A study of the production of cellulose nanocrystals through subcritical water hydrolysis

• Production of cellulose nanocrystals by subcritical water hydrolysis.
• Study of the reaction conditions of the subcritical water hydrolysis of cellulose.
• The importance of the pressure in the reaction yields.

Cellulose nanocrystals (CNC) have a wide range of potential applications. For classical CNC production, amorphous cellulose is hydrolyzed using concentrated sulfuric acid; however, subcritical water can also accomplish this objective. Here, for the first time to the best of our knowledge, we study the experimental conditions employed in subcritical water treatment, to investigate the behavior of the technique and the properties of the products in an experimental domain of 120–200 °C temperature and 8.1–20.3 MPa pressure. We observed the CNC formation in all the different reaction conditions tested; however, the yields were lower than the classical production of CNC. The yield of the reaction was directly proportional to the pressure. On the other hand, temperature had a directly proportional effect on the stability of the suspension and an inversely proportional effect on the whiteness of the CNC produced. The most drastic reaction conditions produced CNCs was chemically indistinguishable from raw cellulose, having the same crystalline structure and crystallinity index, albeit with nanometric size.

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