Improving the properties of kraft paper

Researchers report an amulsion polymerised styrene acrylic/nanocellulose composite coating to improve the strength and hydrophobicity of kraft paper.

Paper-based packaging is gradually coming out as a sustainable alternative to the existing plastic-based packaging culture. Image source: TM-Design - Fotolia (symbol image).

Improving the mechanical and water repelling property of kraft paper will extend its use for packaging application. In a work, researchers have developed a cellulose nanofiber (CNF)-based colloidal polymer nanocomposite that was used as coating for improving those properties of kraft paper. In this case, the polymer latex was obtained by the mini-emulsion copolymerization of styrene (St), 2-ethyl hexyl acrylate (EHA) initiated by ammonium persulfate. The CNFs were incorporated into the styrene-acrylic copolymer matrix by the in-situ polymerisation and ex-situ mixing process keeping the CNF concentration up to 1.0 wt%.

Paper-based packaging materials

All the latexes showed particle size below 100 nm and excellent colloidal stability (Zeta potential > −32 mV) for several months. The nanocomposite films showed improved mechanical properties (tensile strength upto 7.8 MPa, elongation upto 1096 %) than the pristine copolymer. The in-situ prepared nanocomposite at 1.0 wt% CNF showed the highest storage modulus. The latex-coated kraft paper showed improved tensile index (31.0–45.1 Nm/g) compared to the uncoated paper (20.3 Nm/g) and also high hydrophobicity (water contact angle ∼120°) for the ex-situ prepared nanocomposites. As the researchers point out, the results are quite promising to develop paper-based packaging materials using nanocellulose in combination with synthetic polymers.

The study has been published in Progress in Organic Coatings, Volume 182, September 2023.

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