N,N‐Bis(2‐hydroxyethyl)formamide as a New Plasticizer for Thermoplastic Starch

N,N‐Bis(2‐hydroxyethyl)formamide (BHF) was synthesized efficiently and used as a new plasticizer for corn starch to prepare thermoplastic starch (TPS). The hydrogen bond interaction between BHF and starch was proven by Fourier‐transform infrared (FT‐IR) spectroscopy. As detected by scanning electron microscopy (SEM), starch granules were completely disrupted and a continuous phase was obtained. The crystallinity of corn starch and BHF‐plasticized TPS (BTPS) was characterized by X‐ray diffraction (XRD). The thermal behavior of glycerol‐plasticized TPS (GTPS) and BTPS was investigated by differential scanning calorimetry (DSC). The water resistance of BTPS was better than that of GTPS. Generally, at low relative humidity (RH), the tensile strength of BTPS was higher than that of GTPS. At high RH, the elongation at break of BTPS was higher than that of GTPS.     

The Effects of Citric Acid on the Properties of Thermoplastic Starch Plasticized by Glycerol

The effects of citric acid on the properties of glycerol‐plasticized thermoplastic starch (GPTPS) were studied. In the presence of citric acid and glycerol, native cornstarch granules are transferred to a continuous phase as shown by scanning electron microscopy (SEM). As shown by thermogravimetric analysis (TGA), the improvement in thermal stability confirms that the adhesion between citric acid, glycerol, water and starch in TPS was enhanced with the addition of citric acid. It was proven by Fourier transform infrared (FTIR) spectroscopy that citric acid can form stronger hydrogen‐bond interactions with starch than glycerol. Both FTIR spectroscopy and X‐ray diffractometry of citric acid‐modified GPTPS (CATPS) revealed that citric acid can effectively inhibit starch re‐crystallization (i.e. retrogradation), because of the strong hydrogen‐bond interaction between citric acid and starch. Rheology studies revealed that citric acid can obviously decrease the shear viscosity and improve the fluidity of TPS. Citric acid can also improve the elongation of GPTPS and ameliorate the water resistance of GPTPS at high relative humidities, but decreased the tensile stress.     

Retrogradation of Ethylenebisformamide and Sorbitol Plasticized Corn Starch (ESPTPS)

Several thermoplastic starches (TPSs), i.e. ethylenebisformamide, sorbitol and ethylene‐sorbitol plasticized (EPTPS, SPTPS and ESPTPS) were prepared and their retrogradation was investigated by X‐ray diffraction, Fourier‐transform infrared spectroscopy (FT‐IR) and scanning electron microscopy (SEM). These studies revealed that the mixture of ethylenebisformamide (E) and sorbitol (S) was a good plasticizer for corn starch, restraining the retrogradation of the TPSs. The mechanical properties were also investigated of the TPSs after conditioning for 150 days at ambient atmosphere. It indicated that TPS produced by mixed plasticizer possessed better mechanical properties than TPS produced using a single plasticizer (ethylenebisformamide or sorbitol). From the analysis of X‐ray, FT‐IR and SEM data it was hypothesized that some interaction between ethylenebisformamide and sorbitol occurred, which could prevent the plasticizer form separating out of the TPS matrix. As a result, the retrogradation of ESPTPS was limited, resulting in better mechanical properties compared with those of EPTPS and SPTPS.     

Aliphatic Amidediol and Glycerol as a Mixed Plasticizer for the Preparation of Thermoplastic Starch

The synthesis of 2‐hydroxy‐N‐[2‐(2‐hydroxy‐propionylamino)‐ethyl]propionamide (“aliphatic amidediol”) is described. Aliphatic amidediol and glycerol were used as a novel mixed plasticizer for corn starch to prepare thermoplastic starch. Fourier transform infrared (FT‐IR) spectroscopy proved that the mixture of aliphatic amidediol and glycerol could form more stable and strong hydrogen bonds with starch molecules than glycerol alone. By scanning electron microscopy (SEM) and X‐ray diffraction (XRD) it was proven that native starch granules and crystalline structures were broken and starch was plasticized. Tensile testing revealed that TPS plasticized by aliphatic amidediol and glycerol (AGPTPS) showed a better mechanical properties than TPS plasticized by glycerol (GPTPS). Furthermore, the water resistance of AGPTPS was better than that of GPTPS. In addition, dynamic mechanical thermal analysis (DMTA) showed that both storage modulus and glass transition temperature (T_g) of AGPTPS were higher than those of GPTPS.     

