Enhanced mechanical properties,thermal stability of phenolic‐formaldehyde foam/silica nanocomposites via in situ polymerization

Phenolic foam (PF) displays excellent flame, smoke, and toxicity (FST) properties and good insulation properties. Nevertheless, the friability and inferior mechanical properties of PF have critically restricted its application in many fields. A series of phenolic foam/silica nanocomposites (MPF) with different silica contents were synthesized by in situ polymerization in this study. During the in situ polymerization process, the synthesis of phenolic resin/silica nanocomposites and formation of chemical bonding between the components were generated simultaneously. The reactive principle between silica nanoparticles and prepolymer was investigated using Fourier transform infrared spectroscopy (FTIR), and the results of FTIR indicated existence of the chemical reaction between them. Meanwhile, silica can act as “bridge” to form crosslinked network structure. The mechanical, thermal, and friability properties of MPF nanocomposites were characterized. Moreover, the results of microstructure of pure PF and MPFs indicated that the cell size distributions of MPFs are narrower, the cell distributions of MPFs are more uniform, and the cell wall thickness of MPFs is thicker, compared with pure PF. When the content of silica sol was 2 wt%, the compressive strength, compressive modulus, and tensile strength were increased by a factor of 47.37%, 38.55%, and 57.14% compared with that of pure PF, respectively. Furthermore, all MPF nanocomposites exhibited better thermal stability and lower pulverization ratio than that of pure PF. POLYM. ENG. SCI., 55:2783–2793, 2015. © 2015 Society of Plastics Engineers     

The toughening effect and mechanism of styrene‐butadiene rubber nanoparticles for novolac resin

In this article, phenolic nanocomposites were prepared using styrene–butadiene rubber (SBR) nanoparticles with an average particle size of about 60 nm as the toughening agent. The mechanical and thermal properties of phenolic nanocomposites and the toughening mechanism were studied thoroughly. The results showed that when adding 2.5 wt % SBR nanoparticles, the notched impact strength of phenolic nanocomposites reached the maximum value and was increased by 52%, without sacrificing the flexural performance. Meanwhile, SBR nanoparticles had no significant effect on the thermal decomposition temperature of phenolic nanocomposites. The glass‐transition temperature (T_g) of phenolic nanocomposites shifted to a lower temperature accompanying with the increasing T_g of loaded SBR, which showed there was a certain compatibility between SBR nanoparticles and phenol‐formaldehyde resin (PF). Furthermore, the analysis of Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy indicated that there existed a weak chemical interaction between SBR nanoparticles and the PF matrix. The certain compatibility and weak chemical interaction promoted the formation of a transition layer and improved the interfacial bonding, which might be important reasons for the great enhancement of the toughness for phenolic nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41533.     

蒙脱土改性酚醛树脂复合材料的制备与性能研究

为提高酚醛树脂(PF)的热稳定性,利用原位插层法制备了PF/蒙脱土(MMT)、PF/有机化蒙脱土(OMMT)纳米复合材料,并比较了PF、PF/OMMT或PF/MMT经高温热处理后的力学性能和导电性能.研究表明,与PF复合后,OMMT和MMT都形成了剥离型的片层结构.与PF/OMMT复合材料相比,PF/MMT的质量保持率...     

Nanocomposites from phenolic resin and various organo‐modified montmorillonites: Preparation and thermal stability

Phenolic resin (PF)/montmorillonite (MMT) nanocomposites have been successfully prepared using intercalative polymerization of resole‐type phenolic resins in montmorillonites modified by octadecylamine (C18), benzyldimethylhexadecylammonium chloride (B2MH), benzyltriethylammonium chloride (B3E), and benzyldimethylphenylammonium chloride (B2MP). X‐ray diffraction measurements and transmission electron microscope observations showed that clay platelets were partially exfoliated or intercalated after complete curing of the phenolic resins. The cured nanocomposites were named as modifier‐MP (MP means montmorillonite‐phenolic resin), for example, B3E‐MP. Thermogravimetric analysis showed that thermal decomposition temperatures (T_ds) of the cured nanocomposites B2MP‐MP (826 K), B3E‐MP (794 K), and B2MH‐MP (783 K) were much higher than those of C18‐MP (768 K) and cured phenolic resin (737 K). Therefore, thermal stability of the nanocomposites depends mainly on the chemical structure of the organic modifiers. B2MP‐MP possesses the highest T_d since B2MP contains both benzyl and phenyl groups, followed with B3E‐MP and B2MH‐MP whose modifiers contain only one benzyl group. This is attributable to favorable interaction between phenolic resin and organic modifiers containing benzene rings. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5336–5343, 2006     

