Cold compaction of polymeric powders in tapered dies

Tests involving the cold compaction of four polymeric powders in circular section tapered dies were carried out to study the force transmitted through the powders. It was found that the decreasing cross-sectional area could be used to compensate for the force loss in order to keep the transmitted pressure high but the effect was not as large as had been anticipated. The optimum angle of taper was found to be in the region of 75 to 80°. A mathematical model was developed for the compaction of plastic powders in tapered dies. It was found that an equation of the type

could be used to prodict the transmitted pressured in a tapered die from a knowledge of the compaction characteristics for a cylindrical die.     

Development of solid phase radioimmunoassay system using new polymeric magnetic micro-spheres

Magnetic particles were locally prepared by co-precipitation of Fe²⁺ and Fe³⁺ in an ammonia solution. The prepared microsphere were grafted with polyacrylamide acrylic acid by using gamma irradiation polymerization in presence of MBA as a cross linker. AFP antibody was immobilized on these beads and used as a solid phase in radioimmunoassay technique. The immunoreactivity of the developed assay was found to be influenced by different factors such as solid phase volume, incubation time, incubation temperature and storage period. A comparative study was performed between the developed assay system and others two ones. The maximum binding percent attained the value of 19.5% while the sensitivity was observed to be 1.3 IU/mL. The developed assay displayed acceptable precision estimated by repeated analysis of the quality control samples and the clinical samples analyzed by this assay showed a good correlation with that commercial kit (r = 0.998).     

Radial distribution function of freely jointed hard-sphere chains in the solid phase

Monte Carlo simulation is used to generate the radial distribution function of freely jointed tangent-bonded hard-sphere chains in the disordered solid phase for chain lengths of three, four, six, and eight segments. The data are used to create an accurate analytical expression of the total radial distribution function of the hard-sphere chains that covers a density range from the solidification point up to a packing fraction of 0.71. It is envisioned that the correlation will help further progress toward molecular thermodynamic treatment of the solid phase in general and toward perturbed chain theories for the solid phase, in particular.     

Temperature evolution during the compaction of calcium silicate hydrate powders using a compression calorimeter

Journal of Thermal Analysis and Calorimetry - Amorphous calcium silicate hydrate (CSH) undergoes contact-hardening property, i.e. the powder can be hardened by compression. A compression...     

An amine-derivatized, DOTA-loaded polymeric support for Fmoc solid phase peptide synthesis

An amine-derivatized DOTA has been used to modify the surface of a polymeric support for conventional solid phase peptide synthesis (SPPS) following standard Fmoc chemistry methods. This methodology was used to synthesize a peptide-DOTA conjugate that was demonstrated to be a PARACEST MRI contrast agent. Therefore, this synthesis methodology can facilitate Fmoc SPPS of molecular imaging contrast agents.     

Formation of various types of intergranular bond during the compaction of ultra-high-molecular-weight polyethylene reactor powders

The results of mechanical testing of compacted ultra-high-molecular-weight PE reactor powder in air and in adsorption-active liquid environments, which dramatically reduce the interfacial surface energy, were analyzed. The intergranular character of brittle fracture of the samples in air and in decane made it possible to assess the contribution from cohesive intergranular bonds to the overall strength (～75%). It was shown that the formation of intergranular bonds depends on the intensity of molecular mobility in the polymer. The strength of the compacted material was found to be determined to a great extent by the deformation of the boundary layers in contacting grains. The formation of the intergranular layers can be accompanied by such a deep structural rearrangement in the nascent material that the structure of the intergranular layers upon the compaction of various reactor powders with different physical-and-mechanical characteristics becomes approximately the same.     

Phenomena at the powder-wall boundary during die compaction of a fine oxide powder

Fine powders (particle size smaller than 0.1 μm) are often used for the fabrication of modern fine-grained ceramics. During die compaction of such fine powders, special phenomena at the powder-wall boundary can be expected because the size of the particles is of the same order as the size of the wall asperities. In the present paper, the principles of powder mechanics are applied to experimental results obtained with a fine ferric oxide powder. The appearance of a dense boundary layer on the surface of compacts could be related to the occurrence of powder failure during compaction at the die wall.     

Determination of dynamic and sliding friction, and observation of stick-slip phenomenon on compacted polymer powders during high-velocity compaction

Dynamic friction, sliding friction, and the stick-slip phenomenon have been studied on compacted polymer powders during high-velocity compaction. It is particularly important from a practical point of view to distinguish the stick-slip mechanism and the sliding mechanism which occur concurrently. A practical experimental system has been successfully developed to study the dry frictional force and to measure the sliding coefficient between the polymer powder particles and the die wall during high-velocity compaction. Two new components have been introduced as relaxation assists to improve the compaction process by reducing the frictional forces. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by giving a more homogeneous opposite velocity and a better locking of the powder bed in the compacted form with less change in dimensions. The subsequent movement of the particles can be reduced and the powder bed attains a higher density with a minimum total elastic spring-back. The relative time of the stick-slip phenomenon during the compacting stage is also reduced so that the time needed to transfer from an intermittent stick-slip state to a smooth sliding state is reduced and the powder bed slides smoothly. It was found that the dynamic, dry frictional force is intermittent (stick-slip mechanism) at low compaction rates but that at high compaction rates is becomes more smooth (sliding mechanism). Both mechanisms depend on the nature of the powder and on the compaction conditions. At the beginning of the compaction stage, the sliding coefficient decreases due to an increase in the radial to axial stress ratio until the maximum pressure has been reached. During the reorganization stage, more time is needed for large particles to move, rotate and slide due to their relatively large diameter and mass. As a result, the reorganization stage is extended and the stick-slip phenomenon is observed more with increasing particle size. Much better transfer of the pressure throughout the powder bed and less loss of pressure lead to a higher sliding coefficient due to the overall friction during the compaction process. It was found that the sliding coefficient is proportional to the density.

