Study on Properties and Degradation Behavior of Poly (Adipic Acid/Butylene Terephthalate-Co-Glycolic Acid) Copolyester Synthesized by Quaternary Copolymerization
2. Results and Discussion
2.1. GPC and 1HNMR Analysis of PBATGAs
2.2. DSC Analysis
2.3. TG Analysis
2.4. DMA Analysis
2.5. Mechanical Properties
|Sample||Tensile Strength at Break (MPa)||Elongation at Break (%)||Young’s Modulus (MPa)||Yielding Stress (MPa)|
|PBAT||18.6 ± 1.0||896 ± 157||43.0 ± 9.5||7.1 ± 6.5|
|PBATGA10||18.0 ± 0.5||1235 ± 108||28.8 ± 0.8||7.4 ± 0.5|
|PBATGA20||13.0 ± 1.4||1028 ± 322||26.6 ± 3.1||7.2 ± 2.4|
|PBATGA30||9.3 ± 0.5||922 ± 4||24.6 ± 1.8||6.6 ± 1.5|
|PBATGA40||5.9 ± 0.1||463 ± 22||36.0 ± 1.3||4.2 ± 0.2|
|PBAF50 ||15.3 ± 1.1||365 ± 78||41.5 ± 2.9||−|
|PEAT50 ||22.0 ± 0.4||762 ± 7||42.0 ± 2.3||−|
|PBS ||43.7 ± 2.3||561 ± 16||220.0 ± 7.5||32.7 ± 2.2|
|PBSA ||12.8 ± 2.8||21 ± 10||−||−|
|PPC ||6.6 ± 0.4||3 ± 43||−||−|
2.6. Degradation Behaviors of PBATGA Copolymers in Different Buffer Solutions
2.7. Degradation of PBATGAs in Humid Air at Room Temperature
3. Materials and Methods
3.2. Synthesis of PBATGA Copolyesters
- BDO, TPA, AA, MG and CAT−2019 were added into a 100 mL three−flask for reaction, the molar ratio of alcohol and acid was 2.0:1.0, the molar ratios of PTA+AA and MG were 100:0, 90:10, 80:20, 70:30 and 60:40. The esterification reaction was conducted from 200 to 230 °C for 4~5 h under N2 atmosphere until the water yield reached 95% of the theoretical value. Among them, the molar ratios of TPA and AA were 50:50, and the molar ratios of SA and GA were 100:0, 90:10, 80:20, 70:30, 60:40 and 50:50. The corresponding products were named from PBATGA10 to PBATGA40.
- The condenser tube and water separator were removed, then the pressure was slowly decreased to less than 20 Pa and the temperature gradually increased to 230 °C and continued for about 4~5 h. During this period, the mixing speed was slowly reduced to 160~60 r/min according to the change of viscosity. When the viscosity of the product was high or the phenomenon of climbing rod occurred, it was discharged for use. Finally, the obtained white to faint yellow products could be used directly in subsequent tests without further purification. The appearance of the final product is shown in Figure 7. PBAT appears bright milky white, while PBATGA copolyesters appeared light yellow.
- The molecular weight and the molecular weight distribution were investigated using Gel Permeation Chromatography (GPC) on an Acquity APC advanced polymer chromatography system advanced performance gel permeation chromatograph, and the mobile phase was tetrahydrofuran.
- The chemical structure was recorded using 1H NMR on a Bruker Avance NEO 500 MHz apparatus. Deuterated chloroform was the solvent for testing.
- The characteristic viscosity test was performed as follows. First, a sample of about 25 mg was weighed and phenol−tetrachloroethane 1:1 mixed solution was used as a solvent to set the volume in a 25 mL volumetric flask. Under the condition of 30 °C, the outflow time t0 and t of pure solvent and polymers were tested by a three−tube viscometer with a pipe diameter of 0.7~0.8 mm. Each sample was measured three times in parallel, and the average value was obtained, which is the outflow time of the solution to be measured. The formula for calculating the characteristic viscosity is the Solomon–Ciuta method:
- Differential scanning calorimetry (DSC) analysis was performed on a DSC 2500 instrument (TA Company, Boston, MA, USA). A sample with a mass of 10 mg was taken and put into an aluminum pan. The samples were first heated to 200 °C at 10 °C·min−1, kept at 200 °C for 3 min, and then they were cooled to −50 °C at 10 °C·min−1 and kept for 3 min. They were then reheated again to 200 °C at the same heating rate.
