Preparation and properties of the phenolic foams with controllable nanometer pore structure

Phenolic foam with nanometer pore structure and high strength was prepared by using a novel foaming method of phenol–formaldehyde novolac resin solution under pressure. Pore structure and the effects of pressure and resin concentration on it were investigated. Results showed that the mean pore size decreases from 800 to 30 nm with the increase of resin concentration from 0.08 to 0.36 g/mL. The pressure has a great effect on the pore structure and an optimal range (2.0–4.0 MPa) at which the pore size is small in level of nanometer and has a good distribution. The nanometer pore structure resulted in significant improvement of compressive strength and thermal insulation properties of phenolic foam. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

常温下酚醛树脂的可发性研究

研究了酚醛树脂常温发泡的最适宜条件。结果表明,甲醛与苯酚的摩尔比为1.8~2.0,树脂粘度在2~4 Pa.s(36℃),树脂固含量在78%~81%的甲阶酚醛树脂常温发泡效果最好;环境温度在17~25℃时,最适宜常温发泡;发泡剂用量与泡体性能的关系为:发泡剂用量增大,泡沫体表观密度和压缩强度降低,发泡剂用量14.0%后,泡沫体的密度变化不大。环境温度不同,固化剂的种类与比例也不同。     

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.     

Mechanical and morphological properties of cellular NR/SBR vulcanizates under thermal and weathering ageing

The effects of addition of two chemical blowing agents in cellular rubber blend of natural rubber (NR) and styrene‐butadiene rubber (SBR) at a fixed blend ratio of 1 : 1 on cure characteristics, and mechanical and morphological properties were invesigated. The chemical blowing agents used in this work were Oxybis (benzene sulfonyl) hydrazide (OBSH) and Azo dicarbonamide (ADC). Three different fillers, fly ash (FA) particles, precipitated silica, carbon black (CB) at their optimum concentrations of 40 phr were used, the FA and silica particles being chemically treated by bis‐(3‐triethoxysilylpropyl) tetrasulphide. The results suggested that the overall cure time decreased with OBSH and ADC contents. The OBSH was more effective in cure‐acceleration of the NR/SBR blend than the ADC. The NR/SBR vulcanized foams produced by OBSH and ADC agents had closed‐cell structures. The specific density and mechanical properties of the blend tended to decrease with increasing blowing agent content. The CB gave NR/SBR foams with smaller cell size, better cell dispersion, and higher mechanical properties than the precipitated silica and FA particles. The heat ageing and weathering resulted in an increase in tensile modulus and hardness, but lowered the tensile strength, ultimate elongation and tear strength. The elastic recovery for cellular NR/SBR vulcanizates with FA was superior to that with CB and silica, the elastic recovery of the blends decreasing with blowing agent content. Resilience property was improved by the presence of gas phases. The optimum concentration of OBSH and ADC to be used for NR/SBR vulcanizates was 4 phr. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

配方与工艺因素对EPDM模压发泡材料性能的影响

研究了发泡剂Ｈ在ＥＰＤＭ模压发泡材料中的发泡特性、硫化特性以及两之间的匹配关系对发泡效果的影响,同时还考察了配方和工艺因素对发泡体性能的影响。结果表明,为了获得较高的发泡率和良好的发泡质量,应选择硫化诱导期与发泡剂完全分解时间相当的硫化体系;一次硫化的硫化程度决定着胶料出模时的膨胀;二次硫化的发泡材料收缩率较小;高填充时粒径较大的填料对发泡效果的影响较小。     

天然橡胶发泡材料的压缩行为与能量吸收特性

用发泡剂N,N′-二亚硝基五次甲基四胺(简称发泡剂H)制备了天然橡胶(NR)发泡材料,研究了不同密度的NR发泡材料的压缩行为和能量吸收特性。结果表明,随着发泡剂H用量的增加,NR发泡材料的密度与硬度均降低;NR发泡材料的压缩应力-应变曲线有2个阶段:线性弹性阶段和致密化阶段;随着发泡材料密度的减小,线性弹性区变宽,相对弹性模量降低。在应力较小的时候,密度小的NR发泡材料吸收能量较多,在应力较高的时候,密度大的NR发泡材料吸收能量多。随着发泡材料密度的减小,其吸能效率最大值与理想参数最大值提高。     

