Blends of poly(ethylene terephthalate) and epoxy as matrix material for continuous fibre reinforced composites

Abstract

The morphology and mechanical properties of poly(ethylene terephthalate) (PET)–epoxy blends and the application of these blends in continuous glass fibre reinforced composites have been investigated. Epoxy resin was applied as a reactive solvent for PET to obtain homogeneous solutions with a substantially decreased melt viscosity. The epoxy resin in these solutions was cured using an amine hardener according to two different schedules. In the first, high temperature curing at 260°C preceded low temperature crystallisation of the PET at 180°C. In the second, the PET was allowed to crystallise prior to low temperature curing at 180°C. After cure, all blends revealed a phase separated morphology of dispersed epoxy in a continuous PET matrix. The flexural strength and failure strain of all cured blends showed an increase with increasing epoxy content, whereas the high temperature cured blends exhibited overall lower flexural properties than those cured at the lower temperature. Microstructural analysis and flexural properties of continuous glass fibre reinforced PET–epoxy laminates showed that the composites obtained had a low void content. These PET–epoxy laminates had increased inplane shear strength in comparison with unmodified PET based laminates, indicating considerably increased fibre–matrix adhesion.     

Synthesis and characterization of a new class of thermosetting resins: Allyl and propargyl substituted cyclopentadiene derivatives

A series of all-hydrocarbon resins were synthesized by reacting cyclopentadiene allyl chloride, propargyl chloride, or a mixture of allyl chloride and propargyl ide, under phase transfer conditions. Phase transfer reactions with and without added solvents, and with either quaternary ammonium or crown ether catalysts, yielded similar products consisting of a mixture of 1,1-disubstituted cyclopentadiene (minor amount) and 2-3 isomers each of tri-, tetra-, penta-, and hexa-substituted derivatives. No further reaction of each these components possible. The overall substitution pattern varied little with changes in reaction conditions although limiting the allyl chloride content led to still reactive, partially substituted products. Incorporation of all-propargyl and high propargyl-to-allyl mixed functionalities on cyclopentadiene yielded products whose stability was very hindering their thorough characterization. Preliminary evaluation was there-carried out for mixed resins with lower propargyl functionality. The allyl substituted resin (allylated cyclopentadiene, ACP) underwent thermal cure lout initiator at around 200°C while allyl/propargyl substituted resin (7:1 ratio, APCP) showed a faster, lower temperature cure at around 120°C. Cationic cure of ACP was also initiated by a novel sulfonium salt at around 100°C. Neat resin when cured at 200°C gave material with a flexural storage modulus 2 of about 300 MPa. Further cure at 250°C raised the modulus to 1.2 GPa. resin gave composites with excellent properties when used with glass and on fibers. Flexural modulus values (by DMA) of ∼ 66 GPa were obtained for ACP/carbon fiber composites compared with 42 GPa for epoxy/carbon composites made in our laboratories using commercially available materials. The modulus values at 300°C dropped to 10% of the room temperature value for the epoxy composites, while the ACP/carbon composite maintained 60% of its room temperature value at 300°C. When brought back to ambient temperature, the modulus of latter sample had increased to 80 GPa and that of the epoxy composite dropped to 23 GPa. Glass fiber ACP composites performed similar to an epoxy composite up to 200°C but maintained properties up to 300°C while those of the epoxy were drastically reduced. TGA analysis of both cured ACP resin and its composites showed decomposition beginning at 375°C. Three-point-bending tests indicated very high modulus with brittle failure for ACP composites. Scanning electron micrographs showed moderate bonding of the new resin to both carbon glass fiber surfaces. This new class of thermosetting resins offers excellent potential for application in low-cost glass and carbon composites with good thermal and physical properties.     

A novel rapid cure epoxy resin with internal mold release

Mold preparation, material layup, and cure times for thermoset-based composites often limit their use in high-volume applications. As such, new rapid cure epoxy resins are being developed to achieve a complete cycle time within 3 min. In this research, calorimetry and rheometry are used to examine and model two novel rapid cure epoxy resin systems with internal mold release. The rapid cure epoxy resins followed an autocatalytic cure kinetic and William–Landel–Ferry diffusion model. The rapid cure epoxy resin was shown to achieve 94% cure in 2 min at 150°C. However, adding an additional 2.5 wt% internal mold release hindered the first step of the reaction, which delayed the second reaction step since the final degrees of cure were similar. Furthermore, the resin viscosity followed a modified William–Landel–Ferry equation and at 120°C could maintain a viscosity below 5 Pa s for 4.1 min. These models provided valuable insight into the range of processing conditions these novel resins could experience during impregnation and molding processes.     

