Comminution Flashcards
Particle size influences bioavailability - a smaller particle size results in faster dissolution. True or false?
True
What is meant by comminution?
The reduction of solid materials from a bigger mean particle size to a smaller mean particle size
The efficiency of a conventional ball mill is greater than that of a vibratory mill. True or false?
false, vibratory mill more efficient
Dry sieving is usually more efficient than wet sieving. True or false?
False
Wet sieving more efficient
Which milling method is defined as self-classifying?
Cutter mill
Separation efficiency is the effectiveness of a given process in separating particles into oversized and undersized fractions. True or false?
True
How many micrometres is a coarse powder?
> 350
How many micrometres is a medium/fine powder?
100-350
How many micrometres is a fine powder?
50-100
How many micrometres is a very fine powder?
10-50
How many micrometres is a micronised powder?
<10
The sieve method is simpler and more cost effective than microscopy. True or false?
True
The sieve method provides particle shape information. True or false?
False
Which particle size analysis method sorts a large quantity of particles into different size ranges and determines the particle size distribution based on the mass collected in each range?
Sieve method
Mohs’ scale is a quantitative measure of hardness. True or false?
False
Qualitative
Brinell or vickers is a quantitative measure of hardness true or false?
True
Which milling method achieves a particles size of 1-300 micrometres?
Attrition
Which milling method achieves a particles size of 100-100,000 micrometres?
Cutting
What particle size can a ball mill achieve?
1 to 200 micrometres
Which milling method achieves a particles size of 20-100,000 micrometres?
End runner
Which milling method achieves a particle size of 1-1000 micrometres?
Vibration
Which milling method achieves a particle size of 600-200,000 micrometres?
Roller
- Which milling method achieves a particle size of 30 -10,000 micrometres?
Hammer
What particle size can a fluid energy mill achieve?
1-100,000 micrometres
Which milling method achieves a particle size of 10-9,000 micrometres?
Pin mill
What are larger particle sizes usually used for?
granules used in capsules or for suspensions
What type of particles are used in dry powder inhalers?
Small solid particles
How can milling change the characteristics of poorly soluble drugs?
can modify their wetting and dissolution, solubility also directly linked to particle size so important that all particles have similar size, shape and surface characteristics
Why is particle size important in parenteral administration?
influences accumulation of micro-particulates after admin
Size of particle affects manufacturing processes such as mixing but what other characteristics of powders?
flowability and packing properties, quality control to guarantee uniformity, prediction of pharmaceutical effect and efficacy
To adequately describe a particle what do you need?
Precise measurements of at least 3 dimensions
What is the equivalent sphere method?
consider a particle to be a sphere and reduce the 3 dimensions to a single number
What are some shape descriptors used to classify particle shape?
spherical smooth, rounded, acicular, spherical rough, angular, spherical irregular, elongated irregular, dendritic
What is the ideal particle size range?
25-50 micrometres
Why can particle sizes smaller than 15 micrometres be problematic?
they tend to aggregate, affecting quality of the mix and can cause an uneven distribution of the powder
When designing comminution processes what is important to consider?
the toughness, hardness, additional energy requirements and particle shape
The extent of size reduction is always related to what?
Milling time
What is size reduction mainly driven by?
crack propagation, localized stress produces strain in the particles which essentially ruptures the bonds and the crack spreads
Which processes can be used to separate different particle sizes?
agitation methods, brushing methods, centrifugal methods
What are the most common milling methods and how do they work?
Cutter mill (series of knives and blades on a rotor, blades fracture the particles, screen to retain larger material), Roller mill (two rollers, one mechanically driven, second rotated by friction as particles pass through), Ball/vibration mill (filled with porcelain or stainless-steel balls, in ball milling impact causes reduction but in vibrational, reduction occurs because of constant impact and vibration of balls)
