Solid Fat Content Estimation by Differential Scanning Calorimetry: Prior Treatment and Proposed Correction

The objective of this work was to develop a corrected method for solid fat content estimation by differential scanning calorimetry (DSC), as important differences are usually observed between the results given by DSC and pulsed nuclear magnetic resonance (NMR). Cold storage after full melting of fats was necessary to avoid the appearance of exothermic peaks in the modulated temperature DSC thermograms, in order to make an appropriate estimation of melting energy. Different fats were analyzed by NMR and DSC, obtaining considerably higher solid fat content values with the latter, uncorrected method. These differences were attributed to the fact that consumed energy per unit of melted mass tends to increase with the increase of the melting temperature of each fraction of the fats. A linear correlation between melting enthalpy and melting point of different triglycerides was used to estimate the energy per unit of mass consumed at each temperature. From these data, an estimated transformation of melting energy into melted mass was performed and new solid fat content values were calculated. The results obtained from this correction were much closer to the measurements made by NMR, in comparison to the uncorrected DSC method.     

Friction and its effect on the mechanical- to-thermal energy conversion during extrusion of poly(vinylidene chloride)

Solid state friction reduction has been found to be an effective method for extrusion stabilization of a high coefficient of friction (COF) thermally sensitive polymer. A poly(vinylidenechloride) copolymer (PVDC) was studied alone and blended with various polyolefins to change its frictional behavior. COF of the polymer rubbing on a metal surface was measured under conditions typical of an extrusion process. These results correlated well with the measured mechanical energy consumed during extrusion. Of the polyolefins studied, high and low density polyethylene were found to be very effective for lowering friction and improving extrusion performance of the PVDC. Polypropylene was found to be much less effective. Interface temperature where melting occurs due to frictionally generated heat has been experimentally shown to be a function of COF and the bulk metal temperature.     

Co-crystals of Beeswax and Various Vegetable Waxes with Sterols Studied by X-ray Diffraction and Differential Scanning Calorimetry

In this study, mixtures of purified wax and sterols were melted and subsequently cooled. Using X-ray diffraction of the mixed, solid phase, it was shown that for up to 30–40 wt% sterols no measurable re-crystallisation of sterols occurred, i.e. the sterols became dissolved at a molecular level. Probably a form of amorphous co-crystals of sterols and wax is formed if the molecular ratio does not exceed 1:1. Differential scanning calorimetry (DSC) suggests that a minor amount of pure sterols could already be present at lower sterol levels. This may be because of the higher temperature at which the microstructure is probed when using DSC—melting of the wax might lead to crystallisation of the sterols. For application in foods, the structure as probed by X-rays at ambient temperatures is more relevant. When sunflower wax and rice bran wax are used, prevention of sterol crystallisation is even more pronounced, probably because the melting temperatures of these waxes are closer to the melting temperature of sterol crystals. Replacing the beeswax with a saturated fat (heRP70), sunflower oil, or jojoba wax (a liquid wax) substantially increases the amount of crystalline sterols. The difference between the various waxes and fats was qualitatively the same for X-ray diffraction and DSC. Stanols can be incorporated in the same manner and up to similar concentrations. Another insoluble nutritional compound, ursolic acid, has a greater tendency to crystallise in wax. This is probably because the melting temperature of ursolic acid is much higher than that of wax.     

SbSn金属间化合物结构与原油脱硫效果评价

为了考察SbSn金属间化合物的制备条件对材料的结构以及脱硫性能的影响,采用不同的熔融温度,配以喷雾快冷法制备了SnSb金属间化合物.用差热分析和XRD对产物进行了测试表征.对产物的结构进行了模拟计算与讨论,给出了产品制备温度分别在750℃和950℃下的分子点群示意图.发现锡锑化合物在升温过程中,熔体的结构会发生变化,不同熔融温度下制备出的材料的晶体结构不同.脱硫实验结果表明,900℃以上熔融喷雾快冷制备出的材料具有较好的脱硫性能.在SnSb和原油乳化液质量比为1∶20的条件下,950℃下,熔融喷雾快冷制备出的材料一次搅拌24 h可以使原油中的硫含量降低2440.0 μg·g^-1.     

