چكيده لاتين
PVC is considered one of the most widely used polymers. The processing of PVC is carried out at elevated temperatures; however, this polymer is sensitive to high temperatures and undergoes degradation through the loss of HCl gas. Consequently, the use of thermal stabilizers is required. Moreover, pure PVC is inherently rigid and brittle due to dipole–dipole interactions arising from the polar carbon–chlorine bonds in adjacent polymer chains. Therefore, to impart flexibility for many applications, the addition of plasticizers is necessary. In this study, the deep eutectic solvent (DES) Valine:Urea was introduced, and its thermal stabilizing properties in PVC were confirmed through Congo red thermal stability testing (40.76 minutes of stability), oven discoloration testing (color change to brown after 30 minutes), UV-Vis DRS spectroscopy (an absorption of approximately 5.5 in the wavelength range of 311–419 nm), and TGA analysis (onset of the first degradation stage at 184.51 °C). A mechanism for its stabilizing action was also proposed. Furthermore, in the DMTA test, for the PVC sample containing 3 phr of DES, an approximately 2 °C reduction in Tg was observed, and for the PVC sample containing 25 phr of DES, an approximately 42 °C reduction in Tg was recorded compared to the pure PVC sample. This indicates that the DES can also function as a plasticizing aid. Therefore, the Valine:Urea DES can be regarded as an additive with dual functionality. Subsequently, to improve the dispersion of LDH within the PVC matrix and enhance its stabilizing performance, the surface of LDH was modified using PEG and Jeffamine, which were designated as LDH-P and LDH-J, respectively. Thermal stability tests confirmed the positive effect of LDH surface modification with PEG (17.59 minutes of Congo red stability) and with Jeffamine (23.01 minutes of Congo red stability).
To investigate the effect of binary synergistic interactions, combinations of DES and LDH, DES and LDH-P, DES and LDH-J, and DES and zinc stearate were incorporated into PVC. Analysis of the thermal stability tests indicated that these synergistic systems yielded favorable results in stabilizing PVC. Furthermore, by adding a constant amount of zinc stearate to the samples containing DES and LDH, DES and LDH-P, and DES and LDH-J, the ternary synergistic effects of these additives were examined. These systems demonstrated excellent performance in Congo red thermal stability tests, oven discoloration tests, UV-Vis DRS spectroscopy, and TGA analysis. Notably, the color of the ternary DES/LDH-J/zinc stearate sample remained unchanged for 55 minutes in the oven discoloration test. The excellent thermal stability obtained from these synergistic systems is attributed to the presence of multiple thermal stabilization mechanisms, including ammonium salt formation with HCl gas, trapping of HCl, substitution of labile chlorine atoms, and hydrogen bonding interactions, each of which was examined in detail.
Additionally, to evaluate the effect of additive dosage, samples containing two different amounts—3 phr and 1.5 phr—of these stabilizers were prepared, and the resulting data were compared. Subsequently, hardness and tensile tests were carried out to examine the mechanical properties of the aforementioned samples. The highest toughness (2.95 J/cm³) was observed for the sample containing LDH-J.
