Plastic products are indelibly rooted in modern society. However, most of them are randomly discarded in nature, causing serious damage to the environment and polluting terrestrial ecosystems, groundwater, and aquatic biomes. There is widespread concern about preserving the planet
[1]
-
[3]
. Owing to the problems caused by solid waste pollution and considering the enormous energy potential concentrated in the different types of discarded plastics, polymer recycling should be considered an effective solution to minimize the environmental impact of plastic disposal
[4]
-
[8]
. Whether applied as commodity plastic or engineering plastic, polyethylene terephthalate (PET), along with polyolefins, is among the most widely used plastics around the world
[9]
. In 2018, about 20 million tons of food-grade PET bottles were manufactured, but only 845 thousand tons were recycled. In the coming years, it is expected that around 3 million tons will be mechanically recycled
[10]
[11]
. Shirazimoghaddam et al. studied the chemical recycling (depolymerization) of PET in the presence of a niobium catalyst. A high yield of BHET (2-hydroxyethyl terephthalate) precursor and oligomers, considered suitable for repolymerization, was obtained
[12]
. Giraldo-Narcizo et al. experienced the depolymerization of PET using alkaline pretreatment and temperature. The process presented advantages such as higher yield than other technologies
[13]
. Pu et al. synthesized polyurethane elastomer using PET depolymerized from post-consumer bottles as a chain extender. The authors noted the high transparency and extensibility of the final product
[14]
. Ghosh et al. published a study projecting the feasibility of recycling PET bottles for the period 2020-2049. In the study, they emphasized that both chemical and secondary recycling (from selective collection) should improve the circularity of PET bottles and reduce carbon footprints, replacing the manufacture of virgin PET
[15]
. Lerna et al. studied the effect of recycled PET bottles as plastic aggregates on the improvement of concrete ductility. Reduction of heat conduction capacity and limited decrease of compressive strength were reported
[16]
. Roungpaisan et al. conducted a comparative study on recycled filaments derived from PET bottles and PET knitted fabrics. The latter produced a fiber with good formability and better melting spinning, along with additional improvement of thermal and mechanical properties
[17]
. As a material of fossil origin, plastics are potentially combustible materials. A survey carried out in the USA and European Union revealed a high rate of deaths, injuries and significant financial losses due to residential building fires. In this context, the addition of flame retardants to plastic formulations is a way to prevent human and financial losses
[18]
. Fire retardants have gained public interest for the last 30 years owing to their increased importance on personnel safety. Many flame-retardant additives, such as halogen-based, phosphorus-based, metal oxides, and mineral fillers have been used as a measure of fire retardancy plastics
[19]
-
[22]
. Aluminum hydroxide Al(OH)3 has been used in various sectors. Shi et al. investigated a new flame retardant for poly(ethylene terephthalate) (PET) based on hydroxyethyl diphosphate modified with different particles sizes of aluminum hydroxide. The best result was attained by particle size of 10 μm which was ascribed to the combined effects namely decomposition of phosphoric acid and dehydration of Al(OH)3
[23]
. Park et al. highlighted the application of Al(OH)3 as flame retardant for being environmentally friendly, free of acid and halogen
[24]
. Hypophosphites have also been used as a potential flame retardant for polyerster. Yang et al. reported that the addition of 10 wt.% of aluminum hypophosphite in composites of polyethylene terephthalate/glass fiber attained high limited oxygen index and V-0 classification in UL-94 test
[25]
. The synergistic effect of the mixing of diethylzinc hypophosphite (ZDP) and nano-SiO2 as flame retardant for PET was investigated by Zheng and collaborators. The additivation of PET induced classification V-0 for vertical combustible grade and increased its limiting oxygen index from 21% to 30%. The nano-SiO2 imputed better dripping behavior
[26]
. Composite of poly(butylene terephthalate)/glass fiber was composed with rare earth hypophosphite and melamine cyanurate as flame retardants. The authors registered that the mixing induced slight decrease of the thermal stability, reduction in heat release rate and limiting oxygen index
[27]
. Assocition of maleic anhydride and sodium hypophosphite as flame retardant for cotton finishing was evaluated by Wu and Yang. It was revealed that the treatment with this combination reduced the flammability of cotton fleece from the Class III to Class I and it was considered low cost matter
[28]
. Considering the special properties—ion exchange capacity, ion intercalation, ionic conductivity, catalytic activity—of the lammelar phosphates and the expertise of our research group in the synthesis and new applications of zirconium and titanium phosphates
[29]
[30]
, the proposal of this research was to evaluate the effectiveness of ZrP alone and in combination with aluminum hydroxide and sodium hypophosphite as potential flame retardant for post-consumer poly(ethylene terephthalate) (rPET).
