Differences in physico-mechanical behaviors of resol(e) and novolac type phenolic resin based composite bipolar plate for proton exchange membrane (PEM) fuel cell

Composite bipolar plates for Proton Exchange Membrane Fuel Cell (PEMFC) are prepared by compression molding technique using polymer as binder and graphite as electric filler material with some other reinforcements. Study on the effect of resole and novolac type phenolic resin on the properties of composite bipolar plate, such as bulk density, porosity, bulk conductivity, hardness, flexural strength, etc. shows that both of the resin shows different physico-mechanical properties. Moreover, single cell performance analysis also shows variation for resole and novolac based composites. A novel concept of triple continuous structure to provide graphite polymer blends with high electrical conductivity, high shore hardness, high flexural strength, less porosity and low density has been proposed and study on the effect of different types of phenolic resin on the properties and performance of bipolar plate reveals that novolac type powdered phenolic resin gives better mechanical properties than resole type phenolic resin. However, resole type phenolic resin compound has slightly higher electrical conductivity due to more number of polar -OH group presents on its cured form. But due to the less porosity and higher mechanical strength, bipolar plates with novolac type phenolic resin gives better performance in I-V analysis than bipolar plates with resole type phenolic resin.     

改性酚醛树脂的研究进展

综述了橡胶、合成树脂和天然植物油对酚醛树脂的增韧改性和有机硅、胺类、硼钼无机化合物、无机纳米粒子等耐热改性方面的主要研究,并简要介绍了酚醛树脂合成工艺的改性进展。选择耐热性工程树脂如聚砜、聚苯醚、双马来酰亚胺与酚醛树脂通过原位共混形成互穿聚合物网络结构,或采用纳米复合技术制备改性酚醛树脂,可获得高耐热和强韧性的酚醛树脂复合材料,使其在高新技术领域发挥更大的作用。     

Nanoclay and long-fiber-reinforced composites based on epoxy and phenolic resins

In this study, high-performance thermoset polymer composites are synthesized by using both long fibers and nanoclays. Epoxy and phenolic resins, the two most important thermoset polymers, are used as the polymer matrix. The hydrophobic epoxy resin is mixed with surface modified nanoclay, while the hydrophilic phenolic resin is mixed with unmodified raw nanoclay to form nanocomposites. Long carbon fibers are also added into the nanocomposites to produce hybrid composites. Mechanical and thermal properties of synthesized composites are compared with both long-fiber-reinforced composites and polymer- layered silicate composites. The optimal conditions of sample preparation and processing are also investigated to achieve the best properties of the hybrid composites. It is found that mechanical and thermal properties of epoxy and phenolic nanocomposites can be substantially improved. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

New method for interfacial evaluation of carbon fiber/thermosetting composites by wetting and electrical resistance measurements

Interfacial properties were evaluated for carbon fiber (CF) with different thermosetting polymeric matrices in composites. CF tow was wet by phenolic or epoxies, and the interfacial adhesion evaluated by electrical resistance changes. The interfaces between two types of CF tows with phenolic resin and three types of epoxies were investigated. The change in electrical resistance was found to depend on the wettability of CF by the polymer resins, with the more obvious resistance changes being associated with better wettability. The electrical resistance changes were measured 20?min after the polymer resin was dropped on the CF tow. To confirm the relationship between changes in resistance and interfacial properties, both interfacial shear stress (IFSS) and interlaminar shear stress (ILSS) were also measured. The results of these mechanical measurements were generally consistent with the electrical resistance measurements in that the materials with high electrical resistance also exhibited high IFSS and ILSS.     

Mechanical performance of resol type phenolic resin/layered silicate nanocomposites

Clay addition has been shown to affect polymer resins positively in terms of several physical and chemical properties, including mechanical performance, high temperature endurance and durability. These increases are limited only to relatively low concentrations of reinforcement phase, but at these low concentrations polymer/layered silicate nanocomposites (P/LS NC) have shown to exhibit higher mechanical performance than fiber reinforced polymer composites. This is among the several reasons that make P/LS NC's one of the most widely studied class of materials today. In this study, the mechanical performance of resol type phenolic resin/layered silicate nanocomposite specimens was examined by carrying out 3‐point bending, Charpy impact and fracture toughness tests to couple the observations, microstructural analysis is done through X‐ray diffraction and scanning electron microscopy. The effects of especially three factors; cure method, clay amount, and clay modification were investigated. It was concluded that highest mechanical performance was obtained by the acid curing of the phenolic resin with very low amounts (e.g., 0.5%) of either very hydrophobic or very hydrophilic Na‐montmorillonite clay additions. Improvements as high as 7% in flexural strength, 11% in flexural strain at break, 16% in Charpy impact strength, and 66% in fracture toughness values were obtained. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

