Xylan (/ˈzaɪlæn/;[3] /ˈzaɪlən/[4]) (CAS number: 9014-63-5) is a hemicellulose, a polysaccharide mainly composed of xylose residues. It is present in secondary cell walls of plants, dicots and all cell walls of grasses. [5] Xylan is the third most abundant biopolymer on Earth, after cellulose and chi