Synthesis and characterization of starch-modified polyurethane

Corn starch was reacted with urethane prepolymer in order to modifying starch and preparing new hydrophobic copolymers. These copolymers were prepared by two-step reactions. The polycaprolactone terminated hexamethylene diisocyanate (HDI) (as prepolymer) was prepared by introducing diisocyanate on both ends of PCL at a molar ratio of 1:2 (PCL:HDI). The grafting was performed by addition of polycaprolactone based prepolymer to starch solution of DMSO with different weight ratio of starch and prepolymer. The samples were characterized and examined by FTIR and ¹H NMR spectroscopy, DSC analysis, and scanning electron microscopy (SEM). By introducing NCO groups onto the PCL terminals, the FTIR spectrum shows a new sharp peak, representing the NCO groups and formation of prepolymer. By grafting this prepolymer onto starch a NH and urethane band were appeared. The effect of prepolymer percentage on hydrophobicity was measured through contact angle and it was found that increases with increasing amount of prepolymer. Glass transition temperature (T_g) is also affected with increasing amount of urethane linkages. Surface morphology of modified starch was studied by SEM. It was observed that the surfaces of modified starch are rougher and disordered than the surface of unmodified starch particles. This confirms the grafting and modification of starch. This modified starch can be used as filler in biodegradable starch based polymers.     

Selected morphological and functional properties of extruded acetylated starch-cellulose foams

Starch acetates with degrees of substitution (DS) of 1.68 and 2.3 were extruded with 10%, 20% and 30% (w/w) cellulose and 20% (w/w) ethanol in a twin screw extruder at 150, 160 and 170 degrees C barrel temperatures and 170, 200 and 230 rpm screw speeds. X-ray diffractogram (XRD), differential scanning calormetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the morphological properties of extruded foams. A central composite response surface design was applied to analyze the effects of starch type, cellulose content, barrel temperature and screw speed on specific mechanical energy requirement of extruding foams and the radial expansion ratio and compressibility of the extruded foams. XRD showed losses of DS starch and cellulose crystallinity and the formation of new complexes. FTIR spectra revealed that functional groups and chemical bonds were maintained after extrusion. Melting temperatures changed significantly when higher DS starch acetate was used. Cellulose content, barrel temperature and screw speed showed significant effects on thermal, physical and mechanical properties of extruded foams and the specific mechanical energy requirement.     

Effect of water content on the gelatinisation temperature of sago starch

Differential scanning calorimetry (DSC) has been used to study gelatinisation phenomena of sago starch. Two endothermic transitions were observed for starch heated in the presence of a limited amount of water (starch/water=37–50%w/w). These transitions appear to be due to co-operative effects of water-mediated melting of starch crystallites, remaining crystallites and/or amylopectin crystallites. At a water content of 50%, evidence of M₁ endotherm was observed and 85°C represents the effective T_m at the end of melting of native sago starch. The effect of starch concentration on the shape of these two endotherms was studied for sago starch. The experimental data were treated thermodynamically by applying equations describing phase transition of semi-crystalline polymers. The T⁰_m value obtained by extrapolation to v₁=0 was 390.6 K for sago.     

Recrystallization of waxy maize starch during manufacturing of starch microspheres for drug delivery: Influence of excipients

The formation of ordered structure, such as crystallites, in starch was studied by means of differential scanning calorimetry (DSC). The influence of time/temperature treatment and additives such as polyethylene glycol (PEG), bovine serum albumin (BSA) and a carbonate buffer on the formation was investigated. The experiments were planned with a CCC (Central Composite Circumscribed) design. For all three investigated systems it could be concluded that the incubation time at 6 °C was the decisive factor for the amount of ordered structure obtained during the incubation, while the incubation time at 37 °C was the decisive factor for the thermal stability of the crystallites as expressed by T_on, T_m and T_c. The additives seemed to mainly affect the nucleation phase of crystallization process. The additives decreased the time required in order to obtain a certain level of ordering in the incubated starch samples. The carbonate buffer decreased the amount of ordered structure in starch as judged by DSC enthalpy values, while increasing the melting temperature of these structures. The additives PEG and BSA lowered the melting temperatures of the starch in the systems but increased the enthalpy values. By optimization procedure a specific amount of ordered structure with desired thermal characteristics could be predicted.     

