Migration behaviors of wax to surface in rubber vulcanizates

The migration behaviors of wax to the surface in rubber vulcanizates were studied using natural (NR), styrene–butadiene (SBR), and butadiene rubber (BR) vulcanizates. The migration experiments were performed in a convection oven at 60 and 80°C for 14 days. There were less than 10% of the normal alkanes of n-C₂₂H₄₆ to n-C₃₈H₇₈ that migrated to the surface in the vulcanizates and evaporated at 60°C for 14 days. The amount of normal alkanes that migrated to the surface in the vulcanizates and evaporated at 80°C for 14 days was decreased by increasing the molecular weight of the normal alkanes. The migration of the normal alkanes in the NR vulcanizate was more sensitive to the variation of the molecular size of the normal alkanes than those in the BR and SBR vulcanizates. The migration behaviors of the normal alkanes in the vulcanizates were very similar to their evaporation behaviors. Major factors influencing the migration behaviors of the wax were discussed using the calculations of structures of the normal alkanes and evaporation experiments of wax. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2587–2593, 1999     

Influence of rubber composition on migration behaviors of antiozonants in carbon black‐filled rubber vulcanizates composed of NR,SBR, and BR

Migration behaviors of antiozonants in carbon black‐filled rubber vulcanizates with different rubber compositions of natural rubber (NR), styrene–butadiene rubber (SBR), and butadiene rubber (BR) were studied at constant temperatures of 40–100°C and outdoors. Three single rubber‐based vulcanizates, three biblends, and three triblends were used. N‐Phenyl‐N′‐isopropyl‐p‐phenylenediamine (IPPD) and N‐phenyl‐N′‐(1,3‐dimethylbutyl)‐p‐phenylenediamine (HPPD) were employed as antiozonants. Migration rates of the antiozonants became faster with increasing the temperature. The order of the migration rates in the single rubber‐based vulcanizates was BR > NR > SBR. The migration rates in the vulcanizates containing SBR, on the whole, increased with decreasing the SBR content, while those in the vulcanizates containing BR decreased with decreasing the BR content. Difference in the migration behaviors of the antiozonants depending on the rubber composition was explained both by the intermolecular interactions of the antiozonants with the matrix and by interface formed between dissimilar rubbers in the blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 237–242, 2001     

Migration of antidegradants to the surface in NR and SBR vulcanizates

Migration-generating equipment using a vacuum technique was constructed to measure the migration properties of antidegradants to the surface in compounded rubber in a short time. With this equipment, the migration of antidegradants to the surface is accelerated by the fast evaporation of organic molecules on the surface facing the vacuum and the pressure difference applied between two surfaces of the rubber vulcanizate. The effects of initial concentration and temperature on the migration of antidegradants such as 2,6-di-t-butyl-4-methyl phenol (BHT), N-phenyl-N-isopropyl-p-phenylenediamine (IPPD), and N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine (HPPD) were investigated with this equipment. The migration rate was found to be independent of the initial concentration of the antidegradants. BHT and IPPD migrate to the surface of an object faster than HPPD, which is due to molecular size. BHT migrates faster than IPPD at a low temperature of 40°C, while IPPD is faster than BHT at a high temperature of 60–100°C. Antidegradants in NR vulcanizates migrate faster than those in SBR ones. This is because interactions of antidegradants with SBR are stronger than those with NR. To explain the difference in rubber base, calculations with molecular mechanics and dynamics were tried, which gave the results that the interaction of IPPD with polystyrene is much stronger than those with cis-1,4-polyisoprene and cis-1,4-polybutadiene. Activation energies for migration to the surface of NR vulcanizate are 25.8, 30.7, and 38.6 kJ/mol, while those of SBR are 27.6, 36.5, and 51.7 kJ/mol for BHT, IPPD, and HPPD, respectively. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 117–125, 1997     

橡胶防护体系的迁出

介绍橡胶防护体系的迁出机理和影响因素.防护蜡的迁出机理主要有浓度梯度和自由能梯度机理.防护体系的迁出速率与其相对分子质量、结构和熔点,填料品种和用量,橡胶基体性能以及温度等有关.防护蜡和化学防老剂在橡胶层与层之间的迁移、防护蜡在结晶温度范围内的迁出速率及迁出持续性等是近期防护体系迁出的研究重点.     