Mechanical and Thermal Characteristics of Pea Starch Films Plasticized with Monosaccharides and Polyols

Edible starch films were produced from pea starch and various plasticizers (mannose, glucose, fructose, and glycerol and sorbitol) at the ratio of 4.34, 6.50, 8.69, and 10.87 mmol plasticizer per gram of starch. After film specimens were conditioned at 50% relative humidity, mechanical properties (tensile strength, elongation, and modulus of elasticity), water vapor permeability (WVP), moisture content, and thermomechanical properties (G’ and tan8) were determined as a function of plasticizer concentration. At all concentration levels, monosaccharides (mannose, glucose, and fructose) made the starch films stronger (higher tensile strength) and more stretchable than polyols (glycerol and sorbitol), while WVP of monosaccharide‐plasticized starch films were lower than those of polyol‐plasticized starch films, especially at higher plasticizer concentration levels. Except for 4.34 mmol/g of mannose‐plasticized film, all the other films showed similar modulus of elasticity at the same plasticizer concentration. Polyol‐plasticized films had lower T than the monosaccharide‐plasticized films. Glucose‐ and sorbitol‐plasticized films needed more activation energy to go through glass transition than others. After all, research results showed that not only the polyols but also the monosaccharides were effective in plasticizing starch films. It is concluded that molecular size, configuration, total number of functional hydroxyl group of the plasticizer as well as its compatibility of the plasticizers with the polymer could affect the interactions between the plasticizers and starch molecules, and consequently the effectiveness of plasticization.     

Effect of Plasticizers on Mechanical and Barrier Properties of Rice Starch Film

The effect of plasticizers, glycerol, sorbitol and poly(ethylene glycol) 400 (PEG 400), on mechanical and barrier properties of rice starch film has been investigated. Sorbitol‐ and glycerol‐plasticized starch films appeared homogeneous, clear, smooth, and contained less insoluble particles compared to unplasticized rice starch films. PEG 400 did not form plasticized films of suitable characteristics. The softness and stickiness of films improved with increasing concentrations of glycerol and sorbitol. In general, films plasticized with glycerol and sorbitol displayed a better solubility in water than unplasticized films, i.e. 35% (w/w) glycerol and 45% w/w (sorbitol) (optimum solubility). The tensile strength of films decreased especially in the high concentration regime of plasticizers, between 20–45% (w/w) of plasticizer/rice starch film. Through the entire concentration regime, the tensile strength of glycerol‐plasticized films was significantly lower than that of sorbitol‐plasticized films, but their elongation was larger. The water vapor transmission rate (WVTR) through plasticized films and the oxygen transmission rate (OTR) increased with glycerol and sorbitol concentrations, however, glycerol was revealed to be significantly more effective in reducing the tensile strength as well as increasing the WVTR and the OTR compared to sorbitol. With the higher tensile strength and the smaller OTR and WVTR, the 30% sorbitol‐plasticized film reveals an improved coating performance in terms of a reduction of coating failures.     

Crystallization of High-Amylose Starch by the Addition of Plasticizers at Low and Intermediate Concentrations

ABSTRACT:  The antiplasticization effect of plasticizers (that is, polyols and monosaccharides) in starch films was investigated. Pea starch films were plasticized by various polyols and monosaccharides at the levels of 0% to 25% (w/w, plasticizer/starch). After 14 d of storage at 50% relative humidity, the crystallinity of pea starch films increased with increasing concentration of plasticizers from 0% to 20%. Accordingly, moisture content, water vapor permeability, oxygen permeability, and elongation decreased with increasing plasticizer concentration from 0% to 20%, showing the antiplasticization effect. The addition of plasticizers above 20% reduced the crystallinity of starch films, consequently showing the plasticization effect. The results showed that the addition of the plasticizers facilitated the crystallization of the polymer chains through the antiplasticization phenomenon at the concentration range below 15%. Above 20%, plasticizers performed the conventional plasticization effect. Each plasticizer had different critical concentration where the antiplasticization was converted to plasticization.     

