酚醛树脂基三元共聚物的制备及其热解过程分析

以端羧基丁腈橡胶（CTBN）和环氧树脂（CYD）的预聚物为热不稳定聚合物,酚醛树脂（PF）作为炭前驱体聚合物,采用化学共聚方法制备出酚醛树脂基三元共聚物（PF＋CYD＋CTBN）体系。通过红外光谱分析证实CYD中的部分环氧基与CTBN中的羧基反应生成酯键,而剩余的环氧基与酚醛树脂中的酚羟基反应生成醚键,CTBN-CYD预聚物以接枝或嵌段的形式接入到酚醛树脂的固化体系中。通过对不同热处理温度下的三元共聚物进行红外、热重分析及对热解产物的孔径分析表明,三元共聚物中的酯键在450℃时发生断裂,CTBN链段率先从三元共聚物体系中热解选出,并在所得多孔炭材料中形成了孔径主要分布在1～2nm左右的微孔。     

酚醛树脂/碳化硼/聚硼氮烷复合物的固化行为及其热解性能

酚醛树脂作为一种热固性树脂基体具有广泛的应用。为了满足其作为高性能树脂基体在苛刻条件（耐高温和抗氧化）下的使用,进一步提高酚醛树脂的耐热性能并兼顾其工艺性能显得尤为重要。采用含有无机元素的耐热性聚合物（聚硼氮烷）和碳化硼纳米粒子协同改性酚醛树脂的方法,能够克服单独加入碳化硼导致的酚醛树脂固化温度升高的问题。固化动力学分析表明,加入聚硼氮烷的酚醛树脂改性体系,其固化转化率显著高于同温度下酚醛树脂或碳化硼改性酚醛树脂的转化率。同时,聚硼氮烷和碳化硼协同改性酚醛树脂固化物在高温阶段（800～1000℃）的热解稳定性较改性前有大幅度的提高。通过红外光谱分析了不同热解程度下酚醛树脂及其改性物的结构,进一步阐述了聚硼氮烷和碳化硼协同作用对酚醛树脂改性体系固化行为和热解过程的影响机制。上述采用耐热性活性聚合物和碳化硼陶瓷粒子协同改性热固性树脂的方法,有望在高性能复合材料树脂基体中得到运用。     

硼硅氧烷树脂热解行为及动力学研究

采用热重分析法和裂解质谱红外联用技术考察了硼硅氧烷树脂的热解反应行为,将Malek法与Coats-Redfern积分法结合,对实验数据进行动力学解析,得到了硼硅氧烷树脂热解反应的动力学参数。结果表明硼硅氧烷树脂的热解反应分为三段:在250℃以下的低温区,小分子气体放出的同时伴有熔融等发生;在250℃~650℃的高温区,以脱硅甲基反应为主;在650℃~800℃为稳定阶段。通过分析热解过程中产生的气体和固体成分及含量,得出硼硅氧烷树脂热解可能发生的反应。硼硅氧烷树脂的热解反应可以用2/3级动力学方程来描述;随着升温速率的增加,活化能和指前因子均先增加后减小。     

Effect of impregnated phenolic resin on the properties of Si–SiC ceramic matrix composites fabricated by SLS-RMI

Selective laser sintering (SLS) combined with reaction melt infiltration was used to fabricate Si–SiC ceramic matrix composites, and the effects of different concentrations of phenolic resin (PF) on the properties of the SLS green body and carbonized and final Si–SiC samples were investigated. The results showed that the impregnation with PF can increase the bulk density, reduce the porosity of the samples at all stages, and improve the mechanical properties of the reactive bonded samples. The degree of densification and mechanical properties of the sample gradually enhanced with an increase in PF concentration. The main phases of the Si–SiC composites were free Si, α-SiC, β-SiC, plus an extremely small amount of Al–Si alloy, and the SiC and the Si phase contents increased and decreased, respectively, as the concentration of PF increased when measured using Rietveld refinement and image analysis software. The macroscopic properties of the samples improved greatly after precursor infiltration pyrolysis (PIP) treatment with 66.7%vol PF-ethanol solution twice. According to the crystal nucleation-growth theory, it was inferred that the infiltrated PF could provide a certain amount of pyrolytic carbon in the carbonized specimen. During the reaction bonded process, the carbon formed by carbonization pyrolysis first dissolves into the molten Si and reaches saturation. With the further dissolution of carbon, [C] and [Si] in the liquid phase contact each other to form β-SiC nuclei, the nuclei that precipitate at the pore wall position and gradually form a continuous interfacial layer of β-SiC. The β-SiC layer prevents the liquid Si from direct contact with C inside the prefabricated body, therefore, further reactants diffuse through the layer. Finally, the fine crystalline β-SiC grains were fabricated inside the specimen.     

