Caking Tendency Research Articles

Rapid evaluating caking tendency of nonspherical crystals by developing a shape-based crystal bridge growth model

Crystal caking is a decisive factor affecting the quality of high-end fine chemicals, whereas lack of shape-to-caking understanding results in considerable waste of time, severely delaying high-end fine chemical development. On this basis, a morphology-based caking evaluation model is developed with 74% and 96% time savings compared to previous modeling and non-modeling experiments, respectively, while guaranteeing superior accuracy. The crystal morphology is expressed as a function of the aspect ratio and the particle size distribution. The quantitative relationships between these parameters and the caking tendency are deduced, firstly achieving morphology anti-caking criterion establishment. For D-allulose crystals, considering humidity, and particle size, an aspect ratio is below 3 is the standard for combating caking, which has not been reported previously. Herein, the specific effect of crystal morphology on caking behavior is quantitatively described. The knowledge obtained can be applied to rapidly and quantitatively design anti-caking storage systems for products in warehouses.

Influence of multiple parameters on the crystallinity of dairy powders

Caking in powdered foods causes practical difficulties in solubilising the powder and interrupts the free flow from the container during manufacture and final use. This research investigated the caking tendency of cheese and milk powders stored at different relative humidity environment by low field, time domain 1H NMR, Magic Sandwich Echo sequence. The caking tendency of cheese powders was higher than milk powders. On the other hand, surface fat content of whole fat milk powder had an abrupt change due to lactose crystallisation at 60% relative humidity, which corresponded to a critical moisture content of 10%. As an overall conclusion, the lactose content was more dominant than fat content to trigger caking. However, it was inferred that the effect of the salt amount, which differed due to the nature of the samples, was more significant for caking development in milk and cheese powders.

How do morphological changes of caffeine hydrate influence caking

Morphological changes in hydrates during the drying process can cause various potential problems. The crystal properties of caffeine, such as morphology and particle size distribution (PSD), vary with drying temperatures. We studied the mechanism of morphological changes in caffeine hydrate and their effect on caking behavior. During the drying process, caffeine crystals maintained their original needle-like morphology at lower temperatures (≤338 K), whereas numerous burrs were formed on the surface at higher temperatures. The morphological changes at different temperatures can be explained by the correlation between isothermal dehydration data and various kinetic models. A lot of burrs peeled away from the crystal surface and the products had wider PSDs and poorer morphology at higher temperatures because the removal of water in the crystal lattices is accelerated and there is not enough time to rearrange the crystal structure. The accelerated caking test indicated that products after agitated drying at higher temperatures exhibited a higher caking tendency.

Model-based design for water-soluble crystals with anti-caking function by the feedback between caking prediction and crystallization control

Water-soluble crystals with anti-caking function have become high-end products, whereas they are prepared by trial and error due to the lack of quantitative correlation between particle size and caking tendency, as well as the absence of the models for global consideration between caking and crystallization. This work presents a coupled Caking-Size-Crystallization (CSC) model, which connects the front-end crystallization process and the post-end caking process to achieve the closed-loop design of the anti-caking function for the first time. The CSC model can directly generate the optimal cooling trajectory to crystallize the product free of caking. The introduction of the caking constant term, the mean particle size and the Mullin-Nyvlt’s theory improve the design efficiency by an order of magnitude with the precision guaranteed. This model-based approach presents an opportunity to find optimal crystallization operating profiles with diverse crystal seed loading strategies that meet both product function and manufacturability demands.

Rapidly evaluating the caking tendency of sugar alcohols by developing a crystal bridge growth model: A case study of xylitol

Caking of crystalline sugar alcohols is a deleterious and undesired agglomeration process during storage in the food industry. Compared with the time-consuming and labor-intensive conventional caking assessment methods, this work develops a rapid methodology for evaluation of the critical caking cycle of xylitol with over 85% time-saving and 90% labor-saving while guaranteeing the precision accuracy. By developing a Caking-Hygroscopicity-Particle size crystal bridge growth model, the correlation and quantitative relationships among hygroscopic properties, particle size and the critical caking cycle are firstly established and confirmed, which can greatly simplify the most time-consuming and laborious experiments of water sorption measurements and caking tests. Besides, the knowledge obtained can help guide the rapid selection of storage humidity conditions and appropriate particle size distributions for maintaining the desired properties and competitive marketability of crystalline sugar alcohols.

