Chemistry Reference
In-Depth Information
compounds is caused by fast, reversible phototransfer of the proton, taking part in formation
of intra-molecular hydrogen bond but not suppesing excited states of polymer.
Analysis of DTA curves has shown that the main process of crystallization in the
presence of stabilizer proceeds at much lower temperature. This is explained by nucleus
activity of stabilizer and filling interspherulite space by it, preventing the growth of
spherulites. It has been also obserbed on DTA curves that melting of stabilized PETP is
observed at much lower temperature compared with unstabilized one, which is the result of
less perfection of fine spherulite structure of stabilized PETP [270] and plasticizing action of
the additive too.
Nonuniformity of stabilizer distribution in some cases may facilitate the increase of
stabilization efficiency [58]. At nonuniform distribution, connected with crystallinity,
lowmolecular stabilizers obtained on the basis of the same monomer as protected polymer
[74] get definite advantage.
Thus, depending on the nature of the polymer and its structure, on the properties and
mechanism of stabilizer action, high-molecular stabilizers may protect better or weaker than
lowmolecular ones. However, advantage of highmolecular stabilizers becomes undoubted on
exposure to the factors causing volatilization or extraction at the very beginning of extraction.
Advantage of highmolecular stabilizers is displayed more brightly in such polymers which
constantly or periodically must be in contact with water or organic liquids.
Use of lowmolecular stabilizers has essential disadvantages: they do not provide duration
of protective effect under service conditions, since they are quickly consumed at ultra-violet
irradiation, washed-out from the polymer and are lightly volatile. In this connection there
arises the question about possible use of highmolecular stabilizers.
Lately, copolymers have been used as stabilizers [271]. In the work [272] copolymer on
the basis of secondary kapron and polyethylentherephthalate is used for PETP stabilization.
As a result impact elasticity rises by 1,5-2 times and deformation - strength properties by 40-
70%.
According to technological reasons chemical additives in PETP are introduced mainly
into the melt during the process of goods production. In some cases this is the only way for
obtaining stabilized and dyed fibres.
3.3.
M
ODIFICATION OF
PETP
BY
A
DDITIVES OF
P
OLYFUNCTIONAL
A
CTION
As a rule, stabilizing additives are colourless [76]. However, in some case it is preferable
to use dyes as stabilizers, especially if it is necessary to obtain dyed polymers [32, 77, 78, 84].
One of the most rational methods of PETP modification may be introduction of modifiers
into polymer mass. At usual surface dyeing based on diffusive process of dye penetration into
fibre inverse process is realized one way or another - that is yield of the dye from polymer
matrix, which causes reduction of intensity of product dyeing. Besides, due to non-uniformity
of fibres (presence of crystalline and amorphous regions) the dye is non-informly distributed
in them, producing uneven painting and making colourity characteristics worse. It should be
also noted that the process of bath dyeing is not economic because of incomplete bath
extraction and necessity of carrying out additional finishing operations.
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