Curing Of Unsaturated Polyester Resins Research Articles

Sustainable synthesis and characterization of cobalt-based biocatalysts from olive stone waste for enhanced curing of unsaturated polyester resins

The functionalization of native olive wood shell stone for the formation of new active heterogeneous cobalt-based biocatalysts has been conducted. The resulting biocatalysts have been fully characterized using various analytical techniques, including X-ray fluorescence (XRF), elemental analysis, granulometry, X-ray photoelectron spectroscopy (XPS), Fourier-Transform Infrared Spectroscopy (FTIR), thermogravimetry (TGA), moisture content, field-emission scanning electron microscopy (FESEM) and high-angle annular dark-field imaging (HAADF) with energy dispersive X-ray spectroscopy (EDX). The catalytic performance of these new functional heterogeneous materials has been verified by gelation time measurements on a multipurpose unsaturated polyester/styrene/tert-butyl peroxybenzoate system. The results are compared with those obtained using the current workhorse of the industry, which utilizes cobalt-based catalysts, particularly cobalt octoate dissolved in a solvent solution known to have adverse environmental and human health implications.

Oligomeric oxidovanadium(IV) phosphates as a promising alternative to cobalt-based driers and accelerators

This study reports promising catalytic activity of oxidovanadium(IV) dialkyl phosphates those can serve as primary driers for air-drying paints and as accelerators for room-temperature curing of unsaturated polyester resins. It describes an improved synthetic protocol giving title compounds at high yields and clarifies their molecular structure. The behavior in solution and in formulation of alkyd resin was investigated by electron paramagnetic resonance. Strong catalytic activity is documented by standard tests on several commercial alkyd binders and one multipurpose unsaturated polyester resin.

Low-Density Unsaturated Polyester Resin with the Presence of Dual-Initiator.

Dual-initiation is a new orientation of many studies in the curing of unsaturated polyester resin and the manufacture of low-density unsaturated polyester resin (LDUPR) composite materials. In our research, two kinds of low-temperature (40-70 °C) initiators (cyclohexanone peroxide (CYHP) and methyl ethyl ketone peroxide (MEKP)), one kind of medium-temperature (70-130 °C) initiator (tert-butyl peroxy-2-ethylhexanoate (TBPO)), and three kinds of high-temperature (≥130 °C) initiators (tert-butyl benzoate peroxide (TBPB), tert-amyl carbonate peroxide-2-ethylhexanoate (TAEC), and tert-butyl carbonate peroxide-2-ethylhexanoate (TBEC)) were applied to constitute different dual-initiators. Those dual-initiators were a low-temperature dual-initiator (CYHP/MEKP), medium-low-temperature dual-initiators (CYHP/TBPO and MEKP/TBPO), and high-temperature dual-initiators (TAEC/TBPB, TAEC/TBEC, and TBEC/TBPB). In the low-temperature and medium-low-temperature ranges, the LDUPR sample displayed the highest specific compression strength (Ps) of 42.08 ± 0.26 MPa·g-1·cm3 in the presence of the MEKP/TBPO dual-initiator. In the high-temperature range, the LDUPR sample exhibited the highest specific compression strength (Ps) of 43.32 ± 0.45 MPa·g-1·cm3 for the existence of the TAEC/TBPB dual-initiator. It is pointed out that the dual-initiator released more active free radicals, accelerating the initial curing time and the peak time of UPR. More active free radicals caused both high-activity (short-chain) molecules and low-activity (long-chain or intertwined) molecules in resin to cross-link, prolonging UPR's curing process by approximately two minutes and resulting in an improvement of UPR's cross-linking. In the presence of a dual-initiator, the integrated and planar microstructure of LDUPR samples performed uniformly distributed dimples, dispersed external forces, and enhanced samples' specific compressive strength.

Study on Microwave Curing of Unsaturated Polyester Resin and Its Composites Containing Calcium Carbonate.