Melting Characteristics of Coal Ash and Properties of Fly Ash to Understand the Slag Formation in the Shell Gasifier.

The flow temperature (FT) of the coal ash from the Liuqiao no. 2 mine in North Anhui Province (C00) is too high (∼1520 °C) to fit the Shell gasifier due to its relatively high content of SiO2 and Al2O3. To solve this problem, a series of coals were blended with C00 with different ratios, and the relations between FT and the ash composition were investigated. The coal ash was analyzed by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy–EDX to elucidate the mechanism of the improved ash fusion performance and the slag formation in the waste heat boiler of the gasifier. It is shown that FT is relevant to the coal ash compositions as well as the structures formed at high temperatures. The existence of alkaline oxides (CaO, MgO, and Fe2O3) decreases the coal ash FT to a low level. The FT can decrease to <1350 °C to cater to the Shell gasifier by blending C00 and C03 with a mass ratio of 4:6 owing to the plentiful alkaline oxides in C03. The FTIR results indicate that the high flow temperature of C00 is attributed to the formation of mullite at high temperatures. The coal blending with various ratios changes the compositions of CaO, MgO, and Fe2O3, which can form some low-melting-point eutectic compounds with SiO2 and Al2O3 under high temperatures, inhibit the formation of mullite, and thus decrease the ash FT. The coal ash FT was found to have a good linear relation with the ash compositions, which can sever as a reference to the coal blending. According to the model parameters, it is shown that Mg has the most significant promoting effect on the decrease in FT of the coal ash. The caking tendency of fly ash increases with the rising Ca content and an excessive Ca-based fluxing agent used in the coal blending will lead to the aggregation of the Ca-rich clasts around the fly ash particle, resulting in the plugging of the waste heat boiler in the gasifier. Therefore, the Mg-based fluxing agent is more promising to improve the ash fusion performance and reduce the caking tendency of the coal fly ash.

Understanding Caking Phenomena in Industrial Fertilizers

One of the most important problems of the fertilizer industry is that fertilizers show caking tendency during transportation and storage. Caking occurs as a result of interaction at the contact points formed between solid fertilizer particles. These interactions, also called contact mechanisms, are activated by a number of properties that fertilizers have and by environmental conditions. Prevention of caking mechanism is a substantial research subject that directly affects the quality and financial value of the final product and ensures its applicability. Fertilizer in good quality can provide ease in agricultural applications, and directly affect plant nutrition and crop productivity. At this point, there are various promoter practices for obtaining the free-flowing property in fertilizers that can be maintained or suggested during or after production, both in industry and in R&amp;amp;D studies. In order to develop new process control points in the industry, it is important to understand the factors that cause caking and the mechanism of physicochemical interactions that progress depending on these factors. In addition, it is essential to improve the storage conditions of the fertilizer, as well as to maintain its quality until end-use. This paper focuses on the caking behavior of fertilizers in detail, giving brief information about the prevention of caking and various types of anticaking agents.

Variables Affecting Caking on Granular Phosphorous Containing Fertilizers

Granular fertilizers are not usually produced near the regions where they are applied. They have to be stored and transported after their production for long periods before being actually applied on the fields. During this time, most fertilizers, including those containing phosphorous, can agglomerate, or cake, making their manipulation and application more difficult or even impossible. Caking is the result of various physical and chemical processes that may occur simultaneously, which are more or less affected by external and internal variables during their production, storage and transportation process. In this paper, a study of the impact of different variables such as time, temperature, moisture and pressure on the caking tendency of different fertilizers containing phosphorous is presented. The principal variables affecting the caking process are discussed, based on results from mechanical tests and chemical analytical measurements such as scanning electron microscopy and x-ray fluorescence. Solutions to decrease the caking of granular fertilizers, notably by the use of bio-sourced protecting coatings and their characteristics, are also discussed.

