Basic HTML Version
The
EXTRUDER
TIMES
MARCH-APRIL 2006
VOL.01 / ISSUE-02
I N T H I S I S S U E :
Review:
Catalyst:
Mixing Elements
ReCap:
Rockwell Hardness
Brainstorm:
Determining Starve-Feed Intake Capacity
T H E
‘ART OF
COMPOUNDING
THERMOPLASTICS’
USING TWIN-SCREW EXTRUDERS
R E V I E W
Background:
When there are hundreds of different types and varieties of polymers, why
use an additional process called Compounding? The answer is very simple. Most of us
begin our day by using a compounded product. The making of bread dough is a classic
case of everyday use of compounded wheat flour. Actually, this operation can very well
be done using a Twin-screw Extruder, because, the fundamental process of compound-
ing is the same.
Compounding is used to make "new" plastics in modern times, because - a vast variety
of plastic-material(s) is required to 'satisfy' a wide-range of 'applications' and also 'end-
users'. Also, to discover and manufacture a new molecule to fit each one of these
applications is a phenomenally expensive proposition. Compounding offers a quick,
easy, low-cost alternative to discover new molecules. That is the reason why compound-
ing has become such a popular process to modify properties of the base polymer.
Actually, some of the very interesting polymers would have never become commercial
success, if they were not compounded. PVC, for one, is a well-known example. Noryl®
(PPO ® blends from GE Plastics) is another. In fact, until a few years ago, most polymers
were compounded immediately upon synthesis because they would not survive without
additives and stabilizers for more than several hours unless elaborate measures were
taken to protect them from air (oxygen), light and heat. Polypropylene is an example.
There are new processes and technology, which incorporate these additives in the final
stages of the reaction, thereby eliminating the compounding process, which was so
critical for the polymer’s survival.
Process of Compounding – THE 3 M’s
The process of compounding actually consists of several different
unit operations
happening inside the extruder. We would discuss each one of these in detail, but the
basic process can be defined with the
Three M s’ – Melt, Mix, Meter.
Continued...
A special initiative of
CONSULTANC Y SERV I CES , I ND I A
This issue of ET is sponsored by
STEER’s Elements & Components
A GLOBAL CHOICE
• To share breakthroughs and happenings in the
Extruder Industry with special emphasis on
Twin/Single Screw Extruders.
• To serve as an information sharing platform for
STUDENTS, ENGINEERS and COMPOUNDERS.
• To generate triggers and encourage contributions
from scientists, technocrats and teaching
community for new innovations.
A IMS AND OB JECT IVES