Hydroxypropylation improves film properties of high amylose corn starch

• Brittleness of high amylose corn starch film reduced by hydroxypropylation.
• Optimal hydroxypropylation of starch occurred with propylene oxide (PO) at 6% starch weight basis.
• Films with more PO and plasticizer produced more flexible but weaker films.
• Integrity and mechanical properties of film improved by adding glycerol of 15–20% (w/w).

Important characteristics of solvent-cast films prepared with modified high amylose corn starch were compared. The hydroxypropylation of high amylose corn starch with propylene oxide at 3–12% (w/w starch basis) and glycerol as plasticizer reduced film brittleness. Increasingly intact and transparent films with higher elongation at break (E) were obtained with higher concentrations of propylene oxide- E increased from 37.55 to 63.37% for 3 and 12% propylene oxide, respectively. However, corresponding tensile strength (TS) of the films decreased from 15.98 MPa to 8.85 MPa. Plasticizer types (glycerol, sorbitol, xylitol, and mixtures of glycerol/sorbitol or glycerol/xylitol) and contents (10–25%, w/w of starch) strongly affected the film formation and characteristics of hydroxypropylated high amylose corn starch. The hydroxypropylation with 6% (w/w) propylene oxide (6HPHACS) and 20% (w/w) glycerol resulted in optimal cast-films, based on both appearance and mechanical properties. These films exhibited better flexibility with adequate tensile strength and water vapor permeability.