一种吡嗪酯类香料前体的制备及其热性能

为开发吡嗪酯类香料前体,以2,5-二甲基吡嗪氮氧和丙烯酸噻吩甲酯为原料,在醋酸钯的催化下经偶联反应,合成3-(3,6-二甲基-吡嗪氮氧-2-基)丙烯酸噻吩甲酯目标化合物,通过1H NMR、13C NMR、IR、HRMS表征其结构,并采用热重-微分热重（TG-DTG）和热裂解-气相色谱/质谱法（Py-GC/MS）测其热性能。结果表明：目标化合物从170 oC开始降解,主要热失重区间为170 oC~875 oC,在257 oC失重速率最大,总失重为76.5%。在300 oC~900 oC的有氧和无氧裂解氛围下,共鉴定出11种挥发性产物,主要有烷基吡嗪类、2-甲基噻吩、2-噻吩甲醇等特征香味物质,有氧氛围下热裂解产物种类较多,相对含量较高。依据主要裂解产物的种类及相对含量的变化,初步揭示了裂解机理。目标化合物在单料烟中的最适宜添加量为2 mg/kg。     

Effects of thermal aging on degradation mechanism of flame retardant‐filled ethylene–propylene–diene termonomer compounds

Ethylene–propylene–diene termonomer (EPDM) compounds filled with halogenated (Br and Cl) flame retardants (FRs) and Sb₂O₃ were prepared via melt mixing, and their thermal stability, weight loss, and elemental composition were investigated as a function of aging conditions (temperature: 120–380°C, period: ～100 h, and atmosphere: nitrogen and air). The thermal aging was done with thermogravimetic analysis under both isothermal and nonisothermal conditions and a convection oven. Scanning electron microscopy–energy dispersive spectroscopy was used to study the surface morphology and elemental composition of the thermally aged FRs‐filled EPDM compounds. For a better precision of compositional analysis, a laser‐induced breakdown spectroscopy (LIBS) was employed in this study. The thermal degradation behavior of EPDM compounds containing halogenated FRs was strongly dependent on the aging atmosphere (N₂ or air) and type of FRs. The weight loss of the EPDM compounds during thermal aging was found to be quite small in the temperature ranges below 190°C, while it was noticeable above the temperature. The LIBS technique can be an effective and promising analysis tools for analyzing the elemental components in a bulk rubber compound. Two possible mechanisms were proposed for the thermal degradation of the EPDM compounds containing brominated FR and Sb₂O₃. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41324.     

Physical and mechanical properties of PVDF/KNN composite produced via hot compression molding

One of the most important lead-free piezoelectric compounds that has been studied extensively belongs to alkali niobate family, the sodium-potassium niobium (KNN) compound. In this study, KNN/PVDF composite was fabricated through hot compression molding of the components and its mechanical, thermal and electrical properties were studied. For this purpose, KNN was first synthesized by solid-state reaction during two-step calcination and its structural evolution was studied using XRD. Composite samples were prepared at different KNN to PVDF weight ratios. The powder mixture was then formed into disks by hot compression molding. The microstructure of the composite samples was investigated by SEM. The prepared samples were perfectly dense with a density in the range of 97.44% to 99.11% of the theoretical density. The thermal properties of the prepared composites were evaluated by thermogravimetric analysis and it was observed that final weight loss due to material degradation was reduced with increasing KNN weight percent. In addition, samples with higher KNN contents showed increased Young's modulus and yield strength values in compression. In order to investigate the electrical properties, the dielectric constant, dielectric loss factor, piezoelectric charge and voltage coefficients and electric polarization were studied. The results showed that the dielectric constant increased with KNN content. The same trend was observed in the piezoelectric charge coefficient and the dielectric loss factor of the PVDF/KNN composites. At 80 wt% KNN, the composite showed a distinct ferroelectric behavior with a remanent polarization of 0.255 μC/cm² and 20.5 kV/cm coercivity. According to the results of the present study, hot compression molding is an effective method for producing KNN/PVDF composites with improved mechanical and thermal properties compared to its constituents.     

