Highly efficient nucleating additive for isotactic polypropylene studied by differential scanning calorimetry

The influence of an organic phosphate derivative in the crystallization of the monoclinic phase of isotactic polypropylene was studied by differential scanning calorimetry. To analyze the nucleation activity of the additive, the self‐nucleation process of the pure polymer was also studied by thermal techniques. A large increase in crystallization temperatures was obtained even for the lowest concentration of the additive, and its nucleating efficiency is the highest observed for α‐nucleating agents in isotactic polypropylene. The nucleating agent was also observed to increase the stability of the crystals formed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1669–1679, 2002; DOI 10.1002/app.10546     

Low temperature annealing of isotactic polypropylene by differential scanning calorimetry

Differential scanning calorimetry has shown that secondary crystallization occurs in both smectic and monoclinic polypropylene during annealing processes at temperatures as low as 25°C. This effect has been studied in the range 25–130°C. The extent of secondary crystallization increases with both time and temperature of anneal. The rate is increased by prior annealing at either higher or lower temperature; is slightly reduced in samples cooled more slowly from the melt and is significantly reduced in γ-irradiated samples. Rate curves suggest that secondary crystallization consists of a fast process with a half life of a few hours and a slow process which continues for years. The observations are consistent with the currently accepted structural reorganisation theory for annealing at temperatures closer to the melting point. The occurrence of significant secondary crystallization at room temperature has implications with the ageing effect previously observed for some semi-crystalline polymers.     

Lignite–water interactions studied by phase transition—differential scanning calorimetry

Differential Scanning Calorimetry measurements have been made over the temperature range 20 to −50 °C with a cooling rate of 5 °C/min for six raw Victorian lignites, and for some of these lignites after water washing or acid washing. Two small peaks were observed in the region −28 to −36 °C, as found by earlier workers, in addition to a major peak at −5±3 °C which was assigned to the freezing of free water. Solutions of sodium chloride showed a single peak at about −42 °C as well as the main water peak at approximately −20 °C. However, water or acid washing the lignites to remove cations gave samples which retained the small peaks in this region with little change in intensity so that an association between the small peaks and cations or dissolved salts is unlikely. Dry samples of the coals showed no peaks, confirming that these small peaks are associated with coal–water interactions and not with the coal structure or the presence of cations.     

Phase behavior of triolein and tripalmitin detected by differential scanning calorimetry

The thermotropic behavior of triolein, tripalmitin and their mixtues was determined by differential scanning calorimetry. Polymorphic behavior was noted for the triglycerides but the triglycerides were converted to a single form after 4 to 5 successive heating scans. Melting points for each triglyceride were determined for the pure samples and mixtures, and plotted as a phase diagram. The phase diagrams indicate that a phase separation of triglycerides occurred at all concentrations of triolein and tripalmitin. However, the melting peak onset temperature of tripalmitin was shifted by triolein from 56 C at 100 mol % tripalmitin to 37 C at 15 mol % tripalmitin. Similarly, the peak onset temperature of triolein was shifted by tripalmitin from −2.5 C at 100% triolein to −4 C at 95% triolein. Enthalpies were also determined for pure samples and mixtures. These data indicated that when either triolein or tripalmitin were present as the minor component of the mixture, the enthalpy of the minor component was reduced whereas that of the major component was not greatly altered.     

Characterization of the thermal properties of PLA fibers by modulated differential scanning calorimetry

Polylactide (PLA) has been melt spun to produce multifilament continuous yarns. The thermal characteristics of PLA filaments have been investigated using modulated differential scanning calorimetry (MDSC). With MDSC, it is possible to separate the different thermal events and to analyze them more precisely. The influence of hot drawing on thermal properties of PLA filaments has been studied. Hot drawing promotes an increase of glass transition temperature (T_g) and a decrease of heat capacity. The cold crystallization spreads on a larger range of temperature and the peak occurs at a lower temperature. The initial degrees of cristallinity of PLA filaments have been calculated thanks to the reversing and non reversing curves of MDSC. Tensile properties of PLA filaments are also investigated.     

