form in pharmaceutical drug substances and excipients, along with their downstream consequences in drug products and biological systems, is well documented. Out of these solid states, amorphous systems have attracted considerable attention of formulation scientists for their specific advantages, and their presence, either by accident or design is known to incorporate distinct properties in the drug product. Identification of different solid-state forms is crucial to anticipate changes in the performance of the material upon storage and/or handling. Quantitative analysis of physical state is imperative from the viewpoint of both the manufacturing and the regulatory control aimed at assuring safety and efficacy of drug products. Numerous analytical techniques have been reported for the quantification of amorphous/crystalline phase, and implicit in all quantitative options are issues of accuracy, precision, and suitability. These quantitative techniques mainly vary in the properties evaluated, thus yielding divergent values of crystallinity for a given sample. The present review provides a compilation of the theoretical and practical aspects of existing techniques, thereby facilitating the selection of an appropriate technique to accomplish various objectives of quantification of amorphous systems.

Solid state NMR and DSC methods for quantifying the amorphous content in solid dosage forms: an application to ball-milling of trehalose

The purpose of this study was to determine quantitatively the amorphous fraction in crystalline-amorphous powder mixtures of trehalose, in order to assess the ability of the (13)C NMR technique for quantitative amorphous characterization. The NMR method is described in detail and its accuracy is compared to that of the DSC technique. Amorphous trehalose was prepared by mechanical milling. Samples with different amorphous fractions were prepared by physical mixing of purely amorphous and purely crystalline powders. The results reveal a close correlation between the imposed compositions of the physical mixtures and those determined by NMR and DSC, indicating that both are useful and accurate methods for compositional characterization of powders. The NMR method is then used to determine the evolution of the amorphous fraction in a trehalose powder, during a milling procedure which ultimately leads to a fully amorphous state.

Evaluation of Surface and Bulk Characteristics of Cellulose I Powders in Relation to Compaction Behavior and Tablet Properties

The particle properties and solid-state characteristics of two celluloses, Avicel PH101 and cellulose obtained from the alga Cladophora sp., were evaluated and related to the compaction behavior and the properties of the tablets made from them. The surface area of the celluloses was measured at different levels of penetration capacity, ranging from external surface area of particles to molecular texture with Blaine permeametry, Kr-gasadsorption, and solid-state NMR. The important cellulose fibril surface area was best reflected by solid-state NMR, although for the Cladophora cellulose, Kr-gas adsorption also resulted in a surface area of the order of what has been suggested earlier on the basis of the cellulose fibril dimensions. The difference in fibril dimension and, thereby, the fibril surface area of the two celluloses was shown to be the primary factor in determining their properties and behavior. Properties such as the crystallinity and the tablet disintegration could be related to the fibril dimensions. The Cladophora cellulose resulted in rather strong compacts that still disintegrated rapidly. The irregular surface morphology of the particles and the fragmenting behavior of Cladophora probably contributed to the strength of the tablets.

Assessment of amorphous content by microcalorimetry

The amorphous content of model drugs was evaluated by isotherm microcalorimetry. Two model drugs were employed; lactose as a hydrophilic one and erythromycin as a hydrophobic one. When amorphous lactose was loaded in a sample cell with a water vial, a sharp exothermic peak due to the crystallization was observed. When a mixture of the amorphous and the crystalline forms was loaded, the peak area of the exothermic heat flow was proportional to the amorphous content. Quantification could be done with much higher accuracy than by the X-ray powder diffraction method reported in earlier literature. When erythromycin was used as a model drug, the crystallization was not completed by water but by organic solvents, which can dissolve erythromycin. The most adequate solvent for erythromycin was acetonitrile, of which the suitability was elucidated in terms of solubility and vapor pressure. This is the first report in which the role of the vapor pressure on crystallization behavior is discussed. The time needed to obtain the crystallization peak was controlled by mixing acetonitrile with water. The strategy to obtain the crystallization peak by microcalorimetry, which enables quantification of the amorphous content with high accuracy, is discussed.

Directional bonding in compacted microcrystalline cellulose

The mechanical properties of compacts of microcrystalline cellulose (MCC) and silicified microcrystalline cellulose (SMCC) were evaluated by tensile testing, diametric compression testing, and compression testing. For tensile and compression testing, cubic specimens were carefully machined from MCC and SMCC compacts, and the tensile and compression strengths were evaluated both normal and parallel to the compaction direction. The cubic tensile strengths were compared to values obtained from the diametric compression test. The results obtained using the diametric compression test suggested compacts of SMCC exhibit greater strength than those of MCC. In addition, the cubes machined from compacts of MCC and SMCC exhibited directional strength; the direction normal to the compaction direction display ed the greater tensile strength, and the parallel direction had greater compression strength. The diametric compression test afforded strength values with reduced spread compared to the values collected from the cubic tensile test, suggesting that the errors involved in collecting diametric compression test data of compacts are less than those for the cubic tensile test. Analysis of the cubes using X-ray diffraction (XRD) suggested that they display directional structural anisotropy, with the direction normal to the compaction direction being more crystalline than the parallel direction. However, it is not clear whether the difference in the directional strength is solely a consequence of the increased crystallinity or a culmination of crystallographic and mechanical keying effects.

