The paper is a review on the extraction processes of cellulosic fibers from flax and hemp. The two lignocellulosic crops have a long history of use by humans for extraction of the bast fibers among other purposes. The utility of bast fibers declined over time with industrial advances and changes to the economy, but of late, with an increase of focus on environmental impact and sustainability, there is a renewed interest in these resources. The use of biomass-based resource requires an appreciation of plant anatomy and the agronomical variables in their cultivation and harvesting. This review provides an overview of these aspects as well as of the processes of retting for initial weakening of the plant structure in preparation for fiber extraction, degumming to isolate fiber bundles, and delignification.

Natural fibre reinforced plant structures are widely used in nature. These plant structures combine light weight with superior mechanical properties. The fibre orientations in plants are optimized to the occurring forces, especially to the bending of plants by wind forces. Therefore it is important to study the effect of fibre orientation to the mechanical properties of materials in a systematic experimental approach. In this study the effect of reinforcement fibre orientation on mechanical properties of bio-based lyocell-reinforced polypropylene composite was analysed. For this purpose, special technique to produce composites with defined fibre orientation and fibre wetting was developed consisting of the production of intermingled hybrid yarn followed by defined yarn laying and thermoforming processes. The formed composites were subjected to tensile strength tests and dynamic mechanical analyses. The experimentally determined E-modulus was compared with values, calculated from the modified rule of mixture of Virk and Krenchel. The analysis showed that the experimental E-moduli were somewhat smaller than the theoretical values, which is indicative of a less than perfect interfacial bonding between the fibres and matrix. The influence of water on the composite performance was also analysed. It was shown that the composites sorb approximately 30% water by weight, and it has a strong influence on the E-modulus and other performance parameters.

Many biopolymers exhibit a strong complexing ability for multivalent ions. Often such ions form ionic bridges between the polymer chains. This leads to the formation of ionic cross linked networks and supermolecular structures, thus promoting the modification of the behavior of solid and gel polymer networks. Sorption of biopolymers on fiber surfaces and interfaces increases substantially in the case of multivalent ions, e.g., calcium being available for ionic crosslinking. Through controlled adsorption and ionic crosslinking surface modification of textile fibers with biopolymers can be achieved, thus altering the characteristics at the interface between fiber and surrounding matrices. A brief introduction on the differences deriving from the biopolymers, as their interaction with other compounds, is given. Functional models are presented and specified by several examples from previous and recent studies. The relevance of ionic crosslinks in biopolymers is discussed by means of selected examples of wider use.

High performance polymer fibers, such as polyester, aliphatic and aromatic polyamides, are well established in several technical applications, including personal protection equipment, sport, automotive or aerospace. This is due to their excellent thermal, mechanical and chemical properties. In the emerging field of textile based high performance composites and intelligent textiles, polymer fibers are often utilized in hybrids, i.e., in combination with other materials such as polymer matrices or metal coatings. In such cases, the step of activating or functionalizing the fibers is essential to enhance interface strength in the hybrid systems. This review provides a broad overview on recently applied activation and functionalization techniques on high performance polymer fibers including wet chemical and physicochemical treatments (e.g., hydrolysis, oxidation, complexation, deposition, flame, plasma treatment). The main objective is to review possible modification mechanisms, elaborate the effect of the modification on the fiber properties, and address possible applications of these techniques. The review also includes a comparison of the different techniques, thereby providing a better understanding of their potentials and restrictions. While the techniques differ in terms of versatility, handling, and environmental impact they all can, given the right choice of process parameters, provide well-defined fiber surface properties for the intended application.