Highly thermally stable novolac derivatives and their properties in epoxy composites

Two diazo‐coupling novolac derivative resins (carbonyl phenyl azo novolac resin and carbonyl phenol–biphenylene azo novolac resin) were used as flame retardants. The cured resins exhibited elevated glass‐transition temperatures from 115°C (blank) to 195 and 167°C, respectively. The char yield at 800°C was increased, which elaborated the effectiveness of flame retardancy with evaluated limiting oxygen indices around 36 to 40. This was mainly attributed to the increased crosslink densities and highly aromatic contents in the modified phenol novolac derivative resins, which exhibited higher thermal degradation energies. Furthermore, the more effective flame retardancy was expected because of the loss of nitrogen during combustion. Through the evaluation of the cooperative flame retardancy in the organic/inorganic hybrid with char yield and increasing limiting oxygen index percentage, the effects of the filler showed cooperative flame retardancy only with the appropriate addition and with a difference in the crosslinking densities. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

联苯酚醛环氧树脂固化动力学及热性能研究

以4,4'-二氨基二苯砜(DDS)为固化剂,采用非等温示差扫描量热法(DSC)研究了联苯酚醛环氧树脂(BPNE)的固化动力学。通过外推法确定了体系的固化工艺。采用Kissinger、Ozawa法计算出固化体系的表观活化能,根据Crane理论计算得到该体系的固化反应级数。采用DSC,热重分析(TGA)研究了固化物的耐热性。结果表明:BPNE的固化工艺为160℃/2h+200℃/2h+230℃/2h;固化反应的活化能约为61.86kJ/mol,指前因子为5.27×105min-1,反应级数为1.1;玻璃化转变温度(Tg)为167℃,其10%热失重温度为398.1℃,800℃残炭率为29.37%,与双酚A环氧树脂/DDS固化物相比,分别提高了22℃,11.71%。     

新型双组分丙烯酸环氧酯胶粘剂的制备与性能研究

利用丙烯酸环氧酯及环氧树脂E-51为主体,以酸酐为固化剂研制一系列双组分胶粘剂,并对其凝胶化时间、吸水性、拉伸剪切强度、接触角、表面能等各项性能进行了研究.该系列胶粘剂吸水性较低(1.18％～1.78％)、疏水性强、剪切强度最高达30.9 MPa,综合性能良好.     

酚醛型环氧树脂改性氰酸酯复合材料性能的研究

通过DSC分析,粘度、介电性能、力学性能及耐油性测试对酚醛型环氧树脂改性氰酸酯树脂复合材料的性能进行了研究。结果表明,改性氰酸酯树体系在70～160℃具有较低的粘度,理想工艺是在125～130℃下30～45min后开始加压;改性氰酸酯树脂表观活化能和反应级数分别为60.81kJ/mol和0.8846。改性氰酸酯复合材料具有良好的力学性能、介电性能和耐油性能。     

Synthesis and properties of vinyl siloxane modified cresol novolac epoxy for electronic encapsulation

Vinyl siloxane (VS) modified cresol novolac epoxy (CNE) and cresol novolac hardener (CNH) resins are synthesized and both components are capable of further crosslinking. The reaction kinetics for both components are studied so that they can crosslink simultaneously in a designed synthesis procedure. Through careful adjustment of a triphenylphosphine dosage, the glass‐transition temperature (T_g) of CNE/CNH resins can be effectively controlled. Phenomena characteristic of the existence of a diffusion‐controlled reaction are also observed. The relationships between the T_g and crosslinking density for the CNE/CNH resin are explicitly revealed through gel content and swell ratio experiments. CNE/CNH resins with a higher T_g have lower equilibrium moisture uptake because of the higher fraction of free volume. The coefficient of diffusion also shows a similar but less apparent trend. The incorporation of VS incurs a 35% reduction in the equilibrium moisture uptake and a 20% reduction in the coefficient of diffusion for the modified resin. The VS‐modified CNE/CNH resin possesses a lower Young's modulus and a higher strain at break than its unmodified counterpart does. This modified resin can help to alleviate the popcorning problems in integrated circuit packages, which results from hygrothermal stresses. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 652–661, 2001     

Lap shear strength and thermal stability of diglycidyl ether of bisphenol a/epoxy novolac adhesives with nanoreinforcing fillers

