Tensile properties of glass microballoon‐epoxy resin syntactic foams

The effect of hollow glass particle (microballoon) volume fraction in the range of 0.3–0.6 on the tensile properties and fracture mode of syntactic foams is characterized in the present research. Sixteen types of syntactic foams have been fabricated and tested. Four types of glass microballoons, having 220, 320, 380, and 460 kg/m³ density, are used with epoxy resin matrix for making the syntactic foam samples. These foams contain 30, 40, 50 and 60% microballoons by volume. All types of microballoons have the same size but different wall thickness, which reflects as a difference in their density. It is observed that the tensile strength increases with a decrease in the volume fraction of microballoons. All types of syntactic foams showed 60–80% decrease in the tensile strength compared with that of the neat resin. The foams containing low strength microballoons showed lower tensile modulus compared with that of the neat resin, but the presence of high strength microballoons led to an increase in the tensile modulus of the composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1254–1261, 2006     

Poly(dimethylsiloxane)‐toughened syntactic foams

The potential of preformed elastomers as a toughening agent for epoxy–glass syntactic foam has been explored. Poly(dimethylsiloxane) microspheres were prepared by suspension polymerization. The microsphere dimensions could be varied from 58 to 255 µm by tuning the reaction parameters, particularly the stirring speed and feed concentration. Rheological studies indicated that the introduction of microballoons led to an increase in the viscosity of the resin, with the extent being proportional to the microballoon content. The zero shear viscosity increased from ～10³ mPa s at 30 °C to 10⁵ mPa s as the microballoon loading was increased to 40%. Syntactic foams containing varying amounts of microballoons (40–60% v/v) were prepared, and an analogous set of toughened foams were also prepared, where a fraction of the microballoons was replaced with poly(dimethylsiloxane) microspheres (3–7%). The effect of increasing dimensions of the elastomeric microspheres on the mechanical properties was also studied. The improvement in properties was more pronounced when the microsphere size was equivalent to that of the constituent microballoons. An improvement of 40% and 185% in flexural strength and flexural toughness was observed upon the introduction of poly(dimethylsiloxane) microspheres of optimal dimensions (diameter ～63 µm, 5% loading), without any undesirable increase in foam density. However, the compressive properties remained practically unaltered. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45882.     

Mechanical properties of polybenzoxazine syntactic foams

Syntactic foams of polybenzoxazine, containing moderately high volume percentage of glass microballoons, were prepared. The specific gravity decreased with increase in microballoon content. The disproportionate decrease in specific gravity was ascribed to entrapment of air voids during compaction. The high content of microballoon increased the possibility for air voids that tended to get accumulated. The effect of microballoon concentration on tensile, compressive, and flexural strengths of the foams was studied. Tensile and compressive properties were optimized at about 68% by volume of microballoon while flexural strength decreased marginally on increasing the microballoon content. Althought the specific tensile and compressive strength showed a maximum followed by a decrease, the specific flexural strength systematically increased with microballoon content. The increased packing density of syntactic foam of a given constituent composition increased the compressive strength. The property variation was corroborated by morphological features, as evidenced in scanning electron micrographs. The syntactic foams showed “multiple resin‐neck formation” and “disc‐shaped microballoon regions.” The crushing of microballoons during molding was inevitable when compaction was effected to achieve a density beyond the theoretical one. Low‐density syntactic foams tend to fail at lower loads because of fracturing of microballoons. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical and dynamic mechanical properties of epoxy syntactic foams reinforced by short carbon fiber

Epoxy syntactic foams were prepared with diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin, 2.4.6‐tri(dimethylaminomethyl)phenol (DMP‐30), coupling treated microsphere and short carbon fiber. The density of the foam was maintained between 0.56 and 0.91 g/cm³ for all compositions. Compressive, flexural, tensile and dynamic mechanical properties of the foams were investigated with respect to hollow glass microsphere (HGM) and carbon fiber (CF) content. A considerable improvement in the mechanical properties viz. compressive, flexural and tensile strengths was observed for the foams on incorporation of a small quantity of CF. The storage modulus were higher for the foam composites containing CF. The presence of HGM has significant influence on T_g of the syntactic foams, spherical filler diminished the T_g of the syntactic foams due to the plasticizing effect of the coupling treatment of HGM, that is helpful for enhancing damping properties of syntactic foams. POLYM. COMPOS., 37:1960–1970, 2016. © 2015 Society of Plastics Engineers     

