On the interlayer spacing collapse of Cloisite® 30B organoclay (original) (raw)
2011, Polymer Degradation and Stability
... Sara Filippi1*, Massimo Paci1, Giovanni Polacco1, Nadka Tzankova Dintcheva2, Pierluigi Magagnini1 1Dipartimento di Ingegneria Chimica, Chimica Industriale e Scienza dei ... above, was formed into 2 mm thick tablets of 20 mm diameter at room temperature with a Carver press ...
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Crystallographic control on the substructure of nacre tablets
Nacre tablets of mollusks develop two kinds of features when either the calcium carbonate or the organic portions are removed: (1) parallel lineations (vermiculations) formed by elongated carbonate rods, and (2) hourglass patterns, which appear in high relief when etched or in low relief if bleached. In untreated tablets, SEM and AFM data show that vermiculations correspond to aligned and fused aragonite nanogloblules, which are partly surrounded by thin organic pellicles. EBSD mapping of the surfaces of tablets indicates that the vermiculations are invariably parallel to the crystallographic a-axis of aragonite and that the triangles are aligned with the b-axis and correspond to the advance of the {010} faces during the growth of the tablet. According to our interpretation, the vermiculations appear because organic molecules during growth are expelled from the a-axis, where the Ca–CO3 bonds are the shortest. In this way, the subunits forming nacre merge uninterruptedly, forming chains parallel to the a-axis, whereas the organic molecules are expelled to the sides of these chains. Hourglass patterns would be produced by preferential adsorption of organic molecules along the {010}, as compared to the {100} faces. A model is presented for the nanostructure of nacre tablets. SEM and EBSD data also show the existence within the tablets of nanocrystalline units, which are twinned on {110} with the rest of the tablet. Our study shows that the growth dynamics of nacre tablets (and bioaragonite in general) results from the interaction at two different and mutually related levels: tablets and nanogranules.
Powder Technology 204 (2010) 124–130 pgt
The mechanical strength of three carbonate tablets constructed by uniaxial compaction is evaluated using a simple tester, specially designed, as a comparative method, to classify and establish correlations between the measured resistance and the physical and flow properties of each carbonate. The net compression work required to construct the tablets is also compared with the strength of the samples in order to relate it to powder's ability to convert the force applied into effective solid-solid bonds.
Effect of Particle Size on Tablety Weight and Hadness Variation
In order to observe the effect of the size of the powder particles or granule on tablet properties, i.e. tablet weight and hardness, three different sizes of Ascorbic Acid granules of Mesh #14, #30 and #40 have been used to produce tablets and the tablet weight and hardness have been studied with standard methods. It has been found from the result that the flowability and compressibility of the studied granules of Mesh #14, #30 and #40 are excellent. The tablet weight differs with a change in particle/ granule size. Tablet weight variation increases with a decrease in particle/ granule size. Smaller size particles/ granules result in higher tablet weight variation, whereas bigger size particles/ granules result in lower tablet weight variation. Tablet hardness increases with a decrease in particle/ granule size. Based on the tablet hardness, the granule of Mesh #30 is supposed to be better than the granules of Mesh #14 and #40 to be used for the production of specified tablets.
Cold extrusion as a continuous single-step granulation and tabletting process
European Journal of Pharmaceutics and Biopharmaceutics, 2001
The potential of cold extrusion as a continuous granulation/tabletting technique was investigated. Extrudates (B, 9 mm) were produced using twin-screw extrusion, cut manually into tablets (thickness, 4 mm) and dried at 258C for 20 h. a-Lactose monohydrate (200 M) was used as an excipient, PVP (Kollidon w K30) and water as binders, and hydrochlorothiazide as the model drug. The influence of formulation (water content, PVP addition, drug incorporation) and process (total input rate and screw speed) parameters on the process (torque, die pressure, visual evaluation of tablets) and on the tablet properties (tensile strength, friability, disintegration time, porosity) was evaluated. Formulation, as well as process parameters, affected the process feasibility, but had only a minor effect on the tablet properties at conditions that allowed continuous tablet production. All a-lactose monohydrate tablets formulated without and with PVP and produced at optimum conditions showed tensile strengths above 0.7 and 1.5 MPa, friabilities below 1.0 and 0.9%, and disintegration times below 1 and 8 min, respectively. This technique allows single-step granulation/tabletting of pure a-lactose monohydrate, indicating that cold extrusion could be used as alternative tablet production technique for ingredients with poor compaction properties. As the tablets prepared by extrusion have a much higher porosity compared with conventional tablets, this technique could also be useful for tablet production of formulations with poor disintegrating properties. q
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