Understanding the structural disorganization of starch in water-ionic liquid solutions

Using synchrotron X-ray scattering analyses and Fourier transform infrared spectroscopy, this work provides insights into the solvent effects of water : [C2mim][OAc] solutions on the disorganization of a starch semi-crystalline structure. When a certain ratio (10.2 : 1 mol/mol) of water : [C2mim][OAc] solution is used, the preferential hydrogen bonding between starch hydroxyls and [OAc]− anions results in the breakage of the hydrogen bonding network of starch and thus the disruption of starch lamellae. This greatly facilitates the disorganization of starch, which occurs much easier than in pure water. In contrast, when 90.8 : 1 (mol/mol) water : [C2mim][OAc] solution is used, the interactions between [OAc]− anions and water suppress the solvent effects on starch, thereby making the disorganization of starch less easy than in pure water. All these differences can be shown by changes in the lamellar and fractal structures: firstly, a preferable increase in the thickness of the crystalline lamellae rather than that of the amorphous lamellae causes an overall increase in the thickness of the semi-crystalline lamellae; then, the amorphous lamellae start to decrease probably due to the out-phasing of starch molecules from them; this forms a fractal gel on a larger scale (than the lamellae) which gradually decreases to a stable value as the temperature increases further. It is noteworthy that these changes occur at temperatures far below the transition temperature that is thermally detectable as is normally described. This hints to our future work that using certain aqueous ionic liquids for destructuration of the starch semi-crystalline structure is the key to realize green processes to obtain homogeneous amorphous materials

Characteristics of starch-based films with different amylose contents plasticised by 1-ethyl-3-methylimidazolium acetate

Starch-based films plasticised by an ionic liquid, 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]), were prepared by a simple compression moulding process, facilitated by the strong plasticisation effect of [Emim][OAc]. The effects of amylose content of starch (regular vs. high-amylose maize) and relative humidity (RH) during ageing of the samples on a range of structural and material characteristics were investigated. Surprisingly, plasticisation by [Emim][OAc] made the effect of amylose content insignificant, contrary to most previous studies when other plasticisers were used. In other words, [Emim][OAc] changed the underlying mechanism responsible for mechanical properties from the entanglement of starch macromolecules (mainly amylose), which has been reported as a main responsible factor previously. The crystallinity of the plasticised starch samples was low and thus was unlikely to have a major contribution to the material characteristics, although the amylose content impacted on the crystalline structure and the mobility of amorphous parts in the samples to some extent. Therefore, RH conditioning and thus the sample water content was the major factor influencing the mechanical properties, glass transition temperature, and electrical conductivity of the starch films. This suggests the potential application of ionic liquid-plasticised starch materials in areas where the control of properties by environmental RH is desired

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

Facile preparation of starch-based electroconductive films with ionic liquid

Here, we discovered that starch could be straightforwardly processed into optically-transparent electroconductive films, by compression molding at a relatively mild temperature (55 °C or 65 °C), much lower than those commonly used in biopolymer melt processing (typically over 150 °C). Such significantly-reduced processing temperature was achieved with the use of an ionic liquid plasticizer, 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]). A higher [C2mim][OAc] content, lower processing temperature (55 °C), and/or higher relative humidity (RH) (75%) during the sample post-processing conditioning, suppressed the crystallinity of the processed material. The original A-type crystalline structure of starch was eliminated, although small amounts of B-type and V-type crystals were formed subsequently. The starch crystallinity could be linked to the mechanical properties of the films. Moreover, the processing destroyed the original lamellar structure of starch, and the amorphous starch processed with [C2mim][OAc]/water could aggregate on the nanoscale. The films displayed excellent electrical conductivity (> 10−3 S/cm), which was higher with a lower processing temperature (55 °C) and a higher conditioning RH (75%). The incorporation of [C2mim][OAc] reduced the thermal decomposition temperature of starch by 30 °K, while the formulation and processing conditions did not affect the film thermal stability

