Supertough, Ultrastrong and Transparent Bulk Polylactide Sheets Prepared by Rolling at Ambient Temperature

Polylactide (PLA) with high tensile strength is widely recognized as an optimal substitute for petroleum-based plastics, owing to its biodegradability. However, the poor impact strength and elongation at break limit its widespread application in the engineering field. In this work, neat bulk PLA samples with superhigh impact strength and tensile toughness, superstrong tensile strength, and high transparency have been prepared simply by rolling at ambient temperature. It can be found that the impact strength increases with increasing thickness reduction ratio. When the thickness reduction ratio reaches 65%, the maximum notched Izod impact strength reaches 156 kJ/m2, nearly 82 times that for non-rolling-processed neat PLA (1.9 kJ/m2). Meanwhile, remarkable enhancements in both tensile strength and elongation at break are observed, with the values reaching 104 MPa and 63%, respectively. To the best of our knowledge, such astonishing values of impact strength and tensile strength for amorphous transparent neat PLA have not been reported in the literature. The measurement from differential scanning calorimetry shows that the crystallization of PLA is not induced much by rolling. The measurements from small-angle light scattering and scanning electron microscopy show that tightly stacked oriented fiber-like microstructures form during rolling, and the degree of fibrosis of amorphous PLA plays a pivotal role in enhancing the impact and tensile strength for neat PLA. This work provides an opportunity for manufacturing competitive neat bulk transparent polylactide materials.