Gradually modified fibers of Yucca Filifera (Asparagaceae) as biodegradable and mechanical reinforcement of polypropylene composites

Abstract

The preparation and characterization of Yucca Filifera (Asparagaceae) fibers (YFF) and their incorporation into polypropylene (PP) matrices of two molecular weights are reported. Apart from the fibers sectioning and dehydration, saponates, phenols, hemicellulose, and lignin were systematically extracted. Moisture was a primary factor in the as-sectioned samples, and dehydration was followed by volatiles extraction, including saponates and phenols. An optimized mixture of alcohols (80% methanol/20% ethanol v/v) was used to extract the remaining volatiles (adsorbed water, phenols, and saponates). The dried fibers were then cyclically treated in an autoclave using a dilute sodium hydroxide (NaOH) with the purpose of decreasing external lignin and hemicellulose. After extractions, the fiber product was directly incorporated into PP of two molecular weights, film/fiber (PP35) and injection molding (PP11) grades. The average crystallization temperatures from the melt increased slightly in the presence of YFF as an indication of heterogeneous nucleation. Although the crystallization degree decreased perceptibly depending on the fiber content. The apparent viscosity measurements as a function of shear rate, at low fiber concentrations (10 wt%), displayed partial compatibility between the treated YFF and PP11. In contrast, high fiber concentrations (30 wt%) in PP35 showed only a range of partial compatibility at high shear rates. Mechanical elongation and bending demonstrated an increase in the corresponding moduli as an indication of fiber reinforcement with a biodegradable additive. The higher tensile modulus was obtained at the expense of mechanical deformation. Highlights: A desert plant fiber works as reinforcement for PP composites. The fibers preparation extracts saponates, phenols, and partially lignin and hemicellulose. Fibers are heterogeneous enough for compatibility with the PP matrices. Fibers mechanically reinforced PP in proportion to their concentration. Reinforcement depends on the molecular weight of the PP matrix.