天然橡胶生物合成分子调控机制的研究进展

天然橡胶(NR)生物合成的精确调控机制解析是尚未攻克的重要理论问题。综述产胶植物基因组和NR生物合成过程相关基因的调控机制,重点阐述小橡胶粒子蛋白质基因在产胶植物的橡胶合成过程中作用的研究进展,为NR生物合成分子机制以及分子育种研究提供理论参考。指出NR生物合成调控机制的研究与收获技术和提取工艺技术相结合,有助于解析产胶植物的NR合成机制和提高其产胶量。     

天然橡胶的相对分子质量及其分布

采用凝胶渗透色谱研究了天然橡胶(NR)、只含磷脂的NR脱蛋白胶(DPNR)及既不含磷脂又不含蛋白质的NR脱蛋白脱磷脂胶(TE-DPNR)的相对分子质量及其分布。结果表明,NR中存在通过磷脂形成的支化链分子。加入极性溶剂会降低DPNR的相对分子质量,说明DPNR中的大部分支化点可能是由磷脂之间形成的氢键。DPNR胶乳中小粒径橡胶粒子中的分子基本为线型分子,而大粒径橡胶粒子中的分子为支化分子。     

低蛋白天然胶乳的性能与应用

天然橡胶(NR)具有优越的工艺操作性能及物理力学性能,从通用性能来讲,目前尚无其它的材料能替代。NR是由天然生物合成,其主要成分为:橡胶烃、水、非胶物质,其中非胶物质主要由蛋白质、类脂物、丙酮溶物、水溶物、无机盐等组成。一般新鲜胶乳中蛋白质含量占胶乳重的1%～2%,浓缩天然胶乳(NRL)中所含蛋白质占胶乳总重的1.5%～3.5%。由于NRL含有相当数量的蛋白质,蛋白质的吸水性导致了NRL制品的吸湿性、导电性、生热性,不利于制造绝缘制品。蛋白质含量过高,还易使制品发霉。NRL在胶乳行业中占有特殊地位,NRL已广泛应用于医疗及工业领域,…     

机械力化学改性胶粉及其与天然橡胶并用胶性能的研究

分析胶粉在开炼机上的机械力化学改性,研究改性胶粉/天然橡胶(NR)并用胶的性能。结果表明:在开炼机机械力化学作用下,胶粉胶料的交联网络断裂,橡胶分子链断键而形成自由基,实现胶粉改性;随着胶粉在开炼机上薄通次数的增加,胶粉胶料的橡胶分子链断键而形成的自由基浓度增大,改性胶粉与NR的界面相容性和界面结合性逐渐提升,胶粉在NR中的分散更均匀;改性胶粉胶料与NR形成共交联网络,改性胶粉/NR并用胶的拉伸强度和拉断伸长率显著提高。     

利用非橡胶烃成分鉴别NR与IR

NR以其优良的综合性能广泛应用于橡胶工业 ,随着橡胶工业的发展 ,其产量早已满足不了需要。IR是SR中综合性能最好的一类 ,其化学组成和立体结构与NR相似 ,硫化胶的物理性能与NR相当 ,而加工性能优于NR ,在很多橡胶制品中可全部或部分替代NR。NR和IR的结构单元都是异戊二烯 ,常用的橡胶鉴定方法 (如橡胶烃成分和性能鉴定 )难以将二者进行区分。本文介绍了几种根据NR中非橡胶成分鉴别NR和IR的方法。NR由天然胶乳制造而成 ,胶乳中所含非橡胶成分有一部分留在了固体的NR中。NR中的非橡胶成分一般包括蛋白质 (质量分数 0 0 2 0 0 …     

反式-1,4-聚异戊二烯橡胶的并用研究进展

<正>反式-1,4-聚异戊二烯橡胶(简称TPI)又称人工合成杜仲橡胶、古塔波胶或巴拉塔胶,是顺式聚异戊二烯橡胶的同分异构体,与天然橡胶(NR)具有完全相同的化学组成,但其分子链为反式构型。TPI与天然橡胶(NR)、丁苯橡胶(SBR)、顺丁橡胶(BR)等通用橡胶有很好的共混、共硫化性能,当TPI的质量分数为20%~40%时,不仅能保持或提高原胶的各项力     

烷基酚二硫化物SL9210对天然橡胶和天然橡胶/顺丁橡胶并用胶耐老化性能的影响

研究具有新型取代基结构的烷基酚二硫化物SL9210(简称SL9210)对天然橡胶(NR)和NR/顺丁橡胶并用胶耐老化性能的影响。结果表明:SL9210可作为高效硫黄给予体,与橡胶分子交联形成单硫键或双硫键,具有较好的抗硫化返原性能;与未采用烷基酚二硫化物的硫化胶相比,采用烷基酚二硫化物尤其是SL9210的硫化胶耐老化性能提高。     

蒲公英橡胶——一种亟需大力研究的NR

介绍蒲公英橡胶草的特点和培育方法、蒲公英橡胶草橡胶的结构与性能、提取方法以及蒲公英橡胶草的研究进展等.蒲公英橡胶草是一种当年产胶的草本橡胶植物,根部橡胶质量分数(以干草根计)为0.2以上,且品质优良.由于传统NR来源的限制以及石油资源的紧缺,蒲公英橡胶草橡胶有着巨大的应用前景.蒲公英橡胶草生长周期短,产胶量较大,橡胶质地轻、抗过敏,目前在培育上也有一定进展.蒲公英橡胶草中胶乳提取的方法有混合法和流动法,胶乳、固体胶混合提取的方法有湿磨法、干磨法和溶剂法.提高蒲公英橡胶草的含胶量、改进其橡胶提取方法是今后的主要研究方向.     

用热胀离解探讨炭黑/白炭黑与天然橡胶的作用力

将炭黑DZ 13、N 330和N 660及改性的白炭黑TB2和通用白炭黑填充的天然橡胶(NR)在二甲苯中于不同温度下进行离解,外推其离解温度,并通过傅里叶变换红外光谱和热重分析等手段判断填料与橡胶分子链之间的界面结合强度。结果发现,利用溶剂溶胀法外推出的炭黑DZ 13/NR、炭黑N 330/NR和炭黑N 660/NR的结合胶完全离解温度分别为360,334,220℃,表明炭黑DZ 13与NR的化学结合力较强。虽然白炭黑/NR结合胶的离解曲线与炭黑结合胶有所不同,但其外推的完全离解温度均比炭黑低,说明改性白炭黑随着温度的升高,其表面的改性剂在溶剂中被逐渐溶解,从而造成了橡胶分子链的脱离。     

大蒜汁作为橡胶再生剂的研究

研究以大蒜汁作为植物橡胶再生剂的再生机理及其对再生NR硫化胶性能的影响。植物橡胶再生剂可以使硫化胶的交联键断裂，同时限制氧化作用对橡胶分子主链的损害。试验结果表明，当再生剂用量为6份时，再生硫化胶的拉伸强度和拉断伸长率最大，邵尔A型硬度、溶胀度及有效链的平均相对分子质量最小，交联密度最大。     

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.