Abstract
Normal and acetylated rice and waxy maize starches with a blend of nopal mucilage (Opuntia ficus-indica) and glycerol were used for the preparation of laminated and tubular films by extrusion and blown extrusion, respectively. The composition of the formulation was 70% starch (normal or acetylated), 20% glycerol, and 10% nopal mucilage ( w / w ). The degrees of substitution (DS) for acetylated rice starch (0.94) and waxy maize starch (0.76) present high potential for use as a polymeric matrix in packing materials. The use of nopal mucilage can improve the processability of extruded and tubular films by favoring the increase of some mechanical and functional properties. The films elaborated with nopal mucilage and glycerol present a homogeneous relief without breaking, adhesiveness, and contraction once formed. The elongation values of acetylated waxy maize starch films (33%) were higher than those of rice acetylated films (17%), while the blown films presented a 30% decrease in tensile strength, compared to the laminated films. Acetylation generated more hydrophobic material for the rice starch sample, which can be evidenced by a decreased solubility of the laminated films. Films of both sources of acetylated starch showed a significant decrease in water vapor permeability and showed a plasticized starch disposition-type layer without unmelted starch granules.
Highlights
The thermoplastic processing of starch has a wide application for its specified functional properties
The difference in degrees of substitution (DS) values is mainly due to the botanical source where the rice starch reported an amylose concentration (19%) and granular size (2–8 μm) different from those observed in waxy corn maize (
The crosslinking that occurs by the introduction of acetyl groups changes the absorption of water in the material, which modified the shear effect that occurs during extrusion, this effect being more pronounced depending on the conditions of the process used [22]
Summary
The thermoplastic processing of starch has a wide application for its specified functional properties. The application of different thermoplastification processes used in manufacturing synthetic polymers has been applied to the fabrication of biodegradable polymers. These processes include injection molding, extrusion blow molding, injection compression molding, and extrusion [2]. Plasticizers, such as glycerol, sorbitol, glycols, maltodextrin, urea, and surfactants, are often used to improve the mechanical properties of the film, increasing film flexibility and allowing a significant change in their barrier properties [3, 4]. The films were homogeneous with uneven surfaces and little roughness
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