水性环氧树脂制备复合材料的热性能研究

以水性环氧树脂为基体制备了玻璃布/环氧树脂复合材料,用TG、TG-FTIR研究了复合材料和基体的热性能.结果表明,复合材料基体热降解分为两个阶段,复合材料的最大热失重速率峰值温度比树脂基体的最大热失重速率峰值温度低;热红联用分析表明,基体的降解主要发生在热失重第一阶段.动力学研究表明,树脂基体的表现活化能随分解程度增加逐渐增加.     

十溴二苯乙烷阻燃SBR热失重行为研究

利用热重法(TG)和微商热重法(DTG)研究了以十溴二苯乙烷为阻燃剂的阻燃丁苯橡胶在氮气气氛和空气气氛中的热降解失重行为。结果显示,在氮气气氛下,试样SBR/DBDPE和SBR/DBDPE/Sb2O3都只有一个重合在一起的热失重台阶;而在空气气氛下,试样SBR/DBDPE和SBR/DBDPE/Sb2O3均有三个热失重台阶,分别是DBDPE与Sb2O3反应、丁苯橡胶受热分解、成炭物受热分解;通过不同氛围下TG和DTG比较可以看出,裂解气氛不同可以显著地影响样品的热裂解过程,氮气气氛下的失重速率明显小于空气气氛下的失重速率,在氮气氛围下,样品的热分解主要发生在200~500℃,500℃以后热失重缓慢,且三组试样固体残留物的量分别为32.7%、29.6%、32.8%;而在空气氛围下,样品的热分解均主要发生在300~600℃,600℃以后热失重缓慢,且三组试样固体残留物的量为7%、2.1%、5.5%,固体残留量减少。     

多聚甲醛法硼酚醛树脂的热降解动力学

采用热分析技术(TG/DTG)研究了多聚甲醛法合成硼酚醛树脂的热降解性能,利用Friedman法和Flynn-Wall-Ozawa法对其热降解动力学进行了分析,计算出了不同条件下降解过程的活化能Ea。结果表明:树脂的热降解过程分为210～438℃,438～728℃,728～900℃3个阶段,当升温速率为10℃/min时,对应热失重率分别为4.256%,40.326%和23.717%,900℃下静态空气中质量残留31.442%。合成树脂的活化能在各升温速率下的平均值是29.91kJ/mol,反应级数n为2.837。     

基于热分析技术对聚氯乙烯再生料的热稳定性研究

采用热分析技术研究了聚氯乙烯再生料的热稳定性及其热降解行为。结果表明:聚氯乙烯再生料由多组分组成,在220℃时开始放热;分解失重分为两个阶段,第一阶段释放氯化氢气体,第二阶段是增塑剂和碳氢链段的分解;加热时易发生化学变化,因此再生料的加工温度需充分考虑其热稳定性。     

偏氟乙烯—六氟丙烯共聚弹性体热降解动力学的研究

本文采用热重法(TG)研究了偏氟乙烯—六氟丙烯二元共聚弹性体(氟橡胶—26)的热降解动力学,结果表明:氟橡胶—26的热降解按二个热失重阶段进行,计算了它在空气、氯气气氛中二个热失重阶段的热降解反应级数、热降解活化能和频率因子。     

PVC木塑复合材料热解动力学

将木粉按一定比例添加到PVC中得到复合材料,通过热重分析研究复合材料在空气、N2气氛下不同升温速率时的热解行为。通过Doyle和Tang method法计算了木塑材料的降解活化能。利用活化能分布函数,分析了复合材料在热解、燃烧过程中不同阶段的反应活性变化规律。研究表明,热解过程可分为3个阶段,230～360℃为第一失重阶段,360～430℃为稳定阶段,430～580℃为第二失重阶段。升温速率及反应气氛对热解过程有显著影响。由分布活化能模型计算表明,其热解动力学为一级反应,两个失重阶段的活化能分别为220kJ·mol-1和139kJ·mol-1,反应活性随失重率的增加而减少。     

新型DOPO基阻燃剂的合成与研究

以9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)、多聚甲醛、二异丙醇胺为原料,合成出一种新型含氮含磷反应型DOPO类阻燃剂,对其结构进行了表征,并初步研究了这种物质在空气气氛中的耐热性能。结果表明,该产物在178℃开始分解,到700℃剩余10.02%。将其加入到聚氨酯中制备复合材料,在氮气气氛中进行热重测试,发现随其用量加大,复合材料的初始分解温度有逐渐降低的趋势,失重台阶的降解活化能也是逐渐降低,但都比纯聚氨酯的高,证明添加此种阻燃剂之后起到了一定的耐热效果,且当添加量为2份时综合性能最好。其在空气气氛中进行热重测试,在239.7℃开始分解,主要有两大失重平台,分别失重22.06%和10.03%,在700℃时还剩余8.18%。然后探讨了复合材料降解过程的机理。     

