提高酚醛基纤维耐热性的表面处理方法

用硼酸,磷酸和硫酸配制得一种纤维表面浸渍处理液,然后将用热塑性酚醛树脂为原料经熔融纺丝制得的固化纤维用浸渍处理溶液高温处理,可以明显提高纤维的残炭率和耐热性.采用电子扫描显微镜、热分析仪、纤维强力仪和金相显微镜对处理后纤维进行了测试和表征.结果表明:这种处理工艺可以明显提高酚醛纤维在无氧气氛下的耐热性和残碳率.经过处理后,纤维在无氧状态下的残碳率比没处理前大大提高,从600～1000℃,处理后纤维的残碳率比原未处理纤维的残碳率一直保持高7%～10%左右,但是对纤维的直径、拉伸强度和结构无影响或影响甚小.     

高残碳酚醛烧蚀材料的研究

对高残碳酚醛进行了表征,运用正交实验方法研究了CBFTC/HCYPR复合材料的层压成型工艺.结果表明:高残碳酚醛具有较高的残碳率、较窄的分子量分布,适合做烧蚀复合材料基体;当预固化温度为140℃、固化温度为175℃、固化压力为5MPa、固化时间为7min/mm时,CBFTC/HCYPR复合材料的弯曲性能和烧蚀性能最好.     

热处理时间对PAN碳纤维性能影响的研究

聚丙烯腈(PAN)碳纤维由有机纤维经过高温处理得到,其结构和性能与热处理时间密切相关。采用固体核磁共振碳谱仪、热失重分析仪、X射线衍射仪和力学性能分析等研究了热处理时间对预氧纤维结构、碳纤维结构和性能的影响。结果表明:预氧化时间的延长使环化、脱氢和氧化反应形成的—C═N、C═C、C═CH、C═O含量增加,使预氧纤维的稳定性增强,形成的碳纤维微晶尺寸较小、层间距较大,碳纤维拉伸强度和拉伸模量较大,但体密度较低;随着碳化时间的延长,纤维的热稳定性呈现先下降后增强的趋势,碳纤维的微晶尺寸增大,层间距减小,碳纤维的体密度、拉伸强度和拉伸模量增加。     

用固化反应法制备酚醛纤维

将热塑性酚醛树脂熔融纺丝,再在盐酸和甲醛的混合液中进行固化交联反应制备出酚醛纤维,研究纤维的物理和化学变化.结果表明,采用高浓度甲醛能提高交联基团供应体的浓度,也提高了对初生纤维的溶胀作用;盐酸不仅是交联反应的催化剂,也能使酚羟基之间、酚羟基与亚甲基之间发生热缩聚反应.对固化反应过程参数的研究表明,在甲醛浓度18.5%,酸浓度12%和升温速率15.4℃/h时,在固化反应过程中纤维内部、外层的交联反应速度与总的交联反应时间达到最佳匹配,可制备出拉伸强度为260 MPa高度均匀交联的酚醛纤维,在800℃炭化收率达到63%.     

混酸处理对预氧化聚丙烯腈纤维结构和性能的影响

以化学改性的原理,用盐酸和硫酸的混合酸对预氧化聚丙烯腈纤维进行了处理,用红外光谱、DSC、元素分析、裂解色谱-质谱和强度的测定等手段对处理结果进行了研究。分析表明,经混酸处理后在纤维中引进的羧基能够使纤维在随后的高温处理中引发二次环化反应,使得聚合物分子链间的交联度增加、耐热性提高及高温裂解得到抑制,致使最终炭纤维的强度提高了16.3%。     

中空酚醛纤维的熔纺研究及性能表征

以提纯后的热塑性酚醛树脂为原料,用圆弧狭缝式喷丝板进行熔融纺丝,经过固化液固化和热处理一系列工艺,制备出了中空酚醛纤维.结果表明:树脂提纯后可纺性能大大提高,只有在适当的熔纺条件下圆弧狭缝式喷丝板才能纺出中空结构的酚醛纤维,改变的熔纺参数,还可以纺出C形和实心圆形另外两种截面的酚醛纤维.SEM,IR,TG-DSC和强度测试等分析结果表明,所制备的中空酚醛纤维和普通实心酚醛纤维一样,具有较高的固化交联度、分解温度和残炭率,同时具有更好的力学性能.     

稳态强磁场下预氧化PAN纤维取向性能的研究

预氧化PAN纤维(POF)的取向结构是决定最终炭纤维性能的重要因素,利用PPMS产生强度为8,12,16T的稳态强磁场,将处于240,260,280,300℃等不同预氧化阶段PAN纤维分别进行10,30,50min处理。研究发现,POF中存在氰基和碳氮杂环两种磁性单元,PAN纤维的取向由于磁性单元的运动而发生改变。POF的总体取向度随磁场强度的增大和处理时间的延长而增加,晶体取向度随磁场强度的增大呈现先增加后减小的趋势。同时,磁场作用还能促进纤维非晶态向晶态的转变,提高纤维的结晶尺寸和结晶度。     

酚醛纤维交联程度对炭纤维结构和性能的影响

通过控制固化条件获得具有不同交联程度的酚醛纤维,考察其交联程度对经900℃炭化后所获炭纤维结构和性能的影响．结果表明,具有高度交联化酚醛纤维,交联程度低的分子相对较少,热解过程中低分子逸出量少,形成的孔道也相对较少,参与交联缩合的分子相对较多,有利于六方品系炭的形成．由此导致适当温度下炭化所获炭纤维炭化收率高、孔容小、机械拉伸强度和电导率相应较高．     

中空度对中空酚醛纤维性能的影响

利用酚醛树脂纤维在固化中的皮芯效应,控制表皮固化层的交联厚度,用溶剂溶出未交联的芯部,制备出一系列不同中空度的中空酚醛纤维。分别采用SEM、电子纤维强力仪、TG-DSC、自制隔热效果测试仪对不同中空度中空酚醛纤维的截面形貌、力学性能、高温性能和隔热性能进行了考察。结果表明:随着中空酚醛纤维中空度的增加,中空纤维的壁厚变薄,纤维的表观力学性能、热分解温度和残炭率都逐渐降低,实际抗拉强度变化不大,隔热性能大幅提高。     

硼改性酚醛泡沫复合材料的制备与性能研究

为改善酚醛泡沫的耐高温性能,实验将适量的B2O3引入酚醛泡沫,经模压成型、固化后,制备出硼改性酚醛泡沫复合材料;研究了硼改性酚醛泡沫复合材料的微观结构,以及不同的硼含量对酚醛泡沫的压缩性能、耐高温性能的影响。结果表明,硼改性酚醛泡沫的压缩断裂特征为假塑性断裂模式;引入适量的B2O3,可改善树脂基体相的韧性,提高酚醛泡沫复合材料的压缩强度,当B2O3含量为质量分数4%时,酚醛泡沫的压缩强度最大,为10.14 MPa,比纯酚醛泡沫提高了5.18%。硼改性有利于酚醛泡沫的高温稳定性,酚醛泡沫的热分解温度和残碳率均随硼含量的增加而有所提高;当B2O3含量为质量分数7%时,酚醛泡沫的耐高温性能最优,其失重10%时的热分解温度为447℃,比纯酚醛泡沫提高了76.68%;其800℃下的残碳率为66.37%,较纯酚醛泡沫高出16.05%。     

热塑性酚醛树脂对碳纤维环氧树脂基复合材料性能的影响

利用热重分析(TGA)、扫描电镜(SEM)和三点短梁法对添加不同含量的热塑性酚醛树脂(PF)的复合材料体系改性效果进行了研究,考察了不同含量的酚醛树脂对固化体系力学性能及热性能的影响.结果表明,随着酚醛树脂含量的增加,碳纤维环氧树脂基复合材料(CFRP)的弯曲强度和弯曲弹性模量呈递减趋势;层间剪切强度(ILSS)呈现先增加后减小的趋势,当酚醛树脂的含量为20%时,层间剪切强度达到111.31MPa,提高约7%;热稳定性较其它含量时高,复合材料体系的综合性能最好.     

