A comparative study of the degradation of different starches using thermal analysis

Four starches obtained from different sources were treated to thermal analysis and their mechanisms of degradation were deciphered using a rising temperature method of evaluation. A comparison of the solid state reactivity between the four starches was made, using a method known as the alpha(s)-alpha(r) method. By this method, it was possible to differentiate between four starches of completely different plant origin. Potato starch and rice starch were found to have the highest reactivity.     

A comparative study on thermal and catalytic degradation of polybutylene terephthalate

A comparative study on the thermal and catalytic degradation of polybutylene terephthalate (PBT) at atmospheric pressure was conducted. The weight loss of PBT under thermal degradation was significantly influenced by the temperature between 360 °C and 380 °C, but little affected by the PBT particle size. Four groups of catalysts include metal chloride, metal oxide, metal acetate, and metal copper powder were used to test PBT degradation activity. Copper (II) chloride is the most active one for increasing the percentage PBT weight loss more than 100% in comparison with the result of thermal degradation at a temperature of 360 °C for 30 min. PBT and catalyst mixtures can be prepared by impregnation and physical method, the former resulted in a better PBT degradation. The percentage PBT weight loss in the presence of CuCl₂ increased steadily between 320 °C and 380 °C which was different from the results of thermal degradation. The time for obtaining a same percentage PBT weight loss reduced effectively when compared to the catalytic to thermal degradation. The weight ratio of CuCl₂/PBT was tested between 0 and 0.2 and the optimal ratio was 0.1. The gaseous product distribution analyzed by GC/MS for PBT thermal and catalytic degradation revealed almost the same and the major products were ethane, carbon monoxide, carbon dioxide, 1-butene, 2-butene, 1,3-butadiene, and butadiene dimmer. But the relative abundance of major products was changed, especially for 1,3-butadiene increased dramatically, and a new chlorocompound was produced in catalytic degradation. In condensed liquid product, both the number and the molar mass of components were more and greater than that of in gaseous product and 4-heptylacetophenone was the most abundance product. In PBT catalytic degradation, 4-heptylacetophenone and some products were decreased and some even disappeared completely while the abundance of benzoic acid increased and three new products were generated.     

Energetic potential of pyrolyzed biomass from different sources: a comparative study

Journal of Thermal Analysis and Calorimetry - The use of biomass has been a recent trend as a potential feedstock for char generation with improved energetic value. In this work, agricultural...     

The synthesis conditions, characterizations and thermal degradation studies of an etherified starch from an unconventional source

Starch isolated from an under-utilized legume plant (pigeon pea) was carboxymethylated. Influences of reaction parameters were investigated on the degree of substitution (DS) and the reaction efficiency (RE). Studies showed that optimal DS of 1.12 could be reached at reaction efficiency of 80.6% in isopropanol-water reaction medium (40 °C, 3 h). Scanning electron microscopy showed that after carboxymethylation, the granular appearance of the native starch was distorted. Wide-angle X-ray diffractometry revealed that crystallinity was reduced significantly after carboxymethylation. The infrared spectra revealed new bands in the carboxymethyl starch at ν = 1600, 1426 and 1324 cm⁻¹ which were attributed to carbonyl functional groups vibration, -CH₂ scissoring and OH bending vibration, respectively. Broad-band ¹³C NMR of carboxymethyl starch showed an intense peak at δ = 180.3 ppm which was assigned to carbonyl carbon on the carboxymethyl substituent on the AGU (Anhydroglucose Unit). DEPT (Distortionless Enhancement by Polarization Transfer) 135 NMR showed negative signals which correspond to methylene carbons on the AGU. Differential Scanning Calorimetry (DSC) suggests loss of crystallinity after carboxymethylation. Thermogravimetry (TG), Derivative Thermogravimetry (DTG) and Differential Thermal Analysis (DTA) show that thermal stability improved after carboxymethylation. The study provides information on the preparation and characterization of a biomaterial from a new source which could be used alone or in the preparation of other functional polymers for diverse polymer applications.     

