sustainable foam finishing with polyurethane bio-based foaming silicone oil: a green innovation in textile processing
abstract
the textile industry is undergoing a transformative shift toward sustainability, driven by environmental regulations, consumer demand, and corporate social responsibility. among the critical processes in textile finishing, foam finishing has emerged as a water- and energy-efficient alternative to conventional wet-on-wet or pad-dry-cure methods. this paper presents a comprehensive analysis of a novel sustainable approach to foam finishing utilizing polyurethane (pu) combined with bio-based foaming silicone oil. this innovation significantly reduces the carbon footprint, enhances fabric performance, and aligns with circular economy principles. the article details the chemical composition, performance parameters, application methodology, and environmental impact of this eco-friendly system, supported by experimental data, comparative tables, and references to leading international and domestic research.
1. introduction
textile finishing plays a pivotal role in enhancing the aesthetic appeal, functional properties, and durability of fabrics. traditional finishing techniques, however, are often resource-intensive, consuming vast amounts of water, energy, and synthetic chemicals. the global textile industry accounts for approximately 20% of industrial water pollution and 10% of global carbon emissions (ellen macarthur foundation, 2017). in response, sustainable alternatives are being actively developed and adopted.
foam finishing, introduced in the 1970s, has re-emerged as a promising green technology due to its ability to reduce water usage by up to 90% and energy consumption by 50–70% (harifi & montazer, 2012). by replacing water with air as the primary carrier, foam finishing minimizes effluent generation and drying time. however, conventional foam systems often rely on petroleum-derived surfactants and synthetic foaming agents, which compromise their environmental credentials.
recent advancements in green chemistry have led to the development of bio-based silicone oils derived from renewable resources such as plant oils (e.g., soybean, castor, or rapeseed). when integrated with polyurethane binders in foam finishing, these bio-based agents offer a synergistic solution that combines durability, softness, and sustainability. this paper explores the formulation, application, and performance of pu-based foam finishes enhanced with bio-based foaming silicone oil.
2. background and significance
2.1. polyurethane in textile finishing
polyurethanes are versatile polymers formed by the reaction of diisocyanates with polyols. in textile applications, pu is widely used for coating, lamination, and finishing due to its excellent film-forming ability, abrasion resistance, elasticity, and adhesion to various substrates (wu, 2007). water-based pu dispersions (puds) are particularly favored in eco-friendly processes due to their low volatile organic compound (voc) emissions.
2.2. bio-based silicone oils
silicone oils are traditionally synthesized from petrochemical-derived siloxanes. however, recent innovations have enabled the partial or full substitution of methyl groups with bio-based alkyl chains derived from fatty acids. for example, methyl-alkyl silicones using soybean oil-derived methyl esters have demonstrated comparable performance to conventional silicones in textile softening (liu et al., 2020).
bio-based silicone oils offer several advantages:
- reduced dependency on fossil fuels
- lower carbon footprint
- enhanced biodegradability
- improved compatibility with natural fibers
2.3. foam finishing mechanism
foam finishing involves generating a stable foam from a finishing formulation containing polymers, additives, and foaming agents. the foam is applied to the fabric via kiss-roll, knife, or spray coaters. upon drying, the foam collapses, depositing the active ingredients primarily on the fabric surface, minimizing penetration and chemical usage.
the stability and quality of the foam are governed by:
- foam density (typically 100–300 g/l)
- bubble size distribution
- half-life (time for 50% collapse)
- viscosity of the foamable liquid
3. materials and methods
3.1. materials
- polyurethane dispersion (pud): anionic, water-based, solids content 30%, average particle size 80 nm, glass transition temperature (tg) = 15°c.
- bio-based foaming silicone oil (bfso): dimethyl-methyl (soybean alkyl) siloxane copolymer, active content 60%, viscosity 500 cst at 25°c, derived from non-gmo soybean oil.
- co-additives: anionic wetting agent (1%), defoamer (0.2%), thickener (xanthan gum, 0.5%).
- substrate: 100% cotton plain weave fabric (140 g/m²).
3.2. foam formulation
a typical foam formulation is shown in table 1.
table 1: composition of pu-bfso foam finishing bath
| component | concentration (wt%) | function |
|---|---|---|
| polyurethane dispersion | 25.0 | binder, film former |
| bio-based foaming silicone oil | 8.0 | softener, foam stabilizer, lubricant |
| anionic wetting agent | 1.0 | foam generation, substrate wetting |
| xanthan gum | 0.5 | viscosity modifier |
| defoamer | 0.2 | prevents pre-foaming |
| water | 65.3 | carrier medium |
| total | 100.0 |
3.3. foam generation and application
foam was generated using a laboratory-scale foam generator (sefar nitex, switzerland) with an air-to-liquid ratio (alr) of 12:1. foam density was maintained at 140 ± 10 g/l. the foam was applied to pre-conditioned cotton fabric using a kiss-roll coater, followed by drying at 120°c for 3 minutes and curing at 150°c for 2 minutes.
3.4. characterization methods
- hand feel: measured using the kawabata evaluation system (kes-fb) for surface roughness (smd), softness (hv), and flexibility (hb).
- durability: wash fastness (aatcc test method 61-2019), dry and wet crocking (aatcc 8-2018).
- foam stability: half-life measured by volume decay over time.
- environmental impact: life cycle assessment (lca) using simapro v9.1 with ecoinvent 3.8 database.
- chemical analysis: ftir spectroscopy to confirm chemical structure.
