CIRCULAR ECONOMY IMPLEMENTATION IN THE DEVELOPMENT OF FIRE-RETARDANT MATERIALS USED IN CONSTRUCTION, INDUSTRY, AND GENERAL-PURPOSE PRODUCTS

13.03.2022 Abstract During a fire, passive fire protection systems are designed to prevent the spread of flames, smoke, and toxic gases. The new fire-retardant (FR) material, used for passive fire protection, is created by combining copolymers (VC–co–VAc) (Slovinyl KV 173) and PVC K70 with expanded graphite and plasticizers/modifiers such as diisononyl phthalate - DINP, diisononyl terephthalate - DINTP, dioctyl adipate - DOA, as well as plasticizers that are synthesized based on tertiary recycling of waste poly(ethylene terephthalate) (PET), 1-hexadecene, azodicarbonamide (ADC), tri(p-cresyl phosphate), epoxidized soybean oil (ESO) and acrylate emulsion (DH50, Ecrylic, or Flexryl, etc.). The obtained material's morphology was examined using an emission scanning electron microscope (FESEM) field. Tensile testing was used to determine the mechanical properties of the obtained samples, as well as Shore A hardness and toughness using the Charpy impact test. All samples obtained were tested according to non-flammability standards. To conform to the new trend of "green economy," the development of novel eco-friendly FRs with improved thermal and mechanical properties will include careful consideration of environmental protection and sustainable

Preparation glycolysate from the waste polyethylene terephthalate PET EG/PET/PG (PETplast1) PET waste depolymerization was carried out in a four-necked round bottom flask equipped with a condenser, thermometer and inert gas inlet tube. PET glycolysis with PG was performed in the following manner: PG (100 g, 1.32 mol) and Fascat 4100 catalyst (0.50 g, 0.4 mas.%) were added into a reaction flask, and gradual addition of PET (100.0 g, 0.52 mol) was performed to attain complete PET dissolution. The temperature of the reaction was maintained at 180 o C in the course of PET addition, and after it was increased to 210-220 °C and maintained for 8 hours providing efficient mixing. After that period reflux condenser was changed with vacuum distillation apparatus assembled to remove excess of PG. When 57.2 ml of PG was collected the reaction mixture was then cooled to 90 °C before being cast into a storage vessel.

2-EtHexCOOH/EG/PET/DEG/2-EtHexCOOH (PETplast2)
In a four-necked round bottom flask, equipped with a mechanical stirrer, water condenser, thermometer, and a nitrogen inlet tube dried PET (100.0 g, 0.52 mol), DEG (55.12 g, 0.52 mol), and Fascat 4100 (0.62 g, 0.4 percent) were added. The flask was placed in a heated oil bath, and the reaction mixture was kept at 210-220 °C for 6 hours in an inert atmosphere providing efficient mixing. The reaction mixture was cooled to 90 °C after glycolysis, a Dean-Stark water separator was assembled, and 2-ethyl hexanoic acid (0.52 mol) was added to the flask. Xylene (3 wt. % of the reaction mixture) was added to provide water removal forming binary azeotrope, and then the mixture was heated to 210 °C at a rate of 15 o C/h, and held at that temperature until 17 ml of water was separated (stoichiometrically 18.4 ml). The mixture was then cooled to 90 o C before being cast into a storage vessel.
In a four-necked round bottom flask, equipped with a mechanical stirrer, water condenser, thermometer, and a nitrogen inlet tube, dried PET (100.0 g, 0.52 mol), DEG (55.12 g, 0.52 mol), and Fascat 4100 (0.62 g, 0.4 percent) was added. The flask was placed in a previously heated oil bath, and the reaction mixture was kept at 210-220 o C for 6 hours in an inert atmosphere providing efficient mixing. The reaction mixture was cooled to 90 o C after glycolysis, a Dean-Stark water separator was assembled, and MA (49.9 g, 0.52 mol) and HQ (0.31 g) were added to the flask. The mixture was heated to 150 °C with a heating rate of 15 ºC/h and held at a constant temperature for 1.5 h. Afterward, 2-ethyl hexanol (0.52 mol) and xylene (3 wt. %) were added to provide water removal forming binary azeotrope. The mixture was heated to 210 °C at a rate of 15 o C/h, and held at that temperature until 17 ml of water was separated (stoichiometrically calculated 18.4 ml). The mixture was then cooled to 90 o C before being cast into a storage vessel.

