Enhanced mechanical properties and UV shield of carboxymethyl cellulose films with polydopamine-modified natural fibre-like palygorskite

Palygorskite, a natural 1D nanofibre, has been employed as an effective reinforce filler of natural hydrophilic polymer-based nanocomposites because of its high mechanical strength, large specific surface area and high aspect ratio. However, the hydrophilic hydroxyl groups only exist at the edge of the silicate layer of palygorskite nanofibres and in small amounts. Therefore, the reinforcement efficiency for the hydrophilic polymer of palygorskite is limited. To overcome this shortcoming, we constructed a highly hydrophilic polydopamine with catechol groups on the palygorskite nanofibre surface by a facile biomimetic method. Hydrophilic polymer carboxymethyl cellulose nanocomposites incorporated with polydopamine-coated palygorskite were fabricated by solution casting. Results show that the interfacial polydopamine layers not only facilitate the dispersion of palygorskite nanofibres in the carboxymethyl cellulose matrix but also enhance the stress transfer from the carboxymethyl cellulose matrix to the filler, improving the tensile strength and water resistance of the nanocomposites. However, several palygorskite crystals aggregate to form small bundles for the palygorskite with a high mass ratio of dopamine/palygorskite during the modification process. This phenomenon decreases the contact areas between the filler and the carboxymethyl cellulose matrix, thereby decreasing the properties of the nanocomposites. In addition, UV-vis transmittance spectra show that the nanocomposite films reinforced with polydopamine-modified palygorskite can block ultraviolet light below 300 nm, thereby retaining its relatively high transparency in the visible spectrum.