An experimental study on shear stress characteristics of polymers in plasticating single‐screw extruders

Frictional forces (for temperatures less than the melting or devitrification temperature) and viscous forces (for higher temperatures) have important roles on solids conveying and melting processes in plasticating single‐screw extruders. These forces are related to the shear stresses at polymer–metal interfaces. For temperatures at which the frictional forces are the main factor for the shear stresses, it is experimentally difficult to obtain the shear stresses at the polymer–metal interface. The interpretation of the data has further complications due to the frictional energy dissipation at the polymer–metal interface. An instrument called the Screw Simulator was used for further understanding of shear stresses at the polymer–metal interface and comparison of melting fluxes of different resins. This article presents the shear stress and melting flux measurements for low density polyethylene (LDPE), linear LDPE (LLDPE), acrylonitrile butadiene styrene (ABS), and high‐impact polystyrene (HIPS) resins as a function of sliding velocity and interface temperature at a fixed pressure of 0.7 MPa. The relationship between the experimental data and the extrusion process is also discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Additives for processing rigid PVDC copolymers

Polyvinylidene chloride (PVDC) copolymers are highly crystalline materials used in packaging applications because of their strength and excellent barrier properties. The crystalline moiety (～40 to 50%) generally melts from 160 to 170°C and the amorphous phase T_g is between 0 and 35°C depending on the comonomer type and level. PVDC is much less thermally stable than PVC and degrades very rapidly in the same temperature range (i.e. above the T_m) required to process the material. Added plasticizers are utilized to reduce processing temperatures but at the expense of barrier properties. There is a need to process PVDC sans plasticizer to achieve maximum possible barrier properties in multilayer composite sheet and films. Additives will be discussed that have been shown (in laboratory tests) to delay the fusion of the amorphous phase of unplasticized PVDC until the material temperature nears the crystalline melting point, thus reducing the overall heat history with a minimal effect on other important properties.     

LDPE-g-MAH对LDPE/PVDC共混体系性能的影响

以低密度聚乙烯(LDPE)为基体材料,聚偏氯乙烯(PVDC)为共混材料,马来酸酐接枝低密度聚乙烯(LDPE-g-MAH)为相容剂,采用挤出和注塑成型方法制备LDPE/PVDC/LDPE-g-MAH共混物,考察了共混物的力学性能、阻隔性能、热性能和微观形态结构。结果表明:加入25%PVDC,LDPE/PVDC共混物的熔融温度下降了1.79℃,吸油率降低了9.66%,物理力学性能明显下降;加入LDPE-g-MAH后,LDPE和PVDC之间的界面黏结力增强,相容性提高,结晶温度和结晶度略有下降;与纯LDPE相比,含3%LDPE-g-MAH的LDPE/PVDC共混物的断裂伸长率提高了11.63%,缺口冲击强度提高了13.35%,吸油率下降了16.29%,柔韧性和阻隔性明显提高。     

DSC and DMA studies on silane‐grafted and water‐crosslinked LDPE/LLDPE blends

Effects of silane grafting and water crosslinking reactions on crystallizations, melting behaviors, and dynamic mechanical properties of the LDPE/LLDPE blends are investigated using DSC and DMA. From DSC data, cocrystallization of LDPE and LLDPE does not occur, but cocrosslinking of these two polymers is evidenced at the experimental temperature of 100°C, a temperature lower than melting temperatures of both polymers. The water crosslinking reactions of the LLDPE‐rich blends enable development of a new phase having a melting endotherm in between that of LDPE and LLDPE. From the thermal fractionation data, interaction between LDPE and LLDPE is observed, and compatibilization of the blends can be achieved by the crosslinking reactions. From DMA data, the storage moduli of the blends are not found to be consistent with their degrees of crosslinking. The storage moduli of the blends are not simply determined by the degree of crosslinking but determined by very complicated but unclear factors. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1808–1816, 2001     

