A THREE-DIMENSIONAL FINITE ELEMENT MODEL FOR POWDER COMPACTION—TIME-DEPENDENT FORMULATION AND VALIDATION

ABSTRACT

Many industrial powders have been documented to have time-dependent compression response. However, in the literature very few time-dependent formulations are reported for three-dimensional analysis of powder compaction. In the paper, a time-dependent constitutive model, based on the theory proposed by Adachi and Oka, was used in a three-dimensional finite element formulation suitable for PC or desktop environments. The finite element model (FEM) predicts both the stress and density distributions in the powder mass during compression, i.e., from no load to the maximum compression load. A user-friendly interactive GUI (graphical user interface) was developed for the 3-D FEM, making it easy to use. To validate the FEM, microcrystalline cellulose was compressed to form cylindrical pellets using a press. The pellet was used to obtain spatial density distribution using the sectioning method. Then, the measured density distribution was compared with the Adachi and Oka model-based FEM calculated values. The density distributions were predicted within the 95% confidence interval of measured values. In addition, the overall error between the measured and predicted density values throughout the pressed pellet was less than 10%     

A THREE-DIMENSIONAL FINITE ELEMENT MODEL FOR POWDER COMPACTION—TIME-DEPENDENT FORMULATION AND VALIDATION

Many industrial powders have been documented to have time-dependent compression response. However, in the literature very few time-dependent formulations are reported for three-dimensional analysis of powder compaction. In the paper, a time-dependent constitutive model, based on the theory proposed by Adachi and Oka, was used in a three-dimensional finite element formulation suitable for PC or desktop environments. The finite element model (FEM) predicts both the stress and density distributions in the powder mass during compression, i.e., from no load to the maximum compression load. A user-friendly interactive GUI (graphical user interface) was developed for the 3-D FEM, making it easy to use. To validate the FEM, microcrystalline cellulose was compressed to form cylindrical pellets using a press. The pellet was used to obtain spatial density distribution using the sectioning method. Then, the measured density distribution was compared with the Adachi and Oka model-based FEM calculated values. The density distributions were predicted within the 95% confidence interval of measured values. In addition, the overall error between the measured and predicted density values throughout the pressed pellet was less than 10%     

Evaluation of the Dynamic Yield Locus Tester (DYLT)

ABSTRACT

Shear cells based on the constant volume approach are a promising alternative to the conventional constant load techniques. The objectives of this research were to evaluate the dynamic yield locus tester (DYLT) based on the constant volume approach, and the computer controlled Jenkie tester (CCJT) based on the constant load approach. This was done by comparing the flow parameters obtained using the two techniques for BCR limestone, glass fibers, ground silica, microcrystalline cellulose, and wheat flour. Test results showed the flow parameters obtained using the DYLT and the CCJT were comparable at a level of significance of 0.05 for BCR limestone, glass fibers, ground silica, and microcrystalline cellulose. There were significant differences (p > 0.05) between the flow parameters of the DYLT and CCJT for wheat flour.     

MEASUREMENT OF COHESION AND ANGLE OF INTERNAL FRICTION USING CUBICAL TRIAXIAL TESTER AND COMPARISON WITH COMPUTER CONTROLLED SHEAR CELL

ABSTRACT

A flexible boundary-type cubical triaxial tester (CTT) was used to measure the flow parameters, i.e., cohesion and angle of internal friction, of Mohr-Coulomb model. The three test materials used in this study were BCR limestone, ground silica and wheat flour. Flow parameters for these materials have been reported in literature using different shear testers. A comparison between the CTT and published computer controlled shear cell (CCSC) results showed that for: 1) BCR limestone -- at low consolidation loads, the results were comparable; however, there were differences in cohesion at 12.5 kPa and cohesion and angle of internal friction at consolidation stress of 6.6 kPa, 2) ground silica -- flow parameter values were comparable at 2.8 and 8.4 kPa, and 3) wheat flour — cohesion values were different, however, angle of internal friction values were comparable. The differences between the CTT and published shear cell results were attributed to the differing initial bulk density values and lack of knowledge of the shear plane location in the CTT.     

