Thermomechanical and barrier properties of UV‐cured epoxy/O‐montmorillonite nanocomposites

Mixtures of an epoxy resin and organophilic montmorillonites were subjected to ultraviolet (UV)‐induced photopolymerization. Two types of commercially available nanoclays, namely Cloisite 30B and Cloisite Na⁺, were modified through interaction with organic compatibilizers (dodecylsuccinic anhydride, octadecylamine, octadecyl alcohol, and octadecanoic acid). The modified nanoclays, dispersed in the liquid epoxy resin at 5 wt%, were photopolymerized to get nanocomposite films. The kinetics of the photopolymerization was evaluated by means of real‐time Fourier transform infrared spectroscopy. The modified nanoclays and their nanocomposites were characterized through X‐ray diffractometry; transmission electron microscopy showed the presence of intercalated and partially exfoliated morphologies in the nanocomposites. Thermogravimetric and dynamic‐mechanical analyses showed an increase of the thermal properties and an increase of the glass transition temperatures of the nanocomposites compared with that of the neat UV‐cured resin. Finally, the oxygen barrier properties of nanocomposite films, coated on a polyethyleneterephtalate substrate, were evaluated; the decrease of permeability was correlated with the degree of exfoliation of the nanocomposites. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Properties of novel epoxy/clay nanocomposites prepared with a reactive phosphorus-containing organoclay

In this study, a reactive phosphorus-containing organoclay (RPC) was successfully prepared through the cationic exchange reaction of sodium montomorillonite clay with hexyltriphenylphosphonium bromide and surface modification by grafting it with glycidyloxypropyltrimethoxy silane. It is characterized using X-ray diffraction (XRD) and Fourier transform IR (FTIR) measurements. A series of novel epoxy/clay nanocomposites (ERPC) was then prepared with a selected epoxy resin and varying amounts of RPC. The results of XRD and TEM of the nanocomposites showed that the RPC particles were well dispersed in the epoxy matrix with a highly exfoliated structure due to the presence of the reactive epoxide group of RPC. The as-prepared epoxy/RPC nanocomposites (ERPC) were thermally stable up to 388 °C. Thermal stability was increased by increasing the RPC content as indicated by the corresponding activation energies (E_a) and the integral procedural decomposition temperatures (IPDT). Furthermore, the storage modulus in the glass state of the nanocomposites was dramatically increased with the increase in RPC content. In addition, the large increment of limiting oxygen index (LOI) which was 11 units higher than that of the neat epoxy indicates that an extraordinary enhancement of flame retardancy was obtained from the nanocomposite containing 5 wt% of RPC.     

Comparison of the properties of clay polymer nanocomposites prepared by montmorillonite modified by silane and by quaternary ammonium salts

In this work, the silylation of sodium montmorillonite (Na⁺-Mt, Nanofil 757®) was performed using (3-aminopropyl)triethoxy silane (APTES). Different reaction conditions were used varying the reaction time and the amount of the aminosilane. Epoxy-based nanocomposites were prepared with different amounts of silylated Mt or commercial organically modified Mt intercalated with stearylbenzyldimethyl ammonium chloride (Nanofil 2®) and distearyldimethyl ammonium chloride (Nanofil 8®), respectively. The grafting/intercalation of the aminosilane inside the Mt interlayer spaces was studied by means of Fourier transform infrared (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA). After isothermal curing at 90 °C the Mt epoxy nanocomposites were analyzed by means of XRD and dynamic mechanical analysis (DMA). The glass transition temperature of all prepared nanocomposites containing silylated Mt, is slightly higher than that of the neat epoxy (2 to 5 °C). In the presence of 1 to 5 m% of silylated Mt in epoxy matrix the storage modulus increases from about 5 to 15% at 25 °C, respectively, compared to the pristine epoxy matrix, while only 0–4% increase was observed for epoxy nanocomposites with commercial modified Mt.     

