Cellulose Nanocrystals from Fibers of Macauba (Acrocomia Aculeata) and Gravata (Bromelia Balansae) from Brazilian Pantanal.

Ana Carolina Corrêa,José Alexandre Simão,Vitor Brait Carmona,José Manoel Marconcini,Fabio Galvani,Luiz Henrique Capparelli Mattoso

doi:10.3390/polym11111785

Ana Carolina Corrêa, José Alexandre Simão + Show 4 more

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https://doi.org/10.3390/polym11111785

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Abstract

Cellulose nanocrystals (CNC) were obtained from macauba and gravata fibers. Macauba (or Bocaiuva) is a palm tree found throughout most of Brazil and Gravata is an abundant kind of bromelia with 1–2m long leaves, found in Brazilian Pantanal and Cerrado. The raw fibers of both fibers were mercerized with NaOH solutions and bleached; they were then submitted to acid hydrolysis using H2SO4 at 45 °C, varying the hydrolysis time from 15 up to 75 min. The fibers were analyzed by X-ray diffraction (XRD), FTIR Spectroscopy, scanning electron microscopy (SEM) and thermal stability by thermogravimetric analysis (TG). XRD patterns did not present changes in the crystal structure of cellulose after mercerization, but it was observed a decrease of hemicellulose and lignin contents, and consequently an increase of cellulose content with the increase of NaOH solution concentration in the mercerization. After acid hydrolysis, the cellulose nanocrystals (CNC) were also analyzed by transmission electron microscopy (TEM) which showed an acicular or rod-like aspect and nanometric dimensions of CNC from both fibers, but the higher values of aspect ratio (L/D) were found on CNC obtained from gravata after 45 min of acid hydrolysis. The mercerization and subsequent bleaching of fibers influenced the crystallinity index and thermal stability of the resulting CNC, but their properties are mainly influenced by the hydrolysis time, i. e., there is an increase in crystallinity and thermal stability up to 45 min of hydrolysis, after this time, both properties decrease, probably due to the cellulose degradation by the sulfuric acid.

Highlights

Cellulose is a natural semi-crystalline polymer consisting of glucose repeating units bounded by β-1,4-glycosidic bonds; it can be produced and obtained from plants, bacteria and even some animals [1,2]
As the objective is to obtain cellulose nanocrystals, pre-treatments of mercerization and bleaching of the gravata and macauba fibers were carried out in order to extract the highest amount of hemicelluloses and lignin
Cellulose nanocrystals were extracted from macauba and gravata fibers successfully for the first time

Summary

Introduction

Cellulose is a natural semi-crystalline polymer consisting of glucose repeating units bounded by β-1,4-glycosidic bonds; it can be produced and obtained from plants, bacteria and even some animals [1,2]. Cellulose nanocrystals (CNC) are rod-like and highly crystalline materials with diameters in the range of 5–70 nm and lenghs from 100nm up to a few microns. CNC can be obtained by the acid hydrolisis of high content semi-crystalline cellulose materials, such as vegetable fibers [3]. CNC are produced by the crystalline fraction exposure of cellulose fibers to strong acid hydrolysis. The chemical process starts with the removal of superficial polysaccharides followed by cleavage and destruction of amorphous fractions of cellulose. The acid solution must be Polymers 2019, 11, 1785; doi:10.3390/polym11111785 www.mdpi.com/journal/polymers

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