A comparative study of the 5S rRNAs from plant seeds

Summary 1. It has been established that the method of isolating ribosomes by precipitation with ethanol in the presence of Mg²⁺ can be used in the isolation of ribosomes from the seeds of other plants. The isolated 5S rRNAs have the same electrophoretic mobility, while the 5S rRNAs from plants differ sharply from the 5S rRNAs of yeast in electrophoretic mobility which is apparently due to differences in their secondary and tertiary structures.2. In the sprouting of cotton seeds, the amount of total rRNAs first increases (two-day shoots) and then falls (seven-day shoots).Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 56–59, January–February, 1979.     

Synthesis of carboxymethyl potato starch and comparison of optimal reaction conditions from different sources

Carboxymethyl potato starch (CMPS) was synthesized under heterogeneous reaction conditions. The influences of etherification temperature, alkalization and etherification time, sodium hydroxide to monochloroacetic acid (MCA) molar ratio (n_NaOH/n_MCA), theoretical degree of substitution (DS_t), the ratio of isopropyl alcohol (IPA) volume to starch mass (v_IPA/m_st) on degree of substitution (DS) and reaction efficiency (RE) of CMPS were investigated. Compared with the previous literature data, the results had significant difference for the optimal carboxymethylation conditions of potato starch from different sources. CMPS prepared under optimal conditions showed the highest DS and RE, which were 1.36 and 0.88, respectively. Furthermore, the RE value in this work is considerably higher than that reported in the literature. The time of alkalization and etherification were also discussed independently. In addition, CMPS was characterized by Fourier transform infrared spectrophotometry and scanning electron microscopy (SEM). Copyright © 2008 John Wiley & Sons, Ltd.     

Study on the morphology, crystalline structure and thermal properties of yam starch acetates with different degrees of substitution

This study was carried out to understand and establish the changes in physicochemical properties of starch extracted from Chinese yam (Dioscorea opposita Thunb.) after acetylation. Yam starch acetates with different degrees of substitution (DS) were prepared by the reaction of yam starch with glacial acetic acid/acetic anhydride using sulfuric acid as the catalyst. Their formation was confirmed by the presence of the carbonyl signal around 1750 cm-1 in the Fourier transform infrared (FT-IR) spectra. The thermal behavior of the native starch and starch acetate were investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results reveal that the starch acetates are more thermally stable than the native starch. The starch esters showed 50% weight loss at tem- peratures from 328℃ to 372 ℃ , while the native starch underwent 50% weight loss at 325℃ . The glass transition temperature (Tg) of the starch decreased from 273℃ to 226℃. The X-ray diffraction (XRD) patterns could be classified as typical of the C-type for yam starch. X-ray diffraction also showed the loss of the ordered C-type starch crystalline structure and the degree of crystallinity of starch de- creased from 36.10% to 10.96% with the increasing DS. The scanning electron microscopy (SEM) sug- gested that the most of the starch granules disintegrated with many visible fragments with the in- creasing DS.     

Crystal structure, thermal behavior and enzymatic degradation of poly(tetramethylene adipate) solution-grown chain-folded lamellar crystals

Solution-grown chain-folded lamellar single crystals of poly(tetramethylene adipate) (PTMA) were prepared from a dilute solution of 2-methyl-1-propanol by isothermal crystallization. PTMA crystals were hexagonal-shaped and polyethylene decoration of the crystals resulted in a "six cross-sector" surface morphology and showed that the average direction of chain folding is parallel to the crystal growth planes of [110] and [010]. Chain-folded lamellar crystals gave well-resolved electron diffraction diagrams corresponding to all the equatorial reflections of the X-ray fiber diagram obtained from stretched PTMA melt-quenched film (beta structure). The unit cell parameters of the beta structure of PTMA were determined as a = 0.503 nm, b = 0.732 nm and c (fiber axis) = 1.442 nm with an orthorhombic crystal system. The fiber repeat distance is appropriate for an all-trans backbone conformation for the straight stems. The setting angle, with respect to the a axis, is +/-46 degrees for the corner and center chains. Thermal behavior of lamellar crystals has been investigated by means of transmission electron microscopy (TEM) and atomic force microscopy (AFM). The lamellar thickness at the edges of the crystal increased after thermal treatment with taking the molecular chains into recrystallization parts; the holes then opened up at the thickening front of the crystal. The morphological changes of lamellar crystals after enzymatic degradation by Lipase type XIII from Pseudomonas sp. and water-soluble products were characterized by TEM, AFM, gel permeation chromatography, high performance liquid chromatography and fast atom bombardment mass spectrometry. The degradation progressed mainly from the edges of the lamellar crystals without decreasing the molecular weights and the lamellar thicknesses. The central portion of single crystals was often degraded by enzymatic attacks. This result combined with thermal behavior indicates that the loosely chain-packing region exists inside the single crystal, and that molecular chains in this region have higher mobility against thermal and enzymatic treatments.     

