Continuous reactor preparation of thermoplastic modified epoxy‐amine prepolymers

This paper describes a new continuous reactor method to prepare thermoplastic modified epoxy prepolymers for aerospace prepregs with the aim of replacing traditional batch reactors. Compared with batch reactors, the continuous reactor is capable of producing epoxy prepolymers through simultaneous dissolution of polyethersulfone (PES) and 4,4′‐diaminodiphenylsulfone in tetraglycidyl‐4,4′‐ diaminodiphenylmethane (TGDDM). In addition, concurrent chain extension reactions advance prepolymer molecular weights to desired viscosities in less than 2 min of mean residence time. Optical micrographs were used to define how process temperature influences PES dissolution in TGDDM in a continuous reactor. Kinetic studies confirmed that the chain extension reaction in a continuous reactor is similar to that in a batch reactor, and the molecular weights and viscosities of prepolymers were readily controlled through reaction kinetics. Atomic force microscopy was used to confirm similar cured network morphologies for formulations prepared from batch and continuous reactors. Additionally tensile strength, tensile modulus and fracture toughness analyses concluded that mechanical properties of cured epoxy matrices produced from the two reactors were equivalent. © 2014 Society of Chemical Industry     

Oxidative skeleton breaking in epoxy–amine networks

The photo and thermal oxidation of various epoxide–amine tridimensional polycondensates is studied by IR spectrophotometry and DSC. The network degradation results in a decrease of the glass transition temperature (T_g), which is correlated with the quantity of amide groups formed. For each system, the relative yield in skeleton breaks increases with the intensity of internal stresses. A mechanism involving the β scission of α amino alkoxy macroradicals resulting from oxidation of constrained segments of the network is proposed.     

Crack‐healing behavior of epoxy–amine thermosets

This work offers detailed experimental evidence for crack healing in fully formed epoxy–amine polymer networks. Compact tension specimens of diglycidyl ether of bisphenol A (EPON‐828) and 4,4′‐methylene biscyclohexanamine were synthesized at stoichiometry and with an excess or paucity of an amine curing agent. Healing efficiencies were measured on the basis of the regain in the fracture load after a healing protocol was applied. For all systems investigated, the average healing efficiency for first fracture was greater than 50% when healing was conducted at 185°C for 1 h. The crack‐healing behavior was highly repeatable at all stoichiometries, and healing was found to occur for repeated fracture–heal cycles of the same specimen. On the basis of results from size exclusion chromatography for the extractable phase, infrared spectroscopy, and scanning electron microscopy, it is postulated that healing is primarily due to mechanical interlocking of the nodular topology of a fractured crack interface that occurs in the rubbery state and is set in place by vitrification upon cooling. A ½ power dependence of the healing efficiency on the healing time was observed, and this suggests that the interlocking of topographical features is governed by diffusive processes. For networks cured with a large excess of epoxide groups, the recovered fracture load was higher than that of virgin specimens. In this case, polyetherification or homopolymerization of previously unreacted epoxy groups increased the healing efficiency significantly, and this suggests that low degrees of covalent bonding can significantly enhance healing behavior in these systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis,by reactive extrusion,of high molar mass epoxy prepolymers containing rubber preformed particles

High molar mass epoxy prepolymers containing rubber dispersions based on carboxyl-terminated butadiene-acrylonitrile random copolymer (CTBN) were prepared from initially miscible solution of low molar mass epoxy prepolymers, bisphenol A and CTBN-based rubber. During chain extension inside a twin-screw extruder due to epoxy-phenoxy and epoxy-carboxy reactions, a phase separation process occurs. Epoxy-phenoxy and epoxy-carboxy reactions were catalyzed by the triphenyl phosphine. The effect of reaction parameters (temperature, catalyst, reactant stoechiometry) on the reactive extrusion process were analyzed. The structure of the prepolymers showed low branching reactions (2–5%). Low molar mass prepolymers have a Newtonian rheological behavior. Cloud-point temperature of different reactive liquid butadiene acrylonitrile random copolymer (RLP)/epoxy resin blends were measured for different RLP concentrations. It was shown that rubber particles remain insoluble in a range of temperature from room temperature to 180°C, typical of temperatures used for epoxy curing reactions. Prepolymers containing different rubber concentrations were cured using dicyandiamide as the hardener. The practical adhesion of the issued networks to an aluminium alloy increased with rubber concentration. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2447–2456, 1997     