次中温环氧树脂固化剂(8104)的性能研究

本文研究了一种次中温环氧树脂固化剂（８１０４）的工艺性及其固化物的性能。试验结果表明：８１０４固化剂可在５０－８０℃下固化环氧树脂;与环氧树脂的混合物在室温下的适用期大于１０ 小时;固化物具有极好的韧性、良好的耐湿热性能和力学性能。因此,８１０４可用于大面积和大体积的环氧树脂固化施工,也可作为模具树脂、涂料及结构材料的固化剂。     

Exploiting graphene oxide as a potential additive to improve the performance of cold-mixed epoxy asphalt binder

As a green material for high-performance paving, cold-mixed epoxy asphalt (CEA) should be improved in compatibility, mechanical performance, and thermal stability. This work is going to estimate the potential of graphene oxide (GO) as an additive for preparing GO/CEA composites with different GO content from 0 to 0.2 wt%. The influences of GO on the structure and performances of CEA were evaluated by Fourier transform-infrared spectrum, fluorescence microscopy, viscosity, thermogravimetric analysis, tensile test, and dynamic mechanical analysis. Results showed that the functional groups on GO reacted with CEA and improved the compatibility of epoxy resin and asphalt. The viscosity of the GO/CEA composites increased slightly and the pot life decreased significantly, with GO loading increasing. The cured GO/CEA composite with 0.1 wt% GO had the best heat resistance and showed a gentle thermal decomposition. GO improved the toughness of the cured CEA and had a certain weakening effect on its strength. The introduction of GO lowered the glass transition temperature of the cured CEA from 51.4 to 47.1 °C and decreased its storage modulus. The preliminary exploration of this study shows that the modification of GO for CEA is feasible, and it is expected to prolong the service life of CEA.     

The Study of Fiber-Matrix Interactions Via FT-IR Microscopy and NMR Imaging

Model composites of Kevlar-49® and D-glass fiber/epoxy systems were analyzed using NMR imaging and FT-IR microscopy. The surfaces of both reinforcing agents were found to affect the curing process of the epoxy significantly. The NMR images reveal an accelerated rate of cure in the proximity of the fibers as compared with the bulk, indicating strong interactions between the fibers and the matrices. To characterize these interactions spectroscopically, FT-IR microscopy was performed on Kevlar-reinforced microcomposites. Transmission spectra and IR functional group images reveal a preferential segregation of the epoxy resin to the fiber surface. Thin films of epoxy resin deposited on single Kevlar filaments were also examined using FT-IR microscopy. Spectra and IR images from these samples suggest that the amine group of the Kevlar fiber is reacting with the epoxide ring of the resin to catalyze the curing process.     

Characteristics of epoxy resin cured with in situ polymerized curing agent

In order to improve the heat resistance of a cured epoxy resin together with reducing the viscosity of the resin composition, an epoxy resin was cured with a curing agent formed from the radical copolymerization of vinyl monomers during the cure process of the epoxy resin. N-phenylmaleimide and p-acetoxystyrene were used as vinyl monomers of the curing agent. The epoxy resin was cured by the insertion reaction of the ester group of the in situ polymerized curing agent and the epoxy group of the epoxy resin. In the cure system of the epoxy and the phenol resins, reduction of the viscosity of the resin composition was achieved by replacing some or all of the phenol resin with these monomers. When all phenol resins were replaced by these monomers, the viscosity of resin composition (0.01 Pa s at 70 °C) decreased by about 1/2000 compared with that of the system with only phenol resin (21 Pa s at 70 °C). The glass transition temperature (T_g) of the cured resin with no phenols was 174 °C, an improvement of 17 °C compared with that of the system cured with only phenol resin. The flexural strength of the new resins remained unchanged.     

Moisture sorption on the wetting behavior of poly(p-phenylene terephthalamide) fibers in water and epoxy resin

The moisture sorption of poly(p-phenylene terephthalamide) (PPTA) fibers and the effects of moisture on the wetting behavior of these fibers in water and in an epoxy resin were studied. The moisture regains in the Kevlar 149 fibers followed a third order polynomial dependency on increasing relative humidity at 23°C. When preconditioned at 0% relative humidity (R.H.), water wettability of Kevlar 49 fibers was superior to that of Kevlar 149 fibers. Resin wettability of the dried Kevlar 49 fibers, on the other hand, was lower than that of Kevlar 149 fibers. Wettability in water and resin of these two fiber types was affected differently by moisture. Exposure to 97% R.H. moisture level significantly lowered water wettability of Kevlar 49 fibers but did not affect the wettability of Kevlar 149 fibers in water. Resin wettability of Kevlar 49 fibers was improved upon exposure to moisture, but the opposite was observed on Kevlar 149 fibers.     

