Browsing by Author "Sapkota, Janak"

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Cellulosic coatings for fibre-based packaging materials
(2025-05-26) Heinola, Wilma
School of Chemical Engineering | Master's thesis
The environmental impact of plastic overuse has increased demand for sustainable, fibre-based packaging. While such materials are renewable and mechanically strong, their poor barrier performance limits use in food applications. This is typically addressed with fossil-based polymer or aluminium coatings, which compromise recyclability. Biopolymer-based alternatives, such as regenerated cellulose, offer coating solutions that enhance the performance of fibre-based substrates while maintaining environmental compatibility. This thesis investigated regenerated cellulose as a barrier coating for packaging paper using laboratory- and pilot-scale processes. Coating solutions of four cellulose concentrations (2, 4, 6, and 9 wt%) were prepared by alkaline dissolution and applied to commercial base paper via laboratory rod-coating using rods of different sizes, followed by regeneration, washing, and plasticization. The process was then replicated at pilot-scale, where coating was applied via immersion and controlled with a fixed blade at varying line speeds. Barrier and mechanical properties were analysed, and the effects of cellulose concentration and coating grammage were evaluated, along with process scalability. Optimal processability occurred at 6 wt%, with other concentrations yielding less uniform coverages. Laboratory coatings achieved grammages of 12–26 g/m² and thicknesses of 14–22 µm with increasing concentration and rod size, while those of pilot coatings were lower and less variable (5–8 g/m² and 8–10 µm) irrespective of concentration or line speed. Barrier resistance generally improved with increasing cellulose concentration and grammage up to 6 wt%, with some laboratory samples achieving levels comparable to conventional polymers. Tensile strength decreased with coating grammage but improved with concentration, along with tear and puncture resistance. However, nearly all properties of the base paper were negatively affected by the chemical treatment in both processes, indicating a need for less chemically intensive methods for industrial application.
Comparative assessment of chemical and biochemical approaches for the activation of lignocellulosic materials and emerging opportunities for expansin-related proteins
(2024-01) Hiltunen, Salla; Sapkota, Janak; Ioannou, Eleni; Haddad Momeni, Majid; Master, Emma; Ristolainen, Matti
A2 Katsausartikkeli tieteellisessä aikakauslehdessä
Cellulose activation is a necessary step in many industrial processes including production of cellulose derivatives, regenerated cellulose, biofuels and biochemicals. Expansins and expansin-related proteins have been shown to disrupt the fibrillar aggregation and loosen the structure of lignocellulosic materials but typically lack lytic activity. Therefore, they offer a new but rather unexploited possibility for biomass to obtain better accessibility and reactivity. From an applied perspective, expansin-related proteins have been investigated for their potential to promote enzymatic hydrolysis of cellulosic substrates for the purpose of producing biofuels. The aim of this review is to compare conventional and emerging technologies relevant to cellulose activation, and critically evaluate the potential of expansin-related proteins for this purpose. As part of this assessment, methods to evaluate the action of expansin-related proteins on cellulosic substrates are summarized, and reported impacts are discussed in relation to source of the cellulosic substrate and treatment conditions. An outlook on prospective applications of expansin-related proteins is presented.
Debugging periodate oxidation of cellulose: Why following the common protocol of quenching excess periodate with glycol is a bad idea
(2023-06-15) Simon, Jonas; Fliri, Lukas; Drexler, Felix; Bacher, Markus; Sapkota, Janak; Ristolainen, Matti; Hummel, Michael; Potthast, Antje; Rosenau, Thomas
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Periodate oxidation of cellulose to produce “dialdehyde cellulose” (DAC) has lately received increasing attention in sustainable materials development. Despite the longstanding research interest and numerous reported studies, there is still an enormous variation in the proposed preparation and work-up protocols. This apparently reduces comparability and causes reproducibility problems in DAC research. Two simple but prevalent work-up protocols, namely glycol quenching and filtration/washing, were critically examined and compared, resulting in this cautionary note. Various analytical techniques were applied to quantify residual iodine species and organic contaminations from quenching side reactions. The commonly practiced glycol addition cannot remove all oxidising iodine compounds. Both glycol and the formed formaldehyde are incorporated into DAC's polymeric structure. Quenching of excess periodate with glycol can thus clearly be discouraged. Instead, simple washing protocols are recommended which do not bear the risk of side reactions with organic contaminants. While simple washing was sufficient for mildly oxidised celluloses, higher oxidised samples were more likely to trap residual (per)iodate, as determined by thiosulfate titration. For work-up, simple washing with water is proposed while determining potential iodine contaminations after washing with a simple colorimetric test and, if needed, removal of residual periodate by washing with an aqueous sodium thiosulfate solution.