环氧树脂复合泡沫材料的制备研究

以缩水甘油酯环氧树脂(EP)、酸酐固化剂和空心玻璃微珠为主要原料,通过添加一定的活性稀释剂,高温固化制备了EP复合泡沫材料。研究了空心玻璃微珠的表面改性对复合泡沫材料性能的影响。结果表明,复合泡沫材料性能与空心玻璃微珠的表面性能密切相关,当EP/固化剂/稀释剂的质量比为100/120/15、KH-560改性的空心玻璃微珠用量为30份时,所制备的复合泡沫材料密度为0.826 g/cm3,压缩强度达115.8 MPa,比强度为140.2。     

Effect of surface structure of porous silica microballoons on dynamic mechanical properties of amine cured epoxy resin composites

Dynamic mechanical properties were studied for epoxy resin filled with porous silica microballoons with varying surface area, pore radius, pore volume and adsorbed water. The glass transition temperature (T_g) of the composites is 12–14°C lower than the T_g of the unfilled epoxy resin. This T_g depression is attributed to the preferential adsorption of curing agents on the porous silica microballoons. Tg of the composite increases with increase in the adsorbed water on fillers. The storage modulus has a distinct correlation with the Hg-surface area of silica microballoons, which corresponds to the sum of the surface area of pores with radii larger than about 4 nm. Tan δ_c tan δ_m decreases with increasing Hg-surface area.     

Poly(ether imide)‐modified benzoxazine blends: Influences of phase separation and hydrogen bonding interactions on the curing reaction

Polymer blends of polybenzoxazine (PBZ)/poly(ether imide) (PEI) were prepared by the in situ curing reaction of benzoxazine (BZ) resin in the presence of PEI. Phase separation induced by the polymerization of BZ resin was observed. The rheological behaviors, morphologies, and their evolution process of BZ/PEI blends were investigated by rheometer and scanning electron microscope. Phase separation that took place at the early stage of the curing reaction effectively reduced the dilution effect of PEI. Fourier transform infrared (FTIR) results suggested that hydrogen bonds between PBZ and PEI existed during the whole curing process, although weakened with phase separation. The decrease of isoconversion activation energy indicated that the polymerization of BZ resin was facilitated in the presence of such kind of hydrogen‐bonding interactions. By changing the weight fraction of PEI, extensive phase separation was obtained in PBZ blends with 5 and 20 wt % of PEI, in which systems, the crosslinking density and glass transition temperature (T_g) of PBZ‐rich phase were greatly improved compared to this single PBZ system. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

New type of phenolic resin: Curing reaction of phenol‐novolac based benzoxazine with bisoxazoline or epoxy resin using latent curing agent and the properties of the cured resin

In this study, we aimed to reduce the cure time, and to lower the cure temperature of the benzoxazine compound. Therefore, curing reaction of benzoxazine with bisoxazoline or epoxy resin using the latent curing agent and the properties of the cured resins were investigated. The cure behavior of benzoxazine with bisoxazoline or epoxy resin using the latent curing agent was monitored by differential scanning calorimetry and measurements for storage modulus (G′). The properties of the cured resin were estimated by mechanical properties, electrical insulation, water resistance, heat resistance, and flame resistance. As a result, it was confirmed that by using the latent curing agent, cure time of benzoxazine and bisoxazoline or epoxy resin was reduced, and cure temperature was lowered. And it was found that the curing reaction using phenol‐novolac based benzoxazine (Na) as the benzoxazine compound could proceed more rapidly than that using bisphenol‐A based benzoxazine (Ba) as the benzoxazine compound. However, the cured resins from Ba and bisoxazoline or epoxy resin using the latent curing agent showed good heat resistance, flame resistance, and mechanical properties compared with those from Na and bisoxazoline or epoxy resin using the latent curing agent. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study on the performance of syntactic foam reinforced by hybrid functionalized carbon nanotubes

Hollow glass microspheres (HGMs)/epoxy syntactic foam were reinforced by hybrid functionalized carbon nanotubes that were synthesized by simultaneous covalent and noncovalent functionalization of carbon nanotubes. The effect of hybrid functionalized carbon nanotubes on density, mechanical properties, and water absorption of HGMs/epoxy syntactic foam was studied. The study indicated that the dispersion of carbon nanotubes in epoxy resin can be improved by hybrid functionalization. The compression strength of syntactic foam reinforced by hybrid functionalized carbon nanotubes was significantly enhanced. The maximum compressive strength of syntactic foam corresponding to chitosan modified carbon nanotubes approached 60 MPa. Hybrid functionalized carbon nanotubes had little effect on the water absorption ability of syntactic foam, and was less than 1%. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48586.     