Bismaleimide resin modified with diallyl bisphenol A and diallyl p‐phenyl diamine for resin transfer molding

O,O′‐diallyl bisphenol A (DBA) and N,N′‐diallyl p‐phenyl diamine (DPD) were used for the reactive diluents of 4,4′‐bismaleimidodiphenol methane (BDM). The objective was to obtain a modified BDM resin system suitable for resin transfer molding (RTM) process to prepare the advanced composites. The processing behavior was determined by time–temperature–viscosity curves, gel characteristics, and differential scanning calorimetry (DSC). The injection temperature of the resin system in RTM could be 80°C, at which its apparent viscosity was only 0.31 Pa/s, and the apparent viscosity was still less than 1.00 Pa/s after the resin was held at 80°C for 16 h. The gel time test result indicated that at low temperatures, the reactivity of the resin system is low, whereas at high temperatures, the resin could cure very fast, which was beneficial to RTM. The postcure of the cured resin at a given temperature was necessary because the resin had a wide and flat cure exothermic peak, observed by DSC curve. The cured resin displayed both high heat and hot/wet resistance and high mechanical properties, especially tensile strength, tensile modulus, and flexural strength at room temperature, which reached 96.2 MPa, 4.8 GPa, and 121.4 MPa, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2245–2250, 2001     

The Study of Fiber-Matrix Interactions Via FT-IR Microscopy and NMR Imaging

Model composites of Kevlar-49® and D-glass fiber/epoxy systems were analyzed using NMR imaging and FT-IR microscopy. The surfaces of both reinforcing agents were found to affect the curing process of the epoxy significantly. The NMR images reveal an accelerated rate of cure in the proximity of the fibers as compared with the bulk, indicating strong interactions between the fibers and the matrices. To characterize these interactions spectroscopically, FT-IR microscopy was performed on Kevlar-reinforced microcomposites. Transmission spectra and IR functional group images reveal a preferential segregation of the epoxy resin to the fiber surface. Thin films of epoxy resin deposited on single Kevlar filaments were also examined using FT-IR microscopy. Spectra and IR images from these samples suggest that the amine group of the Kevlar fiber is reacting with the epoxide ring of the resin to catalyze the curing process.     

Aminimide as hardener/curing promotor for one part epoxy resin composition

Three kinds of aminimide compounds were examined as latent hardeners/promotors for epoxy resins. Since aminimides are thermolyzed to generate tertiary amine and isocyanate, the compounds are useful as polymerization initiators for the epoxy group as well as promotors for epoxy–acid anhydride reaction. The pot life was over 30 days at 40°C for a formulated one-part epoxy resin system. In comparison with epoxy resins cured with conventional hardeners, several interesting characteristics of the mechanical and electrical properties were observed. In particular, the epoxy resins cured by aminimides exhibited high tensile strength and high impact strength, which make them excellent curing agents for adhesive applications. The reasons for these unique properties are discussed.     

Synthesis and characterization of bis(4‐cyanato‐3,5‐dimethylphenyl)anisylmethane/epoxy/glass fiber composites

Bis(4‐cyanato‐3,5‐dimethylphenyl)anisylmethane was prepared by treating CNBr with bis(4‐hydroxy‐3,5‐dimethylphenyl)anisylmethane and blended with commercial epoxy resin in different ratios and cured at 120°C for 2 h, 180°C for 1 h, and postcured at 220°C for 1 h using diamino diphenyl methane as curing agent. Castings of neat resin and blends were prepared and characterized. The composite laminates were also fabricated with glass fiber using the same composition. The tensile strength of the composites increased with increase in cyanate content (3, 6, and 9%) from 322 to 355 MPa. The fracture toughness values also increased from 0.7671 kJ/m², for neat epoxy resin, to 0.8615 kJ/m², for 9% cyanate ester‐modified epoxy system. The 10% weight loss temperature of pure epoxy (358°C) was increased to 390°C by the incorporation of cyanate ester resin. The incorporation of cyanate ester up to 9% in the epoxy resin increases the T_g from 143 to 147°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Curing kinetics and viscosity change of a two‐part epoxy resin during mold filling in resin‐transfer molding process

