Understanding amylose crystallinity in starch–clay nanocomposites

The amylose–water interaction is part of an important equilibrating process within the starch matrix leading to slow recrystallization of amylose chains and growth of anisotropic properties in the starch matrix. This article highlights the influence of nanoclay on (a) the structural development of amylose crystallinity and (b) the rate of water loss from the starch matrix. By varying the nanocomposites level (1.5–4 wt %), a unique microstructure is obtained that “locks” moisture and it was found that on a per unit weight basis of the starch matrix, addition of 4 wt % nanoclay resulted in additional 8.5% water in the matrix. Also, it was found that increasing the nanoclay from 2 to 4% by weight, the composite modulus jumped by 100% indicating excellent interaction between clay nanocomposites and starch polymer. Analysis of the starch crystallinity data indicates that nanocomposites retard the mobility of the starch molecules (specially the long chain amylose component) to restrict the movement of “associated” water around starch and this increases the “locked” water by ～10%. The results strongly suggest that a new structural unit may be formed by amylose–water–clay interaction which enhances the composites properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 979–987, 2008     

Structure and thermodynamic melting parameters of wheat starches with different amylose content

The hierarchical granule structure of starches with different amylose content extracted from winter wheat was investigated using light microscopy (LM), scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXS), high-sensitivity differential scanning calorimetry (HS DSC) and different thermodynamic approaches. Morphology (size, size distribution and shape), crystallinity of native granules with different amylose content (1.5-39.5%), as well as the cooperative melting unit, thickness of crystalline lamellae, heat capacity drop related to hydration during melting of native granules, and thermodynamic parameters related to the surface of crystalline lamellae were determined. The relationship between structure and thermodynamic properties of mutant wheat starches is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solution grown isotactic polystyrene crystals. I. Degree and distribution of crystallinity; thermal stability

The subject of this paper is the degree of crystallinity and annealing behavior of solution grown single crystals of isotactic polystyrene (IPS) in relation to the fold length, an enquiry which acquires special significance in view of the fact that previously the fold length had been found to be identical over a wide range of crystallization temperatures (T_c). It was found that both crystallinity and thermal stability increase with T_c even over the range of constant fold length thus invalidating the usual assumption that the fold length and crystal properties are uniquely correlated. Further, the crystallinity figures as measured by conventional calorimetry are very low (<50% throughout) which by conventional ideas would require an unrealistically thick amorphous surface layer. However, the “linear crystallinity” (crystal core thickness as determined from x-ray linewidths) is much larger, commensurate with crystallinities in single crystals from other materials. It is suggested that this is the more relevant figure for the subdivision of the lamellas into crystal core and surface layer. The additional amorphous content being otherwise accommodated. Further, this “linear crystallinity” is broadly unaffected by fold length changes induced by heat annealing. The thermal stability (including annealing ability) of the crystals differs markedly whether T_c is above or below ～60°C, a T_c value which is in the range where the fold length is constant, but corresponds to a maximum in the crystallization rate. Possible connections between crystallization conditions and the stability of the resulting crystals (fold length considerations apart) are pointed out.     

含三芳胺聚西夫碱空穴输送材料结晶性、热稳定性和传输性研究

采用缩聚反应合成了两种未见报道的含三芳胺聚西夫碱空穴输送材料（PC－1，PC－2），该材料具有非晶态结构、良好的热稳定性和空穴传输性，用IR，UV－Vis，^1H NMR对所合成的聚合物进行了表征；用XRD技术对在不同溶剂中得到的聚合物的结晶现象进行了研究；用热重分析（TG）和差热分析（DTA）技术对材料在氮气中的热稳定性进行了研究，并进一步用量子化学从头算方法，对电离热（Ip）和前线轨道能进行了计算，结果表明，用二甲苯为溶剂得到的聚合物无结晶现象，PC－1，PC－2均具有良好的热稳定性和空穴传输性。     

合成榍石的抗辐照稳定性和热稳定性

以H2SiO3、CaCO3、TiO2为原料,通过固相反应合成榍石,并对合成的榍石进行热处理和60Co源辐照试验,借助X射线衍射(XRD)、扫描电子显微镜(SEM)、红外光谱(IR)、激光拉曼光谱(LRS)等分析手段,研究合成榍石的抗辐照稳定性和热稳定性.结果表明,辐照累计剂量为5.76×105Gy的60Co源辐照没有造成榍石晶格的辐射损伤,合成的榍石具有良好的抗辐照稳定性;在200℃、400℃、600℃、800℃热处理24h,榍石晶体没有发生物相变化,合成榍石晶体具有良好的热稳定性.     