Material characterization
The cross-section of obtained material was examined using a Mira3 Tescan field emission scanning electron microscope (FE-SEM) set to 20 kV.
The Shore A durometer hardness of the sample was determined using ASTM D2240 [20]. Each hardness value is an average of eight measurements.
An ELEMENTAR Vario EL III CHNS/O analyzer was used for elemental analysis. Bruker Avance III 500 spectrometer was used to record 1H and 13 C NMR spectra in DMSO-d6. Relative to tetramethylsilane, chemical shifts are given (TMS).
The FTIR spectra of the acquired sample were collected using a Thermo Scientific Nicolet 6700 spectrometer in attenuated total reflectance (ATR) mode with a single bounce 45 °F Golden Gate ATR accessory with a diamond crystal and an electrically cooled DTGS detector. The spectra were ATR corrected co-additions of 64 scans at a resolution of 4 cm -1 . Spectra in the wavelength range of 2.5 m to 20 m were recorded using the Nicolet 6700 FTIR spectrometer.
An INSTRON1332 servo-hydraulic testing machine (Instron Ltd., USA) with FASTtrack 8800 control electronics was used to measure the sample's tensile strength. The tensile strength is 5 millimeters per minute. All of the samples were the same length, and three of them were tested, with the mean value calculated and displayed.
The flammability resistance of materials was tested in accordance with the noncombustibility standards AS/NZS 1530.3: 1999 and AS 1530.4-2005.

Results
The synthesized glycolyzate was characterized using NMR, FTIR and volumetric methods. For NMR analysis all products were dissolved in DCM, filtered and after drying and solvent removal used for NMR spectra recording.
The success of the synthesis of PETPlast1 (PET:PG = 1:1) plasticizer was proved based on the results of NMR characterization with a dominance of the following compound (evaluated according to NMR results): 1  The results obtained from NMR and elemental analysis indicate product heterogeneity of the PET based plasticizers. The morphology and porosity of the crosssection of the obtained fire-retardant material are shown in Figure 1 at different magnifications.

. FTIR spectrum of the obtained material with a) PETPlast1, b) PETPlast2 plasticizers and c) FR Sample 3.
The results of the hardness and specific density of the obtained materials are shown in Table 1. The results of testing the mechanical properties, specific weight and resistance to the burning of the obtained materials are shown in Table 2.

