Effect of the Addition of Chili Pepper Powder on Vegetable Oils Oxidative Stability

Red chili pepper represents an excellent source of functional bioactive compounds, and its use as food additive could be useful for protecting other products from spoilage. Olive oils show a limited shelf‐life due to a progressive quality deterioration linked mostly to oxidation reactions providing a loss of quality in terms of organoleptic and healthy properties. In this work, the addition of red chili pepper powder to virgin, extra‐virgin olive and sunflower oils was proved to be effective in improving their stability during 12 months of shelf‐life. Oil stability was monitored by employing the Oxitest system, based on accelerating the oxidation process. Three pepper powders of different pungency were added to the virgin olive oil samples with the aim of investigating whether capsaicinoids could be responsible for the observed effects. The strongest effect was recorded when employing the less pungent pepper showing that the protective effect could not be attributed to the capsaicinoids content. Besides, a screening on different oils demonstrated that the less stable samples received a stronger protective effect. The evaluation of a possible dose‐effect relation was also carried out pointing out that a threshold dose of about 1 % was required to record an effect. The results suggest potential perspectives in the field of food technology, as addition of a small amount of sweet pepper could be proposed to prolong food shelf‐life.     

Evolution of Oxidative Values during Kinetic Studies on Olive Oil Oxidation in the Rancimat Test

A comparative study was carried out in order to evaluate the kinetics of the formation of a number of primary and secondary oxidation products during oxidation of olive oil in the Rancimat test at 100–130 °C. There were good correlations between the Rancimat index (OSI) and stability indices (IP) measured in the Rancimat test with no significant differences in kinetic parameters calculated from them. Mean values of the temperature coefficient, Q₁₀ number, activation energy (E_a), frequency factor (A), and free energy of activation (ΔG⁺⁺) for olive oil oxidation were calculated to be ?3.44 × 10^?2°C^?1, 2.21, 98.91 kJ/mol, 12.17 × 10¹² h^?1, and 128.25 kJ/mol, respectively. Each unit change in E_a was accompanied by an average 1.43 × 10¹² change in A, indicating a higher contribution for factor A than for E_a to the olive oil stability. The E_a and A correlated well with the values of enthalpy and entropy, respectively. The values of OSI or IP could be described well by the ΔG⁺⁺ values. Kinetic data indicated that olive oil stability is more affected by the indigenous antioxidants than by the fatty acid composition.     

真空恒温热处理对PMMA热稳定性的影响

通过热重分析研究了270℃真空热处理条件下,不同热处理时间后聚甲基丙烯酸甲酯(PMMA)的热降解行为,并通过Flynn和Flynn-Wall-Ozawa法求取了这些PMMA样品的起始热分解活化能和热降解过程中不同质量损失率时的活化能。结果表明,在真空热处理过程中,只有具有不饱和末端的PMMA能被降解,而具有饱和末端的PMMA是热稳定的,热处理时间对PMMA的相对分子质量没有影响;通过热处理降解了PMMA中具有不饱和末端的分子链能够提高PMMA的低温热稳定性,热处理时间越长,PMMA中具有不饱和末端分子链的相对比例越低,PMMA的热稳定性越好;降低具有末端不饱和结构PMMA分子链的相对比例能够提高PMMA的起始热降解活化能和低温热降解活化能,但对热降解后期的热降解活化能没有影响。     

CSM对EPDM硫化胶耐热氧稳定性的影响

用热空气老化试验、差示扫描量热法和热重分析法研究添加少量氯磺化聚乙烯（ＣＳＭ）的ＥＰＤＭ硫化胶的热氧稳定性。结果表明：添加ＣＳＭ的ＥＰＤＭ硫化胶第一分解阶段的活化能低于未添加ＣＳＭ硫化胶的，而第二分解阶段的活化能却高于未添加ＣＳＭ硫化胶的。这说明，添加ＣＳＭ能提高ＥＰＤＭ硫化胶耐长期热氧老化性能，但对硫化胶早期的热分解起加速作用     

小分子醇对聚乳酸热稳定性的影响

使用转矩流变仪并结合数学模型方法,研究了小分子醇对聚乳酸(PLA)热稳定性的影响,计算了体系的黏度、流动活化能和降解速率常数。结果表明:醇会促进PLA的降解,添加量越大,对PLA热稳定性的影响越大;在相同添加量下,碳链短的醇比碳链长的醇更能促进PLA的降解,单官能度的醇比双官能度的醇更能促进PLA的降解;相对于羧酸,醇对PLA热稳定性的影响较小。     

A Rapid Method for Determining the Oxidative Stability of Oils Suitable for Breeder Size Samples