改性苯并噁嗪树脂的研究进展

苯并噁嗪树脂是一种新型的酚醛树脂,具有良好热稳定性、力学性能、低吸水性、固化时无小分子释放等优良特性。然而,苯并噁嗪树脂仍存在耐热性及韧性不足的问题。综述了近几年来用热固性树脂、热塑性树脂以及其他新型改性剂对苯并噁嗪树脂改性的研究进展,并展望了其应用前景。     

Ultrasonic properties of phenolic and poly(phenylquinoxaline) polymers

Longitudinal and shear sound speeds and absorptions were measured for a phenolic polymer and a poly(phenylquinoxaline) (PPQ) polymer, from room temperature to 70°C, at a frequency of 1.8 MHz. Phenolic specimens were cured at a maximum temperature of either 120°C, 135°C, or 180°C. The specimens varied in density from 1.217 to 1.229 g/cm³ with no correlation to curing temperature. Longitudinal sound speed in phenolic was found to depend only on density (or specific volume) and not directly on temperature or degree of crosslinking. Sound speeds and elastic constants, in phenolic, are not sensitive to cure temperature but sound a bsorption is: the higher the cure temperature, the lower the absorption. Hence ultrasonic absorption is a possible way to monitor or measure degree of crosslinking. Sound absorption is higher in phenolic than in PPQ, contrary to what is expected for a polymer with high sound speed. This high absorption indicates an additional mechanism of absorption in phenolic not found in PPQ. Also, the sound absorption increases with temperature in phenolic but is constant in PPQ. The Gruneisen parameter of phenolic appears high and that of PPQ about right when compared with other polymers. All of these results suggest there is a molecular transition in phenolic, but not PPQ. Further evidence for a transition comes from specific volume measurements as a function of temperature. The exact temperature of the transition and the molecular process responsible cannot, however, be determined from the measurements reported here.     

Mechanical, thermal and ablative properties of interply continuous/spun hybrid carbon composites

The mechanical and thermal properties of interply hybrid carbon fiber (continuous and spun fabric)/phenolic composite materials have been studied. Hybrid carbon/phenolic composites (hybrid CP) with continuous carbon fabric of high tensile, flexural strength and spun carbon fabric of better interlaminar shear strength and lower thermal conductivity are investigated in terms of mechanical properties as well as thermal properties.Through hybridization, tensile strength and modulus of spun type carbon fabric reinforced phenolic composites (spun CP) increased by approximately 28% and 20%, respectively. Hybrid CP also exhibits better interlaminar shear strength than continuous carbon fabric/phenolic composites (continuous CP).The in-plane thermal conductivity of hybrid CP is 4-8% lower than that of continuous CP. As continuous filament type carbon fiber volume fraction increases, the transversal thermal conductivity of hybrid CP decreases.The erosion rate and insulation index were examined using torch test. Spun CP has a higher insulation index than continuous CP and hybrid CP over the entire temperature range. Hybrid CP with higher content of spun fabric exhibits higher insulation index as well as lower erosion rate.     

非对称型受阻酚类抗氧剂的研究新进展

非对称型受阻酚类抗氧剂以其特殊的结构显著提高了聚合物的抗氧化效率,新型非对称型受阻酚的探索与开发代表了当今世界聚合物抗氧化领域的一大发展趋势。简述了非对称型受阻酚类抗氧剂的结构特性及抗氧化机理,重点介绍了几种典型的半受阻酚类抗氧剂的合成及应用,指出了非对称型受阻酚类抗氧剂的研究方向。     

改性聚乙烯醇缩丁醛胶粘剂的研制

以聚乙烯醇缩丁醛(PVB)为主料，乙醇和乙酸乙酯为溶剂，酚醛树脂为改性树脂，环氧树脂为增粘树脂，自制多元胺类固化剂，采用共混改性法，配制出无色透明、对环境友好、常温、接触压力固化的双组分胶粘剂。对于PVB的结构、PVB与改性树脂的配比、以及溶剂的选择对胶粘剂性能的影响进行了研究。     

Laccase‐mediated grafting of polyphenols onto cationized cotton fibers to impart UV protection and antioxidant activities

