Journal of Bioresources and Bioproducts 10 (2025) 325–335
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Journal of Bioresources and Bioproducts
journal homepage: https://www.keaipublishing.com/en/journals/journal-of- bioresources-and-bioproducts/
Research Article Kraft lignin as wet-strength and wet-stiffness additives for molded pulp materials Eva Pasquier, Jost Ruwoldt ∗
RISE PFI AS, Høgskoleringen 6B, Trondheim 7491, Norway
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Derived from renewable resources, cellulose based materials are gaining new importance due to their recyclability and biodegradability. Still, one fundamental challenge is their high sensitivity to water. The addition of wet strength agents (WSA) is hence necessary to maintain strength and integrity in humid or wet conditions. In this article, technical lignin was used as WSA in bleached kraft pulp, which was thermopressed to materials with the potential to replace plastics. Cationic starch or a cationic flocculant (PCB 20) was used as a retention aid during the filtration process. The effect of moisture during thermopressing and lignin particle size were also studied. The results showed that elevated moisture during pressing had the biggest impact both on dry and wet strength. Wet strength (tensile test), up to 9 MPa, and wet strength retention, up to 12 %, were obtained when moisture was present during pressing. However, the type of flocculant and the size of the lignin particles also had a limited effect on the strength. Wet strength improvement was most probably due to the plasticization of lignin at high temperatures, which was further aided by water. The cellulose-lignin network was strengthened by the melting of lignin, consolidating the network after cooling. The wet stiffness of the cellulose substrates was also increased from 200 to 938 MPa in the presence of lignin, while the elongation was maintained and no embrittlement was observed. The results in this article might hence pave the way for new developments in molded pulp and cellulose based plastics replacement.
Keywords: Lignin Molded pulp
Wet strength agent Lignin nanoparticles Paper sizing Added-lignin thermoformed pulps
1. Introduction
The development of new recyclable and biobased materials is paramount, as the need for replacing single-use plastic has only increased recently to combat microplastic pollution and reduce the environmental footprint of packaging materials. Moreover, plastic packaging composed of multi-layered materials or reinforced composites lacks recyclability ( Mendes and Pedersen, 2021 ; Seier et al., 2024 ). Cellulose and fiber-based packaging are promising solutions, as they can form both biodegradable and recyclable materials ( Curling et al., 2017 ; Oliaei et al., 2021 ). Cellulose based products like paper and board have high recycling rates ( Ibrahim et al., 2023 ). The introduction of molded pulp products to the market should participate in keeping these high rates, hence design for recycling is an important part of the development of new cellulose products. Oliaei et al. (2021) studied the recyclability of thermopressed cellulosic substrates containing 17 % of lignin. Even if the ultimate strength decreased for recycled samples, the substrates were recyclable. Thermoforming of cellulose pulp into 3D objects has been emerging in the last decade as an encouraging replacement for plastic packaging ( Schenker et al., 2021 ; Semple et al., 2022 ; Zhang et al., 2022a ; Freville et al., 2024 ). However, challenges remain for
Peer review under the responsibility of Editorial Office of Journal of Bioresources and Bioproducts. ∗ Corresponding author. E-mail address: jost.ruwoldt@rise-pfi.no (J. Ruwoldt) .
https://doi.org/10.1016/j.jobab.2025.05.001 Received 4 February 2025; Received in revised form 7 April 2025; Accepted 25 April 2025 Available online 10 May 2025 2369-9698/© 2025 The Authors. Publishing Services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )
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