Plant Cuticle-Inspired Polyesters as Promising Green and Sustainable Polymer Materials

Abstract

The plant cuticle is a hydrophobic barrier membrane found mainly on leaf surfaces and fruit skin. This work presents the structural and barrier properties of cuticle-inspired poly(hydroxyhexadecanoate) (PHHA), an ω-hydroxy fatty acid-derived biopolyester. PHHA was copolymerized and cross-linked with glycerol by melt polycondensation, and films were fabricated by compression molding. The study showed the effect of the addition of a trifunctional comonomer on the thermal, mechanical, and barrier properties. The neat PHHA, owing to its higher crystallinity, demonstrated the best water vapor barrier properties, but formed brittle films. The glycerol-copolymerized films, on the other hand, were flexible and displayed a good balance between barrier and mechanical properties. The water vapor transmission rate was overall similar to that of PLA, and limonene (a hydrophobic food component) uptake and diffusivity were lower than that of low-density polyethylene, the commonly used polymer for packaging. In addition, the polyester had UV-blocking properties. The way the films were made yielded a rough surface, mimicking the outer rough wax layer in plant cuticles with high water repellence. Hence, these cutin-inspired polyesters are promising for, e.g., water barrier (packaging/device) applications, provided means of efficient/sustainable production/isolation of the monomer is developed.