2. Experimental2.1. Material
Post-consumer bottles of poly(ethylene terephthalate) (rPET) from the Macromolecules Institute community were used. Zirconium phosphate, phosphoric acid (H3PO4, 85 % wt./mL, Vetec), zirconium (IV) oxide chloride (ZrOCl2.8H2O, Sigma-Aldrich), octadecylamine (Oct, Sigma-Aldrich) and absolute ethanol (99 %) were purchased. Aluminum hydroxide [Al(OH)3, Isofar] and sodium hypophosphite (NaPO2H2·H2O, Isofar) were acquired. All reagents were used as received.
2.2. Post-Consumer Bottles of Poly (Ethylene Terephthalate) (rPET) Treatment
Post-consumer PET bottles were collected from the Macromolecules Institute community. The labels were removed. The bottles were washed with water plus light detergent, rinsed only with water and dried. Following, they were cut into flakes and then ground.
2.3. Synthesis and Modification of Lammelar Zirconium Phosphate (ZrP)
The lammelar ZrP was synthesized following its intercalation with octadecylamine (Oct:ZrP, 2:1) as reported elsewhere
[31]
. The intercalation with octadecylamine aimed at improving the dispersibility between ZrP and its counterparts.
2.4. Masterbatch, Composite and Flammability Specimen Preparation
The following masterbatches were prepared: rPET/ZrP (80/20 wt./wt.%); rPET/Al(OH)3/NaPO2H2·H2O (80/10/10 wt./wt./wt.%) and rPET/ZrPOct/Al(OH)3/NaPO2H2·H2O (80/10/5/5 wt./wt./wt./wt.%) and they were processed in a Teck Tril co-rotating twin-screw extruder (L/D = 36, screw diameter = 22 mm), processing window 120 - 260˚C, at 300 rpm. Samples were labelled as rPET, rPET/ZrP, rPET/Al(OH)3/NaPO2H2·H2O and rPET/ZrPOct/Al(OH)3/NaPO2H2·H2O (
Figure 1
). Composites of rPET/masterbatch (75/25 wt./wt.%) were processed in a Haake Rheocord 9000 torque rheometer at 260=˚C, 60 rpm for 6 minutes. The specimens for flammability test were prepared by compression moulding in a Carver press at 260°C, 5,000 psi. Following, the specimens were cooled at 180˚C C for 2 minutes and finally cooled in a cooling plate, at 20˚C, for 3 minutes. The specimens were identified as FS1 (rPET), FS2 (rPET/ZrP)—represent 5 wt. % of ZrP-, FS3 (rPET/Al(OH)3/NaPO2H2·H2O)—represent 2.5 wt. % for each one—and FS4 (rPET/ZrPOct/Al(OH)3/NaPO2H2·H2O)—represent 2.5 wt. % for ZrP, and singly 1.25 wt. % for Al(OH)3 and NaPO2H2·H2O.
Figure 1. Images of masterbatches after processing: (a) rPET, (b) rPET/ZrP, (c) rPET/Al(OH)<sub>3</sub>/NaPO<sub>2</sub>H<sub>2</sub>·H<sub>2</sub>O and (d) rPET/ZrPOct/Al(OH)<sub>3</sub>/NaPO<sub>2</sub>H<sub>2</sub>·H<sub>2</sub>O.
