During the lamination process, thermoplastic films of the coating 

 material are pressed onto the bare fabric as the film and fabric pass 

 through a set of rollers. The films can be applied to either or both 

 sides of the fabric in any thickness required. Adhesion of coating in 

 the lamination process depends upon the bond formed by the contact of 

 the films through the openings in the base fabric. To insure a strong 

 bond an open weave cloth is necessary. In general, laminated coatings 

 do not result in the yarns of the fabric being as well encapsulated or 

 chemically tied to the coating. Consequently, the yarns often pick up 

 moisture, oil, and bacteria which tend to degrade and discolor the 

 material. In cold climates the freezing and thawing of the moisture 

 trapped in the laminated material can cause the coating to crack and 

 separate from the substrate. 



These are the basic coating techniques in common usage. All methods 

 permit the construction of coated fabrics in a variety of thicknesses. 

 The thickness of the coating can have both good and bad effects. Thicker 

 coatings generally make for heavier, less flexible material, but also 

 result in better protection for the substrate from the elements and 

 increased service life. Like fabric weaves, many variations and combina- 

 tions of the above methods are being used. Each manufacturer of coated 

 fabrics has his own processing technique, making available a wide range 

 of charteristics, quality, and cost. 



SUBSTRATES AND COATINGS 



There are a great many different materials that can be spun or 

 drawn into yarn to serve as the basic fabric and just as many different 

 materials that can be used as coatings. The purpose of this section is 

 to discuss the relevant characteristics of many of these materials and 

 identify the more promising one. References 6 through 24 describe these 

 materials and their characteristics. 



Substrate Materials 



Substrate materials can be either manmade or natural fibers such as 

 cotton and wool. A list of fibers is shown in Table 2 with some key 

 physical and structural properties. Based on the information in Table 

 2, the following were selected as having the most suitable properties 

 for use as substrate material in coated fabrics for containment booms; 

 (1) acrylic (Orion), (2) modacrylic, (3) nylon, (4) polyethylene (low 

 and high density), (5) polypropylene, (6) polyester, and (7) glass. 

 Acetate, nytrile, saran, f luorocarbon, and wood fibers were rejected 

 because of their low strength-to-weight ratio; acrylic, modacrylic and 

 polyethylene were considered marginally acceptable. The strength-to- 

 weight ratio was calculated by dividing the tensile strength of the 

 fibers in pounds per square inch obtained from published literature 

 [6,7,8,13,18,19] by the specific gravity of the fibers. Tensile strength 

 was used rather than breaking strength because the substrate was being 

 evaluated and not a complete coated fabric. 



13 



