Influence of curing conditions on the morphology and physical properties of epoxy resins modified with a liquid polyamine

A diglycidyl ether of bisphenol-A (DGEBA) epoxy resin has been stoichiometrically cured with cycloaliphatic amine 4,4′-diamino-3,3′-dimethylcyclohexylmethane (3DCM) and modified with an amine terminated oligomer polyoxypropylenetriamine (POPTA) at a concentration of 15 wt %. Mixtures, postcured at the same temperature, have been precured at different temperatures. Phase separation takes place before gelation at all precure temperatures used. The variation in the glass transition region of the mixtures has been analyzed by dynamic mechanical measurements. Mechanical properties and fracture toughness of the modified mixtures have been related to their microstructural spherical features. Results are compared to those for the unmodified mixtures cured with different precure temperatures. © 1997 John Wiley & Sons, Inc.     

不饱和聚酯/环氧树脂嵌段共聚树脂的光固化研究

光固化涂料以其节省能源、减少空气污染、固化速度快、适用于自动化流水线涂布等特点而引起涂料行业的关注 .随着世界范围内对环境保护的日益重视和绿色科技的蓬勃发展 ,光固化技术因其能有效地控制空气污染 ,特别是可以大大减少挥发性有机物的排放而越来越受到青睐[1] .不饱和聚酯树脂 (ＵＰＲ)型的光固化树脂是发展最早和销售量最大的光固化树脂 .它是由二元羧酸与多羟基醇共缩合的缩聚物与活性单体的混合产物 ,二元羧酸中含有部分不饱和成分 .主要用于光敏树脂印刷版、光敏油墨、光敏涂料及印刷电路版的光致抗蚀膜等 .但是感光不饱和聚酯…     

Influence of glass transition temperature of crosslinked unsaturated polyester resin/styrene formulations on the final conversion after an isothermal curing at 100°C

SMC (sheet molding compound) is a composite based on fibers‐reinforced unsaturated polyester (UP) resin molded usually at 140°C to 170°C under a pressure of 60 to 100 bars. In order to develop new SMC formulations that can be molded at lower temperature (100°C) for economic and environmental reasons, the formulation of the composite had to be completely modified, both to allow a rapid reaction at 100°C, but also to avoid a vitrification phenomenon due to the fact that the glass transition temperature (Tg) of the SMC parts becomes, during the molding process, higher than the mold temperature. In this paper, the relation between the molding temperature, the glass transition temperature, and the final conversion of UP resin/styrene formulations has been underlined. The Tg of the cured resin was decreased by two different ways. The first way involved the reduction of the crosslinking density of the UP resin by using a blend of two resins, a pure maleic and a more flexible one. This blend allows to adjust the Tg over a temperature range from 197°C (Tg of the pure UP resin) to 75°C (Tg of the pure flexible resin). The second way consisted in the addition of butyl methacrylate (BuMA), a reactive plasticizer, to the formulation, allowing a decrease of the final material's Tg from 197°C to 130°C by replacing 35 wt% of styrene by BuMA. These two methods allow to obtain a final conversion of 99% after 8 minutes of molding at 100°C.     

Flame Retardancy and Kinetic Behavior of Ammonium Polyphosphate–Treated Unsaturated Polyester/Phenolic Interpenetrating Polymer Network

In this study, the flammability and kinetic behavior of flame retardant unsaturated polyester (UP)/phenolic resin were investigated. The flame retardant ammonium polyphosphate (APP) was used in this research to improve the flame resistance of a UP/phenolic resin interpenetrating polymer network (IPN). The flame resistance of UP improved from none to V-0 classification by adding phenolic resin and APP. Kinetic behavior study of UP, UP/phenolic, and APP-filled UP/phenolic IPN was carried out by the Borchardt and Daniels method. The results indicated that modification of flammable UP resin markedly improved the total heat release volume of UP and the flame retardancy of the IPN network structure was also enhanced.     

Oriented array of polyethylene-block-poly(ethylene oxide) nanoplatelets in unsaturated polyesters cross-linked coatings

Transparent coatings of cross-linked unsaturated polyester (UP) containing staggered platelets of polyethylene-block-poly(ethylene oxide) with their normal perpendicular to the substrate have been readily prepared by a solvent assisted spin-coating method. For this purpose, homogeneous liquid dispersions of block copolymer platelets in liquid UP resin have been prepared using a selective solvent, deposited onto flat substrates by spin-coating and converted into a transparent solid layer by photochemical cross-linking. Although such stratified morphology has been already reported for inorganic nanoplatelets (typically clay particles), we report for the fist time the formation of such stratified morphology in fully organic system. The shear-induced origin of this organization has been confirmed by the rheological properties of the uncured systems where a pronounced non-Newtonian behavior has been observed.     

