- Increasing the IV value
- First, what in the hell does this means
- Here what books are saying:
- A polymerization in which the growth
of polymer chains proceeds by condensation
reactions between molecules of all degrees
- Now, there are
quite many publication on the subject
but here we like only to make you understand
what this process does in relation to
- As written before,
Polycondensation put together molecules
to re-form the polymer chain.
- Doing this,
it does transform also some contaminants
into part of the polymer chain with
undesirable side effects and here
are the most common:
- DEG is one of the most important
side products of the polycondensation
- PET which is directly produced by
esterification of Terephthalic acid
usually contains more DEG than PET produced
by transesterification of DMT (Chen,
1998 a). Most of the DEG is formed during the preheating
of the melt- polycondensation by intermolecular dehydration of Ethylene
glycol. The dehydration of Ethylene
glycol is catalysed by acids and therefore
promoted by a high concentration of
- In the course of polycondensation
DEG is also co-polymerised in the polyester
chain causing a decrease in melting
- In general, the melting point
of PET decreases by about 5 °C for
each percent increase in DEG concentration.
- The incorporation of DEG in the
polymer PET also deteriorates mechanical
properties, the hydrolytic and light
stability as well as the thermal and
oxidative degradation behaviour of the material
- There are other
possibilities for the formation of DEG
during the polycondensation and manufacturing
process of PET.
- Carboxyl and
Vinyl end groups
- Another important side reaction
during the production of the polyester
PET is the degradation of polymer chains by
random thermal cleavage of ester links
forming carboxyl end groups and vinyl end
- The amount of carboxyl end groups
is an important factor due to the susceptibility
to hydrolysis of the polymer since
these end-groups have a catalytic effect
in the process as already mentioned above.
- Vinyl end-groups may also polymerise
to polyvinyl esters which are responsible
for the (dis)coloration of PET.
- The vinylester end group of PET
can be transesterified under the formation
- The Acetaldehyde concentration
of PET granules is of great importance
when manufacturing PET bottles for soft
drinks especially when used for carbonated
- Migrating to the beverage, retained Acetaldehyde can cause
an intensive off-flavour.
- Formation of Acetaldehyde
as a by-product of the polycondensation
process of PET.
- Acetaldehyde is not only formed
during the polycondensation process
but also occurs during blow molding of PET
bottles from PET resin.
- All this means it is not only a
solid contamination matter but a chemical
- That's why not a single washing
line manufacturer has the FDA approval;
he just cannot have it
- SSP Solid State Polycondensation
is a step further Melt State Polycondensation
and can achieve an higher molecular
weight and increase the IV up to over
- The longer the chain, the higher
the molecular weight and thus the IV
with which is measured.
- The different SSP systems available.
- SSP can be done in two different
ways; first is the continuous one, normally
used with high production rates, and
the batch process.
- Both systems are using only heat
and time so no chemical additives are
necessary for the process.
- We like continuous system much better
than batch processing but, like any
other case, there is a good and a bad
part on both.
- Continuous process is absolutely
perfect if starting point (the IV value)
is constant; in fact according to heat
and time IV will increase of the same
value but if the value is not constant,
the final one will not be as well.
- On the batch process instead, you
can change the time for each batch depending
on what you put inside the machine;
the cost per Kg is a little bit higher
but the result is absolutely constant,
doesn't matter which IV you did start