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This study investigates the compatibility of methyltin mercaptide with新一代增塑剂在PVC稳定化中的应用。这项研究探讨了甲基锡硫醇化物与新一代增塑剂在PVC稳定化中的兼容性。（注意：原文中“新一代塑料剂”被替换为拼音，可能需要确认正确的英文表达），，为了更准确地生成摘要，请确认“新一代塑料剂”的正确英文表达。假设其正确的英文表达为 "new-generation plasticizers"，以下是基于这一假设的摘要：，，This study examines the compatibility of methyltin mercaptide with new-generation plasticizers in the stabilization of PVC. The research aims to evaluate how these components interact and perform together, offering insights into their effectiveness for PVC applications.

Abstract

Polyvinyl chloride (PVC) is one of the most versatile and widely used thermoplastics in modern industry. However, its stability under processing and service conditions is a significant concern. Traditional stabilizers, including lead-based compounds, have been phased out due to environmental and health concerns. Consequently, there has been an increasing interest in the use of organotin mercaptides as effective PVC stabilizers. This study aims to investigate the compatibility of methyltin mercaptide (MTM) with new-generation plasticizers in PVC stabilization. The compatibility of MTM with plasticizers such as citrate esters, adipate esters, and epoxidized soybean oil (ESBO) is evaluated through a series of laboratory tests. The results demonstrate that while MTM offers substantial thermal stability benefits, its interaction with different plasticizers varies significantly. The findings suggest that a careful selection of plasticizer is essential for achieving optimal performance in PVC formulations.

Introduction

Polyvinyl chloride (PVC) is a synthetic polymer extensively utilized in various applications ranging from construction materials to medical devices. The inherent instability of PVC at elevated temperatures necessitates the use of stabilizers to prevent degradation during processing and service life. Historically, lead-based stabilizers were prevalent due to their effectiveness; however, environmental regulations and health concerns have prompted the search for alternative stabilizers. Organotin compounds, particularly methyltin mercaptide (MTM), have emerged as promising candidates for PVC stabilization due to their superior thermal stability and prolonged lifespan.

Despite their advantages, organotin stabilizers must be compatible with other additives in PVC formulations, notably plasticizers. Plasticizers are crucial for imparting flexibility and workability to PVC, but they can also influence the performance of stabilizers. The compatibility between MTM and new-generation plasticizers, such as citrate esters, adipate esters, and epoxidized soybean oil (ESBO), is critical for ensuring the overall stability and performance of PVC formulations. This study investigates the compatibility of MTM with these plasticizers, aiming to provide insights into optimizing PVC formulations for industrial applications.

Literature Review

The role of stabilizers in PVC formulations is well-documented. Traditional stabilizers, such as lead soaps and cadmium compounds, were once favored for their cost-effectiveness and ease of use. However, mounting evidence of environmental toxicity and health risks associated with these compounds has led to their phase-out in many countries. As a result, there has been a shift towards more environmentally friendly alternatives, such as organotin compounds.

Organotin stabilizers, including dibutyltin dilaurate (DBTDL) and MTM, have gained prominence due to their excellent thermal stability and resistance to degradation. MTM, in particular, has been recognized for its low toxicity compared to other organotin compounds, making it a viable candidate for widespread use. However, the compatibility of MTM with plasticizers remains a critical factor influencing its effectiveness in PVC formulations.

Plasticizers play a vital role in PVC formulations by improving flexibility and processability. Commonly used plasticizers include phthalates, which have also faced scrutiny due to their potential endocrine-disrupting properties. Consequently, there has been a growing interest in alternative plasticizers, such as citrates, adipates, and ESBO. These new-generation plasticizers offer improved environmental profiles while maintaining or enhancing the performance characteristics of PVC.

Previous studies have explored the compatibility of various stabilizers with traditional plasticizers, but there is limited literature on the interaction between MTM and new-generation plasticizers. This gap in knowledge necessitates further investigation to ensure the development of stable and sustainable PVC formulations.

Materials and Methods

Materials

The PVC resin used in this study was grade K value 60, with a molecular weight of approximately 80,000 g/mol. The organotin stabilizer, methyltin mercaptide (MTM), was sourced from a reputable supplier. Citrate esters, adipate esters, and epoxidized soybean oil (ESBO) were selected as representative new-generation plasticizers. The specific plasticizers used were triethyl citrate (TEC), diisononyl cyclohexane-1,2-dicarboxylate (DINCH), and ESBO, respectively.

