Silica-Chitosan Nanocomposite Coatings for Enhancing Hydrophilicity of Polyester Fabric

The hydrophilicity of polyester fabric surfaces has been modified using silica-chitosan nanocomposites. The silica-chitosan nanocomposite was synthesized by the sol-gel method from sodium silicate and various chitosan concentrations of 0 – 1.5% at a pH of 3 – 5. A single jersey knitted polyester fabric was coated by silica-chitosan nanocomposite using the pad-dry-cure method. It was found that the chitosan concentration and the solution pH controlled the formation of various size distributions of sphere nanocomposites with an average size of 96.0-201nm. The coated polyester fabric with sphere silica-chitosan exhibits a rough surface and produces a contact angle approaching 0°, facilitating the polyester fabric's speed-up water absorption and hydrophilic properties.

Chitosan; Hydrophilic; Nanocomposite; Polyester; Sodium silicate

     Sodium silicate has been considered as an alternative inexpensive silica precursor to substitute expensive alkoxide compounds (Hwang, Lee, and Chun, 2021). Researchers have prepared diverse nanostructured silica from sodium silicate (Owoeye, Abegunde, and Oji, 2021; Chiang et al., 2017, 2011; Jesionowski and Krysztafkiewicz, 2002).  However, they synthesized sodium silicate precursor in an alkaline medium to produce non-agglomerated silica nanoparticles. In contrast, the synthesis of silica from sodium silicate in acid conditions tends to result in agglomeration (Zulfiqar, Subhani, and Husain, 2016).

     Chitosan is a unique cationic polysaccharide that can easily be modified with chemicals, radiation, and enzymes (Barleany et al., 2020; Usman et al., 2018). It is a biodegradable biopolymer used in an environmentally friendly synthesis process (Lim et al., 2021; Usman et al., 2018; Kusrini et al., 2015). As a biopolymer, chitosan is a useful polymer for synthesizing metal oxide and encapsulating small particles (Lim et al., 2021; Matusiak, Grzadka, and Bastrzyk, 2018). Recent interest in chitosan has increased due to its structure's presence of main amino groups that acts as crosslinker (Chen, Haase, and Mahltig, 2019; Haerudin et al., 2010).
    This study is aimed to synthesize silica-based chitosan nanocomposites using the sol-gel method from sodium silicate and chitosan. The relationship between pH and chitosan concentration in forming silica-chitosan composites was investigated. The effects of silica-chitosan nanocomposite coating on the polyester fabric surface were demonstrated.

2.1. Material
     Knitted polyester fabric having a single jersey knitted design, mass per unit area 150.6 g/m², thickness 0.57 mm, yarn count 9.61 tex, 51 courses per inch, 43.67 wales per inch was used as a substrate for coating. The fabric samples were knitted on a single Fukuhara machine from 100% polyester filament yarn. Ethanol (99.9%) and acetic acid (98%) were obtained from Merck. Sodium silicate, chitosan, and distilled water were obtained from a local market. All chemical reagents were used without further purification.

2.2. Preparation of precipitated silica-chitosan

     Precipitated silica-chitosan was prepared by mixing sodium silicate with ethanol and distilled water under continuous magnetic stirring. The solution was then divided into three equal parts. Acetic acid was titrated to each solution to adjust the pH value to 3, 4, and 5. Chitosan solution with concentrations of 0%, 0.5%, 1%, and 1.5% was added to the different pH of sodium silicate solutions. Finally, white precipitated silica-chitosan was collected by centrifugation and filtering and then dried in an electric oven at 50^oC for 2 h.

2.3. Coating silica-chitosan on polyester fabric

       Five pieces of polyester fabrics were coated with silica-chitosan nanocomposite using a pad-dry-cure method. The polyester fabric was padded for double-nip and double-dip in a 100 mL bath with a wet pick-up ratio of 70%. The silica-chitosan-treated polyester fabric was then dried at 100^oC for 1 min and cured at 150^oC for 2 min.

2.4. Characterization of silica-chitosan nanocomposite

    The silica-chitosan nanocomposite and coated fabric surface morphology were observed using a Hitachi TM SU-3500 Scanning electron microscope (SEM). The functional groups of nanocomposites were analyzed using a Shimadzu Prestige 21 Fourier-transform infrared (FTIR) Spectrophotometer. The microstructure of the samples was measured using a Bruker X-ray diffractometer (XRD) at 40 kV with a radiation source

2.5. Characterization of the coated fabric surface 
       The polyester fabric surface was evaluated, including water contact angle and absorption. The wettability or absorbency of polyester fabrics was examined before and after treatment using the AATCC test method 79 (AATCC, 2018). In brief, a drop of water is dropped from a fixed height onto the surface of a test specimen. The time required for the specular reflection of the water drop to disappear is measured and recorded as sink-in time. The water contact angle on polyester fabric before and after treatment was measured using a Kyowa KYOWA interFAce Measurement and Analysis System. The volume of the water droplet was set at

3.1. The morphology of silica-chitosan nanocomposites
      SEM examined the surface morphology of the silica and silica-chitosan products; representative images are shown in Figure 1. At pH 3, the silica product synthesized without chitosan (pH 3 Ch 0) depicted a loose spherical particle of various sizes from 50 nm to 200 nm. With increasing chitosan concentration (pH 3 Ch 0.5 – 1.5), the surface morphology did not change, but the silica-chitosan product decreased the size (96.0 nm – 120.3 nm) and was narrowly distributed. The surface morphology of the silica-chitosan product prepared at pH 4 and 5 have the same trend as the surface morphology of the silica-chitosan product prepared at pH 3. 

Figure 1 SEM images of silica and silica-chitosan particles synthesized at different pH and chitosan concentrations