Determination of the cohesion, powder flow speed dependency and caking tendency of cocoa powders

Cocoa is one of the most popular foodstuffs known for centuries and cocoa powders are particularly exposed to caking, a phenomenon of agglomeration of solid particles that disrupt powder functionality. This study aimed to identify the main powder flow characteristics such as caking, cohesion and powder flow speed dependency of cocoa powders, according to their fat content. The loose and tapped bulk density, as well as Carr ratio of cocoa powders, was determined as bulking properties for comparing and interpreting the flowability. The caking was observed in all three samples. With increasing fat content, a decrease in the powder flowability was detected. The mean cake strength of the low fat, reduced fat and full-fat cocoa powders was recorded as 110.42&amp;amp;plusmn;1.71; 164.175&amp;amp;plusmn;1.75 and 207.96&amp;amp;plusmn;0.93, respectively. These results suggest that the fat contents of the food powders may be a useful parameter to describe the powder flowability.

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

Undesired particulate agglomeration can create powder flow issues during manufacturing. Potassium chloride (KCl), a commercial product used in powder form as a potassium source, is known to agglomerate. The main objective is to develop a method to assess KCl agglomeration, then use it to understand its driving forces and the phenomena taking place. Based on industrial data in pharmaceutical manufacturing, the following 5 parameters are considered as critical in terms of agglomeration: conditioning humidity, conditioning time, drying, applied pressure and particle size. Beakers containing 40 g of original or ground KCl powder are compacted under specific humidity conditions in a bell jar. Once the beakers are conditioned, agglomerate hardness tests evaluate agglomeration extent by correlating it with the energy required for powder penetration. This energy is calculated from force-distance curves. The results show that the Area Under the force vs distance Curve (AUC) is a good indicator of agglomeration extent. Thus, the AUC is a scalar and has units of work. Based on AUC analysis, the highest agglomeration is found in conditioning humidity of 85% relative humidity (RH), original particle size, drying and conditioning time of 16 h. The agglomeration of original versus ground particle size powders is further investigated over time in a conditioning test. Preliminary tests validate our method and indicate that KCl premixing with other materials can solve agglomeration problems encountered during manufacturing processes as KCl-particle-particle interactions per unit volume are reduced.

Electrostatic powder coatings of pristine graphene: A new approach for coating of granular and fibril substrates

The use of pristine graphene (pG) based on solution processed coating technologies is often limited by their poor dispersibility in water and organic solvents which prevents to achieve the best performing properties of pG in coating applications. To address these limitations, we developed a dispersant-free coating approach of pG based on their intrinsic solid-lubricity and interlayer electrostatic interactions. The “rotating drum” method was established to provide suitable conditions for electrostatic deposition of pG-powder which is demonstrated on two model substrates with granular and fibril morphologies (urea and acrylic fibers) to improve their physical and electrical properties. The results showed that the pG coating enables to minimize moisture induced caking tendency of commercial urea prills at a relative humidity (RH) of 85% (higher than critical humidity) exhibiting greater moisture rejection ability (∼2 times higher than uncoated urea) and to improve their anti-abrasive properties. The pG-powder coating applied on nonconductive acrylic fibers provides a stable conductive layer (∼0.8 ± 0.1 kΩ/sq) which made them suitable for using in wearable electronics, sensors and electromagnetic interference (EMI) shielding. The developed coating method for pG-powder based on “rotating drum” is generic, simple, eco-friendly, low-cost, and scalable for broad range of coating applications.

How does particle size influence caking in lactose powder?

Particle size distribution (PSD) is known to influence product properties such as flowability and compressibility. When producing crystalline lactose, different steps can affect the PSD of the final powder. The aim of this study was to investigate the influence of PSD on caking and the mechanisms involved. Smaller particles showed higher moisture sorption and a greater caking tendency, measured by dynamic vapor sorption and ring shear testing, respectively. Therefore, moisture sorption isotherms appeared as a valuable tool to predict the effect of PSD on humidity caking, as confirmed by the results of ring shear testing. Controlling the amount of fines, characterized by a higher content of impurities, a larger specific surface area and a broader span of the PSD, was found critical to limit caking. More precisely, both the total surface area and the span of the PSD require close attention as they can significantly influence humidity and mechanical caking.

