Glass transition temperature and thermal decomposition of cellulose powder

Cellulose powder and cellulose pellets obtained by pressing the microcrystalline powder were studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermal gravimetry (TG). The TG method enabled the assessment of water content in the investigated samples. The glass phase transition in cellulose was studied using the DSC method, both in heating and cooling runs, in a wide temperature range from −100 to 180 °C. It is shown that the DSC cooling runs are more suitable for the glass phase transition visualisation than the heating runs. The discrepancy between glass phase transition temperature T _g found using DSC and predictions by Kaelbe’s approach are observed for “dry” (7 and 5.3% water content) cellulose. This could be explained by strong interactions between cellulose chains appearing when the water concentration decreases. The T _g measurements vs. moisture content may be used for cellulose crystallinity index determination.     

Sodium and silver phosphate glasses doped with chlorides of Fe,Mn and Zn

A number of samples of sodium and silver phosphate glasses doped with various compositions of some transition metals viz. iron, manganese and zinc chlorides alongwith undoped samples of sodium and silver phosphate glasses were synthesized and characterized by X-ray diffraction, IR spectral, electrical conductivity and differential scanning calorimetry (DSC). The glass transition temperature (T _g) and crystallization temperature (T _c) values obtained from DSC curves were found to increase with increasing concentration of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses and the following sequence is observed: T _g(–FeCl₃)>T _g(–MnCl₂)>T _g(–ZnCl₂) T _c(–FeCl₃)>T _c(–MnCl₂)>T _c(–ZnCl₂) The increase in T _g and T _c values indicate enhanced chemical durability of the doped glasses. The electrical conductivity values and the results of FTIR spectral studies have been correlated with the structural changes in the glass matrix by the addition of different transition metal cations as dopants.     

The Influence of Drawing in Hot Water on The Morphological Properties of Pet Films as Measured by DSC and Modulated DSC

PET films uniaxially drawn in hot water are studied by means of conventional DSC and modulated DSC (MDSC).Glass transition is studied by MDSC which allows to access the glass transition temperature T _g and the variations of ΔC _p=C _p1−C _pg (difference between thermal capacity in the liquid-like and glassy states at T=T _g). Variations of T _g with the water content (which act as plasticizer) and with the drawing (which rigidifies the amorphous phase) are discussed with regard to the structure engaged in these materials. The increments of ΔC _p at T _g are also interpreted using a three phases model and the 'strong-fragile’ glass former liquid concept. We show that the ‘fragility’ of the medium increases due to the conjugated effects of deformation and water sorption as soon as a strain induced crystalline phase is obtained. Then, ‘fragility’ decreases drastically with the occurring rigid amorphous phase. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Methods Applied to the Glass Transition of Mixed Network AlPO4–BPO4–SiO2 Glasses

Glass transition effect of mixed network AlPO₄–BPO₄–SiO₂ glasses was studied. DTA/DSC and TMA measurements has been applied in the research. It has been found that glass transition effect has structurally sensitive properties. Glass transition temperature T _g, changes of specific heat (Δc _p)and thermal expansion coefficient (α) accompanying the process depend on the nature and the number of components forming the glassy framework. Character of chemical bonds combining them into the glass structure has an influence on the glass transition effect. Its course is dependent on the flexibility of the structure of glasses. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calorimetric and EPR studies of the thermotropic phase behavior of phospholipid membranes

