纳米填料/橡胶体系在贮存中的结构形态变化Ⅱ.结构变化的影响因素及其对性能的影响

综述了纳米填料／橡胶复合体系在熔融态或高弹态贮存停放过程中,影响其结构形态变化的因素,以及贮存停放对复合体系流变性能、物理机械性能和导电性能的影响,并评述了相关的理论模型。纳米填料／橡胶复合体系在熔融贮存过程中的结构变化主要受橡胶的黏度、填料特性及其用量、填料与橡胶之间的相互作用以及加工性能的影响。填料网络结构的絮凝程度强化使复合体系流变性能、动态力学性能降低,但导电性能提高。相关的填料聚集动力学和填料絮凝模型大部分是唯象模型。     

纳米填料/橡胶体系在贮存中的结构形态变化Ⅰ.填料与橡胶及填料与填料的相互作用

阐述了纳米填料／橡胶体系在贮存停放过程中,填料与橡胶之间及填料与填料之间相互作用的变化。结果表明,纳米填料／橡胶体系在贮存停放过程中结合胶的形成是动力学平衡过程,随着停放时间的延长,填料与橡胶之间的相互作用增强,填料与橡胶之间的相互作用活性点面积减小,同时填料与填料之间的相互作用增强,填料网络结构絮凝程度提高。制备纳米填料／橡胶复合材料时,应促进混合体系在贮存停放过程中填料与橡胶之间的物理浸润和化学结合作用,阻止因填料与填料之间相互作用而产生的絮凝现象,使得纳米粒子在橡胶基体中达到纳米级分散和强界面结合。     

SiO2纳米粒子改性填充PC的力学与流变性能

采用SiO2纳米粒子填充改性聚碳酸酯(PC),为使无机纳米粒子在基体PC中分散均匀,经硅烷偶联剂KH-550对SiO2纳米粒子进行表面处理,分析了改性SiO2纳米粒子对复合材料机械与加工性能的影响,并对复合材料进行了分析表征,探讨了无机刚性纳米粒子填充改性典型工程塑料PC的特点并探索其增强增韧的机理,研究了复合物的粘流变性能. 结果表明,改性SiO2纳米粒为球形,在PC基体中分散均匀,湿法改性制备的PC/SiO2纳米粒子复合材料的力学拉伸性能和流变性能最好.     

反应共混改性纳米二氧化硅/炭黑填充溶聚丁苯橡胶的结构与性能

采用动态反应共混法制备了含硫的硅烷偶联剂双-[γ-(三乙氧基硅)丙基]-四硫化物(Si-69)和双-[γ-(三乙氧基硅)丙基]-二硫化物(Si-75)改性纳米SiO2/炭黑填充溶聚丁苯橡胶(SSBR)硫化胶,分析了胶料的微观结构,研究了胶料的物理机械性能和动态力学性能等。结果表明,纳米填料在胶料中呈现较理想的分散状态;当纳米SiO2与炭黑填料的总量为70份时,随改性纳米SiO2用量的增加,SSBR硫化胶的邵尔A硬度、扯断伸长率、永久变形、撕裂强度下降,拉伸强度变化不大,300%定伸应力显著提高,生热明显下降,其中Si-75改性纳米SiO2/炭黑填充的SSBR综合性能更优;纳米填料在橡胶基体中的分散性好,胶料的动态生热低。     

PP/纳米SiO2复合材料的研究

采用傅立叶红外光谱仪(FT-IR)表征了改性前后纳米SiO2粉体的性能特征;通过熔融共混法制备了PP/纳米SiO2复合材料。研究了纳米SiO2用量对PP基体性能的影响。通过力学性能测试、DSC热分析和SEM照片观测,对PP/纳米SiO2复合材料的结构和性能进行了系统的研究。结果表明:当纳米SiO2含量为2%时,PP/纳米SiO2复合材料的综合力学性能最好。DSC表明,纳米SiO2对PP基体有异相成核作用。SEM电镜分析得出,经表面改性的纳米SiO2均匀地分散于PP基体中,从而起到良好的改性作用。     

纳米材料在高性能橡胶开发中的应用进展

在连续相橡胶基体和至少有一维尺寸小于100nm增强剂(分散相)构成的复合材料,称之为纳米复合橡胶,其中传统的炭黑填充橡胶也属于纳米复合橡胶。能够分散在橡胶基体中的纳米材料主要有金属氧化物纳米粒子、金属硫化物纳米粒子、非金     