Influence of spent brewer’s yeast β-glucan on gelatinization and retrogradation of rice starch

The effects of β-glucan (BG) prepared from spent brewer’s yeast on gelatinization and retrogradation of rice starch (RS) were investigated as functions of mixing ratio and of storage time. Results of rapid visco-analysis (RVA) indicated that addition of BG increased the peak, breakdown, setback, and final viscosities, but decreased the pasting temperatures of the rice starch/β-glucan (RS/BG) mixtures. Differential scanning calorimetry (DSC) data demonstrated an increase in onset (T_o), peak (T_p), and conclusion (T_c) temperatures and a decrease in gelatinization enthalpy (ΔH₁) with increasing BG concentration. Storage of the mixed gels at 4 °C resulted in a decrease in T_o, T_p, T_c, and melting enthalpy (ΔH₂). The retrogradation ratio (ΔH₂/ΔH₁) and the phase transition temperature range (T_c − T_o) of the mixed gels increased with storage time, but this effect was reduced by the addition of BG. BG addition also slowed the syneresis of the mixed gels. Results of dynamic viscoelasticity measurement indicated that the addition of BG promoted RS retrogradation at the beginning and then retarded it during longer storage times. The added BG also retarded the development of gel hardness during refrigerated storage of the RS/BG mixed gels.     

Characterization of citric acid/glycerol co-plasticized thermoplastic starch prepared by melt blending

A novel citric acid (CA)–glycerol co-plasticized thermoplastic starch (CGTPS) was prepared by melt blending. The CA content varies from 10% to 40 wt%. Result from Fourier Transform Infrared spectroscopy (FTIR) show that partial esterification occurred during blending. The degrees of substitution and esterification increased as the CA content increased. Results from intrinsic viscosity measurement, laser light scattering (LLS), and FTIR demonstrate the molecular weight of starch decreased as the CA percentage increased. The weight average molecular weight (M_w) of CGTPS with 20 wt% CA was only one-tenth of that without CA under the same processing conditions. Crystal type and crystallinity changes as a function of CA were recorded by X-ray diffraction (XRD). Thermal stability and the glass transition temperature (T_g) were detected by thermogravimetric (TG) and differential scanning calorimeter (DSC). Compared to the traditional GTPS, the novel CGTPS exhibits the special characters of partial esterification, low molecular weight and stronger interaction between starch and plasticizers. These new properties can be expected to prevent retrogradation, promote compatibility with polyesters, improve the processing ability, and adjust the degradation properties.     

Preparation and characterization of biodegradable copolyester-starch based foams

Regular (25% amylose) and waxy corn starches blended to various ratios with Eastar Bio Copolyester 14766 (EBC) were extruded into loose-fill foams using a twin screw extruder. Included in this study were two types of corn starch, three levels of EBC content, and three levels of starch moisture content. Waxy starch produced foams with greater radial expansions and lower unit and bulk densities than regular starch. Regular starch foams had lower water solubility indices (WSIs) than waxy starch foams. Foams made of both types of starch possessed similar mechanical properties. No differences were observed in compressibilities and spring indices of either waxy or regular starch foams. Higher levels of EBC addition resulted in less radial expansion and higher unit and bulk densities. Foams made with 10% EBC had higher compressibility than foams containing 25% EBC. Spring indices of single-piece samples and compressibilities and spring indices of bulk samples were not affected by the differences in the level of EBC addition. At 19% and 22% of moisture contents, foams had greater radial expansion than at 25% moisture content. Unit and bulk densities were not affected by variations in moisture content. At 22% moisture content, a lower WSI of 18.5% was obtained. At 22% moisture content, softer foams were produced. At all three levels of moisture content, no differences were detected in the spring indices.     

Synthesis and properties of pullulan acetate. Thermal properties, biodegradability, and a semi-clear gel formation in organic solvents

Pullulan acetate (AcPL) with various degree of substitution (DS: 1.0–3.0) was synthesized by the reaction of pullulan with acetyl chloride in the presence of pyridine. The product was characterized by gel permeation chromatography (GPC), infra-red (IR) and ¹H NMR spectroscopy. The weight average molecular weights of the products did not decrease less than 190,000 (GPC) in the acetylation reaction. Thermogravimetric analysis (TGA) revealed that AcPL has a higher decomposition temperature (306–363 °C) than unmodified pullulan (295 °C). Differential scanning calorimetry analysis (DSC) revealed that all the AcPLs exhibit a clear T_g, which decreased with increasing DS value in the range of DS 1.0–2.4. The AcPL with DS 2.4 showed the lowest T_g (153 °C), and the AcPL with DS 3.0 had a slightly higher T_g (163 °C). Tensile modulus of AcPL films was comparable to that of a popular cellulose acetate film. The biodegration rate of AcPL decreased with increasing degree of acetylation. The AcPL with DS 3.0 was found to form a semi-clear gel in organic solvents such as dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and 1,4-dioxane.     