The curing kinetics and the resulting viscosity change of a two‐part epoxy/amine resin during the mold‐filling process of resin‐transfer molding (RTM) of composites was investigated. The curing kinetics of the epoxy/amine resin was analyzed in both the dynamic and the isothermal modes with differential scanning calorimetry (DSC). The dynamic viscosity of the resin at the same temperature as in the mold‐filling process was measured. The curing kinetics of the resin was described by a modified Kamal kinetic model, accounting for the autocatalytic and the diffusion‐control effect. An empirical model correlated the resin viscosity with temperature and the degree of cure was obtained. Predictions of the rate of reaction and the resulting viscosity change by the modified Kamal model and by the empirical model agreed well with the experimental data, respectively, over the temperature range 50–80°C and up to the degree of cure α = 0.4, which are suitable for the mold‐filling stage in the RTM process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2139–2148, 2000     

Characterization of the cure of TGDDM/DDS epoxy resins by chemiluminescence I. Spectral and thermal analysis

The emission of weak visible chemiluminescence (CL) during the cure of a tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM)-based epoxy resin, with three different concentrations of 4,4′-diaminodiphenylsulfone (DDS) has been studied at 135°C. Spectral analysis indicates that the CL originates from trace oxidation of the TGDDM resin and the emission intensity is sensitive to the viscosity changes during cure. From thermal analysis data, sharp discontinuities in CL intensity are shown to occur at the gel point. The temperature dependence of CL from a cured resin also shows a sharp discontinuity at T_g. These results indicate that CL provides a sensitive monitor of both the kinetics of gelation and the network formation in this epoxy resin.     

Synthesis and characterization of chlorinated soy oil based epoxy resin/glass fiber composites

Composites with good toughness properties were prepared from chemically modified soy epoxy resin and glass fiber without additional petroleum based toughening agent. Chlorinated soy epoxy (CSE) resin was prepared from soybean oil. The CSE was characterised by spectral, and titration method. The prepared CSE was blended with commercial epoxy resin in different ratios and cured at 85°C for 3 h, and post cured at 225°C for 2 h using m‐phenylene diamine (MPDA) as curing agent. The cure temperatures of epoxy/CSE/MPDA with different compositions were found to be in the range of (151.2–187.5°C). The composite laminates were fabricated using epoxy /CSE/MPDA‐glass fiber at different compositions. The mechanical properties such as tensile strength (248–299 MPa), tensile modulus (2.4–3.4 GPa), flexural strength (346–379 MPa), flexural modulus (6.3–7.8 GPa) and impact strength (29.7–34.2) were determined. The impact strength increased with the increase in the CSE content. The interlaminor fracture toughness (G_IC) values also increased from 0.6953 KJ/m² for neat epoxy resin to 0.9514 KJ/m² for 15%CSE epoxy‐modified system. Thermogravimetric studies reveal that the thermal stability of the neat epoxy resin was decreased by incorporation of CSE. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Novel cycloaliphatic epoxy resins. II. Curing reaction with BF3MEA and its cured properties

The BF₃MEA curing reaction and the cured properties of novel cycloaliphatic epoxy resins (CE-resins), which were derived from an octadienyl compound, were studied. Gelation time and the DSC scan of the CE resins, with BF₃MEA hardener, proved that the reactivity of the CE resins is intermediate among the reactivities of the conventional resins; it was found that the CE resins react faster than DGEBA, but slower than the conventional cycloaliphatic epoxy resins. The pot life of the CE- (III) resin with BF₃MEA hardener proved to be over 30 days at a temperature of 20°C. The thermal properties are affected by the amount of BF₃MEA used and the curing conditions. CE-(III) showed the highest HDT of over 200°C with 2–3 phr of BF₃MEA. The flexural properties of CE-(I) proved to be flexible and tough. CE-(II) exhibited the highest strength and elongation, while CE-(III) had the same flexural properties as DGEBA. Furthermore, the blending of CE-(II) with DGEBA produced greater flexural strength and greater elongation than each original resin had. The thermal stability at elevated temperature and the water resistance of the cured CE resins proved to be inferior to those of DGEBA and novolac epoxy resin, probably due to the use of BF₃MEA. These results suggest the CE resin will provide a new application for a one-component curing system for composites. © 1993 John Wiley & Sons, Inc.     

