Lightweight and eco-friendly methyl cellulose foams featuring moisture-induced form interlocking: A versatile alternative to conventional plastic foams.

The plastic pollution crisis demands sustainable alternatives to petroleum-based foams. Cellulose-based foams, renewable and biodegradable, are a good candidate. In this study, fully degradable cellulose foams are fabricated from methyl cellulose (MC) alone via a simple, additive-free method. The method combines mechanical foaming and oven drying without blowing, stabilizing, or cross-linking agents. First, stable wet foam is obtained by mechanically agitating an aqueous MC solution. Amphiphilic MC molecules stabilize the foam at the air-water interface. During oven-drying, the thermal gelation of MC solidifies the structure into solid foam. The resulting MC foam has a very low density (10.02 mg·cm), high porosity (99.28%), and excellent thermal insulation (thermal conductivity as low as 37.35 mW·m K). It also has moisture-induced form interlocking capability, retaining 89.5% of its original tensile strength when form-interlocked and adhering well to common packaging materials. Additionally, the MC foam can be chemically modified for extra functionalities like flame retardancy and hydrophobicity. This research presents a new way to fabricate lightweight, moisture-induced form interlocking, and eco-friendly cellulose foams as a sustainable and versatile alternative to conventional plastic foams.