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Effect of hydrothermal treatment on composition and porosity of softwoods
Summary
This study looked at how heating wood chips with water (instead of harsh chemicals) can break them down for use in eco-friendly products like paper, potentially replacing plastics that contribute to pollution and microplastics in our oceans. Researchers found that a specific gentle treatment (170°C without added chemicals) worked best, opening up the wood's structure for processing while keeping more of its natural nutrients (hemicellulose) intact, compared to harsher acid treatments that destroyed too much material. This matters because finding cleaner, more efficient ways to process wood into sustainable materials could reduce our reliance on fossil fu
Intertest in utilizing lignocellulosic materials has increased due to the diminishing of fossil resources and their associated impacts such as air pollution, microplastic pollution and ocean acidification. Softwoods, an important biomass resource in northern countries, are highly recalcitrant due to their compact structure, often requiring harsh thermochemical treatments for fiber liberation. These treatments cause substantial hemicellulose loss, which is undesirable in many pulp and paper applications. Hydrothermal pretreatment causes structural changes through hemicellulose dissolution, lignin redistribution, which in turn improves cell wall accessibility and facilitates the diffusion and transport of water, chemicals and enzyme in subsequent conversion processes. Therefore, improving the understanding about hemicellulose and lignin dissolution in relation to porosity could help reduce biomass recalcitrance while improving the yields and hemicellulose retention. The purpose of this thesis is to investigate the relationship between hemicellulose removal, lignin dissolution and cell wall porosity development, with the aim of identifying conditions that increase accessibility while minimizing hemicellulose loss. Wood chips (Norway spruce and Scots pine mix) with relatively uniform size distribution (large accept, ⌀13 nm) were hydrothermally treated under different conditions and analyzed using HPAEC, nitrogen adsorption, Simons’ staining and confocal Raman microscopy to elucidate the compositional and structural changes. Among the acidic treatments, autohydrolysis at 170 °C was effective in increasing porosity while maintaining yields and hemicellulose. Under more severe acidic conditions, pronounced pseudo-lignin formation occurred, making the observation of actual lignin dissolution difficult. Dilute acid treatments resulted in significant hemicellulose loss, which conflicted with the objective of preserving carbohydrate fractions. Alkaline treatments were more effective in improving the cell accessibility while preserving material.