Transmission electron micrographs (TEM) showed that liposome vesicles prepared from DL-α-phosphatidylcholine dimyristoyl (1,2-ditetradecanoyl-rac-glycerol-3-phosphocholine) (DMPC) by the modified reverse-phase evaporation method (mREV) were spherical in shape and in majority of them were less than 100 nm in diameter. Differential scanning calorimetry (DSC) method was used to determine the influence of cholesterol content and pH of Tris-HCl buffer used for the preparation of liposomes on the temperature of phase transition T _C of phospholipids which form the investigated liposome vesicles. The use of DSC method made it possible to determine not only the temperature of the main phase transition of phospholipids but also the temperature of the phospholipid phase transition from the tilted gel phase(L _β′) to the ripple gel phase(P _β′). The results were compared with those obtained with EPR study. EPR study was carried out in the temperature range from 284 to 310 K i.e. below and above the phase transition temperature T _C of DMPC. On the basis of EPR spectra of spin marker 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) incorporated into the liposome, the values of parameters f were determined. Hence TEMPO can be used to observe the change in partition between aqueous and fluid lipid regions. The change in the relative values of f determined for DMPC as a function of temperature shows that this phospholipid undergoes a transition from a ‘gel phase’ to a lamellar smectic liquid crystalline phase in the presence of excess water. The EPR study of TEMPO allowed us to determine the transition temperature T _C. The results were compared with those obtained with DSC method.     

Synthesis of Diblock Copolymers With Cellulose Derivatives. 2. Characterization and Thermal Properties of Cellulose Triacetate-Block-Oligoamide-15

Well-defined A-block-B type cellulose derivatives consisting of cellulose triacetate (CTA) and oligoamide-15 were synthesized. Chemical structures of the diblock copolymers were characterized by MALDI-TOF MS, ¹H-NMR, and GPC. Influence of length of CTA and oligoamide-15 segments on their thermal properties was investigated by means of differential scanning calorimetry (DSC). All diblock copolymers displayed T _g, T _c, and T _m transition temperatures. Their T _g and T _m values increased with the increase of molecular weight of CTA segment. The crystallinity of diblock copolymers increased after isothermal crystallization at 200 °C. Its X-ray analysis revealed that the diblock copolymer had CTA II crystal structure. Thermal analysis supported microphase separation between CTA and oligoamide-15 segments at room temperature, because T _g and T _m values of polyamide-15 are −7 °C and 170–180 °C, respectively.     

Thermal characterization of starch-based polymers produced by <Emphasis Type="Italic">Ophiostoma</Emphasis> spp

The thermal behavior of modified starches (MS) produced by biosynthetic pathway is described based on a comparative analysis with native starches (NS). MS were produced by fermentation in presence of Ophiostoma spp. cultures. Thermogravimetric analysis (TG) with successive derivatives (DTG) and differential scanning calorimetry (DSC) were used for this study. NS results showed a single peak dominating both the TG (DTG) and DSC plots. A double thermal transition event was detected in samples of MS. The procedural decomposition temperature (T _i–T _f; lowest onset temperature of initial and final mass change) was carried out within a narrow interval of temperatures for NS (610–640 °C). This interval could not be reached within the 1,000 °C range in MS. Residues higher than 10% were recorded for MS at this temperature. The presence of the double thermal transition in MS is discussed.     

Elastic Moduli and Activation Energies for an Epoxy/m-XDA System by DMA and DSC

The influence of the resin/diamine ratio on the properties of the system diglycidyl ether of bisphenol A (BADGE n=0/m-xylylenediamine) (m-XDA) was studied. Variation of this ratio resulted in significant effects on the cure kinetics and final dynamic mechanical properties of the product material. The study was made in terms of storage modulus (E′), vss modulus (E″) and molecular mass between cross-links (M_c) at different ratios. Two geometries (cylindrical and rectangular) were considered. The influence of temperature was studied through the activation energy (E_a>), which depends on the epoxy/amine ratio and the geometry of the samples. Glass transition temperatures (T_g>) and glass transition temperatures for thermosets with null degree of conversion (T_go>) were determined by DSC. T_g> decreases when amounts of curing agent greatly in excess of the stoichiometric composition were used. This revised version was published online in July 2006 with corrections to the Cover Date.     

