Abstract
Nowadays, the interest on nanofibrillated cellulose (CNF) has increased owing to its sustainability and its capacity to improve mechanical and barrier properties of polymeric films. Moreover, this filler shows some drawbacks related with its high capacity to form aggregates, hindering its dispersion in the matrix. In this work, an improved procedure to optimize the dispersability of CNF in a thermoplastic starch was put forward. On the one hand, CNF needs a hydrophilic dispersant to be included in the matrix, and on the other, starch needs a hydrophilic plasticizer to obtain a thermoformable material. Glycerol was used to fulfil both targets at once. CNF was predispersed in the plasticizer before nanofibrillation and later on was included into starch, obtaining thin films. The tensile strength of these CNF–starch composite films was 60% higher than the plain thermoplastic starch at a very low 0.36% w/w percentage of CNF. The films showed a noticeable correlation between water uptake, and temperature and humidity. Regarding permeability, a ca. 55% oxygen and water vapor permeability drop was found by nanofiller loading. The hydrolytic susceptibility of the composite was confirmed, being similar to that of the thermoplastic starch.
Highlights
Nowadays, the interest in natural resources to produce natural, renewable, and environmentally friendlier materials has increased
(98% purity, Sigma Aldrich, Madrid, Spain) used as catalyst, sodium bromide (NaBr, ≥99% purity), sodium hypochlorite (NaClO, 5% w/w of chlorine), and sodium hydroxide (NaOH, 98% purity), all supplied by Scharlau, Barcelona, Spain, were the reactants used in the tetramethylpiperidine 1-oxyl (TEMPO)-mediated oxidation
Pre-treatment of Bleached eucalyptus pulp (BEP) fibers: BEP fibers were pre-treated using an oxidation process catalyzed by TEMPO [27]
Summary
The interest in natural resources to produce natural, renewable, and environmentally friendlier materials has increased This social trend has promoted the enhancement of research related to the study of nanoscale products derived from cellulose nanofibers. Among these materials, nanofibrillated cellulose (CNF), together with cellulose nanocrystals (CNCs), are among the most relevant. Aside from the abovementioned environmental criteria, CNF’s intrinsic characteristics—high water uptake capacity, high strength, insolubility in common solvents, and low gas permeability rates—increase the interest in such reinforcements. Hybrid systems based on CNF together with other inorganic compounds, such as graphene [13,14], calcium carbonate [15], or even magnetic particles [16], Polymers 2020, 12, 1071; doi:10.3390/polym12051071 www.mdpi.com/journal/polymers
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