Rate-Dependent Elasto-Viscoplastic Constitutive Model for Industrial Powders. Part 2: Model Evaluation

The PSU-EVP model's constitutive parameters for alumina powder are presented. The PSU-EVP model was also used to back-predict the triaxial test data obtained for MZF and alumina powders using constitutive parameters such as the initial voids ratio (e₀), compression index (λ), and spring-back index (κ). In the case of MZF powder, 8 out of 12 back-prediction cases had average relative difference (ARD) values below 20%. In the case of alumina powder, 7 out of 11 back-prediction cases had ARD values below 20%. Based on the back-prediction results, it was concluded that the PSU-EVP model gave fairly good results for most triaxial test data collected at 0.62 MPa/minute and 6.21 MPa/minute. However, the back-prediction results obtained at 20.7 MPa/minute had high ARD values. A sensitivity analysis was done to study the effect of changes in parameter values on the hydrostatic triaxial compression (HTC) and conventional triaxial compression (CTC) back-prediction results. From the sensitivity analysis,±10% (standard deviation variation from ±0.8σ to ±2.3σ) changes in λ and e₀ mean values had marked effect on the HTC results. However, changes in the λ, κ, and e₀ mean values do not produce any noticeable effect on the CTC prediction results. Overall, the PSU-EVP model can be considered to be the first step towards the development of a more robust and accurate model for prediction of stresses and strains in a dry powder compression process.     

Rate-Dependent Elasto-Viscoplastic Constitutive Model for Industrial Powders. Part 1: Parameter Quantification

ABSTRACT

The rate-dependent mechanical behavior of a dry industrial powder (MZF powder) was studied using a cubical triaxial tester (CTT) within the context of a new elasto-viscoplastic model (PSU-EVP model). The compression and shear properties of the powder were quantified at compression rates of 0.62, 6.21, and 20.7 MPa/minute with pressures up to 11 MPa. Test results demonstrated that the compression and shear responses of the powder were nonlinear, consistent, and reproducible (coefficient of variation or COV ≤ 15%). Also, MZF powder exhibited varying elastic and plastic deformation at different pressure levels that were quantified using statistical correlations (R² > 0.90). For example, the average bulk modulus and shear modulus values for MZF powder increased linearly with pressure (R² > 0.90) at all compression rates. The failure stress values also increased with the increase in mean pressure. For instance, at a compression rate of 0.62 MPa/minute, failure stress increased from 5.0 to 13.3 MPa as the confining pressure increased from 2.2 to 8.5 MPa. Similar effects were noted at compression rates of 6.21 and 20.7 MPa/minute. Overall, failure stress decreased with increasing compression rate. From the data collected, it was demonstrated that compression rate does have substantial effect on the compressibility and shear behavior of powders that can be quantified using the CTT and is suitable for use in the PSU-EVP model.     

Investigation of the physical–mechanical properties of Eudragit® RS PO/RL PO and their mixtures with common pharmaceutical excipients

Ammonio methacrylate copolymers Eudragit^® RS PO and Eudragit® RL PO have found widespread use as key components in various types of extended release solid dosage forms. The deformation behavior of neat polymers and binary mixes was evaluated using Heckel Analysis, strain rate sensitivity, work of compaction and elastic recovery index. Additionally, the compact forming ability of neat materials and binary mixes were evaluated by analyzing their tabletability, compressibility and compactibility profiles. The Heckel analysis of both polymers exhibited a speed-sensitive deformation behavior typical to plastic materials. The yield values of the binary mixes of the polymers with microcrystalline cellulose revealed a linear relationship with the weight fractions of individual components. The yield values of binary mixes of both the polymers with dibasic calcium phosphate exhibited slight negative deviations from linearity. Both polymers exhibited axial relaxation after ejection typical of viscoelastic materials, as measured by the elastic recovery index values. The work of compaction and the elastic recovery index values of the binary mixtures were found to be linearly related to the weight fractions of the individual components thus, confirming ideal mixing behavior based on the composition. Addition of microcrystalline cellulose to both polymers significantly improved their tabletability and compactibility. The tensile strengths of the compacts prepared with neat materials and binary mixes with microcrystalline cellulose, dibasic calcium phosphate and lactose were the function of their solid fraction and independent of the tableting speeds tested; thus, validating compactibility as a reliable parameter in predicting acceptable tablet properties.     

MEASUREMENT OF COHESION AND ANGLE OF INTERNAL FRICTION USING CUBICAL TRIAXIAL TESTER AND COMPARISON WITH COMPUTER CONTROLLED SHEAR CELL

A flexible boundary-type cubical triaxial tester (CTT) was used to measure the flow parameters, i.e., cohesion and angle of internal friction, of Mohr-Coulomb model. The three test materials used in this study were BCR limestone, ground silica and wheat flour. Flow parameters for these materials have been reported in literature using different shear testers. A comparison between the CTT and published computer controlled shear cell (CCSC) results showed that for: 1) BCR limestone -- at low consolidation loads, the results were comparable; however, there were differences in cohesion at 12.5 kPa and cohesion and angle of internal friction at consolidation stress of 6.6 kPa, 2) ground silica -- flow parameter values were comparable at 2.8 and 8.4 kPa, and 3) wheat flour — cohesion values were different, however, angle of internal friction values were comparable. The differences between the CTT and published shear cell results were attributed to the differing initial bulk density values and lack of knowledge of the shear plane location in the CTT.     