Comparative thermal analysis study of two biopolymers, starch and cellulose

The degradation of cellulose and starch samples in air and nitrogen has been investigated by thermal analysis techniques. The techniques employed were differential thermal analysis, rising temperature and temperature jump thermogravimetry. Rate data were obtained from these experiments and Arrhenius parameters calculated from these values. This data was used to determine the mechanism by which the cellulose and starch samples degraded. The Arrhenius parameters were also calculated. The behavior of starch and cellulose upon thermal analysis were compared and are reported.E _act for corn starch was found to be 474 kJ mol^–1 and for a cellulose 242 kJ mol^–1.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Mechanistic study of thermal behavior and combustion performance of epoxy resins: I homopolymerized TGDDM

Tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) undergoes homopolymerization on heating. Intramolecular reactions which compete with crosslinking favor the formation of cyclic structures with increasing thermal and fire resistance of the resin, whereas physical mechanical properties tend to decrease. The mechanism of thermal decomposition of TGDDM is studied by thermogravimetry, differential scanning calorimetry and thermal volatilization analysis with characterization of volatiles evolved and residue left. Thermal degradation of poly-(TGDDM) starts at 260°C with elimination of water from secondary alcoholic groups which is a typical pathway for epoxy resin degradation. Resulting unsaturations weaken bonds in the β-position and provoke the first chain breaking at allyl–amine and allyl–either bonds. With increasing temperature, saturated alkyl–ether bonds and alkyl carbon–carbon bonds are broken first, followed by the most stable alkyl–aryl bonds at T>365°C. The combustion performance of TGDDM is discussed on the basis of the thermal degradation behavior.     

A fluorimetric study of the chemical,photochemical and thermal degradation of poly(vinylchloride)—I. Preliminary comparative studies

Fluorescence emission and excitation spectra of dilute tetrahydrofuran solutions of thermally degraded PVC, (TPVC), photochemically degraded PVC, (PPVC), chemically degraded PVC, (CPVC) and non-degraded PVC are compared. The spectra of CPVC and PPVC are similar and are composed of a mixture of polyene structures while those of TPVC are different. The reasons for these differences are discussed.     

Comparative study of thermal degradation behavior of graft copolymers of polysaccharides and vinyl monomers

The thermal degradation of graft copolymers of both polysaccharides (guar gum and xanthan gum) showed gradual decrease in mass loss. Pure guar gum degraded about 95% but pure xanthan gum degraded about 76% up to 1173.15 K, while graft copolymers of guar gum and xanthan gum degraded only 65–76% up to 1173.15 K. Acrylic acid grafted guar gum and xanthan gum showing two-step degradation with formation of anhydride and ketonic linkage during heating, same pattern of degradation was found for xanthan gum-g-methacrylic acid. Guar gum-g-acrylamide degraded in single step and xanthan gum-g-acrylamide started to degrade above 448.15 K and it is a two-stage process and imparts thermal stability due to the formation of imide linkage with evolution NH₃. Guar gum-g-methacrylamide degraded in three steps due to the loss of NH₃ and CO₂ successively. 4-vinyl pyridine grafted both polysaccharides show single step degradation due to loss of pyridine pendent. N-vinyl formamide grafted guar gum and xanthan gum started to degrade at about 427.15 K, showed two-stage degradation process with the evolution of CO and NH₃ molecules while guar gum-g-(N-vinyl-2-pyrrolidone) degraded into two steps by the loss of pyrrolidone nucleus. Gum-g-2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) showed two-step degradation processes in two successive degradation steps, while xanthan gum-g-AMPS has started degradation at about 427.15 K and completed in five degradation steps. Overall, it was found that the grafted polysaccharides are thermally more stable than pure polysaccharides.     