Effect of cupric ion on thermal degradation of chitosan

The thermal degradation of chitosan and chitosan–cupric ion compounds in nitrogen was studied by thermogravimetry analysis and differential thermal analysis (DTA) in the temperature range 30–600°C. The effect of cupric ion on the thermal degradation behaviors of chitosan was discussed. Fourier transform-infrared (FTIR) and X-ray diffractogram (XRD) analysis were utilized to determine the micro-structure of chitosan–cupric ion compounds. The results show that FTIR absorbance bands of  N H,  C N ,  C O C etc. groups of chitosan are shifted, and XRD peaks of chitosan located at 11.3, 17.8, and 22.8° are gradually absent with increasing weight fraction of cupric ion mixed in chitosan, which show that there are coordinating bonds between chitosan and cupric ion. The results of thermal analysis indicate that the thermal degradation of chitosan and chitosan–cupric ion compounds in nitrogen is a two-stage reaction. The first stage is the deacetylation of the main chain and the cleavage of glycosidic linkages of chitosan, and the second stage is the thermal destruction of pyranose ring of chitosan and the decomposition of residual carbon, in which both are exothermic. The effect of cupric ion on the thermal degradation of chitosan is significant. In the thermal degradation of chitosan–cupric ion compounds, the temperature of initial weight loss (T_st), the temperature of maximal weight loss rate (T_max), that is, the peak temperature on the DTG curve, and the peak temperature (T_p) on the DTA curve decrease, and the reaction activation energy (E_a) varies with increasing weight fraction of cupric ion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

不同受阻胺光稳定剂改性聚丙烯耐光老化性能研究

分析了4种受阻胺光稳定剂在聚丙烯(PP)加工过程中的热稳定性,并研究其单一和复合使用对PP其光稳定性能和力学性能的影响。以失重率为10%时的热分解温度衡量受阻胺光稳定剂的热稳定性,结果表明,受阻胺光稳定剂的加入,使PP的光稳定性能增强;高低分子量受阻胺复合使用,可降低PP的黄变因数和羰基指数,增加其拉伸强度及冲击强度保持率;GW622、GW944和Tinuvin144复合使用效果最佳。     

分子量分布对低密度聚乙烯光氧老化特性的影响

采用衰减全反射红外光谱技术（ATR-FTIR）、热重分析法（TG）、凝胶渗透色谱（GPC）、扫描电子显微镜（SEM）和力学试验比较研究了不同分子量分布指数低密度聚乙烯（LDPE）的光氧老化特性,分析了分子量分布对LDPE化学结构、热稳定性、平均分子量、表面微观形貌和力学性能的影响规律。结果表明分子量分布越宽,LDPE不饱和度增长越剧烈,支化作用增长越显著;分子量分布越窄,羰基指数增长越快;分子量分布对于分子结构的断链行为并无影响。分子量分布指数越大,LDPE起始热分解温度和失重5%对应温度下降更快,热稳定性更容易变差,平均分子量下降更多,表面微观形貌老化现象越严重;弯曲强度和冲击强度受影响更显著,指数为6.0的LDPE老化24 d冲击强度就已丧失。分析认为,分子量越大、分布越窄表明分子链越长、短分子链越少,与氧接触而产生自由基的概率也越小,因此聚乙烯分子量分布越宽,材料越容易老化。     

P(MMA-MA)/OMMT纳米复合材料对PVC共混改性研究

通讨原位插层法制备聚(甲苯丙烯酸甲酯一丙烯酸甲酯)有机化蒙脱十「P(MMA-MA)/OMMT}纳米复合材料,并用其对聚氯乙烯(PVC)讲行共混改性。通讨扫描电镜(SEM)热失重分析(TGA)、动杰力学分析(DMA)拉伸和冲击等力学性能测试研究了共混物的两相相容性、热稳定性及力学性能。结果表明:共混体系两相间有很奸的相容性;随着纳米复合材料添加量的增加,共混体系的耐热性能、储能模量、玻璃化温度和力学性能逐渐增加。当纳米复合材料与PVC共混比达到20/100时,共混体系在10%失重率下的失重温度比纯PVC捍高了17.4℃,玻璃化温度比纯PVC捍高了4.7℃。当纳米复合材料与PVC共混比达到30/100时,体系的综合力学性能最奸,冲击强度和拉伸强度分别较纯PVC捍高了21. 1%和34.7%。     