- Dynamic Thermomechanical Analysis (DMA) was obtained using the DMA 8000 dynamic mechanics analyzer of Perkin Elmer (Waltham, MA, USA). The oscillation frequency was 1.0 Hz, the amplitude was 50 μm, the specimen size was 1.0 mm × 8 mm × 20 mm and the tensile mode test was performed. The test temperature range was −80~100 °C, and the heating rate was 5 °C·min−1. The peak value of the loss factor over this temperature range was the glass transition temperature Tg.
- Thermogravimetric analysis (TGA) was measured using the TGA7 (Thermogravimetric Analyzer) type thermogravimetric analyzer of PerkinElmer (Waltham, MA, USA). The test temperature was 40–800 °C with a heating rate of 20 °C·min−1 under N2 atmosphere.
- For the mechanical properties test, the samples were prepared according to the GB/T1040–1BA type, and the tensile test was conducted by using universal testing machine at room temperature at the tensile speed of 20 mm/min. The tensile strength and elongation at break were calculated and recorded.
- Degradation experiments of PBATGAs samples (0.4~0.5 mm in thickness) were carried out in four buffer solutions of acidic (pH = 2), neutral (pH = 7), alkaline (pH = 12) and 0.2 mg /mL of Lipase in phosphate−buffered solution. All the samples were kept at 37 °C, the buffer solutions were replaced and the samples were taken every 7 days. After cleaning, the samples were dried at 60 °C for 24 h. The degradation behavior was evaluated by the weight percentage of residue, according to the following Equation (6):
- The results of DSC test revealed that the PBATGAs were semicrystalline polyesters with Tm > 100 °C when the content of GA units <40%.
- The results of TGA and tensile test revealed that the PBATGA copolymers possess good thermal and excellent mechanical properties. The tensile strength was 5.98~18.58 MPa, and the elongation at break was more than 463%. In particular, the elongation at break of PBATGA40 was even more than 1200%. These results were better than the most degradable polymers used as membranes.
- The results of DMA test revealed that the Tg values of PBATGA10–40 were between −20.1 °C and −14.5 °C, which are close to the Tg of PBAT (−17.4 °C).
- Regarding the hydrolysis experiment in four kinds of buffer solutions, the weight loss of PBATGA copolymer in descending order, is as follows: pH = 12 > Lipase ≈ pH = 7 > pH = 2. In the alkaline solution with pH = 12, the weight loss of PBATGA40 copolyester was 58.29% after 49 days, and only 12.67% and 17.21% in acidic and neutral solutions, respectively. Lipase could not effectively catalyze the hydrolysis of the ester bonds in PBATGA copolymers.
- GA units can accelerate the degradation of PBAT in the presence of water. Therefore, the above experiments proved that the PBATGA copolyesters are promising candidates for conventional nondegradable plastic products in the field of direct environmental leakage. In the future, efforts to study the shelf life of PBATGA copolyesters in vacuum are very necessary.
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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|Samples||Cooling Scan||Second Heating Scan||TGA||DMA|
|Tonset-Tc (°C)||Tc (°C)||ΔHc (J/g)||Xc (%)||Tm (°C)||ΔHm (J/g)||T5% (°C)||Tdmax (°C)||Tg (°C)|
|Samples||Degradation Time (Days)||Mn (g/mol)||Mw (g/mol)||PDI|
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Wang, Y.; Hou, B.; Huang, L.; Li, B.; Liu, S.; He, M.; Chen, Q.; Li, J. Study on Properties and Degradation Behavior of Poly (Adipic Acid/Butylene Terephthalate-Co-Glycolic Acid) Copolyester Synthesized by Quaternary Copolymerization. Int. J. Mol. Sci. 2023, 24, 6451. https://doi.org/10.3390/ijms24076451
Wang Y, Hou B, Huang L, Li B, Liu S, He M, Chen Q, Li J. Study on Properties and Degradation Behavior of Poly (Adipic Acid/Butylene Terephthalate-Co-Glycolic Acid) Copolyester Synthesized by Quaternary Copolymerization. International Journal of Molecular Sciences. 2023; 24(7):6451. https://doi.org/10.3390/ijms24076451Chicago/Turabian Style
Wang, Yanning, Boyou Hou, Liping Huang, Bingjian Li, Shi Liu, Mingyang He, Qun Chen, and Jinchun Li. 2023. "Study on Properties and Degradation Behavior of Poly (Adipic Acid/Butylene Terephthalate-Co-Glycolic Acid) Copolyester Synthesized by Quaternary Copolymerization" International Journal of Molecular Sciences 24, no. 7: 6451. https://doi.org/10.3390/ijms24076451