Comparative study on composition, structure, and adsorption behavior of activated carbons derived from different synthetic waste polymers

The composition, structure, and adsorption behavior of activated carbons (ACs) derived from three different types of waste polymers, i.e., tire rubber (TR), polyvinyl chloride (PVC), and polyethyleneterephtalate (PET), by KOH activation were compared. The AC derived from PET exhibited the largest surface area (2831 m(2)/g) and pore volume (1.68 cm(3)/g) due to the homogenous aromatic composition of PET. The AC derived from PVC exhibited relatively lower surface area (2666 m(2)/g) but more narrowed pore size distribution (2-3 nm). The complex composition and high ash content of tire particles resulted in AC product with significantly lower surface area (398.5 m(2)/g) and heterogeneous pore width. Adsorption data of methylene blue (MB) were fitted well by Langmuir equation, indicating monolayer coverage on the ACs. The high oxygen content of PET-derived AC heavily affected its adsorption to MB and iodine. Due to the remarkable surface area and highly mesoporous structures, ACs based on both PET and PVC exhibited much higher adsorption capacities than that of TR and commercial coal-based AC (F400). This study demonstrates that the properties of ACs are highly dependent on their starting polymers and the potential of converting synthetic polymer waste into effective adsorbents for environmental remediation and cleanup.     

Study on the morphology, crystalline structure and thermal properties of yellow ginger starch acetates with different degrees of substitution

Yellow ginger starch acetates with different degrees of substitution (DS) were prepared by reacting native starch with glacial acetic acid/acetic anhydride using sulfuric acid as catalyst. X-ray diffraction (XRD) of acetylated starch revealed that the crystal structure of native starch was disappeared and new crystalline regions were formed. Their formation was confirmed by the presence of the carbonyl signal around 1750 cm⁻¹, as well as the reduced hydroxyl groups, in the Fourier transform infrared spectroscopy (FT-IR). The scanning electron microscopy (SEM) suggested most of the starch granules disintegrated with many visible fragments along with the increasing DS. The thermal behavior of the native starch and starch acetate were investigated using thermogravimetric analysis (TGA) and differential thermal analysis (DTA), it was observed that the thermal stability of acetylated starch depends on the degree of substitution. Thermal stability of high DS acetylated starch is much better than that of the original starch when DS reached to 2.67.     

Preliminary thermal characterization of natural resins from different botanical sources and geological environments

The preliminary studies on thermal behavior of differently aged natural resins from Russia (Khatanga), Dominican Republic (El Valle), Colombia and Poland (Jantar) were performed. Thermal stability and behavior under elevated temperature were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC), while the differences in the structure and composition by FT-IR spectroscopy. Analyzed resins show different thermal effects during heating suggesting that possible post-reactions and structural changes occurred. TG results indicated that Dominican, Russian and Colombian resins present relatively high thermal stability under air conditions in the range of 228–300 °C, whereas the mass loss of 5mass% at about 217 °C was observed for Baltic amber. During DSC experiments, the analyzed resins expose thermal events which make impossible determination of glass transition temperature in a raw sample. The results indicate that both TG and DSC cannot be considered as methods for age dating of natural resins and more advanced techniques should be applied. Careful analysis of FT-IR data in the carbonyl region may provide additional information about the composition and history of the natural resin.

