Preparation of cellulose/MWCNTs/TPU micro-foam composites

In this work,we dissolved the α-cellulose in pre-cooled sodium hydroxide (NaOH) and thiourea solution, and dispersed multi-walled carbon nanotubes (MWCNTs) in solution with the help of cetyltrimethylammonium bromide (CTAB), then cross-linked for 48h to form a gel. The gel was placed in distilled water to displace the sodium hydroxide. After the distilled water was neutral, the gel was freeze-dried to obtain a cellulose/MWCNTs aerogel. We prepared cellulose aerogel with 10 wt% MWCNTs, its density is 139.64 mg/cm³. Next, using the aerogel as a template, the thermoplastic polyurethane (TPU) was cast into the aerogel by solution method to obtain a cellulose/TPU/MWCNTs composite. The composite is then foamed by supercritical CO₂, the pressure was maintained at 13.8 MPa and the temperature was maintained at 100°C. The cell size of TPU is about 10 µm and the density is 414.79 mg/cm³. Besides, the compression modulus and compressive strength at 10% compression strain of foaming composite are 0.62 MPa and0.059 MPa.