Enzyme‐mediated in situ functionalization of cotton fibers was studied using laccase. Caffeic acid and morin were used as reactive phenolic substrates for laccase and further employed to the modification of fiber surfaces. Laccase‐mediated oxidation and polymerization reactions of caffeic acid were monitored by ultraviolet–visible spectroscopy. During the wetting process, initial cationization of fiber surfaces using poly(diallyldimethylammonium chloride) followed by enzymatic treatment with phenolic substrates resulted ineffective polymer grafting evidenced by high color stability. Changes of fiber surface properties by polymer grafting, such as morphology and hydrophilicity/hydrophobicity, were tested using scanning electron microscopy and gravimetric absorption tests. An acceptable level of color resistance to washing stress was obtained on caffeic acid treated samples, and a high level of rubbing resistance was obtained on samples treated with both caffeic acid and morin. Regarding the ultraviolet protection test, the cationized and enzymatically functionalized samples showed a very good protection grade (ultraviolet protection factor = 25). Finally, the antioxidant activity test of the modified fibers presented an improvement for radical scavenging potential due to the phenolic compounds incorporated to cotton fibers by laccase‐mediated catalysis. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45801.     

Preparation of crosslinked β‐cyclodextrin polymer beads and their application as a sorbent for removal of phenol from wastewater

BACKGROUND: Phenols are commonly encountered in aqueous effluents from various manufacturing processes such as oil refineries, coke plants, and phenolic resin plants, and are toxic substances that should be removed from the aquatic environment. This paper reports on the preparation of beaded crosslinked β‐CyD polymers, and the removal of phenol by the β‐CyD adsorbent from raw industrial wastewater discarded from phenolic resin processing. RESULTS: Crosslinked β‐CyD prepolymer was synthesized by treatment of β‐CyD with hexamethylene diisocyanate (HDI) at a molar ratio of 1:8. The suspension of the resulting powdery prepolymer in aqueous sodium alginate was added dropwise into an aqueous calcium chloride solution to precipitate the spherical β‐CyD prepolymer gels. The spherical prepolymer gel was lyophilized and re‐crosslinked with HDI to provide the β‐CyD polymer beads. The physical properties of the beads were as follows: average diameter: 3.4 mm; average compressive strength: 2.17 MPa; porosity: 47.0%; specific surface area: 3.48 m² g^?1. The removal of phenol from raw industrial phenolic wastewater with the β‐CyD polymer beads was carried out in either a shaker or an upflow column at 25 °C. After seven episodes of accumulated adsorption, the initial phenol concentration of 89000 ppm decreased to as low as 350 ppm in the shaker and 490 ppm in the upflow column. CONCLUSION: Adsorbent [β‐CyD/HDI(1/8)]/HDI polymer beads having a good regular shape and high mechanical stability were newly prepared by a stepwise crosslinking method. The results of sorption experiments show that the beads exhibit high sorption capacities for phenolics in raw industrial wastewater. Copyright © 2008 Society of Chemical Industry     

Water transport in an epoxy–phenolic coating

Thermoset coatings commonly rely on high cross-linking density to provide enhanced barrier properties. Hence it is surprising that for the industrial epoxy–phenolic network investigated, equilibrium moisture uptake is found to increase with respect to cure time, i.e., with greater cross-linking. Molecular interactions between absorbed water and the resin are characterised using infrared spectroscopy, and water uptake is correlated to network polymer features such as polarity and free volume.     

Physical,Chemical and Mechanical Properties of Hibiscus sabdariffa Fiber/Polymer Composite

Tensile, compressive, flexural and wear resistance properties of Hibiscus sabdariffa fiber-reinforced phenolic (Resorcinol Formaldehyde) resin matrix-based composites were evaluated to assess the possibility of using these fibers as a new eco-friendly material in engineering applications. Polymer composite samples were fabricated by a compression-molding technique developed in our laboratory. The effect of fiber dimension on mechanical properties was evaluated. The interfacial bonding between Hibiscus sabdariffa fiber and the polymer matrix has been found to affect the mechanical properties of the resorcinol formaldehyde resin matrix. It has been observed that particle-reinforced polymer composites exhibit better mechanical properties as compared to short and long fiber-reinforced polymeric composites. These composites were further subjected to an evaluation of morphological, thermal, physical (swelling and moisture absorption) and chemical properties.     

松香改性高分子材料的研究和应用进展

综述了国内外松香改性制备高分子材料的研究现状,分别介绍了松香改性酚醛树脂、聚氨酯、聚丙烯酸、醇酸树脂等高分子材料的制备和应用现状,比较了一步法和两步法制备松香改性酚醛树脂的优缺点,详述了半连续种子乳液聚合法/细乳液聚合法制备松香改性聚丙烯酸酯类高分子材料;对松香综合改性高分子材料的发展趋势进行展望,指出了基于松香双键和羧基综合改性制备色泽浅、软化点高的高分子材料及松香改性其它生物质基类高分子材料的发展潜力,以期促进松香改性高分子材料的制备和应用研究。     

