Robust biaxially stretchable polylactic acid films based on the highly oriented chain network and “nano-walls” containing zinc phenylphosphonate and calcium sulfate whisker: Superior mechanical, barrier, and optical properties

It is urgent to acquire a feasible strategy for balancing the strength and ductility of polylactic acid (PLA) in the application of biodegradable packaging materials. In this study, a new strategy is provided to enhance mechanical, barrier, and optical properties by the synergetic effect of manipulating the amorphous chain entanglement network and constructing the “nano- walls” of highly aligned calcium sulfate whisker (CSW), zinc phenylphosphonate (PPZn), and well-defined crystals via biaxial stretching. PPZn is verified as a nucleator to accelerate the crystallization rate and induce α-form crystals. CSW is regarded as a supporting skeleton to strengthen the entanglement density of the chain network. The extensional stress, which is induced by biaxial stretching, regulates the amorphous chain entanglement network and facilitates the chain orientation. As a result, the synergetic structure displays an outstanding capacity for improving the mechanical, barrier, and optical properties of PLA. Compared to the PLA film, the biaxially stretched PLA/PPZn/CSW films exhibit high strength, excellent ductility, and superior crystallinity, which are significantly increased by up to 53.2%, 381.3%, and 748.9%, respectively. And their gas and water vapor barrier properties remarkably increased by 65.39% and 73.11%, respectively. The optical property with a haze value of 52.4% and good transmittance of 97.4% is also obtained via the synergetic effect. With the excellent comprehensive properties of PLA films, this new strategy explores a new field in environmentally friendly packaging materials and is relevant to future work.