Insights into the action of phylogenetically diverse microbial expansins on the structure of cellulose microfibrils
(2024-04-23) Haddad Momeni, Majid; Zitting, Aleksi; Jäämuru, Vilma; Turunen, Rosaliina; Penttilä, Paavo; Buchko, Garry W.; Hiltunen, Salla; Maiorova, Natalia; Koivula, Anu; Sapkota, Janak; Marjamaa, Kaisa; Master, Emma R.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Background: Microbial expansins (EXLXs) are non-lytic proteins homologous to plant expansins involved in plant cell wall formation. Due to their non-lytic cell wall loosening properties and potential to disaggregate cellulosic structures, there is considerable interest in exploring the ability of microbial expansins (EXLX) to assist the processing of cellulosic biomass for broader biotechnological applications. Herein, EXLXs with different modular structure and from diverse phylogenetic origin were compared in terms of ability to bind cellulosic, xylosic, and chitinous substrates, to structurally modify cellulosic fibrils, and to boost enzymatic deconstruction of hardwood pulp. Results: Five heterogeneously produced EXLXs (Clavibacter michiganensis; CmiEXLX2, Dickeya aquatica; DaqEXLX1, Xanthomonas sacchari; XsaEXLX1, Nothophytophthora sp.; NspEXLX1 and Phytophthora cactorum; PcaEXLX1) were shown to bind xylan and hardwood pulp at pH 5.5 and CmiEXLX2 (harboring a family-2 carbohydrate-binding module) also bound well to crystalline cellulose. Small-angle X-ray scattering revealed a 20–25% increase in interfibrillar distance between neighboring cellulose microfibrils following treatment with CmiEXLX2, DaqEXLX1, or NspEXLX1. Correspondingly, combining xylanase with CmiEXLX2 and DaqEXLX1 increased product yield from hardwood pulp by ~ 25%, while supplementing the TrAA9A LPMO from Trichoderma reesei with CmiEXLX2, DaqEXLX1, and NspEXLX1 increased total product yield by over 35%. Conclusion: This direct comparison of diverse EXLXs revealed consistent impacts on interfibrillar spacing of cellulose microfibers and performance of carbohydrate-active enzymes predicted to act on fiber surfaces. These findings uncover new possibilities to employ EXLXs in the creation of value-added materials from cellulosic biomass.
Insights into the borohydride reduction of dialdehyde cellulose: the dilemma of competing reduction and β-elimination reactions
(2023-09) Simon, Jonas; Fliri, Lukas; Fröhlich, Flavia; Sapkota, Janak; Ristolainen, Matti; Hummel, Michael; Rosenau, Thomas; Potthast, Antje
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Borohydride reduction of dialdehyde cellulose (DAC) is a promising strategy to generate dialcohol cellulose as bio-based alternative to petroleum-based materials. However, the degradation of the polymer backbone according to β-elimination mechanisms limits the practical applications of the reaction. Therefore, we aimed at optimizing the process to suppress degradation reactions by varying reaction time, pH, and reagent stoichiometry. The degree of oxidation (DO) of the DAC intermediates significantly impacts the yields and molecular weights of the isolated dialcohol celluloses, with a “leveling-off” effect at higher DO values. Increasing the amount of sodium borohydride can minimize—but not entirely prevent—chain scissions. Lowering the pH value during reduction slows down the degradation but results in incomplete conversion of the aldehyde functionalities. Our study provides valuable insights into the consequences of side reactions during borohydride reduction of DAC as well as into chemistry and analysis of the dialdehyde cellulose/dialcohol cellulose system. Graphical abstract: About a dilemma in cellulose chemistry: Dialcohol cellulose derived by periodate oxidation and subsequent borohydride reduction of cellulose has received increasing attention in the development of sustainable thermoplastic materials. The present study highlights the challenge of suppressing β-elimination and favoring the reduction pathway to optimize reaction conditions and minimize chain degradation.
Reductive Amination of Dialdehyde Cellulose: Access to Renewable Thermoplastics
(2023-01-09) Simon, Jonas; Fliri, Lukas; Sapkota, Janak; Ristolainen, Matti; Miller, Stephen A.; Hummel, Michael; Rosenau, Thomas; Potthast, Antje
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The reductive amination of dialdehyde cellulose (DAC) with 2-picoline borane was investigated for its applicability in the generation of bioderived thermoplastics. Five primary amines, both aliphatic and aromatic, were introduced to the cellulose backbone. The influences of the side chains on the course of the reaction were examined by various analytical techniques with microcrystalline cellulose as a model compound. The obtained insights were transferred to a 39%-oxidized softwood kraft pulp to study the thermal properties of thereby generated high-molecular-weight thermoplastics. The number-average molecular weights (Mn) of the diamine celluloses, ranging from 60 to 82 kD, were investigated by gel permeation chromatography. The diamine celluloses exhibited glass transition temperatures (Tg) from 71 to 112 °C and were stable at high temperatures. Diamine cellulose generated from aniline and DAC showed the highest conversion, the highest Tg (112 °C), and a narrow molecular weight distribution (Døµ of 1.30).
Towards Tailored Dialdehyde Cellulose Derivatives: A Strategy for Tuning the Glass Transition Temperature
(2024-03-08) Simon, Jonas; Schlapp-Hackl, Inge; Sapkota, Janak; Ristolainen, Matti; Rosenau, Thomas; Potthast, Antje
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The derivatization of dialdehyde cellulose (DAC) has received increasing attention in the development of sustainable thermoplastics. In this study, a series of dialcohol celluloses were generated by borohydride reduction, which exhibited glass transition temperature (Tg) values ranging from 23 to 109 °C, depending on the initial degree of oxidation (DO) of the DAC intermediate. However, the DAC derivatives did not exhibit thermoplastic behavior when the DO of the modified DAC was below 26 %. The influence of introduced side chains was highlighted by comparing DAC-based thermoplastic materials obtained by either oximation or borohydride reduction. Our results provide insights into the generation of DAC-based thermoplastics and highlight a strategy for tailoring the Tg by adjusting the DO during the periodate oxidation step and selecting appropriate substituents in subsequent modifications.