Microwave curing technology has been widely used in resin and its composite materials. In order to study its effect for curing unsaturated polyester resin (UPR) composites containing calcium carbonate (CaCO3) filler, this paper first investigated the influence of microwave power and microwave irradiation time on the curing characteristics of UPR. Then, CaCO3 particles were added to the UPR to investigate the microwave curing effect of the UPR composites containing the CaCO3. The results showed that microwave irradiation could heat the UPR sample evenly, and rapidly cause the chain growth reaction, thus greatly shortening the curing time. The curing degree and products of the samples after microwave curing were consistent with that of the thermal curing. The addition of CaCO3 particles could increase the heating rate of the UPR composites, which would accelerate the curing rate of the UPR. However, higher microwave power could lead to pore defects inside the UPR composites with higher CaCO3 content, resulting in a lower strength. Thus, the compactness of the samples should be improved by reducing the microwave power and prolonging the microwave treatment time.

Effect of Accelerators on the Curing of Unsaturated Polyester Resins: Kinetic Model for Room Temperature Curing

Several iron and vanadium compounds were evaluated as accelerators for curing of unsaturated polyester resins, serving as alternatives to toxic cobalt(II) carboxylates currently in widespread use in the composite industry. The catalytic power of the given metal-based compounds has been verified by gelation time measurements on a multipurpose unsaturated polyester/styrene/methyl ethyl ketone peroxide system. Due to different demands of the application sphere, our detailed investigation of the curing process has covered two extreme situations: the behaviors of the accelerators under adiabatic and isothermal conditions. Exothermic behavior in the thermally isolated system, followed by a K-type thermocouple, enabled recognition of the inhibition of the curing process at high concentration of the accelerator and verification of its thermal stability. At isothermal conditions, a radical copolymerization process has been followed by real-time near-infrared spectroscopy, which enabled the establishment of a kinetic model for precise quantification of the catalytic effect for given accelerators.

Study of Experimental Investigations in the Presence of Ceramic Waste Powder

The paper aims to evaluate the gel time and exotherm temperature properties of the curing of unsaturated polyester resin at various amounts of Methyl ethyl ketone peroxide, cobalt octoate and porcelain powder. The gel time of samples are determined using the simple method, while the exotherm temperature are evaluated using the thermocouple. The variation of these properties is discussed theoretically and experimentally.

Experimental Evaluation of the Curing of Unsaturated Polyester Resin at Various Amounts of Methyl Ethyl Ketone Peroxide, Cobalt Octoate and Porcelain Powder

The goal of this research is to investigate the impact of the three parameters on the cure of the unsaturated polyester resin. The obtained values show the influence of each parameter on the cure and hence enables to establish a time-range with regard of the percentage of the components for a good management of the curing process.

Influence of initiator on the curing of unsaturated polyester resin at 100 °C

AbstractSheet molding compound (SMC) parts are fiber‐reinforced unsaturated polyester (UP) composites molded at 140–170 °C under a pressure of 60–100 bar. For economic and ecological reasons, the aim of this research project is to develop new SMC formulations to modify the molding conditions. For this, SMC formulations were modified and optimized to decrease the molding temperature to 100 °C. The strategy was to change the catalytic system (peroxides) in order to obtain highly reactive formulations at 100 °C. First, the temperatures of initiation of the reaction were determined by rheological and DSC measurements for each peroxide. Second, the UP resin crosslinking kinetics were measured for the various peroxides during an isothermal curing at 100 °C. The results obtained with the three experimental methods are compared and discussed. Finally, the laboratory analyses were validated by SMC molding trials. © 2019 Society of Chemical Industry

Kinetic analysis of isothermal curing of unsaturated polyester resin catalyzed with tert-butyl peroxybenzoate and cobalt octoate by differential scanning calorimetry

The curing kinetic analysis of unsaturated polyester (UP) with tert-butyl peroxybenzoate (TBPB) and cobalt octoate (CoOct) was investigated by differential scanning calorimeter. It was found that apart from enhancing the curing reaction, the less time and lower temperature to cure will be both achieved by the addition of promoter (CoOct). To further study the UP/TBPB/CoOct system, the automatic Kamal model was applied to the experiment. According to the thermokinetic parameters that were evaluated by the automatic Kamal model, the results show that the experimental data fit well with the Kamal model fitting except in the last stage. Considering about the different effects of diffusion control and curing control on the experimental system, a diffusion factor was introduced into the Kamal model; consequently, the fitting results were much better than with Kamal model. Modified Kamal model with diffusion factor was proven to be more suitable for UP resins cured with TBPB and CoOct, since the isothermal runs of differential scanning calorimeter can predict time profiles successfully during the molding process.