基于一步法制备含羧基环氧树脂/纳米二氧化锆复合材料

选用乙烯基三乙氧基硅烷改性纳米二氧化锆,与烯丙基缩水甘油醚、甲基丙烯酸通过自由基共聚法制备了含羧基环氧树脂/纳米二氧化锆复合材料。采用傅里叶红外光谱、X射线衍射分别对改性纳米二氧化锆和含羧基环氧树脂/纳米二氧化锆复合材料进行了表征。结果表明:纳米二氧化锆表面引入了双键;纳米二氧化锆较为均匀地分散在聚合物基体中,其表面灰色部分可能是聚合物形成的包裹。将含羧基环氧树脂/纳米二氧化锆复合材料应用于制革鞣制工艺中,应用结果表明:含羧基环氧树脂/纳米二氧化锆复合材料配合酸皮质量3%的铬粉鞣制坯革收缩温度为102.6℃,增厚率为67.26%,与酸皮质量8%的铬粉鞣制坯革相比,柔软度明显提高,鞣制后废液中的Cr_2O_3含量降低了73.2%。     

Preparation and properties of halogen-free flame retardant epoxy resins with phosphorus-containing siloxanes

Novel epoxy resin modifiers, DOPO–TMDS and DOPO–DMDP were synthesized by addition reaction of divinylsiloxane with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Halogen-free flame retardant epoxy resins were obtained through modification of o-cresol novolac epoxy resin cured by phenol novolac resin using DOPO–TMDS and DOPO–DMDP which were characterized by ¹H NMR, ¹³C NMR, ³¹P NMR and FT-IR measurements. Effects of the phosphorus-containing siloxanes on thermal stabilities, mechanical properties and flame retardant properties of the epoxy resins were investigated. The cured epoxy resins exhibited better mechanical properties and greatly improved flame retardant properties due to the presence of phosphorus-containing siloxanes. The cured epoxy resins with phosphorus loading of 2.0 wt% showed LOI values of 32–33 and achieved UL94V-0 ratings.     

Preparation and properties of LDHs/epoxy nanocomposites

Layered double hydroxides (LDHs)/epoxy nanocomposites were prepared by mixing the amino laurate intercalated LDHs, EPON 828 resin, and Jeffamine D400 as a curing agent. The organo-modified LDHs with hydrophobic property easily disperse in epoxy resin, and the amino laurate intercalated LDHs with large gallery space allow the epoxy molecules and the curing agents to easily diffuse into the LDHs galleries at elevated temperature. After the thermal curing process, the exfoliated LDHs/epoxy nanocomposites were formed. X-ray diffraction was used to detect the formation process of the exfoliated LDHs/epoxy nanocomposites. TEM was used to observe the dispersed behavior of the LDHs nanolayers, and the LDHs nanolayers were exfoliated and well dispersed in these nanocomposites. Owing to the reaction between the amine groups of the intercalated amino laurate and epoxy groups, the adhesion between the LDHs nanolayers and epoxy molecules makes these LDHs/epoxy nanocomposites more compatible. Consequently, the tensile properties from tensile test and the mechanical properties from DMA were enhanced, and the T_g of these nanocomposites from DMA and TMA were increased. Coefficients of thermal expansion (CTEs, below and above T_g) of these nanocomposites from TMA decreased with the LDHs content. The thermal stability of these nanocomposites was enhanced by the well dispersed LDHs nanolayers.     

Control of the functionality of graphene oxide for its application in epoxy nanocomposites

Amino- and epoxy-functionalized graphene oxide (GO) were synthesized separately through a wash-and-rebuild process utilizing two differently terminated silane coupling agents. The modified GO sheets were then incorporated into an epoxy resin to prepare nanocomposites. The addition of 0.2 wt% amino-functionalized GO (APTS-GO) yielded a 32% increase in Young's modulus (3.3 GPa) and 16% increase in tensile strength (81.2 MPa). Less reinforcement was observed with the epoxy-functionalized GO (GPTS-GO) but there was a more significant increase in ductility for GPTS-GO/epoxy, with the fracture toughness (critical intensity factor, K_IC) and fracture energy (critical strain energy release rate, G_IC) nearly doubling at 0.2 wt% loading (1.46 MPam^1/2 and 0.62 kJ/m² for K_IC and G_IC, respectively). Raman spectroscopy measurements revealed that the GPTS-GO was dispersed more uniformly than the APTS-GO in the epoxy matrix, and better interfacial stress transfer was found for the APTS-GO. Thus the wash-and-rebuild process affords a novel strategy for controlling the functionality of graphene in the quest to develop high-performance graphene-based nanocomposites.     