A method utilizing thin-layer chromatography with a flame ionization detector (TLC-FID) was developed for assessing the stability of breeder’s oil seed samples based on the formation of polar compounds. The results showed a linear relationship between peroxide value (PV) and the content of polar material in the oxidized oil. Oil samples oxidized very readily on chromarods, even at low temperature, which is a particular advantage for antioxidant screening. At 45 °C, the oil oxidation rate was relatively low, but the relationship between the content of polar material and reaction time was linear. At 65 °C, if the content of polar material was below 50 %, the above relationship was still linear. At different temperatures, the action of tocopherol appeared to vary slightly. For example, at 65 °C, the oxidative stability of the oil sample was determined by the content of tocopherol, especially γ-tocopherol. At 45 and 55 °C, the oxidative stability was determined by both the content of tocopherol and polyunsaturated fatty acids. Of the tocopherol isomers, γ-tocopherol exhibited the highest antioxidant potency, consistent with the published literature. These results suggest that chromarods provide good media for monitoring oil oxidation for antioxidant screening. A particular advantage is the use of very small oil samples, usually 1–2 μL, and the ability to analyze multiple samples at the same time.     

抗氧剂对PMMA树脂热氧化稳定性的影响及动力学分析

采用热重分析,研究了抗氧剂种类及用量对聚甲基丙烯酸甲酯(PMMA)热氧化稳定性的影响,并采用Kis-singer、Flynn-Wall-Ozawa和Flynn法对其热氧化降解行为进行了动力学分析。结果表明,抗氧剂1010、1076、702和BHT的用量为0.5‰时就能够显著提高PMMA热氧化稳定性,使其起始热分解温度提高70℃左右,而抗氧剂用量进一步提高对改善PMMA的热稳定性意义不大;动力学分析表明,抗氧剂的加入能够提高PMMA质量损失率小于30%时的热降解活化能,而热分解后期由于降解温度高于抗氧剂熔点,抗氧剂气化逸出,抗氧剂不能有效提高PMMA后期热降解活化能,未能达到提高PMMA整体热稳定性的目的。     

纳米二氧化钛对聚丙烯热稳定性影响的研究

采用透射电镜观测纳米二氧化钛(TiO2)颗粒尺寸。通过熔融混合法制备TiO2含量为0~3wt%的PP/TiO2纳米复合材料,之后在180℃下通过模压成型为薄膜。在100℃烘箱中持续热老化24h,并测试热老化前后的力学性能。采用红外光谱研究PP/TiO2纳米复合材料的降解产物,采用扫描电镜分析(SEM)复合材料在热老化后的拉伸破坏断面形态。SEM照片清晰显示二氧化钛在聚丙烯基材中分散均匀。热重分析结果显示二氧化钛的添加能提高PP的热稳定性。     

Influence of Process Variables on the Reactivity of Low Formaldehyde Emission Urea-Formaldehyde Resin

One of the important characteristics of the thermosetting resins such as urea-formaldehyde resin is the cure property. This is an invaluable characteristic for determining the processing capabilities of the resin. Differential scanning calorimetry (DSC) measurements are ideally suited to achieve this end. This paper presents the results of the effect of process variables on the enthalpy of cure of a low formaldehyde emission UF resin prepared by a four-stage process as described in the text. Response surface methodology (RSM) was used to design and the analyze the experiments. Urea (U) was added to the reaction mixture according to a pre-determined program of varying the number of additions and the duration between the additions during the second stage of the process. A mathematical relationship between the process variables and enthalpy of cure was established. The urea-formaldehyde (UF) resin was prepared under optimum conditions. Experiments were performed with the resin so prepared to determine the energy of activation of the curing reaction catalyzed by ammonium chloride.     

纳米SiO2填充PE-LLD复合材料的热稳定性和热氧稳定性研究

采用TG法研究了纳米SiO2含量、界面特性对纳米SiO2填充PE—LLD复合材料热降解和热氧降解性能的影响，并用Dole-Ozawa方法研究了体系的热降解动力学。结果表明：复合材料热降解和热氧降解温度均随纳米SiO2含量的增加而提高，后者提高更为显著。硅烷偶联剂表面改性纳米SiO2填充PE—LLD体系中加入大分子相容剂PE-LLD-g-MAH后，其热稳定性和热氧稳定性均优于未加PE-LLD-g-MAH体系。此外，纳米SiO2含量对复合材料热降解表观活化能Ea影响较大，填充体系的平均热降解表观活化能比基体明显提高，且随着SiO2含量增加而增大；界面特性对Ea的影响较小。     

The Effect of Operational Parameters of the Rancimat Method on the Determination of the Oxidative Stability Measures and Shelf-Life Prediction of Soybean Oil

