This study provides a comprehensive evaluation of how different classes of plasticizers influence the structure, processing behavior, and resulting mechanical and thermal properties of PVC granules (compounds). Plasticizers are one of the most critical formulation components in flexible PVC, directly determining softness, melt viscosity, durability, migration stability, and long-term performance. The research compares commonly used commercial plasticizers including DOP, DINP, DIDP, and DOTP to determine their efficiency and suitability for various industrial applications such as cable insulation, medical tubing, synthetic leather, and footwear.

PVC granules were prepared under identical processing conditions using a twin-screw compounding system. All formulations used the same PVC resin grade (K-value around 65), consistent Ca/Zn stabilizer systems, and identical lubricant packages. Only the plasticizer type was changed. The researchers examined morphological structure using SEM, thermal behavior using DSC and TGA, dynamic mechanical performance via DMA, rheological behavior through capillary rheometry, and mechanical strength through tensile and Shore A hardness testing.

SEM analysis revealed that plasticizer compatibility significantly affects PVC microstructure. DOTP-plasticized PVC showed the most homogeneous morphology with fine polymer–plasticizer dispersion, whereas DOP-based formulations exhibited more defined phase domains due to faster diffusion but lower long-term compatibility. DINP and DIDP formulations exhibited intermediate dispersion characteristics.

Thermal analysis demonstrated that plasticizers lowered PVC’s glass transition temperature (Tg) to varying degrees, with DOP showing the highest plasticization efficiency (largest Tg reduction). However, DOTP exhibited superior thermal stability and slower volatilization at elevated temperatures, making it favorable for long-life applications. TGA results confirmed that DOTP-based compounds had the lowest mass loss during heating, indicating better resistance to plasticizer migration and thermal degradation.

Mechanical testing indicated that DOP-plasticized PVC had higher initial flexibility but suffered from reduced tensile strength and higher migration tendencies. DINP and DIDP offered balanced mechanical properties, but DOTP produced the highest tensile strength, elongation at break, and long-term stability, maintaining performance even after accelerated aging. Shore A hardness tests showed that DOTP formulations achieved consistent softness without excessive plasticization, supporting mechanical durability.

Dynamic mechanical analysis (DMA) showed that DOTP provided a well-defined damping behavior with minimal plasticizer loss during cyclic loading, a key property for electrical and automotive applications. Rheological studies revealed that DOP reduced melt viscosity the most, making processing easier, but DOTP provided more stable melt flow under repeated thermal cycles.

Overall, the study concludes that although DOP remains the most efficient plasticizer in terms of short-term flexibility and processing ease, DOTP significantly outperforms all other tested plasticizers in thermal stability, migration resistance, durability, and mechanical integrity of PVC granules. As a result, DOTP-plasticized PVC is recommended for high-performance applications requiring environmental compliance, long service life, and enhanced safety. This makes DOTP the most suitable replacement for DOP in modern PVC compound formulations.