Influence of silica content on migration of antidegradants to the surface in NR vulcanizates

Migration of antidegradants to the surface in silica-filled natural rubber (NR) vulcanizates was studied with migration-generating equipment using a vacuum technique. 2,6-Di-t-butyl-4-methyl phenol (BHT), N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD), N-phenyl-N′-(1,3-dimethylbutyl-p-phenylenediamine (HPPD), and wax (n-C₂₃H₄₈, n-C₂₄H₅₀, n-C₂₅H₅₂, and n-C₂₆H₅₄) were employed as antidegradants. The migration rate was found to be dependent on the content of silica in the vulcanizates. IPPD migrates faster than BHT and HPPD irrespective of the content of silica. BHT migrates faster than HPPD at 60 and 80°C, but slower than HPPD at 100°C. The migration rates of BHT, IPPD, and HPPD decrease with increase of the silica content from 30 to 70 phr. Wax with a low molecular weight migrates faster than that with a high molecular weight. The migration rate of n-C₂₃H₄₈, irrespective of migration temperature, decreases with increase of the silica content, similar to BHT, IPPD, and HPPD, but those of n-C₂₅H₅₂ and n-C₂₆H₅₄ have a local maximum at 50 phr silica content. The activation energies for migration to the surface in the vulcanizate containing 50 phr of silica are 19.3, 28.7, 40.1, 42.2, 51.6, 58.8, and 65.5 kJ/mol for BHT, IPPD, HPPD, n-C₂₃H₄₈, n-C₂₄H₅₀, n-C₂₅H₅₂, and n-C₂₆H₅₄, respectively. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1821–1828, 1998     

不同硫化体系对天然橡胶的动静态性能的影响研究

分别制备了以炭黑和白炭黑为补强填料的不同硫化体系天然橡胶(NR)复合材料,研究硫化体系对NR胶料静态和动态性能的影响。结果表明:普通硫化体系硫化胶具有较高的交联密度、较好的物理性能和优异的耐磨性能;对于白炭黑补强体系,普通硫化体系硫化胶具有最低的滚动阻力;而对于炭黑补强体系,平衡硫化体系硫化胶具有最低的滚动阻力;胶料拉伸强度的增大有利于耐磨性的提高。     

NR/PP thermoplastic vulcanizates: Selection of optimal peroxide type and concentration in relation to mixing conditions

Thermoplastic vulcanizates (TPVs) from natural rubber (NR) and polypropylene (PP) were studied, prepared by dynamic vulcanization during melt mixing, using various peroxides to crosslink the rubber phase. The objective was to find a proper balance between degree of crosslinking of the rubber and degradation of the PP‐phase, and the tendency of the peroxide to form smelly by‐products, in particular acetophenone. Four types of peroxides were investigated: 2,5‐dimethyl‐2,5‐di(tert‐butyl‐peroxy) hexyne‐3 (DTBPHY), 2,5‐dimethyl‐2,5‐di(tert‐butyl‐peroxy) hexane (DTBPH), di(tert‐butylperoxyisopropyl) benzene (DTBPIB), and dicumyl peroxide (DCP), at two mixing temperatures: 160 and 180°C for a 60/40 NR/PP TPV. The maximum and final mixing torques are clearly related to the intrinsic decomposition temperature of the particular peroxide used, where DCP and DTBPIB turn out to be effective at 160°C, whereas the other two require a higher temperature of 180°C. The best mechanical properties, tensile strength, elongation at break and compression set are obtained at lower mixing temperature with DCP and DTBPIB, presumably due to less degradation of the NR and PP. Unfortunately, these two peroxides form more smelly by‐products than DTBPHY and DTBPH. Dependent on the requirements of the pertinent application, a balanced selection needs to be made between the various factors involved to obtain an optimal product performance of these NR/PP TPVs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The effect of surface energy on the heat transfer enhancement of paraffin wax/carbon foam composites

The influence of carbon foam surface energy on heat transfer through paraffin wax/carbon foam composite was investigated. Carbon foam samples were surface treated and their corresponding surface energy values were measured. A theoretical model was formulated to analyze the mass of paraffin wax absorbed for both pristine and surface activated carbon foam samples based on the concept foam wettability. An experimental study was carried out for heating of the wax/carbon foam composite samples to study the phase change heat transfer due to the melting of wax within the foam matrices. The above studies showed that a greater mass of wax was absorbed within the activated carbon foam samples as compared to the pristine sample which can be due to their greater wettability. This resulted in an improvement in heat transfer rate for the activated samples. The total energy storage rate for the activated composite samples was compared with the pristine sample for the same heating duration and an enhancement of more than 18% was observed for the two activated samples. These studies revealed that the surface energy of carbon foams can play an important role in improving the overall thermal performance of wax/carbon foam composites.     