The infrared analysis was performed in a Perkin Elmer Frontier model instrument, covering the range from 4000 to 500 cm−1, with 60 scans and a resolution of 4 cm−1, using KBr disk.
2.6. Raman Spectroscopy
The Raman spectroscopy was performed using a Raman Microscope equipped with a laser, at a wavelength of 532 nm and a 50x lens, in the range of 4000-200 cm−1. The vibrational modes were evaluated.
2.7. Time-Domain Hydrogen Nuclear Magnetic Resonance (TDHNMR)
Time domain hydrogen nuclear magnetic resonance was accomplished in a Maran Ultra 23 equipment with hydrogen nucleus pulse sequence, equipped with a probe of 18 mm, operating at a frequency of 23 MHz, at 30˚C. The domain distribution curve was acquired, and the relaxation time was determined.
2.8. Wide Angle X-Ray Diffraction (WAXD)
The crystallographic aspect of each sample was monitored in a Rigaku Ultima IV diffractometer with CuKα radiation (λ = 1.5418 Å), 40 kV, 20 mA, a step of 0.05, ranging the 2θ angle from 2˚ to 50˚.
2.9. Thermogravimetry (TGA)
In TA equipment model Q500 the TGA analysis was performed at a range of 30-700˚C, at 10˚C∙min−1 and nitrogen as carrying gas. Mass loss and derivative curves were assessed. The degradation temperature was evaluated.
2.10. Differential Scanning Calorimetry (DSC)
The calorimetry tests were performed in DSC1 STARe SYSTEM following the recommendations specified by ASTM D3418
[32]
. Three cycles were conducted: firstly, heating from 30 to 280˚C at a rate of 10˚C /min, followed by cooling from 280 to 30˚C at the same rate, and finally, another heating cycle identical to the first. For each sample, the crystallization (Tc) and melting (Tm) temperatures were pointed out, as well as the degree of crystallization (Xc) determined through the ratio of PET experimental melting enthalpy (ΔHsample) and the 100% crystalline PET (ΔHref, 130 J∙g−1), considering Xc = (ΔHsample /ΔHref ) ⋅ (1 − Φ), where Φ is the filler weight fraction in each composite
[33]
.
2.11. Rheology
The parallel plate rheology was conducted in TA rheometer, model AR-2000, with a geometry of 25 mm diameter, at 260˚C, strain amplitude of 10−3, from 10−1 to 103 rad/s. The complex moduli (storage and loss) and complex viscosity were determined.
2.12. Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive Spectroscopy (EDS)
Flammability specimens were evaluated by field emission scanning electron microscopy and energy dispersive spectroscopy analysis. A Tescan FESEM model MIRA 4 LMU (LowVac Mode UniVac™) equipment accoupled with an EDS detector (30 mm2 Si3N4 window, resolution lower than 129 eV, MnKα emission line) enabled the viewing of the dispersion and distribution of main elements (zirconium, aluminum, sodium) in each type of flame retardant.
2.13. Flammability Tests
The flammability test was performed following the ASTM D635-22
[34]
using a Bunsen burner and propane/butane gas mixture. Dripping speed, flame extinguishing time, and ignition time were assessed, with the average and standard deviation calculated from three measurements. The whole test was registered by video.
3. Results and Discussion3.1. Infrared Spectroscopy
Figure 2. Spectra of flame retardants at different spectral regions.
Figure 3. Spectra of rPET and masterbatches at different spectral regions.
<xref ref-type="bibr" rid="scirp.145129-"></xref>Table 1. Summary of samples and absorptions.