DSC Cure Kinetics of an Unsaturated Polyester Resin Using Empirical Kinetic Model

In this paper, the kinetics of curing of unsaturated polyester resin initiated with benzoyl peroxide was studied. In case of unsaturated polyester (UP) resin, isothermal test alone could not predict correctly the curing time of UP resin. Therefore, isothermal kinetic analysis through isoconventional adjustment was used to correctly predict the curing time and temperature of UP resin. Isothermal kinetic analysis through isoconversional adjustment indicated that 97% of UP resin cures in 33 min at 120 °C. Curing of UP resin through microwaves was also studied and found that 67% of UP resin cures in 1 min at 120 °C. The crosslinking reaction of UP resin is so fast at 120 °C that it becomes impossible to predict correctly the curing time of UP resin using isothermal test and the burial of C=C bonds in microgels makes it impossible to be fully cured by microwaves at 120 °C. The rheological behaviour of unsaturated polyester resin was also studied to observe the change in viscosity with respect to time and temperature.

Flame retardance and thermal properties of a novel phosphorus-containing unsaturated polyester resin/SiO2 hybrid nanocomposite

AbstractA novel phosphorus-containing unsaturated polyester resin/SiO2 hybrid nanocomposite was prepared from the in-situ curing of unsaturated polyester resin (UP) and triethoxysilane (DI) which was synthesized from the nucleophilic addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and 3- (trieoxysilyl) isocyanate(icteos). The formation of unsaturated polyester resin/SiO2 hybrid nanocomposite (UP-DI) was confirmed by infrared spectra (FTIR) and scanning electron microscopy (SEM). With the increase of DI contents, the limiting oxygen index (LOI) value of the cured UP-DIs was raised from 19 to 29, suggesting a significant improvement in flame retardance. The improved flame retardance could also be revealed by the variations of weight and morphology of char residues. Thermogravimetric analysis (TGA) both in air and in nitrogen was used to estimate mechanism of thermal degradation and activation energy (Ea) of different degree of conversion (α) was calculated by Ozawa’s method. The UP-DI containing 10%DI (UP-DI10) had higher Eathan the pure UP as α>5% because the degradation mechanism was altered by the incorporation of DI.

Kinetics of the curing reaction of unsaturated polyester resins catalyzed with new initiators and a promoter

AbstractIn this article, the curing of unsaturated polyester resins catalyzed with a promoter [cobalt(II) octoate] and free‐radical initiators is presented. The new initiators were formed by the oxidation process of ethyl methyl ketone or cyclohexanone with hydrogen peroxide and the mixture of solvents containing hydroxyl groups. As a reference, a typical curing system containing ethyl methyl ketone hydroperoxide (Luperox) and the promoter was used. The differential scanning calorimetry runs were performed at different heating rates. The experimental data were fitted with the empirical kinetic model. First, the kinetic parameters (activation energy, frequency factor, and reaction order) were obtained with a single reactive process and with the nth‐order reaction f(α), the nth‐order reaction f(α) with autocatalysis, and the first‐order reaction f(α) with autocatalysis. Second, two or three different reactive processes with the nth‐order reaction f(α) for each step were used. The obtained values of the activation energies for the curing of the unsaturated polyester resins with the free radical initiator–cobalt(II) salt catalytic system were in the range 40–60 kJ/mol for the polymerization initiated by the redox decomposition of the initiators and 80–90 kJ/mol for the polymerization initiated by the thermal decomposition of the initiators at high temperatures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1870–1876, 2006

Studies on activity of s-triazine ring containing amine modifiers in curing of unsaturated polyester resins

Summary — The results of the study on the activity of amine modifiers for unsaturated polyester resins obtained by reaction of diethanolamine (3-azapentane-1,5-diol) a nd N-phenyl-2-aminoethanol with 2,4-dichloro-6-methoxy-1,3,5-triazine, 2-chloro-4,6-dimethoxy-1,3,5-triazine or with cyanuric chloride are presented. Effects of the type and amount of amine modifier as well as cobalt accelerator on gelation time and stability of the resins were investigated.