MG49改性CaCO3对NR硫化胶的结构与性能的影响

用接枝率为49％的天甲橡胶（MG49）改性碳酸钙（CaCO3)。通过混炼胶CaCO3的结合胶质量分数，硫化胶的表观交联密度，界面作用强度，蠕变和力学性能等的测定，研究了改性方法和MG49的用量对CaCO3填充NR硫化胶的结构和性能的影响。结果表明：MG49湿法改性增强了CaCO3与NR间界面的作用强度，改善了CaCO3填充NR硫化胶的网络结构，提高了材料的力学性能。MG49最适宜质量分数为10％。     

二维层状超分子化合物[Mn（C8H5NO6）（H2O）2]n的合成及晶体结构研究

分子间的弱相互作用在配位化合物中往往表现为配合物分子内和(或)分子间的配体间相互作用。因此,研究配合物中的配体间弱相互作用就成为由配位化学向超分子化学过渡的桥梁。本文以锰离子为中心离子,以2,4,6-吡啶三羧酸为配体进行晶体合成实验。通过检测手段了解了合成的配合物配体间的弱相互作用。     

The pressure effect on the wax formation in diesel fuel☆

The prevention of wax formation under high pressure on new diesel engine requires a good understanding of the behaviour of the paraffin molecules crystallization. In this work a diesel from a Petrogal refinery was investigated under pressure. In particular the melting curve was measured from atmospheric pressure to 100 MPa by an optical technique. The behaviour of the solid phase with the pressure was also investigated up to 50 MPa by filtration. The results obtained show an increase in the diesel cloud point of about 25 °C at the operating pressure of a common rail engine. It is clear from our results that the increase of the diesel cloud point must be taken into account in the development of new diesel engines where the diesel is injected under high pressure.All the results obtained were successfully predicted with a thermodynamic model able to describe multiphase equilibrium.     

食品塑料包装中抗氧化剂迁移研究

利用高效液相色谱仪对高密度聚乙烯包装中抗氧化剂1076和抗氧化剂168在微波条件下向食物中的迁移行为进行了研究。研究结果表明,微波功率增大、微波时间延长都会使两种抗氧化剂向食物中迁移的程度变大。另外随着时间的延长,在微波加热初期两种抗氧化剂的迁移量显著增高,随着作用时间延长至20 min后,抗氧化剂向食物中的迁移率增加不再明显。两种抗氧化剂向不同食物中的迁移率也不一样,向猪肉中的迁移率最高,米饭次之,向果蔬类食品中的迁移率最小。     

填料-弹性体相互作用对填充硫化胶滞后损失、湿摩擦性能和磨耗性能的影响(续完)

(接上期) 5 耐磨性能 磨耗或磨损是受到填料强烈影响的性能之一.通常认为橡胶磨耗机理是非常复杂的,它不仅涉及材料的机械破坏,如疲劳损坏、撕裂等,而且还涉及机械-化学和热-化学过程.     

Effect of Electric Field on the Migration of Grain Boundaries in Alumina

The effect of an external electric field on the grain-boundary migration in Al₂O₃ ceramics has been investigated. The boundary migration is dependent on the direction and magnitude of the applied bias, and the observed boundary migration behavior is attributed to the presence of an electrostatic potential that inherently forms at the grain boundaries of Al₂O₃ ceramics. The results give experimental evidence that the boundary phenomena in oxide ceramics are related to the grain-boundary potential.     