     

Effect of ammonium polyphosphate on combustion and thermal degradation of aliphatic polyamides

Chain fragments with amide and imide groups are the most abundant degradation products of aliphatic polyamides (APA) which derive from scission of the N-alkylamide bond (-CH₂-NH-). In the case of polyamide 6.6 (PA-6.6), also carbodiimide structures and methyl chain ends are formed, which derive from scission of -CH₂-C(=O)- bond. Cyclic compounds can be formed besides chain fragments, depending on the type of APA. Ammonium polyphosphate (APP) reacts with APA on heating forming phosphoric esters which decompose giving products similar to those obtained from pure APA. APP increases the yield of carbodiimides from PA-6.6 which trimerise to triazine structures. The fire retardant mechanism of APP is discussed on the basis of the thermal degradation of the mixtures.     

Thermal degradation of biodegradable edible films based on xanthan and starches from different sources

Films based on xanthan/wheat starch and xanthan/maize starch were prepared in different proportions and analysed in terms of thermal stability in relation to the degradation reaction in an inert atmosphere. The main gaseous decomposition products were identified by infrared spectroscopy. Xanthan was found to be less thermally stable than starch from different sources. The starch addition to xanthan induced an increase in the film thermal stabilities. The thermal degradation mechanism of xanthan starts with scission of the side chain groups with subsequent scission of the main chain. Starches from maize and wheat presented a constant mechanism of thermal degradation. The proportion of xanthan/starch (50/50) presented a synergistic behaviour which may be associated with changes in the mechanism of the thermal degradation process. The FTIR spectra of the gaseous products during thermal degradation of xanthan showed a broad absorption in the 2750–3300 cm⁻¹ region, probably indicating decomposition of β-d-mannopyranosyl groups, present in xanthan side chains. For pure starches, absorptions related to alcohol O–H stretching (3500–3750 cm⁻¹), CO stretching of CO₂, CO and carbonyl compounds (2361, 2177 and 1743 cm⁻¹, respectively) were observed. For xanthan/starch mixtures (50/50) the same compounds as those for the pure polymer degradation were evolved. However, a shift of the CO to higher wavenumber values indicates that new carbonyl compounds are being formed due to changes in the thermal degradation mechanism.     

Study on thermal degradation and combustion behaviors of PC/POSS hybrids

Polycarbonate/polyhedral oligomeric silsesquioxane hybrids were prepared based on bisphenol A polycarbonate (PC) and trisilanolphenyl-POSS (TPOSS) by the melt blending method. Investigation of transmission electronic microscopy and Fourier transform infrared spectroscopy confirms that the nanoscale TPOSS particles were well dispersed in the PC matrix and there is no chemical reaction between the TPOSS particles and PC matrix during the melt blending. The thermal degradation behaviors of the PC/TPOSS hybrids were investigated. The presence of TPOSS significantly affects the thermal degradation process of PC. The combustion behaviors of the hybrids were evaluated by cone calorimetry experiments. The addition of TPOSS significantly decreased the value of peak heat release rate of the hybrids. Moreover, the addition of TPOSS at 2 wt% leads to the maximum decrease of the PHRR. And scanning electron microscopy and X-ray photoelectron spectroscopy were used to explore the char residues of the pure PC and the hybrids.     

Physical structure and thermal behavior of ethylcellulose

The physical structure and properties of ethylcellulose (EC) powders of different molecular weights were examined. A molecular weight in the range of 20–144 kDa with a large polydispersity was determined. EC thermal analysis revealed a glass transition at ~130 °C and a melting temperature at ~180 °C. Glass transition temperatures increased with polymer molecular weight. Wide angle (WAXS) analysis detected an amorphous broad peak at q = 1.5 Å^?1 and a distinct Bragg’s peak at 12.6 Å, which seems to be related to a supramolecular ordered structure of the polymer. These observations were confirmed using high temperature powder X-ray diffraction analysis where the crystalline peak disappeared above the melting temperature of the polymer. Ultra-small angle (USAXS) results were fitted to the Bouacage fractal unified model and fractals with an average size of 100–600 nm with a relatively smooth surface were predicted. This prediction was confirmed by transmission electron microscopy (TEM) images. According to our results, the EC polymer has a semi-crystalline structure, with crystalline domains within an amorphous background.