Resol‐type phenolic resin from liquefied phenolated wood and its application to phenolic foam

A liquefied wood‐based resol resin was prepared with excellent yield by a reaction of liquefied wood and formaldehyde under alkaline conditions. The effects of various reaction parameters on the extent of the yield of the resol resin, unreacted phenol content, and viscosity were investigated. Milder resol resinification conditions were required as compared to those used in conventional methods. The liquefied wood‐based resol resin was successfully applied to produce phenolic foam using appropriate combinations of foaming agents. Diisopropyl ether with a relatively higher boiling temperature was suitable for the foaming of liquefied wood‐based resol resin. Hydrochloric acid and poly(ethylene ether) of sorbitan monopalmitate were used as a catalyst and a surfactant, respectively. The obtained foams showed satisfactory densities and compressive properties, comparable to those of foams obtained from conventional resol resin. Foams with low density were obtained by the blending of liquefied wood‐based resol resin and conventional resol resin. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 468–472, 2002; DOI 10.1002/app.10018     

Effect of organic acids on the mechanical properties of phenolic resin composites

The effect of salicylic acid and its derivatives on the properties of phenolic resin composites was evaluated. The composites were reinforced with aluminum oxide particles in both solid and hollow forms. Differential scanning calorimetry studies have shown that the reaction rate of phenolic resin was accelerated by salicylic acid, but was not affected by the other compounds. Salicylic acid also reduced the flexural strengths of the phenolic resin composites. The strength was decreased by more than 30% in comparison to that with no acid added. In contrast, two derivatives of this acid—sodium salicylate and 4‐hydroxybenzoic acid—have minimal impact on the flexural strengths of the composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 642–647, 2000     

Flammability properties and mechanical performance of epoxy modified phenolic foams

This work has been mainly focused on the development and optimization of the processing methodology to produce epoxy modified phenolic foams. This study analyzes the relation between the composition and the structure as well as the mechanical and flammability performance of epoxy‐phenolic (E‐P)‐based foams. Phenolic foams modified with different types and compositions of epoxy resin were successfully synthesized and characterized, showing uniform pore structure. Two epoxy resins were used for this approach. One is regular diglycidyl ether of bisphenol A (Epon 826) type and the other is a brominated bisphenol A (DER 542), which has halogen groups in the structure to improve the flammability properties of the resulting foams. Cone calorimeter (ASTM E 1354) was used to measure the heat release rate, the time to ignition, and other flammability properties of the E‐P foams with different types of epoxy resins, under well‐controlled combustion conditions. The mechanical performance of the system was studied and compared with competing foams, such us phenolic, epoxy, and polyurethanes, in aspects of compression, friability, and shear performances. Compared with conventional phenolic foams, E‐P foams exhibit significant improvement in mechanical performance, lower friability and similar resistance to flame. These results demonstrate the potential of the E‐P foam as a flame resistant and high performance core material for sandwich structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1399–1407, 2007     

不同发泡剂及工艺条件对BR／SBR／NR发泡材料相结构及尺寸稳定性的影响

分别采用一段和两段模压法制备了以顺丁橡胶（BR）／丁苯橡胶（SBR）／天然橡胶（NR）为基体的橡胶发泡材料,研究了三种化学发泡剂N,N＇-二甲基戊次甲基四胺（H）、4,4＇-氧代双（苯磺酰肼）（OBSH）以及H／OBSH（质量比1：1）复配对发泡及硫化特性的影-向,以及3种发泡剂和2种成型工艺对收缩率及相结构的影响。结果表明,发泡剂H对硫化性能影响最大,含发泡剂H的混炼胶在分解过程中释放的热量最多;加入3种发泡剂都具有一种较大的泡孔镶嵌在较小的泡孔丛中的泡孔形态;密度和线收缩率均随着时间的增加而增加,经H／OBSH复配的发泡剂更适合该体系成型,材料线收缩率均比单独使用H和OBSH小,两段模压法可以有效地提高发泡材料的尺寸稳定性,收缩率降低至3．88％,同时发泡剂使用率最多可提高31．67％。     

Preparation and properties of rigid polyimide foams derived from dianhydride and isocyanate

