Influence of ionic interactions between nanofibrillated cellulose and latex on the ensuing composite properties

• Ionic forces between latex particles and nanofibrillated cellulose were studied.
• The use of anionic latex resulted in stable dispersions and homogeneous composites.
• The use of cationic latex produced aggregation and non-homogeneous composites.
• The reinforcing effect was acquired by incorporating the nanofibrillated cellulose.

The hydrophilic nature of nanofibrillated cellulose (NFC) impedes its easy incorporation in hydrophobic thermoplastic matrices. This introduces difficulties in composites compounding and achieving the sufficient NFC dispersion within the matrix. The use of matrix in latex form increases the range of applied plastics. However, poor NFC/matrix interfacial adhesion may still result in lower performance composites. The use of ionic interactions is aimed at providing strong interactions at the NFC/matrix interface after film casting and simultaneously the composite homogeneity. In this work, cationic and anionic latexes of poly[styrene-co-(2-ethylhexyl acrylate)] were synthesized via miniemulsion polymerization. The composites were produced by incorporating 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized NFC (up to 5 wt.%) into the latexes, followed by film casting of the ensuing formulations. NFC/latex interactions were examined in terms of the NFC dispersion in the matrix and the ensuing composite mechanical properties. Both elastic modulus and ultimate strength increased for the composites comparing to the neat matrices. The use of cationic latex produced non-stable aqueous dispersions and non-homogeneous composite films, deduced from scanning electron microscopy and tensile experiments. On the contrary, stable aqueous dispersions and homogeneous composites were prepared using anionic latex. X-ray photoelectron spectroscopy revealed differences in chemical composition of the composite top and bottom surfaces.

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