液体NBR增韧酚醛泡沫研究

研究了液体丁腈橡胶(LNBR)对酚醛泡沫的增韧效果.通过红外光谱、万能试验机、热重分析仪等测试手段对改性后酚醛泡沫特征官能团的存在、力学性能、耐热性能分别进行表征分析.实验结果表明:共聚物存在LN-BR与PF(酚醛树脂) 的结构单元;当改性剂用量为0.6份(占树脂总质量)时,泡沫塑料的压缩强度由原来的0.105 MPa提高到0.336 MPa,证明LNBR对PF泡沫有显著的增韧作用;泡沫在802 ℃时失重44%,说明泡沫经改性后具有良好的耐热性能且未影响其热稳定性.     

碱处理对酚醛树脂/剑麻纤维复合材料性能的影响

用碱处理方法对剑麻纤维(SF)进行表面改性,再与酚醛树脂(PF)混合、塑炼、模压成型,制备了PF／SF复合材料,对其冲击强度、弯曲强度、耐磨性、吸水性及热性能进行测试,借助偏光显微镜和扫描电子显微镜观察、分析了复合材料的形态结构。结果表明,经碱处理的SF提高了PF／SF复合材料的综合性能,其原因与界面作用得到加强有关。     

Organomodification of montmorillonite and its effects on the properties of poly(butylene succinate) nanocomposites

The pristine sodium montmorillonite (MMT) was organically modified with hexadecyltrimethylammonium bromide (HTAB) at different contents. The organoclay was characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, energy dispersive X‐ray techniques, and thermogravimetric analysis. Then, poly(butylene succinate) (PBS) nanocomposites were prepared by melt‐mixing process using maleic anhydride‐grafted PBS (PBS‐g‐MA) as compatibilizer. It was found that the mechanical properties of PBS nanocomposites filled with organoclay were apparently higher than that of the nanocomposite filled with MMT. This is attributed to the better filler–matrix interactions between PBS and the organoclay and the better filler dispersion. This is verifiable through the XRD, scanning electron microscopy, and transmission electron microscopy. The addition of PBS‐g‐MA further improved the mechanical properties. It was also found that our laboratory synthesized organoclay modified with HTAB has provided a better reinforcing efficiency when compared with the commercial octadecylamine‐modified organoclay. Besides that the thermal properties of PBS nanocomposites were studied through differential scanning calorimetry. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

A novel polyurethane prepolymer as toughening agent: Preparation,characterization, and its influence on mechanical and flame retardant properties of phenolic foam

A novel phosphorus‐ and silicon‐containing polyurethane prepolymer (PSPUP) was synthesized by the chemical reaction of phenyl dichlorophosphate with hydroxy‐terminated polydimethylsiloxane (HTPDMS) and subsequently with toluene‐2,4‐diisocyanate. The structure of PSPUP was confirmed by Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance. Afterward, a series of phenolic foams (PF) with different loadings of PSPUP toughening agent were prepared. The apparent density and scanning electron microscopy results showed that the addition of PSPUP can increase the apparent density of phenolic foam. The compressive, impact and friability test results showed that the incorporation of PSPUP into PF dramatically improved the compressive strength, impact strength, and reduced the pulverization ratio, indicating the excellent toughening effect of PSPUP. The limiting oxygen index of PSPUP modified phenolic foams remained a high value and the UL‐94 results showed all samples can pass V0 rating, indicating the modified foams still had good flame retardance. The thermal properties of the foams were investigated by thermogravimetric analysis under air atmosphere. Moreover, the thermal degradation behaviors of the PF and PSPUP/PF were investigated by real‐time Fourier transform infrared spectra. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The effect of chain length of flexible diacid on morphology and mechanical property of modified phenolic resin

