Cotton is a proper noun or common noun?

Answer 1

The noun 'cotton' is a common noun, a general word for any cotton in any form.

A proper noun is the name of a specific person, place, thing, or a title; for example:

• Dr. J. Cotton Shallcross, Jr., Internal Medicine and Gastroenterology, Birmingham, AL
• Cotton, MN 55724
• Cotton Hill Studios (production company), Albany, NY
• National Cotton Council of America, Washington, DC
• "27 Wagons Full of Cotton", a play by Tennessee Williams

Answer 2

Words don't have abstract nouns words are nouns - abstract or concrete.

Cotton is a concrete noun.

A2. But the word you seek may be plant, fibre, or textile.