We report a simple procedure to prepare hydrophobic cotton textiles by admicellar polymerization. By in situ incorporations of fluoropolymer on cotton fibers to generate surface roughness, followed by hydrophobization with Octafluoropentamethyl methacrylate (OFPM). After introducing fluoropolymer on the cotton surface, normally hydrophilic cotton has been easily turned to hydrophobic exhibiting static water contact angle of 126° for a 10 µL droplet. The hydrophobic textile becomes highly hydrophobic like lotus leaves, as demonstrated by a static contact angle of 126° and water can roll off on the cotton surface when an octa fluoroalkyl chain is introduced to the cotton surface.
Keywords: Fluoropolymer; Admicellar polymerization; Contact angle.
Cellulose, most abundant polymers on earth is renewable, biocompatible, biodegradable, and inexpensive, and has both interesting physical and chemical properties. An environmentally friendly cellulose based product with great interest has increased tremendously over the last years. A Soft, fluffy cellulosic (90%) fiber cotton has low production cost, low density, good strength in both wet and in dry condition and other unique Properties, make them even more attractive for future applications. Beside this, it is extremely hygroscopic in nature due to the presence of a large number of the hydroxyl group in the cellulosic backbone. So the surface modification of cotton fabric is needed and the act of modification is not a recent one. Inspired by the natural self-cleaning surfaces such as lotus leaves 1 production of self-cleaning clothes has been a hot research topic for several decades. Chemical modification of cotton has been extensively studied for the past few years in order to improve its wrinkle resistance, shrinkage resistance, and dimensional stability 2-4. From fundamental and practical aspects of viewpoint, wettability and repellency are important characters of solid surfaces. These important properties of solid surfaces are controlled by surface geometry and chemical composition (surface roughness) and hydrophobicity deal with lowering the surface free energy with increasing the surface roughness 5.Imparting hydrophobicity in textile industry while retaining comfort and mechanical strength provide a new area. Many functional finishes 6-9 on the cellulosic material has been reported. A number of water repelling agent paraffin, silicone, and fluorocarbons are used by industry with their great interest. But the fluorocarbon-based products were found to enhance oil and water repellency by lowering surface energy with increasing surface roughness 10. Fluorine has a small radius and high electronegativity, thus the covalent bond between ?uorine and carbon is extremely stable. When ?uorine is replaced by other elements such as H and C, in the order –CF3
Figure 4. SEM images of unmodified and modified cotton fabric. The smooth surface of plane unmodified cotton fiber (a); the rough surface of fluoropolymer coated cotton fiber after admicellar polymerization on the cotton surface.
The presence of fluoropolymer on the surface of the treated cotton fabric samples has been also identified by IR(ATR) spectroscopy, as shown in Figs. 3 and 4. In the FTIR spectra of treated cotton, the minor changes are observed, indicating in the admicellar process the internal bonds of in cotton fabric are not destroyed. FT-IR ATR spectra of untreated fabric and fluoromonomers treated fabric in Figure: 3 showed characteristic cellulose peaks around 1100-1200 cm-1.Other characteristic bands related to the chemical structure of cellulose were the hydrogen-bonded OH stretching at 3350-3200 cm-1, the C-H stretching at 2900 cm-1, and the C-H wagging at1314 cm-1. The OH bending of absorbed water was also observed in 1642cm-1. Figure: 3 show an absorbance at around 1751 cm-1 in the FT-IR ATR spectrum of fluorinated cotton, which might be the presence of the carbonyl stretching frequency of COF group. The frequency at 1010 cm-1 is a characteristic frequency of the C-F bond. Shih Hsien Yang et al. has prepared super-hydrophobic films using pulsed hexafluorobenzene plasma and showed characteristic peaks around 999 cm-1.The C-F stretching frequency is absent in case of untreated fabric but appears in the treated fabric indicating polar C-F bond between the cotton fabric and fluoromonomers. This data indicates that the hydrophobic cotton surface was achieved through copolymerization of the two monomers and fluorine is attached to the cotton surface which affects the water repellence behavior of the modified cotton fabric although the two monomers are different in chemical structure. This surface polymerization clearly implies that hydrophobicity is strictly related to the quantities of the attached copolymer to the cotton surface rather than their chemical composition.
Figure: 3 FTIR-ATR spectra: modified cotton fabric and unmodified cotton fabric
We have successfully created an artificial lotus leaf-like cotton surface by using a little quantity of fluoromonomer which shows hydrophobic character after admicellar polymerization. Beside hydrophobicity, the cotton surface exhibits outstanding oleophobicity without changing the breathability and comfortability.
Authors thank Sidho-Kanho-Birsha University, Purulia for the various instrumental facility to submit this paper.