A New Experimental Setup for the Characterization of Bulk Mechanical Properties of Aerated Particulate Systems

This study introduces the development of a new experimental setup using an enhanced triaxial tester and a new methodology for the characterization of fine particulate systems in an aerated condition. Tests were performed using the new setup to study the effects of aeration on two different powders: a highly cohesive precompacted powder and a cohesionless powder, the former being microcrystalline cellulose PH-102, mean particle size 90 w m, and the latter alumina powder, mean particle size 100 µm. The degree of aeration was small and it was of the same order of magnitude as the velocities encountered during the entrapment of air in filling and during other handling processes. The superficial velocity for aeration was about three orders of magnitude lower than that required for fluidization. The immediate results have shown that even a small amount of interstitial air has a dramatic effect on the quasi-static strength and an obvious effect on the elastic parameters of the powder. The quasi-static strength of the alumina powder was reduced by about 20%, at a superficial air velocity of 0.02 m/s, whereas the quasi-static strength of microcrystalline cellulose was reduced by about 17%, at a superficial air velocity of 0.009 m/s. The Young's modulus values were reduced by about 13% on average and the bulk modulus values by about 8% on average for microcrystalline cellulose for the air velocity given above. aerated dry particulate systems elastic parameters compressibility and/or dilatancy boundary failure envelope     

Development of a Medium Pressure Flexible Boundary Cubical Triaxial Tester

ABSTRACT

A medium pressure flexible boundary cubical triaxial tester has been designed and fabricated. In this tester, air pressure up to 70 MPa can be applied to all six surfaces of a 50X50X50 mm cube-shaped powder specimen via flexible rubber membranes. Pressure in a vertical direction (top-bottom faces of the powder specimen) and the pressure in a horizontal direction can be controlled independently. This tester can handle displacements as large as 50 mm in each of the three principal directions. Hydrostatic triaxial compression (HTC) tests. conventional triaxial compression (CTC) tests, and mean effective stress (MES) tests will be conducted on three powders, including a pharmaceutical powder, a ceramic powder, and an aluminum oxide powder. HTC tests will be conducted at 0 to 20 MPa, with 3 loading-unloading cycles. CTC and MES tests will be conducted at several pressure levels from 0 to 20 MPa.     

A New Experimental Setup for the Characterization of Bulk Mechanical Properties of Aerated Particulate Systems

This study introduces the development of a new experimental setup using an enhanced triaxial tester and a new methodology for the characterization of fine particulate systems in an aerated condition. Tests were performed using the new setup to study the effects of aeration on two different powders: a highly cohesive precompacted powder and a cohesionless powder, the former being microcrystalline cellulose PH-102, mean particle size 90 μm, and the latter alumina powder, mean particle size 100 µm. The degree of aeration was small and it was of the same order of magnitude as the velocities encountered during the entrapment of air in filling and during other handling processes. The superficial velocity for aeration was about three orders of magnitude lower than that required for fluidization. The immediate results have shown that even a small amount of interstitial air has a dramatic effect on the quasi-static strength and an obvious effect on the elastic parameters of the powder. The quasi-static strength of the alumina powder was reduced by about 20%, at a superficial air velocity of 0.02 m/s, whereas the quasi-static strength of microcrystalline cellulose was reduced by about 17%, at a superficial air velocity of 0.009 m/s. The Young's modulus values were reduced by about 13% on average and the bulk modulus values by about 8% on average for microcrystalline cellulose for the air velocity given above.

aerated dry particulate systems elastic parameters compressibility and/or dilatancy boundary failure envelope     

An efficient conversion of waste feather keratin into ecofriendly bioplastic film