Thermostable and flame retardant Mesua ferrea L. seed oil based non-halogenated epoxy resin/clay nanocomposites

Bio-based polymer nanocomposites have a unique niche of their own in the domain of green technology. A bio-based sulfone epoxy resin (BPSE) has been synthesized from the monoglyceride of Mesua ferrea L. seed oil, bis(4-hydroxyphenyl) sulfone, bisphenol-A and epichlorohydrin. The formation of resin was confirmed by the determination of viscosity, epoxy equivalent, etc. and the structure was elucidated from FTIR and ¹H NMR spectroscopies. This resin was used as the matrix for the preparation of epoxy/clay nanocomposites by ex situ technique using different doses of organo nano-clay (1, 2.5 and 5%, w/w). XRD, TEM, SEM, FTIR and rheological studies confirmed the formation of nanocomposites with partial exfoliated structure of the nano-clay. The study demonstrated that the tensile strength enhanced from 4 to 11.4 MPa, scratch hardness improved by two-fold, gloss value increased by 20 units, adhesive strength improved by two-fold and thermal stability improved by 19 °C on incorporation of 5 wt% of nano-clay with respect to the pristine polymer. The limiting oxygen index value and UL94 test indicated improvement of flame retardancy of the nanocomposites. The results exhibit the potentiality of these bio-based epoxy/clay nanocomposites for multifaceted advanced applications.     

Preparation of epoxy resin/silica hybrid composites for epoxy molding compounds

Phenolic novolac/silica and cresol novolac epoxy/silica hybrids were prepared through in situ sol‐gel reaction of tetraethoxysilane (TEOS). The formed hybrids were utilized as a curing agent and an epoxy resin in epoxy curing compositions, respectively. Via the two‐step preparation route, the resulting epoxy resin/silica hybrid nanocomposites exhibited good thermal stability, high glass transition temperatures, and low coefficients of thermal expansion. High condensation degree of the condensed silica was observed with a high content of siloxane bridges, p > 85%, measured by ²⁹Si NMR. The two‐step route also provides feasibility of preparation of epoxy resin/silica hybrid nanocomposites compatible with the current processes of manufacturing of epoxy molding compounds. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 4047–4053, 2003     

Preparation and investigation of anticorrosion properties of the water-based epoxy-clay nanocoating modified by Na+-MMT and Cloisite 30B

In this study the effect of using nanoclay particles in two different matrices on anticorrosive performance improvement of a novel water-based epoxy coating was investigated. For this purpose, Na⁺-montmorillonite (Na⁺-MMT) and organo-montmorillonite (Cloisite 30B) were introduced into water-based hardener (RIPI-W.B.H.) and epoxy resin matrices, separately. Nanoclays were added to polymeric matrices using direct mixing under an ultrasonic homogenizer. The coatings were analyzed to ensure the intercalation and distribution of layered silicates by means of X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses. The structure of products is studied by infrared (IR) spectrometer. The corrosion protection performances of the coatings were investigated using salt spray test and electrochemical impedance spectroscopy (EIS) in 3.5% sodium chloride solution. The results showed that using Cloisite 30B in water-based hardener had the best performance and its application in anticorrosion water-based zinc rich epoxy coating approved of it.     

Epoxy-Graphene UV-cured nanocomposites

This work presents the preparation of functionalized graphene sheets (FGS)/epoxy coatings cured by cationic photopolymerization with enhanced mechanical properties. The kinetics of the photopolymerization process for formulations up to 1.5 wt% of graphene were evaluated by means of Real-Time FTIR spectroscopy. The reinforcement of the cured coatings by the graphene was studied by measuring the dynamic-mechanical properties and the surface hardness. An increase of almost 40 °C in the T_g was obtained by adding 1.5 wt% of graphene to the epoxy matrix. A good dispersion state and interaction of the graphene with the matrix were observed by TEM and FESEM analyses.     