Numerical simulation of the mechanical properties of a carbon-fiber-reinforced hollow glass microsphere–epoxy syntactic foam

The addition of carbon fibers has a great influence on the mechanical properties of hollow glass microsphere (HGM)–epoxy syntactic foam. Thus, to elucidate the reinforcement mechanism, the numerical simulation of HGM- and carbon-fiber-filled epoxy matrixes was carried out. The effect of the orientation of carbon fibers on the elastic modulus and stress distribution was studied. The effect of the elastic modulus of the matrix on the change of force was also studied. We noted that the orientation of carbon fibers affected the elastic modulus of the matrix, and when the carbon fibers were distributed in the direction of force, the elastic modulus of the matrix reached its maximum. The maximum stress of HGMs decreased with increasing matrix elastic modulus, and the mechanical properties of the syntactic foam increased with increasing elastic modulus of the matrix. When the carbon fibers were distributed in the direction of the force, the enhancement effect was the best. Because the carbon fibers had a higher elastic modulus than the matrix, the degree of compressive deformation of the carbon fibers was smaller than that of the matrix. During compression, carbon fibers were pulled out and consumed a lot of energy. Thus, the mechanical properties of the syntactic foam were improved. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47083.     

Effects of poly(methyl methacrylate)‐based low‐profile additives on the properties of cured unsaturated polyester resins. I. Miscibility,curing behavior,and glass‐transition temperatures

The effects of three series of self‐synthesized poly(methyl methacrylate) (PMMA)‐based low‐profile additives (LPAs), including PMMA, poly(methyl methacrylate‐co‐butyl acrylate), and poly(methyl methacrylate‐co‐butyl acrylate‐co‐maleic anhydride), with different chemical structures and MWs on the miscibility, cured‐sample morphology, curing kinetics, and glass‐transition temperatures for styrene (ST)/unsaturated polyester (UP) resin/LPA ternary systems were investigated by group contribution methods, scanning electron microscopy, differential scanning calorimetry (DSC), and dynamic mechanical analysis, respectively. Before curing at room temperature, the degree of phase separation for the ST/UP/LPA systems was generally explainable by the calculated polarity difference per unit volume between the UP resin and LPA. During curing at 110°C, the compatibility of the ST/UP/LPA systems, as revealed by cured‐sample morphology, was judged from the relative magnitude of the DSC peak reaction rate and the broadness of the peak. On the basis of Takayanagi's mechanical models, the effects of LPA on the final cure conversion and the glass‐transition temperature in the major continuous phase of ST‐crosslinked polyester for the ST/UP/LPA systems was also examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3369–3387, 2004     

Short beam three point bend tests in syntactic foams. Part I: Microscopic characterization of the failure zones

Scanning Electron Microscopic (SEM) studies were carried out on the failure surface of syntactic foam material tested in a short beam three point bend test (SBT) by employing 21 × 15 × 3 mm³ dimension bearing specimens. The syntactic foams were fabricated using glass microballoons in epoxy binder. The failure of the tensile, compression, and shear dominated regions were studied by SEM at different magnifications. The tensile region had characteristic features, such as partial debonding of the microballoons from the matrix and cracking of glass microballoons, apart from matrix cracking and some river pattern features. The compression side was characterized by crushing and collapsing of microballoons, resulting in accumulation of debris with no apparent river pattern for matrix‐rich regions. The midway positions of the SBT failed surface comprised of deformation bands in the matrix and occasional debonding of microballoons. The morphology recorded in the tensile and compression regions corroborated well with the results obtained on these foam samples in those specimens that were subjected to pure uniaxial tension and compression, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 673–679, 2005     