Polyurethane acrylate/epoxy–amine acrylate hybrid polymer networks

New classes of hybrid polymer networks (HPNs), having variable polyurethane acrylate (PUA) and epoxy–amine acrylate (EAA) compositions, were prepared using initially miscible systems in methyl methacrylate (MMA). The initial systems were based on PUA prepolymer and EAA monomer solutions in MMA. HPNs were a result of epoxy–amine and radical polymerization competition. Phase separation occurred during the course of HPN formation. Mechanical dynamic analysis of the prepared HPNs showed good affinity between the PUA and PMMA phases and lower affinity between the EAA and PMMA phases. Mechanical property evolution and transmission electronic microscopy showed that, for all the composition ranges used in this study (PUA/EAA/PMMA 15/45/40–45/15/40 wt %), the PUA‐rich phase was the continuous phase. EAA‐rich phases, 20–50 nm, in the PUA‐rich matrix were obtained for HPNs containing up to 30 wt % EAA. For higher EAA concentration (45 wt %), 2 μm EAA‐rich phases were obtained in the PUA‐rich matrix. A substructure was also observed in each phase. PUA/EAA copolymers were prepared and used successfully for the compatibilization of the different phases of the HPNs. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2711–2717, 2000     

Effect of epoxy–amine stoichiometry on cured resin material properties

Sizings and/or surface treatments are commonly employed to enhance the interaction of fiber reinforcements in polymer matrix composites. These modifications can induce physical and chemical interactions that cause local stoichiometric imbalances to occur that can affect the properties of the polymer matrix in the vicinity of the fiber surface. This work reports the results of an experimental study of the influence of stoichiometric imbalance on the thermoelastic properties of an epoxy–amine resin. It is shown that the modulus and glass transition temperature are significantly affected by relatively small variations in stoichiometry. These results suggest that a fiber-induced interphase region in thermosetting composites can exhibit material properties that are significantly different from those of the bulk resin. © 1992 John Wiley & Sons, Inc.     

Kinetics modeling of a modified epoxy–amine formulation cured by thermal and microwave energy

The reaction kinetics of a rubber-modified epoxy formulation cured by microwave or thermal energy were investigated. Two phenomenological models were developed to predict the time and temperature dependence of the conversion for the neat and the modified systems. Good agreement was observed between the kinetic models and experimental results generated by chromatographic and calorimetric techniques. The same kinetic behavior was observed whatever the curing process (conventional or microwave heating). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 543–552, 1998     

Biodegradable soy protein–polyester blends by reactive extrusion process

Blends of soy protein concentrate and biodegradable polyester (Eastar Bio Copolyester, EPE) were prepared by using glycerol as a compatibilizing agent. Good miscibility was obtained only when the soy protein was initially combined with glycerol under high shear and at elevated temperatures in an extruder. Under these conditions, partial denaturing of the soy protein led to specific interactions between functional groups of the protein with the glycerol. The extrusion conditions and appropriate screw configuration were the critical factors affecting the reactivity of the protein and hence, the properties of the blends. Screws with large kneading blocks that produced high shear mixing were preferred and led to thermoplastic blends characterized by high elongation and high tensile strength. The morphology of these soy protein/polyester blends was studied by using environmental scanning electron microscopy (ESEM) and indicated good wetting of the soy protein particles within the polyester matrix. The thermal properties were studied by differential scanning calorimetry (DSC) and showed a lower degree of crystallinity and a continuous depression of the melting point of the polyester as the concentration of protein was increased. The possibility of using soy protein concentrate instead of the more expensive (higher purity) soy protein isolate in the preparation of biodegradable resins should lead to new commercial opportunities based on renewable, agricultural byproducts. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3231–3239, 2004     