Study of tensile yielding of isotactic polypropylene

The yielding behavior of isotactic polypropylene (iPP) sheets prepared by hot pressing was studied by tensile testing. The corresponding microstructural changes in the specimens after testing were investigated by image analysis, optical microscopy (OM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The yielding of iPP was found to follow a two‐process Eyring yielding model. In the necked regions, stress‐whitening occurred only in specimens tested over a certain range of strain rates and temperatures. The occurrence of the stress‐whitening was correlated well with the activation of Process II in the two‐process Eyring model. SEM revealed that the stress‐whitening in the necked regions was associated with the formation of craze‐like structures that were parallel to the loading direction. Furthermore, DSC analysis showed that the necked regions of the unwhitened tensile specimens had an additional low‐temperature melting peak. However, no additional melting peaks were found in the stress‐whitened specimens. © 1994 John Wiley & Sons, Inc

Tensile yielding and microstructures of blends of isotactic polypropylene and linear low-density polyethylene

Thin sheets of isotactic polypropylene (iPP) and linear low‐density polyethylene (LLDPE) blends were studied by tensile testing, optical microscopy (OM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Eyring's two‐process yielding theory was used to analyze the data of yield stress as a function of strain rate and temperature, and satisfactory curve‐fitting results were obtained. Furthermore, stress whitening was found to have occurred in the necked regions of tensile specimens under a certain range of yielding conditions. These conditions corresponded to the activation of Process II yielding of Eyring's theory. The whitening was found to be a result of formation of microvoids that initiated at the interface between iPP and LLDPE. © 1995 John Wiley & Sons, Inc

Quantitative surface analysis of hemp fibers using XPS, conventional and low voltage in-lens SEM

Surfaces of hemp fibers with different treatments: (1) as received; (2) water washed; and (3) treated with NaOH, were examined using a combination of conventional Scanning Electron Microscopy (SEM), lignin staining and a novel low voltage in-lens detector SEM technique which provides compositional contrast between polymeric materials on the surface. Surface composition determined using quantitative X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS) showed that the surfaces of the as received fibers and the water washed fibers were predominantly lignin and extractives and only after NaOH treatments was there sufficient oxygen on the surface to allow for the presence of polysaccharides. Using the in-lens backscattered SEM technique, spatial distribution of polymeric materials on the surface was shown to be highly non-uniform. The findings have implications for design of natural fiber composites and the interfacial properties between fiber and matrix

Characterization of stress-whitening of tensile yielded isotactic polypropylene

The microstructure of tensile tested isotactic polypropylene (iPP) specimens was studied by grey level measurement, scanning electron microscopy (SEM), differential scanning calorimetry (d.s.c.) and X-ray diffraction (XRD). SEM revealed that the necked regions of specimens in which stress-whitening had occurred as determined by the grey level measurement had craze-like structures which were parallel to the drawing direction. D.s.c. analysis showed that the necked regions of tensile specimens which remained transparent after yielding had an additional low-melting temperature peak. However, no additional melting peaks were found in the stress-whitened specimens. Inspection of the XRD patterns indicated that, apart from its original α-crystallites (a monoclinic structure) which were broken and reoriented after drawing, there was no new types of crystals formed in the transparent specimens. It was found by quantitative XRD analysis that the crystallites were broken into finer pieces in the whitened specimens than in the transparent ones

The molecular arrangement of Bifenthrin (R) in ether based polyurethane: Designing a synthetic termite barrier

An ether based polyurethane (EPU) was blended with a synthetic pyrethroid, Bifenthrin (R), to produce a material for potential use as a termite barrier for timber structures. FTIR was used to investigate the interaction between the active component and the polymer; whereas distribution of the active was probed using X-ray photoelectron spectroscopy. The aromatic end of the Bifenthrin molecule was found to interact with the hard segments of the EPU, whereas the active end of the Bifenthrin (R) molecule was found to be concentrated at the surface of the blend. The efficacy of the blends was demonstrated to induce high mortality rates when the blend was directly tested against termites. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1635-1639, 201