Granulated polyhalite fertilizer caking propensity

Most fertilizers have some tendency to form agglomerates (caking) during storage. This caking is usually effected by: chemical composition, particle structure, moisture content hygroscopic properties, mechanical strength, product temperature, storage time and pressure. The aim of this study is to provide fundamental information on the performance of POLY4, a trademarked granulated polyhalite fertilizer by Sirius Minerals Plc, under long term storage as a fertilizer and in NPK blends. Evaluation of POLY4 blends “caking” is proposed using accelerated caking tests. These accelerated caking tests are of short duration and for this reason can be used in fertilizer granulation plants on a quality control basis. Crushing and Dynamic Vapour Sorption (DVS) tests for individual granules, and caking and DVS tests for POLY4 blends were performed to monitor the behaviour of POLY4 within the various blends. The addition of POLY4 to the blends has a positive effect on the blends by reducing the caking tendency. It was also found that the sample with the largest amount of POLY4 (50%) has the largest creep rate value and longest estimated storage time approximately 300months.

Impurities enhance caking in lactose powder

Caking of lactose and other dry ingredients is a common problem in the dairy and food industries. The lactose production process includes different purification steps, depending on the type of lactose produced. The aim of this study was therefore to investigate how the remaining impurities (i.e. non-lactose components) affect the caking tendency of the final powder. The results from a combination of different methods, including dynamic vapor sorption, characterization of the physicochemical composition and assessment of caking with a ring shear tester, suggested humidity caking. Larger amounts of impurities in the lactose powder resulted in enhanced moisture sorption and greater caking tendency. These findings emphasize the importance of controlling the washing and purification steps throughout the production process in order to limit caking in the final product.

Evaluation of the ability of powdered milk to produce minitablets containing paracetamol for the paediatric population

The work aims at evaluating the usefulness of powdered milk as a drug matrix for the production of minitablets specifically designed for children. Mixtures made of powdered milk, paracetamol, mannitol, sodium croscarmellose and magnesium stearate (evaluated for flow properties, cohesiveness and caking tendency) were compacted into beams (evaluated for deformation, elasticity and stiffness) and minitablets (evaluated for uniformity of mass, thickness, tensile strength and paracetamol mean dissolution time) and a 23 factorial design performed. The increase on milk fraction in the formulation improved the compressibility of paracetamol and hardness of compacts, reducing weight variation and paracetamol release. A marked decrease on the dissolution time was observed as sodium croscarmellose was added to the milk rich formulations. The increase of the compression force resulted in the production of thinner compacts but had little effect on dissolution time. The production of beams has shown that deformation, bending strength and stiffness increased with both milk and compaction pressure, and decreased with sodium croscarmellose, whereas elasticity decreased when all variables increased. Tensile strength and mean dissolution time described minitablets well, unlike compaction force. The study has proved that powdered milk is suitable for the production of minitablets by direct compression of poor compressible drugs.

SIMULATION OF UREA PRILLING PROCESS: AN INDUSTRIAL CASE STUDY

A local industrial urea prilling tower with a rectangular cross-sectional area under the operating conditions of free convection was mathematically modeled. In this model the prilling process has been simulated by simultaneous solution of the continuity, hydrodynamic, and thermal equations. Temperature distributions of the particles and the cooling air along the height of the tower were calculated from the model. The air temperature profile predicted by the model was compared with the measured air temperature along the tower. The data predicted by the model were almost in agreement with the plant data, indicating the validity of the model. The result of this study suggests that an increase in heat transfer from the particles using installation of induced fans can reduce the temperature of produced prills and hence reduce caking tendency of the prilled urea.