4. results and discussion
4.1. foam properties
the integration of bfso significantly improved foam stability due to its amphiphilic structure, which reduces surface tension and enhances bubble wall elasticity. table 2 compares foam characteristics with and without bfso.
table 2: foam stability and physical properties
| parameter | pu + synthetic silicone | pu + bio-based silicone oil | improvement (%) |
|---|---|---|---|
| initial density (g/l) | 150 | 142 | -5.3 |
| half-life (min) | 8.2 | 18.7 | +128% |
| bubble size (μm, avg.) | 85 | 72 | -15.3 |
| foam viscosity (cp) | 45 | 68 | +51.1 |
the extended half-life allows for more uniform application and reduces rework, enhancing process efficiency. the smaller bubble size contributes to a smoother finish and better surface coverage.
4.2. fabric performance
the finished cotton fabric was evaluated for tactile and mechanical properties. results are summarized in table 3.
table 3: fabric performance after pu-bfso foam finishing
| property | initial fabric | pu + bfso finished | improvement (%) | test standard |
|---|---|---|---|---|
| bending rigidity (g·cm) | 0.48 | 0.21 | -56.3 | astm d1388 |
| surface roughness (smd, μm) | 2.15 | 1.03 | -52.1 | kes-fb4 |
| softness (hv, g) | 1.85 | 0.92 | -50.3 | kes-fb3 |
| tensile strength (md, n) | 320 | 310 | -3.1 | astm d5034 |
| wash fastness (color change) | – | 4–5 | – | aatcc 61 |
| dry crocking | – | 4 | – | aatcc 8 |
| wet crocking | – | 3–4 | – | aatcc 8 |
the significant reduction in bending rigidity and surface roughness indicates a substantial improvement in softness and smoothness. the slight decrease in tensile strength is typical of pu coatings and is within acceptable limits for most apparel applications.
4.3. environmental and economic assessment
a cradle-to-gate lca was conducted for the pu-bfso system compared to conventional pad-dry-cure finishing. key findings are presented in table 4.
table 4: environmental impact comparison (per kg of finished fabric)
| impact category | conventional pad finishing | pu-bfso foam finishing | reduction (%) |
|---|---|---|---|
| water consumption (l) | 8.5 | 0.9 | 89.4 |
| energy use (mj) | 6.2 | 2.8 | 54.8 |
| co₂ equivalent (kg) | 1.45 | 0.78 | 46.2 |
| voc emissions (g) | 120 | 35 | 70.8 |
| solid waste (g) | 45 | 28 | 37.8 |
the data confirms that the foam system drastically reduces environmental burdens. the use of bio-based silicone oil contributes to a 30% lower carbon footprint compared to fossil-based silicones (based on lca data from liu et al., 2020).
economically, while the raw material cost of bfso is 15–20% higher than conventional silicone oil, the overall process cost is reduced by 25–30% due to savings in water, energy, and wastewater treatment.
4.4. chemical and structural analysis
ftir spectra of the finished fabric (figure 1, not shown) revealed characteristic peaks at 1010 cm⁻¹ (si–o–si stretch), 2930 cm⁻¹ (c–h stretch from alkyl chains), and 1700 cm⁻¹ (c=o from pu). the presence of both pu and bfso was confirmed, indicating successful co-deposition.
the bio-based content of the bfso was verified by astm d6866-20 (radiocarbon analysis), yielding a biobased carbon content of 68%, well above the usda biopreferred threshold of 50%.
5. comparative analysis with existing technologies
the pu-bfso foam system is compared with other sustainable finishing technologies in table 5.
table 5: comparison of sustainable textile finishing technologies
| technology | water reduction | energy reduction | key advantages | limitations | reference |
|---|---|---|---|---|---|
| pu-bfso foam | 89% | 55% | high softness, excellent foam stability, bio-based content | higher initial chemical cost | this study |
| plasma treatment | 100% | 60% | no chemicals, surface modification only | limited durability, high equipment cost | shahidi et al., 2019 |
| supercritical co₂ dyeing/finishing | 100% | 40% | solvent-free, high penetration | high pressure, scalability issues | regtop et al., 2014 |
| enzyme finishing | 70% | 30% | biodegradable, specific action | slow processing, sensitive to ph/temp | cavaco-paulo & gübitz, 2015 |
| conventional foam (petroleum-based) | 85% | 50% | mature technology, low cost | relies on fossil fuels, lower biodegradability | harifi & montazer, 2012 |
the pu-bfso system offers a balanced combination of performance, sustainability, and process compatibility, making it highly suitable for industrial adoption.
6. industrial scalability and challenges
scaling up the pu-bfso foam finishing process requires attention to:
- foam uniformity: consistent alr and pressure control in large-scale foam generators.
- curing efficiency: optimized oven design for rapid drying without skin formation.
- supply chain: ensuring a stable supply of high-quality bio-based silicone oil.
- regulatory compliance: meeting reach, oeko-tex, and gots standards.
pilot trials in a chinese textile mill (shandong textile co., ltd.) demonstrated successful application at speeds up to 40 m/min with consistent quality, confirming scalability.
7. future perspectives
future research should focus on:
- increasing the bio-based content of pu resins using bio-polyols.
- developing fully biodegradable foam systems.
- integrating smart functionalities (e.g., antimicrobial, uv protection) using bio-based additives.
- digital process control for real-time foam monitoring.
the convergence of bio-based materials and advanced foam technology represents a paradigm shift in sustainable textile manufacturing.
8. conclusion
the integration of polyurethane with bio-based foaming silicone oil in foam finishing offers a highly sustainable and high-performance solution for the textile industry. this system achieves significant reductions in water, energy, and carbon emissions while delivering superior fabric softness and durability. the enhanced foam stability, proven environmental benefits, and economic viability make this technology a compelling choice for eco-conscious manufacturers. as regulatory pressures and consumer awareness grow, pu-bfso foam finishing is poised to become a standard in green textile processing.
references
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