Thermal-oxidative degradation of polyamide 6,6 containing metal salts

The thermal-oxidative stability of oven aged polyamide 6,6 (PA6,6) doped with Co, Cu, Ni and Zn chlorides combined with KI was examined. Aging caused a depression in melting temperature and an increase in enthalpy of fusion of PA6,6 films due to the formation of a strongly degraded crystalline fraction with a lower molecular weight. A build-up of carbonyl absorption in the range 1700-1780 cm⁻¹ due to primary and secondary photo-oxidation products was detected. The kinetics of carbonyl accumulation was affected by the morphology of the samples, and it was observed that at a later stage of aging the crystalline phase was also involved in the oxidation process. The above mentioned changes were greatest in the case of neat, Co and Ni doped polymer, suggesting that these metal salts acted as pro-oxidants. On the other hand, the use of Cu and Zn chlorides brought about a substantial increase in long-term polymer stabilization.Tensile tests revealed a large reduction in ductility as a result of aging for neat, Co and Ni doped polymer, whereas long-term retention of tensile properties was found for the polymer stabilized with Cu and Zn. The presence of the metal salts combined with KI led to increased stabilization for chlorides of Ni, and Co, owing to the participation of KI in non-radical decomposition of peroxides. No effect due to KI was observed for ZnCl₂.     

Grafting of polyacrylonitrile to granular corn starch

Acrylonitrile grafts readily to granular corn starch in aqueous slurry when initiated by hydrogen peroxide plus activator. Prime evidence for grafting lies in the ease of separating PAN from starch in high yield when the initiator is azobisisobutyronitrile rather than peroxide. Grafting efficiencies are determined by extraction with appropriate solvents: dimethylformamide for homo-PAN, and boiling water for ungrafted starch. Grafting efficiencies of PAN range from 78 to 95%, M?_n values for grafted PAN are 4,000 to 90,000, and frequency of attachment of side chains range from 300 to 1100 glucose units per chain. Increasing the monomer level, at fixed initiator concentration, tends to result in longer rather than more frequent side chains. AN behaves much as has been previously found for MMA, but the somewhat more efficient grafting at more frequent intervals and the more nearly uniform distribution of polymer in the starch granule suggest that AN penetrates the starch granule more readily than MMA.     

Enzymatic hydrolysis of corn starch after extraction of corn oil with ethanol

To develop a yeast strain that is able to produce ethanol directly from starch, α-amylase cDNA (originated from mouse salivary glands) was introduced into the hyploidSaccharomyces diastiticus cells secreting glucoamylase by using a linearized integrating vector. The integrating vector contains aLEU2 gene and the inside of theLEU2 gene was cut byKpnl to make the linearized vector. One of the transformants exhibited 100% mitotic stability after 100 generations of cell multiplication. To improve its ethanol-fermentability, the haploid transformant was rare-mated with a polyploid industrial strain having no amylase activity. The resulting hybrid RH51 produced 7.5 (w/v) ethanol directly from 20% (w/v) soluble starch and its mitotic stability was 100% at the end of fermentation.     

Thermal-oxidative induced degradation behaviour of polyoxymethylene (POM) copolymer detected by TGA/MS

The influence of reprocessing and thermooxidative ageing on the degradation behaviour of a commercial poly(oxymethylene) (POM) copolymer was studied by means of thermogravimetric analysis (TGA) under nitrogen and air atmosphere. Five heating rates were used to evaluate activation energies at several degrees of conversion. TGA-measurements were accompanied by simultaneous monitoring of the evolved gases with a mass spectrometer (MS) coupled to the TGA-furnace outlet. The mass spectra showed that the main degradation product was formaldehyde and that in air further formation of water was detectable. In nitrogen atmosphere aged specimens emitted small amounts of carbon dioxide at the beginning of the mass loss. The activation energy for low degrees of conversion (<5%) increased in air and in nitrogen as a function of the conversion. For higher conversions a difference with progressing degradation emerged: in air, activation energies lowered continuously while they remained nearly constant under nitrogen.     