Mechanical and thermal properties of potassium salts of poly(ethylene‐co‐ethylacrylate): Polyolefin ionomers in the absence of acid groups

The thermal and mechanical properties of ionomers prepared by partial saponification of poly(ethylene‐co‐ethylacrylate) (EEA) with potassium were investigated by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The Vicat softening temperature (VST) and bending modulus were also evaluated. Molecular design of the present EEA‐based ionomers eliminates acid groups, which affect ionic aggregates for conventional ionomers. The DSC results showed that the melting enthalpy and main crystallization temperature decreased as the ion content increased, whereas on the other hand, the crystal melting temperature at about 360 K did not depend on the ion content, and a secondary exothermal peak was observed in the cooling process. The variance of the VST increased as the crystallinity decreased. The temperature‐dependent curves of DMA data of the EEA‐based potassium ionomers with a higher ion content showed elastic plateau even at temperatures above their crystal melting points. Our results indicate the existence of strong cross‐linking mediated by ion aggregates. The quadratic increase of stiffness as a function of ion content, increasing VST with decreasing crystallinity, and elastic plateau of temperature‐dependent moduli above crystal melting temperature are significant characteristics of the EEA‐based potassium ionomers, which contain ionic aggregations without acid group presence. POLYM. ENG. SCI., 55:1843–1848, 2015. © 2014 Society of Plastics Engineers     

Calorimetric study of milk fat/rapeseed oil blends and their interesterification products

Milk fat (MF) and rapeseed oil (RO) blends were analyzed by differential scanning calorimetry (DSC). It was shown that peak and onset temperatures can be used to determine the percentage of each fat in the blend and that the relative enthalpy of one peak assigned to low‐melting triacylglycerols (TAG) can also be used to determine the percentage of RO in the blend. A linear relation was also established between MF content of the blend and its dropping point (DP), indicating that DP can be linearly related with the above DSC data. A blend of MF/RO 70 : 30 (wt/wt) was then chosen as a model system for enzymatic interesterification (EIE). The applicability of DSC analyses to EIE products was checked and a correct correlation could be established between DSC values and the interesterification degree and DP. Among the data from the DSC profiles, the peak associated with low‐melting TAG was the best indicator of the reaction course. In the same way, a high‐melting MF stearin fraction was interesterified with RO. In that case, onset temperatures and peak “a” were better reaction indicators than for the interesterified MF/RO blend. We therefore suggest that values from DSC endotherms could be used to monitor EIE of fat blends.     

Preparations and properties of a high performance semicrystalline copolyimide and composites reinforced with glass fiber

A semicrystalline copolyimide derived from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (s‐BPDA), 1,3‐bis‐(4‐aminophenoxy)benzene (TPER), and 4,4′‐oxydianiline (4,4′‐ODA), end capped with phthalic anhydride (PA), was synthesized. Glass fiber reinforced composite was also prepared by impregnating powdery glass fiber with poly(amic acid) followed by solution imidization techniques. This copolyimide displayed a glass transition temperature of 202°C and a melting temperature of 373°C by differential scanning colorimeter (DSC). Crystallization and melting behaviors were investigated under nonisothermal and isothermal crystallization conditions. Double exothermic peaks were found by DSC when the copolyimide was cooled from the melt and multiple melting behaviors can be observed after the coployimide had been isothermally crystallized at different temperatures. Mechanical properties were investigated by dynamical mechanical analysis (DMA) and tensile experiments. The samples were cured at different temperatures and then tested at different temperatures. Results indicated that the copolyimide and the composite showed excellent mechanical properties. Additionally, this copolyimide also showed lower melt viscosity by rheological analysis. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40345.     

