Studying the Curing Conditions of Unsaturated Polyesters from Secondary Polyethylene Terephthalate Alcoholysis Products

The technological properties of the curing conditions for unsaturated polyesters synthesized on the basis of the alcoholysis products of secondary polyethylene terephthalate and unsaturated polyesters used in the production of fiberglass pipes were studied. It is shown that unsaturated polyesters synthesized on the basis of alcoholysis products can completely replace imported resins of grades 196 and 196A in the production of fiberglass pipes.


Introduction
The disposal of polymer wastes has grown into one of the most urgent problems in environmental protection. This waste cannot be burned, and it must not be buried, because the combustion products of polymer waste further pollute the atmosphere, releasing a large amount of soot and highly toxic combustion products; due to their high resistance to fungi, water and various environments, these products are stored for a long time without decomposing [1] [2].
On the other hand, polymer waste is readily available and inexpensive raw materials for the production of polymer-composite materials [3]- [8].
One of the large-tonnage types of waste, after polyolefins, is polyethylene terephthalate (PET)-containing waste.
Over the past decade, the global production of polyethylene terephthalate (PET) has increased from 37.5 million tons to 70.0 million tons [9] [10] [11] [12] [13]. Of this amount, 21.5 million tons are used in the production of polymer containers, such as bottles. Hundreds of thousands of tons of various polymers and, in particular, 40 -45 thousand tons of PET are annually imported to the Republic of Uzbekistan. Of these, about 90% is recycled into PET forms, which are then shaped into bottles. After using the bottles, they become household polymer waste. Disposal of the generated household polyethylene terephthalate waste is currently relevant.
In recent years, a number of enterprises for the production of fiberglass, sanitary ware, and pipes based on unsaturated polyesters (UPEs) have been organized in the Republic. This has created a demand for this type of polymer material.
In the work [3], based on the alcoholysis products, we obtained UPE suitable for the production of fiberglass pipes.
This article is devoted to the synthesis and the study of the technological parameters of curing new grades of UPE suitable for the production of fiberglass pipes.

Materials and Methods
The used raw materials were recycled PET, namely, that formerly used as bottles for drinks, which crushed in a crusher to a size of 0.5 × 0.5 sm, with melting point of 240˚C -250˚C. Diethylene glycol produced in Russia was first purified by vacuum distillation over a temperature range of 128˚C -135˚C and with a residual pressure of 0.90 -0.97 kgf/sm 2 . The distilled product had a refractive index n d = 1.4472 and ρ = 1.1191 g/cm 3 . Propylene glycol had a refractive index n d = 1.4326 and ρ = 1.036 g/sm 3 . Maleic anhydrideb was used according to SS 11153-75. Phthalic anhydride was used according to SS 5869-77. Zinc acetate was used according to SS 5823-78.
The synthesis of UPE was carried out according to the method described in [3].
As the main alcoholic component, we used the products of alcoholysis of SPET obtained with a ratio of SPET: diethyleneglycol (DEG) = 1:2 mole el. unit/mole, for 6 hours according to the method described in [4], and the UPE itself was synthesized according to the method described in [3].
The suitability of UPEs for processing was assessed according to the following technological parameters adopted in the production of pipes: visual appearance

Discussion of the Results
UPEs of grades 196 and 196A according to technological normative documentation (TND) must correspond to the physicochemical and technological indicators given in Table 1.
In the enterprises of Uzbekistan, in particular JV Ltd. "MEGA MEBIKO", resin grade 196A is used as the protective layer, and resin grade 196 is used as the inner layer of pipes.
Initially, in order to determine the structure of UPEs of grades 196 and 196A, their IR spectra were studied. Therefore, the polyesters were washed to remove styrene and traces of monomers, and then their IR spectra were recorded    Table 3.
It is known that the process of curing unsaturated polyesters is accompanied by intense heat release, the rate and time of which determine the conditions for processing these oligomers.
The speed and time of curing is greatly influenced by the concentration of the accelerator. Therefore, in the studies, the amount of the accelerator varied from 0.3 to 0.5 mass n.
From the data in Figure 2 and       1663 cm -1 , trans allyl groups at 1645, 980 cm -1 , and a sharp decrease in pass bands at 732 -731 cm −1 related to cis-allyl bonds.
The observed evidence suggests that the curing of unsaturated polyester first proceeds due to the polymerization of vinyl (in styrene) and trans-allyl groups (in UPE), and then, after the consumption of trans allyl groups, due to the polymerization of cis-allyl groups [25] [26].
In this case, styrene homopolymerization also occurs with the formation of oligomers, which are involved in the crosslinking of UPE [26]. Table 4 shows the effect of the accelerator system on the physical and mechanical properties of the cured UPE resins.
According to the accepted standard in the joint venture "MEGA MEBIKO", fiberglass pipes were manufactured and withstood the hydrostatic pressure of water equal to 25 atm. A sample is shown in Figure 5.