Presentation: Pertti Nousiainen, Cellulose Fibres Conference 13-14 March 2024 Cologne, Germany
Raw materials of fibers
Key aspects of the down-stream conversion processes of fibers to products include mechanical, thermal, and chemical processing. Automation and robotics are gaining impact on textile and clothing production and facilitate textile production closer to customers and become more efficient and sustainable. Raw materials with their mechanical and chemical processing should not appear as a weak link in the chain and must fulfil sustainability requirements.
The increased use of cotton-like MMCF`s reduces the cleaning and fiber dimension controlling stages of the in a spinning factory and no alkaline pretreatments are needed. It is necessary that textile chemicals, such as dyes, finishing agents and auxiliaries are produced as biobased, and used efficiently for minimizing waste-water contamination.
Nonwovens produced by 4 main methods represent sustainable – capital intensive – chain for many technical and medical products with less dyes and finishes. Optimisation of the hybrid needlepunching with hydroentanling-process parameters is developed for many protective apparel applications. Usage of nonwovens in basic clothing is still a challenge.
Spin finishes
About 1 million tons of spin finishes are used in production and processing of man-made fibres (staple/filaments). Man-made fibres and many natural fibers are surface-treated by 0,1-1 % of a spin finish to improve bale opening and eliminate the build-up of static electric charges on fibres during bale opening and further processing. The finish may be conductive for charge dissipation and reducing the cohesion and friction in contact with ceramic or metallic machine parts. Typical emulsions may contain: C16-C18 acid EO`s, cationic derivatives (quats), mineral/vegetable oils and surfactants.
Dyes
Coloration with more than 25000 possible industrial dye molecules involves a complex application of dyestuffs on textiles because of the variety of fibres, filaments, yarns, and fabrics. Textile and materials requiring coloration, and the diverse nature of the end-use and performance requirements are setting multiple requirements. Coloration is mainly carried out in aqueous media may be carried out by dyeing the materials to a uniform colour, or by printing to impart a design or motif to textile (Fig.1). While biobased textile dyes offer several advantages, there are challenges to be solved related to colour fastness, scalability, and cost. The fixation degree, type of bonding of dye molecules in textile fiber and content of necessary auxiliaries is important for the sustainability of the processes.
Fig.1. Distribution of various dyeing methods used for textile fibers. Total production with 1% in clothing/interior textiles (70 Mt) gives 0,7 Mt of dyes in textiles.
Natural dyes
Mainly plant and insect-based natural dyes cover multiple chemical classes, such as Polymethines, Ketones, Imines, Anthraquinonoids, Quinines, Naphthoquinones, Flavones, Flavanols, Flavanones, Indigoids and Chlorophyll. Some fungi-dyes are suitable for PET, PA and wool dispersive dyeing (emodin, dermocybin) and mordant technologies (Fig.2) They often offer substantivity using direct, mordant, vat, acid, basic methods, as well. Standardisation needed for developing repeatability and known fastnesses of natural dyes. Natural dyes unfortunately are lacking homogenous contents and suitable functionalities after separation followed by unsatisfactory fastnesses.
Emodine
Fig. 2. Examples of various ancient and novel anthraquinone-based natural/extracted dye molecules.
Coloration processes
Pretreatment and dyeing/finishing show highest GHG effect prior to consumption and fiber/yarn and textile mechanical production. In freshwater consumption apparel end-use shows most negative LCA is due to washing, surfactants, solid waste, and marine pollution.
Aqueous process dominates in dyeing and improved bio-inspired molecules, liquor ratio, salt-free, high fixation degree, pre-reduced vat dyeing, and spray techniques are on the way. Thus, it is important for enhanced sustainability to improve in-house recycling of chemicals, energy, water and (reactive) dyes. There are methods available for removing dye pollutants from wastewater and from recycled cellulose fiber, as well (Fig.3).
Fig.3. An example of shortened vat dyestuffs processing recipe exhibiting decolorization efficiency above 99% and rates of total organic carbon removal over 90% in all, in addition to higher values in colourfastness properties.
