Effects of Gamma Radiation on the Physicochemical Properties …
19
Recycling of PET bottles by using natural oleic acid and diethylene glycol is
carried out to obtain unsaturated polyester. Oleic acid is a natural fatty acid from
different plants, and used in food, cosmetic and pharmaceutical industries, as well
as in petroleum applications as additives for pour point improvers. The results show
that the physical and curing properties of the unsaturated resins are competitive
with the commercial polyester, besides that it is easier to apply, due to its longer
gel time. Moreover, they had better thermal stability, and show the conversion of
semi-crystalline to amorphous phases. Moreover, its hardness had an improvement
of 14%, due to the cross-linking of its polymer chains. Thus, this method is viable,
cheaper and friendlier to the environment [11].
Many studies on the depolymerization of polyethylene terephthalate (PET) bottles
have been carried out, to reduce their impact on the environment. Chemical recycling
of PET have been developed through the processes: (a) alcoholysis, which consist in
the transesterification of alcohol with PET at 180–80 °C using an organometallic as
catalyst; (b) hydrolysis, where PET is hydrolyzed in water, in an acidic or alkaline
medium, at high pressure and temperature, for to obtain scissions of polymer chains;
(c) aminolysis, where primary amines reacts with PET from 20 to 100 °C; and zinc
acetate, lead or potassium sulfate are used as catalysts; (d) ammonolysis, where
ammonia reacts with PET from 70 to 180 °C, at 2 MN/m
2 pressure, and zinc acetate
is used as a catalyst; (e) Glycolysis, through PET transesterification reaction from
180 to 240 °C at constant pressure. In the process, the mixture of reagents produces
excess of glycolic materials, which can be used for production of new products;
which include unsaturated polyester resins, polyurethanes, and epoxy resins, among
others; besides is economically viable. Glycolysis is not applicable only to waste
unsaturated polyester resin, this can support some technical modifications and be
used for different resins. Sometimes, the treated waste may contain calcium carbonate
particles or fibers [12].
The chemical process is carried out by a mixture of glycols (ethylene, propylene,
diethylene, dipropylene and neopentyl). According to the boiling points of the glycols, thermal process has been carried out from 180 to 250 °C. However, other types
of glycols have been used, but the final cost of the product increase, for example
(1,3-butanediol, types of bisphenol A). Some catalysts as sodium methylate, sodium
ethylate, sodium hydroxide and methanesulfonic acid have been studied.
Thermo-hardened polyester is crushed and then treated with glycols for its easy
degradation. Different tools have been used for crushing process, including hammer
mills, chain impact, cutting and rollers. Moreover, particle sizes ranging from 200
to 300 μm produce the highest milling efficiency.
At the glycolysis temperature, glass fibers can be recovered from the unsaturated
polyester resins. Such recovered fibers can be used as raw material to obtain recycled
polyester resins, which have good mechanical properties, high flexibility when they
are used as molding material.
19
Recycling of PET bottles by using natural oleic acid and diethylene glycol is
carried out to obtain unsaturated polyester. Oleic acid is a natural fatty acid from
different plants, and used in food, cosmetic and pharmaceutical industries, as well
as in petroleum applications as additives for pour point improvers. The results show
that the physical and curing properties of the unsaturated resins are competitive
with the commercial polyester, besides that it is easier to apply, due to its longer
gel time. Moreover, they had better thermal stability, and show the conversion of
semi-crystalline to amorphous phases. Moreover, its hardness had an improvement
of 14%, due to the cross-linking of its polymer chains. Thus, this method is viable,
cheaper and friendlier to the environment [11].
Many studies on the depolymerization of polyethylene terephthalate (PET) bottles
have been carried out, to reduce their impact on the environment. Chemical recycling
of PET have been developed through the processes: (a) alcoholysis, which consist in
the transesterification of alcohol with PET at 180–80 °C using an organometallic as
catalyst; (b) hydrolysis, where PET is hydrolyzed in water, in an acidic or alkaline
medium, at high pressure and temperature, for to obtain scissions of polymer chains;
(c) aminolysis, where primary amines reacts with PET from 20 to 100 °C; and zinc
acetate, lead or potassium sulfate are used as catalysts; (d) ammonolysis, where
ammonia reacts with PET from 70 to 180 °C, at 2 MN/m
2 pressure, and zinc acetate
is used as a catalyst; (e) Glycolysis, through PET transesterification reaction from
180 to 240 °C at constant pressure. In the process, the mixture of reagents produces
excess of glycolic materials, which can be used for production of new products;
which include unsaturated polyester resins, polyurethanes, and epoxy resins, among
others; besides is economically viable. Glycolysis is not applicable only to waste
unsaturated polyester resin, this can support some technical modifications and be
used for different resins. Sometimes, the treated waste may contain calcium carbonate
particles or fibers [12].
The chemical process is carried out by a mixture of glycols (ethylene, propylene,
diethylene, dipropylene and neopentyl). According to the boiling points of the glycols, thermal process has been carried out from 180 to 250 °C. However, other types
of glycols have been used, but the final cost of the product increase, for example
(1,3-butanediol, types of bisphenol A). Some catalysts as sodium methylate, sodium
ethylate, sodium hydroxide and methanesulfonic acid have been studied.
Thermo-hardened polyester is crushed and then treated with glycols for its easy
degradation. Different tools have been used for crushing process, including hammer
mills, chain impact, cutting and rollers. Moreover, particle sizes ranging from 200
to 300 μm produce the highest milling efficiency.
At the glycolysis temperature, glass fibers can be recovered from the unsaturated
polyester resins. Such recovered fibers can be used as raw material to obtain recycled
polyester resins, which have good mechanical properties, high flexibility when they
are used as molding material.