Isothermal crystallization kinetics of polypropylene by differential scanning calorimetry. I. Experimental conditions

Reliable isothermal crystallization kinetic studies can be achieved by differential scanning calorimetric techniques only under restricted conditions. In the case of isotactic polypropylene, our results indicate that those conditions are met in the range of 3°C below the isothermal crystallization temperature T_c. Experimentally, it is only in this range when the complete crystallization peak can be registered by the DSC and depicted in a thermogram. Just around this temperature interval, the Avrami exponent n = 3 for bulk crystallization, whereas for any other test the isothermal temperature T_it, nonisothermal conditions prevail and the Avrami exponent deviates from the expected value. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 970–978, 2004     

Distribution of lamella thicknesses in isothermally crystallized polypropylene and polyethylene by differential scanning calorimetry

The procedure for obtaining lamellar thickness distribution from differential scanning calorimetry (d.s.c.) curves is presented. The method has been used to study melt-crystallized polypropylene and polyethylene. The melting of the samples as registered by d.s.c. has been analysed and information regarding lamellae thickness is presented. The results obtained were consistent with the thicknesses of lamellar crystallites derived from small-angle X-ray scattering (SAXS) patterns.     

Study of structure and thermal properties of polypropylene and chlorinated polypropylene by infrared spectroscopy and differential scanning calorimetry

The infrared spectra of chlorinated polypropylene (CPP) are interpreted and tentative assignments of C—Cl stretching vibration of CPP are proposed. Recently, infrared spectrophotometry has been applied as a useful tool for the investigation of polymer transitions. The solid-state transition in isotactic polypropylene (IPP) was studied by infrared method in the range of ?50° to 30°C; and from the temperature dependence of the peak absorbance, transition at -10°C was detected. This temperature of -10°C agrees well with the T_g2 detected by other methods. From these results, it is presumed that T_g2 is attributed to a motion (thermal expansion) of IPP segments in either crystalline and amorphous region. The thermal transition of chlorinated isotactic polypropylene (CIPP) was also examined with differential scanning calorimetry and infrared method, and two thermal transitions were observed. A higher transition (T_H) has a minimum at a degree of chlorination of about 39 wt-%; and a lower transition (T_L) changes linearly with increasing degree of chlorination. Infrared results indicate that T_H may be associated with a motion (thermal expansion) in chlorinated segments, and T_L may be associated with a motion in unchlorinated segments. These results of infrared studies also suggest that CIPP may have a block structure.     

Polymorphism of milk fat studied by differential scanning calorimetry and real-time X-ray powder diffraction

The crystallization behavior of milk fat was investigated by varying the cooling rate and by isothermal solidification at various temperatures while monitoring the formation of crystals by differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD). Three different polymorphic crystal forms were observed in milk fat: γ, α, and β′. The β-form, occasionally observed in previous studies, was not found. The kind of polymorph formed during crystallization of milk fat from its melted state was dependent on the cooling rate and the final temperature. Moreover, transitions between the different polymorphic forms were shown to occur upon storing or heating the milk fat. The characteristic DSC heating curve of milk fat is interpreted on the basis of the XRD measurements, and appears to be a combined effect of selective crystallization of triglycerides and polymorphism.     

Characterisation of waxes by differential scanning calorimetry

The characterisation of hydrocarbon and natural waxes by differential scanning calorimetry is described. It is shown that the determination of the melting, cooling and remelting curves of a wax, and comparison with the corresponding curves of authenticated waxes, affords a rapid and valuable method for the identification of many waxes. Heats of transition of many waxes are also given.     

Barium titanate characterization by differential scanning calorimetry

Differential scanning calorimetry (DSC) was used to characterize barium titanate formed after decomposition of barium titanyl oxalate. Three different methods of the oxalate precipitation reaction were used to prepare barium titanyl oxalate which after calcinations result in barium titanates with different barium to titanium ratio (A/B). It appears that two factors have effect on Curie temperature: barium to titanium ratio and mechanical stress introduced by milling.     

