Transcrystallization in self‐reinforced polylactic acid composites and its effect on interfacial and tensile properties

Abstract The transcrystalline layer (TCL) constitutes a cylindrical crystal structure enveloping a reinforcing fiber, which plays a pivotal role in influencing the interfacial stress transfer within composite materials. However, its potential impact on interfacial shear strength ( IFSS ) and tensile properties of self‐reinforced polylactic acid composites (SRPLA) have been largely overlooked. In this study, the growth of TCL with isothermal crystallization time was observed. The development of TCL had an optimum effect on interfacial bonding ( IFSS increased by 57.3%) after 10 min of isothermal crystallization due to improved “anchoring” effect caused by the interaction between the amorphous region in both TCL and the matrix. Prolonged isothermal crystallization time reversed this effect due to less chain entanglements as a result of spherulites growth and transcrystalline structure perfection. In terms of tensile properties, the development of the TCL exhibited a detrimental effect on tensile strength and strain at break, ascribed to a transition of tensile failure mode from a fiber‐dominated failure mode to a matrix‐dominated failure mode, yet yielded a positive influence on Young's modulus. This study offers crucial insights and guidance for comprehending the impact of TCL on SRPLA properties, thereby facilitating the potential for optimization of SRPLA properties. Highlights In‐situ observation of the TCL growth in SRPLA. Insight into impact of TCL development on IFSS and tensile properties. Essential guidance for SRPLA performance optimization.