[46]
-
[48]
. Absorptions of rPET/ZrP were assigned at 3595; 3510; 3431; 2965; 2909; 2629; 2532; 2386; 2286; 2106; 1722; 1615; 1579; 1505; 1456; 1410; 1372; 1342; 1244; 1098; 1042; 1016; 966; 872; 792; 726 cm−1. rPET/Al(OH)3/NaPO2H2·H2O absorptions were registered at 3435; 2964; 2908; 2379; 2347; 2313; 2109; 1960; 1719; 1615; 1579; 1505; 1455; 1411; 1373; 1344; 1241; 1173; 1120; 1098; 1042; 1017; 972; 898; 873; 845; 793; 662; 631 cm−1. The rPET/ZrPOct/Al(OH)3/NaPO2H2·H2O absorptions appeared at 3420; 2963; 2922; 2855; 2381; 2110; 1960; 1719; 1640; 1618; 1579; 1554; 1505; 1456; 1410; 1373; 1344; 1262; 1244; 1172; 1120; 1095; 1043; 1017; 972; 898; 872; 843; 794; 725; 631 cm−1. A more careful observation of the masterbatches’ spectra showed that in each spectral region, their contour closely resembles that of rPET, although some specific flame retardant absorptions can be visualized. In summary, no significant changes were observed in the spectra, indicating the absence of chemical interaction between the components.
3.2. Raman Spectroscopy3.3. Time-Domain Hydrogen Nuclear Magnetic Resonance (TDHNMR)
Domain distribution curves are shown in
Figure 6
. Two relaxation regions with high (below 5 × 103 ms) and low (between 450 – 1250 × 103 ms) molecular mobility are observed in pure rPET. With the addition of ZrP, the high mobility region of rPET shifts to higher relaxation times, showing increased intensity, and a new region emerges between 50 - 60 × 103 ms. The domain at higher relaxation time showed no change. A similar behavior was observed when the Al(OH)3/NaPO2H2·H2O was added.
Domains with higher molecular mobility exhibited shorter relaxation times compared to those for ZrP. On the contrary, the domain with lower molecular mobility was enlarged and shifted to higher relaxation times. Also, the ZrPOct/Al(OH)3/NaPO2H2·H2O showed a tendency towards lower relaxation times, although the decrease was less pronounced than in the two previous cases. No change was noticed for the domain with higher relaxation times. Xerogels of
Figure 4. Raman spectra of flame retardants.
Figure 5. Raman spectra of rPET and masterbatches.
Figure 6. Domain distribution curves of the rPET and masterbatches.
poly (vinyl alcohol) (PVA) filled with silica nanoparticle (SiO2) were studied by Rodrigues and collaborators. Through time domain nuclear magnetic resonance, it was noticed that SiO2 altered the PVA molecular mobility although there was not chemical interaction between them
[55]
. In general, all flame retardants showed some effect on the molecular mobility of rPET. It was assumed that the shift of the relaxation time and the enlargement of domains could be associated with the dispersion and distribution of flame retardants within the two relaxation regions of rPET.
3.4. X-Ray Diffraction
Figure 7
displays the diffraction pattern of the flame retardants. The ZrP showed diffraction angles at 12.3 (hkl plane), 20.4, 25.6, 34.6, 38 and 48.6˚, as reported by Mendes and collaborators
[31]
. The main Al(OH)3 diffraction angles at 14.5-15.7 (020)*, 18.9 (002)**, 20.6 (200)**, 28.2 (120)*, 32.2, 38.3 (031)*, 40.7 and 49˚ (200)* are representative of the mixing of its crystalline forms—boehmite (orthorhombic)* and gibbsite (monoclinic)**, as reported by Bian and co-authors
[37]
. The NaPO2H2·H2O showed the main diffraction angles at 11, 14.5, 15.2, 27.2, 28.7,
Figure 7. Diffraction pattern of the flame retardants.
Figure 8. Diffraction pattern of the rPET and masterbatches.
