Cellulose nanostructured films from pretreated açaí mesocarp fibers: physical, barrier, and tensile performance

ABSTRACT

Background:

During de-pulping of açai (Euterpe oleracea) for juice production in the Amazonia, large amounts of fibrous waste are daily discarded, a promising substrate for production of high-value cellulose nanofibrils. Therefore, this study sought to evaluate the modifications of açai surface fibers submitted to chemical pretreatment steps and compare the quality of nanostructured films produced with different cycles of mechanical nanofibrillation.

Results:

A 2-hour pretreatment (at 5% of NaOH) followed by two NaOH/H₂O₂ bleaching steps resulted in fibers with increased length and reduced diameter compared to raw fibers while preserving fiber integrity and cellulose I structure. The increase of fibers’ grinding cycles from 3 (minimum to gel point) to 21 (maximum suspension thickness) resulted in nanofibril films with higher crystallinity properties, uniform thickness, compacted morphology, and smoother surface. Nanofibril films formed after different numbers of passages exhibited similar mechanical strength, but distinct barrier properties.

Conclusion:

Açaí waste films produced with fibers submitted to 3 grinding cycles can be recommended for packaging applications that demand easily dissolving, such as instantaneous food. Oppositely, açaí fibers subjected to 21 cycles in grinder provide films suitable for water-resistant packaging, ideal for secondary coatings of papers and paperboards.

Keywords:
Alkaline pretreatment; Bleaching steps; Crystalline index; Barrier properties; Packaging

HIGHLIGHTS

Açaí waste contains short and handily removable lignocellulosic fibers.

Pretreatments raise crystalline index, individualize and clean açaí fibers.

3-grinder-passages nanofibrils form films applicable for easily dissolving packaging.

21-grinder-passages nanofibrils form films applicable for barrier resistant packaging.