Nanoreinforcing fillers have shown outstanding mechanical properties and widely used as reinforcing materials associated to polymeric matrices for high performance applications. In this study, a series of multiwalled carbon nanotubes (MWCNTs)‐, nano‐Al₂O₃‐, nano‐SiO₂‐, and talc‐reinforced epoxy resin adhesives composites were developed. The influence of different types and contents of nanofillers on adhesion, elongation at break, and thermal stability (under air and nitrogen atmospheres) of diglycidyl ether of bisphenol A (DGEBA)/epoxy novolac adhesives was investigated. A simple and effective approach to prepare adhesives with uniform and suitable dispersion of nanofillers into epoxy matrix was found to be mechanical stirring combined with ultrasonication. Transmission electron microscopic and scanning electron microscopic investigations revealed that nanofillers were homogeneously dispersed in epoxy matrix at optimized nanofiller loadings. Adhesion strength was measured by lap shear strength test as a function of nano‐Al₂O₃ and MWCNTs loadings. The results indicated that the lap shear strength was significantly increased by about 50% and 70% with addition of MWCNTs and nano‐Al₂O₃ up to a certain level, respectively. The highest lap shear strength was reached at 1.5 wt % of nano‐Al₂O₃ loading. MWCNTs at all loadings (except 3 wt %) and nano‐Al₂O₃ have enhanced onset of degradation temperature and char yield of the adhesives. By combined incorporation of 0.75 wt % nano‐Al₂O₃ and 0.75 wt % MWCNTs into the epoxy novolac/DGEBA blend adhesives a synergistic effect was observed in the thermal stability of the adhesives at high temperatures (800°C). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40017.     

Special-purpose epoxy adhesives

Characteristics of epoxy adhesives for special purposes are described. These adhesives are used for joining together various substrates based on polyamides, ferrite, quartz, ceramics, and resins based on fluoroorganic rubbers.     

酚醛环氧树脂的改性研究进展

概述了常见的3种酚醛环氧树脂的特点,着重从结构改性、有机物改性和无机物改性3个方面介绍了近年来酚醛环氧树脂的耐热和增韧改性的研究原理和方法,最后展望了酚醛环氧树脂改性的新方法。     

气干性酚醛环氧乙烯基树脂的研制

采用交联共聚法合成了气干性酚醛环氧乙烯基树脂。研究了物料配比、阻聚剂用量、反应温度对反应的影响,测试了树脂的耐腐蚀性、气干性和力学性能。结果表明,酯化过程最佳工艺条件为:反应温度110～115℃,反应时间2.5 h,醇、酸物质的量比1.1∶2,阻聚剂质量分数0.05%,催化剂质量分数0.3%。交联聚合过程最佳工艺条件为:反应温度75～85℃反应时间2.0 h,改性剂(甲苯二异氰酸酯)加入质量5%。合成的树脂的弯曲强度为101 MPa,弯曲模量3.66 GPa,冲击强度11.4 kJ/m2,气干性、韧性、固化性能均超过同类树脂,可用于耐温强腐蚀场合以及用作表面涂层、耐温腻子基体树脂、自流平树脂等。     

Thermal and electrical properties of glass fiber reinforced o‐cresol novolac epoxy composites cured with allylated phenol novolac hardener

An allyl group was introduced into a phenol novolac hardener to improve the thermal and electrical properties of glass fiber reinforced o‐cresol novolac epoxy composites. Based on ¹H NMR analysis, it was found that the degree of allylation was measured as 12.5% and 15.3% of allylated moieties underwent Claisen rearrangement. Thermal and electrical properties of the prepared composites were investigated by thermal mechanical analysis, dynamic mechanical analysis and dielectric measurements. Their thermal expansion coefficient and glass transition temperature measured by thermal mechanical analysis varied from 20.1 to 18.0 ppm K^?1 and 132.5 to 170.9 °C, respectively, due to allylation of the phenol novolac hardener. From the storage modulus at the rubbery plateau, it was confirmed that these improvements were mainly caused by an increase in the crosslink density of the matrix resin owing to allyl groups. The electrical properties of the composites, however, showed no noticeable changes by allylation of the phenol novolac hardener. Copyright © 2012 Society of Chemical Industry     

Thermo-mechanical properties of rosin-modified o-cresol novolac epoxy thermosets comprising rosin-based imidoamine curing agents