Mycotoxin separation on thin layer of corn starch

Summary Twelve mycotoxins were separated on corn starch thin layers with the solvent systems: benzene, toluene, xylene and mixture of benzene-toluene-cyclohexane-ethanol (abs.) (3:3:5:0.1). R_f-values were determined. The effect of solvent systems on mycotoxin fluorescence was also described.     

Preparation of novel porous carbon spheres from corn starch

Irregular porous carbon spheres were successfully prepared from Na₂SnO₃ coated corn porous starch by carbonization. The product was characterized with X-ray diffraction and scanning electron microscope (SEM). It is verified that the irregular porous carbon spheres are composed of disordered carbon, and the skeleton and pores of the corn porous starch was well preserved after carbonization. The pore size of the irregular porous carbon spheres is almost the same, which is similar to that of the porous starch. And the pore size decreases from about 0.91 μm to 0.53 μm measured from the SEM pictures. The texture of the irregular porous carbon spheres is mainly determined by that of porous starch.     

Thermal stability and degradation of starch derivatives

Thermal behaviour of different starch derivatives, i.e. starch esters and ethers having degree of substitution (DS) in the range of 0.02–0.18 were studied. Potato, maize and wheat starches were used. Measurements were carried out by coupled thermal analysis/ mass spectrometry method (STA-MS) in air atmosphere. The major DTG peak during the investigation for starch derivatives is observed below 300°C. The mass loss up to a temperature of 300°C is about 50%. The most abundant ions found areH₂O⁺ and CO₂ ⁺. For the studied starch derivatives with a low degree of substitution (DS<0.18) no correlation was found between thermal stability and the level of substitution regardless of the nature of substitution.     

Ethanol production from corn starch in a fluidized-bed bioreactor

The production of ethanol from industrial dry-milled corn starch was studied in a laboratory-scale fluidized-bed bioreactor using immobilized biocatalysts. Saccharification and fermentation were carried out either simultaneously or separately. Simultaneous saccharification and fermentation (SSF) experiments were performed using small, uniform κ-carrageenan beads (1.5–2.5 mm in diameter) of co-immobilized glucoamylase and Zymomonas mobilis. Dextrin feeds obtained by the hydrolysis of 15% drymilled corn starch were pumped through the bioreactor at residence times of 1.5–4h. Single-pass conversion of dextrins ranged from 54–89%, and ethanol concentrations of 23–36 g/L were obtained at volumetric productivities of 9–15 g/L-h. Very low levels of glucose were observed in the reactor, indicating that saccharification was the rate-limiting step. In separate hydrolysis and fermentation (SHF) experiments, dextrin feed solutions of 150–160 g/L were first pumped through an immobilized-glucoamylase packed column. At 55°C and a residence time of 1 h, greater than 95% conversion was obtained, giving product streams of 162–172 g glucose/L. These streams were then pumped through the fluidized-bed bioreactor containing immobilized Z. mobilis. At a residence time of 2 h, 94% conversion and ethanol concentration of 70 g/L were achieved, resulting in an overall process productivity of 23 g/L-h. Atresidence times of 1.5 and 1 h, conversions of 75 and 76%, ethanol concentrations of 49 and 47 g/L, and overall process productivities of 19 and 25 g/L-h, respectively, were achieved.     

Electronic detection of the enzymatic degradation of starch

[reaction: see text] The enzymatic degradation of starch can be monitored electronically using single-walled carbon nanotubes (SWNTs) as semiconducting probes in field-effect transistors (FETs). Incubation of these devices in aqueous buffer solutions of amyloglucosidase (AMG) results in the removal of the starch from both the silicon surfaces and the side walls of the SWNTs in the FETs, as evidenced by direct imaging and electronic measurements.     

Mechanical degradation of gelatinized starch upon hydroacoustic treatment

Mechanical degradation of gelatinized starch upon hydroacoustic treatment in a rotary pulse installation was studied by spectrophotometry of the iodine-starch complexes and analysis of the concentrations of the terminal reducing groups. The energy efficiency of hydroacoustic and ultrasonic mechanical degradation was estimated.     

