聚氨酯的化学降解及其性能

简单介绍了聚氨酯的水解、热降解、热氧化降解和紫外线降解的反应机理。举例比较了加入或未加入稳定剂的聚氨酯弹性体在降解试验前后的拉伸强度及其它性能变化,指出了添加稳定剂可改善聚氨酯弹性体的抗降解稳定性。     

聚氨酯材料的降解机理及其稳定剂

综述了聚氨酯(PU)材料的光降解、热氧化降解、水解等降解机理,以及用作光稳定剂、热氧化稳定剂、水解稳定剂的产品种类及其协调作用.聚氨酯材料的使用环境不同,降解机理也不同,正确选用稳定剂并进行应用是提高PU材料性能的一种简单而有效的手段.     

聚氨酯材料的化学降解机理

聚氨酯材料的化学降解基理研究有针对回收利的醇解、胺解、醇胺解、磷酸酯解等研究,有针对改进材料稳定性的水解、热降解、热氧化降解、光降解基理研究,本文介绍了几种化学方法的降解基理。     

硝酸酯基聚醚聚氨酯的老化降解：Ⅰ.薄层层析法检测降解产物中的胺

用薄层层析法定性检测出硝酸酯基聚醚聚氨酯老化降解产物中的胺，推断降解机理为氨基甲酸酯中Ｃ－Ｎ键的断裂，讨论了影响检测的各种因素。     

脂肪族聚醚型聚氨酯弹性体热降解机理及热稳定性

采用酯交换缩聚法,以聚四氢呋喃醚二醇（PTMEG）和1,6-六亚甲基二氨基甲酸甲酯（HDU）为原料,以1,4-丁二醇（BDO）为扩链剂,以二丁基氧化锡为催化剂制备脂肪族聚醚型聚氨酯（PU）弹性体。用TGA和FTIR考察聚氨酯弹性体的热降解机理及原料组成对聚氨酯热降解过程的影响。结果表明：聚氨酯弹性体的热降解过程包括两个阶段,分别为硬段（氨基甲酸酯）和软段（聚醚多元醇）的降解,其中硬段（氨基甲酸酯）的降解主要降解产物为碳化二亚胺、CO₂、四氢呋喃及水,软段（聚醚多元醇）的降解主要产物为四氢呋喃和水。随着硬段含量的降低,聚氨酯弹性体初始热降解温度由282℃上升至327℃,聚氨酯弹性体的热稳定性升高。     

各类抗氧化剂对聚醚酯热氧化降解的抑制规律

从探讨聚醚酯热降解和热氧化降解的机理和抗氧化剂的作用原理着手，讨论了各类抗氧化剂对共聚醚酯热氧化稳定性的影响。通过聚合物的特性粘度「η」，端羧基含量「ＣＯＯＨ」，热重分析，差热分析，红外光谱分析等测试分析，确定了各类抗氧化剂抑制共聚醚酯热氧化玫解的规律，并证实了它们之间的协同效应。     

第六十四讲 聚氨酯材料开拓汽车轮胎市场的新蓝海

聚氨酯又称聚氨基甲酸酯,简称PU,是由二元或多元有机异氰酸酯与多元醇化合物反应而得的一类主链上带有重复氨基甲酸酯(-NHCOO-)基团的聚合物的总称,它的化学结构比一般热塑性弹性体复杂,除反复出现的氨基甲酸酯基团外,分子链中往往还含有酯基、醚基、芳香基等基团。由聚氨酯材料制作的轮     

聚氨酯材料的老化降解

评述了聚氨酯材料在紫外线，水，热氧及化学介质条件下的老化降解机理；综述了聚氨酯材料老化降解的研究进展。     

新型低成本耐老化聚氨酯弹性体的研究

以酯基间有2~6个碳原子的聚酯二元醇（CMA-24、CMA-44、CMA-254、CMA-66）、甲苯二异氰酸酯和扩链剂3,5-二甲硫基甲苯二胺（DMTDA）为原材料,通过预聚体法制备了一种耐水解聚酯型聚氨酯弹性体。探讨了水解稳定剂、防酶剂、紫外线吸收剂和抗氧剂等助剂对聚氨酯弹性体性能的影响,测定了耐水解聚酯型聚氨酯弹性体的耐湿热老化和耐海水性能。结果表明,通过添加适量的水解稳定剂、防霉剂、紫外线吸收剂和抗氧剂可大幅度提高聚酯型聚氨酯弹性体的耐湿热老化和耐紫外线老化性能,特别是耐海水性能较传统的聚酯型聚氨酯弹性体提高了5倍以上。     

降解型聚氨酯专利技术分析

聚氨酯材料是一种具有氨基甲酸酯基重复结构单元的聚合物材料。聚氨酯具有特殊的化学结构,因而具备了优良的物理机械性能,是一种具有广泛应用的高分子。本文通过检索、统计、分析降解型聚氨酯材料的专利申请文献,综述了降解型聚氨酯的主要技术路线。     