Microwave exfoliated reduced graphene oxide epoxy nanocomposites for high performance applications

Graphene has captured the attention of scientific community due to recently emerging high performance applications. Hence, studying its reinforcing effects on epoxy resin is a significant step. In this study, microwave exfoliated reduced graphene oxide (MERGO) was prepared from natural graphite for subsequent fabrication of epoxy nanocomposites using triethylenetetramine (TETA) as a curing agent via in-situ polymerization. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), C¹³ NMR spectroscopy, X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible (UV–vis) spectroscopy were employed to confirm the simultaneous reduction and exfoliation of graphene oxide. The reinforcing effect of MERGO on epoxy resin was explored by investigating its static mechanical properties and dynamic mechanical analysis (DMA) at MERGO loadings of 0 to 0.5 phr. The micro-structure of epoxy/MERGO nanocomposites was investigated using scanning electron microscope (SEM), transmission electron microscope (TEM) and XRD techniques. The present work reports an enhancement of 32%, 103% and 85% in tensile, impact and flexural strength respectively of epoxy by the addition of even 0.25 phr MERGO. At this loading elastic and flexural moduli also increased by 10% and 65%, respectively. Single-edge-notch three-point-Bending (SEN-TPB) fracture toughness (K_IC) measurements were carried out where a 63% increase was observed by the introduction of 0.25 phr MERGO. The interfacial interactions brought about by graphene also benefited the dynamic mechanical properties to a large extent in the form of a significant enhancement in storage modulus and slightly improved glass transition temperature. Considerable improvements were also detected in dielectric properties. The epoxy nanocomposite also attained an ac conductivity of 10⁻⁵ S/m and a remarkable increase in dielectric constant. The simple and cost effective way of graphene synthesis for the fabrication of epoxy/MERGO nanocomposites may be extended to the preparation of other MERGO based polymer nanocomposites. This remarkable class of materials has thrown open enormous opportunities for developing conductive adhesives and in microelectronics.     

Synthesis,cationic polymerization and curing reaction with epoxy resin of 3,9‐di(p‐methoxybenzyl)‐1,5,7,11‐tetra‐oxaspiro(5,5)undecane

A new spiro ortho carbonate, 3,9‐di(p‐methoxybenzyl)‐1,5,7,11‐tetra‐oxaspiro(5,5)undecane was prepared by the reaction of 2‐methoxybenzyl‐1,3‐propanediol with di(n‐butyl)tin oxide, following with carbon disulfide. Its cationic polymerization was carried out in dichloromethane using BF₃‐OEt₂ as catalyst. The [¹H], [¹³C]NMR and IR data as well as elementary analysis of the polymers obtained indicated that it underwent double ring‐opening polymerization. The polymerization mechanism is discussed. The curing reaction of bisphenol A type epoxy resin in the presence of the monomer and a curing agent was investigated. DSC measurements were used to follow the curing process. In the case of boron trifluoride‐o‐phenylenediamine (BF₃‐OPDA) as curing agent, two peaks were found on the DSC curves, one of which was attributed to the polymerization of the epoxy group, and the other to the copolymerization of the monomer with the isolated epoxy groups or homopolymerization. However, when BF₃‐H₂NEt was used as curing agent, only one peak was present. IR measurement of the modified epoxy resin with various weight ratios of epoxy resin/monomer was performed in the presence of BF₃‐H₂NEt as curing agent. The results demonstrate that the conversion of epoxy group increases as the content of monomer increases. The curing process and the structure of the epoxy resin network are discussed. © 2000 Society of Chemical Industry     

Numerical simulation for bubble growth during supercritical CO2 foaming epoxy resin process based on chemorheology

The bubble growth process of epoxy resin foams has been evaluated through a combination of numerical simulation and chemorheology. It was discovered that rheological properties play an essential role in forecasting bubble growth during supercritical CO₂ epoxy resin foaming. Time–cure superposition was conducted revealing that shear storage modulus increased from 10⁻³ to 10⁶ Pa during the curing reaction process. The complex viscosity increased up to 10⁵ Pa s and the characteristic relaxation time increased up to 53.1 s with the curing degree. The epoxy resin with high rigid modulus could effectively inhibit bubble growth. Furthermore, the simulation results indicated that the bubble growth process for epoxy resin foams was influenced by both the CO₂ content and CO₂ plasticization on rheology properties.     