Effect of banana and plasticizer types on mechanical,water barrier,and heat sealability of plasticized banana‐based films

Unripe banana flour and starch were used to formulate plasticized banana‐based films (flour film, PBF; starch film, PBS) with two types of plasticizers (glycerol, Gly; sorbitol, Sor) and a mixture of Gly‐Sor on film properties. PBS showed greater water barrier, elongation at break, toughness, and transparency, but lower efficiency in heat sealability than PBF. However, the easier and a higher yield in the preparation process of PBF lead to higher UV and visible light barrier than PBS which could be due to its protein content and the presence of phenolic compounds in PBF. Both banana films plasticized with Sor showed high glossiness, high efficiency in heat sealability, and mechanical and water barrier properties; however, the undesirable recrystallization of white crystals resulted in lower film flexibility. Thus, Gly‐Sor was preferred without change of water barrier but strengthened heat sealability. Therefore, banana‐based film might be considered as a green food packaging material.

Practical applications

Banana flour and starch from unripe bananas can be used as safe food ingredients for food products and as green biodegradable packaging materials. Banana flour film showed similar mechanical properties as banana starch film but involved easier processing and higher yield in the preparation of banana flour. Moreover, banana flour films had higher efficiency in heat sealability with the potential to protect the packed food from UV–visible light deterioration. Furthermore, an easier way to modify proper film properties is by the proper selection of the plasticizer. A mixture of plasticizers (glycerol and sorbitol) showed high potential to improve long‐term physical stability such as through UV–visible light prevention, and improved mechanical properties and heat sealability of plasticized banana‐based films. Briefly, plasticized banana flour film with a mixture of plasticizer will be potential, alternative biodegradable packaging material to reduce the use of nonbiodegradable synthetic plastic materials in food applications.     

增塑剂对淀粉浆料性能的影响

针对淀粉浆膜脆硬,柔韧性差的缺点,将甘油、尿素、柠檬酸氢二铵等增塑剂分别以不同量加入淀粉中,并对浆膜的吸湿率、断裂强力、断裂伸长率、耐屈曲性及浆液粘附性等进行了测试分析。结果表明,使用增塑剂能改善淀粉浆膜的脆硬性能,且提高了淀粉对纯棉粗纱的粘附性;其中柠檬酸氢二铵对淀粉质量分数为1％时,对改善淀粉浆膜各项性能及纯棉粗纱粘附性的效用最大。     

Effects of Extrusion Temperature and Plasticizers on the Physical and Functional Properties of Starch Films

Cornstarch, at 20% moisture content (dry basis, d.b.), was mixed with glycerol at 3:1 ratio to form the base material for extruded starch films. Stearic acid, sucrose and urea, at varying concentrations, were tested as secondary plasticizers for the starch‐glycerol mixture. The ingredients were extruded at 110 and 120°C barrel temperatures to determine the effects of extrusion temperature, plasticizer type and their concentrations on the film‐forming characteristics of starch, as well as their effects on selected physical and functional properties of the films. The physical and mechanical properties of the films were studied by scanning electron microscopy (SEM) and tensile testing, while the glass transition and gelatinization properties were analyzed using differential scanning calorimetry (DSC). The interactions between the functional groups of starch and plasticizers were investigated using Fourier‐transform infrared (FTIR) spectroscopy. The water vapor permeability (WVP) properties of starch films were determined using ASTM standard E96‐95. Scanning electron micrographs exhibited the presence of native and partially melted starch granules in the extruded films. The tensile stress, strain at break and Young's modulus of starch films ranged from 0.9 to 3.2 MPa, 26.9 to 56.2% and 4.5 to 67.7 MPa, respectively. DSC scans displayed two glass transitions in the temperature ranges of 0.1 to 1°C and 9.6 to 12°C. Multiple melting endotherms, including that of amylose‐lipid complexes, were observed in the thermoplastic extrudates. The gelatinization enthalpies of the starch in the extruded films varied from 0 to 1.7 J/g, and were dependent largely on the extrusion temperature and plasticizer content. The shift in the FTIR spectral bands, as well as the appearance of double‐peaks, suggested strong hydrogen bonding interactions between the starch and plasticizers. The WVP of starch films ranged from 10.9 to 15.7 g mm h^‐1 m^‐2 kPa^‐1, depending on the extrusion temperature and the type of plasticizer used.     