30.4, 31.7, 34.9, 41.7 and 47.3˚, which are attributed to different crystalline planes
[52]
. The Al(OH)3/NaPO2H2·H2O diffraction angles appeared at 16.1, 18.8*, 21.6, 25.4, 26.2, 28.7**, 31.8*, 34.5**, 39.2, 43.8*, 46*, 47.5** and 49.1˚. The ZrPOct/Al(OH)3/NaPO2H2·H2O diffraction angles appeared at 4, 5.6, 7.5, 9.3, 10.7*, 11.7*, 14.7, 15.1*, 21.6*, 22.1*, 23*, 24*, 25*, 26*, 27.3, 29*, 29.6, 30, 31, 33, 34*, 35, 36**, 36.5**, 37**, 39**, 41*, 42*, 45*, 46*, 47* and 49.4˚*. The diffraction peaks below 10˚ could be attributed to the intercalation in ZrPOct. The diffraction peaks (*) and (**) were attributed to aluminum hydroxide and sodium hypophosphite, respectively.
Figure 8
presents the X-ray diffractions of rPET and masterbatches. The rPET showed two amorphous halos around 23 and 44˚. This could be attributed to the effect of quenching during the extrusion process, as described by Albitres et al. in an article on poly(ethylene terephthalate) with nano-titanium phosphate nanocomposites
[46]
. In addition to the amorphous halo of rPET, the main diffraction angles of ZrP are highlighted in the rPET/ZrP diffractogram
[56]
. X-ray diffraction patterns of rPET/Al(OH)3/NaPO2H2·H2O and PET/ZrPOct/Al(OH)3/NaPO2H2·H2O presented a similar profile. The diffractogram showed the amorphous halo of rPET and some diffraction angles of the flame retardants. Similar to FTIR results, by X-ray diffraction the mixing of flame retardant did not reveal apparent chemical interaction among them.
3.5. Thermogravimetry
Figure 9
exhibited the mass loss and derivative curves of the rPET and masterbatches. The rPET and rPET/ZrP curves exhibited only one decay while rPET/Al(OH)3/NaPO2H2·H2O and rPET/ZrPOct/Al(OH)3/NaPO2H2.H2O two ones. Although the mass loss and derivatives curves showed very slight fluctuation in the range of 200˚C until Tonset, both curves showed quasi imperceptible variations at the same range. The difference of the residues was associated to the flame retardants.
Table 2
condensed the values of Tonset and Tmax and residue of each sample. Liu et al. investigated the disproportionation of sodium hypophosphite by thermogravimetry
[57]
. They detected three degradation steps around 310˚C (12.6%), 370˚C (3.5%) and 430˚C (0.5%). Qin et al. studied the action of aluminum hydroxide on mechanical properties, flame retardancy and combustion behavior of polypropylene
[58]
. Thermogravimetry indicated that under nitrogen atmosphere its degradation process occurred at only one step around 230˚C - 350˚C releasing water and generating Al2O3. While the onset of degradation was largely unaffected, the retardants did influence the degradation pathway, as evidenced by the significant increase in final residue, a key mechanism of flame retardancy.
3.6. Differential Scanning Calorimetry (DSC)
Figure 9. Mass loss and derivative curves of rPET and masterbatches.
<xref ref-type="bibr" rid="scirp.145129-"></xref>Table 2. Thermogravimetric properties of rPET and masterbatches.
Sample
Tonset/˚C
Tmax/˚C
Resdídue/%
rPET
405
432
13
rPET/ZrP
408
436
15
rPET/Al(OH)3/NaPO2H2·H2O
406
430
14
rPET/ZrPOct/Al(OH)3/NaPO2H2·H2O
406
430
18
Figure 10. Calorimetric curves of rPET and masterbatches.
<xref ref-type="bibr" rid="scirp.145129-"></xref>Table 3. Samples’ T<sub>cc</sub>, T<sub>m</sub> and X<sub>c</sub>.
Sample
Tcc/˚C
Tm*/˚C
X/%
rPET
214
240/249
39
rPET/ZrP
213
216/238/248
38
rPET/Al(OH)3/NaPO2H2·H2O
217
242
30
rPET/ZrPOct/Al(OH)3/NaPO2H2.H2O
216
242
33
*second heating cycle.
3.7. Rheology
Figure 11. G’, G” and complex viscosity curves of rPET and matserbatches.