The effect of bismaleimide resin on curing kinetics of epoxy–amine thermosets

An analysis of the cure kinetics of several formulations composed of diglycidyl ether of bisphenol-A (DGEBPA) and aromatic diamines, methylenedianiline (MDA) and diaminodiphenyl sulfone (DDS), in the absence and presence of 4,4′-bismaleimidodiphenylmethane (BM) was performed. The dynamic differential scanning calorimetry (DSC) thermograms were analyzed with the help of ASTM kinetic software to determine the kinetic parameters of the curing reactions, including the activation energy, preexponential factor, rate constant, and 60 min ½ life temperature. The effects of substitution of one curing agent for another, their concentration, and the absence and presence of BM resin and its concentration on curing behavior, ethalpy, and kinetic parameters are discussed. © 1996 John Wiley & Sons, Inc.     

用反应挤出法合成苯乙烯-异戊二烯嵌段共聚物

以同向紧密啮合双螺杆挤出机为反应器,有机锂为引发剂,采用混合单体加料方式,本体法一步合成了苯乙烯-异戊二烯嵌段共聚物。核磁共振谱图和透射电子显微照片均表明该共聚物具有纳米级多嵌段结构,其物理机械性能受异戊二烯质量分数的影响。     

反应挤出合成S/B嵌段共聚物的研究

以同向紧啮合双螺杆挤出机为反应器、有机锂为引发剂,采用混合单体加料方式,本体法一步合成了苯乙烯-丁二烯嵌段共聚物。^1H-NMR图谱表明该丁苯共聚物的结构以嵌段为主,无规链段为辅。其力学性能则体现出受丁二烯质量分数的影响。     

Selection of thinner for epoxy–amine system used as binder for polymeric mortars

Epoxy resin mortars are mainly used in the implementation of precast items used in the civil engineering field. The workability of these mortars represents a major obstacle to the development of this field. In order to improve this property, different types of thinners are selected to study their effect on the rheological properties of the epoxy–amine system. Rheological tests are performed in order to estimate the resin gel point and to measure its viscosity during the crosslinking reaction. It appears that viscosity is the lowest for mixtures prepared with methyl octanoate, o‐xylene, and butyl glycidyl ether. Methyl octanoate is chosen as an ecofriendly thinner. The curing process is evaluated by varying the amount of the selected thinner using isothermal and dynamic DSC to determine the end of crosslinking. The mechanical properties using dynamic mechanical analysis (DMA) and tensile resistance testing of the cured epoxy resin with different amounts of methyl octanoate are also investigated. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43970.     

Compatibilization of starch–polyester blends using reactive extrusion

Maleic anhydride (MA) and dicumyl peroxide (DCP) were used as crosslinking agent and initiator respectively for blending starch and a biodegradable synthetic aliphatic polyester using reactive extrusion. Blends were characterized using dynamic mechanical and thermal analysis (DMTA). Optical micrographs of the blends revealed that in the optimized blend, starch was evenly dispersed in the polymer matrix. Optimized blends exhibited better tensile properties than the uncompatibilized blends. X‐ray photoelectron spectroscopy supported the proposed structure for the starch–polyester complex. Variation in the compositions of crosslinking agent and initiator had an impact on the properties and color of the blends. POLYM. ENG. SCI. 46:248–263, 2006. © 2006 Society of Plastics Engineers     

Antibacterial materials: structure–bioactivity relationship of epoxy–amine resins containing quaternary ammonium compounds covalently attached