Water sorption and glass transition of freeze-dried camu-camu (myrciaria dubia (H.B.K.) Mc Vaugh) pulp

Differential scanning calorimetry (DSC) was used to determine phase transitions of freeze-dried camu-camu pulp in a wide range of moisture content. Samples were equilibrated at 25°C over saturated salt solutions in order to obtain water activities (a_w) between 0.11–0.90. Samples with a_w>0.90 were obtained by direct water addition. At the low and intermediate moisture content range, Gordon–Taylor model was able to predict the plasticizing effect of water. In samples, with a_w>0.90, the glass transition curve exhibited a discontinuity and T^’_g was practically constant (–58.8°C), representing the glass transition temperature of the maximally concentrated phase(T_g ).     

Physical Aging of Maltose Glasses as Measured by Standard and Modulated Differential Scanning Calorimetry

The physical aging characteristics of maltose glasses aged at two temperatures below the glass transition temperature, T_g, (T_g-10°C and T_g-20°C) from 5 to 10 000 min were measured by standard differential scanning calorimetry (SDSC) and modulated differential scanning calorimetry (MDSC). The experimentally measured instrumental T_g, the calculated T_g, and the excess enthalpy values were obtained for aged glasses using both DSC methods. The development of excess enthalpy as a function of aging time, as measured by both SDSC and MDSC, was fit using the Cowie and Ferguson and Tool-Narayanswamy-Moynihan models. The change in the T_g values and the development of the excess enthalpy resulting from physical aging measured by the two DSC methods are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rigid amorphous fraction in poly(ethylene terephthalate) determined by dilatometry

Volumetric thermal analysis of semicrystalline poly(ethylene terephthalate), PET, with different content of crystalline phase was carried out using mercury-in-glass dilatometry. The effect of crystals on the thermal properties of amorphous phase (glass transition temperature, T _g, thermal expansion coefficients, α) were determined. At cold-crystallization (106°C, up to 4 h), crystalline content of 2.4–25.3 vol.% was achieved. Increasing content of crystalline phase broadens the glass transition region and increases T _g. The change of thermal expansion coefficient during glass transition is lower than that predicted by the two-phase model, which indicates the presence of a third fraction — rigid amorphous fraction (RAF), whose content steadily increases during crystallization. However, its relative portion (specific RAF) is significantly reduced. Further significant decrease in specific RAF appears after annealing at a higher temperature.     

Changes of mechanical properties in cold-crystallized syndiotactic polypropylene during aging

Many semicrystalline polymers undergo a process of aging when they are stored at temperatures higher than their glass-transition temperature (T _g). Syndiotactic polypropylene was quenched from the melt to −40 °C, crystallized from the glassy state at 20 or 40 °C and stored at the respective temperature for different aging times up to 7200 h. A significant increase in the tensile modulus and stress at yield and a decrease in strain at yield were observed for both aging temperatures. Differential scanning calorimetry (DSC) scans of aged material showed an endothermic annealing peak 15–30 °C above the previous aging temperature, the maximum temperature and enthalpic content of which increased with aging time. The position and the shape of the melting peak were not affected by aging. Scans of the storage modulus obtained from dynamic mechanical analyser measurements indicated a softening process starting at about 20 °C above the aging temperature and correlating with the annealing peak detected by DSC. Density measurements and wide-angle X-ray scattering investigations revealed that neither the crystallinity increased significantly nor did the crystal structure change. So the observed property changes induced by aging are attributed to microstructural changes within the amorphous phase. Furthermore, it could be shown by annealing experiments carried out at 60 °C, that aging above T _g is, analogous to aging below T _g (physical aging), a thermoreversible process. Received: 18 September 2000 Accepted: 2 January 2001     

An analysis of the thermal aging behaviour in high-performance energetic composites through the glass transition temperature

Differential scanning calorimetry (DSC) was used to analyze the thermal aging behaviour in energetic composite materials where a hydroxyl-terminated polybutadiene (HTPB)/isophorone diisocyanate elastomer is the polymeric matrix. Different parameters from the analysis of the glass transition, such as the glass transition temperature (T_g), were used in order to monitor this isothermal aging at 65 °C during a total time of 3000 h, finding an increasing and broadening T_g. In addition, the accelerated aging behaviour of these materials was also studied by a classical method, based on the change of mechanical properties such as those of Young's modulus or strain at break. The correlation between both methodologies was examined, demonstrating that an analytical technique such as DSC allows the evaluation of the actual state of composite solid propellants with a small sample and a straightforward measurement.     

