Different characteristic effects of ageing on starch-based films plasticised by 1-ethyl-3-methylimidazolium acetate and by glycerol.
The focus of this study was on the effects of plasticisers (the ionic liquid 1-ethyl-3-methylimidazolium acetate, or [Emim][OAc]; and glycerol) on the changes of starch structure on multiple length scales, and the variation in properties of plasticised starch-based films, during ageing. The films were prepared by a simple melt compression moulding process, followed by storage at different relative humidity (RH) environments. Compared with glycerol, [Emim][OAc] could result in greater homogeneity in [Emim][OAc]-plasticised starch-based films (no gel-like aggregates and less molecular order (crystallites) on the nano-scale). Besides, much weaker starch-starch interactions but stronger starch-[Emim][OAc] interactions at the molecular level led to reduced strength and stiffness but increased flexibility of the films. More importantly, [Emim][OAc] (especially at high content) was revealed to more effectively maintain the plasticised state during ageing than glycerol: the densification (especially in the amorphous regions) was suppressed; and the structural characteristics especially on the nano-scale were stabilised (especially at a high RH), presumably due to the suppressed starch molecular interactions by [Emim][OAc] as confirmed by Raman spectroscopy. Such behaviour contributed to stabilised mechanical properties. Nonetheless, the crystallinity and thermal stability of starch-based films with both plasticisers were much less affected by ageing and moisture uptake during storage (42 days), but mostly depended on the plasticiser type and content. As starch is a typical semi-crystalline bio-polymer containing abundant hydroxyl groups and strong hydrogen bonding, the findings here could also be significant in creating materials from other similar biopolymers with tailored sensitivity and properties to the environment.
Ministry of Education Engineering Research Center of Starch & Protein Processing, Guangdong Province Key Laboratory for Green Processing of Natural Products and Product Safety, College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, China; Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld 4072, Australia; College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China.
Binjia
B
Zhang
Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld 4072, Australia; School of Chemical Engineering, The University of Queensland, Brisbane, Qld 4072, Australia. Electronic address: f.xie@uq.edu.au.
Fengwei
F
Xie
Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld 4072, Australia; School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia.
Tianlong
T
Zhang
Ministry of Education Engineering Research Center of Starch & Protein Processing, Guangdong Province Key Laboratory for Green Processing of Natural Products and Product Safety, College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, China. Electronic address: felchen@scut.edu.cn.
Ling
L
Chen
Ministry of Education Engineering Research Center of Starch & Protein Processing, Guangdong Province Key Laboratory for Green Processing of Natural Products and Product Safety, College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, China.
Xiaoxi
X
Li
School of Chemical Engineering, The University of Queensland, Brisbane, Qld 4072, Australia.
Rowan W
RW
Truss
Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld 4072, Australia; School of Chemical Engineering, The University of Queensland, Brisbane, Qld 4072, Australia.
Peter J
PJ
Halley
The University of Alabama, Tuscaloosa, AL 35487, USA; 525 Solutions, Inc., 720 2nd Street, Tuscaloosa, AL 35401, USA.
Julia L
JL
Shamshina
International Institute for Nanocomposites Manufacturing (IINM), WMG, University of Warwick, CV4 7AL, UK.
Tony
T
McNally
The University of Alabama, Tuscaloosa, AL 35487, USA; Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, QC H3A 0B8, Canada.
Robin D
RD
Rogers
D005990:Glycerol / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D010968:Plasticizers / Q000737:chemistry; D013213:Starch / Q000737:chemistry* / Q000378:metabolism*; D013997:Time Factors
D007093:Imidazoles; D010968:Plasticizers; D013213:Starch; D005990:Glycerol; C518739:1-ethyl-3-methylimidazolium
1-Ethyl-3-methylimidazolium acetate; 1-Ethyl-3-methylimidazolium acetate (PubChem CID: 11658353); Ageing; Glycerol (PubChem CID: 753); Ionic liquid; Plasticizer; Relative humidity; Starch (PubChem CID: 24836924); Starch-based materials; Water (PubChem CID: 962)