Chitosan spinning processes

There are several types of spinning processes described to produce chitosan fibres:

Electrospinning is described as a suitable method to obtain chitosan nano-und microfibres for biomedical and filtration applications (Ibrahim et al. Reference Ibrahim, Alhalafi, Emam, Ibrahim and Mosaad2023). Chitosan is dissolved in harsh solvents (e.g., concentrated organic acids or trifluoroacetic acid/dichloromethane) or in mixed aqueous systems with auxiliary polymers such as polyethylene oxide or polyvinyl alcohol (PVA) to reduce viscosity and electrostatic repulsion between protonated amino groups (Ibrahim et al. Reference Ibrahim, Alhalafi, Emam, Ibrahim and Mosaad2023; Yang et al. Reference Yang, Wang, Lou and Meng2025). Under a high voltage (typically 10–30 kV), a charged jet is drawn from a Taylor cone at the spinneret tip. The solvent evaporates during flight, and a non-woven chitosan (or chitosan blend) web is collected on a grounded target.

More recently, solution blow spinning (SBS) and microfluidic blow spinning (MBS) have been applied to chitosan-containing systems (Wang et al. Reference Wang, Shan, Huang, Penkova and Su2025). In SBS, a polymer solution is drawn into fibres by a high-velocity gas stream rather than an electric field; this avoids high voltage but gives similar non-woven structures. MBS uses microfluidic channels and gas-assisted jetting to produce finer, composition-controlled fibres. The above methods are certainly more suitable for producing nano- and microfibres. A different method, wet-spinning, is used to produce macrofibres.

For wet-spinning, chitosan is first dissolved in dilute organic acid (typically aqueous acetic acid; other acids such as dichloroacetic or urea–acetic mixtures have also been used) to form a “dope” chitosan. The dope is extruded through a spinneret into an aqueous coagulation bath. Common baths for coagulation of chitosan fibres have an alkaline pH. In the bath, protonated chitosan is neutralised and precipitates as a continuous filament, followed by washing, drawing (stretching in water or alcohol) and drying. (Agboh and Qin Reference Agboh and Qin1997; Ilyas et al. Reference Ilyas, Aisyah, Nordin, Ngadi, Zuhri, Asyraf, Sapuan, Zainudin, Sharma, Abral, Asrofi, Syafri, Sari, Rafidah, Zakaria, Razman, Abd Majid, Ramli, Azmi, Bangar and Ibrahim2022). We used the classic wet-spinning method as well to produce chitosan-based macrofibres, the conditions used for spinning are described in the following sections.

Key processing parameters for chitosan wet-spinning

Suitable chemical parameters, whether in terms of chitosan properties, spinning solution parameters or coagulation bath conditions, are fundamental to the production of chemical fibres, as is maintaining an optimal operating window.

• • Chitosan intrinsic properties have a great impact on the overall performance of the process since these are determining the solubilisation, the coagulation and finally the fibre properties. Purity, molecular weight and degree of deacetylation (DDA) are the main factors influencing the chitosan production process and fibres: Purity determines how much of the resulting fibres consist of the chitosan; impurities disturb the spinning process at the same time interfering the fibre properties. Solid impurities could be removed by filtration beforehand (Qin, Reference Qin1990: 37). The molecular weight needs to be high enough to ensure chain entanglement and thus fibre formation. High molecular weight increases viscosity of the spinning dope and diameter of the resulting fibre (da Silva et al. Reference da Silva, Barbosa, de Souza, Lima, Duarte, Navarro, Silva and Fook2025). Lower molecular weight eases spinning but can lead to weaker fibres. For optimal production of uniform fibres without beads, chitosan with medium molecular weight is recommended (Li et al. Reference Li, Liu and Zhao2025; Qin, 1990: 37). DDA is another crucial factor that influences charge density, solubility and viscosity, as well as coagulation behaviour. Higher DDA results in higher solubility and viscosity.

• • Extrinsic conditions such as concentration, solvent and pH are likewise decisive: In wet-spinning of chitosan, the polymer concentration critically determines the dope viscosity and spinnability, where higher concentrations generally improve filament cohesion in the resulting fibre but eventually hinder extrusion due to excessive viscosity (Maevskaia et al. Reference Maevskaia, Dresvyanina, Yudenko and Yudin2018). Moreover, optimal concentration ranges are required to achieve uniform coagulation and mechanically robust fibres, as overly dilute dopes lead to discontinuous or weak filaments, while overly concentrated systems compromise molecular orientation during solidification (Kuznik et al. Reference Kuznik, Kruppke and Cherif2022; Nechyporchuk et al. Reference Nechyporchuk, Yang Nilsson, Ulmefors and Köhnke2020; Peniche et al. Reference Peniche, Razonado, Alcouffe, Sudre, Peniche, Osorio-Madrazo and David2024).