Determination of the glass transition temperature in thin polymeric films used for microelectronic packaging by temperature-dependent spectroscopic ellipsometry

We characterized the glass transition temperature T_g of thin polyimide films by temperature-dependent spectroscopic ellipsometry and compared the results to DSC measurements of the bulk polymer. The effect of the curing temperature on T_g and the thermal expansion α(T) was analyzed. An improved ellipsometric data evaluation was used to get most precise and reliable T_g data. T_g increased with increasing curing temperature, while the bulk T_g was considerably lower than the thin film T_g. Both observations are attributed to the temperature sensitive release of the imidization by-product 2-hydroxyethyl methacrylate (HEMA) and crosslinker components as well as decomposition products from the material. Variation in the curing temperatures of 230–380 °C led to an increase in the T_g of 34 °C.     

Curing behavior of epoxy resins with a series of novel curing agents containing 4,4′-biphenyl and varying methylene units

A new homologous series of curing agents (LCECAn) containing 4,4′-biphenyl and n-methylene units (n = 2, 4, 6) were successfully synthesized. The curing behaviors of a commercial diglycidyl ether of bisphenol-A epoxy (E-51) and 4,4′-bis(2,3-epoxypropoxy)biphenyl (LCE) by using LCECAn as the curing agent have been investigated by differential scanning calorimetry (DSC), respectively. The Ozawa equation was applied to the curing kinetics based upon the dynamic DSC data, and the isothermal DSC data were fitted using an autocatalytic curing model. The glass transition temperatures (T _g) of the cured epoxy systems were determined by DSC upon the second heating, and the thermal decomposition temperatures (T _d) were obtained by thermogravimetric (TG) analyses. The results show that the number of methylene units in LCECAn has little influence on the curing temperatures of E-51/LCECAn and LCE/LCECAn systems. In addition, the activation energies obtained by the dynamic method proved to be larger than those by the isothermal method. Furthermore, both the T _g and T _d of the cured E-51/LCECAn systems and LCE/LCECAn systems decreased with the increase in the number of methylene units in LCECAn.     

Synthesis and Thermal Behavior of Poly(2-hydroxyethoxybenzoate) and Its Copolyesters with ε-caprolactone

Poly(2-hydroxyethoxybenzoate), poly(ε-caprolactone), and random poly(2-hydroxyethoxybenzoate/e-caprolactone) copolymers were synthesized and characterized in terms of chemical structure and molecular mass. The thermal behavior was examined by DSC. All the samples appear as semicrystalline materials; the main effect of copolymerization was lowering in the amount of crystallinity and a decrease of melting temperature with respect to homopolymers. Flory's equation described well the T _m-composition data. Amorphous samples (in the 20–100%2-hydroxyethoxybenzoate unit concentration range) obtained by quenching showed amonotonic decrease of the glass transition temperature T _g as the content of caprolactone units is increased. The Wood's equation described the T _g-composition data well. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of thermoplastic toughening agent on glass transition temperature and cure kinetics of an epoxy prepreg

The isothermal time–temperature-transformation (TTT) cure diagram is developed in this article to investigate the effect of thermoplastic toughening agent on glass transition temperature (T _g) and cure kinetics of an epoxy carbon fiber prepreg, Cycom 977-2 unidirectional (UD) tape. The glass transition temperature was measured using differential scanning calorimetry (DSC) over a wide range of isothermal cure temperatures from 140 to 200 °C. Times to gelation and vitrification were measured using shear rheometry. The glass transition temperature master curve was obtained from the experimental data and the corresponding shift factors were used to calculate the activation energy. The kinetic rate model was utilized to construct iso-T _g contours using the calculated activation energy. It was observed that the iso-T _g contours did not follow the behavior of the neat epoxy resin, since they deviated from the gel time curve. This deviation was believed to be the effect of the thermoplastic toughening agent. The behavior of the neat epoxy resin in 977-2 was shown by constructing the iso-T _g contours using the activation energy obtained from gel time modeling.     

