结构胶粘接厚度对建筑幕墙抗形变能力影响分析

隐框式建筑幕墙是当前建筑幕墙设计的主要形式,其结构胶粘接厚度对于幕墙安全性尤为关键,因此分析了结构胶粘接厚度对建筑幕墙抗形变能力影响。根据胶粘剂力学性能中的拉伸弹性模量与剪切模量进行结构胶粘接厚度计算,确定建筑幕墙最佳结构胶粘接厚度,并分析建筑幕墙结构胶变形性能,获取了结构胶拉伸变形同剪切变形的相关性。根据结构胶相关拉伸剪切强度测试标准,利用电子万能测试机进行结构胶粘接厚度对结构胶变形能力的影响测试和结构胶变形对建筑幕墙抗变形能力的影响测试。测试结果显示当结构胶粘接厚度达到最优值后,随着粘接厚度逐渐增加结构胶粘剂拉伸与剪切强度整体表现为逐渐降低状态,而粘接厚度下降则易导致胶粘剂粘接强度下降;结构胶受外力加载条件下产生的变形是建筑幕墙结构变形位移量的20%左右。     

底涂晾置时间和次数对聚氨酯胶剪切强度的影响

以电泳钢板和钢化玻璃板为基材,经活化和底涂处理后用聚氨酯胶黏剂粘接,考察底涂晾置时间和底涂次数对于聚氨酯胶黏剂粘接强度的影响。结果表明,晾置时间低于5 h是合适的,剪切强度变化不明显。底涂次数对于剪切强度影响较大,涂刷1次时,随着底涂晾置时间的增加,剪切强度变化不明显;涂刷2次以上,剪切强度下降明显。     

室温固化双组分环氧树脂结构胶的研究

以环氧树脂(EP)和二乙烯三胺基甘油正丁基醚(593)固化剂为基体,以自制底胶和预处理过的石英粉为填料,制取室温固化双组分EP结构胶。研究了不同配方、粘接工艺对EP结构胶粘接性能的影响。实验结果表明,该EP结构胶在室温条件下具有优异的粘接性能,用于粘接45#钢/钢时,其室温拉伸剪切强度为27.4MPa;该EP结构胶浇铸体的拉伸强度为44.6MPa,拉伸模量为6.82GPa;一种新的自制底胶和经KH-560偶联剂处理过的石英粉填料是拉伸剪切强度显著提高的关键因素。     

胶接工艺对粘接强度的影响

介绍了胶接件的表面处理以及胶黏剂的配制、涂胶、晾置、黏合和固化等因素对粘接强度的影响。表面处理介绍了常用方法,重点描述表面粗糙度与粘接强度的关系。胶黏剂的配制介绍了温度平衡、组分调整与预混、混合调配和配制顺序。涂胶介绍了涂胶方法和注意事项。晾置介绍了不同种类胶黏剂的晾置时间。黏合介绍了粘合方法和时机。固化介绍了固化方式、方法和固化条件三要素,重点描述固化温度、时间和压力与粘接强度的关系。     

风电叶片用双组分聚氨酯胶粘剂的研制

考查了自制缓凝剂用量对混合后胶粘剂黏度和适用期的影响,以及多元醇对胶粘剂强度的影响,添加填料及其他助剂制备了双纽分聚氨酯结构胶。该胶混合后适用期达65min,本体拉伸强度迭39．5MPa,拉伸剪切强度达17．5MPa．且胶片韧性好,应用于风力发电行业的叶片粘接效果好,应用前号广阔。     

材料线膨胀系数对拉伸剪切性能的影响

为了研究被粘接材料的线膨胀系数对胶接件拉伸剪切性能的影响,用改性环氧树脂(EP)胶粘剂粘接不同材料,并对该胶接件进行拉伸剪切强度试验和温度影响试验。研究结果表明,被粘接材料的线膨胀系数不同会导致胶层在热冷变化过程中受到内应力作用而破坏,同时热空气进入胶层会导致胶层氧化变色,致使胶粘剂界面结合强度和胶粘剂自身强度降低;两种被粘接材料的线膨胀系数差异越大,经热冷变化后胶接件的拉伸剪切性能越低;在相同条件下,热冷变化温差越大,胶接件的拉伸剪切性能越低。     

