6396
Also , the presence of structural defects in the system will stiffen the system upon low strain , but reduces the elastic limit from more than 20 % strain for pristine graphene to less than 10 % strain when defects are present .
 Chemical: pristine graphene
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: pristine graphene