Adipic acid (DA4), suberic acid (DA6), sebacic acid (DA8), and dodecanedioic acid (DA10) were used to improve the brittleness of resol type phenolic resin (PF). Chemical reaction of PF with diacid was manifested by a shift of carbonyl stretching peak of diacid to a higher frequency in FT-IR spectra. The modified PF with diacid showed an optimum content (0.0014 mol) and an optimum chain length of diacid (n=6, i.e. DA6) to improve effectively its brittleness. The highly cured phenolic resins with DA4 and DA6 were found to have homogeneous morphologies, but those with DA8 and DA10 had phase-separated morphologies in scanning electron microscopy (SEM) images. The slightly cured PFs with DA4, DA8, and DA10 exhibited phase-separated morphologies, but that with DA6, a homogeneous morphology on SEM micrographs. Furthermore, the latter was confirmed by a proton spin-lattice relaxation time (T₁^H) measurement on solid-state ¹³C NMR spectra. It was found by X-ray diffraction and differential scanning calorimeter that the phase-separated part of modified phenolic resin was a crystalline phase of unreacted diacid. The highly improved toughness of modified PF with DA6 was attributed to the inherently homogeneous morphology with domain sizes around 20-30 nm scale found by the T₁^H measurement.     

Chemical Bonding between Phenolic Resins and Polyhedral Oligomeric Silsesquioxanes (POSS) in Inorganic–Organic Hybrid Nanocomposites

Three classes of inorganic–organic hybrid phenolic resin/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were synthesized. Multifunctional dichloromethylsilylethylheptaisobutyl-POSS (POSS-1), trisilanolheptaphenyl-POSS (POSS-2), and poly(phenylsilsesquioxane) uncured POSS (POSS-3) were employed. Nonfunctional POSS-4 (octaisobuty1-POSS) was blended into the uncured phenolic resin and cured under the same conditions used for the other three nanocomposite classes. Weight ratios of 99/1, 97/3, 95/5 and 90/10 were prepared for the POSS-1, 2 and 4 series and 99/1, 97/3 and 95/5 ratios for the POSS-3 nanocomposites. POSS-1 incorporation into this phenolic resin network increases T _g and broadens the tan peak (DMTA) range. T _g and E′ values at T>T _g both increase with higher POSS-1 content. In contrast, incorporating 5 wt% of POSS-2 into the phenolic resin network lowers T _g to 193 from 213°C for the neat phenolic resin. All values of E′ for POSS-2 composites were higher, than those of the phenolic control in both glassy and rubbery regions. The T _g values of the 1 and 10% POSS-2 systems were higher. Incorporating 10 wt% of POSS-1 or POSS-2 improved the heat distorsion temperature and moduli (E′=123 and 201 GPa at 265°C, respectively, versus 56 GPa for the pure phenolic resin). Increases in E′ for T>T _g and T<T _g were also observed for all POSS-3 nanocomposites. However, the E′ at T>T _g and the T _g values of the POSS-4 composites were lower than those of the control resin. Octaisobutyl POSS-4 cannot form chemical bonds to the resin and could be extracted from its composites with THF. POSS derivatives were not present in residues extracted by THF from the phenolic resins containing POSS-1, 2 or 3, because each of these derivatives were chemically bound within the phenolic resin. Subsequent heating cycles produce much larger increases in T _g and E′ values in the rubbery region for the POSS-1, 2 and 3 composites than for the neat phenolic resin or for the POSS-4 systems. An erratum to this article can be found at     

PU/PA纳米粒子改性酚醛树脂胶粘剂的研究

采用自乳化法制备PU/PA纳米粒子,并对酚醛树脂进行增韧改性.考查了丙烯酸酯单体种类、用量以及环氧树脂用量对改性酚醛树脂粘接性能的影响.借助TG、DSC、SEM和TEM对改性酚醛树脂体系的耐热性能、固化反应和微观形态进行了表征.结果表明,PU/PA纳米粒子的加入使酚醛树脂的常温和高温粘接强度显著增加,提高了酚醛树脂的固...     