Isothermal degradation of cis-1,4-polyisoprene vulcanizates

The isothermal degradation of high cis-1,4-polyisoprene vulcanizates having different crosslinking structures was investigated by a measurement of weight loss of sample, IR and NMR, gel permeation chromatography (GPC), and gas chromatography (GC). The degradation behavior of dicumy peroxide-cured sample is similar to that of the uncrosslinked one. On the other hand, a sulfur-cured sample is very different from the other samples. At the initial stage of the degradation, weight loss in this sample is faster than that in an uncrosslinked one. Furthermore, a microstructural change in this polymer occurring by thermal degradation is also very much larger than microstructural changes in the others. This will be attributed to polythiyl radicals produced by the scission of polysulfide crosslinkages. Although the polyisoprene chain undergoes random scission along the main chain above 473 K under inert gas or in vacuo, a molecular weight distribution of the residue after thermal degradation was broadened as the degradation proceeded. That is to say, the fragments having enormous molecular weight increase together with the production of lower molecular weight compounds. This indicates the occurrence of crosslinking reaction and the addition of polymer radicals to carbon–carbon double bonds in another polymer molecule in the thermal degradation process. Such reactions are thought to take place in the crosslinked polymers, in particular the sulfur-cured polymer, in larger quantities. Thermal degradation mechanisms were discussed in some detail.     

Hydrolysis and thermal degradation of poly(L‐lactide) in the presence of talc and modified talc

Talc and talc modified with trimethoxy(octadecyl)silane (O‐talc) were melt compounded with poly (L ‐lactide) (PLA). The crystallization behavior, tensile properties, and impact strength of the PLA composites were examined before and after the incorporation of talc and O‐talc. The molecular weight of PLA in the PLA composites was measured as a function of the hydrolysis time and temperature. The effect of talc and O‐talc on the thermal stability of PLA was examined and quantified by the activation energy of thermal degradation and the integral procedural decomposition temperature value determined from the corresponding thermo‐gravimetric analysis weight loss profiles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal degradation behaviour of multi‐walled carbon nanotube‐reinforced poly(L‐lactide) nanocomposites

BACKGROUND: Polymer/multi‐walled carbon nanotube (MWCNT) composites are one of the most promising alternatives to conventional polymer composites filled with micrometre‐sized fillers. This approach can also be applied for the improvement of mechanical properties and thermal stability of biodegradable aliphatic polyesters, such as poly(L ‐lactide) (PLLA), which have been receiving increasing attention due to environmental concerns. Thermal degradation behaviour provides useful information for the determination of the optimum processing conditions and for identification of potential applications of final products. RESULTS: The PLLA/MWCNT composites investigated showed a higher thermal degradation peak temperature and onset temperature of degradation along with a higher amount of residue at the completion of degradation than neat PLLA. Moreover, PLLA/MWCNT composites with a greater MWCNT content showed higher activation energy of thermal degradation than those with a lower MWCNT loading, which confirmed the positive effect of MWCNT incorporation on the enhancement of PLLA thermal stability. CONCLUSION: This study explored the thermal degradation behaviour of PLLA/MWCNT composites by observing the weight loss, molecular weight and mechanical properties during non‐isothermal and isothermal degradation. The incorporation of MWCNTs into the PLLA matrix enhanced considerably the mechanical properties and thermal stability. Copyright © 2009 Society of Chemical Industry     

Influence of macromolecular structure of novel 2- and 4-armed polylactides on their physicochemical properties and in vitro degradation process