The thermal stability of polyphenylene

Conclusions The thermal stability of polyphenylene produced by oxidative dehydropolycondensation of benzene was investigated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 744–748, April, 1971.     

The thermal stability of polymethylidenephthalide

Conclusions On the basis of a study of the destructive transformation of polymethylidenephthalide it was found that its decomposition is a radical-chain depolymerization process taking place randomly.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 926–928, April, 1970.     

The thermal stability of polyetherimide

A technique called bivariate fitting has been devised for obtaining kinetic parameters of thermal decomposition of polyetherimide from TGA data. In this way an apparent order of 5·33 was obtained, an apparent activation energy of 192kJ/mol, and a pre-exponential factor of 1·45 × 10¹²min⁻¹. Compared with other methods such as Friedman's⁵ and Ozawa's,⁶ this method was found to be a good approach to the solution of the kinetics of the decomposition. The products of the thermal degradation of the polymer were also analysed by ir, elemental analysis and pyrolysis/gas chromatography/mass spectrometry. A decomposition mechanism is suggested.     

The thermal stability of chalcogenide glasses

Crystallization processes of Ge_xS_1-x (0.322≤x≤0.44) glasses have been studied by thermal analysis and a new simple method of kinetic analysis is proposed. This method allows the definition of an appropriate model characterizing the crystallization process of glass, as well as calculation of reliable kinetic parameters. Results of kinetic analysis allow definition of a thermal stability criterion which has a general applicability for any glass-forming system. ICTA Young Scientist Award presentation     

Effects of hydrolysis conditions on the morphology,crystallinity, and thermal stability of cellulose nanocrystals extracted from kenaf bast fibers

Cellulose nanocrystals (CNC) were first isolated from kenaf bast fibers and then characterized. The raw fibers were subjected to alkali treatment and bleaching treatment and subsequent hydrolysis with sulfuric acid. The influence of the reaction time on the morphology, crystallinity, and thermal stability of CNC was investigated. Fourier transform infrared spectroscopy showed that lignin and hemicellulose were almost entirely removed during the alkali and bleaching treatments. The morphology and dimensions of the fibers and acid-released CNC were characterized by field emission scanning electron microscopy and transmission electron microscopy. X-Ray diffraction analysis revealed that the crystallinity first increases upon hydrolysis and then decreases after long durations of hydrolysis. The optimal extraction time was found to be around 40 min during hydrolysis at 45 °C with 65% sulfuric acid. The thermal stability was found to decrease as the hydrolysis time increased. The electrophoretic mobility of the CNC suspensions was measured using the zeta potential, and it ranged from −8.7 to −95.3 mV.     

The thermal and oxidative stability of polychlorinated metallocenes

An examination of the thermal and oxidative stability of polychlorinated ferrocenes indicated a decreasing trend in thermal stability and an increasing trend in oxidative stability with increasing chlorine content. The enhanced oxidative stability is best explained on the basis of inductive electron withdrawal from the iron atom by the chlorine atoms. The reduction in thermal stability may also be explained on the basis of the electron-withdrawing inductive effect of the chlorine substituents producing a weakening of the metal-to-ring bonding, although steric crowding due to an eclipsed conformation of the chlorine atoms is also a possible factor in the reduction. 1,1′, 2,2′-tetrachloroferrocene and 1,1′, 2,2′, 3,3′, 4,4′-octachloroferrocene were found to exhibit mesophase formation.     

The role of pore size and structure on the thermal stability of gold nanoparticles within mesoporous silica

Highly dispersed gold particles (<2 nm) were synthesized within the pores of mesoporous silica with pore sizes ranging from 2.2 to 6.5 nm and different pore structures (2D-hexagonal, 3D-hexagonal, and cubic). The catalysts were reduced in flowing H2 at 200 degrees C and then used for CO oxidation at temperatures ranging from 25 to 400 degrees C. The objective of this study was to investigate the role of pore size and structure in controlling the thermal sintering of Au nanoparticles. Our study shows that sintering of Au particles is dependent on pore size, pore wall thickness (strength of pores), and pore connectivity. A combination of high-resolution TEM/STEM and SEM was used to measure the particle size distribution and to determine whether the Au particles were located within the pores or had migrated to the external silica surface.     