纳米氧化铝填充EPDM制备高性能复合材料

采用纳米氧化铝(Al_2O_3)为填料,制备不同配比的EPDM/Al_2O_3复合材料,并分别研究了复合材料的机械性能、导热系数和微观形貌。研究结果表明,随着Al_2O_3用量的增加,复合材料的力学性能表现得更为优异,导热系数也明显增加;纳米Al_2O_3的用量增加至100份,复合材料的导热系数增加至0.53 W/(m·K),压缩疲劳值增加的较少,大大降低了填料与橡胶基体之间的摩擦,因此表现出较小的热量积累。在同一配比下,填充纳米Al_2O_3的复合材料与其他填料的机械性能接近,导热系数明显增加,比炭黑N550填充复合材料的热导率高约32.3%,比聚氯乙烯(PVC)填充复合物的热导率高出57.7%。Al_2O_3填料在橡胶基体中可以均匀地分散,复合材料的交联网络较为完善,对于延长材料的使用寿命具有重要意义。     

氧化石墨烯与白炭黑并用填充丁苯橡胶纳米复合材料的性能

采用乳液共混与机械剪切法制备氧化石墨烯/白炭黑/丁苯橡胶纳米复合材料,并对其综合性能进行研究。结果表明:两种并用填料在橡胶基体中均能达到纳米级分散,且白炭黑粒子填补了氧化石墨烯片层间的空隙。氧化石墨烯的加入延长了复合材料的正硫化时间,改变了其交联密度。氧化石墨烯等量替代白炭黑,可以提高橡胶基体中填料的有效体积分数,改善复合材料的物理性能和动态力学性能。氧化石墨烯的加入使复合材料的耐磨性能显著提高。与白炭黑填充相比,氧化石墨烯/白炭黑填充复合材料的60℃时损耗因子有所降低,能进一步降低滚动阻力,但其0℃的损耗因子也呈现降低趋势,对复合材料抗湿滑性能不利。     

纳米SiO2对甲基乙烯基硅橡胶结构和性能的影响

采用沉淀法和气相法纳米SiO2补强硅橡胶,考察纳米SiO2的添加量和比表面积对结合橡胶量、橡胶吸附层厚度以及硅橡胶补强力学性能的影响．通过溶胀平衡实验计算填料补强能力参数C值,并通过扫描电镜观察填料纳米SiO2在硅橡胶中的分散状态．结果表明：填料添加量对硅橡胶力学性能的影响效果显著,当质量比为0．4时,补强橡胶具有较好的力学综合性能,结合橡胶量增大至49．24％,吸附层厚度增至6．87nm,对于气相法纳米SiO2,增大填料比表面积有利于提高结合橡胶量,改善填料的补强效果,补强硅橡胶热稳定性也相应提高,此外填料的C值也随之增大,选一步验证了填料的补强效果增强．     

二氧化硅纳米粒子在橡胶中的“薄膜”和“互扣”补强作用

研究二氧化硅纳米粒子在橡胶中的“薄膜”和“互扣”补强作用。通过分析二氧化硅纳米粒子和纳米粒子链在聚二甲基硅氧烷（PDMS）基体中的分散现象,得出硅橡胶基体中填料富集区的PDMS分子“薄膜”和纳米粒子链的“互扣”具有类似于贝壳珍珠层的补强功能,可提高复合材料的强度和韧性；纳米级补强材料的空间形态对复合材料性能有着极大的影响。     

Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM

Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.     

Insect antifeedant properties of anthranoids from the genusVismia

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.     

Many Drugs of Abuse May Be Acutely Transformed to Dopamine,Norepinephrine and Epinephrine In Vivo

It is well established that a wide range of drugs of abuse acutely boost the signaling of the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis, where norepinephrine and epinephrine are major output molecules. This stimulatory effect is accompanied by such symptoms as elevated heart rate and blood pressure, more rapid breathing, increased body temperature and sweating, and pupillary dilation, as well as the intoxicating or euphoric subjective properties of the drug. While many drugs of abuse are thought to achieve their intoxicating effects by modulating the monoaminergic neurotransmitter systems (i.e., serotonin, norepinephrine, dopamine) by binding to these receptors or otherwise affecting their synaptic signaling, this paper puts forth the hypothesis that many of these drugs are actually acutely converted to catecholamines (dopamine, norepinephrine, epinephrine) in vivo, in addition to transformation to their known metabolites. In this manner, a range of stimulants, opioids, and psychedelics (as well as alcohol) may partially achieve their intoxicating properties, as well as side effects, due to this putative transformation to catecholamines. If this hypothesis is correct, it would alter our understanding of the basic biosynthetic pathways for generating these important signaling molecules, while also modifying our view of the neural substrates underlying substance abuse and dependence, including psychological stress-induced relapse. Importantly, there is a direct way to test the overarching hypothesis: administer (either centrally or peripherally) stable isotope versions of these drugs to model organisms such as rodents (or even to humans) and then use liquid chromatography-mass spectrometry to determine if the labeled drug is converted to labeled catecholamines in brain, blood plasma, or urine samples.     

Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.     

Novel polyurethane coating technology through glycidyl carbamate chemistry

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.