乙烯/乙酸乙烯酯/甲基丙烯酸离聚体的合成、表征及性能

以乙烯/乙酸乙烯酯/甲基丙烯酸三元嵌段聚合物为基体合成了它的钠、锌盐离聚体。通过FT IR谱图以及DSC、TGA曲线证明了钠、锌离子与甲基丙烯酸发生了反应,玻璃化温度、熔点有提高;同时经过力学性能测试表明合成的离聚体在力学性能方面有改进。硬脂酸锌是离聚体的有效增塑、增强剂,离聚体的拉伸强度随着硬脂酸锌用量的增加而增加,其最大用量为30%。     

The Glassmelting Process: II, Glass Structure and the Effects of "Melting History" on Glass Properties

Interpretations are made of experimental and practical aspects of glass structures in terms of a postulated distribution of anionic structures in glass. The existence of effects determined by the "melting history" of a glass is demonstrated by specially programmed experiments on viscosity and tensile strength. The viscosity curve of glass melted at a relatively low temperature lies above that for the same glass which had been previously melted at high temperatures. The two curves merge in the high-temperature region. It also is found that the tensile strength of glass fibers increases as the maximum melting temperature increases.     

Dielectric and dynamic mechanical relaxation behaviour of poly(ethylene 2,6-naphthalene dicarboxylate). II. Semicrystalline oriented films

The dielectric and dynamic mechanical behaviour of bi-stretched non-treated and annealed semicrystalline poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) films are studied as a function of different morphologies obtained by thermal treatments at temperatures close to the melting temperature of a semicrystalline film. Differential scanning calorimetry (DSC) shows that the glass transition temperatures do not change significantly with the thermal treatment for bi-stretched films. However, the melting temperatures and the degree of crystallinity increase with the value of annealing temperature. Both dielectric relaxation spectroscopy (DRS) and dynamic mechanical analysis (DMA) display three relaxation processes. In order of decreasing temperature, can be observed: the α-relaxation due to the glass transition, the β^∗-process assigned to cooperative molecular motions of the naphthalene groups which aggregate and the β-relaxation due to local fluctuations of the carbonyl groups. The α-relaxation process shifts to higher temperatures for the 250 and 260 °C treated bi-stretched semicrystalline samples compared to the sample thermally treated at 240 °C according to DRS data but shifts to lower temperatures according to the DMA measurements for the three annealed samples. This discrepency results from the different sensitivity of each methods with regards to the release of orientation. At a fixed frequency the temperature associated to β^∗-relaxation is lower for the non-treated bi-stretched semicrystalline samples than for the treated ones using DMA but no difference can be seen in DRS. The associated apparent activation energies are rather high which suggest cooperative motions. It is assumed that the orientation of the samples prevents coupling between the naphthalene groups due to the stretched chain configuration in the amorphous phase. The activation energy for the β-process given by DRS is independent of the thermal treatment and the value agrees with those found for poly(ethylene terephthalate) (PET) and amorphous PEN. Evidence of the decrease of orientation in the sample with thermal treatment can be seen via the onset of mobility, both by DRS and DMA. Thus, the orientation induces a greater change of properties compared to the crystalline samples obtained from the thermal treatment of an amorphous sample. Finally, a three phase model is proposed since there is evidence of a rigid amorphous phase present in PEN biaxially stretched samples which was favoured by the dependence of dielectric relaxation strengths on the degree of crystallinity for the β^∗- and α-relaxation.     

一种判定RDX热分解机理函数与热安全性的方法

将DSC、TG数据与Malek法相结合研究了RDX的热分解,得到外延起始温度Le0、拐点温度T、峰顶温度Tp、分解终止温度Tf、分解焓变ΔH、表观活化能E、指前因子A、反应级数n、热爆炸临界温度Tb和自加速分解温度TSADT;利用TG热分析得到RDX热分解的起始分解温度T0、质量损失Δm%、最大质量损失速率及对应的温度...     

Isothermal crystallization, melting behavior and crystalline morphology of syndiotactic polystyrene blends with highly-impact polystyrene

Syndiotactic polystyrene (sPS) blends with highly-impact polystyrene (HIPS) were prepared with a twin-screw extruder. Isothermal crystallization, melting behavior and crystalline morphology of sPS in sPS/HIPS blends were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). Experimental results indicated that the isothermal crystallization behavior of sPS in its blends not only depended on the melting temperature and crystallization temperature, but also on the HIPS content. Addition of HIPS restricted the crystallization of sPS melted at 320 °C. For sPS melted at 280 °C, addition of low HIPS content (10 wt% and 30 wt%) facilitated the crystallization of sPS and the formation of more content of α-crystal. However, addition of high HIPS content (50 wt% and 70 wt%) restricted the crystallization of sPS and facilitated the formation of β-crystal. More content of β-crystal was formed with increase of the melting and crystallization temperature. However, α-crystal could be obtained at low crystallization temperature for the specimens melted at high temperature. Addition of high HIPS content resulted in the formation of sPS spherulites with less perfection.     