A review of ZrO2 nanoparticles applications and recent advancements

The many branches of nanoscience have made significant strides and advancements during the past ten years, as has the entire scientific community. Zirconia nanoparticles have several uses as adsorbents, nanosensors, nanocatalysts, and other types of nanomaterials. Their outstanding biomedical uses in dental care and drug delivery, as well as their intriguing biological characteristics, such as their anti-cancer, anti-microbial, and antioxidant activity, have further encouraged researchers to investigate their physicochemical properties using various synthetic pathways. Due to the popularity of zirconia-based nanomaterials, the current research comprehensively examines several synthesis techniques and their effects on the composition, dimensions, forms, and morphologies of these nanomaterials. In general, there are two methods for creating zirconia nanoparticles: chemical synthesis, which uses hydrothermal, solvothermal, sol-gel, microwave, solution combustion, and co-precipitation processes; and a greener method, which uses bacteria, fungi, and plant components. The aforementioned techniques have been evaluated in the present review for achieving particular phases and shapes. A thorough analysis of zirconia-based nanomaterial's uses is also included in the review. Furthermore, comparisons with their equivalent composites for various applications as well as the influence of particular phases and morphologies have been added. The final portion includes the summary, future outlook, and potential application.     

Semiochemistry of the Goldeneyed Lacewing Chrysopa oculata: Attraction of Males to a Male-Produced Pheromone

Gas chromatographic-electroantennographic detection (G3C-EAD) experiments showed that antennae of males and females of the goldeneyed lacewing, Chrysopa oculata Say (Co. = Chrysopa), consistently responded to four compounds extracted from the abdominal cuticle of males:nonanal, nonanol, nonanoic acid, and (1R*,2S*,5R*,8R*)-iridodial. These compounds were not detected from abdominal cuticle of females. Thoracic extracts of both sexes contained antennal-stimulatory 1-tridecene and EAD-inactive skatole. Chrysopa oculata adults were most sensitive to (1R,2S,5R,8R)-iridodial standard at an EAD-response threshold between 0.1 and 1 pg, which was 10-100 times lower than thresholds for nonanal and nonanoic acid, and up to 10,000 times lower than thresholds for other compounds tested. A similar EAD response pattern was also found in another Chrysopa sp. (Co. quadripunctata Burmeister). In field-trapping experiments, (1R,2S,5R,8R)-iridodial was the only male-specific compound that attracted Co. oculata males. Males also were weakly attracted to (1R,4aS,7S,7aR)-nepetalactol (an aphid sex pheromone component), probably due to the 5% (1R,2S,5R,8R)-iridodial present in the synthetic sample as an impurity. A herbivore-induced plant volatile, methyl salicylate, increased attraction of males to (1R,2S,5R,8R)-iridodial, whereas 1-tridecene was antagonistic. No females were caught in the entire study. Scanning electron micrographs revealed numerous male-specific, elliptical epidermal glands on the 3rd-8th abdominal sternites of Co. oculata, which are likely the pheromone glands. Another lacewing species, Chrysoperla rufilabris (Burmeister) (Cl. = Chrysoperla), did not produce male-specific volatiles or possess the type of gland presumed to produce pheromone in Co. oculata males, but (Z)-4-tridecene was identified as a major antennal-stimulatory compound from thoracic extracts of both sexes of Cl. rufilabris. Thus, (1R,2S,5R,8R)-iridodial (or its enantiomer) is now identified as a male-produced male aggregation pheromone for Co. oculata, the first pheromone identified for lacewings.     

Graphene-Based Sensors for the Detection of Bioactive Compounds: A Review

Over the last years, different nanomaterials have been investigated to design highly selective and sensitive sensors, reaching nano/picomolar concentrations of biomolecules, which is crucial for medical sciences and the healthcare industry in order to assess physiological and metabolic parameters. The discovery of graphene (G) has unexpectedly impulsed research on developing cost-effective electrode materials owed to its unique physical and chemical properties, including high specific surface area, elevated carrier mobility, exceptional electrical and thermal conductivity, strong stiffness and strength combined with flexibility and optical transparency. G and its derivatives, including graphene oxide (GO) and reduced graphene oxide (rGO), are becoming an important class of nanomaterials in the area of optical and electrochemical sensors. The presence of oxygenated functional groups makes GO nanosheets amphiphilic, facilitating chemical functionalization. G-based nanomaterials can be easily combined with different types of inorganic nanoparticles, including metals and metal oxides, quantum dots, organic polymers, and biomolecules, to yield a wide range of nanocomposites with enhanced sensitivity for sensor applications. This review provides an overview of recent research on G-based nanocomposites for the detection of bioactive compounds, providing insights on the unique advantages offered by G and its derivatives. Their synthesis process, functionalization routes, and main properties are summarized, and the main challenges are also discussed. The antioxidants selected for this review are melatonin, gallic acid, tannic acid, resveratrol, oleuropein, hydroxytyrosol, tocopherol, ascorbic acid, and curcumin. They were chosen owed to their beneficial properties for human health, including antibiotic, antiviral, cardiovascular protector, anticancer, anti-inflammatory, cytoprotective, neuroprotective, antiageing, antidegenerative, and antiallergic capacity. The sensitivity and selectivity of G-based electrochemical and fluorescent sensors are also examined. Finally, the future outlook for the development of G-based sensors for this type of biocompounds is outlined.     