• • Chitosan is only soluble when amino groups are protonated (typically pH < 6), and solvent choice strongly affects surface tension. Aqueous acetic, formic, citric or lactic acid and mixed systems (e.g., acetic acid with water/ethanol) are commonly used. Mohammadkhani et al. (Reference Mohammadkhani, Kumar Ramamoorthy, Adolfsson, Mahboubi, Hakkarainen and Zamani2021) suggested to apply adipic acid to increase tensile strength of the fibres. But there are also some new concepts utilising ionic liquids for solubilisation of chitosan (Kuznik et al. Reference Kuznik, Kruppke and Cherif2022; Kuznik et al. Reference Kuznik, Kruppke, Pötzsch and Cherif2024) by the dissociation of hydrogen bonds.

• • Wet-spinning conditions and post-treatment: Coagulation bath composition (type and concentration of base, presence of salts or organic coagulants), bath temperature and draw ratio govern filament continuity, orientation and crystallinity (Dresvyanina et al. Reference Dresvyanina, Dobrovol’skaya, Popryadukhin, Yudin, Ivan’kova, Elokhovskii and Khomenko2013). Higher bath temperature and appropriate plasticisers improve spinnability and mechanical performance (Nechyporchuk et al. Reference Nechyporchuk, Yang Nilsson, Ulmefors and Köhnke2020). In general, neutralisation is followed by washing (in water or alcohol) and drying under tension; this is essential to develop tensile strength and dimensional stability; drying conditions strongly affect extensibility and moisture sensitivity.

The role of cross-linkers, processing aids and blends

Despite the previous mentioned, it is generally known that the chitosan fibres lack superior mechanical strength (Hahn et al. Reference Hahn, Bossog, Hager, Wunderlich, Breier, Stegmaier, Zibek, van den Broek and Boeriu2019). Various methods are employed to circumvent process limitations or enhance fibre performance, including general processing aids, cross-linkers, plasticisers and other polymers.

Beyond the primary spinning route, the stability and performance of chitosan fibres are strongly governed by post-spinning cross-linking. Cross-linking strengthens wet-spun chitosan macrofibres by enhancing intermolecular network stability, improving their mechanical integrity and resistance to deformation during textile processing at the same time suppresses re-dissolution or excessive swelling in aqueous media. Common cross-linkers are sodium tripolyphosphate or glutardialdehyde (Vega-Cázarez et al. Reference Vega-Cázarez, López-Cervantes, Sánchez-Machado, Madera-Santana, Soto-Cota and Ramírez-Wong2018), whereby Chi et al. (Reference Chi, Li, Meng, Qiao, Yang, Zhou, Liu and Li2026) used citric acid to enhance fibre rigidity. As part of this project, work was carried out using various bio-based polycarboxylic acids to cross-link the chitosan fibre. However, the fibres became so brittle that they could not be used or optimised.

Polymers commonly blended with chitosan to improve wet-spinning performance and the mechanical properties of textile-grade macrofibres include PVA, which enhances filament strength, cohesion and processability (Vega-Cázarez et al. Reference Vega-Cázarez, López-Cervantes, Sánchez-Machado, Madera-Santana, Soto-Cota and Ramírez-Wong2018), and cellulose nanofibrils (CNFs), which increase tensile properties and stability during spinning. Such blends improve dope rheology, fibre homogeneity and final mechanical performance, enabling more robust and uniform chitosan-based textile fibres.

In wet-spinning, additives in the coagulation bath (Na₂SO₄, ethanol, sodium dodecyl sulfate) and plasticisers (urea, glycerol) have been used to adjust viscosity and filament quality (Nechyporchuk et al. Reference Nechyporchuk, Yang Nilsson, Ulmefors and Köhnke2020; Vega-Cázarez et al. Reference Vega-Cázarez, López-Cervantes, Sánchez-Machado, Madera-Santana, Soto-Cota and Ramírez-Wong2018). Glycerol is one of the most widely used low molecular weight plasticisers for chitosan-based films and membranes and was thus used in our case in the spinning dope to improve the fibres performance. In case of chitosan films, it forms hydrogen bonds with the –OH and –NH₂ groups of chitosan, disrupts inter-chain associations and increases chain mobility. Thus, it could be assumed that this results in enhanced chain flexibility and extensibility, while reducing molecular orientation stability during solidification, leading to decreased tensile strength and stiffness.