A series of rigid polyimide (PI) foams were synthesized via the reaction of a first solution with a second solution. The first solution was isocyanate‐terminated polyimide prepolymers; the second solution contained deionized water and surfactant. The effect of different water contents and isocyanate index on the structures and properties of rigid PI foams were investigated. The apparent density, hardness, compressive strength, and the 5% weight loss temperatures (T_5%) decreased with the increase of water content. With the increase of isocyanate index, the apparent density and the T_5% values decreased, whereas the glass transition temperatures (T_g) increased and the hardness, compressive strength first increased and then decreased. The rigid PI foams composed of closed‐cells were confirmed by scanning electron microscopy. The maximum compressive strength of rigid PI foams prepared was up to 1.31 MPa. Moreover, excellent thermal stability was presented with the T_5% values were all above 360°C and the residual weights of the foams (R_w) were more than 50% at 800°C. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

甲醛/苯酚配比对可发性甲阶酚醛树脂性能的影响研究

以苯酚、多聚甲醛、甲醛溶液为原料,NaOH为催化剂,采用逐步共聚的聚合工艺,制备可发性甲阶酚醛树脂,采用环保型发泡剂、匀泡剂、实验室自制复合酸固化剂制备阻燃保温酚醛泡沫材料。研究了甲醛/苯酚配比(物质的量之比即F/P)进行单因素分析,对可发性甲阶酚醛树脂的物理性能、有毒物质残余量、分子结构和活性的影响以及与树脂可发性的关系。结果表明,当F/P=2.0时,可发性甲阶酚醛树脂的粘度为2 680 mPa.s,游离甲醛含量为0.75%,游离苯酚含量为2.3%,羟甲基含量为34.83%,泡沫表观密度为0.050 7 g/cm3。     

酚醛树脂基多孔材料泡孔结构的控制及性能研究

通过添加不同种类的助表面活性剂的方法达到控制孔径的目的。研究表明添加助表面活性剂有助于减少发泡过程中液泡的消泡行为:随着聚醚二醇类助表面活性剂相对分子质量的增大,酚醛树脂基多孔材料的泡孔孔径均呈先减小后增大的趋势,其中聚丙二醇类助剂对多孔材料泡孔的调节性能最为优异。不同分子质量的聚醚二元醇类助表面活性剂也对酚醛树脂基多孔材料的压缩强度有着重要的影响。通过多次试验最终实现了对泡孔孔径的良好控制,内部孔结构分布均匀,孔径分布窄;同时还使得酚醛树脂基多孔材料的压缩性能得到提高。     

Dynamic mechanical properties of acrylic rubber blended with phenolic resin

The dynamic mechanical properties of blends of phenolic resin (PF) and acrylic rubber (ACM) were investigated. PF had good compatibility with ACM and played an important role in the damping of the ACM/PF blends. With the increase of PF content and molecular weight, the peak of loss factor (tan δ) of blends shifted to a higher temperature and became much wider, indicating the convenience to adjust the value of tan δ peak and the temperature range. Fourier Transform infrared spectroscopy detected that the intermolecular hydrogen bonding between the PF hydroxyl groups and the ACM carbonyl groups had made a great contribution to the improvement of damping. Compared with the organic small molecule used in our previous study, PF gifted the blends with equivalent damping performance and much better stability and a lower cost for the application of damping materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A study of rigid polyurethane foams: The effect of synthesized polyols and nanoporous graphene

Rigid polyurethane foams (RPUF) with nanoporous graphene (NPG) were synthesized and their properties, including density, mechanical, morphological, and thermal‐resistant properties were studied. In the current work, polyols of the RPUF formulation were synthesized and NPG content was varied from 0.1 to 0.5 wt %. Scanning electron microscopy (SEM) observation was used to observe the dispersion of NPG and cell size in the RPUF nanocomposites. Only 0.25 wt % of NPG improved compressive strength and modulus respectively by 10.7% and 66.5%. The TGA analysis confirmed that an increase in NPG loading slightly increase the degradation temperature of the samples. These results additionally indicated that NPG enhances the mechanical properties of the RPUF nanocomposites more effectively compared to other nanoparticles (clay, silica etc.). The superiority of NPG over other nanoparticles can be attributed to unique two‐dimensional geometrical morphology and a higher specific surface area. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45001.     