SiO_2杂化环保型酚醛树脂的研究与制备

以正硅酸乙酯(TEOS)为前驱体,成功制备了玻璃纤维增强型改性PF(酚醛树脂)基复合材料的基体树脂——环保型纳米SiO2/PF。研究结果表明:当w(TEOS)=10%时,PF/SiO2复合材料的综合性能相对最好,其拉伸强度(758 MPa)、弯曲强度(945 MPa)和冲击强度(261 kJ/m2)分别比未改性体系提高了144%、53%和30%;改性PF体系的最大失重速率温度比纯PF体系提高了40～50℃,其热分解第二阶段的活化能由134.41 kJ/mol升至240.72 kJ/mol;玻璃纤维增强型PF/SiO2复合材料的线烧蚀率和质量烧蚀率分别比纯PF体系降低了22.5%和8.4%。     

剥离型酚醛树脂/蒙脱土纳米复合材料研究

用十六烷基三甲基溴化铵(CTAB)对蒙脱土进行了有机化处理,使蒙脱土由亲水性变成亲油性。采用XRD、FTIR及TEM研究了有机蒙脱土及其在酚醛树脂中的剥离行为,制备了酚醛树脂/蒙脱土纳米复合材料并测试了其层间剪切性能和烧蚀性能。实验结果表明,经CTAB处理的蒙脱土与酚醛树脂具有良好的相容性,且CTAB的含量较多时所制得的有机蒙脱土的结构较好,根据Bragg方程计算,CTAB用量超过蒙脱土量50%时,蒙脱土的片层间距由原来的1.48 nm增加到2.33 nm;有机蒙脱土用量小于5%时生成完全剥离型酚醛树脂/蒙脱土纳米复合材料;与碳布增强酚醛树脂复合材料相比,碳布增强酚醛树脂/蒙脱土纳米复合材料的力学性能和烧蚀性能均有一定的提高和改善,层间剪切强度随蒙脱土含量的增多而增大,蒙脱土用量为15%时,层间剪切强度提高了27.1%,线烧蚀率在用量为3%时降低了48.5%,质量烧蚀率变化不明显。     

酚醛树脂耐热改性研究进展

对酚醛树脂(PF)耐热性的改性研究进行了综述,改性后的PF耐热性得到了显著提高。耐热改性方法包括苯并噁嗪化合物改性PF、纳米材料改性PF、硼(B)改性PF、钼(Mo)改性PF、双马来酰亚胺(BMI)改性PF和有机硅改性PF等。     

13C CP/MAS NMR analysis of cure characteristics of phenol formaldehyde resin in the presence of wood composite preservatives and wood: effect of ammonium pentaborate and copper compounds

The effect of typical wood composite preservatives, ammonium pentaborate (APB), nanosize copper oxide and basic copper carbonate, on the cure characteristics of phenol formaldehyde (PF) resin in the presence of wood was evaluated by solid-state ¹³C nuclear magnetic resonance with cross-polarization and magic angle spinning (CP/MAS). With the introduction of APB the absorption intensity and peak area of PF resin at 129.5?ppm was reduced, and the carbons in methylene bridges shifted from 65.8 to 73.5?ppm, which were the result of hydrogen bond formation between ammonium in APB and oxygen of phenolic hydroxyl, as well as coordination bond between the boron in APB and oxygen in phenolic hydroxyl and/or unreacted hydroxymethyl. In addition, the peak area at 152.7?ppm increased with the addition of poplar powder for the overlap of cellulose, hemicellulose, and lignin chemical shifts with the active groups in PF resin. However, the connection status of critically active chemical groups of condensed polymer structure in cured PF resin such as the existence of phenolic ring, phenolic hydroxyl, methylene bridges, and hydroxymethyl linkage are unchanged. Combined with relative increase in the amount of carbon in methylene bridges from 2.42 to 2.56, drop in number of carbons of unreacted hydroxyls from 1.19 to 1.07, and the reported increase in physical and mechanical properties, the nanosize copper oxide improved the curing degree of PF. Furthermore, the similar analysis indicated that basic copper carbonate delayed the curing degree of PF.     

Synthesis of novel nanocomposites reinforced with 3D graphene/highly-dispersible nanodiamonds nano-hybrids

The phenolic resin-based ternary nanocomposites were prepared successfully by filling a three-dimensional (3D) graphene network structure embedded with highly-dispersible nanodiamonds into the resin matrix. Firstly, 3D graphene/nanodiamonds hydrogels were fabricated via self-assembly approach in a self-made dispersing medium, in which the volume ratio of ethanol absolute to deionized water was equal to 1:1. Then water molecules within the as-prepared hydrogels were replaced with resol by means of soaking and appropriate heat treatment. In-situ polymerization technique was employed subsequently to afford the ternary nanocomposites of phenolic resin/3D graphene/nanodiamonds, while the dispersion of nanodiamonds remained decent. The obtained nanocomposites exhibited high hardness and compressive strength, where the measured values were 31.1% and 24.7% higher than that of the composites procured from direct dispersion of nanodiamonds in phenolic resin matrix, respectively.     