Effect of the molecular structure of phenolic novolac precursor resins on the properties of phenolic fibers

A series of phenolic resins with different weight-average molecular weights (M_w) and ortho/para (O/P) ratios were prepared. The effect of the phenolic precursor resin structure on the structure and properties of the resulting phenolic fibers was investigated. The structures of the resins and fibers were characterized by nuclear magnetic resonance spectroscopy, gel permeation chromatography, melt rheometry, dynamic mechanical analysis, and thermogravimetric analysis. The results show that the O/P ratio, unsubstituted ortho and para carbon ratio (O_u/P_u), and M_w of the phenolic resins play an important role in determining the properties of the phenolic fibers. The tensile strength of the phenolic fibers increases with increasing novolac precursor O_u/P_u ratios, corresponding to low O/P ratios, at comparable resin M_w values. Also, the tensile strength of the phenolic fibers increases with increasing novolac M_w values at comparable O/P ratios. Phenolic fibers with high tensile strength and good flame resistance characteristics were generated from a phenolic precursor resin, possessing a high weight-average molecular weight and a low O/P value.     

石墨/酚醛树脂复合材料双极板的制备与性能

双极板是质子交换膜燃料电池的重要组成部分,石墨与聚合物的复合材料双极板是目前研究的重要方向。采用模压热固化二步法,以酚醛树脂为粘结剂、天然鳞片石墨为导电骨料、炭黑为添加剂制备了质子交换膜燃料电池用复合材料双极板。系统研究了不同种类石墨对石墨/酚醛树脂复合材料电性能和抗弯强度的影响。结果表明:以天然鳞片石墨为导电原料时,所制备的石墨/酚醛树脂双极板的性能最好;添加导电炭黑能有效提高石墨/酚醛树脂复合材料的电导率;在复合材料制备中加入4wt%的碳纤维,碳纤维-石墨/酚醛树脂复合材料的抗弯强度提高了29%;碳纤维表面液相氧化处理能有效提高纤维与基体间的结合强度,随着处理时间的延长与处理温度的升高,碳纤维-石墨/酚醛树脂复合材料的电导率和抗弯强度都有很大程度的提高;最终固化温度主要影响酚醛树脂的交联程度,随着最终固化温度的升高,酚醛树脂的交联程度增加,电导率增大,但抗弯强度有一定程度减小。     

A study on crosslinking of phenolic fibers

Phenolic fibers (PFs) were prepared by the crosslinking of heat-meltable spun filaments derived from melt-spinning of a novolac resin with well-controlled molecular weight of 2000 g mol⁻¹, in a combined solution of formaldehyde and hydrochloric acid. The reaction of the heat-meltable spun filaments with the solution of formaldehyde and hydrochloric acid was investigated. IR spectrometer, scanning electron microscopy (SEM), and electrical tensile strength apparatus were employed to characterize the change of functional groups, the distribution of crosslinkage in the interior and surface, and the tensile strength of PFs, respectively. The influence of different parameters during the curing reaction, such as formaldehyde and hydrochloric acid concentration, the effect of heating rate on the properties and structure of the cured fibers were examined. It was found that with a formaldehyde concentration of 18.5%, a hydrochloric acid concentration of 12% and a heating rate of 15.4 °C h⁻¹ homogeneous highly crosslinked phenolic fibers with the maximum tensile strength of 260 MPa were obtained.     

动态硫化法制备尼龙6/马来酸酐接枝三元乙丙橡胶高韧合金

采用酚醛树脂(PF)、硫磺(S)与过氧化二异丙苯(DCP)作交联剂,研究了马来酸酐接枝三元乙丙橡胶(EPDM-gMAH)的动态硫化对增韧尼龙6(PA6)性能的影响。结果表明,采用PF硫化体系且硫化剂用量为EPDM-g-MAH的1.5%,PA6与EPDM-g-MAH质量比为80/20的合金的综合性能较好,其拉伸强度与缺口冲击强度较未硫化PA6/EPDMg-MAH(80/20)合金分别提高69.5%与128.8%,主要是由于动态硫化提高了PA6与EPDM-g-MAH的相容性。动态硫化还提高了PA6/EPDM-g-MAH合金的热稳定性、PA6的结晶温度和结晶速率。     

Microstructures and mechanical properties of pyrocarbons produced from phenolic resin with added Ni(NO3)(2)北大核心CSCD

A refractory containing graphite is commonly used in the metallurgical industry in locations subject to severe thermal shock because of the high thermal conductivity and good thermal shock resistance of graphite. However, a refractory that uses phenolic resin as the carbon precursor is brittle, and to improve its strength and toughness, Ni(NO3)(2) is added to the resin to catalyze the in-situ formation of carbon nanofibers/nanotubes. The microstructure and mechanical properties of the Ni( NO3)(2) -modified phenolic resin carbons, were characterized by XRD, SEM, TEM and mechanical tests. Results indicate that carbon nanofibers/nanotubes (2% by volume) were formed within the pyrocarbons as a result of the nickel catalyst and these are interconnected to form a network structure. The nanocarbon fibers/tubes significantly improve the bend strength, elastic modulus, tensile strength and fracture toughness of the pyrocarbons and their fracture energies are increased accordingly.     

