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Figure 2.38. Thermal destruction of PVA-films in vacuum - initial (1) and dyed (2-4): 2 - LIX, 3 -
LXI, 4 - LXIII at 175-250°C.
Curves of the loss of mass of dyed PVA samples at warming up in the air during an hour
depending on temperature of warming up are given in Figure 2.38. They show that at
temperatures of warming up to 225°C the loss of mass is not more than 10% but at further
rise of temperature the loss mass increases.
Introduction of covalently linked dyes LIX, LXI, LXII reduces loss of PVA mass,
moreover the highest effect is observed in phthalocyanine dye LXII, then in LIX and
antrachinone dye LXI hardly influences the depth of polymer decomposition. Inactive dyes
LX and LXII even slightly increase the depth of decomposition, exception is phthalocyanine
dye LXIV, which shows stabilizing effect though much less, than covalently linked dye
LXIII. So, depth of decomposition of undyed PVA during warming up at 300°C is 74%,
while introduction of dye LXIV reduces it up to 51% and covalently linked dye LXIII - up to
35%. Oxidation processes of initial and dyed by active and deactivated dyes PVA are
characterized by complex reactions, which distort the picture of decay.
A little different picture is observed during warming up in vacuum. Curves of loss of
samples mass, warmed up during an hour, depending on temperature, are given in Figure
2.38. As it is seen the loss of mass of undyed sample increases almost linearly with the rise of
temperature up to 250°C, while inhibitive effect up to 200-215°C is observed in dyed samples
and this shows that oxygen is the first to react under oxidation at this temperature. At much
higher temperatures depth of dyed samples decomposition increases very quickly, and for the
dye LXI it even exceeds in initial PVA. Depth of decomposition is less in samples dyed by
azodye LIX, especially phthalocyanine LXII. At temperature 250°C the rate of mass loss is
0,75g/min (Figure2.38, curve 2) and 0,5 g/min (Figure 2.38, curve 4) respectively.
When analyzing gaseous product of PVA decomposition in vacuum it was stated that
main volatile products are H 2 O was defined quantitatively by the reaction with calcium
hydride and by gasochromatography determination of hydrogen, being released during the
reaction:
CaH 2 + 2H 2 O = Ca(OH) 2 + 2H 2
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