Biomedical Engineering Reference
In-Depth Information
The PMA destruction is two-staged and it is accompanied by absorption of the energy in
the form of heat. The first endothermic maximum is observed at t
dest1
= 326
о
С; the second
one, at t
dest2
=397
о
С (Figure 3.A, curve 4). The destruction being completed, the loss of the
PMA specimen mass was 87%. Analogous data on the PMA destruction are given by S.
Madorsky [30]. When analyzing the products of the PMA pyrolysis it was revealed that a
substantial release of volatile products (9.8 mass%) began at 292
о
С. A sharp increase in the
concentration of gaseous products (from 34.8 to 74.1 mass%) was observed at 325-329
о
С. At
399
о
С, the concentration of volatile products reached 96.8 mass%.
A CHS/MA block-copolymer is characterized by the transitions typical for both polymers
(Figure 2, Table 1). Chitosan does not affect the PMA temperature t
с
. In its turn, PMA
slightly decreases t of CHS (up to 31
о
С), does not affect its t
с1
(72
о
С), and increases t
с2
(125
о
С). The PMA does not practically affect the chitosan destruction (Figure 2, curve 3).
Only the loss of the specimen's mass decreases (by 2.5 times as compared to individual
chitosan) since the concentration of polysaccharide in the copolymer is 25%.
No -transition of CHS was revealed in the mixture of homopolymers and its vitrification
temperature did not change (Figure 3.A, Table 1). A distinctive feature of the mixture was the
plasticizing action of adsorbed water on PMA (Figure 3.B, Table 1). A proportional decrease
in t
с
(PMA) was observed at an increase in the Н
2
О concentration in the specimen. The
destruction of the mixture was similar to that in chitosan (Figure 3.A, curve 3), while the loss
of mass in this case takes an intermediate position between CHS and block-copolymer (Table
1).
We revealed variations in the temperature of CHS relaxation transition under the action
of
Aspergillus terreus
on the CHS/MA block-copolymer. These variations are observed both
under the direct action of micromycetes (series No.2) (Figure 4) and in case of their indirect
action taking the effect of the
Aspergillus terreus
vital life products into account (series No.1)
(Figure 5). Under the action of the fungi, the specimens of the block-polymer demonstrated a
relaxation transition at t<0
о
С (Figure 4 and 5). It is likely to be related with minor (oligomer)
residues of CHS macromolecules formed under the action of micromycetes. The fungi do not
affect t of the chitosan in case of the indirect action of their vital life products, while at the
direct action of micromycete flocci t of chitosan decreases by 5.5
о
С as compared to the
initial copolymer. In both cases, a substantial decrease in its t
с1
and t
с2
, is observed, the
vitrification of amorphous chitosan microregions taking place at the lower temperature if the
film is placed under the nutrient medium seeded with
Aspergillus terreus
(series No.1), while
highly-ordered microregions vitrify if the film is positions on a two-week-old fungi lawn
(series No.2). This case can be related to both partial destruction of highly-ordered CHS
microregions and the plastisizing effect on CHS from the side of low-molecular products of
the fungi vital life. The temperature of PMA vitrification in this case does not practically
change (Table 1).
The effect of the fungi is the most pronounced in the copolymer destruction. The process
remains two-staged but, however, it becomes endothermic (Figure 4 and 5, curves 3), i.e., the
sign of the energy effect changes. The destruction temperature increases as well (t
dest1
by 23
and 24
о
С; t
dest2
by 17 and 10.5
о
С). It can hardly be related to the formation of a protein
component of the products of the fungi vital life since, e.g., based on our data [31-33] the
serum proteins of human blood decompose ay lower temperatures (155-263
о
С). The obtained
temperatures of destruction of the copolymer specimens treated with micromycetes are closer
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