Feathers biomass from poultry industry is considered as an important waste product, which creates serious environmental problems. In this study, keratin was extracted from waste chicken feathers using sodium sulfide as a reducing agent under optimized conditions. The extracted keratin particles were used to develop a bioploymeric film by adding microcrystalline cellulose as nano-additive agent. The calculated yield of 80.2% was obtained for keratin from feathers dry weight 25 g (w/w). The extracted keratin was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis, differential scanning calorimetry, wide-angle X-ray diffraction. The physiochemical characteristics of the feathers were compared with the keratin powder. The regenerated keratin particles preserved their chemical composition, thermal strength and stability after chemical extraction. The extracted keratin particles showed 10–20-µm spongy porous microparticles in SEM analysis. The keratin powder was used to synthesize a bioplastic film using glycerol (3.5%) and microcrystalline cellulose (0.2%) in NaOH for 48 h at 60 °C. The calculated thickness of bioplastic film was 1.12 × 10^?4 mm with tensile strength of 3.62 ± 0.6 MPa. The Young’s modulus and break elongation for synthesized bioplastic film were 1.52 ± 0.34 MPa and 15.8 ± 2.2%, respectively. The feather and keratin showed maximum similarity index of 64.74% (l-alanyl, l-alanyl, l-alanine, p-nitroanilide) and 64.32% with d-pantethine, respectively, using OMNIC Specta software. Overall, the study presented a highly efficient method to convert the waste feather biomass into a bioplastic film which can be used in biopolymer, biomedical and pharmaceutical industries.     

Flow Properties of Cohesive Powders Tested by a Press Shear Cell

The most important design parameters for roller presses can be referred to flow and compression characteristics of bulk materials. Usually the flow properties are measured in the low stress range 1–50 kPa at the shear rate of about 1 mm/min. But this does not fit the stress regimes in the roller press. Therefore, the compression and flow behavior of the powder have to be investigated at higher pressures, shear rates, and shear displacements. These properties of bulk materials in the so-called medium pressure range 50–1000 kPa can be analyzed using a press shear cell. Tests were implemented with limestone, bentonite, and microcrystalline cellulose at average 23°C powder bed temperature using shear rates from 0.00042 to 0.042 m/s and a more realistic preshear displacement from 0.1 to 2 m for practical applications in powder compaction. Physical observation based compression functions were developed for the low and medium pressure range, which include simple equations for the compression rate and specific compression work.     

Development and tableting of directly compressible powder from electrospun nanofibrous amorphous solid dispersion

This work was carried out to explore the unknown area of converting non-woven fibres, prepared by high speed electrospinning, into a directly compressible blend by mixing with excipients. An experimental design, with independent variables of compression force and fillers fraction, was realized to investigate tabletability of electrospun material (EM) and to produce hard tablets with appropriate disintegration time. The models proved to be adequate; fitted to the results and predicted values well for the optimal tablet, which was found to be at 76.25% fillers fraction and 6 kN compression force. Besides standard characterizations, distribution of EM was investigated by Raman mapping and scanning electron microscopy revealing the propensity of EM to cover the surface of microcrystalline cellulose and not of mannitol. These analytical tools were also found to be useful at investigating the possible formation of the so-called gelling polymer network in tablets. Scanning electron microscopic pictures of tablets confirmed the maintenance of fibrous structure after compression. The moisture absorption of EM under increasing humidity was studied by dynamic vapour sorption measurement, which suggested good physical stability at 25 °C and 60% relative humidity (corroborated by modulated DSC). These results demonstrate the feasibility of a pharmaceutically acceptable downstream processing for EMs.     

Seebeck coefficient and electrical conductivity of mesoscopic nanocrystalline SrTiO3

In the present study, we investigate the effect of the grain boundaries on both the electrical transport and the thermoelectric properties. For this purpose, the Seebeck coefficient and the electrical conductivity of a model material, such as nominally pure SrTiO₃ (single crystal, microcrystalline, and nanocrystalline), is measured under oxidizing conditions. The impedance spectroscopy measurements reveal a strong change of the conduction properties of the nanocrystalline sample compared with the unperturbed bulk properties, namely a reduction of the p-type conductivity by two orders of magnitude at high oxygen partial pressure. Similarly, the Seebeck coefficient values of the nanocrystalline sample exhibit remarkable deviations from the single crystal ones: Under oxidizing conditions, values up to 2160 μV K^?1 (at 575 °C) are detected. More importantly, in the nanocrystalline sample, the dependence of the Seebeck coefficient on the concentration of the charge carriers is found to be four times larger than in the single crystal.     

Characterization of the Grinding Behavior of Binary Mixtures of Clinker and Colemanite

The purpose of this study is to determine the grindability and kinetic behavior of clinker and colemanite in cement production when they are ground separately and together. Bond and Hardgrove grindability methods were employed to determine grindability properties clinker and colemanite by varying proportions. Bond work index (BWI) values of clinker and colemanite are 18.89 kWh/t and 12.33 kWh/t, respectively. BWI value of mixture decreases by added colemanite and the experimental BWI values of mixtures were lower than those of calculated, considering their proportions. Hardgrove grindability index (HGI) values of clinker and colemanite are 51.81 and 99.62, and Blaine fineness values are 920 cm²/g and 2430 cm²/g, respectively. As colemanite addition increases HGI and Blaine fineness values also increase. Experimental Blaine fineness values are greater than calculated values meaning that during intergrinding different ingredients do not show the same behavior as in the case of separate grinding. These findings explain that clinker particles have an abrasion effect thus an extra grinding effect on colemanite particles. The specific rates of breakage were determined through kinetic experiments to understand the grinding mechanisms of colemanite, clinker and their mixtures. The model parameters of S_i, a_T, and α were established in kinetic experiments.     