胶粘剂剪切模量的测试方法研究

参考ASTM D 3983—98标准的相关测试方法,设计出粘接夹具和剪切测试夹具,对3种环氧胶粘剂的剪切强度和剪切模量进行了测试试验,分析了拉伸剪切载荷-形变关系、测试了温度(-55℃、24℃和125℃)以及胶层厚度对剪切强度和剪切模量的影响。结果表明:本测试方法可以实现在不同温度环境条件下对胶粘剂剪切强度与剪切模量的测试,结果稳定可靠;胶层厚度对剪切强度和剪切模量测试结果影响十分显著,推荐胶接长度为15 mm左右,胶层厚度控制在0.30 mm左右。     

环氧结构胶固化工艺对胶接接头性能的影响

以XH-11环氧结构胶为研究对象,采用正交试验法进行多因素试验设计,研究了固化温度、固化时间、晾置时间、表面粗糙度等因素对金属胶接接头拉伸剪切强度和冲击强度的影响,得出了最佳固化条件,并通过数据统计分析得到影响因素为自变量的力学性能回归方程,为胶接接头的强度预测提供参考.     

长适用期丙烯酸酯结构胶黏剂的研究

室温固化丙烯酸酯胶黏剂由于适用期短,操作时间不够的问题限制了其在粘接较大面积材料中的应用。制备了一种适用期为40min的丙烯酸酯结构胶黏剂,并对其进行了含磷丙烯酸酯对适用期影响的研究,探讨了长适用期丙烯酸酯结构胶黏剂的耐温性能、耐热老化、耐水老化性能,采用热重分析对胶黏剂进行了分析。结果表明:含磷丙烯酸酯含量为3%时,胶黏剂适用期可达40min;制备的丙烯酸酯胶黏剂耐温性能较好,80℃和100℃剪切强度分别为11.75MPa、6.49MPa;丙烯酸酯胶黏剂经100℃老化8000h后,80℃和100℃剪切强度上升分别为14.04MPa、8.54MPa,室温和60℃剪切强度下降分别为14.76MPa、14.21MPa;在耐水老化8000h后,60℃和80℃剪切强度变化很小分别为17.62MPa、11.52MPa。     

激光表面处理提高铝合金胶接接头强度的研究

粘接作为重要的汽车轻量化连接技术之一,胶接接头的强度和性能是我们关注的重点,胶接接头的强度和性能完全取决于胶粘剂接触的表面类型,因此在粘接之前对基材表面进行一定处理是粘接工艺中最重要的环节之一。金属的表面处理包括溶剂擦拭、机械打磨、化学清洗和酸蚀。激光表面处理是一种新型绿色环保的表面处理工艺,它可以高速有效的清洁材料表面附着物,并且改变材料表面微观结构及材料表面自由能及浸润性。从而提高粘接接头十字拉伸强度、单搭接拉伸剪切强度和接头耐水性能。通过激光处理,所有接头的破坏形式由界面破坏转为内聚破坏。对铝合金环氧结构胶2098G胶接接头而言,十字拉伸强度、剪切强度和水浴剪切强度,激光处理后比溶剂擦拭分别提高了17.8%,133.8%,88.1%。对铝合金聚氨酯结构胶TS6015胶接接头而言,十字拉伸强度、剪切强度和水浴剪切强度,激光处理后比溶剂擦拭分别提高了698%,225%,223%。激光表面处理有效的使铝合金胶接接头的强度达到胶的本体强度的94%~100%,是铝合金粘接的有效表面处理方法。     

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.     

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.     

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.