Vinyl‐containing silicone resin as the crosslinking agent of heat‐curable silicone rubber

Heat‐curable silicone rubber (HCSR) was prepared by using vinyl‐containing silicone resin (VSR) as the crosslinking agent instead of polyvinylsilicone oil (C gum). Mechanical properties and crosslink density of the vulcanizates were measured. The results indicate that VSR is a good crosslinking agent for HCSR. The tensile strength, tearing strength, elongation at break, and hardness of the vulcanizate can reach 10.2 MPa, 29.1 kN/m, 720%, and 58 SHA, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3123–3127, 2002; DOI 10.1002/app.10054     

集成电路密封用高纯邻甲酚醛环氧树脂的制备

ECN树脂中的可水解氯含量是决定树脂质量的—个重要指标。本文研究了反应温度、ECH/OCN配比、反应时间和碱用量等因素的影响,取得了规律性的认识,并获得最佳配方,制备出高纯度的ECN树脂系列产品。     

Diterpene resin acids: Major active principles in tall oil against Variegated cutworm,Peridroma saucia (Lepidoptera: Noctuidae)

Tall oil, a by-product of the kraft process for pulping softwood, has been shown to have insecticidal properties. In the present study, the active principles in tall oil against the variegated cutworm,Peridroma saucia Hübner, were investigated. GC-MS analysis showed that abietic, dehydroabietic, and isopimaric acids were major resin acid components of crude tall oil and depitched tall oil. When crude tall oil samples of differing resin acid composition were incorporated into artificial diet at a concentration of 2.0% fresh weight, they suppressed larval growth by 45–60% compared to controls. This suppression was significantly (P0.05) correlated with the equivalent contents of abietic, dehydroabietic, isopimaric, and total resin acids. These results were also evident from a diet choice test, showing that the second-instar larvae obviously selected diets with low levels of resin acids when different diets were randomly arranged in a Petri dish. Bioassays with pure resin acids (abietic, dehydroabietic, and isopimaric acids) demonstrated that all individual chemicals have similar bioactivity against this insect. Comparison of the bioactivities of depitched tall oil and an equivalent mixture of pure resin acids in thePeridroma chronic growth bioassay indicated that pure resin acids and depitched tall oil share a common mode of action to this insect. This study confirms that resin acids are major active principles in tall oil against the variegated cutworm, but other chemicals likely also contribute to the bioactivity of tall oil.     

The chemical feeding ecology ofNeodiprion dubiosus schedl,N. rugifrons midd., andN. lecontei (Fitch) on jack pine (Pinus banksiana lamb.)

Two monophagous sawflies,Neodiprion dubiosus andN. rugifrons, actively avoid feeding on the current season's needles of jack pine,Pinus banksiana, while the polyphagousN. lecontei feeds indiscriminately on foliage of all age classes. Bioassay studies with needle extracts indicate thatN. dubiosus andN. rugifrons larval feeding preference is governed by a group of tricyclic diterpene resin acids. Resin acids commonly occur in needles of all ages; however, levopimaric, palustric, dehydroabietic, and neoabietic acids were at higher concentrations in the new needles.N. dubiosus was significantly deterred from feeding on 1-year-old foliage when treated with the pure resin acids, palustric and levopimaric, at 0.5 and 1.0 mg/ml MeOH.N. rugifrons larvae were deterred from feeding by pure dehydroabietic, neoabietic, and palustric acids at 1.0 mg/ml MeOH.     

Bulk and Interphase Effects in Aged Structural Joints

Although structural adhesives are becoming widespread in numerous applications, one important limitation at present is the long term behaviour of bonded assemblies under conditions of high humidity, especially at elevated temperatures. This study presents a comparison between bulk properties of a structural epoxy resin and its behaviour in a torsional joint consisting of a hollowed-out cylinder bonded to a plate—both substrates being in stainless steel. Exposure to ca. 100% relative humidity at 70°C leads to modification of the bulk properties of the polymer, notably reduction of its elastic modulus. Although this may explain some differences in behaviour of the torsional joint, premature failure is attributed to weaknesses in the interphase zone.

Auger Electron Spectroscopy (AES) has been employed to investigate both unbonded steel surfaces and fracture zones. Although prolonged exposure to water leads to a more extensive degree of (apparently) adhesive failure at the interface polymer/metal, AES has shown the presence of non-negligible quantities of carbon, attributed to residual polymer. Failure would seem to occur, at least partly, in a weak interphase of the polymer, near, but not at, the interface.

Various possible causes are evoked. For dry failure, residual polymer may be due to the topography of the metal surface and/or local modification of the adhesive during cure. In the case of aged joints, in addition there are potential effects due to swelling and differential stresses, secondary bond failure and molecular chain scission within the polymer, all provoked by the presence of water.     

国外聚甲醛生产技术现状与发展

综述了国外主要甲醛生产厂商的工艺技术，树脂生产技术的发展和品种开发情况。     

弱酸性条件起始合成MUF树脂工艺研究

为了开发一种新的在"弱酸—弱碱—弱酸—弱碱"条件下合成三聚氰胺-尿素-甲醛树脂(MUF)的工艺,对弱酸性条件下起始合成MUF工艺进行研究.探讨了在不同酸性阶段加入的三聚氰胺对脲醛树脂性能的影响,找出最佳的三聚氰胺改性脲醛树脂的合成工艺.在最佳工艺基础上,评价三聚氰胺用量对MUF树脂性能的影响以及对胶合板性能的影响,并对MUF树脂和普通脲醛树脂进行红外分析.结果证明:三聚氰胺在甲醛与尿素一次缩聚之后加入,对脲醛树脂改性效果最好,其胶合板湿剪切强度与甲醛释放量之间达到较好平衡,胶合板甲醛释放量为0.63mg/L,湿剪切强度为1.03MPa.红外谱图分析表明:三聚氰胺分子以亚甲基与脲醛树脂分子链相连并有可能嵌入脲醛树脂分子链中,形成一定数量的醚键,使三聚氰胺在脲醛树脂中真正起到骨架作用.     

树脂增强选择性激光烧结多孔金属件的研究

针对选择性激光烧结(SLS)间接方法成型的金属零件形坯,经脱脂和高温烧结后形成的零件存在大量孔隙和空洞,其致密度和强度都较低,不能满足实际应用要求的问题,采用改性耐高温环氧树脂浸渗零件烧结坯的方法,使多孔金属件致密化,并粘结内部金属网架,提高零件的机械性能.对浸渗烧结坯的拉伸强度的测试和扫描电镜(SEM)以及热失重(TGA)的分析结果表明,浸渗树脂后的烧结坯拉伸强度提高了约4倍;改性环氧树脂和金属网架粘结在一起,形成一个密实的网络结构,致密度大幅提高;零件可在200℃的温度下使用.该方法可以制造注塑模具和功能零件.     

Milled fibre reinforced epoxy resin — an engineering polymer composite

A milled fibre reinforced epoxy resin composite (MFRE) has been developed for low temperature use. It is resistant to fracture at temperatures down to at least 77 K in direct contact with liquefied gases. It can be used as an adhesive, a gap-filling mastic or a moulding compound for difficult cryogenic applications. The characteristics of the material and some applications are described.