Embedding zinc oxide (ZnO) nanostructures into textiles has gained attention for applications such as ultraviolet (UV) protection, durability, and maintaining fabric breathability. Various methods exist for integrating ZnO into textiles, each with distinct advantages and limitations. This article evaluates dip-coating and in-situ growth techniques, assesses washing durability, breathability, and ultraviolet protection factor (UPF) ratings, and compares performance across cotton, polyester, and blended fabrics.
**Dip-Coating Method**
Dip-coating involves immersing textiles in a ZnO nanoparticle suspension, followed by drying and curing. The process is straightforward and scalable, making it suitable for industrial applications. The concentration of ZnO nanoparticles in the suspension, immersion time, and curing temperature influence the coating's uniformity and adhesion.
Studies indicate that dip-coated cotton fabrics achieve UPF ratings exceeding 50 when treated with 5% ZnO nanoparticle suspensions. Polyester fabrics, due to their hydrophobic nature, require surface modification (e.g., plasma treatment) to enhance ZnO adhesion. Blended fabrics show intermediate performance, with UPF ratings dependent on the composition ratio of natural to synthetic fibers.
A limitation of dip-coating is the potential for nanoparticle aggregation, which reduces coating homogeneity. Multiple dipping cycles improve coverage but may compromise fabric breathability. Measurements show a 10-15% reduction in air permeability for heavily coated cotton, while polyester experiences a 5-10% reduction due to its inherent lower breathability.
**In-Situ Growth Method**
In-situ growth involves synthesizing ZnO nanostructures directly on textile fibers through chemical reactions. Common approaches include hydrothermal synthesis, where fabrics are treated with zinc precursor solutions (e.g., zinc nitrate) and heated to induce ZnO crystal growth. This method yields well-anchored nanostructures with high durability.
Cotton fabrics treated via hydrothermal synthesis exhibit UPF ratings above 50, with minimal reduction in breathability (less than 5% air permeability loss). The in-situ method enhances washing durability, as ZnO crystals are chemically bonded to fiber surfaces. After 20 washing cycles, UPF retention remains above 80% for cotton and polyester.
Polyester fabrics benefit from in-situ growth due to the formation of ZnO nanorods, which enhance UV blocking without significantly altering fabric handle. Blended fabrics show variable performance; for example, a 50/50 cotton-polyester blend retains 75% of its UPF rating after repeated washing.
**Washing Durability**
Washing durability is critical for practical applications. Dip-coated textiles exhibit faster UPF degradation, with ratings dropping by 30-40% after 20 washes due to nanoparticle detachment. In-situ grown ZnO demonstrates superior adhesion, with less than 20% UPF loss under the same conditions.
Pretreatments such as silane coupling agents improve dip-coating durability, reducing UPF loss to 20-25%. However, these additives may affect fabric softness. In-situ growth does not require additional binders, making it more suitable for long-term applications.
**Breathability Assessment**
Breathability is measured by air permeability and moisture vapor transmission rate (MVTR). Untreated cotton has an MVTR of approximately 2500 g/m²/day, which decreases by 10-20% after ZnO application. Dip-coating tends to reduce breathability more than in-situ growth due to pore blockage by loose nanoparticles.
Polyester’s baseline MVTR is around 2000 g/m²/day, with a 5-10% reduction post-treatment. Blended fabrics balance breathability and performance, with MVTR reductions of 8-15% depending on the fiber mix.
**UPF Performance Comparison**
UPF ratings vary by fabric type and treatment method:
Fabric Type | Dip-Coating UPF | In-Situ Growth UPF | UPF After 20 Washes (Dip) | UPF After 20 Washes (In-Situ)
Cotton | 50+ | 50+ | 30-35 | 40+
Polyester | 40-45 | 50+ | 25-30 | 40+
Blended (50/50) | 45-50 | 50+ | 30-35 | 35-40
Cotton outperforms polyester in dip-coating due to better nanoparticle adhesion, but polyester excels in in-situ growth because of its structural stability. Blended fabrics offer a compromise, with moderate performance in both methods.
**Conclusion**
In-situ growth of ZnO nanostructures provides superior washing durability and breathability retention compared to dip-coating. Cotton fabrics are ideal for dip-coating when high initial UPF is needed, while polyester benefits more from in-situ growth. Blended fabrics offer balanced properties but require optimization based on the intended application. Future work should focus on scalable in-situ techniques to enhance commercial viability.