Cellulose crystallites

This article discusses advances in understanding the structural and physicochemical characteristics of suspensions of cellulose crystallites prepared by acid hydrolysis of natural cellulose fibres. Consideration of recent developments in visualization of crystallite ultrastructure may provide clues to suspension behavior. In addition, novel applications in a diverse range of fields are presented, from iridescent pigments to biomolecular NMR studies.

Characterisation of particle properties and compaction behaviour of hydroxypropyl methylcellulose with different degrees of methoxy/hydroxypropyl substitution

The particle characteristics and compaction behaviour of hydroxypropyl methylcellulose (HPMC) powders from two different suppliers were studied regarding effects of methoxy/hydroxypropyl substitution. Samples included Methocel K4M (low substitution ratio), E4M (medium) and F4M (high) and the corresponding substitution ratios from Metolose: 90 SH 4000, 60 SH 4000, and 65 SH 4000. Characterisation of the particle properties and compaction behaviour of the pure polymers suggested that reported differences in drug release behaviour of Methocel E4M compared with the other two powders may be related to the lower powder surface area, differing particle morphology and lower fragmentation propensity during compaction. In addition, compacts of Methocel E4M were weaker when tested in both axial and radial directions and had different porosity and elastic recovery properties. There were no differences between the polymers in degree of disorder, as evaluated by solid-state nuclear magnetic resonance spectroscopy. The different behaviour of Methocel E4M could, however, be related to the overall higher total degree of substitution of this polymer and in particular the high content of methoxy groups compared to the other polymers. The methoxy substituent is hydrophobic and may, when present in sufficiently high concentrations, change the particulate and mechanical properties of the powder, thus potentially affecting the compactability. The high content of methoxy groups might also decrease the development of inter- and intraparticulate hydrogen bonds during compaction, and suppress the actions of the hydrophilic hydroxypropyl groups, both of which could affect drug release.

The influence of engravings on the sticking of tablets. Investigations with an instrumented upper punch

The purpose of this study was to investigate the influence of engravings on the sticking of tablets. Therefore, an instrumented upper punch capable of measuring the pull-off force, which occurs when the punch detaches itself from the upper surface of a tablet, was equipped with small cones of different angles between the punch face and the cones' lateral face. The cones could be screwed into a threaded hole at the center of the punch face. The adhesion forces of two formulations known to stick to engravings during production increased with a greater steepness of the cones' lateral face. With microencapsulated acetylsalicylic acid, no quantitative differences could be found between the adhesion forces obtained with plain and modified punch faces, indicating that the sticking behavior of the substance was not affected by shear forces. Starch 1500 showed higher adhesion force signals in comparison to those obtained with a plain punch face. Microcrystalline cellulose, which gave no adhesion force signals with a plain punch face and did not stick to the cones, showed distinct pull-off signals. The instrumented upper punch equipped with shear cones is a valuable instrument for detecting the adhesion caused by engravings and is therefore a helpful tool for tablet formulation development and the design optimization of tablet identification.

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.

Characterization of compressibility and compactibility of poly(ethylene oxide) polymers for modified release application by compaction simulator

Poly(ethylene oxide) polymers (PEO) appear to have great potential for controlled release applications. These polymers are hydrophilic with good water solubility, low toxicity, and high swelling capacity. As part of formulation optimization for a large-scale solid dosage form production, physicomechanical characterization of PEO was undertaken using a compaction simulator. Heckel plots for all PEOs were constructed, and yield pressures (Py) at different punch velocities were calculated from the linear portion of the plots. Low Py values, increase of Py with increasing punch speed, upward curvature of the plot, and strain rate sensitivity values indicate that the densification process and consolidation mechanism for PEOs of various molecular weights (0.2 x 10(6) to 7 x 10(6)) are identical and follow plastic deformation. PEOs have a high degree of crystallinity (57-85%) and show significant axial recovery (15-25%) upon decompression and ejection. The low Py values (58-78 MPa) and low mean compaction pressures demonstrate that volume reduction (compressibility) under pressure is excellent. However, due to viscoelastic behavior and large axial expansion, tablets of relatively low tensile strength are produced. These observations suggest the need to blend PEO with highly compactible excipients in order to produce tables on a high-speed production press.