Particle Technology Flashcards
(26 cards)
Milling Def
Breaking down the larger mass formed in agglomeration (granulation and direct compression) into smaller more desirable particle size. Smaller particles are better mixed (larger surface area).
Particle size in tableting
Effects particle flow and filling of equipment and then pharmacokinetic release in body (LADME)
Way of standardizing particle characteristics
Approximate sphere/equivalent diameter. Allows for comparison of particles of irregular shapes. Compare diameter, area and perimeter of particle. Particles of same sample can be compared on distribution
Particle Size Distribution
When samples particles aren’t monosized (don’t have same equivilent diameter. Particle diameter on x-axis and particle frequency on y. A narrower curve indicates increased validity in interpreting samples characteristics
Positive Distribution Def
Graph where tail points to right
Methods of Particle size analysis
sieve, microscopic, light scattering and coulter Counter
Coulter Counter Outline
Change in electrical stimuli
Sieve Analysis Outline
Powder is passed through device containing trays with holes in them. The further down the tray the smaller the hole. All hole sizes are standardised across sieves (pharmacopia tells shelf of particles and diameter is infered from there). The coarsest particles in sample should be on highest tray containing powder and finest particles in sample are on lowest. Device shakes itself to ensure that no particles are stuck in wrong tray
Sieve Analysis Advantages
Both separates out and analyses both mass and size of diameters. Masses of particles in individual trays can be weighed
Sieve Analysis Disadvantages
Can’t be used in manufacturing. batch processing size is too small
Microscopic Analysis Def
3 types: light, scanning electron and transmission electron microscopy. Adavantage: tells shape of particles aswell as size
Light Microscopy
Equivalent diameter analysis using calibrated scales. Compare perimeter and area
Scanning Electron Microscopy Outline
Particle fine resolution. See particle shape and surface characteristics
Transmission Electron Microscopy Outline
Transectional ultra structure of very fine samples
Size Reduction (Comminution)
Localising stress along weak points of particles (impurities, discontinuities) promotes propagation of cracks
Energy Applied (E) Outline
Higher E = smaller particles. Process is very inefficient (most energy lost as heat). High E may increased in polymorphism and amorphous solids formation
Milling Def
Particle size reduction by mechanical means. 5 methods: cutting, impact, compression, attrition and impact & attrition
Cutter Mill Outline
High shear, used to create coarse particles. Sample passes through series of stationary and rotating knives. Particles of wanted size pass through screen and are collected. Follows dry granulation
Hammer Mill Outline
High impact forces, creates coarse particles. Samples hit by rotating hammers (both flat and knife edged hammers), particles of ideal size are passed through screen. Large amount of heat produced (inefficient, unsuitable to thermosensitive drugs). Used in mixing and wet grinding
Vibration Mill Outline
Impact forces, produces fine particles .Steel/porcelain balls are bounced up and down in machine containing powder. Wet grinding
Ball Mill Outline
Shear attrition, produces small particles. Cylinder containing heavy balls and particles rotates. Particle is broken down when between 2 particles rub together. Note: sample should be of certain volume (too high = cushioning, too low = too high shear forces), rotation speed is also importnat (aim for cascade of balls
Fluid Energy Mill
Fine particles, attrition. Powder funelled into rotating drum containing high velocity liquid. Particles broken by attrition (coliding cith fluid) and impact (colliding with eachother)
Methods of powder separation Outline
Sieving, sedimentation, eulration and cyclone
Sedimentation Forces
Gravitational and Centrifugal