TG-FTIR分析技术在PVC热降解过程研究中的应用

利用热失重-红外光谱联机分析技术(TG-FTIR)研究了聚氯乙烯(PVC)共混物在氮气气氛下、30～900℃范围内的热降解行为。结果表明:PVC共混物的热降解过程可分为3个阶段,分别在200～380℃,380～570℃和570～758℃范围内。其中,第一阶段主要为PVC脱HCl反应阶段,热降解产物主要为HCl;第二阶段主要为共轭多烯结构的裂解和环化,产物为低烃类化合物、苯及其衍生物;第三阶段为碳酸钙的分解反应,产物为CO2。     

三种不同致孔剂的阳离子交换树脂热失重分析

通过热失重法并结合元素分析,研究了3种不同致孔剂的阳离子交换树脂功能基团的热分解。结果表明,25~400℃范围内,3种树脂的热分解分为2个阶段,其中一阶失重是功能基团上结合水脱去的过程,二阶失重是聚苯乙烯骨架未发生分解,功能基团发生分解的过程。本文的研究对于离子交换树脂行业有一定参考意义。     

基于热失重法的热塑性聚氨酯热氧老化特性分析及其降解动力学模型

采用热塑性聚氨酯（TPU）在40℃、50℃、60℃、70℃下进行人工加速热老化,利用热失重分析法（TG）对TPU热降解过程进行分析,探讨了TPU在老化过程中的热失重特性及其热降解动力学模型。测试结果表明,TPu热失重过程可分为硬段和软段热裂解两个阶段;硬段和软段各自最快热降解速率随老化温度和时间的增加没有明显变化。然而,通过对TPU热失重5％时对应的温度进行分析,得出该温度随着热氧老化时间的延长而逐渐下降,说明TPu的热稳定性随老化时间的延长而逐渐降低。采用Coats—Redfern方法对TPU的热降解动力学进行研究,结果表明,TPU的热降解符合0级反应动力学方程。     

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.     

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.     

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.     

Methyl 2,4,6-decatrienoates Attract Stink Bugs and Tachinid Parasitoids

Halyomorpha halys (Stål) (Pentatomidae), called the brown marmorated stink bug (BMSB), is a newly invasive species in the eastern USA that is rapidly spreading from the original point of establishment in Allentown, PA. In its native range, the BMSB is reportedly attracted to methyl (E,E,Z)-2,4,6-decatrienoate, the male-produced pheromone of another pentatomid common in eastern Asia, Plautia stali Scott. In North America, Thyanta spp. are the only pentatomids known to produce methyl 2,4,6-decatrienoate [the (E,Z,Z)-isomer] as part of their pheromones. Methyl 2,4,6-decatrienoates were field-tested in Maryland to monitor the spread of the BMSB and to explore the possibility that Thyanta spp. are an alternate host for parasitic tachinid flies that use stink bug pheromones as host-finding kairomones. Here we report the first captures of adult and nymph BMSBs in traps baited with methyl (E,E,Z)-2,4,6-decatrienoate in central Maryland and present data verifying that the tachinid, Euclytia flava (Townsend), exploits methyl (E,Z,Z)-2,4,6-decatrienoate as a kairomone. We also report the unexpected finding that various isomers of methyl 2,4,6-decatrienoate attract Acrosternum hilare (Say), although this bug apparently does not produce methyl decatrienoates. Other stink bugs and tachinids native to North America were also attracted to methyl 2,4,6-decatrienoates. These data indicate there are Heteroptera in North America in addition to Thyanta spp. that probably use methyl 2,4,6-decatrienoates as pheromones. The evidence that some pentatomids exploit the pheromones of other true bugs as kairomones to find food or to congregate as a passive defense against tachinid parasitism is discussed.     

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.     

Highly moisture-proof polysilsesquioxane coating prepared via facile sol-gel process

A highly moisture-proof polysilsesquioxane coating was obtained from a new bis-silylated precursor, which was synthesized from 3-aminopropyltriethoxysilane (APTES) and m-xylylene diisocyanate (m-XDI) in tetrahydrofuran (THF) and verified by ¹H MAS NMR. For direct comparison purposes, an SiO₂ coating was also prepared by the Stöber method using tetraethoxysilane (TEOS) as the reactant. Interestingly, the coating obtained from the polysilsesquioxane sol exhibited a much higher moisture resistance capability than its counterpart, which was attributed to its more compact feature between nanoparticles as characterized by N₂ absorption experiment and transmission electron microscopy (TEM). Furthermore, its high transparency of about 92% showed potential for application in the protection of optical crystals.