Tablets, pellets, capsules, and granules are the most common forms of administering drug dosages in the pharmaceutical industry.
ThisI must say is due to their convenience and suitability administration as well as delivery of drugs for systemic effects.
Many people are unlikely to have considered the complicated processes that go into the research, development, and production of tablets.
Granules to tablets
Tablets are a product of the dry granulation process which transforms powders into granules without the use of liquids.
And while dry granulation may also be done by slugging, roller compaction is the most common technique used for this process.
In this case, as materials pass between the two pressure rollers, they are compacted and densified into flakes, or ribbons.
These are then reduced to a uniform granule size by milling.
Dry granulation as earlier mentioned is the best method for processing soluble and thermally sensitive materials.
In this section, therefore, we are going to look at the various types of pharmaceutical roller compactors based on several elements.
So read on;
A problem that operators experience in roll compaction is bypassed.
This is where some bit of materials remain in the nip region of the roller system for an unspecified amount of time.
Roller orientation is one of the three things that influence bypass in roller compaction processes.
Different orientations of roller compactor
The type of roller orientation in your machine will determine how much or often you’ll experience a bypass of material.
With this in mind, there are three types of material feeding orientations, some of which address this issue.
● Horizontal orientation
This is the most common design roller systems for dry granulation.
And just as the name suggests, the rollers here are oriented horizontally.
You can see this in figure (b).
In comparison to the other two designs, the loss of material due to bypass in horizontal roller orientation is higher.
Due to this, the use of the side seals on compactor deigns has been adopted by various manufacturers to help reduce material bypass.
● Vertical orientation
If your applications involve using low dosages of material, then a vertical roller orientation may work for you.
You can see this is a figure (a) above.
This is mainly because material movement in this design is not dependent on gravity.
As such, there is usually very minimal loss of material to bypass in this design.
● Incline orientation
Rollers of this design lie on the horizontal and vertical plane.
Here, there is usually little to no bypass material during compaction.
Have a look at figure (c) above.
As a matter of fact, using the incline roller orientation tends to decrease bypass by 15-20%.
This is quite significant, particularly where maximum productivity is needed.
Generally, roller orientation as I’ve said earlier influences bypass in roller compaction.
And high levels of the bypass, in this case, is known to cause blend segregation as well as affect material uniformity.
The feeding system of a roll compactor machine is significant in ensuring blend uniformity.
It also provides for easy control of processing parameters.
A feed system that provides non-uniform compacts may lead to poor quality of final output.
It may also lead to the generation of excessive fines and uncompact materials which may jeopardize the whole production process.
As I’ve told you before, the feed screw mechanism is most common in roll compactors.
In this regard, you have the option of choosing between twin and single pre-compression for your feed screw system.
Feed screw mechanism
In which case, the twin pre-compression feeder system works best for broader roller gaps as it can feed it with material more uniformly.
Please note;
Advancements in roll compactor feeder systems have led to the invention of vent feeders.
This system comprises;
A stirrer inside the feeding unit that ensures an even flow of material towards the screw feeder.
The screw feeder which forces the material down to the gaps between the pressure rollers
A vacuum system, which facilities the flow of hard to transport, high voluminous and fluidizing materials.
A roll compactor has two equal diameter counter-rotating rollers.
Take note that the gap between the roller units determines the efficiency of the dry granulation process.
Fixed vs. variable roller gap
The rollers come in two designs;
● Fixed gap
The fixed gap roller design features a constant and predetermined gap.
Note that the speed of the screw feeder mainly controls the flow of material in this gap design.
As such, the density of compacts you’ll be getting will be entirely consistent.
Understand also that fixed gap system tends to produce ribbons/flakes of the same shape and size.
However, it allows for non-homogenous material feeding, which causes changes in porosity of the compacts produced.
This also causes variations in the roller pressure that could consequently lead to non-desirable changes in the quality of granules produced.
● Variable Gap
Variable gap roller designs come with movable rolls.
These give out an even roller pressure that is accomplished by controlling both the gap width and the screw feeder speed.
The advantage of this roller unit design is that it has a less bypass propensity.
Being able to change the roller gap provides room for adjusting the density profile with the robustness of the granules.
This, in turn, affects the mechanical properties of the tablets, positively.
Like roller orientation, roller surface also tends to influence bypass in roller compaction processes.
The surface of the roller is significant in maintaining back pressure on the flow of material.
a-smooth, b-corrugated and c-fluted roller compactor
This is so that the material does go through the nip region any speedier than the rolls are rotating.
To reduce bypass, therefore, you may want to use a corrugated roll surface in your roll compactor for dry granulation.
Note that there are two main types of roll surfaces used in the pharmaceutical industry.
There are the smooth surfaces and the corrugated roll surface.
The latter, as I’ve just said, is best for reducing bypass.
It’s also convenient for use when compacting aerated, light and fluffy materials when aiming to increase their bulk density.
Smooth roller surfaces are best when looking to minimize sticking problems.
These are the primary variables that determine the suitability of any roll compactor machine for any particular application.
The bottom line?
I believe that with this you can comfortably choose the best pharmaceutical roll compactor for dry granulation.
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