高速混合条件下不同增塑剂对热塑性淀粉结构及性能的影响

目的:研究在一定高速混合温度下增塑剂种类对材料的结构与性能产生的影响,为今后TPS在降解材料领域的应用提供依据。方法:通过高速混合的方法制得三种不同增塑剂(甘油、甲酰胺、尿素)增塑的热塑性淀粉(TPS)样品,对保存在室温及65RH%湿度下的样品的各项性能进行测试。结果:SEM结果说明:增塑剂能在一定程度上破坏和改变淀粉颗粒的形态。XRD测试表明:甲酰胺塑化的TPS(FPTPS)和尿素塑化的TPS(UPTPS)的耐回生性能好于甘油塑化的TPS(GPTPS)。TG测试表明:三种塑化剂塑化的热塑性淀粉的热稳定性次序为甘油<甲酰胺<尿素。FTIR谱图可得出几种塑化剂与淀粉形成氢键的能力为:尿素>甲酰胺>甘油。结论:甲酰胺和尿素作为淀粉增塑剂,其塑化的热塑性淀粉的综合性能要优于甘油。     

增塑剂对高直链淀粉基生物降解薄膜力学性能的影响

以高直链玉米淀粉为原料,利用微波辐射加热工艺将淀粉糊化,通过溶液浇铸法制备淀粉基薄膜。探讨了不同增塑剂以及复合增塑剂对高直链淀粉基薄膜性能的影响。结果表明,甘油、山梨醇和木糖等增塑剂对淀粉的塑化作用是比较显著的。与单一的增塑剂相比,复合增塑剂所制备的材料的力学性能更加优良,尤其是甘油与木糖复合增塑所制备的淀粉基薄膜性能更好。     

Mechanical Properties, Water Vapor Permeabilities and Solubilities of Highly Carboxymethylated Starch-Based Edible Films

ABSTRACT: Tensile strength (TS), elongation (E), water vapor permeabilities (WVP) and solubilities were determined for highly carboxymethylated starch (HCMS)-based edible films plasticized with sorbitol (S), xylitol (X), mannitol (M) and glycerol (G). TS and E of HCMS-based film increased as the concentration of plasticizer S, M or × increased. TS of the HCMS-based film containing combined plasticizers were higher than those of films containing single plasticizer. The WVP of HCMS-based films seemed to decreased as the concentration of M, X or G plasticizer increased. Increasing plasticizer concentrations in HCMS-based film resulted in decreasing solubility of the films.     

Preparation of a Novel Thermoplastic Starch (TPS) Material using Ethylenebisformamide as the Plasticizer

In this paper, ethylenebisformamide was synthesized and used as a novel plasticizer for corn starch to prepare thermoplastic starch (EPTPS). FT‐IR spectra showed that the absorption bands of the C‐O groups of the starch molecules were shifted to lower wavenumbers, which indicated that a strong and stable hydrogen bond had been formed between ethylenebisformamide and starch. By scanning electron microscope (SEM) native individual corn starch granules were proved to transfer to a continuous phase. The crystallinity of native corn starch, GPTPS (glycerol plasticized corn starch) and EPTPS was characterized by X‐ray diffraction (XRD). Water resistance of EPTPS was better than that of GPTPS. It decreased from 50.2% for GPTPS to 37.8% for EPTPS. The mechanical analysis showed that elongation at break increased markedly, being 260% for the EPTPS containing 35% (w/w) ethylenebisformamide. Thermal stability of GPTPSs and EPTPSs was also determined by thermogravimetric analysis (TGA). The glass transition temperature T_g, as measured by dynamic mechanical thermal analysis (DMTA), of EPTPS was higher than that of GPTPS.     