Operational parameters of the Rancimat method, including oil sample size, airflow rate, and temperature, were evaluated to determine their effects on the oxidative stability index (OSI), temperature coefficient, Q ₁₀ number, and shelf-life prediction for soybean oil. Operational parameters of the Rancimat method had statistically significant effects (P < 0.05) on the OSI. Whenever the oil sample size and airflow rate at a given temperature were such that the air-saturated condition could be established, the OSIs showed no statistically significant differences. As temperature increased, OSIs decreased, while their average coefficient of variation (CV) increased. In general, the conditions where the sample was saturated with air and had a relatively lower CV were an oil sample size of 6 g at all temperatures and airflow rates, then 3-g oil sample size at low temperatures (100 and 110 °C) and low airflow rates (10 and 15 L h⁻¹). The temperature coefficient and Q ₁₀ number were found to be independent of the oil sample size and airflow rate, and their mean values for soybean oil were calculated to be −3.12 × 10⁻² °C⁻¹ and 2.05, respectively. Oil sample size and airflow rate showed a significant effect on shelf-life prediction for soybean oil. Therefore, choosing the right levels of these operational parameters in the Rancimat method may produce the least possible difference between predictions from long-term storage studies and the OSI test.     

粉体对泡沫灭火剂发泡能力和热稳定性影响研究

研究了纳米二氧化硅、硅微粉、石墨、纳米级铜粉对于蛋白泡沫的发泡能力及热稳定性的影响,并且测试了形成的复合泡沫的热稳定性,结果表明：将耐烧粉体直接添加进灭火泡沫中有望增强其抗烧能力和灭火性能。在常温下纳米二氧化硅以及纳米级铜粉能与蛋白泡沫较好的结合为复合泡沫,添加测试粉体后复合泡沫的热稳定性均有明显增强,其中添加纳米二氧化硅和纳米级铜粉的复合泡沫整体性能良好,无泡沫排液和聚并现象,可以起到良好的隔热作用。     

淀粉/天然橡胶复合材料的结构与热稳定性研究

将淀粉进行糊化改性,将改性淀粉在乳液状态下与天然胶乳共混,制备淀粉/天然橡胶复合材料。利用扫描电镜(SEM)和热重分析(TG)表征复合材料的结构,并测定了其力学性能。研究结果表明:淀粉经糊化后,淀粉粒子在天然橡胶中分散均匀,粒径明显减小,复合材料的热稳定性和力学性能明显提高。     

聚酰胺66纤维的热稳定性研究

采用热重分析(TG)和热裂解气质联用(Py-GC/MS)方法研究了聚酰胺66纤维的热稳定性和热裂解机制。结果表明:聚酰胺66纤维在氮气气氛中的热分解过程为一步反应,热分解活化能为186.4 kJ/mol,470℃以上可完全分解,热稳定性良好。聚酰胺66纤维的热裂解产物主要是环戊酮,峰面积百分比达24.27%。     

组合添加剂对离子钯活化液稳定性的影响

研制出一种能够有效提高离子钯活化液稳定性的组合添加剂。实验结果表明:以乙酸钠、对苯二酚、维生素C为组合添加剂时,能有效提升离子钯活化液的稳定性,并改善化学镀镍层的性能。     

水滑石在钙锌复合体系中的热稳定性研究

以普通的碱性物质为参比，用刚果红、转矩流变仪等方法测试了水滑石在钙锌体系协同作用下对PVC树脂静态和动态热稳定时间的影响。试验结果表明。水滑石改善PVC树脂的热稳定性效果明显优于在Ca／Zn体系中用的辅助组分弱碱A，在PVC中的适宜用量为2份左右。并简单探讨了水滑石的热稳定机理。     

聚苯胺/氧化钇复合材料的合成及热稳定性研究

合成了对甲基苯磺酸(p-TSA)掺杂的导电聚苯胺(PANI)及聚苯胺/氧化钇(PANI/Y2O3)复合材料.比较了不同实验条件对两种材料电导率的影响,研究了两种材料的热稳定性及粒径分布.结果表明,在所研究实验条件下,PANI/Y2O3的电导率低于PANI,而热稳定性则优于PANI;Y2O3的掺入使PANI的粒径减小.     

完全混合流反应器热稳定性的探讨

通过对完全混合流反应器热稳定性的定性和定量分析．分别从进料温度和进料流量操作参数对完全混合流反应器热稳定性的影响进行了探讨,得出完全混合流反应器的热稳定条件．对非稳定的操作点如何改造成稳定的操作点提出了建议,进一步得出完全混合流反应器允许的最大温度差,结论对实际生产具有一定的指导意义。