Investigation of readily processable thermoplastic-toughened thermosets. II. Epoxy toughened using a reactive solvent approach

The fracture toughness of epoxy thermosets was increased by up to 220% using very low-molecular-weight (∼ 1000 g/mol) imide thermoplastic. The objective was to produce a low-viscosity prepolymer that could be easily autoclave-processed to give a tough thermoset. Here, an homogenous epoxy prepolymer was prepared by first synthesizing very low-molecular-weight linear aromatic imide (∼ 1000 g/mol) directly in a liquid allyl phenol reactive solvent, followed by dissolution of the epoxy (Epon® 825) and the cure agent (DDS) directly in the thermoplastic solution. The allyl phenol both cures into the epoxy network, through phenol functional groups, and accelerates the cure. The viscosity of the pure epoxy was 1.4 Pa · S at 30°C. The prepolymer formulations ranged from ∼ 5–33 Pa · S at 30°C, but all reduced to less than 1 Pa · S at 90°C. The onset of cure is well above 90°C so the prepolymer viscosity is within the range for autoclave processing. The cured resin plaques were not transparent, but phase-separated domains were not found by scanning electron microscopy, indicating that the domain size is below the detection limit of the instrument. The reactive solvent causes a decrease in both the T_g and the high temperature modulus of the thermoset. Introduction of the thermoplastic results in partial recovery of the T_g and modulus. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 935–942, 1998     

Preparation and properties of novel hybrid resins based on acetylene‐functional benzoxazine and polyvinylsilazane

A serial of addition‐curable hybrid resins for resin matrix of advanced composites are prepared by thermal prepolymerization between acetylene‐functional benzoxazine(BZ) and polyvinylsilazane(PSN) with various weight ratios. Processing capability of BZ‐PSN resin is investigated by measuring viscosity. Cure behavior is investigated by differential scanning calorimetry (DSC) and Fourier transform infrared (FT‐IR) spectra. Thermal property of cured BZ‐PSN resin is investigated by Thermogravimetric analysis (TGA) and Dynamic mechanical analysis (DMA). BZ‐PSN resin shows a low viscosity of 40–180 mPa·s between 60 and 90°C, and maintains the low viscosity for 6 h, indicating that the resin is suitable for resin transfer molding (RTM) process to fabricate composites. DSC results show that BZ‐PSN resin can be cured completely at about 250°C without adding any other curing additives. FT‐IR shows the reaction between BZ and PSN take place. TGA shows that thermal stability of cured BZ‐PSN resin is increased with the content of polyvinylsilazane increasing both in nitrogen and in air. DMA shows cured hybrid resins have excellent thermal properties. The excellent processability and thermal properties suggest that BZ‐PSN resin is a promising candidate for resin matrix of advanced composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3794–3799, 2013     

Phenolic‐epoxy matrix curable by click chemistry—synthesis,curing, and syntactic foam composite properties

Alkyne functional phenolic resin was cured by azide functional epoxy resins making use of alkyne‐azide click reaction. For this, propargylated novolac (PN) was reacted with bisphenol A bisazide (BABA) and azido hydroxy propyloxy novolac (AHPN) leading to triazole‐linked phenolic‐epoxy networks. The click cure reaction was initiated at 40–65°C in presence of Cu₂I₂. Glass transition temperature (Tg) of the cured networks varied from 70°C to 75°C in the case of BABA‐PN and 75°C to 80°C in the case of AHPN‐PN. DSC and rheological studies revealed a single stage curing pattern for both the systems. The cured BABA‐PN and AHPN‐PN blends showed mass loss above 300°C because of decomposition of the triazole rings and the novolac backbone. Silica fiber‐reinforced syntactic foam composites derived from these resins possessed comparable mechanical properties and superior impact resistance vis‐a‐vis their phenolic resin analogues. The mechanical properties could be tuned by regulating the reactant stoichiometry. These low temperature addition curable resins are suited for light weight polymer composite for related applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41254.     

Effects of resin storage aging on rheological property and consolidation of composite laminates

The ability to predict the viscosity of thermoset resin is important to understand the manufacturing process of composites and optimize the processing parameters. During resin or prepreg storage course, the cure reaction may happen and the degree of cure increases gradually. The storage aging effect reduces the fluidity of resin, and hence alters the processability of resin. In this article, the rheological properties of an epoxy resin and a bismaleimide resin used in composite autoclave process were measured and a viscosity model was established, which can predict the viscosity progression during cure for different aging degree of resin. Moreover, a computer simulation method was used to study the effects of aging degree on the composite consolidation and the processing operations. It is found that the viscosity model of aged resin can be obtained by modified dual Arrhenius model of fresh resin with the dynamic rheological measurement. The resin aging strongly alters the flowability, so influences composite consolidation. According to the simulated results, the processing parameters need to be adjusted to achieve cured composites with appropriate fiber content. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers