Compaction behaviour of mannitol-cocoa powder mixtures and their resulting tablet strength and disintegration characteristics

Cocoa powder is an important ingredient in the confectionery industry and, mannitol is an alternative sugar alcohol. In this work, mannitol powder was mixed with cocoa powder and compacted into tablet form via the uniaxial die compaction process. The frictional, compaction, tablet mechanical and disintegration properties were studied due to their importance in characterizing the behaviour of the tablets during processing and its final product characteristics at varying mannitol contents. The composition of mannitol in the mannitol-cocoa tablet varied at 95% w/w, 50% w/w and 5% w/w, while pure 100% w/w mannitol and cocoa tablets were set as controls. The compaction pressures used in making the tablets varied at 37.67 MPa, 75.34 MPa, 113.01 MPa, 150.68 MPa and 188.35 MPa. The compaction behaviour of the powder during the compaction process was evaluated using the plastic work and the maximum ejection stress values. The tablet strength was determined using the tensile strength method and tablet disintegration study was also conducted. The results showed that the increase in the compaction pressures increased the plastic work, maximum ejection pressure, tablet strength and also its disintegration time. The tablet formed having 95% w/w mannitol composition exhibited the highest plastic work value of 10.32±0.01 J, highest maximum ejection pressure value of 4.4±0.06 MPa, highest tensile strength value of 1.06±0.04 MPa and shortest disintegration time of 171±51 s amongst the three different mannitol compositions studied. Meanwhile, the effects of mannitol composition in the tablet on these observed responses were also dependent upon the compaction pressures used during tablet formation. In conclusion, the addition of mannitol improved the tablet strength and shorten the disintegration time in the experimental range employed in this study.

Particulate Scale Numerical Investigation on the Compaction of TiC-316L Composite Powders

This paper presents a numerical investigation on the 2D uniaxial die compaction of TiC-316L stainless steel (abbreviated by 316L) composite powders by the multiparticle finite element method (MPFEM). The effects of TiC-316L particle size ratios, TiC contents, and initial packing structures on the compaction process are systematically characterized and analyzed from macroscale and particulate scale. Numerical results show that different initial packing structures have significant impacts on the densification process of TiC-316L composite powders; a denser initial packing structure with the same composition can improve the compaction densification of TiC-316L composite powders. Smaller size ratio of 316L and TiC particles (R316L/RTiC = 1) will help achieve the green compact with higher relative density as the TiC content and compaction pressure are fixed. Meanwhile, increasing TiC content reduces the relative density of the green compact. In the dynamic compaction process, the void filling is mainly completed by particle rearrangement and plastic deformation of 316L particles. Furthermore, the contacted TiC particles will form the force chains impeding the densification process and cause the serious stress concentration within them. Increasing TiC content and R316L/RTiC can create larger stresses in the compact. The results provide valuable information for the formation of high-quality TiC-316L compacts in PM process.

Materials characterization of advanced fillers for composites engineering applications

Four different minerals were investigated; hollow spheres of calcium carbonate, platy mica, needle like wollastonite and glassy perlite and characterized via iGC for surface energy, Freeman powder rheology for flow characterization, cyclic uniaxial die compaction for modulus of elasticity and frequency dependent sound absorption properties. Particle surface energy and particle shape strongly affected the packing density of powder beds. In the case of higher porosity and thus lower bulk density, the powders acoustic absorption was higher in comparison with higher packing density materials. Surface energy profiles and surface energy distributions revealed clear convergence with powder rheology data, where the character of the powder flow at defined consolidation stresses was mirroring either the high cohesion powders properties connected with the high surface energy or powder free flowing characteristics, as reflected in low cohesion of the powder matrix.

Die Wall - Vs. Bulk Lubrication in Warm Die Compaction: Density, Microstructure and Mechanical Properties of Three Low Alloyed Steels

The influence of die wall lubrication during warm die compaction on densification, microstructure and mechanical properties of three low alloy ferrous powders was investigated. Specimens were sintered at 1250°C. Die wall lubrication leads to higher green and sintered density and enhances the dimensional stability. It does not affect the microstructure of the matrix, while pores are smaller and more rounded than in bulk lubricated specimens. In TRS tests, both strength and deformation are higher in die wall lubricated specimens than bulk lubricated ones.

An Experimental Investigation on the Effect of Sintering Temperature and Holding Time to the Characteristics of Fecual Powder Compacts Formed at Elevated Temperature

This paper presents the experimental investigation on the effect of sintering schedule to the final properties of FeCuAl powder compacts formed at elevated temperature through a lab-scale uniaxial die compaction rig. Iron (Fe) powder ASC100.29 was used as a main powder constituent and mixed with elemental powders which are copper (Cu) and aluminum (Al). The weight percentage of powder mass was divided into four, i.e., iron (91.7 wt%), copper (7.5 wt%), aluminum (0.5 wt%), and zinc stearate (0.3 wt%) as lubricant. All the powders were mixed through mechanical blending at a rotation speed of 30 rpm for 30 min. The mixed powder mass was compacted at 150˚C by 425 MPa of axial loading from upward and downward simultaneously. Subsequently, the defect-free green compacts were sintered under controlled argon gas atmosphere at three different sintering temperatures, i.e., 800˚C, 900˚C and 1000˚C for 120 min, 150 min and 180 min, respectively at constant sintering rate of 10˚C/min. Afterwards, the sintered samples were characterized for their physical properties, electrical properties, mechanical properties and their microstructures were evaluated. The results revealed that higher flexure stress was acquired by sample sintered at 1000˚C for 120 min and their microstructures were found to be better, i.e., the particles were bonded perfectly.

Numerical Simulation of Densification of Cu–Al Mixed Metal Powder during Axial Compaction

The densification mechanism of Cu–Al mixed metal powder during a double-action die compaction was investigated by numerical simulation. The finite element method and experiment were performed to compare the effect of the forming method, such as single-action die compaction and double-action die compaction, on the properties of compact. The results showed that the latter could significantly raise the densification rate and were in good agreement with Van Der Zwan–Siskens compaction equation. The effects of the different initial packing structures on the properties of the compact were studied. The results showed that a high-performance compact could be obtained using a dense initial packing structure at a given compaction pressure. Additionally, the effects of the Al content and compaction pressure on the relative density and stress distribution were analyzed. It was observed that, with an increase in the Al content at a given compaction pressure, the relative density of the compact increased, whereas the stress decreased. Furthermore, when the Al content was fixed, the relative density and stress increased with increasing compaction pressure. The relationship between the relative density and the compaction pressure under different friction conditions was characterized and fitted according to the Van Der Zwan–Siskens compaction equation. The influence mechanisms of die wall friction on the compaction behavior were investigated. It was revealed that friction is a key factor that causes the inhomogeneity of the powder flow and stress distribution. Finally, the effects of the dwell time and height–diameter ratio on the densification behavior were analyzed, and it was found that an increase in the dwell time promoted the densification process, whereas an increase of the height–diameter ratio could hinder the process.