Crystallization of Nylon 11 under compressive high strain rates

The mechanical behavior of semicrystalline Nylon 11 was studied at strain rates between 10^?3 and 8800 s^?1. X‐ray diffraction and DSC were employed to examine the crystal structure and the crystallinity content. The as‐received material comprised a mixed structure of a predominately triclinic (α) form. DSC revealed that the material gave rise to two melting peaks. The compressive flow stress of Nylon 11 experienced a large increase at 1200 s^?1 and decreased at higher strain rates. The maximum level of the flow stress corresponded with a higher level of crystallinity and a structure mainly of a pseudohexagonal form. The subsequent drop in stress at higher rates was associated with a decrease in the crystallinity content and a mixed crystal structure, different from that observed in the as‐received material. After compression, the low melting peak disappeared and the material melted over an increased temperature range. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2031–2038, 2001     

Thermal polymerization of thiol–ene network‐forming systems

The thermal polymerization of a tetrafunctional thiol (PETMP) and divinyl ether (TEGDVE) was monitored by temperature‐ramping differential scanning calorimetry (DSC) and the effects of inhibitor type and concentration, oxygen inhibition and initiator type were studied. The incorporation of inhibitors was required to produce a stable system at room temperature. Butylated hydroxytoluene (BHT) inhibited polymerization at low temperatures, but was inefficient at high temperatures and polymerization rates, and hence BHT is an ideal stabilizer. In contrast, a nitroxide inhibitor (NO‐67) was a very effective inhibitor and no polymerization occurred until all of the nitroxide was depleted. The presence of oxygen retarded the onset of polymerization but did not change the final conversion significantly. Polymerization with initiators having higher half‐life temperatures shifted the DSC peak to higher temperature because the rate of initiator decomposition and thus initiation was slower. Rheological investigations of the cure at different temperatures revealed that the gel time decreased significantly with increasing cure temperature, and the calculated apparent activation energy for PETMP/TEGDVE was 54 kJ mol^?1. Dynamical mechanical thermal analysis of the cured material was undertaken and frequency‐superposed results revealed that the glass transition region of PETMP/TEGDVE/azobisisobutyronitrile was much narrower than that of free‐radically cured dimethacrylate, but was similar to that of an epoxy resin cured with an aromatic diamine. This behaviour could be attributed to PETMP/TEGDVE network homogeneity, or to the less constrained crosslinks in the PETMP/TEGDVE network. Copyright © 2007 Society of Chemical Industry     

Phase stability and melting behavior of the α and γ phases of nylon 6

The phase stability and melting behavior of nylon 6 were studied by high‐temperature wide‐angle X‐ray diffraction and differential scanning calorimetry (DSC). The results show that most of the α phase obtained by a solution‐precipitation process [nylon 6 powder (Sol‐Ny6)] was thermodynamically stable and mainly melted at 221°C; the double melting peaks were related to the melt of α crystals with different degrees of perfection. The γ phase formed by liquid nitrogen quenching (sample LN‐Ny6) melted within the range 193–225°C. The amorphous phase converted into the γ phase below 180°C but into the high‐temperature α phase at 180–200°C. Both were stable over 220°C. α‐ and γ*‐crystalline structures were formed by annealing but were not so stable upon heating. Typical double melting peaks were shown on the DSC curve; melt recrystallization happened within the range 100–200°C. The peak at 210°C was mainly due to the melting of the less perfect crystalline structure of the γ phase and a fraction of the α phase; the one at 219°C was due to the high‐temperature α‐ and γ‐phase crystals. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011