Synthesis and characterization of phenolic resol resin blended with silica sol and PVA

The phenolic resol resin (PF) has a wide application in industry, but its poor tensile ductility and insufficient mechanical strength have severely limited its application. To overcome these limitations, in this study, the mixtures of silica sol and poly(vinyl acohol) (PVA) were used to modify the PF. The structure, morphology, mechanical properties, and thermal stability of these hybrid materials were investigated by FTIR, SEM, tensile shear test (TSS), and TG. FTIR spectra indicated that the multiple reactive functional silanol group Si OH on the surface of SiO₂ particles reacted with PVA and PF. Compared with pure PF, the composite 50‐50‐3% exhibited the maximum shear strength which increased by 158%, whereas the elongation at break increased by 63%. Morphological results agreed well with the mechanical properties. The TG results suggested that the composite material 50‐50‐3% and pure PF had almost the same thermal stability because silica sol and PVA had opposite effects on the heat resistance of the hybrid materials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and mechanical properties of lightweight hybrid geopolymer foams reinforced with carbon nanotubes

A lightweight hybrid geopolymer foams reinforced with carbon nanotubes (CNTs) was exploited by adding the CNTs into geopolymeric matrix through hydrogen peroxide method. The synergistic effects of nanotubes and foaming agent on the phase evolution, microstructure, and mechanical properties were investigated. After introduction of nanotubes, the geopolymer foams reinforced with CNTs (CNTs/KGP) still showed amorphous structure. Porosity of the foams increased with the H₂O₂ content and decreased with the increase in CNTs content. The addition of CNTs (1-9 wt%) in foams refined the distribution of pore size from 523 to 352 μm. Compression strength of the CNTs/KGP samples elevated with the increasing content of CNTs, which was contributed to the crack propagation and bridging of CNTs in foams. The CNTs/KGP foams with considerable porosity show potential applications in adsorption, filtration, membrane supports, other industries, etc     

纳米炭纤维含量对其酚醛复合材料性能影响

采用纳米炭纤维对酚醛树脂改性,通过力学性能、烧蚀性能测试以及电镜和X-射线光电子能谱(XPS)分析研究了纳米炭纤维含量对炭/酚醛树脂基复合材料性能的影响。结果表明,当纳米炭纤维质量分数为15%时,其改性复合材料的层间剪切强度最大,达到31.17 MPa,氧乙炔线烧蚀率最小,为0.020 mm/s。分析了其改性机理,指出纳米炭纤维在树脂中的分散均匀程度是获得理想复合材料性能的关键。     

Biodegradable foams of poly(lactic acid)/starch. I. Extrusion condition and cellular size distribution

Biodegradable foams derived from poly(lactic acid) (PLA) and starch were prepared by extrution using water as a blowing agent and talc as nucleation agent. Foam cellular size and size distribution was significantly affected by extrusion conditions (i.e., extruder temperature profiles, die diameters, and screw speed), and material compositions, (i.e., water concentration, PLA/starch ratio, and nucleation agent concentration). Foam with a relatively fine cellular size and uniform cellular size distribution was obtained under optimized conditions of PLA/starch ratio at 40/60, 15% water, 195°C temperature before the die, 3‐mm die nozzle diameter, 200‐rpm screw speed, and 2% talc. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Properties of rigid polyurethane foams blown by HCFC 141B and distilled water

Rigid polyurethane foams (PUFs) were prepared from polymeric 4,4′‐diphenylmethane diisocyanate, polyester polyol, 1,4‐butane diol, silicone surfactant, hydrochlorofluorocarbon (HCFC) 141B, and distilled water. The properties and structure of the PUFs were investigated with differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and a universal testing machine. The density of the PUF blown by distilled water and/or HCFC 141B decreased from 175.7 to 28.2 kg/m³ with an increase of blowing agents. From the SEM results, the average cell size of the PUF blown by distilled water increased from 150 to 290 μm with the distilled water content. From the DSC results, the glass‐transition temperature (T_g) of the PUF blown by distilled water increased from 85.7 to 101.7°C with increasing distilled water content, whereas the T_g of the PUF blown by HCFC 141B remained unchanged with HCFC 141B content. The compressive strength and modulus of the PUF blown by a mixture of distilled water and HCFC 141B was increased from 0.13 to 0.25 MPa and from 3.00 to 7.23 MPa, respectively, with the distilled water content at the sample density of about 44.0 kg/m³. The increase of the compressive strength and modulus of the PUF at the same density was related to the increase of the T_g from 86.0 to 100.9°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 486–493, 2001