Influence of spray-drying operating conditions on Rhamnus purshiana (Cáscara sagrada) extract powder physical properties

The aim of this work was to study Rhamnus purshiana (Cáscara sagrada) extract spray-drying in order to obtain powders with good rheological properties for direct compression (DC) and stability attributes. The experiments were carried out in a Büchi B-290 Mini Spray Dryer using colloidal silicon dioxide as carrier agent. A 2 5 − 1 fractional factorial statistical design was used to find adequate spray-drying operating conditions to produce Cáscara sagrada powders with good flow, good compactability properties, high process yield, low moisture content, low hygroscopicity, and caking tendency. Morphology, size, structural and thermal properties of the particles were also evaluated. The operating variables studied were air inlet temperature, atomization air flow rate, pump feed rate, aspiration capacity, and feed solids concentration. The 2 5 − 1 factorial experimental design used was a good strategy to establish spray-drying operating conditions to produce Cáscara sagrada extract powders with good properties for direct compression and high process yields. Colloidal silicon dioxide was an effective drying adjuvant. Its use in relatively high concentrations together with low atomization air flow rates improved powder flowability, increased the product's glass transition temperature, and decreased its moisture content and hygroscopicity.

Poster Session 1: Material Science

Objectives - Powdered and granulated particulate materials make up most of the ingredients of pharmaceuticals and are often at risk of undergoing unwanted agglomeration, or caking, during transport or storage. This is particularly acute when bulk powders are exposed to extreme swings in temperature and relative humidity, which is now common as drugs are produced and administered in increasingly hostile climates and are stored for longer periods of time prior to use. This study explores the possibility of using a uniaxial unconfined compression test to compare the strength of caked agglomerates exposed to different temperatures and relative humidities. This is part of a longer-term study to construct a protocol to predict the caking tendency of a new bulk material from individual particle properties. The main challenge is to develop techniques that provide repeatable results yet are presented simply enough to be useful to a wide range of industries. Methods - Powdered sucrose, a major pharmaceutical ingredient, was poured into a split die and exposed to high and low relative humidity cycles at room temperature. The typical ranges were 20–30% for the lower value and 70–80% for the higher value. The outer die casing was then removed and the resultant agglomerate was subjected to an unconfined compression test using a plunger fitted to a Zwick compression tester. The force against displacement was logged so that the dynamics of failure as well as the failure load of the sample could be recorded. The experimental matrix included varying the number of cycles, the amount between the maximum and minimum relative humidity, the height and diameters of the samples, the number of cycles and the particle size. Results - Trends showed that the tensile strength of the agglomerates increased with the number of cycles and also with the more extreme swings in relative humidity. This agrees with previous work on alternative methods of measuring the tensile strength of sugar agglomerates formed from humidity cycling (Leaper et al 2003). Conclusions - The results show that at the very least the uniaxial tester is a good comparative tester to examine the caking tendency of powdered materials, with a simple arrangement and operation that are compatible with the requirements of industry. However, further work is required to continue to optimize the height/ diameter ratio during tests.

Preparation and characterization of ibuprofen–cetyl alcohol beads by melt solidification technique: effect of variables

Ibuprofen (IBU) exhibits short half-life, poor compressibility, flowability and caking tendency. IBU melt has sufficiently low viscosity and exhibits interfacial tension sufficient to form droplet even at low temperature. A single step novel melt solidification technique (MST) was developed to produce IBU beads with lower amounts of excipient. Effect of variables was studied using a 3 2 factorial approach with speed of agitation and amount of cetyl alcohol (CA) as variables. The beads were evaluated using DSC, FT-IR and scanning electron microscope (SEM). Yield, micromeritic properties, crushing strength and release kinetics were also studied. Spherical beads with a method yield of above 90% were obtained. The data was analyzed by response surface methodology. The variables showed curvilinear relationship with yield in desired particle size range, crushing strength and, bulk and tap density. The drug release followed non-Fickian case II transport and the release rate decreased linearly with respect to amount of CA in the initial stages followed by curvilinearity at later stages of elution. The effect of changing porosity and tortuosity was well correlated.

Formulation of Caking‐Resistant Powdered Soups Based on NMR Analysis

ABSTRACT: This study demonstrates that the caking tendencies of powdered soups could be altered by adjusting the proportions of existing ingredients in the recipes without using anticaking chemicals. The composition adjustment was guided by the knowledge of the caking tendencies of individual ingredients, which was acquired with a low field nuclear magnetic resonance (NMR) instrument. This study showed that increasing the proportions of caking‐resistant ingredients in soup recipes lowered the caking tendency. Multiple regression models based on the data from NMR experiments and storage tests were used for prediction of days‐until‐caking (DUC) values of soup products stored at different temperatures (37 to 65°C).