Preparation Of Superhydrophobic Cotton Fabrics By γ-ray Irradiation And Study On The Fabric Serviceability

The superhydrophobic phenomenon displays the water contact angle on the solid surface higherthan150°. Numerous studies suggest that the superhydrophobic property is attributed to acombination of the surface structure and low surface energy. The superhydrophobic surfaces haveattracted great interest due to their potential applications in our daily life and industry, such aswater-proof, oil/water separation, self-cleaning, anti-icing (anti-frost) and so on. Based on theprevious related research work in our group, in the following work we mainly perform the studyon fabricating superhydrophobic fabrics using functional polymers, and systematically studyingon the mechanical durability, thermal healing effect, the air permeability and the water vaportransmission rate of the superhydrophobic fabrics. The superhydrophobic fabrics with patternstructure prepared by physical woven method were further studied. There were mainly five aspectswe focused on:The superhydrophobic cotton fabrics were prepared by grafting alkyl methacrylates withdifferent alkyl chain length onto cotton fabrics through simultaneous radiation. The surfacemorphology and composition of the as-prepared samples were characterized by FT-IR spectra,XPS, XRD, TGA, etc. The results suggested that the poly (alkyl methacrylates) had been graftedonto the cotton fabrics successfully. The graft dynamic was further studied, such as the effect ofthe monomer concentration and alkyl chain length on the degree of grafting.The effects of degree of grafting and the alkyl chain length on the superhydrophobicity weresystematically investigated. The results showed that when the surface of the cotton fabric wassufficiently covered by the hydrophobic graft polymers, it became superhydrophobic. Furthermore,the longer alkyl chains would result in lower degree of grafting needed for superhydrophobicity.The rolling angles were also measured to determine the dynamic behaviour of water on the fabricsurface. In our study, the surface of the grafted cotton fabrics showed the similar wetting behaviourto rose petals, that is, the superhydrophobic state (static contact angle>150°) with high adhesiveforce. The high sticky behaviour is related to the contact model of the water on the grafted cottonfabrics.The abrasion durability and self-healing effect of the superhydrophobic cotton fabrics were studied. As covalent bonds were formed between the poly (alkyl methacrylate) and cotton fabricsat the molecular level, the grafted cotton fabrics showed excellent mechanical abrasion durability.The superhydrophobicity could be retained for thousands of abrasion cycles at a load of9N.Furthermore, through the steam ironing process, the superhydrophobicity could be regeneratedeven after the yarns were ruptured during the abrasion test. The self-healing mechanism was dueto the distribution of the graft chains in the bulk phase during the radiation-induced graftpolymerization procedure, which indicated that the technology was a good approach to prepare theself-healing superhydrophobic materials, not limited to the fabrics.The superhydrophobic cotton fabrics exhibited considerable resistance to air permeabilitywhereas the water vapor transport was almost the same as the pristine cotton. The reason was thatthe air permeability of the fabric was mainly related to its porosity, thickness and pore diameter.The thickness would increase and the pore size would decrease significantly after graftpolymerization. Whereas the permeation of water vapor through the perforated cotton fabricobeyed Fick’s law (the absorption, diffusion and desorption mechanism), and the capillary actionwas also the key factor affecting the water vapor transport. The grooves on the surfaces of thegrafted cotton samples became deeper and narrower than that of the pristine cotton, leading tostronger capillary effect to transfer water vapor quickly. Furthermore, the water-proof finishmethod had effectively decreased the interaction between the surface of the fabric and watermolecules, leading to a fast wicking of the vapor out of the fabric. Therefore, the combination ofthe decreased air permeability and the ideal water vapor transmission rate created breathable andcomfortable fabrics as dressing materials.The superhydrophobic textiles with pattern structure were initially knitted through non-chemical method using the sewing and embroidery machine. The effect of parameters, that is thefiber radius R, the distance between the fibers D, and the fiber length L on the contact angles wassystematically studied. The result showed that when the distance between the neighbor fibers was0.7mm, the water could sit between the fibers which belonged to the Cassie contact model, andthe surface showed excellent superhydrophobic property. When the length of the fiber was longenough (>3mm), the water showed robust superhydrophobic state.In conclusion, the study present here demonstrates that the superhydrophobic fabrics can beeasily achieved with the radiation induced graft polymerization method. The grafted cotton fabrics possesses excellent functional properties, such as the mechanical durability, the self-healing effect,combined with ideal water-proof, wind-proof and water vapor permeable properties. Furthermore,the graft polymerization method by irradiation is also applied for modifying fibrous materialswithout reactive groups.