Biomedical Engineering Reference
In-Depth Information
For the salt form of chitosan to be converted into a protonation one, the films were
treated with a 5% solution of NaOH (for 5 min) followed by rinsing in distilled water up to
pH 7.
The CHS/PMA mixture was prepared by precipitation with ethanol from the
corresponding solutions of homopolymers and the obtained residue was dried in a vacuum
cabinet till constant mass. Biodegradation was performed in the presence of strains of
Aspergillus terreus
which, based on the results of the previous studies, proved to be the most
efficient for the given compositions [7].
The investigations lasted 20 weeks. The micromycetes were offered by the All-Russia
Collection of Microorganisms (Pushino, Moscow Region). To reveal the effect of
biodestruction on physical-chemical properties of polymer compositions, three series of
experiments were carried out according to State Standard (GOST 9.049-91, method 1) to
estimate the contribution of the direct action of micromycetes and the products of their vital
activity [9].
In series No.1, the films were placed under the solid completely agarized Chapek-Dox
medium (the medium surface was seeded with the fungi), while in series No.2 the specimens
were placed on a two-week-old lawn with fungi. The specimens of polymer compositions not
subjected to the action of the fungi served as a reference.
The DTA in the range of 190-350
о
С was chosen as the method for investigating physical-
chemical properties of the polymer compositions. The design of the device and the
experimental technique are described in [10, 11]. Quartz served as a reference.
The charges of the specimen and the reference were 0.2-0.3 g. The specimen temperature
and the temperature difference between the specimen and the reference were measured with a
chromel-copel thermocouple with an error of 0.5 degrees. The thermocouple was calibrated
using a reference platinum resistance sensor and reference substances within the entire
temperature range. The experiment was carried out in the helium atmosphere. The heating
rate in the experiments was 5 degrees/min.
A deviation from linearity did not exceed 1%. Three heating and cooling cycles were
accomplished for each specimen. After the first heating up to 150
о
С, the adsorbed water was
removed from the specimen by vacuumization directly in the thermal chamber of the DTA
setup and its concentration was determined by weighing.
During the third heating cycle the specimen was subjected to destruction. The enthalpy of
CHS combustion was determined in a modified V-08MA calorimeter with a static
calorimetric bomb [12]. The calorimetric system was calibrated using the reference benzoic
acid of K-2 grade ( U
c
= 26460.0 J/g when weighed in the air).
The energy equivalent of the system was W = 14805 3 J/degree with a doubled quadratic
deviation from the mean of 0.02%. The CHS was burned in the form of pellets embedded in
paraffin at the oxygen pressure of 3
●
10
6
Pa. Based on the data of chromatographic analysis,
the oxygen contained the following impurities, mol%: 0.8 of N
2
; 0.002 of CO and CO
2
; and
0.001 of hydrocarbons.
The substance in a quartz crucible was ignited by a condenser discharge to a platinum
wire connected with the substance via a cotton thread. The temperature rise was measured
with two platinum resistance sensors and the SH1516 digital voltmeter connected to the
bridge circuit.
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