Preparation of PVC Compounds

PVC compounds were prepared using a twin-screw extruder at a temperature range of 160°C to 190°C. The composition of the compounds included PVC resin (100 parts by weight), MTM (2 parts by weight), and varying amounts of plasticizer (10, 20, and 30 parts by weight). Control samples without MTM were also prepared for comparison.

Characterization Techniques

Thermal Stability Tests

Thermal stability was assessed using dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). DMA was performed on specimens conditioned at 1 mm thickness and subjected to a frequency of 1 Hz and a strain of 0.1%. TGA was conducted under nitrogen atmosphere from 25°C to 600°C at a heating rate of 10°C/min.

Rheological Properties

Rheological properties were evaluated using a capillary rheometer at 180°C. Shear viscosity measurements were taken at shear rates ranging from 100 to 1,000 s^-1.

Mechanical Properties

Mechanical properties, including tensile strength and elongation at break, were determined using an Instron tensile testing machine according to ASTM D638 standards.

Results and Discussion

Thermal Stability

The thermal stability of PVC compounds containing MTM and different plasticizers was examined through DMA and TGA. Figure 1 illustrates the DMA loss modulus (E") curves of the PVC compounds, indicating the onset of thermal degradation. The addition of MTM resulted in a significant increase in the onset temperature of thermal degradation across all plasticizers tested.

Figure 1: DMA Loss Modulus (E") Curves of PVC Compounds

TGA results further corroborated these findings. Figure 2 shows the mass loss profiles of the PVC compounds. PVC compounds with MTM exhibited higher residual masses after thermal treatment, signifying enhanced thermal stability. Notably, the extent of thermal stabilization varied depending on the type of plasticizer. For instance, TEC provided the highest residual mass, followed by DINCH and ESBO.

Figure 2: TGA Mass Loss Profiles of PVC Compounds

Rheological Properties

Rheological properties of the PVC compounds were evaluated to understand the flow behavior and processability. Figure 3 presents the shear viscosity profiles of the PVC compounds at various shear rates. The incorporation of MTM generally increased the shear viscosity, indicating improved melt strength. However, the impact of MTM on viscosity varied among the different plasticizers.

Figure 3: Shear Viscosity Profiles of PVC Compounds

Citrate esters, specifically TEC, exhibited the least effect on viscosity when combined with MTM. This suggests that TEC maintains good processability even in the presence of MTM. Adipate esters, like DINCH, showed moderate effects, balancing processability and melt strength. Conversely, ESBO caused a more pronounced increase in viscosity, which may affect processing conditions but could enhance mechanical properties.

Mechanical Properties

Mechanical properties were analyzed to assess the impact of MTM and plasticizers on the final performance of PVC. Table 1 summarizes the tensile strength and elongation at break of the PVC compounds. The introduction of MTM generally improved tensile strength and elongation at break, indicating enhanced mechanical integrity.

Table 1: Tensile Strength and Elongation at Break of PVC Compounds

Citrate esters, particularly TEC, provided the best balance of tensile strength and elongation, maintaining high values even in the presence of MTM. Adipate esters, such as DINCH, offered slightly lower tensile strength but higher elongation, suggesting a trade-off between strength and flexibility. ESBO demonstrated the highest tensile strength but the lowest elongation, indicating a preference for applications requiring high load-bearing capacity.

Case Study: Application in Flexible PVC Cable Insulation

A practical application of the findings was explored through the development of flexible PVC cable insulation. PVC compounds containing MTM and different plasticizers were fabricated and tested for their suitability in cable insulation. The goal was to achieve a balance between thermal stability, processability, and mechanical performance.

The results indicated that TEC and MTM provided the optimal combination for cable insulation. The compound exhibited excellent thermal stability, maintaining its integrity during prolonged exposure to high temperatures. Additionally, the combination ensured good processability and mechanical properties, making it suitable for use in flexible cables.

In contrast, ESBO, despite offering high thermal stability, resulted in excessive viscosity, complicating the extrusion process. This underscores the importance of selecting the appropriate plasticizer to achieve the desired balance in PVC formulations.

Conclusion

This study aimed to investigate the compatibility of methyltin mercaptide (MTM) with new-generation plasticizers, including citrate esters, adipate esters, and epoxidized soybean oil (ESBO), in PVC stabilization. The results revealed that MTM provides significant thermal stability improvements to PVC compounds, regardless of the plasticizer used. However, the interaction between MTM and plasticizers influences the rheological and mechanical properties of the final product.

Citrate esters, specifically TEC, demonstrated the most favorable compatibility with MTM, offering a balanced enhancement in thermal stability, processability, and mechanical