Crystallization and melting characteristics of iPP nucleated by a sustainable eggshell powder-supported β-nucleating agent

Abstract

The β-form crystals in isotactic polypropylene (iPP) are proved to be favorable and effective for developing general iPP plastics with high performance. Herein, sustainable eggshell power decorated with calcium pimelate (DES), an effective β-form nucleating agent for iPP, was fabricated via the interaction between pimelic acid and Ca2+ on the surface of eggshell powder at elevated temperature. DSC and FTIR analysis identified the reaction occurred and formation of calcium pimelate on surface of the eggshell powder. Then, the effects of the functionalized eggshell powder on the nonisothermal and isothermal crystallization behavior, melting characteristics and polymorph structures were investigated. From the nonisothermal crystallization experiments, the incorporation of supported β-form nucleator greatly enhanced the crystallization temperature of iPP. The content of β-form crystals (Kβ) could reach a value as high as 87% at 5 mass% DES load. Moreover, the crystallization and melting characteristics of iPP nucleated by DES were not changed under multiple scan conditions with melt temperature range from 190 to 250 °C. Interestingly, from the investigation of isothermal crystallization and subsequent melting behavior, it was found that DES is a temperature-dependent selective nucleator for inducing iPP crystallization. Main α-form crystals or β-form crystals could form when using high or low crystallization temperatures, respectively. Particularly, these results demonstrated a possibility to tailor the ratio of α-form crystals to β-form crystals by simply choosing isothermal crystallization conditions. Then the crystallization mechanism based on thermodynamics and kinetics factors was further discussed.