Discussion
On the cross-section of the obtained material recorded on the SEM, it can be seen that the material is mainly homogeneous with low porosity. Analysis of SEM images using Image Pro Plus software showed that the porosity amounts to 2.19%.
The FTIR spectrum of the obtained material with glycolysate from PET, PETPlast1 and PETPlast2, and FR Sample 3 are shown in Figure 2. The -OH group stretching vibration, in the FTIR spectra of PETPlast1 and PETPlast2, appeared as a broad absorption band at 3399 and low intensity band at 3511 cm -1 , respectively. The methylene and methyl groups stretching vibration was found in the region 2957-2852 cm -1 . The strong absorption bands at 1721 and 1716 cm -1 , found for PETPlast1 and PETPlast2, respectively, indicate the presence of C=O ester group vibration. Also, C-O-C stretching vibration, observed at 1100 and 1101 cm -1 , and aromatic ring out-of-plane deformation vibration at 724 and 728 cm -1 , respectively [21], confirmed the structure of the synthesized plasticizer. The stretching vibrations of C-O bond in the ester group were assigned to the absorption peak at 1246 and 1247 cm -1 [22]. The bands in the region 872-724 cm -1 was ascribed to the C=C stretching (skeletal) vibration of the p-substituted benzene ring [23].
The Shore hardness results are a useful measure of the relative resistance to indentation of different polymer grades. Despite the fact that these data cannot be used to predict other polymer qualities like strength, they are frequently employed as a mechanical performance metric [26]. According to the results shown in Table 1, it can be seen that the addition of PET plasticizer increased the hardness of the obtained material. The hardness of the material with VC-co-VAc copolymer and PET/PG plasticizer increased by 19.1 %. The addition of PETPlast2 plasticizer increased the hardness by 10.6 % but the addition of PETPlast3 increased by 6.38 %. The hardness of the material containing PVC K-70 copolymer is lower, and the addition of PETPlast1, PETPlast2, and PETPlast2 plasticizers increased the Shore hardness from 1.72 % to 8.62 %, respectively. Furthermore, the addition of PET plasticizers raised the specific density and expansion coefficient of the given materials. Table 2 shows that Sample 1 has the highest tensile strength. The addition of plasticizer from PET and other flame retardants reduced material tensile strengths [27]. Tensile strength is reduced by 8.16 % when PETPlast1 plasticizer is added to VC-co-VAc copolymer materials, by 14.3 % PETPlast2, and 18.4% sa PETPlast3 plasticizers. PVC K-70 had a similar reduction in tensile strength. The addition of PETPlast1, PETPlast2, and PETPlast3 plasticizers results in 17.4 %, 19.6 %, and 26.1 % reductions, respectively. Materials containing PETPlast1, PETPlast2, and PETPlast3 plasticizers, on the other hand, have higher elongation values than materials containing commercial plasticizers.
The Charpy impact strength test is a standard ASTM test for determining toughness. This is due to the fact that an impact test indicates a material's toughness, or impact strength, which is the ability of the material to absorb energy during plastic deformation. A tough material is one that has high impact resistance. Toughness is the result of combining strength and ductility. To be tough, a material must have sufficient strength and ductility to withstand cracking and deformation under impact loading. The toughness of the material with VC-co-VAc copolymer and the addition of PETPalst1, PETPlast2, and PETPlast3 plasticizers decreased from 2.55 % to 7.1 % in the Charpy impact test. This reduction ranges from 3.05 to 8.4 % for FR containing PVC K-70.
All obtained samples were tested in accordance with non-flammability standards (AS/NZS 1530.3: 1999 and AS 1530.  [28]. When the experiment was terminated, the samples behaved according to the prescribed standards, halting the flow of air and the spread of fire for 3 hours. All of the samples presented meet the requirements of the standard.

Conclusion
Plasticizers derived from waste PET were synthesized and used to create expanding fire-retardant materials with improved thermal stability in this study. The process of preparing firefighting materials is divided into two stages.
The first phase involves the mixing of copolymers (VC-co-VAc) (Slovinyl KV 173) and PVC K70 with expanded graphite and plasticizers/modifiers such as diisononyl phthalate -DINP, dioctyl adipate -DOA, as well as plasticizers synthesized based on tertiary recycling of PET such as: PETPlast1, PETPlast2, and PETPlast3, 1-hexadecene, azodicarbonamide (ADC), tri(p-cresyl phosphate), epoxidized soybean oil (ESO) and acrylatepoly (vinylacetate) emulsion DH50. The second stage involves molding the obtained mixture to create samples of various sizes that are then tested.
According to the results, the addition of plasticizers derived from waste PET increased the hardness of fire-retardant materials by 1.72 % to 19.1 % when compared to materials containing commercial plasticizers. The addition of PET plasticizers and other flame retardants decreased the tensile strength of the material from 8.16 % to 26.14 %. According to Charpy, the toughness of the material is also reduced from 2.55 % to 8.4 %. The addition of PET plasticizers raised the specific density and expansion coefficient of the given materials. All obtained samples were tested in accordance with the nonflammability standards and met the requirements of the standard. If an economically viable recycling process is implemented, the implementation of a circular economy could turn environmental challenges into opportunities for development.