Figure 12. Cross over point of the samples.
<xref ref-type="bibr" rid="scirp.145129-"></xref>Table 4. Crossover point: G”/G’ and frequency.
Sample
G”/G’
ang frequency x102/rad s−1
rPET
-
-
rPET/ZrP
1.08
0.08
0.99
8.5
rPET/Al(OH)3/NaPO2H2.H2O
1.02
2.1
rPET/ZrPOct/Al(OH)3/NaPO2H2.H2O
1.03
3.4
The rPET did not present a crossover point within the studied range. The rPET/ZrP presented two crossover points: one around 101 rad/s and another in the vicinity of 103 rad s−1. The rPET/Al(OH)3/NaPO2H2.H2O and PET/ZrPOct/Al(OH)3/NaPO2H2.H2O showed crossover points between 102 - 103 rad s−1. In general, when G’ was higher than G”, the samples showed solid-like behavior, but when G’ < G”, liquid-like behavior prevailed. Exceptionally, rPET/ZrP seemed to have a second crossover point at a higher frequency, where elastic behavior predominated.
Table 4
summarizes the values of the crossover point (G”/G’) and frequency of the samples. Simon-Stoger et al. examined poly(ethylene terephthalate) waste streams, including selective income (SI), sorting residue (SR), and refuse-derived fuel (RDF) contaminated with organics, to assess the quality of PET waste
[61]
. Oscillatory rheology was carried out in combination with other analyses. The authors associated the crossover point to each PET waste stream and molecular weight distribution. In summary, they concluded that flame retardants exert a substantial influence on the samples’ G’, G’’, complex viscosity, and crossover point. The rPET/Al(OH)3/NaPO2H2.H2O and PET/ZrPOct/Al(OH)3/NaPO2H2.H2O presented similar behaviors, while for rPET/ZrP behaved differently, probably owing to its nanometric dimension. The rheological behavior of the samples is believed to be influenced by the particle dimensions of the flame retardants and the two relaxation regions of rPET.
3.8. Fesem/Eds
Figure 13(a)
shows the FESEM/EDS images of the transversal section of the flammability specimen divided into bottom, intermediate, and top portions. For all
Figure 13. FESEM and EDS of (a) specimen transversal section, (b) FS2, (c) FS3 and (d) FS4.
composites,
Figure 13(b)-(d)
reveal the dispersibility and distribution of the flame retardants within all composites. The left column corresponds to the FESEM image of each specimen from bottom to top. The right columns indicate the dispersibility and distribution of Zr, Al and Na in each composite.
Figure 13(b)
(FS2) showed well-dispersed and distributed ZrP particles across the bottom, intermediate, and top regions of the flammability specimen’s transverse surface.
Figure 13(c)
(FS3) disclosed the dispersibility and distribution of Al and Na. Both aluminum hydroxide and sodium hypophosphite exhibited poor dispersion and distribution across the bottom, intermediate, and top regions.
Figure 13(d)
(FS4) once again demonstrated that ZrPOct was highly dispersed and distributed. The ZrP seemed to have improved the dispersion and distribution of aluminum hydroxide and sodium hypophosphite, but it was still inadequate. The results reflected the influence of the flame retardants’ particle size on their dispersion and distribution within rPET matrix.
3.9. Flammability
Figure 14
depicts the monitoring of the flammability test. From left to right, it shows the burning of the specimen and the dropping of molten material onto the bottom platform. For FS1 (rPET), the specimen burned continuously. The falling drop sustained the flame, and even upon reaching the platform, the flame persisted. For FS2 (rPET/ZrP), immediately after the drop fell, the flame on the specimen extinguished. The drop maintained the flame for a certain time during its fall, but it extinguished before reaching the platform. Specimen FS3 (rPET/Al(OH)3/NaPO2H2.H2O) behaved similarly to FS1. The specimen burned continuously. The falling drop kept the flame and even after reaching the platform the flame persisted. Although there was some similarity in behavior with the FS3, the FS4 (rPET/ZrPOct/Al(OH)3/NaPO2H2.H2O) showed a tendency toward flame extinction even upon reaching the platform.