Mechanical properties,thermal stability,and flame retardance of novolac‐type phenolic resin blended with poly(dimethylsiloxaneadipamide)

Mechanical properties (flexural strength, flexural modulus, and notched Izod impact strength), thermal stability, and flame retardance of poly(dimethylsiloxane adipamide) (PDMSA)‐toughened novolac type phenolic resin were investigated. Mechanical properties of modified novolac‐type phenolic resin increase with PDMSA contents, because the soft segment of PDMSA absorbs the loads in the network of brittle novolac‐type phenolic resins. TGA results show that the thermal degradation temperatures are higher than 400°C, and the temperature of 10% weight loss increases with increasing the PDMSA content. The char yield increases with novolac‐type phenolic resin content. The morphologies of the fracture surface of the modified novolac‐type phenolic resin were investigated by scanning electron microscopy (SEM). Morphological results agree with those from mechanical properties of the modified novolac‐type phenolic resin. The modified novolac‐type phenolic resin also shows excellent flame retardance that is UL‐94, V‐1, and the limited oxygen index is higher than 35. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 631–637, 2001     

Laccase-initiated reaction between phenolic acids and chitosan

Phenolic acids are known to possess antioxidant activities whilst chitosan is a biocompatible polymer with antibacterial activity against a broad spectrum of bacteria. Merging both types of molecules could therefore provide several potential applications. In this work, antioxidant properties of phenolic acid–functionalized-chitosan were investigated after being prepared from structurally-different phenolic acids (caffeic and gallic acids) and chitosan using the laccase from Trametes versicolor as the reaction initiator. A laccase-mediated oxidation kinetic of phenolic acids was monitored by UV–vis spectroscopy and cyclic voltammetry, as well as spin-trapping electron paramagnetic resonance spectroscopy (ST-EPR). The pH was shown to have a significant effect on the degree of phenolic acid self-polymerization, indicating the involvement of phenolate anions within the formations of coupled polyphenol products, and their functionalities, i.e. antioxidant activity. All the phenolic acid-functionalized-chitosans displayed greatly improved ABTS radical cation scavenging capacities, compared with the untreated chitosan.     

Evaluation of the properties and microstructure of plastomeric polymer modified bitumens

This paper presents a laboratory study of modified bitumen containing plastomeric polymers; Evatane® 2805, Elvaloy® 3427, and Elvaloy® 4170. A 50/70 penetration grade base bitumen has been mixed with plastomeric polymers at different proportions by means of a high shear laboratory type mixer. The properties and microstructure of the samples have been determined and characterized using conventional and empirical test methods and fluorescence microscopy respectively. Qwin Plus image analysis has also been investigated in order to determine the % area distribution of plastomeric polymers throughout the base bitumen. The results indicated that polymer modification improved the conventional properties of the base bitumen such as; penetration, softening point, temperature susceptibility, etc. The microstructure and properties of the polymer modified bitumens are dependent on the type of polymer, the solubility of polymer in bitumens and polymer content. At low polymer contents, the samples revealed the existence of dispersed polymer particles in a continuous bitumen phase, whereas at high polymer contents a continuous polymer phase has been observed for the Evatane® 2805 and Elvaloy® 3427 polymers. Among the plastomeric polymers no significant polymer phase has been observed for the reactive terpolymer Elvaloy® 4170 although its conventional properties have been improved. It is also found out that a relationship exists between the polymer content and percent area distribution of polymers except for reactive terpolymer.     

Solubilization of single-walled carbon nanotubes by entanglements between them and hyperbranched phenolic polymer

Hyperbranched phenolic polymer (HBP) was prepared by Lewis acid-catalyzed polycondensation of bifunctional phenolic monomer with trifunctional phenolic monomer. By choosing an appropriate Lewis acid, HBP was successfully obtained. By using physical adsorption of HBP on a single-walled carbon nanotube (SWCNT) surface, solubilization of SWCNTs was examined. SWCNTs were soluble with extended branches of HBP in N,N-dimethylformamide (DMF) solution, while they were insoluble in a linear phenolic polymer. In the presence of shrinking branches of HBP in tetrahydrofuran, SWCNTs were hardly soluble. Entanglements between extended branches of HBP and SWCNT in DMF solution resulted in high solubility of SWCNTs.     

酚醛-环氧结构胶粘剂的研制

论述了酚醛－环氧结构胶粘剂的制备原理及工艺，讨论了影响酚醛－环氧结构胶粘剂的性能因素，在环氧树脂中加入酚醛树脂后，二者形成了一个体型缩聚物，再加入聚砜进行改性，使制得的酚醛－环氧结构胶粘剂具有较高的剪切强度和耐热性，且具有一定的韧性和抗氧化性。