# Production of Microfibrilated Cellulose from Fast-Growing
## 3 Results and Discussion
### Approaching Several Applications of the MFC Samples  
The potential of fast-growing poplar and olive tree pruning as raw materials for the production of MFC has been demonstrated, obtaining samples with similar properties to MFC produced from a commercial eucalypt pulp. For that, PFI refining as pretreatment followed by microfluidization was employed, resulting in MFC samples with low fibrillation yields but high mechanical properties and low wettability. In spite of the low nanofibrillation yields obtained for the three samples, both the micro- and the nanofibrils contained in the three suspensions could be sufficient to improve the final mechanical properties of Paper and cardboard products [61; 62]. This reinforcement effect is the result of the larger specific surface area of the micro- and nanofibers, which allow more interactions with the adjacent fibers in the fiber Paper matrix. In this sense, [PERSON] et al. [63] concluded that a high nanofibrillation yield is not necessary to improve mechanical Paper/cardboard properties. Then, they observed better mechanical properties (SCT index, tensile index, bursting index, and porosity) using microfibrillated cellulose obtained from softwood pulp by mechanical treatments (with low nanofibrillation yields between 5-19%) as reinforcement agent compared to nanofibrillated cellulose produced by TEMPO-mediated oxidation pretreatment and homogenization (with higher nanofibrillation yield of 94%). In the same way, [PERSON] et al. [32] improved the mechanical properties (breaking length, Young's modulus, tear index, and burst index) of recycled Paperboard when MFC obtained from orange tree pruning by PFI refining and microfluidization (with nanofibrillation yield of 21%) was used as a reinforcement additive. In addition, an analysis of the cost of increasing Paper properties such as breaking length reported by [PERSON] et al. [44] indicated that TEMPO-oxidized CNFs were more expensive than MFCs from mechanical pretreatment, the latter offering similar increases at lower prices. On the other hand, a possible reduction in aspect ratio (which could be related to a reduction in DP) in MFC samples could also be of special interest for their use as reinforcement agents in polymeric matrices [64].  
In addition, the films produced from the three MFC samples showed interesting mechanical properties, one of the main requirements for Packaging applications [46]. The strength values of the resulting films are comparable to previous microfibrillated cellulose films with suitable mechanical properties (tensile index of 146 Nm g\({}^{-1}\) and elongation at break of 8.6%) for Packaging [53]. Together with the mechanical properties, barrier properties to gases such as oxygen are also important in Packaging applications [54]. The high crystallinity of the three mechanical MFC samples as well as the low wettability could also suggest good barrier properties of the resulting films. In this sense, [PERSON] et al. [65] emphasized that high crystallinity of polymers improves barrier properties. Moreover, when the relative humidity increases, an important reduction in barrier properties was detected due to the adsorption of water and film swelling [66]. Then, a low wettability of films would prevent this decrease in barrier properties at high relative humidity. Finally, the high opacity determined in the three MFC films could lead to an improvement in the film barrier to UV and visible light, increasing the products shelf-life that can be altered by these radiations [67; 68].  
Nevertheless, the hypotheses are only discussed with regard to their possible applications based on the properties described for the obtained MFC samples, which would have to be tested in future works.