硼酚醛固化环氧树脂的热分解动力学

用热重分析研究了苯酚型硼酚醛固化环氧树脂的热分解动力学,测定了反应级数和反应速率常数,讨论了该树脂的热性能.     

GG-g-PAA/LOESS复合高吸水性树脂的制备与性能

以瓜尔胶(GG)、丙烯酸(AA)和黄土(LOESS)为原料,过硫酸铵(APS)为引发剂,N,N'-亚甲基双丙烯酰胺(MBA)为交联剂,采用水溶液聚合法制备了瓜尔胶接枝聚丙烯酸/黄土(GG-g-PAA/LOESS)复合高吸水性树脂。采用FTIR和SEM对其结构进行了表征,研究了LOESS的添加量对复合高吸水性树脂的溶胀能力和溶胀动力学的影响,考察了复合高吸水性树脂的保水性能、反复溶胀性以及在不同pH溶液中的吸水性能。结果表明,瓜尔胶、丙烯酸和LOESS发生了接枝共聚,体系中引入LOESS能够显著提高复合高吸水性树脂的吸水性能。当LOESS的质量分数为2%时,该树脂最高吸水倍率可达602 g/g,室温下6 d后,其保水率仍达28%,5次反复溶胀,吸水倍率仍能保持初始时的49%。此外,该复合高吸水性树脂还表现出优异的pH稳定性。     

超高相对分子质量聚乙烯树脂的溶胀性能研究

通过自行设计的溶胀性能测试方法,讨论了超高相对分子质量聚乙烯(UHMWPE)树脂的生产工艺、相对分子质量、树脂质量分数、粒径分布以及溶剂等因素对溶胀性能的影响。结果表明,不同厂家生产的UHMWPE树脂的溶胀性能有区别,随着相对分子质量增大,树脂的溶胀温度升高,溶胀时间变长;树脂质量分数提高,不利于树脂的充分溶胀;适当的粒径范围,能使树脂具有良好的溶胀性能;溶剂溶解性能的差异,对树脂的溶胀有较大的影响。     

DCPD/苯乙烯共聚树脂的热分析研究

采用差示扫描量热(DSC)法和热重(TG)分析法考察了双环戊二烯(DCPD)/苯乙烯(St)共聚树脂在N2中的热分解过程,并根据Friedman法(多加热速率法)和Kissinger法(代替高解析法)计算出热分解反应的动力学参数。在动力学研究的基础上,对DCPD/St共聚树脂使用寿命进行了预测。结果表明:DCPD/St共聚树脂的热分解反应过程大致可分为前期(失重率≤20%)、中期(失重率为30%～80%)和后期(失重率≥90%)3个阶段,前期和中期反应可以认为是1级反应,中期反应的平均活化能为150.43 kJ/mol;热分解温度随着升温速率的增加而提高,热分解反应活化能随着失重率的增加而增大;当温度低于200℃时,DCPD/St共聚树脂具有较好的热稳定性。     

鑫源煤在有机溶剂中的溶胀特性研究

对不同溶胀时间、不同溶剂、矿物质、预处理和金属无机盐等实验条件下鑫源低阶烟煤的溶胀行为和溶胀动力学进行了研究.结果表明,随着时间的延长,溶胀率逐渐增大,48 h溶胀基本达到平衡,溶胀特征是典型的slow-climbing-type溶胀;煤在混合溶剂中的溶胀率大于单一溶剂中的溶胀率,在极性溶剂中的溶胀率大于非极性溶剂中的溶胀率;脱除矿质元素后,煤溶胀率增大;溶胀、酸洗和碱洗使煤溶胀率增大,烘干使煤溶胀率减小;溶胀动力学表明,该煤的溶胀行为符合一级反应动力学方程,在THN和吡啶溶剂中的表观活化能均小于20 kJ/mol,这与煤中范德华力的破坏相对应,溶胀机制是由Case-Ⅱ扩散控制的.     