Optimum dispersion conditions and interfacial modification of carbon fiber and CNT–phenolic composites by atmospheric pressure plasma treatment

Electric resistance measurements were used to determine the optimal dispersion conditions for carbon nanotubes (CNTs) in phenolic resins. Plasma treatment is frequently used to modify carbon fiber surfaces to improve adhesion of the fibers to matrices. Such treatment might also influence carbon fiber tensile strength. In order to determine the effect of atmospheric pressure plasma treatment on carbon fiber tensile strength and interfacial bonding strength, change in tensile strength of the fiber was studied at different gage lengths before and after the plasma treatment. The wettability of carbon fibers was improved significantly after only 10 s of plasma treatment. Such plasma treatment resulted in a decrease in the advancing contact angle from 65° to 28°. Surface energies of carbon fiber and CNT–phenolic composites were measured using the Wilhelmy plate technique, indicating that the work of adhesion between plasma treated carbon fibers and CNT–phenolic composites was higher than it before plasma modification. The interfacial shear strength (IFSS) and apparent modulus were also increased by plasma treatment of the carbon fibers.     

Molecular dynamics study of the interfacial strength between carbon fiber and phenolic resin

The interfacial strength between carbon fiber and phenolic resin is studied using molecular dynamics simulations to demonstrate that carbon fiber-reinforced carbon matrix composites (C/C composites) have improved tensile strength. Simulations are performed using two carbon fiber models, one of which has only carbon atoms and the other has carbon atoms and some fluorinated carbon groups. The carbon fiber models are regarded as two-layer graphite, and the phenolic resin model is treated as cross-linked structures. All force field parameters are based on the Dreiding force field. The tensile stress and interfacial fracture energy are calculated for the estimation of the interfacial strength. The results show that the model including the fluorinated carbon groups has lower interfacial strength than the model having only carbon atoms, up to a certain coating ratio of fluorinated carbon groups. Similarly, within the limits of the coating ratio, the interfacial fracture energy of the fluorinated carbon fiber model is lower than that of carbon fiber model having only carbon atoms.     

纳米铜改性酚醛树脂及其应用性能

采用新发明的原位生成法成功地制备了摩擦材料用纳米铜改性酚醛树脂。利用XRD和TEM对所制备的树脂进行了表征。结果显示,纳米铜的粒径为10~40 nm,呈近球形。进行了TGA、冲击试验和摩擦试验。结果表明,纳米铜改性酚醛树脂的耐热性有较大提高,与纯酚醛树脂相比,其初始分解温度和半分解温度可分别提高31℃和46℃;纳米铜改性酚醛树脂基摩擦材料的韧性和摩擦学性能有明显改善,与纯酚醛树脂基摩擦材料相比,冲击强度提高44%,热衰退率和磨损率分别降低约50%和2/3。建立了酚醛树脂/纳米铜复合材料的界面模型,并探讨了纳米铜改善酚醛树脂及摩擦材料性能的机理。      

改性碳纳米管处理碳纤维的效果表征

采用浓硫酸/浓硝酸氧化处理多壁碳纳米管(MWCNTs),再将氧化后的碳纳米管与硅烷偶联剂(KH560)进行接枝,制备了硅烷偶联剂表面化学修饰的MWCNTs。在此基础上,将改性前后的碳纳米管分散在环氧树脂体系中,涂覆处理碳纤维。研究处理前后碳纤维力学性能和界面性能的变化。通过红外光谱(FTIR)和透射电镜(TEM)分析,表明KH560已成功接枝到多壁碳纳米管上;通过分散性实验证明了改性后的碳纳米管分散性提高;对处理后的碳纤维进行力学性能测试,并用扫描电镜(SEM)观察分析断面形态变化,结果表明,当碳纳米管的含量为0.5%时,改性碳纳米管处理的碳纤维拉伸强度和拉伸模量分别提高23.83%和7.11%,界面性能增强。