Tannic acid: A sustainable crosslinking agent for high glass transition epoxy materials

Epoxy thermosets have revolutionized the coating, adhesive, and composite industries but the chemicals from which they are synthesized have significant effects on the environment and human health not only precure but also after crosslinking has occurred. In this study, we propose tannic acid (TA) as an alternative epoxy hardening agent for commercially available epoxy resin, the diglycidyl ether of bisphenol A (DGEBA). The resulting thermosets were characterized by Fourier transform infrared spectroscopy, optical microscopy, dynamic mechanical analysis, differential scanning calorimetry, compression testing, and thermogravimetric analysis. The results from this study showed that at temperatures above 100 °C, the compatibility of TA in DGEBA was significantly increased for loading levels up to 37% weight of TA in DGEBA, something that has not been seen before in literature. It was also discovered that at high loading levels, the resulting materials had glass transition temperatures at and above 200 °C. The resulting material was proposed as a more sustainable alternative to amine or acid hardened epoxy thermosets and was particularly useful in high‐temperature applications. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1468–1480     

A study of the combustion and fire-retardance behaviour of unsaturated polyester/phenolic resin blends

The thermal degradation and combustion behaviour of an interpenetrating network (IPN) structure of unsaturated polyester UP resin and a resole type of phenolic resin was studied. Thermal gravimetric analysis (TGA) was used to monitor the degree of thermal decomposition for the UP/phenol IPN structure and the change of the oxygen index (OI) was used to describe the variation of the combustion behaviour. The smoke density was measured via a non-flaming process to detect the amount of smoke generated during the combustion. A homemade cone calorimetric dynamic flammability evaluation system was assembled to analyse the gas evolved and to measure the heat release rate (HRR) during the combustion. Under simulated conditions of a burning field at the temperature of 757°C, the variation of the concentration of carbon monoxide (CO) and the HRR of the UP/phenol IPN structure were studied. The results show that modification of the essentially flammable UP resin by the phenol structure to form an IPN system cannot only remarkably improve the heat resistance but also help to suppress the smoke, toxic gas and heat release during the combustion.     

高岭土对不饱和聚酯树脂的热稳定性、阻燃及力学性能的影响

不饱和聚酯树脂;高岭土;纳米复合材料;原位聚合;阻燃;成炭     

Polyhedral oligomeric silsesquioxane (POSS) reinforced-unsaturated polyester hybrid nanocomposites: Thermal,thermomechanical and morphological properties

Unsaturated polyester (UP)-POSS hybrid nanocomposites have been developed successfully through the reaction between maleimide groups Octa (maleimido phenyl) silsesquioxane (OMPS) and olefinic reactive sites (maleimide and styrenic units) present in the unsaturated polyester resin system through free radical polymerization using benzoyl peroxide (BP) as the initiator. The hybrid molecular structure of nanocomposites resulted was evaluated by FT-IR spectroscopy. The data obtained from XRD, SEM and TEM analysis ascertain the presence of homogeneous morphology and nanoscale dispersion of OMPS into the polyester hybrid nanocomposites. Data resulted from thermal (DSC and TGA) and thermo-mechanical (DMA) studies indicated that the incorporation of octamaleimide functionalized POSS into unsaturated polyester systems appreciably improved the thermal properties of the hybrid nanocomposites according to their percentage concentration.     

Thermomechanical properties of cured isophtalic polyester resin modified with poly(ε-caprolactone)

The effect of a low profile additive, poly(ε-caprolactone) (PCL), on the thermal and mechanical properties of unsaturated polyester resins (UP) was investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and tensile tests. The morphology of the systems has been studied by scanning electronic microscopy (SEM). Two PCL molecular mass were selected (PCL2: M _n = 2000 g mol⁻¹ and PCL50: M _n = 50000 g mol⁻¹) to analyze the influence of the molecular mass and the content of PCL on the UP resins and to establish the relation between thermomechanical behavior and morphology. DSC and DMTA glass transition temperatures (T _g) of the UP cured samples containing PCL indicate that PCL2 is miscible with UP whereas for UP + PCL50 system, T _g values are very close to the ones corresponding to neat UP. Besides in UP + PCL2 systems, one phase morphology is observed in which PCL2 would act as solvent of the reacting mixture along curing process; however, UP + PCL50 systems present phase-separated morphology. The presence of PCL2 and PCL50 in UP resin leads to a decrease of the tensile strength and the Young′s modulus as much notorious as the PCL concentration increases. For UP + PCL2 system the elongation at fracture increases in relation to neat UP, increasing as well with the PCL content.     

