Surface properties of urethane coating containing perfluorinated additives

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Abstract

A series of alcohols containing perfluorinated segments F(CF2)m(CH2)n–OH (m = 8, 10 and n = 10) were synthesized. First, the alcohols were reacted with fatty acid to produce several esters (i.e. F(CF2)m(CH2)n–OOC–R (m = 8, 10 and n = 10)) containing perfluoro group by a condensation reaction, and characterized by FT-IR, GC, and surface tension. The esters were found to be soluble in ethyl ether, toluene, hexane, ethyl acetate, chloroform, and acetone, but insoluble in methyl alcohol, ethyl alcohol and isopropyl alcohol. Preliminary experiments on 1,2-dichloroethane solutions showed a remarkable decrease of surface tension upon the addition of the esters. In addition, the esters using urethane resin were coated onto a glass substrate using a spin-coating method. It was found that the contact angle of coated films ranged from 100° to 120°, depending on the structure of fatty acid esters. As a part of experiments, the water-repellency of coated paper and cotton was evaluated, and it was observed that the water droplet on the film surface was not permeated for 2 weeks.

Introduction

As the industry develops, precision machinery and various industry parts have been forced to be operated under the harsh condition. For these reasons, surface modification, which gives self-cleaning property on the material surface, has been developed [1]. There are several ways to improve surface properties, which include physical treatments such as thermal treatment, plasma treatment, and electrolysis and chemical treatments such as film coating. Among chemical treatments, fluoro-resin has been widely used as a surface coating material with its water repellent and oil repellent properties due to the low surface tension and low friction coefficient [2], [3], [4]. So far, several coating materials such as a series of perfluoroalkyl acrylate polymers [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18] and fluorine modified polyurethane surface modifier [19] have been developed. Although these polymers have low surface tension as well as water- and oil-repellent properties, they showed poor solubility to the general hydrocarbon solvents. Poor long-term surface properties due to the weak bonding force between surfaces and coating materials should be overcome in order to extend their applications.

In this paper, we describe the synthesis of a series of fatty acid esters (FmHn-Ester) that are chemically stable. Fluorine groups and methylene units in molecules provide not only low friction coefficient but also better solubility to the general hydrocarbon solvents. In addition, water-repellent properties of urethane resin containing newly synthesized fatty acid esters were evaluated by measuring contact angle of water droplet onto the coated films.

The fatty acid ester, Zonyl-Ester, was also synthesized in order to compare its properties with the corresponding fatty acid ester, FmHn-Ester.

Section snippets

Materials and methods

ω-Perfluoroalkyl-1-alkanols (FmHnOH) were obtained using the method described in the literature [20]. Zonyl BA-L (F(CF2)nCH2CH2OH), stearic acid, oleic acid, linoleic acid and elaidic acid were purchased from Aldrich Chemical Co. p-Toluene sulfonic acid (p-TSA) (Junsei Chemical Co.) was used as the catalyst. 1H NMR and FT-IR spectra were recorded on a 300 MHz Brucker DPX-300 instrument and on a Jasco FT-IR 610 spectrophotometer, respectively. GC (HP 5890, HP-1 30 m column) was used to identify

Synthesis and general properties

All of the esters were prepared by esterification of fatty acid and ω-perfluoroalkyl-1-alkanols in the presence of an acid catalyst. The synthetic routes to these esters are shown in Scheme 1. The completion of esterification was ensured with the observation of new single peak on the GC, indicating fatty acid ester.

Various spectroscopic techniques were used to confirm the structures of the esters. The FT-IR spectra of F10H10OH (F(CF2)10(CH2)10OH), elaidic acid (CH3(CH2)7CHdouble bondCH(CH2)7C(double bondO)OH) and

Conclusions

For low surface energy materials, a family of fatty acid esters containing perfluoro groups was synthesized by the esterification of perfluoro alcohol and fatty acid. The solubility of fatty acid ester was found to be good for the hydrophobic solvent such as ethyl ether, toluene, ethyl acetate, chloroform, hexane, and acetone; however, it was poor for the hydrophilic solvent such as methyl and ethyl alcohols. The cmc and γcmc depended on the structure of the esters; the cmc's of Zonyl-LA,

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