Chemistry Reference
In-Depth Information
Another characteristic feature of polyethyleneterephthalate is almost plane configuration
of chains and presence of two centres of symmetry on each repeat unit [188]. These two
features cause the ability of PETP to crystallization [189]. Crystallization of PETP flows with
formation of spherulite structure leading to polymer turbidity.
These features stipulate properties of PETP-fibre. PETP-fibre is classified as strong,
resilient, elastic fibre, having low creep. Fibre strength depends on molecular weight of the
polymer, its dispersion, on the processes of shaping and drafting of the fibre. Permissible
operating temperature of use is 120-130
0
C. Important advantage of PETP filaments is their
high resistance to tensile deformation. PETP fibre is thermoplastic - it softens, begins to glue
and loses its form at intense heating. These changes take place in temperature range of 180-
200
0
C[190]. Owing to thermoplasticity strength characteristics decrese and breaking
elongation increases.
Polyester fibres, specifically PETP, possess high thermal stability and sufficient
resistance to light effect and atmospheric action. However, effect of high temperatures, to
which PETP is subjected in the process of synthesis and processing into products, may cause
thermal destruction of polymer and in the absence of oxygen. Decrease of molecular mass,
increase of end groups quantity, extraction of volatile products, the main of which are
terephthalic acid, acetaldehyde and carbon oxide are observed at PETP thermal destruction.
Besides these substances, anhydride groups, benzoic acid, p-acetyl-benzoic acid, ketones,
acetals are identified in the compound mixture of the products of thermal decay [34].
As a result of thermal destruction, owing to formation of volatile products polymer mass
losses take place. Mass losses at 310
0
C are 1%. The main stage of decay (up to 85%) ends at
487
0
C and at 610
0
C polymer completely burns out [191].
It should be noted that the results of thermodestruction investigations made by different
authors are different which is caused by different conditions of experiment carrying out,
specifically, atmospheres of different inert gasses have been used for investigation of thermal
destruction.
The process of PETP thermal decay in argon is similar to the process taking place in
nitrogen atmosphere, while in the air mechanism of destruction is different. It is shown in the
work [192] that in the atmosphere of inert gas only one stage of decay takes place and all
kinetic parameters of decay (temperature of maximum mass losses, energy of activation, rate
of destruction and so on) grow with the increase of molecular weight. But in the atmosphere
of air two stages of PETP-fibre destruction are observed. At the first stage kinetic parameters
of decay decrease with the growth of temperature and polymer molecular mass. These
changes are expressed more brightly at the second stage of the decay process.
Surrounding atmosphere influences the formation of either decay product in the process
of destruction. So in the work [193] it has been found that in nitrogen atmosphere at
isothermal heating at 160
0
C mainly benzoic acid and esters are formed. Since oxidative
processes are absent at thermal destruction in nitrogen atmosphere then one may come to a
conclusion that benzoic acid and esters are the products of thermal decay of PETP fibre. At
thermal destruction of PETP-fibre thermal decay plays a very important role, especially at the
beginning of the destruction process.
Results of above mentioned works, where the effect on thermal destruction of alcoholic
residues, constituting polyester are very important. Polytrimethylterephthalate has been
synthesized in the work [192], and polybutylene terephthaeate - in the work [193]. Thermal
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