苯并口恶嗪/环氧树脂共聚固化过程研究

采用FT-IR、DSC研究苯并口恶嗪与环氧树脂通过熔融搅拌混合均匀后,固化过程中2种树脂发生开环共聚合的可能性。结果表明:苯并口恶嗪与环氧树脂熔融混合后,在高温区(180℃,200℃)发生了共聚反应,苯并口恶嗪开环过程形成的中间体可以作为环氧树脂的固化剂使用。玻璃化转变温度随着共聚体系中环氧树脂含量的增加先升高,环氧树脂质量分数超过30%后降低,当苯并口恶嗪与环氧树脂的质量比为70/30时,Tg达到最高(218℃),熔融共混在一起程度上提高了共聚体的玻璃化转变温度。     

Blends of polybenzoxazine/poly(acrylic acid): hydrogen bonds and enhanced performances

This work focuses on exploring the role of the additional hydrogen bond donor moiety‐containing polymer poly(acrylic acid) (PAA) in the hydrogen bonds and properties of polybenzoxazines. Thorough studies showed that PAA could not only decrease the curing temperature of benzoxazine resin, but also give additional hydrogen bond donors that were beneficial to the hydrogen bonding interactions and performances of polybenzoxazine/PAA blends. As the hydrogen bonds varied, the glass transition temperature and tensile modulus of the polymer blends changed in accordance with the hydrogen bonds. The results revealed that the introduction of the hydrogen bond donor moiety‐containing polymer was beneficial for hydrogen bonding interactions, which could improve the performances of polybenzoxazines. This novel insight is anticipated to be of help to researchers in the development of more polybenzoxazines and polybenzoxazine blends with enhanced properties. © 2017 Society of Chemical Industry     

Flame retardancy and dielectric properties of dicyclopentadiene‐based benzoxazine cured with a phosphorus‐containing phenolic resin

A dicyclopentadiene‐based benzoxazine (DCPDBZ) was prepared and separately copolymerized with melamine–phenol formaldehyde novolac or phosphorus‐containing phenolic resin (phosphorus‐containing diphenol) at various molar ratios. Their curing behaviors were characterized by differential scanning calorimetry. The electrical properties of the cured resins were studied with a dielectric analyzer. The glass‐transition temperatures were measured by dynamic mechanical analysis. The thermal stability and flame retardancy were determined by thermogravimetric analysis and a UL‐94 vertical test. These data were compared with those of bisphenol A benzoxazine and 4,4′‐biphenol benzoxazine systems. The effects of the diphenol structure and cured composition on the dielectric properties, moisture resistance, glass‐transition temperature, thermal stability, and flame retardancy are discussed. The DCPDBZ copolymerized with phosphorus‐containing novolac exhibited better dielectric properties, moisture resistance, and flame retardancy than those of the melamine‐modified system. The flame retardancy of the cured benzoxazine/phosphorus‐containing phenolic resins increased with increasing phosphorus content. The results indicate that the bisphenol A and 4,4′‐biphenol systems with a phosphorus content of about 0.6% and the dicyclopentadiene system with a phosphorus content of about 0.8% could achieve a flame‐retardancy rating of UL‐94 V‐0. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of VB‐a/POSS hybrid monomer and its polymerization of polybenzoxazine/POSS hybrid nanocomposites

A benzoxazine monomer (VB‐a) containing an allyl groups was synthesized through the Mannich condensation of bisphenol A, formaldehyde, and allylamine (bisphenol‐A and allylamine as VB‐a). This monomer was then reacted with polyhedral oligomeric silsesquioxane (POSS) through hydrosilylation, followed by thermal curing to form poly(VB‐a)/POSS hybrid nanocomposites. The curing behavior of the nanocomposites was monitored using Fourier transform infrared spectroscopy (FTIR), and their thermal and morphological properties were investigated through thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and scanning electron microscopy. DMA revealed that the glass transition temperatures of the poly(VB‐a)/POSS nanocomposites were higher than that of the pristine poly(VB‐a), presumably because the POSS cages effectively hindered the motion of the polymer chains. TGA confirmed that the thermal degradation temperatures and char yields of the polybenzoxazines increased after incorporation of the POSS moieties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

