Complex sentence: Cellulose is the main ingredient of textiles made from cotton, linen, and other plant fibers and into rayon, an important fiber that has been used for textiles since the beginning of the 20th century.
Split into simpler sentences: Cellulose is the main ingredient of textiles made from cotton, linen, and other plant fibers. It can be turned into rayon, an important fiber that has been used for textiles since the beginning of the 20th century.