Effect of fatty acid positional distribution and triacylglycerol composition on lipid by-products formation during heat treatment: III—Cyclic fatty acid monomers study

The influence of isomeric triacylglycerols (TG) containing 18:3n-3 and 18:2n-6 on the formation of cyclic fatty acid monomers (CFAM) after heat treatment was assessed. Diacid TG, containing linoleic acid (L) or linolenic acid (α-Ln) along with palmitic acid (P), and positioned either in the central position (PLP and PLnP, respectively), or in one of the two outer positions (PPL and PPLn, respectively) were synthesized. Monoacid TG of trilinolein and trilinolenin mixed with tripalmitin were also prepared. The CFAM formed after heating were analyzed after total hydrogenation. The results obtained with the model TG were compared to another model consisting of a canola oil and its randomized counterpart. In diacid TG, the location of α-Ln in the central position of the TG molecule (PLnP) greatly enhanced the formation of the CFAM upon heating at temperatures below 240°C. On the other hand, 18:3n-3 in monoacid TG (LnLnLn) was highly resistant to CFAM formation within the same range of temperatures (180–220°C). The TG structure, more than the TG composition, seemed to explain the differences in the CFAM formation between the original canola oil and its interesterified counterpart. Like α-Ln, 18:2n-6 was more prone to cyclization when attached at the central position of the model TG. Conversely, the influence of the TG composition on the cyclization rate was less important for L than for α-Ln. It was concluded that positioning the C18 polyunsaturated fatty acid in the central position of TG rendered the oils much more sensitive to the cyclization reaction upon heat treatment.     

Fracture prediction in non-isothermal viscous pressure bulging of aluminum alloy sheet using ductile fracture criterion

The failure of AA3003 aluminum alloy sheet metal was predicted for non-isothermal viscous pressure bulging (VPB). Utilizing the coupled thermo-mechanical finite element method combined with ductile fracture criterion, the calculations were carried out for non-isotherm VPB at various temperatures and the influences of the initial temperature of viscous medium on failure mode of bulge specimens were investigated. The results show that the failure modes are different for the non-isothermal VPB with different initial temperatures of viscous medium. For the non-isothermal VPB of AA3003 aluminum alloy sheet with initial temperature of 250 ℃, when the initial temperature of viscous medium ranges from 150 to 180 ℃, the formability of sheet metal can be improved to a full extent. The validity of the predictions is examined by comparing with experimental results.     

α/β复合成核剂成核聚丙烯的结晶形态及非等温结晶动力学研究

以山梨醇类S20成核剂为α成核剂与HHPA-Ba和PA-03两种β成核剂分别复配得到α/β复合成核剂。利用DSC和偏光显微镜考察了该复合成核剂对成核等规聚丙烯(iPP)结晶形态的影响,并采用Cazé法研究了成核iPP的非等温结晶动力学。实验结果表明,复合成核剂可减小成核iPP的球晶尺寸,成核iPP最终的结晶形态由复合成核剂中两种成核剂的含量决定。不同配比的复合成核剂均可提高iPP的结晶温度、缩短iPP的结晶时间、提高iPP的成型速率。成核iPP的Avrami指数在4⁵之间,最佳配比的S20/HHPA-Ba复合成核剂(S20成核剂的含量为40%(w))成核的iPP以混合成核模式结晶。以S20为α成核剂的α/β复合成核剂对成核iPP的结晶行为和结晶形态的影响基本一致。     

聚芳醚酮树脂非等温结晶动力学及其复合材料湿热老化性能EI北大核心CSCD

聚芳醚酮(poly(aryl ether ketone),PAEK)热塑性复合材料因其突出的韧性、耐老化性能、耐疲劳性能,以及成型加工低成本、高效率、可回收等一系列优势,得以替代部分传统热固性复合材料,并已在国外航空等高端工业领域取得成功应用。PAEK是一种半结晶高聚物,复合材料不同的成型工艺条件导致树脂基体聚集态结构的差异,对其力学性能、耐老化性能等均存在显著的影响。对国产PAEK树脂的结晶动力学进行了研究,通过控制成型降温条件,采用模压工艺制备了树脂结晶度不同的连续碳纤维增强复合材料,并对其进行了湿热老化处理,评价了老化处理前后复合材料的弯曲性能。结果表明:采用较大的降温速率能够提高树脂的结晶速率,但会降低树脂的结晶度。在随炉冷却、空气冷却和水冷却三种不同的降温条件下,制备的复合材料结晶度分别约为36.3%,29.7%,26.5%,结晶度的显著差别导致复合材料的弯曲强度随结晶度的降低而减小。经湿热老化处理240 h后的弯曲强度保留率分别为88.8%,86.7%,86.6%,较高的结晶度能够较好地抵抗水对复合材料界面的破坏,提升复合材料的耐湿热老化性能。     

