Effects of nucleating agent content on the microstructure and macroscopic performances of polypropylene analyzed by non-isothermal crystallization behaviors and isothermal crystallization morphologies

Direct attainment of the crystal state corresponding to desired performances in processing can improve the productivity of semi-crystalline polymer products. This work tried to propose the idea to approach the target by exploring the effects of nucleating agent content on non-isothermal crystallization kinetics, isothermally crystallization morphologies and macroscopic properties of polypropylene (PP). The nucleating agent content varied from 0 to 0.5 phr, and all samples were prepared by melting blending at 180°C as the antioxidant and lubricant ensured fine stability and processing. The differential scanning calorimetry results and non-isothermal crystallization kinetics indicated that introducing 0.3 phr nucleating agent advanced both initial crystallization and melting about 10°C and improved crystallization rate and crystallinity. Besides, 145°C was determined as an isothermal crystallization condition by setting temperature gradient, and the crystallization kinetics were described by a power-law equation well. The average crystal size was refined to 40 μm uniformly and crystallization time was reduced to 1.5 min as loading 0.5 phr nucleating agent, contributing to the significant improvements in tensile and physical properties. Thus, adding such a short-time heat insulation procedure into the non-isothermal cooling stage during processing can obtain desired crystal state directly with loading adequate nucleating agent.