Preparation of High‐Strength and Super‐Toughness Polypropylene Without Internal Stress via Combining Pressure‐Induced Flow Processing and Low‐Temperature Supercritical <scp> CO ₂ </scp> Saturation

ABSTRACT This work presents the design and fabrication of high‐strength, super‐tough polypropylene (PP) with eliminated internal stress, achieved through the integration of pressure‐induced flow (PIF) processing and low‐temperature supercritical CO 2 (scCO 2 ) saturation. Comparison of the effects of compression ratio (CR) on the microstructure, internal stress, orientation, crystallization, dynamic mechanical properties, and mechanical properties before and after low‐temperature scCO 2 saturation treatment was conducted. PIF processing can produce a “brick and mud” biomimetic structure, which increases the impact strength and tensile strength by 16.5‐fold and 2.7‐fold, respectively, compared to the specimen that did not undergo PIF processing, respectively. However, the Raman spectroscopy analysis showed that the compressive stress existed in PIF‐PP samples and increased with increasing CR. Following treatment with low‐temperature scCO 2 saturation, the compressive internal stress was effectively eliminated while preserving the integrity of the “brick and mud” biomimetic architecture. In comparison to PIF‐PP samples, the S‐PIF‐PP samples exhibited a slight reduction in orientation, crystallinity, storage modulus, relaxation temperatures, and mechanical properties, and yet maintained outstanding impact strength (66.7 kJ/m 2 ) and tensile strength (105.5 MPa). Furthermore, a mechanism of simultaneous reinforcement and toughening, as well as internal stress reduction was proposed. Overall, the integration of PIF processing with low‐temperature scCO 2 saturation technology offers a novel approach for optimizing the performance of PP.