生物质热固性树脂的研究进展

综述了近5年来生物质热固性树脂,包括环氧树脂、酚醛树脂和聚氨酯等研究进展。概述了几种生物质热固性树脂的制备方法、合成条件和反应原理,分析了生物质热固性树脂的性能如玻璃化转变温度(T_g)、热分解温度、拉伸强度、弯曲强度、断裂伸长率、弹性模量、硬度、溶胀率、残炭率、可降解温度、游离酚含量和游离甲醛含量等,并与非生物质热固性树脂(双酚A环氧树脂、酚醛树脂和聚氨酯等)进行了比较。展望了生物质热固性树脂的发展前景。     

硅醇基POSS改性有机硅树脂的热性能

以甲基苯基有机硅树脂作为基体,硅醇基笼形倍半硅氧烷(POSS)作为改性剂,研究了不同POSS加入量和不同POSS加入方式对有机硅树脂热性能的影响,并对不同结构硅醇基POSS改性的有机硅树脂的热性能进行了综合评价。结果表明,采用三硅醇苯基POSS作为改性剂且其质量分数为5%时,通过加热反应方式制备的改性甲基苯基有机硅树脂起始热分解温度和900℃热失重率分别为448.3℃和15.45%。与未改性的甲基苯基有机硅树脂相比,起始热分解温度提高了48.9℃,900℃热失重率降低了6.37%。     

吸油树脂的结构及性能

以甲基丙烯酸丁酯和丙烯酸丁酯为单体,采用悬浮聚合法制备了吸油树脂.通过傅里叶变换红外光谱和热重分析表征了其结构和组成.研究了吸油树脂对不同油品的吸油率、吸油速率和缓释性能以及吸油树脂的吸油动力学.结果表明:吸油树脂热分解温度为366.68℃,其吸油性能符合一级动力学,对不同油品的吸油速率与油品的极性有关,对CCl4的吸...     

酚醛改性苯并噁嗪树脂耐烧蚀材料的研究

对不同组成苯并口恶嗪/酚醛共混树脂体系进行了研究,内容包括共混树脂的反应动力学参数计算、共固化机理、热分解动力学以及耐烧蚀性能等。结果表明:酚醛与苯并口恶嗪树脂共混后可以改变苯并口恶嗪的固化机理,酚醛树脂的加入使口恶嗪分子由热开环变为活泼氢开环,在较低温度下就可以反应,降低了固化反应温度。同时共混树脂可以使固化过程收缩率和小分子挥发物比传统的酚醛树脂低,可以减少烧蚀试样的表面裂纹,致密的碳化层具有一定附着强度,提高了共混树脂烧蚀性能。该共混体系可以作为宇航领域中1种性能优良的耐烧蚀树脂体系。     

聚二甲基硅炔树脂的热分解与介电分析

采用镁条、溴乙烷、苯乙炔为原料,通过格氏试剂反应法与二甲基二氯硅烷反应,成功制备了二甲基二苯乙炔基硅烷(DDPES),采用红外(FT-IR),核磁共振(~1H-NMR,、~(13)C-NMR、~(29)Si-NMR)对其结构进行表征分析,并通过热聚合法制备聚二甲基二苯乙炔基硅烷(PDDPES)树脂。借助TG-DTG技术分析了PDDPES树脂的热性能。采用6种动力学方法分别为:Kissinger、FWO、Coats-Redfern、ABSW、KAS和Tang法,研究了PDDPES树脂的热分解行为,并测试了该树脂的介电性能。实验结果表明,PDDPES树脂的平均热分解活化能为166. 80 k J/mol,热分解过程遵循随机成核机理和随后生长机理,树脂在2～18 GHz频率下的介电常数实部为2. 45～2. 85,介电常数虚部为0. 05～0. 30;损耗角正切值为0～0. 11,因此,该树脂是一种新颖的透波材料用树脂基体。     

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.