Drying lecture 20 Flashcards Preview

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Flashcards in Drying lecture 20 Deck (16):
1

Why is drying important in quality tests, in what concepts?

flowability
stability
dry granulation
compaction

2

Define moisture content:

the amount of water contained in a material

3

Define Mv:

% moisture by volume: the molecules of water per unit volume by the total number of molecules per unit volume

4

Define relative humidity:

the amount of moisture in the air as a % of the max amount of moisture that the air can hold

5

What is the relation between temp, RH and water vapour?

the higher the temp, the more water vapour that the air can hold and so there is a decrease in RH

6

Define dew point:

just as increasing temp decreases RH, decreasing temp will increase RH and when RH reaches 100%, water vapour will condense to form dew

7

During drying, what 2 factors can change?

1. moisture content (water can evaporate)
2. temperature (can decrease to reduce heat-exchange with the material)

8

Define hygroscopic substances:

attract and hold water molecules from the surrounding environment e.g. paper (if less moisture in the air, paper will release water) and some plastics

9

Total moisture = ...

FREE (unbound) + EQUILIBRIUM (bound)

10

How can equilibrium moisture be varied?

by varying external conditions such as adding a desiccant like silica gel or phosphorous pentoxide to reduce RH

11

What are the 2 types of solute migration?

1. inter-granular migration = solute moves between granules towards the surface (differences in solute composition between granules)
2. intra-granular migration = granules are separated during the process (even distribution of solute within a granule)

12

How can you reduce solute migration (to ensure homogeneity)?

a) Initial moisture content
b) Slow convective drying
c) Drying by microwave radiation
d) Dynamic drying methods

13

What are the 3 methods to dry wet solids?

1. fluidised bed dryer (convection)
2. microwave (radiation)
3. vacuum oven (conduction)

14

What are the 2 methods to dry solutions and suspensions?

1. spray dryer
2. freeze-drying

15

Why is solvent removal useful?

to prevent chemical and microbial degradation

16

Is a low temp or high temp better to prevent drug degradation?

low