Preparation and properties of new flame retardant unsaturated polyester nanocomposites based on layered double hydroxides

The preparation of new layered double hydroxides/unsaturated polyester (LDH/UP) nanocomposites was performed and the effect of LDH on the resin properties was studied. Two different organo-LDHs have been prepared, adipate-LDH (A-LDH) and 2-methyl-2-propene-1-sulfonate-LDH (S-LDH); in order to evaluate the influence of these nanofillers, samples with two different concentrations were dispersed in the matrix. The physical, thermal, mechanical and fire reaction properties of nanocomposites were studied. Intercalated layered structures were observed for the different organo-LDH loadings (1 and 5 wt%). Mechanical properties studied under flexural tests show that incorporation of organo-LDH in the resin reduces the flexural strength of polyester resin while the flexural modulus is unchanged for the S-LDH/UP composites and increased with 1 wt% of A-LDH. Adding 1 wt% of A-LDH to the resin produces an important reduction on the flexural strength, but an increase of the flexural modulus. The study of fire reaction properties, using cone calorimeter, suggested a significant reduction in the UP flammability, by 46 and 32%, by incorporating 1 wt% of A-LDH and 5 wt% S-LDH, respectively. Mass loss curves show enhanced char formation with the different loads tested while the amount of evolved smoke remains quite unchanged.     

IFSS, TG, FT-IR spectra of impregnated sugar palm (Arenga pinnata) fibres and mechanical properties of their composites

This study aimed to investigate the effect of resin impregnation on the interfacial shear strength (IFSS), thermogravimetric (TG) and fourier transform infrared (FT-IR) of sugar palm (Arenga pinnata) fibres. In addition, the effect of resin impregnation on the mechanical properties of sugar palm fibre reinforced unsaturated polyester (UP) composites was also studied. The fibres were impregnated with UP via vacuum resin impregnation process at a pressure of 600 mmHg for 5 min. Composites of 10, 20, 30, 40 and 50 % fibre loadings were fabricated and tested for tensile and flexural properties. It was observed that the impregnation process caused the fibres to be enclosed by UP resin and this gave a strong influence to the increase of its interfacial bonding by the increase of its IFSS from single fibre pull-out test. It was also observed with TG and FT-IR spectra that the impregnated fibre had lower moisture uptake than the control and there was no significant increase in thermal stability of the impregnated fibre. The sequence of fibre decomposition started from the evaporation of moisture, hemicelluloses, cellulose, lignin and finally ash content and the presence of these components were proven by FT-IR spectra. For the composite specimens, due to the high interfacial bonding of the impregnated fibre and the matrix, the impregnated composites showed consistently higher tensile strength, tensile modulus, elongation at break, flexural strength, flexural modulus and toughness than the control samples. It was also observed that 30 % fibre loading gave optimum properties.     

Composite cure kinetic analysis of unsaturated polyester free radical polymerization

Curing kinetics of unsaturated polyester resin system exhibiting apparent induction periods was investigated by modeling free radical initiation and propagation processes. The isothermal curing induction time as well as the maximum-rate time provided the same activation energy in the Arrhenius relation, and therefore, the isothermal curing master curve was constructed by using the reduced time method. Two model elementary rate equations for radical and monomer were proposed to describe the free radical polymerization of unsaturated polyester resin systems. The power law was adopted to express the conversion dependence function of the initiation efficiency and the monomer reaction rate. Demonstrating the capability of the developed model, the agreement between experimental and predicted data was excellent in both isothermal and dynamic-heating conditions, even with the same model parameters in different thermal conditions. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2447–2456, 1997     

The influence of chemical modification of unsaturated polyesters on viscoelastic properties and thermal behavior of styrene copolymers

The influence of chemical modification of unsaturated polyesters on viscoelastic properties and thermal behavior of styrene copolymers has been investigated by DMA and TG analyses. Chemical modification of unsaturated polyesters obtained in polycondensation of cyclohex-4-ene-1,2-dicarboxylic anhydride (THPA), maleic anhydride (MA) and suitable glycol: diethylene glycol (DEG) or triethylene glycol (TEG) was performed using 38–40% peracetic acid. It allowed to selective and successful oxidation of carbon-carbon double bonds in unsaturated polyesters giving modified unsaturated polyesters/unsaturated epoxypolyesters/containing both carbon-carbon double bonds in polyester chain and new functional groups-epoxy groups in cycloaliphatic rings. Both unsaturated polyesters and unsaturated epoxypolyesters were used as a component of styrene copolymers cured with different hardeners. It has been demonstrated that the use of modified unsaturated polyesters as a component of styrene copolymers allowed obtaining more stiffness and more cross-linked network structure compared to styrene copolymers based on unmodified polyesters. The higher values of storage modulus, glass transition temperatures and better thermal stability for styrene copolymers based on unsaturated epoxypolyesters were obtained.     