双酚A型苯并恶嗪/酚醛体系固化物的性能研究

将双酚A型苯并恶嗪(BOZ-a)和线形酚醛树脂按照不同的配比进行共混固化,制备了浇铸体(BPx,x表示线形酚醛在共混树脂中的质量分数)。采用力学性能,吸水性测试,动态热机械分析和热重分析研究了酚醛树脂含量对浇注体性能的影响。结果表明,随着共混体系中酚醛树脂含量的增加,浇铸体弯曲强度呈下降趋势,玻璃化转变温度及交联密度也逐渐降低,但弯曲模量、初始储能模量、硬度和热稳定性均呈先上升后下降的趋势,而吸水率呈先减小后增加的趋势。BP20体系综合性能优良,初始模量最大,达到7.384 GPa,玻璃化转变温度为168℃,7 d吸水率为0.116%,5%热失重温度为285℃。     

Elastic and plastic properties of epoxy resin syntactic foams filled with hollow glass microspheres and glass fibers

Representative volume elements of syntactic foams with a random filling of short glass fibers and hollow glass microspheres in epoxy resin were established by a random sequential adsorption method. The fiber volume fraction was set at 4%, and the microsphere volume fraction range was from 5 to 30%. This numerical simulation was studied with ANSYS software. The influence on the elastic and plastic mechanical properties of syntactic foams of the microsphere volume fraction and relative wall thickness were investigated, and the plastic strain evolution process in the composites was analyzed. The results show that the compressive yield limit and Young's modulus values of the syntactic foams decreased with increasing microsphere volume fraction when the microsphere relative wall thickness was 0.02, but these properties were enhanced with increasing microsphere volume fraction when the relative wall thickness exceeded 0.04. The specific strength and tangent modulus values of the composites increased with increasing microsphere volume fraction. In addition, we observed that the yield stress, Young's modulus, and tangent modulus values of the syntactic foams were obviously enhanced by the addition of glass fibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44188.     

Morphology and properties of poly(benzoxazine‐co‐urethane)s based on bisphenol‐S/aniline benzoxazine

Poly(benzoxazine‐co‐urethane) was prepared by melt‐blending bisphenol‐S/aniline‐type benzoxazine (BS‐a) with isocyanate‐terminated polyurethane (PU) prepolymer based on 2,4‐toluene diisocyanate and poly(ethylene glycol), followed by thermally activated polymerization of the blend. The copolymerization reaction between BS‐a and PU prepolymer was monitored using Fourier transform infrared spectroscopy. The morphology, dynamic mechanical properties, and thermal stability of the poly(benzoxazine‐co‐urethane) were studied using scanning electron microscopy, dynamic mechanical analysis, and thermogravimetry. Homogeneous morphology is shown in scanning electron micrographs of the fracture surfaces of poly(benzoxazine‐co‐urethane)s with different urethane weight fractions, and the roughness of the surface increases with urethane content increasing. Correspondingly, a single glass transition temperature (T_g) is shown on the dynamic mechanical analysis curves of the poly(benzoxazine‐co‐urethane)s, and the T_g is higher than that of the polybenzoxazine. With increase in the urethane content, the T_g and water absorption of poly(benzoxazine‐co‐urethane) increase, whereas the storage modulus and thermal stability decrease. POLYM. ENG. SCI., 53:2633–2639, 2013. © 2013 Society of Plastics Engineers     

Epoxy resin–polyethersulphone blends

A series of amine-cured epoxy resin systems and the blends of these containing up to 50% polyethersulphone (PES) were evaluated in terms of curing behavior, microstructure, and mechanical and dynamic mechanical thermal properties. The epoxy networks were based on a 2 : 1 mixture of triglycidyl-p-aminophenol and the polyglycidylether of a phenolformaldehyde novolac, and a curing agent of 3,3'-diaminodiphenylsulphone (DDS). The curing mechanism and the rate of curing were affected by the DDS and PES contents. Reaction between the epoxy resin and hydroxyl groups attached to PES was indicated in epoxy-rich formulations. Phase separation, evident in all the blends, was affected by the curing rate. Various blend morphologies were observed depending on the epoxy network/thermoplastic composition. Blending improved ductility and toughness-related properties, particularly at 20–40% PES contents, which corresponded to spinodal/co-continuous morphologies. Changes in glass transition behavior were attributed to possible variations in intermolecular free volume. © 1994 John Wiley & Sons, Inc.