Low-Density All-Cellulose Composites Made from Cotton Textile Waste with Promising Thermal Insulation and Acoustic Absorption Properties

In this study, cotton textile waste (CTW) scraps were used as a starting material to develop low-density all-cellulose composites (ACC–CTWs) via a partial dissolution approach with a NaOH/urea solvent system combined with a vacuum-assisted process. The effect of immersion times on the morphology and characteristics of the resultant ACC–CTWs was examined. These ACC–CTWs exhibited a bulk density of 0.29–0.31 g/cm3. As the immersion time increased, a greater proportion of cellulose I (CTW) was converted to regenerated cellulose (cellulose II). This led to a reduction in its crystallinity. Moreover, the immersion time had a significant effect on the surface and structure of ACC–CTWs, affecting their flexural properties, thermal conductivity, and sound absorption properties. The obtained ACC–CTWs had low thermal conductivity (0.036–0.108 W/mK) and outstanding sound absorption properties, with noise reduction coefficient (NRC) values ranging from 0.68 to 0.83, which are comparable to those of typical building materials. Therefore, the prepared eco-friendly lightweight ACC–CTWs have the potential to serve as effective thermal and acoustic insulation materials in building and construction applications.