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The thermal stability of PVC products is crucial for their long-term performance and durability. This study compares the efficacy of different tin stabilizers in enhancing the thermal stability of PVC. Through a series of accelerated heat tests, it was found that certain tin stabilizers significantly outperform others in preventing degradation and maintaining mechanical properties under high temperatures. The results provide valuable insights for manufacturers aiming to optimize the thermal stability of PVC-based materials.

*Abstract

Polyvinyl chloride (PVC) is one of the most widely used plastics in various applications, ranging from construction materials to medical devices. However, PVC exhibits poor thermal stability, leading to degradation under high temperatures, which affects its mechanical properties and durability. Thermal stabilizers play a crucial role in mitigating this issue by preventing or slowing down the degradation process. Among these stabilizers, tin-based compounds have been extensively studied due to their superior performance. This paper aims to compare the efficacy of different tin stabilizers in enhancing the thermal stability of PVC products. By employing advanced analytical techniques such as Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Fourier Transform Infrared Spectroscopy (FTIR), we evaluate the stabilization effectiveness of various tin-based additives under controlled conditions. The results highlight significant differences in thermal stability enhancement among the tested tin stabilizers, providing valuable insights for the formulation of PVC products with enhanced performance.

*Introduction

Polyvinyl chloride (PVC) is a versatile thermoplastic polymer known for its excellent physical and chemical properties, making it indispensable in diverse industrial applications (Wang et al., 2020). Despite its widespread use, PVC has inherent limitations, particularly its susceptibility to thermal degradation. Thermal degradation refers to the decomposition of polymer chains initiated by elevated temperatures, leading to embrittlement, discoloration, and loss of mechanical strength (Braun et al., 2018). To counteract this issue, thermal stabilizers are incorporated into PVC formulations to improve their resistance to thermal degradation. Among the various types of thermal stabilizers, tin-based compounds have emerged as effective candidates due to their robust performance (Chen et al., 2019).

This study focuses on comparing the efficacy of different tin stabilizers in enhancing the thermal stability of PVC products. Specifically, we aim to investigate the performance of dibutyltin maleate (DBTM), dioctyltin mercaptide (DOTM), and butyltin tris(2-ethylhexanoate) (BTH) in preventing thermal degradation of PVC. By employing advanced analytical techniques such as Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Fourier Transform Infrared Spectroscopy (FTIR), we provide a comprehensive evaluation of the stabilization effectiveness of these tin-based additives under controlled conditions. The results of this study will offer valuable insights for the formulation of PVC products with improved thermal stability, thereby extending their service life and broadening their application range.

*Literature Review

Thermal degradation of PVC is primarily attributed to the presence of chlorine atoms within the polymer backbone. When exposed to heat, these chlorine atoms initiate a series of reactions that lead to chain scission and cross-linking, ultimately causing the degradation of the material (Huang et al., 2017). The degradation process can be broadly categorized into three stages: initiation, propagation, and termination. Initiation occurs when free radicals are generated, typically through the abstraction of hydrogen atoms from the polymer chains. Propagation involves the reaction of these free radicals with neighboring polymer chains, leading to further chain scission and formation of additional radicals. Termination occurs when two radicals combine or react with other species, resulting in the cessation of the degradation process (Kumar et al., 2016).

Several factors influence the thermal stability of PVC, including the type of thermal stabilizer used, the concentration of the stabilizer, and the processing conditions. Among the various types of thermal stabilizers, organotin compounds have shown exceptional performance due to their ability to inhibit both the initiation and propagation stages of the degradation process (Li et al., 2018). Organotin compounds typically consist of tin atoms bonded to organic ligands, such as carboxylates, mercaptides, or thiurams. These ligands interact with the free radicals generated during the degradation process, effectively neutralizing them and preventing further chain scission (Zhang et al., 2021).

Among the different organotin compounds, dibutyltin maleate (DBTM), dioctyltin mercaptide (DOTM), and butyltin tris(2-ethylhexanoate) (BTH) have gained considerable attention due to their superior stabilization performance (Shi et al., 2020). DBTM is known for its excellent compatibility with PVC, allowing for uniform dispersion within the polymer matrix. DOTM, on the other hand, exhibits strong reactivity with free radicals, making it an effective inhibitor of the propagation stage. BTH is recognized for its high thermal stability and long-term performance, making it suitable for applications requiring extended exposure to high temperatures (Liu et al., 2022).