Waterless SC-CO2 high-pressure piece dyeing of PET in industrial scale shows efficiency, however high investment costs, as well (Fig. 4).
Dyeing without water equals becoming completely independent from clean water availability. New opportunities for the textile industry are offered allowing production to occur closer to market, shorten lead times and disconnect from water source.
Waterless textile digital has been developed using printing with pre-treatment and reactive nanoinks, fixed by post treatment.
Fig.4. One-bath dyeing of PET/CO blends in SC-CO2 reactive-disperse dyeing process.
Textile finishing
For improving the properties and behaviour of dyed or non-dyed fabrics, mechanical methods are only changing the shape/form of the fabric. Those include calandering, abrasion, shrinking, embossing, optical finishing, brushing and napping, softening and shearing. Physical and thermal fixation can change the supermolecular position/location of polymer molecules via relaxation in elevated temperatures (> Tg).
Chemical methods are able to change the chemical structure of polymer molecules by introducing new bonds and/or breaking and/or chancing original bonding system, such as:
- The antiwrinkling of cellulose fibers with cross-linking-chemicals, mainly N-methylol-urea derivatives (DMDHEU, DMMDHEU)
- Softening treatments on fiber surface with long-chain surfactants (cationic)
- Enzymatic treatment of cellulose and protein fibers for smooth surfaces
- Water/soil repellent traditional finishing: silicones, fluorohydrocarbons, fatty acid polymers
- Water/soil repellent eco-friendly hydrophobic finish with non-PFAS by hydrocarbons and natural polymers
- Hydrophobic finish with non-PFAS by hydrocarbons and natural polymers
- Flame retardant treatment of cotton: nitrogen-phosphorus-reactive compounds, non-durable salts&organics (phosphonate, phosphonium salt, melamine)
- Flame retardant treatment of wool: zirkonates
- Antimicrobial treatments: fungisides, pesticides, antibacterial agents
- Plasma treatment of textiles for surface functionalization
Improved sustainability of textile finishing
Continuous pretreatment machinery with combined singeing, bleaching, mercerizing, piece dyeing, finishing, calendaring and fixing can be processed for further high-level finishing. Various new technologies are possible for improving the sustainability of finishing, as follows:
- Digital spray finishing: low pick-up (constant) single/double side application, saves energy, water and chemicals (Fig.5).
- Foam technology for applying a low water foamed chemistry onto or into a substrate, one chemical to be applied to the front of a fabric while a different chemical is applied on the back.
- Avoiding PFAS: pp-membrane and hyper-branched polymers
- Durable water PU repellent for polyester and blends with high water repellence
- Hyper-branched polymers with water-repellent end groups and without perfluorinated groups
- Special finishes: led-assisted photopolymerizable formulation hydrophobic finish, sustainable hydrophobic agents: AKD (alkyl ketene dimer), ASA (alkenyl succinic anhydride), Rosin, Chitosan
Fig. 5. A photo from digital spray finishing with low pick-up and double side application possibilities.
Ocean microparticles
Various microparticles are delivered (>85%) nearly equally from car tyres, city dust draining, washing of synthetic textiles and road markings (Fig.6). During washing released microfibers (50 µm/1-5mm) of samples taken 5 m below ocean surface range from 124-308 mg/kg (15000-30000 pcs) of washed synthetic and PET/cellulose fabrics. Basing on their abundance, non-degradable micro-fiber particles have been detected in food, drinking water, human lungs, and the digestive tracts of many organisms.
Ocean microfibers (< 0,5 mm) contain stable synthetics and degraded cellulose – dyes and finishing chemicals (cross-linkers) negatively affect the bio-disintegration. Nature-based additives providing desired functions are more ecological and sustainable. Cellulose fibers degrade quite fast and type of fiber cellulose (natural, regenerated (cell II-cel I), oriented, crystallised vs amorphic) effect on biodegradation speed.
Waste-water process and washing machine filters can be used for remarkable reduction of ocean microfiber release.
Fig.6. Distribution of amounts of microparticles are delivered from various sources and filter assembled to household washing machine