Natural weathering of rape straw flour (RSF)/HDPE and nano-SiO2/RSF/HDPE composites

The use of wood polymer composites (WPCs) in industries has been growing, and this is fueled in part by the use of WPCs in the construction industry. Rape straw flour (RSF)/high-density polyethylene (HDPE) composites as WPCs can also be applied in the construction industry. As a result, the durability of RSF/HDPE composites after natural exposure becomes a concern. Fourier transform infrared (FTIR) spectroscopy is used to monitor the development of degradation products, such as carbonyl groups and vinyl groups, and to determine changes in HDPE crystallinity. Differential scanning calorimetry (DSC) is also used to analyze changes in HDPE crystallinity. The results indicate that the carbonyl index was roughly lower for the RSF/HDPE composites than for the nano-SiO₂/RSF/HDPE composites, and the concentration of vinyl groups was generally much larger for the RSF/HDPE composites than for the nano-SiO₂/RSF/HDPE composites. At the same time, carbonyl index and vinyl index decrease with an increasing depth of composites, particularly decreasing strongly from 100 to 200 μm. The crystallinity of the samples increase because of natural aging, and the values of crystallinity derived by DSC are smaller than those derived by FTIR.     

Physical properties and enzymatic digestibility of acetylated ae, wx, and normal maize starch

The physical properties and enzymatic digestibility of acetylated starches prepared in the laboratory from high amylose (Hi-Maize™ 66% amylose; and GELOSE 50, 47% amylose), waxy (MAZACA 3401X, 3.3% amylose), and normal (22.4% amylose) maize starches provided by Starch Australasia Limited were studied. Acetylation decreased temperature at peak viscosity, while slightly increasing peak viscosity compared to the matching unmodified starch. It increased cool paste viscosity except in the case of normal starch. All the acetylated starches had lower onset temperature (T_o), intermediate temperature (T_p), completion temperature (T_c) and endothermic energy (ΔH) than their unmodified starches, but acetylation increased swelling power and solubility. After acetylation, the hardness of all the starch gels decreased; adhesiveness decreased and springiness increased except for waxy starch where it was the reverse; cohesiveness increased in each case. Acetylation increased the clarity of all the starches, except for waxy which showed a decrease. Acetylation increased the enzymatic digestibility compared to the unmodified starches.     

Compatible ternary blends of chitosan/poly(vinyl alcohol)/poly(lactic acid) produced by oil-in-water emulsion processing

Ternary compatible blends of chitosan, poly(vinyl alcohol), and poly(lactic acid) were prepared by an oil-in-water (O/W) emulsion process. Solutions of chitosan in aqueous acetic acid, poly(vinyl alcohol) (PVA) in water, and poly(lactic acid) (PLA) in chloroform were blended with a high-shear mixer. PVA was used as an emulsifier to stabilize the emulsion and to reduce the interfacial tension between the solid polymers in the blends produced. It proved to work very well because the emulsions were stable for periods of days or weeks and compatible blends were obtained when PVA was added. This effect was attributed to a synergistic effect of PVA and chitosan because the binary blends PVA/PLA and chitosan/PLA were completely incompatible. The blends were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), stress-strain tests, and Fourier transform infrared spectroscopy (FTIR). The results indicated that despite the fact that the system contained distinct phases some degree of molecular miscibility occurred when the three components were present in the blend.     

