SIZE REDUCTION AND SIZE SEPERATION

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Dhiraj S.Nikam Assistant Professor Bharati Vidyapeeth’s College of Pharmacy Navi Mumbai SIZE REDUCTION AND SIZE SEPERATION 1

SIZE REDUCTION:

Size reduction: Size reduction is the process of reducing the particle size of a substance to a finer state. Size reduction process is also referred to as comminution and grinding. When the particle size of solids is reduced by mechanical means it is known as milling . Objectives and applications 1.High surface area shows rapid rate of dissolution . 2.Fine powders have increased surface area and contact with solvents. 3.To enhance rate of drying . 4.Improve mixing and minimize segregation. 5.Topical preparations having good spredability . 6.To increase the adsorption property e.g Kaolin 7.Fine areosol particles better enter in lungs e.g.Inhalers in asthama 8.Cosmetics containing fine powders are less gritty and smooth to apply. 9.To increase therapeutic effectiveness . eg.Progesterone SIZE REDUCTION 2

SIZE REDUCTION:

10.The stability of emulsions is increased by decreasing the size of the oil globules. 11.The physical appearance of ointments, pastes and creams can be improved by reducing its particle size. 12.There is an increase in antiseptic action for calomel ointment when the particle size of calomel is reduced. Limitations 1.Fine powders due to increase surface may forms the lumps. 2.Size reduction may lead to physiochemical instability. eg . Loss of volatile matter, softening, melting. 3.Since fine powders are more reactive they are more sensitive to chemical degradation. SIZE REDUCTION 3

SIZE REDUCTION:

Factors affecting size reduction 1.Hardness: It is a surface property of the material. It is frequently confused with a property named strength. An arbitrary scale of hardness has been devised known as Moh’s Scale; Moh’s Scale = 1 is for graphite Moh’s Scale < 3 is for soft material Moh’s Scale > 7 is for hard material Moh’s Scale = 10 is for diamond The harder the material the more difficult it is to reduce in size . SIZE REDUCTION 4

SIZE REDUCTION:

Toughness: If material is strong enough to withstand great strain without breaking. e.g. Surface of fibrous drug is tough. Abrasiveness: Abrasiveness is a property of hard materials (particularly those of mineral origin) and may limit the type of machinery that can be used. If material have rough, irregular surface and weak intermolecular bonding at surface. Stickiness: Stickiness is a property that causes considerable difficulty in size reduction, for material may adhere to the grinding surfaces, or the meshes of the screen may become choked.e.g . Gum acacia(binder),Kaolin such inert substances can be used to control. Slipperiness: Slippery powder is difficult to hold for cutting and milling, so if their melting point is low then they can be melted or softened. Low melting point: Low m.p powders may become soft and sticky eg . Ibuprofen, waxes, polyethylene glycol . Remedy- Cooling the material or using the cold water jacketed mills can minimize it. SIZE REDUCTION 5

SIZE REDUCTION:

Layered structure: Some substances like minerals have weak lines or layer that split easily e.g Shells used in shanka bhasma . Fibrous structure: Cellular vegetables crude drugs produces long fibrous powders, which are light and bulky and difficult to grind. Moisture content: Moisture content influences a number of properties that can affect size reduction, for example, hardness, toughness or stickiness. E.g -Less than 5 % is suitable. Bulk density: Light weight bulky powders require bigger hoppers. e.g. starch powder. Degree of size reduction: It is advisable to reduce the particle size not in one operation because it undergoes softnening , melting and may lead to thermal degradation due to heat generated. SIZE REDUCTION 6

SIZE REDUCTION:

Principle of size reduction: Laws governing energy and power requirement of size reduction: Assumption: Energy required to produce a change dL in a particle of a typical size dimension L is a simple power function of L: dE / dL = KL n (1) Where, dE is the differential energy required dL is the change in a typical dimension L is the magnitude of a typical length dimension K and n are constants SIZE REDUCTION 7

SIZE REDUCTION:

Kick’s assumption: assumed that the energy required to reduce a material in size was directly proportional to the size reduction ratio d L /L. This implies that n in equation. (1) is equal to -1. n = -1 Therefore, dE / dL = K / L which gives dE = K dL / L Upon integration, we get E = K ln ( L initial / L final ) Kick also assumed that K = K k f c Where, K k is Kick's constant f c is the crushing strength of the material Therefore , E = K k f c ln ( L initial / L final ) Kick’s Law Application: It has been found, experimentally, that for the grinding of coarse particles in which the increase in surface area per unit mass is relatively small, Kick's Law is a reasonable approximation. SIZE REDUCTION 8

SIZE REDUCTION:

Rittinger’s assumption: n = -2 Therefore, dE / dL = K / L 2 which gives dE = K dL / L 2 Energy required to reduce a material in size is directly proportional to the surface area change. Upon integration, we get E = K ln (1 / L final – 1 / L initial ) Using K = K R f c where K R is Rittinger's constant f c is the crushing strength of the material Therefore , E = K R f c ln (1 / L final – 1 / L initial ) ( Rittinger’s Law) Application: For the size reduction of fine powders, on the other hand, in which large areas of new surface are being created, Rittinger's Law fits the experimental data better. SIZE REDUCTION 9

SIZE REDUCTION:

Mechanism of Size Reduction: Cutting – Material is cut by means of a sharp blade or knife. Compression – Material is crushed by application of pressure. Impact – Impact occurs when the material is more or less stationary and is hit by an object moving at high speed or when the moving particle strikes a stationary surface. In either case, the material shatters to smaller pieces. Usually both will take place, since the substance is hit by a moving hammer and the particles formed are then thrown against the casing of the machine. Attrition – In attrition , the material is subjected to pressure as in compression, but the surfaces are moving relative to each other, resulting in shear forces which break the particles. SIZE REDUCTION 10

SIZE REDUCTION:

SIZE REDUCTION Cutting: (Cutter Mill ) Principle and operation: 1.Works on principle of cutting material by rotating and stationary knives. 2.Rotaing knives attached to motor. 3.Material fed in hopper comes in between rotating and stationary knives and cuts in to small pieces. 4.Depending upon required size of the product a screen of particular mesh size is attached to outlet. 5.Material of larger size is retained in mill and product of required size comes out. Application : It is used to cut tough , fibrous drugs such as roots , wood peels before extraction. Product size ( # 20-80) 11

SIZE REDUCTION:

SIZE REDUCTION Compression (Roller Mill) Principle and operation: 1.Material is compressed by material under pressure. One roller is driven by motor and other is set free. 2.When fed material is placed in gap between rollers and roller starts rotating by friction in opposite direction of first roller. 3.Gap between rollers are set according to particle size . Application: For grinding hard material such as seeds before extracting fixed oils. 12

SIZE REDUCTION:

SIZE REDUCTION Impact:(Hammer Mill) Principle and Operation: 1.Swinging hammers are attached to rotor and covered with stout metallic casing. 2.Fed material is ejected by impact of high speed hammers. Screen of particular mesh size is attached to outlet. 3.Material of larger size is retained in mill and the product of required size comes out. 4.Due to swinging hammers, there are less chances of jamming the mill. Application: Use for coarse or moderately fine powder. 13

SIZE REDUCTION:

SIZE REDUCTION Impact and Attrition:(Ball mill) Principle and operation: 1.Rotating cylinder (metal, porcelain) containing loose balls( metal-lead-antimony) rotates on horizontal axis. 2.These balls occupy 30 to 50% of cylinder volume. 3.These balls lifted up and falls down in cascade. 4. At slow speed- balls slide over each other. High speed- Due to high centrifugal force balls pushed out toward wall and does not reduce size much. 5.Therefore speed of balls should be optimum speed so that balls will be lifted at top and falls down. Application: Used for dry and wet grinding. To produce fine powder without dust. 14

SIZE REDUCTION:

SIZE REDUCTION Impact and attrition:(Fluid energy mill) Principle and operation: 1.Size reduction occurs due inter-particular attrition and impact on turbulent particles. 2.Made up of loop of pipe internal diameter 2 to 20 cm and height 1-2 m. 3. Pipe allows free movement of particles in steam of high velocity air. 4. High degree of turbulence causes the impact and attrition. 5.The cyclone collector fitted at outlet gives sufficiently fine powder.( 1 to 30 micron) Application: Suitable for heat sensitive drugs such as antibiotics and vitamins. 15

SIZE REDUCTION:

SIZE REDUCTION Properties and applications of selected size reduction equipment 16

SIZE SEPARATION:

Size separation: Technique use to classify particles on the basis of size. Applications: 1.Monosized particles undergoes less segregation. 2.Filing of particles in capsule ensures more uniformity in weight and dose. 3.Coarse granules with little fine powder ensure good flow ability. 4.Fines produced during transport and processing can be separated. 5.Fine powders pass through mesh no.85 are used for topical application and mesh no. 60 are for oral administration. SIZE SEPARATION 17

SIZE SEPARATION:

SIZE SEPARATION Particle size analysis : 1.Optical microscopy: (0.2-150 um): Can distinguish aggregates from single particles I mage analysis computers each field can be examined, and a distribution obtained. For submicron particles it is necessary to use either TEM (Transmission Electron Microscopy) or SEM (Scanning Electron Microscopy). TEM and SEM (0.001-5µm) 18

SIZE SEPARATION:

Methods of particle size analysis: 2 .Sieving: 1.Most widely used method of analysis. 2.Different grades of sieves are used for sifting the powders and preparing the granules of required particle size. 3.Material which does not pass through through I sieve called as tailing. 4. Tailing should never be rejected because they may contain the medicinally active constituents . The tailing may be added to the next batch of the drug to be ground . SIZE SEPARATION 19

SIZE SEPARATION:

SIZE SEPARATION 20

SIZE SEPARATION:

Material used for sieve: a.Iron - Cheap but rusting may occur, so it is protected by coating. b.Copper -Avoid risk of iron contamination, but it is soft material and meshes can be destroyed easily. So use copper alloys-made of phosphorus- bronz , it possesses good resistance to corrosion. c.Stainless still: Most expensive material, and recommended for pharmaceutical purpose. d.Non metals- Man made fibers like-nylon and terylene . SIZE SEPARATION 21

SIZE SEPARATION:

Principles of sieving:(Mechanical sieving method) 1.Agitation: a. Oscillation - The sieve is mounted in a frame that oscillates back and forth, and material roll on surface. b . Vibration- Here , the mesh is vibrated at high speed, often by means of an electric device using the 50-Hertz alternations of alternating electric current. c . Gyration - The sieve is given a rotary movement of small amplitude, but of considerable intensity, giving a spinning motion to the particles. 2 . Brushing method: spiral brush rotating on the longitudinal axis of the sieve . 3. Centrifugal method: vertical cylindrical sieve with a high-speed rotor inside the cylinder, particles are thrown out because of centrifugal force. SIZE SEPARATION 22

SIZE SEPARATION:

Advantages Easy to perform Wide size range Inexpensive Disadvantages Known problems of reproducibility Wear/damage in use or cleaning Irregular/agglomerated particles Rod-like particles : overestimate of under-size Labour intensive SIZE SEPARATION 23

SIZE SEPARATION:

II. Sedimentation method- When particles are too small to be screened effectively or when large quantities of material are to be handled, methods involving differences in the rates of settling of particles of different sizes and of different materials are used. Sedimentation : The process by which particulates settle to the bottom of a liquid and form sediment. Stokes' Law predicts the settling velocity of small spheres in fluid, either air or water. where w is the settling velocity, ρ is density (the subscripts p and f indicate particle and fluid respectively), g is the acceleration due to gravity, r is the radius of the particle and μ is the dynamic viscosity of the fluid. SIZE SEPARATION 24

SIZE SEPARATION:

SIZE SEPARATION Sedimentation : Andreason pipet method : Consist of tall vessel called sedimentation vessel (500 ml), fitted to glass stoppered joint and 10 ml pipet. 1 % suspension of the powder is prepared in a suitable liquid medium which is then placed in the sedimentation vessel. 10 ml sample is withdrawn at specific time interval and samples are dried and the residues are weighed. Weights of the dried samples the percentage of the initial suspension is calculated for particles having sizes smaller than the size calculated by Stoke’s equation for that time 25

SIZE SEPARATION:

Advantages Equipment required can be relatively simple and inexpensive. Can measure a wide range of sizes with considerable accuracy and reproducibility. Disadvantages Sedimentation analyses must be carried out at concentrations which are sufficiently low. Large particles create turbulence, are slowed and are recorded undersize. Careful temperature control is necessary to suppress convection currents. The lower limit of particle size is set by the increasing importance of Brownian motion for progressively smaller particles. Particle re-aggregation during extended measurements. Particles have to be completely insoluble in the suspending liquid. SIZE SEPARATION 26

SIZE SEPARATION:

SIZE SEPARATION Particle size analysis Coulter Counter (0.6 to 120 um) Testing tube surrounded by highly conducting electrolyte The number and size of particles suspended in an electrolyte is determined by causing them to pass through an orifice an either side of which is immersed an electrode. The changes in electric impedance (resistance) as particles pass through the orifice generate voltage pulses whose amplitude are proportional to the volumes of the particles . These pulses are amplified and counted electronically, and particles and particle size distribution is displayed on computer. 27

SIZE SEPARATION:

SIZE SEPARATION Cyclone separator: The suspension is introduced tangentially at fairly high velocity, so that a rotary movement takes place within the vessel. The rotary flow within the cyclone causes the particles to be acted on by centrifugal force, solids being thrown out to the walls, hence falling to the conical base and out through the solids discharge. Application : suspensions of a solid in a gas, usually air. 28

SIZE SEPARATION:

SIZE SEPARATION Air Separator: It involves mechanical force for movement of air. Rotating disc and vanes develop rotatory movement of air. By controlling speed of rotation it is possible to separate particles of definite size. Fine particles are carried forward by air and velocity drops the leave air stream. 29

SIZE SEPARATION:

SIZE SEPARATION Elutriation method: Based upon counter flow of fluid(air/water) and settling particles through vertical columns. As airflow goes upwards, the dense particles leaves the stream and sediment down in bottom. So air flow carries only light particles and collected by separate vessel. 30

SIZE SEPARATION:

Particle size distribution: It is mathematical function that defines the relative amount, typically by mass, of particles present according to size. PSD is also known as  grain size distribution. Powders of polydispersed system and number or weight of particles lies within certain range. Measurement techniques are-Sieving, elutriation, optical counting, sedimentation. SIZE SEPARATION 31

Powders:

Classification: Powders Internal (Oral) External Parenteral Bulk powders Dusting Divided Bulk Insufflation Simple divided Antacid Dentifrices Compound Laxative Snuff Enclosed in sachet Dietary Tablet trituration Effervescent Powders 32

POWDERS:

Def : A Pharmaceutical powder is a mixture of finely divided drugs or chemicals in a dry form meant for internal or external use. Advantages of powders : 1-Flexibility of compounding. 2-Good chemical stability 3-Rapid dispersion of ingredients (because of small particle size ) Disadvantage 1-Time-consuming preparation 2-Inaccuracy of dose( size of measuring spoon, density of powder, humidity, degree of settling , fluffiness. 3-Unsuitability for many unpleasant tasting, hygroscopic and deliquescent drugs POWDERS 33

POWDERS:

Simple Powder: Only one ingredient either crystalline or amorphous. Compound powder: Contain two or more than two API are mixed together. e.g. Rx Aspirin 300 mg Paracetamol 150 mg Caffeine 50 mg Marketed preparation- 1.Acidin with belladona powder 2.Bismag powder POWDERS 34

POWDERS:

Tablet Triturates: It is mixture of dilution of mixture with potent substance.. Small quantity of solids are mixed together on white paper sheet by spatula or knife. Large quantities are mixed by mortar and pestle. Procedure: 1- Reduce the drug to a moderately fine powder in a mortar. 2-Add about an amount of diluents & mix well by thorough trituration in the mortar . 3-Done by geometrical dilutions e.g -100 mg potent drug to be mixed with 900 mg of lactose. So take 100 mg potent drug + 100 mg lactose sum is 200 mg. Then take this 200 mg of mixture and add 200 mg of lactose. POWDERS 35

POWDERS:

Oral rehydration powder (Effervescent Granules) : They contain a soluble medicinal agent mixed with citric acid, tartaric acid and sodium bicarbonate. Before administration they are suspended and dissolved in water, on dissolution it produces CO 2 and result acid base reaction with effervescence. The carbonated water produced serves as mask for saline and bitter taste of drug. CO 2 accelerates flow of gastric juice and accelerate absorption of medicament. Effervescent Granules are prefer over effervescent powder in order to decrease rate of dissolution of substance upon addition of water. POWDERS 36

POWDERS:

Method of preparation: Reaction: 3NaHCO 3 + C 6 H 8 O 7 .H 2 O = C 6 H 5 Na 3 O 7 +3CO 2 +3H 2 O ( Citric acid) (sodium citrate) 2NaHCO 3 + C 4 H 6 O 6 = C 4 H 4 Na 2 O 6 + 2CO 2 + 2H 2 O (tartaric acid) ( sodium tartarate ) Citric acid and tartaric acid both are used because- If citric acid alone is used, it contains water molecule of crystallization which is liberated on heating, and will make the mass to wet and difficult to pass through sieve. If tartaric acid alone is used, it is anhydrous so some non-solvent liquid have to be used for granulation, otherwise the resulting granules will be firm but will crumble readily gives salty taste. Citric acid partially neutralizes NaHCO3 ,rest of all NaHCO3 will be neutralized by tartaric acid. Marketed Preparation: 1.Eno fruit salt (Smith kline ) 2.Cetri-soda (Abbot labs) 3.Rhino (Mehta Unani ) Effervescent tablet- Pepfiz ( Ranbaxy lab) POWDERS 37

POWDERS:

Dusting Powder : (For external application) They are used for antiseptic, astringent, antiperspirant, absorbents, protective and lubricant purpose. They are homogeneous very fine state and pass through sieve 120. They should flow easily, spread uniformly and stick to skin They are prepared by mixing two or more ingredient with starch, kaolin or talc which are sterilized before use. If get inhaled they cause pulmonary inflammation. Packaging -They are dispensed in sifter top containers or pressure aerosols, and applied by powder puff, brush or gauze. Rx Purified talc, sterilized 50 gm Starch,in powder 25 gm Zinc oxide 25 gm Label: Zinc, starch and talc dusting powder POWDERS 38

POWDERS:

Theory: Talc and Kaolin must sterilized by heating 160 C for 1hr. Purified talc has excellent flow and lubricant. Starch as an absorbents. Zinc oxide acts as an antiseptic and absorb moisture. Marketed Preparations: 1.Cibazol dusting powder (Contains- Sulphathiazole ) 2.Nebasulf dusting powder (Pfizer Ltd.) 3.Salcylic acid compound dusting (Alpine) POWDERS 39

POWDERS:

Insufflations: Finely divided powders meant for introduction to body cavities such as ears, nose, tooth sockets. It is transfer through apparatus. Disadvantage: 1.It is difficult to obtain measured quantity of uniform dose. 2. P owder may get blocked when powder is wet or apparatus is wet. Dentifrices : Helps the tooth brush to clean the surfaces of teeth. They have cleansing action. Marketed Tooth powder: 1.Clinso-dent (ICPA Health product) 2.Flixon flavored denture (ICPA Healyh products) Marketed Tooth pastes 1.Sensolin (Warren Pharma ) 2.Mentadent (Hindustan Lever) 3.Desent tooth paste ( Indoco Remedies) POWDERS 40