Rosin-modified o-cresol novolac epoxy resin (AEOCN) was synthesized by condensation of rosin acid with o-cresol formaldehyde novolac resin (AOCN). The AEOCN resin was further epoxidized using epichlorohydrin and sodium hydroxide. Rosin-based imidoamine curing agents (IAMDK, IASDK, and IAEDK) were also prepared by reacting dimaleopimaryl ketone (DMPK), a dimerized rosin product with aromatic diamines. The chemical structures of all synthesized products were confirmed by FTIR, ¹H-NMR, ¹³C-NMR, and DEPT-135° spectroscopic techniques. The curing process of rosin-modified epoxy cured with imidoamine crosslinkers was studied using differential scanning calorimetry (DSC) and the results were compared to o-cresol novolac epoxy resin (EOCN) and some previously reported commercial-based systems. The thermal and mechanical properties of the cured epoxy thermosets were determined using a thermogravimetric analyzer (TGA) and a universal testing machine (UTM), respectively. The chemical resistance analysis was carried out by immersing cured epoxy coated panels in 1M NaOH, 1MHCl, and 1M NaCl solutions. The results were evaluated in terms of % weight loss method and the morphological changes that appeared due to chemical exposure were also investigated via scanning electron microscopy (SEM). This study presents the economical synthetic approach towards high-performance bio-based epoxy coating materials impending to replace some of the petrochemical compounds in coating industries.     

Synthesis, characterization, and properties of novel novolac epoxy resin containing naphthalene moiety

A series of novel novolac epoxy resins containing naphthalene moiety with different molecular weights were synthesized via condensation of bisphenol A and 1-naphthaldehyde, followed by epoxidation with epichlorohydrin. The chemical structure of the naphthalene epoxy thus obtained was characterized using FTIR, ¹H NMR spectra and GPC analyses. The naphthalene epoxy was cured with 4,4′-diaminodiphenyl sulfone (DDS) and the cured products were characterized with thermogravimetric analysis, dynamic mechanical analysis, and X-ray diffraction. Compared with the diglycidyl ether of bisphenol A (DGEBA), the cured naphthalene epoxy resin showed remarkably higher glass transition temperatures (T_gs), enhanced thermal stability and better moisture resistance. When the molar ratio of 1-naphthaldehyde to bisphenol A was 0.67, the optimal thermal resistance was observed.     

Aging effects on the electrical properties of silver-filled epoxy adhesives

Electrically conductive adhesives, such as silver-filled epoxies, are used in many applications where standard soldering or direct metal-to-metal connections are not feasible. Anomalous behavior at these connections has been observed as the development of increasing resistance over time in the absence of mechanical failure between the adhesive and substrate. The results of aging of electrically conductive adhesive joints to aluminum- and gold-metallized substrates show that little change occurs at low humidity under an ambient flow of nitrogen. With increasing humidity and temperature, there is a measurable increase in resistance over time, particularly in the case of aluminum-metallized substrates. Secondary ion mass spectrometry (SIMS) was used to investigate interfacial phenomena that may be responsible for increasing resistance observed in the aluminum-metallized samples exposed to accelerated aging. Preliminary results from this technique indicate the presence of an oxide layer between the adhesive and the metallization layer that is consistent with increasing resistance measured for samples exposed to accelerated aging. The results also support the conclusion that deterioration at the adhesive-aluminum interface, and not degradation in the bulk adhesive, is the primary cause of increasing resistance.     

酚醛环氧树脂的改性研究进展

概述了常见的3种酚醛环氧树脂的特点,着重从结构改性、有机物改性和无机物改性3个方面介绍了近年来酚醛环氧树脂的耐热和增韧改性的研究原理和方法,最后展望了酚醛环氧树脂改性的新方法。     

Effects of novolac resin modification on mechanical properties of carbon fiber/epoxy composites

The epoxy resin matrix of carbon fiber (CF)‐reinforced epoxy composites was modified with novolac resin (NR) to improve the matrix‐dominated mechanical properties of composites. Flexural strength, interlaminar shear strength (ILSS), and impact strength were measured with unfilled, 7 wt% NR, 13 wt% NR, and 18 wt% NR filled to epoxy to identify the effect of adding NR on the mechanical properties of composites. The results showed that both interfacial and impact properties of composites were improved except for flexural property. The largest improvement in ILSS and impact strength were obtained with 13 wt% loading of NR. ILSS and impact strength were improved by 7.3% and 38.6%, respectively, compared with the composite without NR. The fracture and surface morphologies of the composite specimens were characterized by scanning electron microscopy. Intimate bonding of the fibers and the matrix was evident with the content of 7–13 wt% NR range. Decrease of crosslinking density and formation of NR transition layer were deduced with adding NR. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Relationship between mechanical properties of and crack progogation in epoxy resin adhesives

