17885
Due to hydrogen bonding between their surface hydroxyl groups , unmodified CNCs ( H - CNCs ) aggregate easily and are often difficult to disperse .
 Chemical: hydrogen; Chemical: hydroxyl
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: hydrogen; Chemical: hydroxyl