Fracture Model of Fine Bulk Powder Structures

ABSTRACT

Using several line powders (particle size 15-65 μ m). the rheological parameters of tensile strength ( σ_f,mb) and plastic deformation coefficient (Y) were experimentally measured at ambient and elevated temperatures. In order to be aeratable. the rheological parameters of a specific powder should satisfy the equation of σ_f,mb = 0.11Y^{0 89.}The formation of agglomerates or dead zones can be predicted. By introducing the “Quasi porous solid body model,” the theoretical derivation of the criterion characteristic curve was accomplished using solid fracture theory.     

Compaction Properties of Spheronized Binary Granular Mixtures

Two spheronized granular formulations containing 20% anhydrous lactose/80% microcrystalline cellulose (MCC) and 80% anhydrous lactose/20% microcrystalline cellulose were blended in various proportions and compressed. Physical-mechanical properties of the resulting compacts were investigated using tableting indices and compared with powder mixtures of the same compositions. The compacts were compressed at a solid fraction of 0.80 for both powder and bead mixtures. An additional set of bead compacts were made at a solid fraction of 0.87. The thickness of the compacts was measured in the post-ejection stage to investigate their expansion behavior. The tensile strength with and without a stress concentrator and the dynamic indentation hardness of the compacts were determined. The brittle fracture index (BFI) and bonding index (BI) values were also calculated. The microstructure of the beads and compacts were investigated using scanning electron microscopy to observe the bonding phenomena. The results showed that the compacts made from beads underwent different compaction/consolidation behaviors than the powders of the same lactose/MCC compositions. For powdered compacts, the tensile strength with or without a stress concentrator increased with increasing MCC content while the compacts made from beads showed the opposite trend. However, this trend was not seen in the indentation hardness test. The resulting BFI values were all low due to the plastic nature of the materials selected. The BI values of the bead and powder compacts also exhibited opposite tendencies and reflected the divergent mechanical properties of the materials presented in granulated and powdered forms. Microstructure studies revealed the bonding states between the beads in the compacts. Discrepancies in mechanical properties were related to the compressibility, compactibility, and porosities of the excipients studied.     

Optimization of coag-flocculation processes of a newly synthesized quaternized oil palm empty fruit bunch cellulose by response surface methodology toward drinking water treatment process application

An optimization of coagulation and flocculation of kaolin suspension by a newly synthesized quaternized oil palm empty fruit bunch cellulose denoted as a 9QC was investigated using the central composite design of the response surface methodology. The influences of coag-flocculant dosage, pH, and kaolin suspension on turbidity removal efficiency and sludge volume index responses were studied and assessed according to a 2³ full factorial design. The developed quadratic models revealed that the overall optimum values to obtain the highest performance of the responses were 62.5 mg/L of coag-flocculant dosage, pH 7, and 1400 mg/L of kaolin concentration. The predicted optimum responses were found to be in close proximity to the observed responses. The coag-flocculating of river water using 9QC carried out at the optimum values showed encouraging results as compared to alum which is commonly used in drinking water treatment process.     

Synthesis and properties of regenerated cellulose-based hydrogels with high strength and transparency for potential use as an ocular bandage

Cellulose is a biologically derived material with excellent wound-healing properties. The high strength of cellulose fibers and the ability to synthesize gels with high optical transparency make these materials suitable for ocular applications. In this study, cellulose materials derived from wood pulp, cotton, and bacterial sources were dissolved in lithium chloride/N,N-dimethylacetamide to form regenerated cellulose hydrogels. Material properties of the resulting hydrogels, including water content, optical transparency, and tensile and tear strengths, were evaluated. Synthesis parameters, including activation time, dissolution time, relative humidity, and cellulose concentration, were found to impact the material properties of the resulting hydrogels. Overnight activation time improves the optical transparency of the hydrogels from 77% to 97% at 550 nm, whereas controlling cellulose concentration improves their tear strength by as much as 200%. On the basis of the measured transmittance and strength values of the regenerated hydrogels prepared via the optimized synthesis parameters, Avicel PH 101, Sigma-Aldrich microcrystalline cellulose 435236, and bacterial cellulose types were prioritized for future biocompatibility testing and potential clinical investigation.