The Emerging Roles of Chromogranins and Derived Polypeptides in Atherosclerosis,Diabetes, and Coronary Heart Disease

Chromogranin A (CgA), B (CgB), and C (CgC), the family members of the granin glycoproteins, are associated with diabetes. These proteins are abundantly expressed in neurons, endocrine, and neuroendocrine cells. They are also present in other areas of the body. Patients with diabetic retinopathy have higher levels of CgA, CgB, and CgC in the vitreous humor. In addition, type 1 diabetic patients have high CgA and low CgB levels in the circulating blood. Plasma CgA levels are increased in patients with hypertension, coronary heart disease, and heart failure. CgA is the precursor to several functional peptides, including catestatin, vasostatin-1, vasostatin-2, pancreastatin, chromofungin, and many others. Catestatin, vasostain-1, and vasostatin-2 suppress the expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in human vascular endothelial cells. Catestatin and vasostatin-1 suppress oxidized low-density lipoprotein-induced foam cell formation in human macrophages. Catestatin and vasostatin-2, but not vasostatin-1, suppress the proliferation and these three peptides suppress the migration in human vascular smooth muscles. Chronic infusion of catestatin, vasostatin-1, or vasostatin-2 suppresses the development of atherosclerosis of the aorta in apolipoprotein E-deficient mice. Catestatin, vasostatin-1, vasostatin-2, and chromofungin protect ischemia/reperfusion-induced myocardial dysfunction in rats. Since pancreastatin inhibits insulin secretion from pancreatic β-cells, and regulates glucose metabolism in liver and adipose tissues, pancreastatin inhibitor peptide-8 (PSTi8) improves insulin resistance and glucose homeostasis. Catestatin stimulates therapeutic angiogenesis in the mouse hind limb ischemia model. Gene therapy with secretoneurin, a CgC-derived peptide, stimulates postischemic neovascularization in apolipoprotein E-deficient mice and streptozotocin-induced diabetic mice, and improves diabetic neuropathy in db/db mice. Therefore, CgA is a biomarker for atherosclerosis, diabetes, hypertension, and coronary heart disease. CgA- and CgC--derived polypeptides provide the therapeutic target for atherosclerosis and ischemia-induced tissue damages. PSTi8 is useful in the treatment of diabetes.     

A review of liquid silicone rubber injection molding: Process variables and process modeling

Liquid silicone rubber (LSR) is an elastomer molded into critical performance components for applications in medical, power, consumer, automotive, and aerospace applications. This article reviews process behavior, material modeling, and simulation of the (LSR) injection molding process. Each phase of the LSR injection molding process is discussed, including resin handling, plastication, injection, pack and hold, and curing; and factors affecting the molding process are reviewed. Processing behavior of LSR is marked by transient interactions between curing, shear rate, temperature, pressure, and tooling. Therefore, current LSR models for curing, viscosity, pressure, and temperature are discussed. Process dynamics and material modeling are combined in LSR injection molding simulations with applications in mold design, troubleshooting process-induced defects, and management of shear stress and non-uniform temperatures between LSR and substrates during overmolding. Finally, case studies using commercial simulation software are presented, which have shown cavity pressure and flow front advancement within 3% of experimental values. Optimization of LSR materials, data collection, model fitting, venting, and bonding remain areas of continued interest.     