The objective of this study was to analyse how macromolecular structure of polylactides influences their properties and degradation rate. To achieve this, novel 2- and 4-armed PDLLA and PLLA (noted as 2b and 4b) were synthesized by ring-opening method. 1,4-butanediol and pentaerythritol were used as initiators and stannous octoate was used as catalyst. The obtained polymers were investigated in terms of molecular weight by size exclusion chromatography, thermal properties by differential scanning calorimetry and thermogravimetry, and hydrophilicity by the contact angle measurements. The in vitro degradation test was carried out in PBS solution at 37 °C by means of the mass loss, water uptake, molecular weight and thermal properties changes. The branched polylactides including 2bPDLLA, 4bPDLLA, 2bPLLA and 4bPLLA were successfully synthesized and the average molecular weights were around 40-45 kDa. The numbers of arms in each polymer just slightly influenced the thermal properties and the contact angle. The crystallinity of 4bPLLA was 23 %, whereas for 2bPLLA it was 41 %. The degradation rates of both 2b and 4bPLLA were similar and the degradation process was similar only during first 7 weeks. After this period, the degradation rate of 4bPDLLA increased. Consequently, thermal properties and degradation profiles of the branched polymers would depend on plural factors, such as chain length and crystallinity in branched structure.     

Thermal degradation behavior and kinetic studies of polyacrylamide gel in TiO2 nanoparticles synthesis

Polyacrylamide gel (PAMG) method is a simple, fast and cheap method used for the synthesis of a wide variety of nanopowders. However, no adequate results have been reported on the thermal degradation behavior of PAMG which can be very effective on the final product properties. In this work, thermal degradation behavior of PAMG in the presence of TiCl₄ as a precursor salt for synthesis of TiO₂ nanoparticles was examined in comparison with linear polyacrylamide (LPAM) and pure PAMG by thermogravimetry/differential thermal analysis. Their thermal degradation kinetics was investigated, as well. The results showed that thermal degradation of all samples occurred in two stages at different onset temperatures. Despite the high thermal stability of pure PAMG compared to LPAM, the presence of TiCl₄ as a mineral material in PAMG structure decreases the thermal degradation onset temperature, considerably. Furthermore for LPAM and PAMG, majority of weight loss occurs in the second stage, but in PAMG with TiCl₄ the weight loss occurs mainly at the first stage. For more detailed investigation, residual materials were characterized by Fourier transform infrared spectroscopy and X-ray diffraction (XRD) techniques, attributing this trend to the presence of mineral materials in PAMG structure. XRD and transmission electron microscopy were also applied to confirm anatase crystalline structure and nanoscale distribution of the TiO₂ particles synthesized via PAMG method.     

Effect of catalyst on the thermal degradation of a polycyanurate thermosetting system

The thermal degradation of a polycyanurate thermosetting material was examined by monitoring glass temperature and weight loss at various temperatures ranging from 180 to 220°C. The effect of the cocatalysts, nonylphenol and copper naphthenate, which are generally used to facilitate curing, were also studied. A decrease in T_g is observed with increasing time at elevated temperatures in the systems containing copper naphthenate, with the onset of degradation occurring sooner with higher concentrations of the copper compound. No change in T_g occurred at long times in systems containing only nonylphenol. Weight loss studies were used to calculate an apparent activation energy of degradation. It was found to be approximately 50 kcal/mol. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 127–131, 1997     

New rigid vinyl compound molding technology

During injection molding, it is not uncommon for shear heating to cause localized temperatures exceeding 300°C. This heating, if not suppressed, can cause vinyl degradation. Three main factors influence shear heating. They are (a) mold design, especially restrictions such as small gates; (b) injection conditions, especially injection velocity; and (c) compound viscosity. To address the compound factor, two new vinyl compounds have been created for custom injection molding, which are especially designed to suppress the shear heating temperatures. Geon® M3700 has good impact at room temperature, and Geon® M3800 has outstanding impact at room temperature and at low temperatures. These compounds use a new technology that produces a balance of properties never before achievable. These innovative compounds show enhanced processability including improved static thermal stability, improved shear stability, tolerance of higher injection screw rpms, tolerance of higher injection speeds, the ability to mold at lower injection pressures, reduced molding cycles, and the ability to fill thin part walls. Also designed into the compounds are improved color fastness during exposure to light, improved appearance, and reduced corrosiveness. Other properties such as impact strength, tensile strength, modulus, heat deflection temperature, hardness, UL flammability rating, specific gravity, and mold shrinkage remain comparable to older technology.     