Determination of cellulose accessibility by differential scanning calorimetry

The thermal behavior of various cellulose samples with different degrees of crystallinity as measured by X-ray diffraction techniques was studied with a differential scanning calorimeter (DSC). The broad endothermic peak which appears between 110 and 160°C is due to loss of absorbed (bound) water. Since a direct relationship was observed between the area of this peak and the crystallinity of the sample, a new procedure for estimating cellulose accessibility (which is related to crystallinity) was proposed and developed. DSC curves obtained on cellulose samples preconditioned at certain constant relative humidities were used to determine sample accessibilities by the proposed method. The accessibility values obtained by DSC showed excellent agreement with crystallinity values determined by more traditional techniques. Completely amorphous cellulose was obtained by anhydrous deacetylation of cellulose triacetate and was used as the standard amorphous cellulose material.     

Study of polyethylene blends by differential scanning calorimetry

The melting behaviors of linear and branched polyethylene blends were studied using a Perkin-Elmer DSC-1B differential scanning calorimeter. Three endothermic peaks were occasionally observed in the DSC thermogram on polyethylene blends which had not been subjected to any isothermal annealing. The nature of the third intermediate temperature peak is discussed in relation to the prior cooling rate, the blend composition and the molecular structures of both components. The results appear to indicate that the intermediate peak is associated with the fusion of the hybrid crystallites of linear and branched polyethylenes. These hybrid crystallites seem to be formed on the rapid cooling of lean linear polyethylene blends. Blends containing low molecular weight branched polyethylene seem inclined to form the hybrid crystallites.     

Triglyceride specific heat determined by differential scanning calorimetry

The specific heats of the three polymorphic forms of trilaurin, trimyristin, tripalmitin and tristearin have been determined by differential scanning calorimetry (DSC). Results from -90 to +100 C for the triglycerides were obtained and compared with the literature values determined by classical methods. Agricultural Research Service, US Department of Agriculture.     

The measurement of fatty solids by differential scanning calorimetry

A method has been developed for the measurement of the solids content of vegetable and animal fats by differential scanning calorimetry. Although precision is about half that of existing dilatometric methods, this is a rapid procedure, designed for hydrogenation control. Elapsed analysis time for the determination of solids at two temperatures is about 40 min, compared with 3 to 4 hr by dilatometry. Procedures are outlined employing either of two commercially available instruments.     

Characterization of multicomponent polyethylene blends by differential scanning calorimetry

The melting behavior of physical blends prepared from low, medium, and high density polyethylene was examined by differential scanning calorimetry. Binary low/high and ternary low/medium/high density polyethylene blends showed two endothermic peaks which were attributed to the melting of the lower and higher density components. The percent crystallinity of the blends was calculated according to an additivity relationship using the crystallinity of the pure components. These results compared favorably with an experimental crystallinity measured from the area under the melting curves.     

Characterization of epoxy thermosetting systems by differential scanning calorimetry

Differential Scanning Calorimetry (DSC) is used to study the curing behavior of epoxy systems. For non-catalyzed diamine-epoxy systems, the reaction enthalpy ΔH and the glass transition temperature T_g are evaluated and related to the structure of the hardener. A method is developed to determine the activation energy. The effect of variations in the amine-to-epoxy ratio r on T_g is also examined. A maximum value is observed for r = 1. Then, the influence of benzyldimethylamine as catalyst in an anhydride/DGEBA system and in three diamine/DGEBA systems is reported. In the cases of DDS and DDA curing agent the maximum value of T_g is shifted, to r = 0, 6. The results are explained by different reaction mechanisms.     

Curing behavior of a novolac‐type phenolic resin analyzed by differential scanning calorimetry

Curing of a novolac‐type phenolic resin was studied by DSC. The kinetic analysis was performed by means of the dynamic Ozawa method at heating rates of 5, 10, 15, and 20°C/min. This analysis was used to determine the kinetic parameters of the curing process. The activation energy was found to be 144 kJ/mol. It was found that the Ozawa exponent values decreased with increasing reaction temperature from 3.5 to 1, suggesting a change in the reaction mechanism from microgel growth to diffusion‐controlled reaction. The reaction rate constant was found to range from 123.0 to 33.6 (°C/min)ⁿ. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1678–1682, 2003