Micronization of a Soft Material: Air-Jet and Micro-Ball Milling

Abstract

Abstract. The air-jet and ball-mill are frequently used in fine micronization of active pharmaceutical ingredients to the order of 1-5 μm, which is important for increasing dissolution rates, and also for pulmonary delivery. In this study, we investigated the ability of air-jet and ball-mill to achieve adequate micronization on the lab scale using a model soft material, Pluronic® F-68. Material mechanical properties were characterized using the nanometer 600. Pluronic® F-68 was ball-milled in a micro-mill at different material weights and durations in liquid nitrogen vapor. In comparison, a lab scale air-jet mill was used at various milling parameters according to a full factorial design, where the response factors were particle yield and particle size distribution, which was analyzed using laser diffraction and scanning electron microscopy. The yield achieved with the micro-ball mill was 100% but was~80% for the air-jet mill, which reduced the size of Pluronic® F-68 from 70 μm to sizes ranging between 23-39 μm median diameters. Ball milling produced particles less than 10 μm after 15 min. Although air-jet milling proved capable of particle size reduction of the relatively soft material Pluronic® F-68, limitations to the lower size range achievable were observed. The feed rate of the material into the air jet mill was a significant factor and slower feed rates lead to smaller sizes by allowing more time for particle collisions and subsequent particle breakage to occur. Micro-ball milling under cold condition was more successful at achieving a lower range particle size reduction of soft materials.

Nanotechnology for Energy Storage

“…The processes responsible for size reduction and separation within the milling chamber were investigated intensively in the 1960s by Rumpf and Kuerten [70]. Although much is known on the particle size reduction of hard and crystalline materials, the jet milling is a grinding process of using highly compressed air or other gases, usually in a vortex motion, to impact fine particles against each other in a chamber [71][72][73][74]. This technique involves a grinding energy created by gas streams from horizontal grinding air nozzles, whose main interest is the very low pollution of ground powders.…”

Lactose microparticle formation from finely atomised droplets

“…To achieve this, several techniques can be implemented in order to reduce the particle size and distribution. For example, micro-ball or air-jet milling can be used to achieve an average particle size to approximately 5 μm (Saleem and Smyth, 2010). The size distribution of bulk particles is reduced based on the principle that collision between particles imparts stress, resulting in fracture and breakup of the bulk particles into smaller ones (Saleem and Smyth, 2010;Yokoyama and Inoue, 2007).…”

“…For example, micro-ball or air-jet milling can be used to achieve an average particle size to approximately 5 μm (Saleem and Smyth, 2010). The size distribution of bulk particles is reduced based on the principle that collision between particles imparts stress, resulting in fracture and breakup of the bulk particles into smaller ones (Saleem and Smyth, 2010;Yokoyama and Inoue, 2007). In micro-ball milling, the bulk powder is centrifugally rotated in a chamber with small metal balls which aid in the micronisation process (Bensebaa, 2013).…”

“…Moreover, inefficiencies of milling on soft material were also observed; a freezing process is sometimes required in order to reduce the elasticity of the material (Saleem and Smyth, 2010). On the other hand, atomised droplets produced during spray drying have a wide variation of droplet size.…”

Engineering hydrophobically modified chitosan for enhancing the dispersion of respirable microparticles of levofloxacin

“…This is usually achieved by micronization/jet milling [19]. Powders produced by such high energy processes exhibit strong inter-particulate attractions, leading to agglomeration.…”