Non-Fluorinated Water Repellent Finishing Of Fabrics By Sol-Gel Process

The water repellent finishing of fabrics has a long history and there are many water repellent finishing agents which have been studied and widely used.The fluorochemicals are at present the most favorable agents due to their excellent and durable water repellency.However disadvantages of fluoroalkyl compounds are the high cost and a potential risk for human health and environment and which has caused wide public concern.Therefore,water repellent fabrics were prepared via sol-gel process using non-fluoro compound,alkyltialkoxysilanes,in this paper.Silica sol was prepared via ammonia hydrolysis of tertraethoxysilane.Water repellent cotton and polyester fabrics were successfully obtained first by dip-coating the silica sol and then immersing in the hydrolyzed alkyltrialkoxysilanes.Silica sols with different sizes were prepared by controlling the concentration of ammonia.The influence of silica nanoparticle sizes,structure and concentration of alkyltrialkoxysilanes on water repellency of fabrics were discussed.After treating with 3wt%hexadecyltrimethoxysilane(HDTMS) pretreated by silica sol, Superhydrophobic cotton fabric with water contact angle higher than 150°can be obtained, polyester fabric with water contact angle higher than 140°can also be prepared,and the spray rating of the fabrics is 5.To investigate the water repellency of treated fabrics under condition of daily use,washing tests were performed on them and the influence of washing cycles on contact angle of water on fabrics was discussed.The water contact angle on cotton fabrics decreased from 155°to 95°,and on polyester fabrics the contact angle decreased from 143°to 110°after 30 washing cycles.Silica element was detected on the treated cotton fabric surface by energy dispersive spectroscopy and FTIR,physical properties of cotton fabric showed slight change after treatment.Scanning electron microscopy was used to observe the fabric surfaces treated with and without silica sol.The roughness of the treated fiber was increased compared with the original fiber.The increased roughness and the use of alkyltrialkoxysilanes are the major cause of the water repellency of fabrics.In order to simplify the technology and enable to industrialization,pure silica sol and with 3-glycidyloxypropyltrimethoxysilane co-condensed silica sol were modified by alkyltrialkoxysilanes and then different modified silica sols with water repellency were prepared. The influence of silica nanoparticle sizes,structure and concentration of alkyltrialkoxysilanes,and washing cycles on water repellency of fabrics were discussed.With addition of 4wt% hexadecyltrimethoxysilane(HDTMS) to silica sols coatings on fabrics,superhydrophobic cotton fabric with water contact angle higher than 150°can be prepared,polyester fabric with water contact angle higher than 140°can also be obtained,and the spray rating of the fabrics is 5.After 30 washing cycles,the water contact angle on cotton fabrics is higher than 122°which is higher than the water contact angle reported in the related literature,and on polyester fabrics the contact angle is above 131°.Scanning electron microscopy was used to observe the cotton fabric surfaces treated with and without modified silica sol.The fabric after treatment showed a particulate surface.Physical properties of fabrics showed slight change after treatment.