Potassium chloride caking tendency: A parametric study of cake break energy

Finite Element Analysis of Extrinsic Parameters on the Onset of Tensile Strength in Powders

Most food, pharmaceutical, and chemical industries rely heavily on the supply of free-flowing powders that finds their application in raw materials, additives, and manufactured products. Improper storage conditions combined with environmental factors affect the free-flowing ability of powders. An undesirable transformation of these free-flowing powders into a coherent mass that resists flow is called caking. An important metric that can be used to measure the caking propensity of a material is the tensile strength, which is essentially the resistant stress needed to separate two layers of materials using an isostatic tensile strain. Even though several models have quantified the propensity of caking, the complex nature of interactions between the powder and its micro-environment makes the prediction of caking a challenging task. In the present work, the onset of tensile strength in isomalt with changes in temperature, relative humidity, and consolidation pressures using a shear cell was modeled using a finite element approach. The study found that at a consolidation pressure of 3 kPa and relative humidity of 85±0.1%, an increase in temperature by 5˚C increased the tensile strength of isomalt by a factor of 2. On the other hand, at a constant temperature of 25˚C, an increase in relative humidity from 85±0.1% to 86±0.1% registered an increase in tensile strength by 42.7%. This study also found that an increase in consolidation pressure from 3 kPa to 6 and 9 kPa increased the tensile strength by a factor of 1.79 and 2.54, respectively. The model had good agreement with the measurements and had an overall MAPE of 12.13%. This model can be applied to study the influence of extrinsic parameters on the propensity of caking during storage of bulk solids.

Study of zeolite anti-caking effects for fertilisers by 1H low-field NMR

Caking is associated with the consolidation of dry powder and granules, leading to losses of function and/or quality. It has been object of studies in the pharmaceutical, food and fertiliser areas since 1920's because of its significant impact on product quality and value. Caking has been described as a three-step event consisting of sorption-dissolution-recrystallisation phases and constitutes a critical factor in fertilisers losses during storage while also hampering fertiliser application. Current methods for the evaluation of water sorption dynamics are expensive, time-consuming and/or inaccurate. This manuscript describes an unprecedented application of low-field ¹H NMR relaxometry for the kinetic study of humidity uptake, in real-time, by urea mixed with different concentrations of an anti-caking agent (zeolite). The proposed method allows to follow the water uptake in different domains of the mixed fertiliser/zeolite samples. To our knowledge, this dynamic has not been observed and quantified so far in real-time. Furthermore, we presented the use of 2D-ILT for kinetic studies, being the first dimension the usual transverse relaxation and the second dimension the kinetic one. With this approach, the NMR relaxation times T₂ correlated to time constants associated with the uptake kinetics of the water. This method could be extended to several kinetic studies and experiments with temperature variation. Depending on the kinetics of the studied process, the kernel of the Laplace transform must be suitably adapted.

Expedited Investigation of Powder Caking Aided by Rapid 3D Prototyping of Testing Devices

Powder caking can dramatically affect powder handling and downstream production processes. Understanding the key factors that contribute to bulk powder caking is crucial. This article introduces the Hirschberg caking device (HCD), which is a 3D-printed device allowing for parallel testing of powder caking in a cylindrical geometry. In the HCD setup, the powder sample is stored in controlled conditions in the sample holder. On removal of the sample holder, the caked powder will remain in the shape determined by the sample geometry while the remaining powder will fall down. Caking indices can be calculated based on image analysis and weight measurement. The results obtained for the caking of lactose monohydrate with the HCD were in good agreement with the results obtained by a ring shear tester. In addition, a strain tester was used to measure the strength of the formed cakes. Using this approach, critical storage conditions and the required concentration of a given anticaking agent (talc) for lactose monohydrate could be identified. This work demonstrates the potential of rapid prototyping in powder characterization by introducing a fast and affordable approach for exploring and trouble-shooting powder caking.