Aging Effects on Sorbitol‐ and Non‐Crystallizing Sorbitol‐Plasticized Tapioca Starch Films

The effect of aging on the properties of tapioca starch films plasticized with either sorbitol (S) or non‐crystallizing sorbitol (NCS) was investigated in this study. Tapioca starch, plasticizer and deionized water were mixed, heated, cast on high‐density polyethylene plates and dried at ambient conditions. The results showed that S was more effective in plasticizing fresh starch film than NCS. However, sorbitol crystallization was observed in S‐plasticized starch film after one month of storage, while there was no crystallization observed in NCS‐plasticized starch film after two months of storage. Mechanical properties of both S‐ and NCS‐plasticized starch films changed significantly with time, but with less change in the NCS‐plasticized films. Tensile strength, elastic modulus and toughness increased over time; conversely, elongation decreased. Additionally, the water vapor transmission rate decreased as storage time increased. The fact that mechanical properties of both S‐ and NCS‐plasticized films changed is likely due to an increase in crystallinity of the starch in the films with time.     

Effect of temperature and plasticizer molecular size on moisture diffusion of plasticized‐starch biopolymer

Using starch pellets as precursor for traditional edible food packaging for making thermoformed products is an excellent idea. We report here the complex water migration behaviour of starch pellets as influenced by plasticizer type and concentration at various temperatures. The evidence for synergistic interaction between plasticizers and water within starch is shown by the reduced effective moisture diffusivities and moisture migration fluxes at different overall plasticizer concentrations. In addition, the effective moisture diffusivities showed stronger dependence on moisture concentration and the plasticizer molecular weight even though the moisture flux was comparable. The drying process was characterized by two effective diffusion coefficients (D₁, D₂) and interestingly, the coefficients were an order of significance apart. Peleg model was investigated for predicting the drying behaviour and it is shown that the Peleg constants k₁ and k₂ increase with temperature. k₂, a material structure parameter, showed variation by addition of plasticizers, indicating that plasticizers were able to modify fundamental structure; and xylitol showed greater average k₂ values than glycerol. Further, k₁, a moisture diffusivity parameter, was affected by temperature and Arrhenius relationship was used for activation energy values for k₁ of plasticized starch. It is shown that compared to starch and water, presence of plasticizer had many order of significance higher k₁ and confirm the hypothesis that plasticizers can ‘lock’ in water within the new structure. Xylitol showed better stability in controlling moisture diffusivities and migration fluxes as compared to glycerol.     

Glass-transition behaviour of plasticized starch biopolymer system – A modified Gordon–Taylor approach

Two plasticizers namely, glycerol and xylitol, based on their similar molecular size (˜6.3 Å) but different molecular weights (Glycerol-92; Xylitol-152) were selected for studying the glass-transition behaviour (rubber like behaviour) in multi-plasticized starch biopolymer with about 70% amylopectin structure. In the calorimetry measurements, glass-transition temperatures (onset temperature for bulk viscous flow) of plasticized samples were higher than non-plasticized samples at low water activities, thus showing typical antiplasticization behaviour. However, when plasticizer concentration was increased up to 15% and 20% wt, all plasticized samples showed significant reduction in glass-transition temperature. We used a modified Gordon–Taylor model to understand the competitive plasticization of glycerol and xylitol in presence of water, and suggest that competitive plasticization exists and occurs at a threshold amount of matrix free water content, due to strong three-way interactions: starch–plasticizer, plasticizer–plasticizer/water and starch–water. This competitive interaction is significant in determining the onset temperature for viscous flow behaviour; at higher matrix water content, the Gordon–Taylor constant was relatively unaffected by the plasticizer amount, and water was the dominant plasticizer. A new interaction parameter that separates the starch–plasticizer interaction in a starch–plasticizer–water system is also discussed.     

