Dear Abishek Pravin Manoharan, please check the following documents. My Regards

10.1039/C4NR01756K

http://dx.doi.org/10.1590/0104-1428.2413

My article and the references cited in will give you all you need to estimate the number of hydroxyl groups on the surface of CNCs (more accessible) and the ones inside (less accessible).

Here is the article: Go to section 3.1:Article On the Para/Ortho Reactivity of Isocyanate Groups during the...

The C6 hydroxyl is available for reaction but only on every other anhydroglucose unit. The C2 and C3 hydroxyl groups are involved in intra-cellulose bonding, however, there are some oxidants that will oxidize these such as periodate. The attached paper discusses methods for determining the theoretical content of carboxylic acid groups - the same equations may be used for answering your questions with some modification.