## 4 Conclusions  
CMFs with good reinforcing capacity for starch films were obtained from RS, a waste material derived from the agricultural and food industry, using a green process and mechanical defibrillation. Fibrils with a major cumulative frequency of lengths below 200 \(\upmu\)m and 5-15 \(\upmu\)m of thickness were obtained. Incorporation of CMFs into starch matrices at 3 wt%, the most optimal content, led to stiffer and more resistance to break films for both non-modified and DH-modified corn starch films. Likewise, fibers at 3 and 5 wt% improved the oxygen and water vapor barrier capacity of TPS films but did not modify barrier properties of TPSDH films. Fibers interfered starch gelatinization during the starch-glycerol thermo-processing, more markedly in DH-modified starch with modified granular structure, giving rise to non-gelatinized starch granules into the film matrix. The dispersed phase (starch granules or fibers) also modified the optical properties of the TPS films, making them slightly less transparent. Therefore, it can be concluded that RS is a good source of CMFs that can be used to improve properties of starch films with different purposes, such as their use as food packaging material. This contributes to the valorization of the agricultural and food waste into added-value materials, useful for improving the  
Figure 7: Differential scanning calorimetry (DSC) thermograms taken during first heating scan of thermoplastic starch (TPS) and TPS modified by dry heating (TPSDH) films with different contents of cellulose microfibers (CMFs).  
performance of biodegradable food packaging materials. Likewise, this study further confirms that the DH process of starch represents a green physical method to enhance the water barrier capacity and tensile strength of starch films. Future studies will deal with the hydrolysis resistance of these microcomposite films and their practical application as packaging materials in food preservation.  
P.A.V.F. conceptualization, methodology, formal analysis, investigation, writing--original draft preparation, writing--review and editing: C.I.L.F.A.: conceptualization, methodology, formal analysis, investigation, data analysis; S.T.-G.: writing--original draft preparation, writing--review and editing; C.G.-M.: conceptualization, methodology, investigation, writing--original draft preparation, writing--review and editing; A.C.: conceptualization, methodology, investigation, writing--original draft preparation, writing--review and editing; A.C.: conceptualization, methodology, investigation, writing--original draft preparation, writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Spanish Ministry of Science and Innovation (MICI), grant number PID2019-105207 RB-I00.  
Not applicable.  
P.A.V.F. is grateful to Generalitat Valenciana (GVA) for the Grisolia P/2019/115 grant. C.L.F.A. acknowledges the Sao Paulo Research Foundation (FAPESP) for the Research Internships Abroad (BEPE) fellowship (2020/10498-0). [PERSON] acknowledges MICI for his Ramon y Cajal contract (RYC2019-027784-I).  
The authors declare no conflict of interest.