燃煤过程中铬迁移转化和排放控制的研究进展

论述了煤燃烧过程中铬迁移转化和排放控制的研究进展。介绍了国内外各地煤中铬的含量。对铬在燃煤过程中迁移转化机理的研究成果进行了说明。简要总结了铬排放的控制技术,并提出了研究的不足以及今后铬释放的研究方向。     

操作参数和流体物性参数对水力旋流器的迁移率的影响

在迁移率计算模型的基础上,本文对水力旋流器的迁移率与分流比、流量及物性参数之间的关系进行了分析与计算。结果表明,在分流比不变的条件下,流量和物性参数对迁移率的影响只表现在改变分割尺寸d50上,流量、物性参数及分割尺寸的变化遵循旋流器数Hy=const.的规律。当分流比改变时,分割尺寸略微变化,但迁移率MP'与无因次液滴直径△＝d/d50之间的关系不变。这两点与Thew的回归结果略有区别。在分流比、流量及物性参数同时变化时,本文根据计算结果给出了迁移率及旋流器数与分流比之间的关联式,据此可预估不同操作参数与物性参数下的迁移率。     

The miR-106b/NR2F2-AS1/PLEKHO2 Axis Regulates Migration and Invasion of Colorectal Cancer through the MAPK Pathway

Increasing numbers of miRNAs have been observed as oncogenes or tumor suppressors in colorectal cancer (CRC). It was recently reported that hsa-miR-106b-5p (miR-106b) promoted CRC cell migration and invasion. However, there were also studies showing contradictory results. Therefore, in the present study, we further explore the role of miR-106b and its downstream networks in the carcinogenesis of CRC. We observed that the expression of miR-106b is significantly increased in Pan-Cancer and CRC tissues compared with normal tissues from The Cancer Genome Atlas (TCGA) database. Furthermore, we used Transwell, Cell Counting Kit-8, and colony formation assays to clarify that miR-106b promotes the migratory, invasive, and proliferative abilities of CRC cells. For the first time, we systematically screened the target mRNAs and lncRNAs of miR-106b using TCGA database and the bioinformatics algorithms. Dual-luciferase reporter assay confirmed that NR2F2-AS1 and PLEKHO2 are the direct targets of miR-106b. Furthermore, NR2F2-AS1 acts as a competing endogenous RNA (ceRNA) to regulate PLEKHO2 expression by sponging miR-106b. The results of Gene set enrichment analysis (GSEA) and Western blot indicated that they play important roles in CRC progression by regulating MAPK pathway. Thus, miR-106b/NR2F2-AS1/PLEKHO2/MAPK signaling axis may suggest the potential usage in CRC treatment.     

酶法酯交换过程中不饱和脂肪酸对其酰基位移的影响

酶法制备结构酯的过程中,由于酰基位移的发生而生成了副产品．并影响了产品质量。研究了Lipozyme IM和猪胰脂酶催化橄榄油与硬脂酸甲酯反应,油酸、亚油酸、亚麻酸的相对酰基位移率的比较。结果显示：双键越多酰基位移越小,猪胰脂酶催化时脂肪酸酰基位移程度大于Lipozyme IM。     

The effect of selective location of carbon nanotubes on electrical properties of thermoplastic vulcanizates

Three types of conductive thermoplastic vulcanizates (TPVs) were prepared by blending polypropylene (PP), carbon nanotubes (CNT), and carboxylic acrylonitrile butadiene ultrafine full‐vulcanized powdered rubber (xNBR‐UFPR). The CNT locations were different in these three types of TPVs, i.e., CNTs were localized in PP matrix, in the xNBR‐UFPR phase, or mainly in the interface. It had been found that TPV with CNTs localized mainly in the interface had the lowest conductive percolation threshold among these three types of TPVs. The volume resistivity of the TPV with 2 phr CNTs was as small as 220 Ω?cm. Moreover, the conductive TPV possessed good mechanical properties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electrodeionization 1: Migration of Nickel ions absorbed in a rigid, Macroporous Cation-exchange Resin

The removal of nickel ions from a packed bed of ion-exchange material under an applied potential is studied. This process involves the use of an electrodialysis type cell in which the centre compartment is filled with a packed bed of ion-exchange particles. The bed width, concentration of nickel in the resin and electrolyte concentration were varied. Emphasis was placed on the rate of nickel migration, current efficiency and the effective mobility of nickel in the system. The purpose of the study is to aid in the development of a system for the continuous removal of heavy metal ions from dilute solutions.