The textile industry is among the biggest in the world, and it continues to grow with the increasing population and the addition of new interesting areas such as technical textiles and composites. The materials used for textiles are to almost 50% petrol based followed by almost 25% cotton. This means that one single crop (cotton) is dominating the textile market of renewable fibres. However, as mono-cultural agriculture is a disadvantage for biodiversity, the amount of textile materials needs to be increased for increased sustainability. This thesis contributes to this increased diversity of textile materials through different treatments that can be used to tailor the properties of jute and paper yarn. With the knowledge on how to alter the material properties, it is possible to find new application areas for materials that are not utilised to their full production potential. Both jute and paper yarn could take a larger part of the materials used for textiles if their full range of properties’ alterations were known.

Jute is a traditional crop that has been used for textiles for centuries. In this thesis work, microwaving of jute yarn in submerged conditions has been used to alter the tensile properties of the yarn. Tenacity and elongation can be enhanced by the use of specific treatment conditions, such as tension and a combination of power and time. Such a microwave treatment can also be used for alterations of jute weave, giving opportunities to alter the properties of PVA-impregnated jute weave. Through PVA impregnation, the jute weave shows changed dynamic mechanical properties, such as increased stiffness and damping. PVA-impregnated jute weave does not form as much dust as untreated jute and, therefore, could lead to increased health and working conditions.

When it comes to paper yarn for textile purposes, it has traditionally been produced from long-fibre plants such as abacá, hemp (Japan) or mulberry (Korea). In this thesis, the practical use of paper yarn has been focused on paper made from Swedish resources. The fibres are then much shorter, which influences the textile production and properties, and improvements are needed. To enhance the knitting of the paper yarn, the influence of commonly used textile finishing agents was investigated. It was found that glycerol has a high add-on, silicone-based finishing agents decrease the yarn-metal-friction, and wax increases the yarn-metal friction. The tensile properties of the paper yarn are also affected by the treatments, which mainly decrease them.

Paper yarn behaves differently from regular yarn when it comes to the relationship between increased twist and the breaking stress and –strain. Therefore, there is an interest in modelling the properties of paper yarn. This thesis shows the possibility of modelling Young’s modulus (E) of the yarn as a function of the orientation distribution of the fibres in the yarn's paper. Where elongation upon tensile load is connected to the bending of the individual fibres, it turns out that the E-modulus can be affected by the orientation of the fibres in the paper.

An overview of the materials and research themes in this thesis is as follows. Two cellulose-based materials—jute and paper yarn—were selected as the primary focus. For the traditional material jute, a new method for tailoring its properties was explored: microwaving. For the more novel material, paper yarn, the influence of conventional textile finishing agents on improving the knit ability of the yarn was investigated. In addition, the modulus of paper yarn was modelled to demonstrate how its mechanical properties depend on the orientation distribution of the fibres within the paper structure.

This thesis demonstrates the potential for tailoring the material properties of both jute and paper yarn, thereby enabling new applications for materials previously considered limited in use. Through the careful selection of sustainable materials and appropriate treatments, this work aims to contribute to a more sustainable future for the textile industry.