Development of dimethylsiloxane based tetraglycidyl epoxy nanocomposites for high performance,aerospace and advanced engineering applications

A study was made in the present investigation on bis(p-aminophenoxy) dimethylsiloxane based tetraglycidyl epoxy nanocomposites in order to determine its suitability for use in high performance applications. The synthesis of the siloxane tetraglycidyl epoxy resin denoted as ‘F’ was done and it was characterized by Fourier transform infrared spectra (FT-IR) and ¹H, ¹³C nuclear magnetic resonance (NMR) spectra. Nanoclay and polyhedral oligomeric silsesquioxanes (POSS)-amine nanoreinforcements denoted as N1 and N2 were incorporated into the synthesized epoxy resin. Curing was done with diaminodiphenylmethane (DDM) and bis(3-aminophenyl) phenylphosphine oxide (BAPPO) curing agents denoted as X and Y respectively. The mechanical, thermal, flame retardant and water absorption behavior of the epoxy nanocomposites were studied and the results are discussed.     

配位插层法制备三聚氰胺-甲醛树脂/Cu2+ -蒙脱石纳米复合材料

采用微波加热溶液交换法分两步将提纯后的天然膨润土转变为Cu2 -膨润土(铜基土),通过三聚氰胺单体与Cu2 -蒙脱石层间Cu2 的配位作用,把三聚氰胺单体引入蒙脱石层间,然后加入甲醛经插层原位聚合制备三聚氰胺-甲醛树脂/Cu2 -蒙脱石纳米复合材料。X-射线衍射结果表明蒙脱石的层间距由1.25 nm增加到1.58 nm,所得产物为三聚氰胺-甲醛树脂/Cu2 -蒙脱石插层型纳米复合材料。     

Synthesis of epoxy resin–silica nanocomposites provided from perhydropolysilazane as a curing reagent and the precursor of silica domain

Epoxy resin–silica nanocomposites with spherical silica domains with 29.0 nm in diameter in an epoxy resin matrix were synthesized from Bisphenol‐A type epoxide monomer, 2,2‐bis(4‐glycidyloxyphenyl)propane (DGEBA), and perhydropolysilazane (PHPS, ? [Si₂? NH]_n? ). The volume fraction of silica domain in the composite varied from 5.4 to 37.8 vol % by varying the feed ratio of PHPS to the epoxide monomer. The reaction mechanism of epoxy group and PHPS was investigated by using glycidyl methacrylate as a model compound of the epoxy monomer by ¹H‐nucular magnetic resonance and Fourier transform infrared spectrometry. Ammonia gas provided by the decomposition of PHPS with moisture converted PHPS to silica and cured the epoxy monomer. The curing of epoxy monomer preferably proceeded than the conversion of silica. The addition of 1,4‐diaminobutane drastically accelerated the rate of curing; white and hard epoxy resin–silica nanocomposites were obtained. The good thermal stability of the composite prepared with DGEBA/PHPS/1,4‐diaminobutane was observed by thermogravimetric analysis. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Epoxy nanocomposites with octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane

The POSS-containing nanocomposites of epoxy resin were prepared via the co-curing reaction between octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane (OpePOSS) and the precursors of epoxy resin. The curing reactions were started from the initially homogeneous ternary solution of diglycidyl ether of bisphenol A (DGEBA), 4,4′-Diaminodiphenylmethane (DDM) and OpePOSS. The nanocomposites containing up to 40 wt% of POSS were obtained. The homogeneous dispersion of POSS cages in the epoxy matrices was evidenced by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and atomic force microscopy (AFM). Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) showed that at the lower POSS concentrations (<30 wt%) the glass transition temperatures (T_gs) of the nanocomposites almost remained invariant whereas the nanocomposites containing POSS more than 40 wt% displayed the lower T_gs than the control epoxy. The DMA results show that the moduli of the nanocomposites in glass and rubbery states are significantly higher than those of the control epoxy, indicating the nanoreinforcement effect of POSS cages. Thermogravimetric analysis (TGA) indicates that the thermal stability of the polymer matrix was not sacrificed by introducing a small amount of POSS, whereas the properties of oxidation resistance of the materials were significantly enhanced. The improved thermal stability could be ascribed to the nanoscaled dispersion of POSS cages and the formation of tether structure of POSS cages with epoxy matrix.     

Synthesis and characterization of epoxy based nanocomposites

Epoxy‐clay nanocomposites were synthesized to examine the effects of the content and type of different clays on the structure and mechanical properties of the nanocomposites. Diglycidyl ether of bisphenol‐A (epoxy) was reinforced by 0.5–11 wt % natural (Cloisite Na⁺) and organically modified (Cloisite 30B) types of montmorillonite. SEM results showed that as the clay content increased, larger agglomerates of clay were present. Nanocomposites with Cloisite 30B exhibited better dispersion and a lower degree of agglomeration than nanocomposites with Cloisite Na⁺. X‐ray results indicated that in nanocomposites with 3 wt % Cloisite 30B, d‐spacing expanded from 18.4 Å (the initial value of the pure clay) to 38.2 Å. The glass transition temperature increased from 73°C, in the unfilled epoxy resin, to 83.5°C in the nanocomposite with 9 wt % Cloisite 30B. The tensile strength exhibited a maximum at 1 wt % modified clay loading. Addition of 0.5 wt % organically modified clay improved the impact strength of the epoxy resin by 137%; in contrast, addition of 0.5 wt % unmodified clay improved the impact strength by 72%. Tensile modulus increased with increasing clay loading in both types of nanocomposites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1081–1086, 2005     

Thermo mechanical behaviour of unsaturated polyester toughened epoxy–clay hybrid nanocomposites

The intercrosslinked networks of unsaturated polyester (UP) toughened epoxy–clay hybrid nanocomposites have been developed. Epoxy resin (DGEBA) was toughened with 5, 10 and 15% (by wt) of unsaturated polyester using benzoyl peroxide as radical initiator and 4,4′-diaminodiphenylmethane as a curing agent at appropriate conditions. The chemical reaction of unsaturated polyester with the epoxy resin was carried out thermally in presence of benzoyl peroxide-radical initiator and the resulting product was analyzed by FT-IR spectra. Epoxy and unsaturated polyester toughened epoxy systems were further modified with 1, 3 and 5% (by wt) of organophilic montmorillonite (MMT) clay. Clay filled hybrid UP-epoxy matrices, developed in the form of castings were characterized for their thermal and mechanical properties. Thermal behaviour of the matrices was characterized by differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Mechanical properties were studied as per ASTM standards. Data resulted from mechanical and thermal studies indicated that the introduction of unsaturated polyester into epoxy resin improved the thermal stability and impact strength to an appreciable extent. The impact strength of 3% clay filled epoxy system was increased by 19.2% compared to that of unmodified epoxy resin system. However, the introduction of both UP and organophilic MMT clay into epoxy resin enhanced the values of mechanical properties and thermal stability according to their percentage content. The impact strength of 3% clay filled 10% UP toughened epoxy system was increased by 26.3% compared to that of unmodified epoxy system. The intercalated nanocomposites exhibited higher dynamic modulus (from 3,072 to 3,820 MPa) than unmodified epoxy resin. From the X-ray diffraction (XRD) analysis, it was observed that the presence of d ₀₀₁ reflections of the organophilic MMT clay in the cured product indicated the development of intercalated clay structure which in turn confirmed the formation of intercalated nanocomposites. The homogeneous morphologies of the UP toughened epoxy and UP toughened epoxy–clay hybrid systems were ascertained from scanning electron microscope (SEM).