不同塑化剂对柠檬酸淀粉酯成膜性能的影响

以甘油、乙二醇、山梨醇和壳聚糖为塑化剂,机械活化柠檬酸淀粉酯为原料,以断裂伸长率为评价指标,通过SEM、FT-IR、TGA和接触角的分析,探讨不同塑化剂对淀粉酯成膜性能的影响。结果表明,不同塑化剂对淀粉酯的影响不同。不同塑化剂对淀粉酯膜的断裂伸长率影响为甘油>山梨醇>乙二醇>壳聚糖>原淀粉。添加塑化剂能使淀粉酯更好地成膜。SEM分析表明,以甘油和壳聚糖为塑化剂的淀粉酯膜具有更多网状结构,表面透气性好;以乙二醇和山梨醇为塑化剂的淀粉酯膜更为致密,表面相对光滑,气密性更好。FT-IR表明,淀粉酯膜均成功塑化且具有相同峰型,说明不同塑化剂的塑化机理基本相同。TGA显示,热分解温度与塑化剂分子大小及羟基含量存在密切关系。接触角分析表明,不同塑化剂对于淀粉酯膜的亲水性各不相同,其亲水性大小为山梨醇>甘油>壳聚糖>乙二醇。     

氨基增塑剂对淀粉浆料的增塑作用

为满足无PVA浆料配方中对淀粉增塑作用的更高要求,以浆液黏度、黏度热稳定性、黏附性及浆膜性能为评价指标,研究几种氨基化合物对淀粉浆料的增塑作用.所研究的氨基化合物包括苯胺、一乙醇胺、尿素等,通过对比实验筛选出性价比较高的淀粉浆料增塑剂,探索合理的用量.结果表明:使用增塑剂能改善淀粉浆膜脆硬的属性,提高它的断裂伸长率和耐...     

Macromolecular Changes in Extruded Starch‐Films Plasticized with Glycerol,Water and Stearic Acid

Native corn starch, plasticized with water, glycerol and stearic acid, was extruded in a conical twin‐screw extruder and sheeted into 0.4–0.6 mm thick films. The effects of extrusion and plasticizers on gelatinization, as well as the molecular and structural changes, in thermoplastic starch were analyzed. The onset and peak gelatinization temperatures of extruded starch varied from 42–46°C and 52.9–56.9°C, respectively, depending on the glycerol content. The enthalpy of gelatinization of extruded thermoplastic starch in excess water varied from 3.6–7.6 J/g, which also increased with plasticizer content. Amylose‐lipid complexes were formed during extrusion, and their enthalpies depended on the initial stearic acid and moisture contents. High‐performance size‐exclusion chromatography (HPSEC) data revealed that the starch underwent fragmentation during extrusion even under highly plasticized conditions, but the degradation was not severe as compared to previous findings. The relative percentages of amylopectin and amylose in native starch were 76.9 and 23.1%, respectively, which were changed to 71.3–76.6% and 23.4–28.7% in the extrudates. The average molecular weights of amylopectin and amylose in the extrudates ranged from 1.55×10⁷–2.07×10⁷ and 4.35×10⁵–7.39×10⁵, respectively. On the other hand, the molecular weights of amylopectin and amylose in native corn starch were observed as 2.27×10⁷ and 4.68×10⁵, respectively. Cross‐polarization magical angle spinning (CP/MAS) and high‐power decoupling (HP‐DEC) nuclear magnetic resonance (NMR) spectra of thermoplastic starch revealed the characteristics of amylomaize starch, confirming HPSEC results that the amylopectin macromolecules underwent fragmentation into amylose‐like fractions. In the extrudates, glycerol was found to be less mobile and entrained within the starch network.