Close-up images of the chitosan fibres

Figures 4 and 5 show close-up images in a cross-sectional view of the chitosan fibres. Due to the size, the fibres could be clearly identified as macrofibres with a diameter of hundreds of µm depending on the geometric magnitude of the cross-section. A more amorphous form on the outer side and a higher crystallinity on the inner core could be recognised indicating a skin-core-effect during coagulation. The fibres revealed a homogeneous, but a bean shape form as also described by Dresvyanina et al. (Reference Dresvyanina, Dobrovol’skaya, Popryadukhin, Yudin, Ivan’kova, Elokhovskii and Khomenko2013). According to them, this was due to the action on the moist fibre located on the uptake reel of compaction stresses.

Figure 4.

Chitosan wet-spun fibres in different processing states. The image in Figure 4 was taken using a stereomicroscope under reflected light.

Figure 5.

A scanning electron microscope image of a cross-section of several fibres.

Photos ©DITF.

Biodesign as a framework for bio-based textile materials

As outlined in the preceding sections, the development of chitosan fibres is primarily driven by advances in polymer chemistry, solution processing and fibre engineering. However, the translation of such fibres into textile and fashion applications requires an additional perspective that extends beyond material performance alone. In this context, biodesign provides a conceptual and methodological framework that integrates scientific material development with design-led exploration and application-oriented prototyping. In recent years, biodesign has developed into a distinct field of research and practice that integrates biological knowledge, systems and materials into design processes (Broega et al. Reference Broega, Cunha, Carvalho and Providência2023). Rather than treating materials as passive inputs, biodesign understands them as active agents whose properties, origins and transformations shape both design outcomes and application scenarios (Collet Reference Collet, Karana, Giaccardi, Nimkulrat, Niedderer and Camere2017; Geaney Reference Geaney2022). Within fashion and textile design, biodesign encompasses two closely related approaches: working directly with living organisms, such as bacteria, fungi or algae, and working with bio-based or bio-fabricated materials derived from renewable biological resources (Mihaleva, Reference Mihaleva2020; Scarpitti Reference Scarpitti2022). This distinction is relevant for chitosan, which is not a living material itself but originates from biological waste streams and retains properties that are closely linked to its biological function.

The increasing interest in biodesign within the fashion industry is strongly linked to the sector’s environmental impact and the search for alternative material sources. Textiles have been identified as one of the product categories with the highest environmental burden, driven by fossil-based fibres, intensive chemical processing and limited end-of-life options (Collet Reference Collet2018; Kääriäinen and Niinimäki Reference Kääriäinen and Niinimäki2019). While efficiency improvements and recycling strategies remain important, they are widely considered insufficient to achieve a fundamental transformation of the sector. Biodesign has therefore been discussed as a means to rethink material production at a more systemic level, shifting from extractive models towards regenerative and bio-based material cultures (Balar and Kowalczyk Reference Balar and Kowalczyk2025; Muthu Reference Muthu2023; Rognoli et al. Reference Rognoli, Petreca, Pollini and Saito2022).

Within this discourse, bio-based materials play a crucial intermediary role. Unlike fully living systems, they can often be processed using existing industrial infrastructures while still offering reduced environmental impact and new functional or experiential qualities (Scarpitti Reference Scarpitti2022). Chitosan, derived from chitin, exemplifies this position. Although it is not grown as a living textile, it originates from biological waste streams and retains material properties that are closely linked to its biological function. The wet-spinning process described above does not merely produce a filament with defined mechanical properties but enables the exploration of chitosan as a textile material whose behaviour must be evaluated across multiple scales, from polymer solution to fibre, textile structure and finally garment or prototype.

