TITLE:
Significant Improvement of Mechanical Properties for Polyvinyl Alcohol Film Prepared from Freeze/Thaw Cycled Gel
AUTHORS:
Taishi Fukumori, Takahiko Nakaoki
KEYWORDS:
Polyvinyl Alcohol; Mechanical Properties; Freeze/Thaw Cycle; Film
JOURNAL NAME:
Open Journal of Organic Polymer Materials,
Vol.3 No.4,
October
30,
2013
ABSTRACT: The mechanical properties
of polyvinyl alcohol (PVA) films prepared by evaporating water from freeze/thaw
cycled gel were investigated as a function of the number of freeze/thaw cycles.
The maximum stress of the PVA film prepared by freeze/thaw cycling was larger
than that prepared without the freeze/thaw cycle process. The largest maximum
stress was 46.2 MPa for a film prepared with 10 freeze/thaw cycles, which was twice as large as
that for a cast PVA film without freeze/thaw cycling (22.3 MPa). This is due to the
formation of small crystallites during the freeze/thaw cycle process. Furthermore,
when the film was annealed at 130°C, the maximum stress was as high as 181 MPa
which was comparable to that for
PVA films prepared using additives. The crystallinity is not the main factor
that determines the maximum stress for either the non-annealed or annealed
freeze/thaw cycled films, but the glass transition temperature is well
correlated with the maximum stress, irrespective of the annealing process. This
is due to the different molecular morphology; the non-annealed freeze/thaw cycled film
consists of many small crystallites, but the annealed film consists of larger
crystallites formed during the annealing process.