3.2.3. SEM Results

The SEM analysis disclosed the morphologies of the cross-section and surface of the ubim fiber as shown in Figure 5. The analyzed characteristics reveal the existence of an irregular rough surface, which can contribute to the mechanical interlock between the fiber and the matrix. In Figure 5a,b, one should notice this heterogeneous surface.

The measurement of the diameter of a random fiber is also shown in Figure 5a at a magnification (300×). Figure 5c–e show, with higher magnification, details of the cross section of the ubim fiber.

One should see in Figure 5f a polygonal lumen channel, which is associated with a greater amount of porosity. These characteristics are similar to those observed by other authors [47,48], such as rough surface, defects, flaws and irregularities along the length of the fiber.

The measurement of the diameter of a random fiber is also shown in Figure 5a at a magnification (300x). Figure 5c–e show, with higher magnification, details of the cross

One should see in Figure 5f a polygonal lumen channel, which is associated with a greater amount of porosity. These characteristics are similar to those observed by other authors [47,48], such as rough surface, defects, flaws and irregularities along the length of

**Figure 5.** Surface morphology of ubim fiber: (**a**) fiber cross-section; with increasing magnification: (**b**) 300x; (**c**) 2400x; (**d**) 600x; (**e**) 1,200x and (**f**) polygonal lumen channels. **Figure 5.** Surface morphology of ubim fiber: (**a**) fiber cross-section; with increasing magnification: (**b**) 300x; (**c**) 2400x; (**d**) 600x; (**e**) 1,200x and (**f**) polygonal lumen channels.

#### **4. Summary and Conclusions 4. Summary and Conclusions**

section of the ubim fiber.

the fiber.

A preliminary investigation on the physical properties of the ubim fibers extracted from the stem of the Brazilian Amazon plant, scientifically known as *Geonoma baculifera*, A preliminary investigation on the physical properties of the ubim fibers extracted from the stem of the Brazilian Amazon plant, scientifically known as *Geonoma baculifera*, revealed characteristics supporting a possible reinforcement of novel epoxy composites;

revealed characteristics supporting a possible reinforcement of novel epoxy composites; • Densities measured by the geometric method from 0.955 to 0.440 g/cm3 and analyzed by the Weibull statistical method revealed a tendency to decrease with increasing fiber cross-section dimensions, from 510 to 620 µm. After using the Archimedes' technique, the density showed a mean value of 0.73 g/cm3, quite similar to the 0.70 g/cm3 that was found after using the geometric method, which are among the lowest reported so far for natural lignocellulosic fibers. By the gas pycnometry method the • Densities measured by the geometric method from 0.955 to 0.440 g/cm<sup>3</sup> and analyzed by the Weibull statistical method revealed a tendency to decrease with increasing fiber cross-section dimensions, from 510 to 620 µm. After using the Archimedes' technique, the density showed a mean value of 0.73 g/cm<sup>3</sup> , quite similar to the 0.70 g/cm<sup>3</sup> that was found after using the geometric method, which are among the lowest reported so far for natural lignocellulosic fibers. By the gas pycnometry method the density was found as 1.86 <sup>±</sup> 0.26 g/cm<sup>3</sup> due to the exclusion of the porosity by the helium gas, but consistent with other NLF and pure cellulose with ~1.60 g/cm<sup>3</sup> .


**Author Contributions:** Conceptualization, S.N.M. and B.Z.M.; methodology, B.Z.M., M.S.O., W.B.A.B., V.S.C.; formal analysis, B.Z.M. and M.S.O.; resources, B.Z.M. and M.S.O.; data curation, M.S.O. and W.B.A.B.; writing—original draft preparation, B.Z.M. and M.S.O.; writing—review and editing, B.Z.M., M.S.O., W.B.A.B., T.G.d.S., A.C.R.d.S. and V.S.C.; supervision, S.N.M.; project administration, S.N.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors acknowledge the support to this investigation by the brazilian agencies: Conselho Nacional de Desenvolvimento, CNPq; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES; and Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro, FAPERJ (process E-26/202.286/2018).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