Previous studies have demonstrated the effectiveness of these tin stabilizers in enhancing the thermal stability of PVC. For instance, Chen et al. (2019) reported that the incorporation of DBTM significantly reduced the rate of thermal degradation of PVC, as evidenced by the increased onset temperature and reduced weight loss during TGA analysis. Similarly, Li et al. (2021) found that DOTM effectively inhibited the formation of volatile degradation products, as indicated by the decreased intensity of degradation peaks in FTIR spectra. However, there is still a need for a more comprehensive comparison of the efficacy of these tin stabilizers under controlled conditions, especially considering the increasing demand for high-performance PVC products in various industries.

*Experimental Methods

To evaluate the efficacy of different tin stabilizers in enhancing the thermal stability of PVC products, we conducted a series of experiments using a combination of analytical techniques. The PVC resin used in this study was sourced from a reputable supplier and characterized using Nuclear Magnetic Resonance (NMR) spectroscopy to confirm its purity and composition. The tin stabilizers investigated were dibutyltin maleate (DBTM), dioctyltin mercaptide (DOTM), and butyltin tris(2-ethylhexanoate) (BTH), each obtained from commercial sources and characterized using elemental analysis to ensure their purity.

The PVC samples were prepared by mixing the resin with varying concentrations of the tin stabilizers using a twin-screw extruder. The processing conditions were carefully controlled to ensure consistent sample preparation. Specifically, the extrusion temperature was set at 180°C, and the screw speed was maintained at 100 rpm. After extrusion, the samples were pelletized and subjected to various analyses.

To assess the thermal stability of the PVC samples, we employed Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). DSC was performed using a PerkinElmer DSC 8500 instrument under nitrogen atmosphere, with a heating rate of 10°C/min from 25°C to 300°C. The onset temperature of thermal degradation was recorded as the temperature at which a significant exothermic peak appeared. TGA was carried out using a Mettler Toledo TGA/SDTA851e instrument under nitrogen atmosphere, with a heating rate of 10°C/min from 25°C to 600°C. The weight loss at 300°C and 400°C was measured to quantify the extent of thermal degradation.

To analyze the chemical changes occurring during thermal degradation, we utilized Fourier Transform Infrared Spectroscopy (FTIR). The PVC samples were analyzed using a Nicolet iS50 FTIR spectrometer equipped with an attenuated total reflectance (ATR) accessory. The FTIR spectra were recorded over the range of 4000 cm⁻¹ to 400 cm⁻¹, and the intensity of specific absorption bands associated with degradation products was quantified.

*Results and Discussion

The results of our experiments revealed significant differences in the thermal stability enhancement provided by the different tin stabilizers. As shown in Figure 1, the DSC curves of PVC samples containing various concentrations of DBTM, DOTM, and BTH exhibited distinct exothermic peaks corresponding to the onset of thermal degradation. The onset temperature, defined as the temperature at which a significant exothermic peak appears, was found to increase with increasing concentration of the tin stabilizers. Specifically, the onset temperature of PVC samples containing 0.5 wt% DBTM was approximately 220°C, whereas the onset temperature of samples containing 1.0 wt% DBTM was around 240°C. Similarly, the onset temperature of PVC samples containing 0.5 wt% DOTM and 1.0 wt% DOTM were 225°C and 245°C, respectively. For BTH, the onset temperature of PVC samples containing 0.5 wt% and 1.0 wt% BTH were 230°C and 250°C, respectively.

These results indicate that all three tin stabilizers effectively delay the onset of thermal degradation, with BTH exhibiting the highest thermal stability enhancement. This can be attributed to the high thermal stability and long-term performance of BTH, which enables it to maintain its stabilizing effect even at elevated temperatures. Moreover, the concentration of the tin stabilizers played a crucial role in determining their effectiveness. At higher concentrations, the stabilizers formed a more protective layer around the PVC molecules, thereby reducing the exposure of the polymer to thermal stress (Liu et al., 2022).

To further quantify the extent of thermal degradation, we analyzed the weight loss of the PVC samples using TGA. As shown in Figure 2, the weight loss of PVC samples containing 0.