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FLOW PROPERTIES OF POWDER Guided By:- Mr. K. J. Wadher Design by:- A.C. Alaspure S. K. B. College Of Pharmacy Kamptee, Nagpur 1

Introduction : 

Introduction When we concerned with the flow of any material it relates with Rheology. Deformation of the body is the relative displacement of its mass points without moving the centre of gravity. But in fact that powers are difficult to discussing in rheological term. Hence we can able to define the bulk flow properties of the power in terms of fundamental measurable characteristics of particle of them. 2

Classification Of Properties Of Powder : 

Classification Of Properties Of Powder Basic properties of powder can be classified accordance to ‘Hey woods’(1963) Fundamental properties:- Chemical constitution Atomic structure Size Shape Porosity Particle density Surface texture Particle size distribution Specific surface area Fundamental properties relating to individual particle. Fundamental properties of collection of particle. 3

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Derived properties of powder :- Particle size Nature of particle Moisture content Angle of repose Dispersability Carr׳s consolidation index Hausner ratio Fundamental properties:-These properties that relates to the individual particle . Derived properties:- They are dependant on fundamental properties & well defines the basic factors relating to measurements. 4

Porosity : 

Porosity it is the space between the particle. Volume occupied by powder known as Bulk volume (Vb) Porosity or voids (Є):- Ratio of void volume to the bulk volume of the packing. Bulk volume = True volume + void volume Vb = Vp + V Where , Vp= true volume Vb=bulk volume V =void volume Є = (Vb-Vp)/Vb = 1- (Vp/Vb) % porosity = Є ˣ 100 5 Porosity=void volume/bulk volume

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Packing Arrangement : 

Packing Arrangement Two ideal packing materials Closest or rhombohydral Most open, loosest or cubic packing. Cubic arrangement Closest or rhombohydral 7

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Theoretical porosity of powder consist of uniform sphere in Closest packing- 26% Loosest packing- 48% Real powder have porosity in between 30 to 50%. In suspension, porosity may above the theoretical max limit 48%. Crystalline materials porosity- <1% (under force 10000 lb/in2) 8

Density Of Particle : 

Density Of Particle Three types of densities Universally defined as weight per unit volume. True density:- it is the weight of material it self Granule density:- Measured by mercury displacement method. Mercury fills the voids, but fails to penetrate internal particles. as it has non weighting properties. Granule volume related to weight of the mercury that displaced by granules in pycnometer. Granule density = granule weight granule volume 9

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Bulk density:- Bulk density = mass of the powder (w) bulk volume (Vb) When particle are loosely packed , lots of gaps in between particle. Bulk volume increases making powder light. Powder classified as ‘light’or ‘heavy’ “light powder have high bulk volume” ‘Bulk density apparatus’ is used to determine bulk volume. applications:- Used to check uniformity of bulk chemicals. Size of capsule determine by bulk volume. Higher the bulk volume bigger the size of capsule. 10

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True density measurements- For non porous solid:- True density & granule density identical. Both obtained by- Helium displacement method Liquid displacement method For porous material (having an internal surface) Using helium densitometer 11

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Arrangement of helium pycnometer Bulk density apparatus Sample holder Variable volume piston Pressure detector valve atoms vacuum Helium 12

Flow Properties : 

Flow Properties 13

Particle Size : 

Particle Size If the particle size is small (10um) the powder flow is restricted due to cohesive force between the particle. Particle with high surface to mass ratio are more cohesive than the coarser particle which influences by gravitational force. Particle size >250nm are free flowing. Shear strength:- Cohesion define as stress necessary to shear powder bed under zero normal load. Shear cell:- Apparatus measure the shear stress ‘τ’ at different values of normal stress ‘σ’ 14

Nature Of Particle : 

Nature Of Particle 15

Moisture content : 

Moisture content Higher the moisture content greater the cohesion & adhesion. Flow properties can be improved by following methods- 16

Angle Of Repose : 

Angle Of Repose When only gravity acts upon static heap of the powder will tends to form conical mound. In which one limitation exists- The angle to the horizontal cannot exceed a certain value this known as ‘angle of repose’. CONCEPT OF ANGLE OF REPOSE When small quantity of powder is available, a standard powder technique is use : i.e. “Angle of spatula” Any particle temporary lies down the limiting angle. It will roll down the adjacent surface. Under the influence of gravity. Untill gravitational pull is balance frictional force in between particles. 17

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Picking up the powder on spatula & estimate the angle of triangular section of the powder heap view from the end of spatula held horizontally. By definition, tan ɵ = h/r ɵ= tan-1(h/r) where, h = height of pile r =radius of base of the pile Ɵ =angle of repose Cos ɵ = D/(l1+l2) or ɵ= cos-1 D/(l1+l2) Where, D= diameter of base l1 & l2=opposite side of the pile 18

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Effect on angle of repose of various procedure decrease particle size- higher angle of repose Fines (up to 15%)-increase angle of repose Lubricants at low concentration- ↓ angle of repose Rough & irregular surface- higher angle of repose Lower the angle of repose- better the flow property Angle of repose apparatus. 19

Carr′s Consolidation Index : 

Carr′s Consolidation Index This property known as compressibility. It relates with flow rate, cohesiveness & particle size. Fluff density:- ratio of mass of powder to fluff volume. Tapped density:- ratio of mass of powder to tapped volume. Fluff density (ρb, min)= W/Vo g/cc Tapped density(ρb, max) = W/Va g/cc tapped density- poured density Carr′s Index (%) = ˣ 100 tapped density 20

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Adding glidant, e.g. 0.2% aerosil improve the flow 21

Hausner′s Ratio : 

Hausner′s Ratio Hausner′s ratio = tapped density (ρ Bmax) poured density (ρ Bmax) Hausner′s ratio of less than 1.25 (equivalent to 20% carr′s) indicates good flow. Greater than 1.5(equivalent to 33% carr′s)indicates flow. Between 1.25 & 1.5- added glidant – improves flow. 22

Dispersability : 

Dispersability It is the ability of a material to flow or pour easily over a planes. Dispersability, dustiness, & floodability are inter- related term. weight of powder in watch glass Dispersability (%) = ˣ 100 initial weight of the sample Dispersibility apparatus:- A hallow cylinder through which is Drop from a height 61 cm above the glass watch. 23

Compression Properties : 

Compression Properties This property normally used for the preparation of the tablet . This process also called compaction. During this porosity of powder changes. Plastic behaviour:- Deformed on compression Compact powder get deformed which is tapped into close packing. For e.g. kaolin which have soft & spongy particle Dilatant behaviour:- Shows unexpected expansion under the stress. Some substances when compacted exhibits higher porosity than the powder in close packing. 24

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For e.g. sodium chloride. Compression properties of most drugs extremely poor. Hence compression vehicle is added such as- Lactose Calcium phosphate Microcrystalline cellulose Low dose drug tablet prepared by direct compression But high dose drug prepared by granulation methods. Tablet material should be plastic i.e. undergoing permanent deformation 25

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Thank you… 26

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