Cure kinetics of thermosetting bisphenol E cyanate ester

Resin injection repair is a common method to repair delamination damage in polymer matrix composites (PMCs). To repair high-temperature PMCs, the resin should have a very low viscosity, yet cure into a compatible adhesive with high temperature stability. Normally, thermosetting polymers with high glass transition temperatures (T _g) are made from monomers with high room temperature viscosities. Among the high temperature resins, bisphenol E cyanate ester (BECy, 1,1’-bis(4-cyanatophenyl)ethane), is unique because it has an extremely low viscosity of 0.09–0.12 Pa s at room temperature yet polymerizes as a cross-linked thermoset with a high T _g of 274°C. BECy monomer is cured via a trimerization reaction, without volatile products, to form the high T _g amorphous network. In this study, the cure kinetics of BECy is investigated by differential scanning calorimetry (DSC). Both dynamic and isothermal experiments were carried out to obtain the kinetic parameters. An autocatalytic model was successfully used to model isothermal curing. The activation energy from the autocatalytic model is 60.3 kJ mol⁻¹ and the total reaction order is about 2.4. The empirical DiBenedetto equation was used to evaluate the relationship between T _g and conversion. The activation energy of BECy from the dynamic experiments is 66.7 kJ mol⁻¹ based on Kissinger’s method, while isoconversional analysis shows the activation energy changes as the reaction progresses.     

Effect of MoO<Subscript>3</Subscript> additions on the thermal stability and crystallization kinetics of PbO–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–As<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The present paper reports on the effect of MoO₃ on the glass transition, thermal stability and crystallization kinetics for (40PbO–20Sb₂O₃–40As₂O₃)_100−x –(MoO₃) _x (x = 0, 0.25, 0.5, 0.75 and 1 mol%) glasses. Differential scanning calorimetry (DSC) results under non-isothermal conditions for the studied glasses were reported and discussed. The values of the glass transition temperature (T _g) and the peak temperature of crystallization (T _p) are found to be dependent on heating rate and MoO₃ content. From the compositional dependence and the heating rate dependence of T _g and T _p, the values of the activation energy for glass transition (E _g) and the activation energy for crystallization (E _c) were evaluated and discussed. Thermal stability for (40PbO–20Sb₂O₃–40As₂O₃)_100−x –(MoO₃) _x glasses has been evaluated using various thermal stability criteria such as ΔT, H _r , H _g and S. Moreover, in the present work, the K _r(T) criterion has been considered for the evaluation of glass stability from DSC data. The stability criteria increases with increasing MoO₃ content up to x = 0.5 mol%, and decreases beyond this limit.     

Thermal analysis of environmentally compatible polymers containing plant components in the main chain

Environmentally compatible polymers such as poly(ε-caprolactone) (PCL) and polyurethane (PU) derivatives from PCL's were synthesized from saccharides, polysaccharides and lignins such as glucose, fructose, sucrose, cellulose, cellulose acetate, alcoholysis lignin, kraft lignin and sodium lignosulfonate. Flexible and rigid PU sheets and foams were also prepared by the reaction of OH groups of saccharides and lignins with isocyanates such as toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). Glass transition temperatures (T_g's), cold-crystallization temperatures (T_cc's) and melting temperatures (T_m's) of saccharide- and lignin-based PCL's and PU's were determined by differential scanning calorimetry (DSC), and phase diagrams were obtained. Methods of controlling mechanical properties such as stress and elasticity of PU's through changing thermal properties such as glass transition temperature were established. Thermogravimetry (TG) and TG-Fourier transform infrared spectrometry (FTIR) were also carried out in order to analyze the degradation temperature and evolved gases from the above obtained polymers. This revised version was published online in July 2006 with corrections to the Cover Date.