Chemistry Reference
In-Depth Information
Table 3.1 Comparison of Herman's crystalline orientation factors (
f
a
,
f
b
) for single-layer
and co-extruded PP and LDPE
Single PP
Co - extruded PP
Single PE
Co - extruded PE
f
c
(
c
- axis)
f
b
(
b
- axis)
f
c
(
c
- axis)
f
b
(
b
- axis)
f
a
(
a
- axis)
f
b
(
b
- axis)
f
a
(
a
- axis)
f
b
(
b
- axis)
TUR
3.5
0.11
0.12
−
0.22
0.14
±
0.02
−
0.21
±
0.01
−
0.07
0.06
±
0.02
−
0.03
±
0.02
10
0.21
−
0.31
0.22
±
0.02
−
0.32
±
0.01
0.27
−
0.18
0.19
±
0.02
−
0.11
±
0.01
PP, polypropylene; PE, polyethylene; LDPE, low - density polyethylene; TUR, take - up ratio .
shown in Table 3.1 and Figure 3.22. As noted earlier, this difference
arises from relaxation of high- molecular - weight LDPE chains, which
could have acted as fi brillar nuclei for row- nucleated structure. Thus,
crystallization time difference for the onset of crystallization of PP and
LDPE plays an important role in determining the orientation and
morphology of the components during PP/LDPE bilayer blown fi lm
extrusion [56,57]. The present results show that crystallinity develop-
ment in individual components has a profound effect on the micro-
structure and properties of the multilayer fi lms relative to that observed
in single - layer fi lms. Thus, Raman spectroscopy can serve as a powerful
tool for estimation of microstructure development during the produc-
tion of multilayer fi lms that are of paramount importance in industrial
applications.
3.8 CONCLUDING REMARKS
In this chapter, the application of Raman spectroscopy for real- time
process monitoring during single- and multilayer blown fi lm extrusion
was demonstrated. The crystallinity and orientation evolution during
single - layer blown fi lm extrusion of polyolefi ns helped in the formula-
tion of processing- structure - property (PSP) relationships and also
validating process model predictions. For bilayer (PP/LDPE) blown
fi lm extrusion, online Raman spectroscopy was used to investigate the
effect of co-extrusion on the microstructure of the components during
the process. The crystallinity values obtained from Raman spectroscopy
were found to be comparable to those obtained from XRD. Thus, it can
be said that Raman spectroscopy offers an inexpensive, powerful, and
viable option for real-time characterization of polymer fi lms during
processing.
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