title: Establishing whether the structural feature controlling the mechanical properties of starch films is molecular or crystalline.
abstract: The effects of molecular and crystalline structures on the tensile mechanical properties of thermoplastic starch (TPS) films from waxy, normal, and high-amylose maize were investigated. Starch structural variations were obtained through extrusion and hydrothermal treatment (HTT). The molecular and crystalline structures were characterized using size-exclusion chromatography and X-ray diffractometry, respectively. TPS from high-amylose maize showed higher elongation at break and tensile strength than those from normal maize and waxy maize starches when processed with 40% plasticizer. Within the same amylose content, the mechanical properties were not affected by amylopectin molecular size or the crystallinity of TPS prior to HTT. This lack of correlation between the molecular size, crystallinity and mechanical properties may be due to the dominant effect of the plasticizer on the mechanical properties. Further crystallization of normal maize TPS by HTT increased the tensile strength and Young's modulus, while decreasing the elongation at break. The results suggest that the crystallinity from the remaining ungelatinized starch granules has less significant effect on the mechanical properties than that resulting from starch recrystallization, possibly due to a stronger network from leached-out amylose surrounding the remaining starch granules.
authors.affiliation: School of Pharmacy, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China; The University of Queensland, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, Brisbane, QLD 4072, Australia.
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.affiliation: The University of Queensland, Australian Institute for Bioengineering and Nanotechnology, Brisbane, QLD 4072, Australia.
authors.forename: Fengwei
authors.initials: F
authors.lastname: Xie
authors.affiliation: The University of Queensland, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, Brisbane, QLD 4072, Australia.
authors.forename: Jovin
authors.initials: J
authors.lastname: Hasjim
authors.affiliation: The University of Queensland, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, Brisbane, QLD 4072, Australia.
authors.forename: Torsten
authors.initials: T
authors.lastname: Witt
authors.affiliation: The University of Queensland, Australian Institute for Bioengineering and Nanotechnology, Brisbane, QLD 4072, Australia; The University of Queensland, School of Chemical Engineering, Brisbane, QLD 4072, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Halley
authors.affiliation: School of Pharmacy, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China; The University of Queensland, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, Brisbane, QLD 4072, Australia. Electronic address: b.gilbert@uq.edu.au.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Gilbert
keywords: Crystallinity; Hydrothermal treatment; Mechanical properties; Molecular structure; Starch