The microstructure of the polymer is composed of deposited
(crystals) and amorphous fragments. Their rate is specified as
percentage of crystalline. The quantity of fragments created is
mainly influenced by the ability of the material to crystallize, but
the thermal-kinetic conditions also have a considerable impact
(KREBS, 2006). For example, if slower cooling is applied, it
gives the spherolites more time to grow than with faster cooling
and the result is the creation of fewer, but bigger spherolites.
Conversely, using more intensive cooling causes the creation of
more, but smaller spherolites (KREBS, 2006). For blow molding
process, this means that by intensively cooling the effective
interface, polymer/ mold, a large number of small spherolites
should be created. Low heat transfer of the effective interface,
air/ polymer, gives the spherolites enough time to grow to larger
sizes. The difference in morphology increases with increasing
product thickness and a faster cooling rate of the mold (external
cooling system). How does this influence the connection to a
progressive internal cooling method? From the theoretical
statement introduced above, it can be assumed that the
spherolites would be smaller and the structure more uniform.
The influence of the different cooling rates at both interfaces on
the microstructure across the product was observed using
polarization microscopy. The results, which are shown in
figure 2, showed that no structural changes were noted. This
result was found for all tested samples of both of the examined
materials. The explanation could be found through
experimentation of the cooling settings. Water at five degrees
centigrade is circulated in the mold, which is the lowest
recommend temperature to produce the product without causing
rejection (through the effect of sweating). If a higher cooling
temperature or a thicker product were tested, the results could be
different