甜菜碱对异戊橡胶热降解性能的影响

采用热重分析法研究氮气气氛下甜菜碱对异戊橡胶(IR)热降解性能的影响。结果表明:添加甜菜碱不会改变IR的热降解机理;添加甜菜碱的IR胶料的起始降解温度、最大降解温度和反应活化能均比未添加甜菜碱的IR胶料高,表明甜菜碱提高了IR胶料的热稳定性。     

Influence of thermal aging on the electrical properties of poly(vinyl chloride)

This article reports on the study of the thermal aging of poly(vinyl chloride) (PVC) used in medium‐ and high‐voltage cables. It is shown that the thermal aging leads to the degradation of the material and to the modification of its electrical properties. The degradation is all the more important and faster as the temperature is high. This degradation is attributed to a progressive evaporation of the plasticizer at the beginning of aging and to a weight loss of stabilizer followed by a change in the color of polymer and a release of hydrochloric acid at more advanced stages of aging. It also results in a crosslinking of the material and a shrinking of samples. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4728–4733, 2006     

Thermal stability of modified poly(vinyl chloride) by TGA

The stability of poly(vinyl chloride), as measured by thermogravimetric analysis, is significantly different from that of other thermoplastics. It is shown that the onset of weight loss can be correlated with the development of color in a processed resin. It is further shown that the ingredients within a rigid polyvinyl chloride compound drastically alter its thermal behavior. The effect of lubricant and stabilizer on the degradation of poly(vinyl chloride) is stressed.     

低分子量双端羟基聚苯醚的合成研究

通过2,6-二甲基苯酚和四甲基双酚A氧化共聚合成低分子量聚苯醚,研究了单体配比、催化剂添加比例对聚合反应的影响,对反应产物进行了红外光谱、比浓黏度、分子量、产率、热失重、差示扫描量热法(DSC)、羟值等性能的表征与测试,成功制备出了分子量范围在1 500～3 000具有双端羟基的聚苯醚并确定了最佳合成工艺,产率均在70...     

Thermal degradation of high‐temperature fluorinated polyimide and its carbon fiber composite

High‐temperature polymers are being used for a broad range of applications, such as composite matrices for structural applications (e.g., high speed aircraft). Polyimides are a special class of polymers that meet the thermal and oxidative stability requirements for high temperature composite aerospace applications. A weight loss study was performed on a fluorinated polyimide resin and its carbon fiber composite in an effort to determine its thermal stability and degradation mechanisms. Experiments were conducted using a preheated oven and thermogravimetric analysis to obtain the weight loss. Regardless of the method used, the resin and composite exhibited excellent thermal stability (less than 1% weight loss) below 430°C, regardless of 2–20 min of exposure. After 20 min of exposure at 510°C, the composite remained relatively stable with only 5.3% weight loss using the oven technique, whereas the neat polyimide sustained 12.6%. When degradation occurred, it was found to be the result of thermolysis and oxidation (to a lesser extent). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Zinc hydroxystannate and zinc stannate as flame‐retardant agents for flexible poly(vinyl chloride)

The flame‐retardant and smoke‐suppressant properties of inorganic tin compounds such as zinc hydroxystannate (ZHS) and zinc stannate (ZS) were investigated in a comparison with alumina trihydrate, magnesium hydroxide, and Sb₂O₃ through the limiting oxygen index test and smoke density test. The flame‐retardant mechanisms were studied through the char yield test, SEM, quantitative analysis, thermogravimetry and differential thermal analysis. The thermal degradation in air of flexible PVC treated with the above compounds was studied by thermal analysis from ambient temperature to 800°C. The results showed that tin compounds such as ZHS and ZS could be used as a highly effective flame retardant for flexible PVC, and it appears that the tin compound may exert its action in both the condensed and vapor phases, but mainly in condensed phases as a Lewis acid. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1469–1475, 2005