Fabrication of a Transparent and Biodegradable Cellulose Film from Kraft Pulp via Cold Alkaline Swelling and Mechanical Blending

The alarming accumulation of nondegradable plastic films in the ecosystem and the threats they pose have urged an active search for bio-derived and biodegradable alternatives. While cellulosic film has many advantages such as high transparency, superb mechanical properties, and biodegradability, it is generally fabricated from dissolved cellulose or nanocellulose, involving chemical and energy-intensive processes. In this paper, we successfully demonstrate that cellulose pulp can be processed into a transparent film without fully going through dissolution or nanofibrillation. Specifically, with a combination of cold NaOH swelling and mild mechanical blending using a household blender, Kraft pulp (mean length of 1.66 mm) can be disintegrated into much finer microfibers (mean length decreased from about 540 to 240 μm as the treatment cycle increases from 1 to 4), which can be densely packed into a compact film by ultrafiltration. The prepared cellulose film shows high transmittance (89% at 650 nm with an integrated sphere), good thermal stability (Tmax of 350 °C), high mechanical strength (99.7 MPa tensile strength and 5.7 GPa Young's modulus), good underwater structural stability (17.1 MPa tensile strength after being immersed in water for 30 days), as well as excellent biodegradability (completely degrades in 19 days when buried in soil).