The mechanism and stability of thermal transitions in hair keratin

Differential Scanning Calorimetry (DSC) has been applied to study the interactions between components of human hair keratin. Keratin is a biopolymeric composite made of several proteins forming basically two phases: amorphous matrix and crystalline microfibrillar phase. Water, the content of which depends on atmospheric humidity, is also an integral part of keratin structure. The following processes are apparent from the DSC: removal of loosely bound water (ca. 70°C), a transition in the amorphous phase (155°C) and melting/denaturation of the -crystalline phase (233°C). The process occurring in keratin at ca. 155°C has an opposite character to a glass transition; we refer to this process as the toughening transition. The area of the -keratin peak increases significantly upon annealing at temperatures from 80°C to 150°C and decreases for higher annealing temperatures. Water affects both the crystalline and amorphous phases of keratin. The process similar in nature to annealing — induced recrystallization in synthetic polymers is strictly correlated with removal of strongly bound fraction of water in keratin.     

The effect of chain extension on the thermal behaviour and crystallinity of reactive extruded recycled PET

Recycled poly(ethylene terephthalate) (R-PET) was chain extended with pyromellitic dianhydride (PMDA) in a commercial size twin-screw reactive extrusion system. Temperature-modulated differential scanning calorimetry (TMDSC) was used to evaluate the effect of the chain extension process on the thermal transitions and crystallinity of R-PET. Reactive extruded recycled PET (RER-PET) samples were tested based on different PMDA concentration and reactive extrusion residence times. The glass transition temperature (T _g) did not show a significant change as a function of PMDA addition or the extrusion residence time. Melting temperature (T _m) and crystallisation temperature (T _c) decreased with increasing PMDA concentration and with increasing extrusion residence time. RER-PET samples showed double melting peaks, it is believed that different melting mechanism is the reason behind this phenomenon. The crystallinity of RER-PET samples is lower than that of R-PET. RER-PET samples at constant PMDA concentration showed a decrease in crystallinity with increasing extrusion residence time. Results suggest that the reactive extrusion process is more dependent on PMDA concentration rather than reactive extrusion process residence time.The first author would like to acknowledge Advanced Engineering Center for Manufacturing (AECM) and Visy Industries for their financial support to this study.     

Degree of crystallinity and lattice thermal conductivity of polyethylene at low temperatures

The lattice thermal conductivity of a semicrystalline polymer was studied at low temperatures by calculating the total lattice thermal conductivities of four samples of polyethylene with different degrees of crystallinity between 0.43 and 0.81 and temperatures between 0.4 and 20 K. The contributions of the crystalline and noncrystalline natures and their percentage contributions were taken into account. The predicted lattice thermal conductivity of polyethylene was in fairly good quantitative agreement with the experimental value, and showed a strong crystallinity dependence, with a distinctive cross-over point at about 2 K.     

The thermal stability of some pulping materials

The thermal stabilities of three annual plants (reed, kenaf and Glycyrrihiza glablra L.) are studied. Various types of pulps were prepared from reed stalks by employing the soda, kraft and soda-anthraquinone processes. Their thermal stabilities are reported.It is shown that the thermal stability measured thermogravimetrically depends, to some extent, on the amount of lignin remaining in the raw materials, i.e. the kappa number.The activation energy of the decomposition process and the decomposition temperatures of the pulps are also reported.     

The thermal stability of two substituted thioamides

A derivatographic investigation was performed on the thermal behaviour of three thioamides and the nonisothermal kinetic parameters for the liquid-phase decomposition of N-acetylthiobenzamide were determined.     

Pseudohexagonal crystallinity and thermal and tensile properties of ethene–propene copolymers

Structural (X‐ray diffraction), melting (differential scanning calorimetry), as well as mechanical (tensile tests) characterizations on uncrosslinked ethene–propene copolymer samples, obtained using a metallocene‐based catalytic system and having an ethene content in the range 80–50% by mol, are reported. Samples with an ethene content in the range 80–60% by mol present a disordered pseudohexagonal crystalline phase, whose melting moves from ≈ 40°C down to ≈ −20°C as the ethene content is reduced. The dramatic influence of the crystalline phase on tensile properties of uncrosslinked ethene–propene copolymers is shown. In particular, highest elongation at break values are obtained for samples being essentially amorphous in the unstretched state and partially crystallizing under stretching. On the other hand, lowest tension set values (most elastic behavior) are observed for samples presenting, already in the unstretched state, microcrystalline domains acting as physical crosslinks in a prevailing amorphous phase. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1095–1103, 1999