Nevertheless, chitosan wet-spinning should not be understood as an impact-free material route. Although chitosan can be derived from chitin-rich waste streams, conventional chitin and chitosan production involves a chemically intensive deproteinisation, demineralisation and in particular a deacetylation step, typically relying on strong acids and bases such as HCl and NaOH – in some cases in very high concentrations and at temperatures above 100 °C. Life-cycle assessments have shown that the environmental hotspots of chitosan production vary by supply chain, with chemical inputs and energy use being key contributors (Bashiri et al. Reference Bashiri, De Aguiar Saldanha Pinheiro, Tappi, Rocculi, Kaleda and Vilu2024; Mohammadi et al. Reference Mohammadi, Khounani, Hosseinzadeh-Bandbafha, Foong, Yusoff, Shahbeik, Abdul Razak, Lam, Sheikh Ahmad Tajuddin, Aghbashlo, De Tender and Tabatabaei2025; Muñoz et al. Reference Muñoz, Rodríguez, Gillet and Moerschbacher2018; Shetranjiwalla and Ononiwu Reference Shetranjiwalla and Ononiwu2025). The wet-spinning process further requires acidic dissolution, alkaline coagulation, washing and drying. In the present study, aqueous acetic acid was used as a comparatively mild solvent system, but neutralisation, wastewater treatment and drying energy remain relevant factors for future scale-up. The key factor in improving sustainability is undoubtedly the proper treatment of the high salt load in the coagulation bath. Compared with conventional textile fibres, whose impacts include land and water use, fossil resource dependence, chemical processing and wastewater generation (Bianco et al. Reference Bianco, De Bona, Zanetti and Panepinto2023; Gonzalez et al. Reference Gonzalez, Lou and Chi2023), the advantage of chitosan does not lie in simple substitution. Rather, its relevance emerges from the combination of biological origin, potential use of waste streams, biodegradability and functional properties such as moisture uptake, skin compatibility and antimicrobial activity.

Properties of the chitosan thread for further processing

Within a material-driven design context, the relevance of a newly developed fibre material is closely tied to its behaviour during textile processing and its capacity to enter established making practices. Design research on emerging materials emphasises that fibres must be evaluated not only through isolated material parameters, but through their functional translation into yarns, textile structures and ultimately wearable or spatial applications (Karana et al. Reference Karana, Barati, Rognoli and Zeeuw van der Laan2015; Rognoli et al. Reference Rognoli, Petreca, Pollini and Saito2022).

The continuous chitosan thread (Figure 6) produced via wet-spinning enables processing using conventional textile techniques such as weaving, knitting and twisting, thereby distinguishing it from chitosan nano- or microfibres obtained through electrospinning or blow-spinning, which are typically limited to nonwoven applications. At the same time, the filament exhibits properties that require careful negotiation within textile processing: Its comparatively low tensile strength, limited extensibility and pronounced moisture sensitivity directly influence yarn handling, textile density and structural design. The material’s relatively high susceptibility to tearing meant that it could not be produced on a large scale using mechanical knitting machines or weaving looms. In order to produce a textile fabric nonetheless, a mixed-material approach was chosen: The warp threads of the fabric consist of conventional silk threads, which on the one hand ensure increased tension during weaving and on the other hand create a trajectory to chitin due to the material origin of silkworms. The weft threads, in turn, were produced from the developed chitosan thread in order to enable the largest possible tactile material applications. Therefore, these characteristics were not treated as shortcomings, but as material constraints that actively informed textile construction and aesthetic outcomes (Karana et al. Reference Karana, Barati, Rognoli and Zeeuw van der Laan2015).

Figure 6.

Chitosan wet-spun fibres in different processing states: (1) Single wet-spun chitosan thread (2) Woven chitosan-silk fabric (3) Raw chitosan powder (4) Three-ply twisted chitosan thread (5) Circular-knitted chitosan thread (6) Dried prawn shells.

©Photo SurrealLabor/Julia Ihls.

The practical handling of the chitosan filament confirmed this material-specific performance envelope. In the dry state, the filament had a smooth but slightly rigid and glassy hand, with a tactile quality closer to a fine monofilament than to a conventional soft staple yarn. During winding, twisting and weaving, the material responded sensitively to local bending, friction and sudden changes in tension. Rather than allowing continuous high-speed textile processing, it required slow handling, wide bending radii and reduced thread tension. Contact with moisture increased flexibility but also made the filament more vulnerable to deformation and local sticking, confirming that humidity and handling conditions are central parameters for textile processing. These observations became part of the design process: the material was not forced into standard textile behaviour, but was approached through techniques and structures that could accommodate its stiffness, fragility and surface friction. Several textile techniques were therefore explored in order to evaluate how the filament behaves under different structural conditions: Twisting was tested to improve handling and bundle several filaments into a more textile-like thread, but excessive twist increased local stress and could lead to breakage. Knitting was explored using a semi-automatic circular knitting machine, yet loop formation placed repeated bending stress on the filament and was therefore only possible at very open loop sizes and with careful handling. Weaving proved to be the most suitable technique for the prototype, as it allowed the chitosan filament to be inserted as a weft material while the main tensile load was carried by a stronger warp system. A plain-weave structure was therefore selected for the tunic-like textile because it provided a clear and stable construction while keeping the interlacing logic technically simple. The silk warp functioned as the load-bearing element of the textile, enabling the fabric to be held under tension during weaving without exposing the chitosan filament to continuous longitudinal stress. The chitosan filament was inserted as the weft, thereby maximising its tactile and visual presence on the fabric surface while reducing the mechanical demands placed on it. The warp density was intentionally kept relatively open. This reduced friction at the interlacing points, limited abrasion of the chitosan filament and allowed the material’s stiffness and larger filament diameter to remain visible as part of the textile’s aesthetic.