环氧树脂改性感光不饱和聚酯树脂的制备

用环氧树脂与不饱和聚酯反应 ,形成UP -PEP -UP嵌段共聚物 ,加入活性单体 ,制成改性感光树脂 .进行紫外光固化 ,结果表明 ,改性后的感光不饱和聚酯树脂的耐碱性、热稳定性和表面硬度大大提高 ,固化收缩率明显降低     

Mechanical properties of unsaturated polyester resins in relation to their chemical structure: 2. Plastic deformation behavior

The plastic deformation behavior of unsaturated polyester (UP) networks has been investigated in compression at constant strain-rate over a wide temperature range. The temperature evolution of the activation parameters is directly related to the local molecular dynamics of the different networks previously characterized by dynamic mechanical spectroscopy and high resolution ¹³C solid-state NMR. © 1994 John Wiley & sons, Inc.     

Novel biobased resins from blends of functionalized soybean oil and unsaturated polyester resin

Biobased unsaturated polyester (UPE) materials containing epoxidized methyl soyate (EMS) were processed with cobalt naphthenate as a promoter and 2‐butanone peroxide as an initiator. A certain amount of the UPE resin was replaced by EMS. The combination of the UPE and EMS resulted in an excellent combination for a new biobased thermoset material with a relatively high elastic modulus and a constant glass transition temperature with up to 25 wt % replacement with EMS. The Izod impact strength was almost constant while the amount of EMS was changed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 698–704, 2007     

Post-irradiation crosslinking of partially cured unsaturated polyester resin

The post-irradiation crosslinking of unsaturated polyester (UP) resin samples irradiated to different doses was monitored during the 15-days period. The post-reaction sensitivity of three experimental techniques was evaluated. Significant changes were detected by extraction analysis that also included determination of the free styrene content. The most substantial changes were detected by differential scanning calorimetry, even up to 5 days after the irradiation. The sensitivity and reproducibility of FTIR was the lowest. The first two techniques detected the influence of particular reaction periods, at which the radiation crosslinking was terminated, on the post-reaction.     

Flame-retardant properties of epoxide and unsaturated polyester resins modified with tertiary phosphine oxides containing chlorinated phenoxy groups

The flame-retardant properties of the epoxide resin “Epoxa AP-2” and the unsaturated polyester resin “Vinalkid 550P” modified with dimethyl(2,4,6-trichlorophenoxymethyl)phosphine oxide (DMPO), methyl-bis(pentachlorophenoxymethyl)phosphine oxide (MBPO) and tris(2,4,6-trichlorophenoxymethyl)phosphine oxide are examined. It is established that all three products are effective fire-retardants for epoxide as well as for unsaturated polyester resins. The effect is notable at about 10–15% presence. The oxygen indexes, determined by the ASTM-D-2863 method, show an increase of several units in comparison with the unmodified resins. The fire-retardant action of DMPO, MBPO and TTPO is significantly enhanced by the addition of Sb₂O₃.     

Effects of nano ZnO on strength and stability of unsaturated polyester composites

ZnO–glass fiber–unsaturated polyester composites have been prepared. On exposure to the metal halide lamp, their resistance to ultraviolet (UV) degradation is evaluated. Experimental results show that ZnO can reduce the UV degradation of the unsaturated polyester matrix. ZnO can significantly retard the UV degradation process of the matrix resin, and can also increase the impact strength of the composites under the experimental conditions. Differential scanning calorimetry (DSC) analyses also indicate that the addition of ZnO to unsaturated polyester may retard the crosslink process and catalyze the decomposition of the resin. However, after more than 40 hr of UV irradiation, it was crosslinked. SEM fracture morphology shows that nano ZnO could hinder crack growth and induce more cracks, and when the content of ZnO reaches 6 wt%, the impact fracture mechanism changes abruptly and plastic deformation appears, which indicates that 6 wt% for ZnO in unsaturated polyester could be considered as the critical content. Around the critical content, the particles are near enough to interact with each other and this results in the change of fracture mechanism. The results also indicate that the proper content of ZnO added into an unsaturated polyester could prolong the durability and lessen the reject rate of transparent glass fiber–polyester composites. Copyright © 2008 John Wiley & Sons, Ltd.