Synthesis of monodisperse carbonaceous beads with ordered mesoporous structure

Ordered mesoporous carbonaceous (OMC) beads were synthesized by a combination of the syringe injection (SI) method and the evaporation-induced self-assembly (EISA) method. In the SI method, a phenol-formaldehyde (PF) resin solution used as a carbon source is injected into an oil phase, in which the PF resin solution is insoluble, by carefully controlling the viscosity of the PF resin solution. Ordered mesoporous structure was formed based on the EISA method by adjusting the temperature for polymerization of the PF resin. Consequently, monodisperse OMC beads were obtained.     

木质素改性高耐磨酚醛树脂的制备及性能研究

利用酶解木质素(EHL)和腰果壳油(CNSL)改性热塑性酚醛树脂,讨论了不同酚醛摩尔比、CNSL用量和1,4-丁二醇对改性树脂性能的影响。研究表明,木质素及腰果壳油双改性的酚醛树脂耐热性能优于腰果壳油改性的酚醛树脂。改性后酚醛树脂基摩擦材料具有良好的摩擦磨损性能,更适合作为摩擦材料的树脂基体。     

Nanoporous phloroglucinol-formaldehyde carbon aerogels for electrochemical use

Phloroglucinol-Formaldehyde (PF) organic aerogels were prepared from alcoholic sol-gel polycondensation of phloroglucinol with formaldehyde using KOH as base catalyst and followed by supercritical drying with carbon dioxide. Subsequent pyrolysis of PF organic aerogel under He flow produced carbon aerogels. Textural properties of PF organic and carbon aerogels were obtained by nitrogen adsorption-desorption, and their specific capacitances were measured by cyclic voltammetry. The resultant PF carbon aerogels were mostly mesoporous material with high surface area. The nanoporous structure and electrochemical behavior of PF carbon aerogels could be controlled by the molar ratio of phloroglucinol to catalyst (P/C) and carbonization conditions. PF carbon aerogels exhibited the highest surface area in excess of 1,200 m²/g and specific capacitance up to 250 F/g in comparison to other carbons.     

Curing kinetics of nano cupric oxide (CuO)-modified PF resin as wood adhesive: effect of surfactant

The effect of nano cupric oxide (CuO) in combination with surfactants on the curing kinetics of phenol-formaldehyde (PF) resin, as well as the bonding strength of plywood prepared using the modified resin was investigated in this study using dynamic and isothermal differential scanning calorimetry. The result showed that the incorporation of nano CuO along with alkane surfactant made in the laboratory clearly reduced the apparent activation energy of the PF resin and improved the addition and condensation reactions of the PF resin. Inclusion of the surfactant had the further effect of compensating the influence of diffusion control caused by nano CuO alone. The shear strength of plywood suggested that the addition of nano CuO (1%) alone or in combination with alkane surfactant (0.55%) or sodium lignosulfonate (0.55%) in the PF resin mixture was sufficient to meet the requirement of wood-based composites manufacturing.     

改性热塑性酚醛树脂的制备及残炭率的影响因素

在苯酚和甲醛原料中加入一定量的SiO2粉体改性剂,可成功制备出改性热塑性PF(酚醛树脂)。以热塑性PF的残炭率为考核指标,采用单因素试验法优选出制备硅改性PF的最优方案。结果表明,当m(苯酚)∶m(甲醛)=(1.30～1.36)∶1时,硅改性PF的残炭率较高且变化不大;当w(SiO2粉体)=0.9%、反应温度为90℃和反应时间为3 h时,改性热塑性PF的残炭率相对较高;此时,Si元素已均匀分布在PF基体树脂上,掺杂的SiO2有助于提高热塑性PF的耐热性能。     

碳纳米管改性酚醛树脂固化动力学研究

采用非等温示差法分析了碳纳米管改性酚醛固化反应过程,运用Kissinger和Ozawa法对其进行了动力学研究,得到了反应活化能。结果表明:碳纳米管改性PF树脂的固化反应为吸热反应;相应的峰始温度(Ti)为106.4℃,峰顶温度(Tp)为118.2℃,峰终温度(Tf)为157.6℃,固化体系的表观活化能Ea为111.094 kJ/mol,频率因子为9.56×10-5/s,反应级数为0.965,并得到了固化反应动力学方程。