Different Effect of Two Commonly Used Stearate Acid Scavengers on Polypropylene Crystallization Promotion Performance of a Sorbitol-Type Nucleating Agent

For Zieglar–Natta (Z–N) polypropylene (PP) to which a nucleating agent (NA) was added to regulate the properties, selecting an appropriate acid scavenger, a necessary additive for Z–N PP, is important for optimizing the effectiveness of the NA. However, the impact of various acid scavengers on the performance of NAs has not been systematically studied. In this work, the effect of two most widely used acid scavengers, calcium stearate (CaSt₂) and zinc stearate (ZnSt₂), on PP crystallization promotion performance of a commonly used NAs, NX8000 (a typical representative of sorbitol-type NAs family) was systematically investigated. It was found that CaSt₂ did not significantly alter the crystallization temperature (T_c) of PP containing NX8000, while ZnSt₂ was detrimental to the nucleation benefit of NX8000, especially in the NA concentration range, where effective nucleation began but remained below the “critical saturation concentration”. The mechanism study showed that CaSt₂ added to PP almost remains chemically unchanged during heating and exhibits no significant impact on the NA. Differently, ZnSt₂ undergoes chemical reactions in a matrix at elevated temperature, producing stearic anhydride, which reacts with NX8000. As a result, a portion of the NA is consumed, leading to a reduction in its efficacy. Our work not only contributes to a comprehensive understanding of mechanisms when multiple additives are used simultaneously but also helps optimize additive formulations to maximize the performance of each component.