PF/PDMS-OH流变性能对其泡沫材料泡孔结构的影响

分别将质量分数为10%,15%和20%的端羟基聚硅氧烷(PDMS–OH)通过机械共混的方法改性酚醛树脂(PF),进而采用化学发泡的方法制备PF/PDMS–OH泡沫复合材料。采用旋转式流变仪表征共混体系的稳态及动态流变性能,研究黏弹性对树脂发泡过程的影响。傅立叶变换红外光谱表征PDMS–OH与树脂在固化过程中的化学反应。扫描电镜表征不同共混体系下泡孔的结构与形态。结果表明,加入15%PDMS–OH的共混体系具有最利于发泡成型的黏弹性,且可与PF形成化学交联作用,对PF泡沫的泡孔形态影响显著。同时红外表征显示,PDMS–OH与PF在固化过程中发生化学交联,这种互穿交联网状结构为PF及泡沫提供了更多稳定的柔性链段。     

Silica sol modified phenolic resin and its effect on mechanical properties of Al2O3-SiC-C bricks

Phenolic resin(PF) is commonly used as a binder in Al₂O₃-SiC-C bricks; however, it reduces the strength and accelerates the damage after carbonisation under temperatures of 300–800 °C. To improve the medium-temperature mechanical properties of Al₂O₃-SiC-C bricks, the mechanism of silica sol modify PF was analyzed, and silica sol modified phenolic resin (PFS) was introduced into Al₂O₃-SiC-C bricks to explore the effect of PFS on the mechanical properties of Al₂O₃-SiC-C bricks. The results showed that the silanol groups (Si-OH) in the silica sol can react with the hydroxyl groups (-OH) in the PF to form a Si-O-C bond, which makes PFS have a higher residual carbon rate and greater thermal stability. Overall, the introduction of PFS enhances the mechanical properties of the Al₂O₃-SiC-C bricks. When the content of silica sol in PFS is 10 wt%, the cold modulus of rupture and compressive strengths increased by 62.6% and 22.1%, respectively.     

Viscoelastic and electrical properties of RGO reinforced phenol formaldehyde nanocomposites

Graphene oxide was reduced (RGO) by naturally abundant potato starch and incorporated in phenol formaldehyde resin (PF). The PF/RGO nanocomposites were successfully fabricated by the combination of solution processing and compression molding. Here, nanocomposites composed of 0.05 wt% to 1 wt% RGO were prepared. The incorporation of RGO into the PF matrix was significantly affecting the dynamic mechanical characteristics of the nanocomposites such as storage and loss modulus and tan δ. The degree of entanglement (N), effectiveness of filler (β_f ), reinforcement efficiency factor (r), cross-link density (v_c ), and adhesion factor (A) were evaluated from the modulus values. Besides, the phase behavior of the nanocomposites was analyzed with help of Cole–Cole plot. The electrical properties of the nanocomposites have been studied concerning change in filler loading and frequency. The dielectric constant (ε′), dielectric loss (ε″) and conductivity were increased with increase in wt% of filler for the entire range of frequencies (20 Hz to 30 MHz) and the results showed that the electrical conductivity of the nanocomposites can be explained by percolation theory. The Maxwell-Garnet model was employed to calculate the theoretical dielectric constant of PF/RGO nanocomposites.     

环氧及酚醛树脂增韧改性氰酸酯树脂研究

用环氧树脂(EP)及酚醛树脂(PF)对氰酸酯树脂(CE)进行增韧改性,对改性CE的凝胶时间和DSC曲线进行研究并确定了改性CE的固化工艺。红外光谱分析表明改性CE固化时形成了柔韧性结构。研究了改性CE的力学性能、热性能、电性能及微观形态,发现EP的加入可增加CE的柔韧性,PF的加入可使CE的热稳定性损失减小。当CE/EP/PF的质量比为70/15/15时改性CE的弯曲强度和冲击强度分别从改性前的123.6 MPa、5.2 kJ/m2提高到134.5 MPa、16.7 kJ/m2,耐热性及电性能改变不大。