Integrated Biobased Processes for Nanocellulose Preparation from Rice Straw Cellulose

Round 1

Reviewer 1 Report

Remarks to the Authors: 

In the manuscript, Tinoi. J. and coworkers describe an incorporated biobased process for the preparation of nanocellulose using cellulase catalyzed hydrolysis associated with green organic acid hydrolysis and ultra-sonication pretreatment. Nanocellulose with different nano-morphology, including cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), amorphous nanocellulose (ANC), cellulose microfibrils (CMFs), microcrystalline cellulose (MCC), and cellulose nanoyarn (CNY), hold great potential for the development of advanced functional materials. Considering the appealing mechanical properties, high surface area for modification, biocompatibility and biodegradability of nanocellulose, as well as the abundance of rice straw in Thailand, this manuscript reports a useful process approach for highly efficient preparation of nanocellulose from natural rice straw. From my point of view, this study highly fits the scope of Processes and will surely be of interest to a wide audience in material, chemistry, and biology. Not only the maximum nanocellulose content based on the reported combination process has been significantly improved (up to 65%), but also mild conditions, low energy cost and green organic acids could be applied in this process approach compared with the other methods, such as acid-catalysis, enzymatic hydrolysis, oxidation, and hybrid methods. Overall, the manuscript is easy to follow and the results and conclusion are sound. I recommend publication after the listed minor issues have been addressed properly.

-        Materials section, I was also unable to find out what cellulases were used and only very brief information about cellulase was mentioned. Again, this would be important information to assess the comparisons and apply this protocol. Some basic information, including source, storage form, and dosing should be added.

-        The description of “Forage Fiber Analysis” for the determination of lignocellulosic composition of raw and treated rice straw should be given.

-        In the reference list I think the authors could add more references to papers on nanocellulose fabrication and nanocellulose based functional materials. Several key references are here missing.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript is devoted to the production of nanocellulose from rice husk waste. According to the data given by the authors, it can be concluded that it is important to process this type of waste and offer methods for isolating nanocellulose from rice waste. In my opinion, the work deserves attention, but before publication, a number of issues need to be clarified and a number of corrections made. Unfortunately, the authors overlook the content of silicon in cellulose, which can reach significant values. The work contains a large number of errors and typos. I recommend that the authors round the obtained values to tenths, otherwise it is necessary to describe the reliability of the results obtained in the methodological part. Lines 21, 22. "All prepared nanocellulose represented a functional group as original cellulose" is an unfortunate expression. It is natural that if a substance contains other functional groups, then it will not be cellulose ... Line 23. "nanocellose" is a typo. Lines 31, 32. Cellulose is not extracted from bacteria, they produce it... Lines 33-35. authors should note that MCCs and CMFs that are micron in size are classified in the nano category. Line 101. A comma "cellulose hemicellulose" must be added. Table 2. The authors need to add the content of silicon in the system to the table. Line 302. How do the authors explain the close zeta potential values of -34.2 and -34.5 mV? For nanocellulose via enzymatic hydrolysis and ultrasonication-assisted pretreatment, in our opinion, the zeta potential values should have a wide distribution. 3.3.3. Functional group of Nanocellulose Structure. What crystallinity values are obtained for samples from FTIR data? Based on the 895 (900) band, one can speak of a greater misorientation in the NC_Ultra+Enz+Ox sample compared to NC_Enz, which is inconsistent with the XRD data?! Table 5. The data given in the table do not correlate with the diffraction patterns. I am very worried about the presented values of the crystallinity index for a number of samples! It is necessary to evaluate the crystallinity by other methods (not the Segal method) and compare with the results of IR spectroscopy. Figure 4. In the photographs, the quality of the scale bar needs to be improved. Lines 495, 496. "The nanocellulose suspension had colloidal stability." - did the authors evaluate the rheological properties? How does the viscosity and elastic properties of the system change?

Author Response

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Author Response File: Author Response.pdf