Redesigning Inorganic-Organic Hybrid Polymer Coatings for Sustainable, Heat-Sensitive Substrates: Achieving Oxygen Barrier and Martens Hardness at Room Temperature

The majority of materials today are still derived from nonrenewable resources, leading to resource depletion and environmental pollution. Although sustainable alternatives exist, their limited performance - e.g., inferior oxygen barrier properties and reduced mechanical stability - has hindered widespread adoption. Functional coatings hold high potential to overcome these shortcomings. However, many conventional coatings have been developed for petroleum-based substrates utilizing thermal, ultraviolet (UV), or chemical curing methods, which require high energy inputs or potentially toxic agents. To address this issue, we have developed an inorganic-organic hybrid polymer coating (IOHPC) that exhibits low oxygen transmission rate (OTR) and high Martens hardness (HM) at room temperature (RT) without toxic hardening agents, maintaining the integrity of heat-sensitive substrates. The key was to select the perfect metal alkoxide within an IOHPC to ensure efficient network formation and material performance, as verified by ATR-FTIR, 29Si-CP-MAS NMR spectroscopy, X-ray photoelectron spectroscopy, HM, and OTR measurements. Importantly, the material properties were effectively transferred to three classes of heat-sensitive sustainable films - recycled high-density polyethylene (RHDPE), polylactic acid (PLA), and reduced-thickness polypropylene (PP) - achieving OTR in the range of 22-31 cm3/(m2·d·bar). This IOHPC shows promise for application on next-generation sustainable substrates, offering excellent OTR and HM while preserving substrate integrity and reducing energy consumption.