基于TG模式的历史关系数据库的研究

给出了ＴＧ模式的形式化定义,并结合实例对该模式进行了深入的分析和研究,指出了其优缺点,并提出了对该模式的下一步研究思想。     

纳米碳酸钙改性聚丙烯共聚物的非等温结晶动力学

用DSC手段考察了反应釜内原位共聚制备的含有成核剂及纳米碳酸钙的聚丙烯(PP)共聚物的非等温结晶行为。结果表明，成核剂使PP共聚物的结晶温度升高，结晶度降低，结晶速率略有提高。而纳米碳酸钙则大幅提高了PP共聚物的结晶温度和结晶速率，结晶度也增加了约10％。并采用Ozawa法和Caze法描述了非等温结晶动力学。     

The Influence of Grain Size on Decomposition Reaction of Limestone in Dispersing State

The thermal behavior and kinetic parameters of decomposition reaction of limestone in a temperature-programmde mode were investigated by means of TG,The experumental results shour that the kinetic model functions in different forms for the theermal decomposition rdactions of different limestone grain sizes in dispersing state under the almosphere of static air are 4(1-a)^3/4 for small size limestone and (1-a) for large size limestone.Information was obtained on the relationship among the decomposition temperature.decomposition time.decomposition fraction.decomposition reaction rate constant and grain grain size of limestone.     

MgF2 as a non‐conventional catalytic support. Surface and structure characterization

The paper presents results of studies on the structure of MgF₂ support, performed using various experimental methods such as XRD, IR, temperature‐programmed techniques and low‐temperature nitrogen adsorption. MgF₂ is characterized by an XRD spectrum with over 40 patterns, which enabled us to follow the changes in crystallite size and internal tension caused by the thermal treatment. TPE‐H₂O and TG allowed an estimation of the surface OH groups concentration as ∼3–4 nm^-2. This revised version was published online in July 2006 with corrections to the Cover Date.     

热重分析法研究煤粉燃烧过程动力学的Arrhenius方程修正式

煤粉的燃烧过程常被作为能量的提供者应用于不同工业,为研究升温速率对煤粉燃烧过程动力学的影响.本文采用热重分析法对20℃/min、25℃/min、30℃/min和35℃/min升温速率下的煤粉燃烧过程进行分析.结果表明:随升温速率的提高,煤粉燃烧过程有明显的热滞后现象.根据煤粉燃烧过程的特点,以反应速率曲线波谷对应的温度点,将着火点到燃尽点的燃烧过程划分为两个阶段,并分别采用界面化学反应模型和内扩散模型来描述相应阶段的动力学过程.由所获得动力学参数可知,不同升温速率下活化能E_(ai)和指前因子Ai的动力学补偿效应可表示为ln A_i=a E_(ai)+b,升温速率β对活化能E_(ai)的影响可表示为E_(ai)=△E_alnβ_i+E_(a0).随将常用的Arrhenius方程ln k_i=-E_(a0)/RT+ln A_0修正为ln k_i=-E_(a0)/RT+△E_a(a-1/RT)lnβ_i+ln A_0来描述升温速率β对煤粉燃烧过程反应速率常数k的影响.而后,采用10℃/min、15℃/min、40℃/min和45℃/min升温速率下的煤粉燃烧试验对Arrhenius方程修正式的外推性进行验证,效果良好.因此,Arrhenius方程修正式不仅能很好地描述升温速率β对煤粉燃烧过程化学反应速率常数k的影响,而且还具有一定的外推性.     

间位芳纶纤维及浆粕的热性能分析

采用DSC、TG热分析方法对几种不同的芳纶纤维和浆粕的热性能进行了分析,研究了其受热后重量和能量随环境温度和受热时间的变化.DSC曲线表明短纤维未出现玻化转变温度,结晶峰也未出现,浆粕无定型部分的玻璃化转变温度在283℃左右,在300℃以后出现冷结晶现象.TG分析表明短切纤维与浆粕在400℃以上出现失重分解,浆粕失重速率大于纤维失重速率.