Ageing of rubbery thermoplastic barley and oat starches

Barley thermoplastic starch nanocomposite films reinforced with nanocellulose

Despite being one of the starch producers, barley has yet to be widely studied for thermoplastic starch applications, including nanocellulose thermoplastic composites, due to its uses in the food and beverage industries. However, only 20% of barley is used in the malting industry to produce both alcoholic and non-alcoholic beverages, and 5% is used as an ingredient in a wide variety of foods. As the fourth most important cereal in the world after wheat, corn, and rice, barley can be considered an interesting biomass source to produce biodegradable thermoplastics, stemming from its starch constitution. Therefore, this review attempts to highlight the barley starch properties and its potential utilization for nanocellulose thermoplastic starch composites. Several studies involving barley-based starch in thermoplastic production and nanocellulose reinforcement for properties enhancement are also reviewed, particularly in the attempt to provide various options to reduce and replace the uses of harmful petroleum-based plastic.

Mechanical properties of tef starch based edible films: Development and process optimization

The non-biodegradable synthetic plastic is one of the greatest challenges facing the food packaging business since it seriously harms the environment. To solve this problem, non-biodegradable plastic may be disposed of more affordably and with less harm on the environment by using edible starch-based biodegradable film. Therefore, the present study was focused on the development and optimization of tef starch based edible films based on mechanical properties. In this study response surface methodology was employed by considering 3-5g of tef starch, 0.3-0.5% of agar and 0.3-0.5% of glycerol. The prepared film showed the tensile strength of 17.97-24.25 Mpa, elongation break of 1.21-2.03%, elastic modulus of 17.58-108.69 MPa, puncture force of 2.55-15.02 N, puncture formation of 9.59-14.95 mm. The findings showed that as glycerol concentrations in the film-forming solution increased, the prepared tef starch edible films' tensile strength, elastic modulus, and puncture force declined while their elongation at break and puncture deformation increased. Tef starch edible films' mechanical characteristics, including as tensile strength, elastic modulus, and puncture force, were increased by the increase of agar concentration. The optimized (from 5 gm tef starch, 0.4 g agar and 0.3% glycerol) tef starch edible film exhibited higher tensile strength, elastic modulus, and puncture force while lower elongation at break and puncture deformation. The composite edible film based tef starch with agar exhibited good mechanical properties and can be suggested for application in food industry as food packaging.

Mechanical Behavior of Thermoplastic Starch: Rationale for the Temperature-Relative Humidity Equivalence

This paper aimed at understanding and rationalizing the influence of both temperature and relative humidity on the mechanical behavior of thermoplastic starch (TPS). DMA experiments revealed that water molecules impact the crosslinking network by reducing the intermolecular hydrogen bond density, resulting in a less dense entanglement network. In addition, the in-situ X-ray characterization during hydration of starch revealed structural changes, which were ascribed to conformational changes in the starch chain, due to their interaction with the uptake water molecules. Finally, the study of TPS uniaxially stretched at different temperatures and humidity showed that the mechanical behavior of TPS could be rationalized by considering the ΔT parameter, which corresponds to the temperature difference between the drawing temperature and the glass transition temperature of TPS.

Improving Functional Properties of Cassava Starch-Based Films by Incorporating Xanthan, Gellan, or Pullulan Gums

The effect of the partial substitution of cassava starch in edible films for 10 and 20 wt% of gellan, xanthan, or pullulan gums was analysed in films obtained by casting. The tensile properties, barrier capacity to water vapour, and oxygen and water sorption isotherms of the samples were analysed. The blend of starch with gellan gum was effective to reduce the moisture sorption capacity of starch films while reducing water vapour permeability, enhancing the film strength and resistance to break and preserving films against starch retrogradation throughout the storage time. Xanthan gum improved the tensile behaviour of the starch films, but did not reduce their water sorption capacity and water vapour permeability. Pullulan did not notably improve the functional properties of the starch films. Gellan gum at 10 and 20 wt% in the blend could be used to obtain starch films with more adequate properties for food packaging purposes.

Effect of amylose:amylopectin ratio and rice bran addition on starch films properties

The influence of the amylose:amylopectin ratio on the properties of pea, potato and cassava starch films and the effect of the incorporation of rice bran of two different particle sizes were studied. The structural, mechanical, optical and barrier properties of the films were analyzed after 1 and 5 weeks. The high content of amylose gave rise to stiffer, more resistant to fracture, but less stretchable films, with lower oxygen permeability and greater water binding capacity. Although no changes in the water vapour permeability values of the films were observed during storage, their oxygen permeability decreased. Throughout storage, films became stiffer, more resistant to break, but less stretchable. Rice bran with the smallest particles improved the elastic modulus of the films, especially in high amylose content films, but reduced the film stretchability and its barrier properties, due to the enhancement of the water binding capacity and the introduction of discontinuities.

Innovative thermoplastic chitosan obtained by thermo-mechanical mixing with polyol plasticizers

Chitosan shows a degradation temperature lower than its melting point, which prevents its development in several applications. One way to overcome this issue is the plasticization of the carbohydrate. In this work plasticized chitosan was prepared by a thermo-mechanical kneading approach. The effects of different non-volatile polyol plasticizers (glycerol, xylitol and sorbitol) were investigated. The microstructure and morphology were determined using FTIR, XRD, TEM and SEM in order to understand the plasticization mechanism. Sorbitol, which is the highest molecular weight polyol used, resulted in plasticized chitosan with the highest thermal, mechanical and rheological properties. On the other hand, the sample plasticized with glycerol, the lowest molecular weight polyol, had the most important amorphous phase content and the lowest thermal, mechanical and rheological properties. Also, when the polyol content increased in the formulation, the plasticized chitosan was more amorphous and consequently its processability easier, while its properties decreased.

Enhanced stability of rubbery amylose-rich maize starch films plasticized with a combination of sorbitol and glycerol

Well known aging problems with rubbery starch films are the migration of plasticizer and increased crystallinity leading to embrittlement. The effects of a combination of sorbitol and glycerol used as plasticizers on mechanical, moisture permeability and solid-state properties of rubbery amylose maize starch (Hylon VII) films were studied. The films were prepared by casting and were exposed to conditions of 25 degrees C/60% relative humidity (RH) and 40 degrees C/75% RH for 9 months. The starch films plasticized with a combination of sorbitol and glycerol (1:1) at equal amount to the polymer weight, were shown to be the most stable alternative of the studied films during the 9 months storage period. The water vapor transmission (WVTR) of the films did not change during the period of storage and neither did the elongation at break, but the tensile strength increased. X-ray diffraction (XRD) results showed that during storage no crystallization had occurred. The combination of sorbitol and glycerol prevented the migration of the plasticizer molecules out of the film.