Figure 15
presents the images of each specimen after the completion of the flammability test. The images represent, from left to right, the right side view, bottom side view, and left side view, respectively. For all samples, there was no significant warping of the specimens during the test, only a protuberance formed at the bottom of the specimen due to the polymer melting. Wang et al. investigated the action of zirconium aminotrimethylene phosphonate (ZrATMP) in the flame retardancy of epoxy resin (EP), registering a significant increase in the char residue. They pointed out that the improvement of flame retardancy and smoke suppression was attributed to the formation of a dense char layer. This char layer acted as a physical barrier, heat insulation, mass exchange and suppressed combustion reactions
[62]
.
Table 5
discloses dripping speed (drops 5s-1), flame extinguished time and ignition time of the samples. The sequence for dripping speed and flame extinguishment time is as follows: rPET, rPET/Al(OH)3/NaPO2H2.H2O, rPET/ZrPOct/Al(OH)3/NaPO2H2.H2O, rPET/ZrP. For ignition time, the sequence is rPET/ZrPOct/Al(OH)3/NaPO2H2.H2O, rPET, rPET/Al(OH)3/NaPO2H2.H2O, rPET/ZrP. Lessan et al. studied the combination of
Figure 14. Monitoring of flammability test for rPET (FS1) and composites (FS2, FS3 and FS4).
Figure 15. FS appearance after flammability test: (a) FS1, (b) FS2, (c) FS3 and (d) FS4; from left to right: right side view; bottom side view and left side view.
<xref ref-type="bibr" rid="scirp.145129-"></xref>Table 5. Flammability data for rPET and composites.
Sample
Dripping speed/drops 5s−1
Flame extinguished time/s
Ignition time/s
FS1
4.7 ± 0.6
20.16 ± 0.35
12.25 ± 1.17
FS2
1.0 ± 0
0.78 ± 0.40
10.77 ± 1.86
FS3
4.0 ± 0
10.49 ± 2.49
11.82 ± 2.82
FS4
2.5 ± 0.7
6.94 ± 2.24
13.50 ± 2.00
sodium hypophosphite (SHP), maleic acid (MA), triethanol amine (TEA) and nano TiO2 as flame retardant. Authors registered that the presence of 5% SHP increased the limit oxygen index from 18.6 to 23
[63]
. Goudarzia et al. prepared a composite based on poly(vinyl alcohol) with nano-aluminum hydroxide. UL-94 flammability test indicated high flame resistance (V-0). They concluded that the dispersion of the nano-aluminum hydroxide causes some obstruction decreasing the emission of the volatilization product and the thermal transport among polymer decomposition
[64]
. The results emphasized how the particle size of flame retardants influenced their dispersion and distribution within the rPET matrix. The best findings were shown for ZrP nanoparticles.
4. Conclusion
Post-consumer PET (rPET) from beverage bottles was filled with three different inorganic matters and structural, crystallographic, termal, relaxometry and flammability evaluations were performed. Analysis of the chemical structure did not indicate any chemical interactions among the components. According to NMR, FESEM/EDS, rheology, and flammability tests, the dimension of the flame retardants—nanometric or micrometric—was a crucial factor in their dispersion and distribution inside the rPET matrix. Considering the parameters studied here, the values of dripping speed, flame extinguishment time, and ignition time were particularly relevant for ZrP nanoparticles.
Data Availability Statement
The datasets generated during and/or analyzed during the current study are not publicly available due to the data are not public (Belong to my Institution—Universidade Federal Rio de Janeiro-UFRJ, Brazil).
Acknowledgements
The authors would like to thank the Federal University of Rio de Janeiro (UFRJ), Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nivel Superior (CAPES) Finance Code 1, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ): processo n˚ E-26/263616/2021; processo E-26/210.032/2024, for supporting this research.
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