Sheet-extruded films from blends of hydroxypropylated and native corn starches, and their characterization]

摘要

Sheet-extruded films from the blends of hydroxypropylated normal corn starch (HP) and native normal corn starch (NS) at weight ratios of 100:0, 90:10, 70:30, 50:50, 30:70, and 0:100 were prepared and characterized. Glycerol and water were added as plasticizers at 11 and 27% starch weight, respectively. The highest tensile strength (TS) and longest elongation to break (EB) for dry films were observed at 70:30 HP: NS ratio, which was 25.76 MPa, and 3.97%, respectively. However, TS and EB of this 70:30 blend extruded starch film exhibited low resistance upon wetting for 10s. The film TS and EB were reduced to 13.26 MPa and 3.35%, respectively. Addition of 0.5% (wt/wt starch) succinic acid (SA) as a cross-linker to 70:30 HP: NS starch blend before film extrusion positively affected both TS and EB of films upon wetting; rather higher TS (16.64 MPa) and EB (4.85%) values were observed, which indicated improvement in water resistance of the films. Sheet-extruded films from 70:30 HP: NS blends resulted in improved dry strength, and upon cross-linking with SA, improved wet strength as well. The films had smooth and compact structure, which was explained by esterification/transesterification reactions promoted by SA, and confirmed by Fourier-transform infrared spectroscopy analysis.Practical Applications Manufacturing packaging films from biological sources, as well as coating materials, would be beneficial to the environment along with wider applications. Biobased packaging materials include both edible coatings and edible films along with primary and secondary packaging materials, and could also have non-food applications. They are derived from renewable sources and are potentially biodegradable through composting (which is a technique for waste management). Hydroxypropylation of starch results in wider functionality, and sheet-extrusion can result in more flexible and transparent films. Blends of 70:30 HP: NS resulted in stronger sheet-extruded films; testing of both dry and wet strengths of films indicated its suitability for both as edible coating (wet application), and other dry coatings/ films. These blend film can be an alternative to synthetic packaging films within their limitations.