Fibers made from biopolymers are one solution for conserving both resources and the environment. However, these fibers currently have limited strengths, which limit their use for textile applications. In this paper, a biopolymer stereocomplex poly(-lactide) (scPLA) formation on a technical scale of high-molecular-weight poly(D-lactide) (PDLA) and poly(L-lactide) (PLLA) is presented. This scPLA material is the basis for further research to develop scPLA yarns in melt spinning with technical strengths for technical application. scPLA is compared with standard and commercially available semi-crystalline PLA for the production of fibers in melt spinning (msPLA) with textile strengths. Differential scanning calorimetry (DSC) gives a degree of crystallization of 59.7% for scPLA and 47.0% for msPLA. X-ray diffraction (XRD) confirms the pure stereocomplex crystal structure for scPLA and semi-crystallinity for msPLA. scPLA and msPLA are also compared regarding their processing properties (rheology) in melt spinning. While complex viscosity of scPLA is much lower compared to msPLA, both materials show similar viscoelastic behavior. Thermal gravimetric analysis (TGA) shows the influence of the molecular weight on the thermal stability, whereas essentially the crystallinity influences the biodegradability of the PLA materials.

Upscaling lignin-based precursor fibre production is an essential step in developing bio-based carbon fibre from renewable feedstock. The main challenge in upscaling of lignin fibre production by melt spinning is its melt behaviour and rheological properties, which differ from common synthetic polymers used in melt spinning. Here, a new approach in melt spinning of lignin, using a spin carrier system for producing bicomponent fibres, has been introduced. An ethanol extracted lignin fraction from LignoBoost process of commercial softwood kraft black liquor was used as feedstock. After additional heat treatment, melt spinning was performed in a pilot-scale spinning unit. For the first time, biodegradable polyvinyl alcohol (PVA) was used as a spin carrier to enable the spinning of lignin by improving the required melt strength. PVA-sheath/lignin-core bicomponent fibres were manufactured. Afterwards, PVA was dissolved by washing with water. Pure lignin fibres were stabilized and carbonized, and tensile properties were measured. The measured properties, tensile modulus of 81.1 ± 3.1 GPa and tensile strength of 1039 ± 197 MPa, are higher than the majority of lignin-based carbon fibres reported in the literature. This new approach can significantly improve the melt spinning of lignin and solve problems related to poor spinnability of lignin and results in the production of high-quality lignin-based carbon fibres. This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)’.

The development of efficient fiber-based air filter media with increased dust storage capacity and reduced pressure gradient is a key to the advancement of filtration systems in residential ventilation. However, the manufacturing of homogeneous deep-air filter media remains challenging due to the complexity of fiber formation and the predominantly unregulated deposition of fibers in nonwoven structures. This study aims to address these challenges by utilizing continuous crimped islands-in-the-sea fibers for highly porous and efficient filter textile applications, which can be integrated into ventilation system components such as heat exchangers. To define the required filter parameters for the production of highly porous and efficient filter textiles, a mathematical model to simulate the filter characteristics of separation efficiency and pressure drop was derived based on relevant filter theories and evaluated using computational fluid dynamics simulations combined with discrete element method and current literature. The microfibers, essential for the project’s objectives, were produced using the islands-in-the-sea melt spinning technique for polyamide 12, incorporating a water-soluble polyvinyl alcohol as the sea component. The resulting microfibers had diameters of 803 ± 83 nm and exhibited a technical strength of 61.25 ± 1.83 cN/tex. The microfibers were subsequently crimped by two texturing processes: bulked continuous filament and false twist texturing. The force–elongation curves of the textured yarns were analyzed to assess the fiber crimp structure and its suitability for air filtration media. The mathematical model describing fiber crimp and curvature was validated by using scanning electron microscopy. The findings indicate that the ratio of the single islands-in-the-sea fiber bending radius to the microfiber diameter is a critical parameter for producing highly porous structures. It was observed that the false twist texturing process resulted in a threefold crimping contraction of 32.4 ± 4.0%, in comparison with the bulked continuous filament process. Furthermore, it is necessary to analyze both crimp contraction and fiber curvature in order to evaluate the potential of crimped yarns in the development of highly porous and efficient filter textiles. The proposed approach offers promising applications in air filtration, enhancing system efficiency and longevity.