POWDERS:

Dry Syrup: Definition: These are suspensions of commercial dry mixture that require addition of water at the time of dispensing. Rational: 1.Inadequate chemical stability of drug in aqueous vehicle. 2.To avoid physical stability problems like viscosity changes, conversion in polymorphic form. Required characteristics of for Dry syrup: 1.Powder blend must be uniform mixture of appropriate conc. Of each ingredient. 2.Dusting reconstitution powder blend must disperse quickly and completely in aqueous vehicle. 3.Final product must have acceptable taste ,odor and appearance. POWDERS 41

POWDERS:

Formulation: 1.Suspending agents: e.g-Acacia,MCC,Sodium cmc,povidone 2.Sweetners- Sucrose, mannitol , dextrose,aspartmate 3.Wetting agent: These are surfactants increases wetting of hydrophobic drugs. e.g - polysorbate 80,sodium lauryl sulphate 4.Buffers-Sodium citrate buffer 5.Preservatives- Sodium benzoate 6.Flavours-Raspberry,Pineapple Marketed Preparation: 1.Amoxicillin trihydrate 2.Ampicillin 3.Cephalexin 4.Diclofenac sodium POWDERS 42

POWDER MIXING:

Significance: This operation makes two or more components (API) get uniformly distributed in powder bed. Mechanism of mixing: 1.Convection: Large group of particles moving together in mixer to achieve uniformity (macroscopic mixing) 2.Sher: One layer of powder particles move to another layer of particle-used when powder layers are from different particles(semi microscopic mixing) 3.Diffusion :It is movement of individual particle, volume of powder bed increases because of convection and shear. Voids between particles increases great potential to individual particles to mix together. POWDER MIXING 43

POWDER MIXING:

POWDER MIXING Tumbling Mixers/Blenders Used for powders with similar densities. Includes V-Shape, rotating cubes, cylindrical, double cone, Y-cone mixers. They mix powders with good flow ability Disadvantage: Segregation (separation) of drug from powder components may occur due to difference in particle size. 44

POWDER MIXING:

POWDER MIXING Ribbon mixer: Principle: Mechanism of mixing is shear, high shear rate is effective in breaking lumps and aggregates. powder bed lifts up and cascade at bottom of container. Construction : helical blades mounted on shaft with left and right hand twist. Uses: mixing finely divided solids, wet solid mass. Solid- liquid and solid -solid mixing can be done. Advantage: High shear rate can be applied by baffles, which bring rubbing and breakdown of aggregates. Disadvantage :1.Movement of particles is two dimensional. 2.Shearing action is less. 3.It has fixed speed drive 45

POWDER MIXING:

POWDER MIXING Planetary Mixers: Principle: Mechanism of mixing is shear. Shear is applied between moving blade and stationary wall. Mixing arm moves around its own axis and central axis to get uniform mixing. Construction: consist of vertical shell, blade mounted from top of bowl, mixing shaft driven by gear. Uses: Break agglomerates rapidly, can achieve d ry and wet granulation. Advantage: Speed of rotation can be varied. Disadvantage: Mechanical heat is built up within powder mix, It has limited size 46

POWDER MIXING:

POWDER MIXING Nautamixer : Principle and working: Based upon convection, shear and diffussion . Consist of bottom discharger and rotating screw fastened to upper end of rotating arm. Screw coveys the product to the top ,where it can flow back to the powder feed. Vertical impeller and horizontal rotating arm induces convection, shear and diffusion. 47

POWDER MIXING:

POWDER MIXING Fluid bed mixer: Principle: Air movement is used for mixing, air is admitted at the base at an angle which gives tumbling action and spiral movement to the powder. Construction: Stationary mixer either vertical or horizontal of stainless steel. Wire mesh is placed at bottom of vessel, which acts as support. Air is allowed from beneath the mesh and material is circulated by using the fan. Advantage: 1.Reduce mixing time. 2.Mixing is intimate and efficient. 3.useful for dry and wet massing 4.Also used for coating . 48

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