Physico-chemical and morphological characteristics of New Zealand Taewa (Maori potato) starches

The physico-chemical, morphological, thermal, pasting, textural, and retrogradation properties of the starches isolated from four traditional Taewa (Maori potato) cultivars (Karuparera, Tutaekuri, Huakaroro, Moemoe) of New Zealand were studied and compared with starch properties of a modern potato cultivar (Nadine). The relationships between the different starch characteristics were quantified using Pearson correlation and principal component analysis. Significant differences were observed among physico-chemical properties such as phosphorus content, amylose content, swelling power, solubility and light transmittance of starches from the different potato cultivars. The starch granule morphology (size and shape) for all the potato cultivars showed considerable variation when studied by scanning electron microscopy and particle size analysis. Starch granules from Nadine and Moemoe cultivars showed the presence of large and irregular or cuboid granules in fairly high number compared with the starches from the other cultivars. The transition temperatures (T_o; T_p; T_c) and the enthalpies (ΔH_gel) associated with gelatinization suggested differences in the stability of the crystalline structures among these potato starches. The Moemoe starch showed the lowest T_o, while it was higher for Tutaekuri and Karuparera starches. Pasting properties such as peak, final and breakdown viscosity and texture profile analysis (TPA) parameters of starch gels such as hardness and fracturability were found to be higher for Nadine and Huakaroro starches. The Nadine and Huakaroro starch gels also had lower tendency towards retrogradation as evidenced by their lower syneresis (%) during storage at 4 °C. Principal component analysis showed that the Tutaekuri and Nadine cultivars differed to the greatest degree in terms of the properties of their starches.     

Laboratory composting of extruded starch acetate and poly lactic acid blended foams

Composting of extruded foams made of starch acetate and poly lactic acid (PLA) with pre-conditioned yard waste was studied using a laboratory composting system. Extruded foams of high amylose starch were used as the control. Degradation was measured by analyzing the exhaust gases for carbon dioxide. There were significant differences in the amounts of carbon dioxide produced in the vessels containing foams of high amylose starch and foams of starch acetate blended with 20% or 30% PLA. The high amylose starch foams completely degraded within 15 days. The starch acetate foams with 0% PLA took longer, with evolution of carbon dioxide still measurable after 55 days. The rate of degradation was faster for foams with higher PLA contents. The starch acetate foams took even longer to degrade. The maximum time was found to be 130 days for the starch acetate foams.     

Extruding foams from corn starch acetate and native corn starch

Because of the hydrophilic characteristics of native starch foams and the cost of modifying starch, the uses of starch and modified starch foams are hindered. To decrease hydrophilicity and cost of starch foams, native corn starch was blended with starch acetate and extruded. A twin-screw mixing extruder was used to produce the foams. Native starch content, screw speed, and barrel temperature had significant effects on molecular degradation of starches during extrusion. The melting temperature of extruded starch acetate/native starch foam was higher (216 degrees C) than that for starch acetate (193.4 degrees C). Strong peaks in the X-ray diffractograms of extruded starch acetate/native starch foam suggested new crystalline regions were formed. Optimum conditions for high radial expansion ratio, high compressibility, low specific mechanical energy requirement, and low water absorption index were 46.0% native starch content, 163 rpm screw speed, and 148 degrees C barrel temperature.     

Synthesis and characterization of a novel potato starch derivative with cationic acetylcholine groups

A novel substance, cationic acetylcholine potato starch (CAPS), was developed for the first time. The synthesis process had three steps: first, carboxymethyl potato starch (CMPS) was synthesized under sodium hydroxide alkaline condition and in isopropyl alcohol organic media; second, bromocholine chloride (BCC) was synthesized with sulphuric acid as a catalytic agent; finally, CAPS was synthesized by the reaction of CMPS with BCC in N,N'-dimethylformamide (DMF). The degree of substitution (DS) of CAPS was determined by ammonia gas-sensing electrode and elemental analysis. CAPS was characterized by Fourier transformed infrared (FTIR) and near infrared (FTNIR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC).     

Nature of thermal transitions of native and acid-hydrolysed pea starch: Does gelatinization really happen?

Thermal transitions of native and acid-hydrolysed starch were investigated for the first time by employing differential scanning calorimetry (DSC) in combination with field emission scanning electron microscopy (FE-SEM) to examine morphological changes in the starch after hydrothermal treatment in the DSC pans. The characteristic, well-defined endothermic transition was observed in the DSC traces for native starch and starch after one day of acid hydrolysis, but after two days of hydrolysis the endothermic transition became broad and undefined. After heating in DSC pans, native starch was observed visually and with SEM to have formed a gel, whereas starch granules hydrolysed for one day appeared to have undergone only limited swelling and coalescence. Starch that had been hydrolysed for two or more days appeared powdery and SEM images revealed that the granules had undergone very little swelling. The thermal transitions of native and acid-hydrolysed starch are interpreted in terms of the theory of polymer swelling and dissolution. Native granules and granules with only minimal acid damage are able to swell within the constraints of the water-limited conditions of DSC, but as acid hydrolysis progresses the capacity of the granules to swell is decreased and endothermic transitions are increasingly due to dissolution of polymer chains. An exothermic transition that followed the main endothermic transition is proposed to be due to the condensation of water vapour on the lid of the DSC pan.     

