The wide use of particulate materials in industry has elicited various problems that are related to particle size variations (increase or decrease) in diverse mechanical processes. One of the main problems is the low accuracy of designing size reduction systems. The particles break as a result of continuous loads higher than their strength. The particles may also break due to repeated loads lower than their strength (a phenomenon related to fatigue). Therefore, a characterization of particle strength with static and repeated loads is crucial. The current work introduces and validates the fatigue model which development is based on the theoretical model. The modified model enables us to calculate particle strength decreases with every additional loading event. The model depends on six empirical and material related parameters, and was validated by appropriate experiments with a variety of NaCl particle sizes. Since the fatigue effect among particulate materials is a very common event, this study may enable the simulating comminution processes with higher accuracy.

CONTEXT:Silicone oil is used as a valve lubricant in pressurized metered dose inhalers (pMDIs). Its possible impact on drug delivery, through such effects as particle aggregation, has recently been discussed.OBJECTIVE:To examine the effects of a range of directly spiked silicone oil amounts on pMDI performance.MATERIALS AND METHODS:pMDI canisters containing a corticosteroid medicinal compound, HFA134a and accurately measured amounts of silicone oil (0, 200, 400 and 550 µg) were prepared. Samples were characterized for actuation weight, aerodynamic size (by Andersen cascade impaction, ACI), charge (by electrical low-pressure impaction, ELPI) and product appearance by visual imaging.RESULTS AND DISCUSSION:Actuation weights were unaffected by silicone oil. A small increase in aerodynamic size was observed in the presence of silicone oil as a shift from stage 5 to impactor throat. No significant change in medicinal compound recovery was seen (t-tests, p > 0.05). Fine particle fraction as a percentage of dose delivered (FPF) was unchanged, as was particle size distribution derived from charge measurements, with the addition of silicone oil (t-tests, p > 0.05). Canister opening did not indicate container interaction but that sedimentation occurred in the presence of silicone oil. Decanted suspensions containing silicone oil were more transparent. Possible interactions inside and outside the pMDI canister are described.CONCLUSION:As demonstrated previously with an alternative experimental design the study showed that silicone oil has little effect on product performance, when added to a model pMDI formulation at levels that could potentially be observed as a leachable from the metering valve.

In a classical jet-mill, the particles that are forced by air into a circular motion are colliding with other particles as well as with the walls. Such collisions might break the particles thereby reducing the particle size. The air enters the mill at the periphery and exits at the center. The centrifugal and the drag forces are acting simultaneously on each particle in the grinding chamber. These forces define classification phenomenon between finer and coarser particles. For fine particles, the drag force towards the mill exit is larger than the centrifugal force and particles will move out the mill chamber with the air stream. In this research, experiments to define the cut size of particles were conducted. We also tested a number of parameters, such as air flow rate, nozzle angle and nozzle diameter. The classification equation requires knowledge of the radial air velocity and the tangential particle velocity. An extensive numerical investigation led to usable equations that take into account not only all of the above parameters but also the chamber mill diameter, the grinding chamber height, the classifier height, the outlet diameter and the number of nozzles. Inserting the numerical correlations into the force balance resulted in a practical and accurate classification equation. A comparison of the experimental and calculated results showed good agreement for dilute flows.