Multifunctional polylactic acid biocomposite film for active food packaging with UV resistance, antioxidant and antibacterial properties.

Antibacterial packaging used to control the growth of microorganisms in food is of great value for prolonging the shelf life of food. In this study, a bio-based antibacterial agent PDI based on zwitterionic and stereochemical synergistic antibacterial was designed and synthesized, and it was simultaneously introduced into polylactic acid (PLA) matrix with antioxidant o-vanillin (oVL) and plasticizer glycerol (GL). A series of PLA/oVL/PDI composite membranes with antibacterial, antioxidant and anti-ultraviolet properties were prepared by solution casting method. The results showed that the mechanical properties of the composite film were significantly improved compared with pure PLA (tensile strength increased by 37 %, elongation at break increased by 209 %), which was mainly attributed to the microphase separation structure induced by synthetic bio-based antibacterial agent, which improved the mechanical strength of PLA matrix, and the hydrogen bond formed by glycerol, o-vanillin and carbonyl group in PLA molecules plasticized PLA matrix. At the same time, the antibacterial rate of PLA/oVL/PDI composite membrane against Escherichia coli and Staphylococcus aureus can reach >95 %. Packaging experiments showed that PLA/oVL/PDI series composite films could effectively extend the shelf life of fresh bananas and apples for 5 days, and had great application prospects in preservative food packaging.

Interfacial Synthesis of an Ultrathin Two-Dimensional Polymer Film via [2 + 2] Photocycloaddition.

A carbon-carbon-linked, ultrathin, two-dimensional (2D) polymer film was prepared at the air/water interface through photochemically triggered [2 + 2] cycloaddition. The preorganization of the monomers on the water surface and the subsequent photo-polymerization led to the successful preparation of the ultrathin 2D polymer film. The obtained film is continuous, free standing, and has a large area (over 50 µm2). Transmission electron microscopy (TEM) and atomic force microscopy (AFM) give clear evidence of the ultrathin film morphology. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) indicate successful photo-induced [2 + 2] polymerization.

Donor-Acceptor Interactions Induced Interfacial Synthesis of an Ultrathin Fluoric 2D Polymer by Photochemical [2+2] Cycloaddition.

Invited for the cover of this issue is the group of Prof. Dr. Yingjie Zhao at Qingdao University of Science and Technology. The image depicts the ultrathin two-dimensional polymer reported in this work. Read the full text of the article at 10.1002/chem.202004797.

Donor-Acceptor Interactions Induced Interfacial Synthesis of an Ultrathin Fluoric 2D Polymer by Photochemical [2+2] Cycloaddition.

Two-dimensional polymers (2DPs) have attracted much interest due to their unique 2D atomic-thick covalent network with periodically linked monomers. The preparation of mono- or few-layered 2DPs with highly ordered structures is still a big challenge. Herein, we report a preparation of ultrathin 2DP film based on photo-triggered [2+2] cycloaddition at the air/water interface. The pre-assembly process induced by the D-A interactions before the polymerization plays a key role in constructing the highly ordered structure. The precise structure and chemical compositions of the continuous 2DP films were proved by selected area electron diffraction (SAED), Tip-Enhanced Raman Spectroscopy (TERS) and molecular-mechanics-based structural simulation.