Bifunctional aminoalkyldimethylpropylammonium salts (N‐(3‐aminopropyl)‐N,N‐dimethylpentylammonium chloride, N‐(3‐aminopropyl)‐N,N‐dimethyloctylammonium chloride, N‐(3‐aminopropyl)‐N,N‐dimethyldecylammonium chloride, N‐(3‐aminopropyl)‐N,N‐dimethyldodecylammonium chloride) are synthesized and their structure‐dependent antibacterial effect against Gram‐negative Escherichia coli and Gram‐positive Lactococcus lactis is investigated. To this end, resins prepared from bisphenol A diglycidyl ether (2,2‐bis[4‐(glycidyloxy)phenyl]propane) and diethylenetriamine (2,2′‐diaminodiethylamine) as matrix and the bifunctional aminoalkyldimethylpropylammonium salts in a ratio of 6 mol% compared to epoxy components are used. A dependence of antibacterial effect on alkyl chain length of the quaternary ammonium compounds is observed for both species. Furthermore, resins with N‐(3‐aminopropyl)‐N,N‐dimethyldecylammonium chloride in varying concentrations up to 16 mol% for both organisms show a concentration‐dependent antibacterial effect of the quaternary ammonium salt. The antibacterial materials are characterized by differential scanning calorimetry, infrared spectroscopy and rheological studies. © 2013 Society of Chemical Industry     

Gas and water transport properties of epoxy–amine networks: Influence of crosslink density

The gas and water transport properties were studied on seven epoxy–amine networks that differ by their di/mono epoxy composition and their cure cycle. The characteristic parameters of transport M_∞ and D were determined in each case, and they show that the solubility and diffusion coefficients are influenced by their composition. The solubility increases with the extend of cure and with the decrease of dangling chains, and in both cases the evolution of the diffusivity is inverse. The variations of the solubility and diffusivity have been discussed as a function of two parameters: polar groups and unrelaxed holes of the glassy networks. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2058–2066, 2001     

Cyanuric acid–epichlorohydrin prepolymers

In this study, we investigated the reaction of cyanuric acid and epichlorohydrin (ECH). SnCl₄ was used as a catalyst. Several reaction conditions were tested, and the products were analyzed by means of Fourier transform infrared and ¹H‐NMR spectroscopy, hydroxyl group content, molar mass, elemental and thermal analysis, viscosity, and density. ECH reacted with the amine groups of the cyanuric acid ring to form lateral chains that contained chloroalkyl and hydroxyl end groups. Full substitution of the amine groups was observed in all of the synthesized products. The solvent used in the synthesis was found to be very important for the structure of the final prepolymers. When N,N‐dimethylformamide was used, relatively low‐molar‐mass prepolymers of cyanuric acid and ECH were obtained. When solvents with low dielectric constants were used, no reaction with cyanuric acid was observed. The prepared prepolymers were thermally stable up to 160°C. At this temperature, degradation started via the lateral chains. The viscosity of the products decreased as the ECH–cyanuric acid ratio increased, whereas the density remained basically constant. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3684–3691, 2006     

Synthesis and structure–property relationships of UV-curable urethane prepolymers with hard–soft–hard blocks

UV-curable urethane prepolymers derived from diisocyanates, rigid diols, and polypropylene glycols of different molecular weights and end-capped with 2-hydroxylethyl methacrylate were prepared by stepwise addition reactions. These prepolymers have the common structure, HEMA-hard segment-soft segment-hard segment-HEMA. As the weight ratio of soft segment to hard segment and thus the rigidity varied, the cured films from these prepolymers exhibited a wide range of mechanical and other key properties such as oxygen permeability.     

