茂金属线型低密度聚乙烯共混性能的研究

研究了茂金属线型低密度聚乙烯(mLLDPE)、mLLDPE/低密度聚乙烯(LDPE)共混物的热性能、流变性能及薄膜样品的基本性能。热性能结果表明,在mLLDPE中添加LDPE使样品的结晶温度明显下降;毛细管流变试验结果表明,LDPE的添加使mLLDPE的剪切敏感性显著提高,利于其加工;薄膜样品性能研究结果表明,mLLDPE使得LDPE的力学性能明显提高,光学性能明显改善。     

LLDPE-g-GMA增容LLDPE/PET共混物的研究

采用熔融挤出法制备了线型低密度聚乙烯接枝甲基丙烯酸缩水甘油酯(LLDPE-g-GMA)反应增容LLDPE/聚对苯二甲酸乙二醇酯(PET)共混物,用拉力试验机、差示扫描量热仪(DSC)和毛细管流变仪研究了LLDPE-g-GMA对共混物的力学性能、结晶性能及流变性能的影响。结果表明,LLDPE-g-GMA有效地提高了LLDPE/PET共混物的拉伸和冲击性能,同时也提高了LLDPE的结晶速率;流变性能测试证明LLDPE-g-GMA提高了共混物熔体的表现黏度,表明LLDPE-g-GMA有效地改善了不相容共混物两相之间的相容性。     

FFS袋用吹塑薄膜原料的性能研究

本工作研究了茂金属线型低密度聚乙烯(mLLDPE)/低密度聚乙烯(LDPE)共混物的流变性能及所制薄膜性能.结果表明:mLLDPE的加工性能较差,w(LDPE)为20％即可明显改善mLLDPE的加工性能,随着LDPE用量的增加,mLLDPE/LDPE共混物的加工性能改善更为明显;随着w(mLLDPE)的增加,用mLLD...     

含氟塑料加工流变剂在mLLDPE中的应用

研究了3种含氟塑料加工流变剂对茂金属线型低密度聚乙烯(mLLDPE)挤出性能的影响;比较了不同流变剂添加到mLLDPE中,在单、双螺杆挤出机中的挤出特性。结果表明:含氟塑料加工流变剂可以明显降低mLLDPE的挤出扭矩,消除挤出熔体破裂,改善薄膜制品的外观质量。     

共混型热塑性弹性体的研究—废胶粉／聚乙烯的静态硫化

采用废胶粉与线型低密度聚乙烯共混,通过静态硫化的方法制备热塑性弹性体。探讨了静态硫化工艺下的有关条件对共混体的物理机械性能、粘弹性能和挤出流变性能的影响。     

LDPE与mLLDPE共混改善mLLDPE的流变性能

通过毛细管流变实验,测定了茂金属催化体系生产的茂金属线型低密度聚乙烯(mLLDPE)/低密度聚乙烯(LDPE)共混物的流变特性.加入LDPE,mLLDPE的临界剪切速率增大;推迟了mLLDPE挤出过程中熔体破裂现象的产生;熔体强度提高,改善了吹膜过程中膜泡的稳定性.     

mLLDPE/LDPE共混物的流变性能

采用恒速双毛细管流变仪研究了茂金属线型低密度聚乙烯(mLLDPE)与低密度聚乙烯(LDPE)共混物的高速挤出流变行为.混入LDPE[w(LDPE)为10%～30%]后,共混物黏度比纯mLLDPE低,挤出胀大比和入口压力降比纯mLLDPE高; mLLDPE高速挤出时的压力振荡现象得以改善,熔体在毛细管内壁的应力集中效应减弱;共混不能改善mLLDPE的挤出畸变,与纯料相比,共混物的各种挤出畸变(包括鲨鱼皮畸变、黏-滑畸变、熔体破裂)加重,第二光滑挤出区消失.mLLDPE与LDPE共混相容性较好,共混物熔点位于2种纯料之间.     

增容剂PE-LD-g-MAH对低密度聚乙烯／木质素共混体系性能的影响

研究了低密度聚乙烯(PE-LD)与马来酸酐(MAH)的接枝共聚物PE-LD-g-MAH对低密度聚乙烯/木质素共混体系微观形态、流变行为、热性能和力学性能的影响。DSC-TC综合热分析表明,添加增容剂的共混体系的熔融温度降低,热稳定性提高;流变性能分析表明,共混体系的加工性能良好;扫描电子显微镜(SEM)分析显示,添加增容剂后木质素分散相尺寸明显减小,分散程度提高;PE-g-MAH可以有效提高低密度聚乙烯/木质素吹塑薄膜的力学性能,且当木质素、低密度聚乙烯和PE-LD-g-MAH质量比为25/75/10时,力学性能最优。     

再生胶/低密度聚乙烯热塑性弹性体的流变性能

测定了动态硫化再生胶(RR)/低密度聚乙烯(LDPE)共混物的流变曲线、挤出胀大值和粘度等,讨论了并用比、温度、交联剂用量、返炼次数等因素的影响,评价了共混物的加工性能。结果表明,共混物属假塑性流体,服从指数定律,流动指数n值为0.18—0.42。其表现粘度的绝对值低于按线性共混规则预测的粘度。挤出胀大值较小,可在一般塑料加工设备上进行挤出、模压和注射成型。     

应力集中效应对熔体挤出流动不稳定性的影响

用双毛细管流变仪研究了线型低密度聚乙烯、低密度聚乙烯及其共混物在较宽速率范围内的流变行为,通过分析流场中应力集中效应与不稳定流动的关系,从而控制不稳定流动现象。结果表明:挤出物在口模入口处的应力集中占总压力的15%以上时,一般导致毛细管人口压力降的无规振荡及挤出物的整体无规则波动和破裂;整条毛细管上的挤出压力发生振荡,挤出物外观发生光滑段和粗糙段交替出现的有规畸变。     

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.