Sugar Alcohol-Based Deep Eutectic Solvents as Potato Starch Plasticizers

Abstract

The aim of this work was to prepare sugar alcohol-based deep eutectic solvents (DES) and test them as starch plasticizers. Thermoplastic starch (TPS) films were obtained via a simple and convenient thermocompression method. Influence of starch/DES premixtures conditioning (preheating, storage time) on TPS properties was investigated. TPS/sorbitol (S)-based DES exhibited similar tensile strength (TS) (8.6 MPa) but twice higher elongation at the break (ε) (33%) when compared with TPS plasticized only with S. Extra treatment, i.e., heating or prolonged storage time, facilitated starch/DES plasticizing. Starch with selected DES was also extruded and the influence of preconditioning and extrusion rotational speed were subsequently studied on thermocompressed films. Extrusion at 100 rpm led to films with TS up to ca. 10 MPa and ε up to 52%. Some differences in film samples morphology obtained via two processing methods were observed. X-ray diffractograms revealed that extruded samples exhibited a V-type peak at 18.2°, with intensity depending on plasticizer total molecular size. Applied techniques (mechanical tests, XRD, Dynamic Mechanical Analysis (DMA), FTIR-Attenuated Total Reflection (ATR), and moisture sorption) indicated that S-based DES forms stronger interactions with starch than glycerol (G) only used as conventional plasticizer, thus leading to better mechanical properties and inhibited tendency to starch recrystallization (studied up to one year).

Non-volatile conductive gels made from deep eutectic solvents and oxidised cellulose nanofibrils

“…Some works have used deep eutectic solvents as plasticisers for starch or cellulose to create conductive lms with improved mechanical properties. [20][21][22] Others have used DESs as polymerisation media, e.g. of 2-hydroxyethyl methacrylate 23,24 or poly(ethylene glycol) diacrylate, 25 to obtain eutectogels.…”

Effect of Plasticizers on Properties, Retrogradation, and Processing of Extrusion‐Obtained Thermoplastic Starch: A Review

“…However, their toxicity limits their application, [53][54][55] due to the fact that they can be precursors for the formation of carcinogenic compounds for humans such as nitrosamines and nitramines. [56] Novel plasticizers such as low transition temperature mixtures (LTTM) and glycerol and deep eutectic solvents (DES) have shown a good plasticizing effect on starch due to the fact that they exhibit less hygroscopicity, [57] can generate crosslinking with the polysaccharide, [44] and obtain more amorphous materials. [49] Studies reported by other authors have identified and made the most of the advantages offered by mixtures of different plasticizers, to the fore being glycerol-sorbitol, [7,51,58] ureaethanolamine, [59] urea-formamide, [60] and sugars-glycerol.…”

“…Although a large number of substances with which to plasticize starch have been studied, [25,41,57,[61][62][63][64] reporting good results in thermoplastic materials obtained by extrusion, much of the field awaits exploration. New plasticizers that have been tested by compression molding or casting could have great application potential using extrusion.…”

“…[70] This conditioning allows a greater diffusion of the plasticizer in the mixture, obtaining a more stable process. [57,69,72] Once the mixture has finished the conditioning period, it is extruded under the conditions of process and plasticizer content that guarantee the thermoplasticization of the starch. [73] Studies have been reported that evaluate the molecular interaction between the plasticizers and the starch to facilitate the processing of TPS by extrusion.…”

“…For example, quaternary ammonium salt combined with urea or glycols forms effective modifiers that produce flexible plastics with good mechanical properties that are comparable to some polyolefin plastics. Despite the efforts made by different researchers, [51,55,57,58,87,88] there is still a long way to go to match the properties of synthetic plastics and, above all, ensure that these properties are maintained during their useful life. This represents a wide field of study that must be approached from different perspectives, such as the type and amount of plasticizer, natural reinforcements, modifications to both starch and already proven plasticizers, co-plasticization, and new technologies, among other strategies that may be useful for this purpose.…”