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Browsing by Author "Aalto, Angela"

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  • Aalto, Angela (2019)
    Today it is desirable to utilise and reproductive sidestream materials from the industry. The food industry generates lot of sidestream waste which could be utilised in various products. Grain hulls are one example. The aim of this work was to study the structure and chemical features of sidestream oat and barley hulls from the industry. Furthermore, the potential to use hull fractions with pulp to produce kraft paper was examined. The grain structure and chemical features of oat and barley have been studied extensively in the food industry but hulls barely at all. The intention was to study lipids, hemicellulose sugars and lignins. From the perspective of paper production, it was important to examine hulls fibres (anatomy), fibre separation and fibre wall fibrillation. Kraft paper must possess specific mechanical properties. Sufficient fibrillation and fibre network of the plant fibres renders paper durable. The hull fibres were examined with a light microscope. The hulls were macerated before microscopy. Compounds, lipids, organic acids and sugars were extracted with hexane and acetone in the Accelerated Solvent Extraction. The samples were analysed with gas chromatography-mass spectrometry. The hemicellulose sugars of the hulls were isolated with methanolysis and analysed with a gas chromatography-flame ionization detector. The hull lignins were defined with pyrolysis-gas chromatography-mass spectrometry. The other compounds of the samples were extracted with acetone by Accelerated Solvent Extraction before pyrolysis determination. The oat and barley hulls were milled with a disc refiner and added to the softwood (pine) pulp in a Valley hollander beater. The pulp was milled for 90 min and the pulp filtration was measured with a Schopper-Riegler freenes tester. Also, water retention value was calculated. Sheets of paper were made with a conventional sheet mould. The aim grammage of the paper sheets was 60 g/m². The mechanical, physical and optical properties of the paper sheets were measured. The properties measured were thickness, density, surface smoothness/roughness, air permeability, opacity, light scattering, light absorption, brightness, tensile strength, breaking strength, elongation, bursting strength and tearing strength. Half of the paper sheets were calandered. The chemical properties of oat and barley hulls did not differ significantly from each other. The same hemicellulose sugars were found in the hulls of both grains, however more mannose and arabinose were found in oat hulls. The hulls of both grains had almost the same total hemicellulose quantity. The quantity and quality of lignins were also similar in both grain hulls. Guaiacyl lignin was dominant in both hulls. Minor differences in hemicellulose sugars does not have an impact on paper production. The hull fibres were very similar in microscopic examination, but oat hulls were somewhat longer than barley hulls. These differences did not impact the separation of fibres, the fibrillation of fibre wall or paper making. Oat hulls were harder, which became most apparent in the calandering and appearance of the sheets. Barley hulls were darker but the mechanical and physical properties of the grain hull paper sheets were quite similar. The hull fractions amount in the pulp (10% or 20%) did not significantly impact the results. The milled hull fractions were not distributed evenly in the sheets, the fibres did not separate properly and no internal or external fibrillation occurred. As mentioned before, the sheets were not homogeneous and the standard deviation of the sheet properties were partly significant. Adding the hull fractions to the pulp was successful and the milled hull fractions did not fall off the sheets. Calandered sheets were smooth and glossy. Moreover, the sheets were visually pleasing. This study indicated that it is possible to use hull fractions for paper and kraft paper production. The paper mostly met the same quality requirements as commercial paper. More research is needed for further optimisation. More research into the chemical properties of oat and barley hulls is also needed, because of the hulls of both grains contain antioxidant components and could provide more information about advanced fibre separation and fibre wall fibrillation.