A more homogeneous density distribution in the compacted powder and a smaller pressure loss during compaction has a major influence on the sliding coefficient and on the quality of the compacted material.     

DSC studies of solid polymeric electrolytes

Relations are demonstrated between the conductivity, phase structure and thermal history of some solid polymeric electrolytes. The results obtained for systems based on commercially available polymers, e.g. (ethylene oxide), and for specially synthesized materials are presented. Special emphasis is placed on the correlation between the crystallinity, glass transition temperature, melting temperature and conduction properties of the polymeric electrolytes.This work was supported financially by the Rector of Warsaw University of Technology according to research program 503/164/220/1.     

Room-temperature structures of solid hydrogen at high pressures

By employing first-principles metadynamics simulations, we explore the 300 K structures of solid hydrogen over the pressure range 150-300 GPa. At 200 GPa, we find the ambient-pressure disordered hexagonal close-packed (hcp) phase transited into an insulating partially ordered hcp phase (po-hcp), a mixture of ordered graphene-like H(2) layers and the other layers of weakly coupled, disordered H(2) molecules. Within this phase, hydrogen remains in paired states with creation of shorter intra-molecular bonds, which are responsible for the very high experimental Raman peak above 4000 cm(-1). At 275 GPa, our simulations predicted a transformation from po-hcp into the ordered molecular metallic Cmca phase (4 molecules∕cell) that was previously proposed to be stable only above 400 GPa. Gibbs free energy calculations at 300 K confirmed the energetic stabilities of the po-hcp and metallic Cmca phases over all known structures at 220-242 GPa and >242 GPa, respectively. Our simulations highlighted the major role played by temperature in tuning the phase stabilities and provided theoretical support for claimed metallization of solid hydrogen below 300 GPa at 300 K.     

The evaluation of solid phase micro-extraction fibre types for the analysis of organic components in unburned propellant powders

This work describes the evaluation of various solid phase micro-extraction (SPME) fibre types for the detection of compounds originating from particles of unburned propellant powders. These compounds may also be found in association with organic gunshot residues (OGSR). Seven SPME fibres were assessed based on their ability to extract the compounds of interest (diphenylamine (DPA), 4-nitrodiphenylamine (4-NDPA), ethyl centralite (EC), nitroglycerin (NG) and dibutyl phthalate (DBP)) from four ammunition types across three calibres (9 mm, 5.56 mm and 7.62 mm). Extracts were analysed by gas chromatography/mass spectrometry (GC/MS). Results indicated that the 65 μm polydimethylsiloxane/divinylbenzene (PDMS/DVB) was the most suitable fibre type for the extraction of these compounds across the ammunition types tested. Optimal extraction time parameters were also assessed with a 35-min period determined to be suitable. A number of previously unreported considerations for extracting propellant powders and potentially OGSR related materials are discussed.     

Synthesis of YAP phase by a polymeric method and phase progression mechanisms

The phase formation kinetics of YAP (YAlO₃) synthesized through the polymeric precursor method was investigated by thermal analysis, X-ray diffraction and FT-IR spectroscopy. We demonstrated that the YAP synthesis is highly dependent on the heat and mass transport during all stages of the synthesis route. In the first stages, during the preparation of amorphous precursor, “hot spots” need to be suppressed to avoid the occurrence of chemical inhomogeneities. Very high heating rates combined with small amorphous particles are advantageous in the last stage during the formation of crystalline phase. We were able to synthesize nanosized particles of YAP single phase at temperatures around 1100 °C for future preparation of phosphors or ceramics for optics.     

Dynamics and flow-induced phase separation in polymeric fluids

The past few years have seen many advances in our understanding of the dynamics of polymeric fluids. These include improvements on the successful reptation theory; an emerging molecular theory of semiflexible chain dynamics; and an understanding of how to calculate and classify `phase diagrams' for flow-induced transitions. Experimentalists have begun mapping out the phase behavior of wormlike micelles, a `living' polymeric system, in flow: these systems undergo transitions into shear-thinning or shear-thickening phases, whose variety is remarkably rich and poorly understood. Polymeric ideas must be extended to include the delicate charge and composition effects which conspire to stabilize the micelles and are strongly influenced by flow.     

Effect of trifluoroacetic acid upon Boc-aminoacyl- and Box-peptidyl-resins. Description of a new polymeric support for solid phase peptide synthesis.

The behavior of Boc-aminoacyl- and Boc-peptidyl-OCH₂-resins towards TFA/CH₂Cl₂ solutions has been studied. The results obtained point out the difficulty of finding an optimum TFA concentration which achieves total deprotection without substantial acidolytic losses. The synthesis of a new polymeric support which minimizes this problem is described.