Kinetics and thermal characterization of epoxy‐amine systems

The curing behavior of epoxy resins was analyzed based on a simple kinetic model. We simulated the curing kinetics and found that it fits the experimental data well for both diglycidylether of bisphenol A–4,4′‐methylene dianiline and diglycidylether of bisphenol A–carboxyl‐terminated butadiene acrylonitrile–4,4′‐methylene dianiline systems. The kinetic results showed the curing of epoxy resins involves different reactive process and reaction stages, and the value of activation energy is dependent on the degree of conversion. By analyzing the effect of vitrification, at low curing temperature, we found the curing reaction at the later stage was practically diffusion‐controlled for unmodified resin, and the rubber component did not markedly decrease T_g at the early stage of reaction as would be expected. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2401–2408, 1999     

Synthesis and properties of elastomer‐modified epoxy–methacrylate sequential interpenetrating networks

The structure and properties of copolymerized sequential‐interpenetrating networks (SeqIPNs) synthesized from amine‐cured epoxies and free‐radical polymerized dimethacrylates were examined. Materials were synthesized with and without the incorporation of an epoxy‐terminated butadiene–nitrile reactive elastomer. Synthesis proceeded through full thermal cure of the epoxy–amine network, followed by polymerization of the methacrylate network. The methacrylate reactions were free‐radically induced using thermal (peroxide‐initiated) or photochemical [electron‐beam (e‐beam)] techniques. Fourier transform infrared spectroscopy was used to monitor epoxy–amine step‐growth polymerization in situ and to measure final cure conversion of methacrylates. Structural examination of the IPNs using atomic force microscopy and scanning electron microscopy revealed microphase separation in the neat–SeqIPN materials and macroscopic phase separation of rubber‐rich domains for elastomer‐modified networks. Dynamic mechanical analysis of the SeqIPN determined that the properties of the network are strongly dependent on the cure conditions. Furthermore, the viscoelastic behavior of the e‐beam–cured SeqIPN could be adequately described by the Williams–Landel–Ferry and Kohrausch–Willams–Watts equations, presumably because of a strong coupling between the epoxy–amine and methacrylate networks. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 530–545, 2001     

Biodegradable and functionally superior starch–polyester nanocomposites from reactive extrusion

Biodegradable starch‐polyester polymer composites are useful in many applications ranging from numerous packaging end‐uses to tissue engineering. However the amount of starch that can form composites with polyesters without significant property deterioration is typically less than 25% because of thermodynamic immiscibility between the two polymers. We have developed a reactive extrusion process in which high amounts of starch (approx. 40 wt%) can be blended with a biodegradable polyester (polycaprolactone, PCL) resulting in tough nanocomposite blends with elongational properties approaching that of 100% PCL. We hypothesize that starch was oxidized and then crosslinked with PCL in the presence of an oxidizing/crosslinking agent and modified montmorillonite (MMT) organoclay, thus compatibilizing the two polymers. Starch, PCL, plasticizer, MMT organoclay, oxidizing/crosslinking agent and catalysts were extruded in a co‐rotating twin‐screw extruder and injection molded at 120° C. Elongational properties of reactively extruded starch‐PCL nanocomposite blends approached that of 100% PCL at 3 and 6 wt% organoclay. Strength and modulus remained the same as starch‐PCL composites prepared from simple physical mixing without any crosslinking. X‐ray diffraction results showed mainly intercalated flocculated behavior of clay at 1,3,6, and 9wt% organoclay. Scanning electron microscopy (SEM) showed that there was improved starch‐PCL interfacial adhesion in reactively extruded blends with crosslinking than in starch‐PCL composites without crosslinking. Dynamic mechanical analysis showed changes in primary α‐transition temperatures for both the starch and PCL fractions, reflecting crosslinking changes in the nanocomposite blends at different organoclay contents. Also starch‐polytetramethylene adipate‐co‐terephthalate (PAT) blends prepared by the above reactive extrusion process showed the same trend of elongational properties approaching that of 100% PAT. The reactive extrusion concept can be extended to other starch‐PCL like polymer blends with polymers like polyvinyl alcohol on one side and polybutylene succinate, polyhydroxy butyrate‐valerate and polylactic acid on the other to create cheap, novel and compatible biodegradable polymer blends with increased toughness. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1072–1082, 2005