Different characteristic effects of ageing on starch-based films plasticised by 1-ethyl-3-methylimidazolium acetate and by glycerol

Abstract

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.

Starch–zinc complex and its reinforcement effect on starch-based materials

“…2018), poly(trimellitic glyceride) (Zhang, Cheng, Lin, Zhou, & Zhu, 2018), ionic liquids (Liu & Jin, 2016;Xie et al, 2014;Zhang et al, 2016;Zhang et al, 2017) and eutectic solvents (Magdalena & Caisa, 2017). However, these plasticizers always have their respective disadvantages such as poor stability, low efficiency, high toxicity, and high costs.…”

Effect of heat-moisture treatment on multi-scale structures and physicochemical properties of breadfruit starch

“…Based on the Woolf-Bragg's equation: d = 2π/q, the average thickness (d) of semi-crystalline lamellae is corresponding to the q position of a scattering peak can be calculated (Tan et al, 2015;Zhang et al, 2016). Fig.…”

Highly functional green materials platform: Starch-ionic liquid-carbon nanotube polymer melt nanocomposites

“…In terms of the elongation at break, RMS-A27 and RMS-B27 seem to be over-plasticized because the measurements for these samples have decreased compared to those in RH52%. These results are similar to that observed in two other studies using [Emim][OAc] as plasticiser , Zhang et al, 2016. Such a low mechanical strength may limit the material application and, hence, it is necessary to investigate methods to strengthen this material.…”

“…Such results are supported by similar studies which suggest that the decrease of thermal degradation temperature of the starch is caused by molecular weight decrease during solution processing with heat (Xie et al, 2014, Zhang et al, 2016.…”

“…In comparison, the relative humidity during conditioning of the samples, and thus the sample water content, had a predominant influence on the material properties. A high amylose content starch plasticized by [Emim][OAc] was also investigated (Zhang et al, 2016). It was shown that, compared to glycerol, [Emim][OAc] can achieve greater homogeneity and flexibility in starch-based materials because it provides stronger starch-IL interactions which weaken the starch-starch interactions.…”