The translation of the chitosan filament into woven and knitted samples makes tangible how fibre-level properties discussed in the preceding sections manifest at the textile scale. Hygroscopic behaviour, surface friction and flexibility become perceptible through handling and wear, while the material’s intrinsic antibacterial properties and skin compatibility – well established in biomedical research – gain relevance when considered in relation to bodily proximity and next-to-skin applications (Costa et al. Reference Costa, Silva, Veiga, Tavaria and Pintado2018; Mihaleva, Reference Mihaleva2020; Scarpitti, Reference Scarpitti2022). In this sense, textile processing functions as a critical testing ground in which the suitability of chitosan fibres for fashion and design contexts can be assessed beyond purely mechanical performance.

Formfinding and design process: translating material properties into concept and form

The design process underlying this project follows a material-driven design approach in which formfinding emerges through iterative engagement with material behaviour, processing constraints and embodied experimentation (Del Gesso Reference Del Gesso2021; Karana et al. Reference Karana, Barati, Rognoli and Zeeuw van der Laan2015). Rather than starting from a predefined garment typology, the development of textile samples and prototypes evolved in close dialogue with the properties of the wet-spun chitosan filament. Within this process, textile techniques such as weaving and knitting act as mediating practices that translate polymer- and fibre-scale characteristics into human-scale experiences. They reveal how parameters such as moisture uptake, stiffness or limited elasticity influence not only structural stability but also drape, tactility and bodily interaction. This aligns with the notion of “materials biography,” which frames materials as evolving entities whose origin, transformation and potential lifecycle are embedded within the design outcome (Rognoli et al. Reference Rognoli, Petreca, Pollini and Saito2022). By foregrounding the marine origin of chitosan used in this project and its transformation through wet-spinning, the design process contributes to a narrative that connects biological resource, technical processing and speculative application.

Conceptually, the formfinding process is anchored in the double meaning of the ancient Greek term chitón (χιτών), from which the word chitin is etymologically derived. On the one hand, chitón refers to an ancient garment worn directly on the body, characterised by its proximity to the skin and its function as a basic textile interface between body and environment. On the other hand, the term denotes chitons as primitive marine molluscs, whose bodies are protected by overlapping mineralised shell plates. This semantic duality between textile intimacy and biological armour provided a conceptual framework for translating the inherent properties of chitosan into form and structure.

Within the design process, this duality was explored through a layered textile logic (Figure 7). A woven, tunic-like structure made from the wet-spun chitosan filament addresses the material’s suitability for next-to-skin applications, foregrounding properties such as moisture regulation, antibacterial behaviour and bodily proximity (Uslu Reference Uslu2024).

Figure 7.

Chiton prototype consisting of a tunic-like woven textile layer and a semi-rigid chitosan-composite outer wrap. The woven textile uses silk as the load-bearing warp and wet-spun chitosan filament as the weft, while the outer layer translates the protective shell logic of biological chitin into a scale-like composite structure.

©Photo SurrealLabor/Marius Probst.

In handling and wear, however, the material did not behave like a lightweight silk fabric that visually and physically recedes on the body. The chitosan filament had a smooth, slightly elastic and nylon-like hand, with a translucent, rubber-like quality likely influenced by the glycerol plasticiser. On the skin, the woven textile initially produced a cool sensation, while its limited breathability made the wearer continuously aware of it as a distinct second layer. Rather than disappearing into comfort, the textile therefore acted as a perceptible interface between skin, material and environment.

In contrast, a second, more rigid and scale-like layer investigates chitosan-based composites as a protective outer structure, referencing the shell-like function of biological chitin. The chitosan-composite wrap differed markedly from the woven textile layer. While the woven fabric behaved as a close, skin-aware interface, the composite sheets acted more like semi-rigid bio-based plates or foils. They could bend within a limited range but did not drape or fold like fabric. On the body, this created a protective distance rather than intimate contact, translating the shell-like reference of chitin into a spatial outer layer.