and synthetic hydrophobic polymers, for example, vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyvinyl methyl ether; noncrosslinked polyacrylamide; polyacrylic acid and acrylic metal salts thereof; acrylic resin such as water-soluble styrene-acrylic resin; water-soluble styrene-maleic acid resin; water-soluble vinylnaphthalene-acrylic resin; water-soluble vinylnaphthalene-