Effect of glycerol on behaviour of amylose and amylopectin films

The effect of water and glycerol on sorption and calorimetric T_gs of amylose and amylopectin films were examined. The mechanical properties of the films were also analysed under varying glycerol content at constant RH and temperature. Based on changes observed in sorption and tensile failure behaviour glycerol was strongly interacted with both starch polymers. Even though water was observed to be more efficient plasticiser than glycerol, glycerol also affected the T_g. But in spite of the observed decrease in T_g under low glycerol contents brittleness of the films increased based on changes in elongation. The increase in brittleness of both polymers was also in agreement with their actual behaviour. At around 20% glycerol great change in the rheological properties occurred. Above 20% glycerol amylose film showed much larger elongation than the low glycerol content films and was still strong but the amylopectin produced a very week and non-flexible film.     

Preparation of semi-interpenetrating polymer networks composed of chitosan and poloxamer

Through semi-interpenetration of polymer networks with poloxamer, mechanical properties of chitosan (CS) sponge were increased for wound dressing application. Synthesis of poloxamer macromer was confirmed by proton nuclear magnetic resonance (1H NMR) spectra. Possible interactions between CS and poloxamer in semi-interpenetrating polymer networks (SIPNs), and changes in crystalline structures of both polymers were evaluated by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), respectively. Swelling behavior, thermal analysis, mechanical properties, and morphology of SIPNs were studied by thermal gravimetric analysis, differential scanning calorimetry (DSC), compressive modulus measurement, and scanning electron microscopy (SEM), respectively. Preparation of poloxamer macromer, and intermolecular hydrogen bonding between CS and poloxamer were confirmed by NMR and FTIR, respectively. Melting temperature of poloxamer in SIPNs decreased due to prevention of crystallization by incorporation of CS. Formation of SIPNs with poloxamer and increasing poloxamer content in CS/poloxamer SIPNs increased mechanical strength of CS sponge compared with CS/poloxamer blend. Formation of SIPNs with poloxamer remarkably increased water content of CS due to hydrophilicity of CS and poloxamer. These results suggest CS/poloxamer sponges prepared by SIPNs method have good possibility for wound dressing application owing to rapid water adsorption, high mechanical strength, and interconnected cross-sectional morphology of SIPNs.     

Molecular and granular characteristics of corn starch modified by HCl-methanol at different temperatures

Native corn starch was hydrolyzed with 0.36% HCl in methanol at 25 and 45 °C for periods of time up to 240 h. The action of acid penetration and hydrolysis was investigated by confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), high-performance anion-exchange chromatography (HPAEC) and high-performance size-exclusion chromatography (HPSEC) equipped with viscometry, right-angle laser light scattering (RALLS) and refractive index (RI) detectors. Corn starch hydrolyzed at 45 °C for 240 h showed strong intensity of APTS (8-amino-1,3,6-pyrenetrisulfonic acid) fluorescence and sharp growth ring structure. Exocorrosion over the surface of corn starch was only observed on the corn starch hydrolyzed at 25 °C for 240 h and observed on all corn starch hydrolyzed at 45 °C. The M_w and R_h of acid-hydrolyzed corn starch decreased with increasing the degree of hydrolysis. The acid hydrolysis rate in methanol of corn starch was mainly dependent on the temperature, which dominated the penetration efficiency of acid.     

A study of the effect of water on the glass transition of 1:1 mixtures of amylopectin, casein and gluten using DSC and DMTA

The glass transition temperature (T_g) and mechanical properties of binary mixtures of the food biopolymers amylopectin, casein and gluten have been studied in the ratio 1:1 in the presence of water. In general these polymers appear to be immiscible, showing two glass transitions due to the two polymers when there is sufficient difference between the T_gs of the two components. Increasing the water content reduces the T_g of both components.