Fouling of a ceramic microfiltration membrane by corn starch hydrolysate

The effect of operating parameters on fouling of a ceramic microfiltration membrane by corn starch hydrolysate of 95 dextrose equivalence was studied. Transmembrane pressures above 100 kPa had little or no effect on flux. Cross-flow velocity had a significant beneficial effect. The rate of flux decline was reduced significantly when the feed was adjusted from its natural pH of 4.2 to 10. However, this resulted in a dark brown clarified syrup (permeate). Scanning electron microscopy showed extensive fouling layers on the alumina surface with conventionally processed dextrose solutions and the least fouling layer with corn starch hydrolysate adjusted to pH 10. Maximum steady state flux for unconcentrated hydrolysate at its natural pH was 178 LMH obtained at low transmembrane pressures (103 kPa, 15 psi) and high cross-flow velocities (5 m s⁻¹). Adjustment of the pH to 10 can increase the flux by 40%.     

Retrogradation characteristics of high hydrostatic pressure processed corn and wheat starch

High hydrostatic pressure (HHP) has been investigated as an alternative to thermal processing for food preservation. HHP has been known to affect high molecular weight polymers causing phase change. Starch is gelatinized at a pressure on the order of 600–700 MPa, at 25 °C. Gelatinized starch recrystallizes during storage affecting the texture and shelf life of food products. The effect of HHP processing on the crystallization of starches from different botanical origins during storage at 4 and 23 °C was investigated. Crystallization kinetics of HHP treated wheat and corn starch gels were compared using DSC. The effect of crystallization on structure was evaluated in terms of storage modulus. The rate of retrogradation depended on the storage temperature (23 °C and 4 °C) and the botanical origin of the starch. The least crystallization was observed in HHP treated wheat starch stored at 23 °C. The storage modulus increased with crystallization of starch.     

Sorption of alkyl acetates from aqueous solutions by corn starch cryotextures

Capillary gas chromatography was used to study noncovalent sorption ofn-butyl,n-hexyl, andn-octyl acetates from aqueous solutions by corn starch cryotextures. In the concentration range of 0.5–15.0 mmol L⁻¹, about 38%n-butyl acetate, 70%n-hexyl acetate, and 98%n-octyl acetate are extracted from aqueous solutions. The sorption of the alkyl acetates depends on the alkyl chain length, indicating the hydrophobic character of their interaction with the corn starch cryotexture. No competitive sorption between acetates in the mixture was observed. Binding of alkyl acetates occurs during the cryosponge formation, due probably to the templation at the stage of starch sol, fixation in the cryosponge, and sorption on the surface of its walls. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1943–1945, October, 1998.     

Light-induced starch degradation in non-dormant turions of Spirodela polyrhiza

Continuous red light controls starch degradation in turions of Spirodela polyrhiza[Dölger, K., U. K. Tirlapur and K.‐J. Appenroth [1997]Photochem. Photobiol. 66, 126–127 (1997)]. This light could be replaced by repeated red light pulses with the reciprocity law fulfilled over a large range of fluence rates. The effect of red light pulses repeated every 24 or 12 h for 6 days was reversible by subsequent far‐red light pulses. In contrast, hourly applied red pulses were irreversible by far‐red light. This discrepancy was explained by showing the starch degradation activity of far‐red pulses themselves. The investigated process was categorized as a phytochrome low fluence response with an unusual property: requirement of light treatment for several days. A partial fulfillment of this requirement was obtained with a red pulse followed by a dark period and a 24 h continuous irradiation. These results suggest the existence of two separate steps in the process of starch degradation in turions: formation of a sprout (=sink) during the pulse‐induced germination, and starch degradation in the storage tissue (=source) induced by the second light treatment.     

Gas chromatographic determination of sorption of aroma substances by corn starch cryosponges

The sorption ofRosmarinus Officinals L. essential oil components by the corn starch cryosponge was studied. The hydrophobic interactions of monoterpene hydrocarbons with polysaccharides of the starch result in their quantitative sorption. The sorption of aroma compounds containing oxygen atoms is twofold lower. the templating effect of mono- and disaccharides (glucose, sucrose, maltose, and some essential oil components) was found.     