Crack propagation in a series of amine-cured epoxy resin adhesives in both the bulk material and adhesive joints has been studied as a function of the formulation of the resins and the conditions of testing using a linear elastic fracture mechanics approach. In both cases propagation was found to take place in either a stick—slip (unstable) or a continuous (stable) manner; the particular type of propagation depending upon the amount and type of hardener used and the temperature and rate of testing. A constant crack opening displacement (δ) has been shown to be a unique failure criterion for continuous propagation with δ having approximately the same value in both bulk material and joints. However δ was found to increase in the stick—slip mode of propagation. These crack propagation characteristics have been related to the compressive yield behaviour of each material as determined by uniaxial compression tests performed on the epoxy resins. Possible mechanisms of crack propagation have also been discussed.     

Elastomer modification of epoxy based film adhesives: adhesive and mechanical properties

Three approaches were employed to improve the flow and sandwich bonding properties of a nylon-carrier supported film adhesive based on carboxyl terminated butadiene acrylonitrile (CTBN)-modified novolac epoxy resin. These included the addition of a commercial acrylate flow modifier, replacement of novolac epoxy partly with solid diglycidyl ether of bisphenol A (DGEBA) resins, and replacement of CTBN partly with an epoxy functional acrylate terpolymer (EPOBAN). Adhesive properties such as lap shear strength (LSS), T-peel strength (TPS) and flatwise tensile strength (FTS) on honeycomb core bonded sandwich specimens were evaluated using aluminium adherends. The addition of the flow modifier in low concentrations enhanced the flexibility of the system and resulted in a marginal increase in LSS, TPS and FTS. Replacing novolac epoxy partly with solid DGEBA resulted in a less brittle system with enhanced LSS and TPS, but with reduced FTS due to the decreased flow characteristics. A substantial increase in FTS was observed when CTBN was partly replaced with EPOBAN. The introduction of EPOBAN resulted in good flow and fillet properties and the optimum FTS was obtained for the composition based on 25/75 CTBN/EPOBAN ratio. Mechanical properties of selected systems were also studied in addition to adhesive properties.     

Early-age tensile properties of structural epoxy adhesives subjected to low-temperature curing

The early-age mechanical property development of structural adhesives during low temperature curing is critical for the outdoor construction of engineering structures, such as bridges or buildings. Construction of these structures is also carried out during winter time at low curing temperatures. Experimental investigations showed that the development of the tensile properties of a commercial structural epoxy adhesive strongly depended on the curing temperature. Lower curing temperatures significantly decelerate the process and consequently the rate of development of mechanical properties. At 0 °C, curing was inhibited or did not initiate at all. Tensile strength and stiffness developed at the same rate, although the former was slightly delayed compared to the latter. Significant development of the mechanical properties began only after the onset of material vitrification. This was in contrast to the development of the glass transition temperature, which increased particularly before vitrification. A proposed analytical model predicted the development of mechanical properties well, particularly under low isothermal and cyclic temperature conditions.     

Preparation and properties of heat and ultraviolet‐induced bonding and debonding epoxy/epoxy acrylate adhesives

Heat and ultraviolet (UV)‐induced bonding and debonding (BDB) adhesives were designed and prepared through blending an epoxy resin, diglycidyl ether of bisphenol A (DGEBA) with an epoxy acrylate resin, bisphenol‐A epoxy acrylate resin (BEA). The variation of the chemical structure of DGEBA and BEA in the sequential heat‐ and UV‐curing processes was characterized by Fourier transform infrared spectroscopy (FTIR). The FTIR results indicate that DGEBA and BEA successfully took part in both the heat‐curing and UV‐curing processes. The effects of the mass ratio of BEA to DGEBA, amount of heat‐curing agent, type of diluents, and UV irradiation time on the BDB properties of BDB adhesive were systematically investigated. The results show that the bonding strength increases with the decrease of the mass ratio of BEA to DGEBA and with the increase of the amount of heat‐curing agent in a certain range. The debonding strength decreases with the increase of the mass ratio of BEA to DGEBA. The mass ratio of BEA to DGEBA was set at 10 to ensure the ratio of the bonding strength to debonding strength greater than 10 times. The debonding strength of BDB adhesives also depends on the UV irradiation time, decreasing with the increase of UV irradiation time in a certain range. Based on the FTIR results and the dependence of the bonding and deboning strengths on the reaction conditions, a possible BDB mechanism of BDB adhesive was proposed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46435.