Using symmetry to understand the attributes of color

The common attributes of color are distinguishable by their symmetries. Hue, saturation, chroma, chromaticness, whiteness, and blackness symmetries are discussed. Symmetries are generally not sufficient to specify unique formulas for color attributes, nor are they an endorsement of color model accuracy. However, symmetries do provide constraints for valid formulae, which are useful even when symmetries are only approximate. They also provide an alternate conceptual understanding of color attributes that differs from standard color science definitions. Symmetries provide a simplified framework for calculating groups of colors that share color attributes. Color models examined include the Hunt Model, a simple color model (SCM), various CIE color spaces, and IPT. A general functional form describes symmetries and scaling laws for many color models, and exceptions are discussed. © 2007 Wiley Periodicals, Inc. Col Res Appl, 33, 27–44, 2008     

Potential of Polyvinylidene Fluoride/Carbon Nanotube Composite in Energy,Electronics, and Membrane Technology: An Overview

Polyvinylidene fluoride (PVDF) is a semicrystalline thermoplastic and electroactive polymer with piezoelectric and pyroelectric properties, thermal stability, elasticity, and chemical resistance. PVDF exits in five different phases (α, β, δ, γ, and ε-phase). Unique properties of this polymer enhances its use in chemical, biomedical, and electronic industries such as supercapacitors, transducers, actuators, and batteries. Carbon nanotube (CNT) is used as reinforcement to exploit full potential of PVDF in energy, electronics, and membrane technology. The nanofiller affects morphology, piezoelectric, pyroelectric, electrical, dielectric, thermal, and mechanical properties of PVDF-based nanocomposite. CNT content and chemical modification influence properties as well as application of PVDF.     

Pheromonal activity of single castoreum constituents in beaver,Castor canadensis

Behavioral activity of single components of beaver castoreum was demonstrated for the first time. In four experiments samples were presented to free-ranging beaver in their family territories. First, responses to whole castoreum and anal gland secretion (AGS) from males and females were tested. Second, 24 compounds, known to be constituents of beaver castoreum, were individually screened for activity. Four of these consistently released immediate responses during the observation periods. These are the phenols 4-ethylphenol and 1,2-dihydroxybenzene and the ketones acetophenone and 3-hydroxyacetophenone. In the most complete responses, the beaver sniffed from the water, were attracted to the odor, swam toward its source, went on land, and then approached, sniffed, pawed, and scent-marked the artificial scent mound. 4-Ethoxyphenol, a compound not yet found in castoreum, also released these responses. Five additional compounds resulted in a few delayed visits to the samples during the night following the observations, as evidenced by destroyed scent mounds. These are 4-methyl-1,2-dihydroxybenzene, 4-methoxyacetophenone, 5-methoxysalicylic acid, salicylaldehyde, and 3-hydroxybenzoic acid. Third, mixtures of 24 and six compounds were tested. Responses to these mixtures could be as strong as those to whole castoreum. Fourth, the four regularly active compounds were tested in two additional beaver populations and proved to be active there, too. The response was strongest in the densest beaver population.     

Enhancing the daytime conspicuity of pedestrians through the usage of fluorescent materials

The issue of daytime, pedestrian visibility, especially where occupational activities are involved, can be well served by bringing existing and related knowledge on high-visibility materials together with new product capabilities. Formulated strategically, this information can beneficially serve the personal safety of our society. This particular form of personal safety involves being seen, most critically, by operators of motorized vehicles. Therefore, the issues of visibility, visibility enhancement, and conspicuity are focused upon through the use of high-visibility materials. High-visibility materials include but are not limited to retroreflective forms. In daytime and dusk/dawn conditions, fluorescent-colored products can serve as high-visibility materials used to effectively generate enhanced conspicuity. the time has now come to more aggressively research what we may intuitively believe and then apply this knowledge. to more fully grasp what is involved, we must take into account the following: 1. a basic understanding of fluorescence, 2. basic human vision and perception, 3. situations calling for enhanced conspicuity, 4. strategies for use, 5. product development, 6. specfications, guidelines and standards, 7. public education, and awareness. © 1995 John Wiley & Sons, Inc.     

Analyses of Avocado (Persea americana) Nectar Properties and their Perception by Honey bees (Apis mellifera)

Honey bees are important avocado pollinators. However, due to the low attractiveness of flowers, pollination is often inadequate. Previous work has revealed that avocado honey is relatively unattractive to honey bees when compared with honey from competing flowers. We characterized avocado honey and nectar with respect to their odor, color, and composition of sugars, phenolic compounds, and minerals. Furthermore, we tested how honey bees perceive these parameters, using the proboscis extension response bioassay and preference experiments with free-flying bees. Naïve bees were indifferent to odors of avocado and citrus flowers and honey. Experienced bees, which were collected in the field during the blooming season, responded preferentially to odor of citrus flowers. The unique sugar composition of avocado nectar, which contains almost exclusively sucrose and a low concentration of the rare carbohydrate perseitol, and the dark brown color of avocado honey, had no negative effects on its attractiveness to the bees. Phenolic compounds extracted from avocado honey were attractive to bees and adding them to a solution of sucrose increased its attractiveness. Compared with citrus nectar and nonavocado honey, avocado nectar and honey were rich in a wide range of minerals, including potassium, phosphorus, magnesium, sulfur, iron, and copper. Potassium and phosphorus, the two major minerals, both had a repellent effect on the bees. Possible explanations for the presence of repellent components in avocado nectar are discussed.