Microstructure and surface composition of corn starch cryogels with sorbed organic flavoring agents

The surface composition and surface microtopography of corn starch cryogels obtained from a 3% starch sol containing organic flavoring agents were studied by X-ray photoelectron spectroscopy and scanning electron microscopy. The cryogels withn-octanol,n-octyl methyl ketone, andn-octyl acetate have a well-developed microtopography and their surface layer (5–20 nm) is enriched in sorbed compounds.n-Octyl acetate, unliken-butyl acetate, influences the composition and microstructure of the cryogel surface. The sorbedn-octyl acetate occupies 20–25% of the surface, which has a well-developed topography and a porous structure. Drying and evacuation do not change the concentration of the organic sorbates having a C₈ alkyl group in the surface layer. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 312–314, February 2000.     

Co-determination of sodium metabisulfite and starch in corn syrup by flow injection coulometry

During the processing of corn syrup for commercial use, starch, in the form of alpha -amylose, must be completely broken down to its D -glucopyranose units. Sodium metabisulfite is added to the corn syrup as a preservative. Flow Injection Coulometry was used to perform an automated assay of these analytes, both individually and jointly. The sodium metabisulfite concentration, over a range of 3.5 x 10(-4)-2.9 x 10(-2)M, is determined by coulometric flow injection titration with generated iodine, using spectrophotometric endpoint detection at 530 nm. Analysis over this range produced a relative standard deviation of < 1.5% and was found to correlate very well with manual titrations. The determination was performed in the presence of varying amounts of starch, and was found to be independent of the starch concentration. Starch was determined, when no sodium metabisulfite was present, from the absorbance level after the reaction of the sample with a specific amount of iodine. In the presence of sodium metabisulfite, the rate of the accumulation of the starch/iodine interaction product after the metabisulfite titration endpoint, at a constant reagent generation rate, was used. A relative standard deviation of < 1.4% was obtained for all starch analyses, with a very good correlation (correlation coefficients 0.997) with the known relative concentration. The use of the FIC technique to perform analyses by specific amount and excess reagent generation is demonstrated, along with dual analyte determination.     

DSC study on the thermal properties of soybean protein isolates/corn starch mixture

The use of soybean protein isolates (SPI) and corn starch (CS) for the manufacturing of textured protein by thermo-mechanical means requires a characterization of their thermal properties. SPI and CS mixtures were examined at starch mass fractions from 0 (pure SPI) to 100 (pure CS). The blends were determined by means of differential scanning calorimetry, with water content of 30, 50, and 70 % and heating rate of 5 and 10 °C min^?1 over 20 to 130 °C. The results obtained showed that protein in the blend increased the onset (T _o) and peak (T _p) temperatures of the starch gelatinization, while starch in the blend decreased the ΔH and ΔT_1/2 of the protein. T _o , T _p, and ΔT_1/2 of SPI and CS decreased significantly with the increase of water content. T _p and ΔT_1/2 of SPI and CS had a marked increase with an increase of heating rate from 5 to 10 °C min^?1. These results suggested that there was no chemical reaction between SPI and CS when they were heated from 20 to 130 °C. SPI in the blend restricted the CS gelatinization, while the presence of CS protected the SPI from denaturation. The increasing water content did promote thermal transition of the mixture. Higher heating rate leads to higher transition temperature.     

Preparation and characterization of lithium ion conducting ionic liquid-based biodegradable corn starch polymer electrolytes

Thin films of biodegradable corn starch-based biopolymer electrolytes were prepared by solution casting technique. Lithium hexafluorophosphate (LiPF₆) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BmImTf) were employed as lithium salt and ionic liquid, respectively. With reference to the temperature dependence study, Arrhenius relationship was observed. The highest ionic conductivity of (6.00 ± 0.01) × 10⁻⁴ S cm⁻¹ was obtained at 80 °C. Based on x-ray diffraction (XRD) result, the peaks became broader with doping of ionic liquid revealing the higher amorphous region of the biopolymer electrolytes. Ionic liquid-based biopolymer electrolytes exhibited lower glass transition temperature (T _g).