Effect of dual-initiator on low temperature curing of unsaturated polyester resins

In low temperature composite manufacturing processes, a major concern is how to control the resin gel time and cure time and how to achieve a high resin conversion with low residual volatile organic chemicals. In this study, a cobalt promoter catalyzed dual-initiator system was used to control the reaction rate and resin conversion of unsaturated polyester resins. A mechanistic kinetic model was developed to predict the reaction kinetics with dual initiators. This model can be used to simulate the isothermal and dynamic reaction rate and conversion profiles. It can also be utilized to predict the effect of promoter concentration on UP resin cured at low temperatures. The dual-initiator system was applied in the vacuum-assisted resin transfer molding process at room temperature. The kinetic model, in conjunction with the heat transfer analysis, was able to successfully predict the temperature profiles during the molding processes.

Behavior of nonazeotropic compositions of a styrene–unsaturated polyester resin analyzed through FTIR spectroscopy and dynamic mechanical thermal analysis

AbstractStyrene is one of the comonomers most frequently used in the curing of unsaturated polyester resins. The use of nonazeotropic compositions leads to the formation of networks, in which the styrene–polyester ratio varies significantly during curing, as shown through FTIR spectroscopy. Dynamic mechanical thermal analysis (DMTA) showed how the variation in the styrene content affects the network structure that is formed. The results showed a decrease in network density in the systems in which the azeotropic composition was not used. The styrene content is therefore a factor that governs the curing process, in addition to the ultimate properties of the cured resins. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3618–3625, 2003

DC-electrical conductivity as a method for monitoring radiation curing of unsaturated polyester resins III. Evaluation of results

The results of DC-electrical conductivity monitoring of radiation and thermally initiated crosslinking of unsaturated polyester resins are interpreted using conductivity data itself instead of commonly used logarithmic data form. The main setbacks of logarithmic conductivity data were the shift toward longer reaction time compared to non-logarithmic conductivity data and extraction analysis results and pronounced scattering at the end of the reaction so it was impossible to detect vitrification point. By revision of approach to analysis of results, full sensitivity of the electrical conductivity method to structural changes in the reacting system was shown. The apparent rate constants calculated from conductivity itself showed the influence of upper liquid–liquid transition on the rate of radiation induced reaction that could not be seen if the logarithm of conductivity was used. Influence of dose rate effects and electrical field effects on reaction rate were detected too and confirmed by DSC measurements. All details of reaction can be detected using first derivative of conductivity and in the case of thermally initiated reaction two maxims of reaction rate were found that are probably caused by local increase of temperature due to highly exothermic reaction.

Inhibitors in Curing of High Reactive Unsaturated Polyester Resin

The behaviour of 16 hydroquinone-quinone systems used as inhibitors in the curing of unsaturated polyester resin catalyzed by dibenzoyl peroxide was studied. The resin used in the experiments did not contain any inhibitor added in the manufacture process. To increase its reactivity the resin was accelerated by tertiary aromatic amines. In order to determine the influence of the inhibitors mixture on the resin properties induction times at 70°C, viscosities and gelation times were measured.

Microgelation of unsaturated polyester resins by static and dynamic light scattering

The microgelation phenomenon during the curing of unsaturated polyester resin was investigated by both static and dynamic light scattering before gelation. The results of static light scattering revealed that the polymer molecular weight increased with degree of curing. The second virial coefficient, A2, decreased slowly in the initial stage of curing and decreased dramatically at a conversion around α ∼ 8.7%, indicating a drastic decrease of compatibility between the polyesters and styrene. Two modes of the size distribution of the microgel particles during curing were observed by dynamic light scattering. The small particles consist of primary unsaturated polyester molecules. The large ones consist of microgel particles formed by linking adjacent polyester molecules. The sizes of the microgel particles increased in the initial stage of curing, then decreased slightly at a conversion of α ∼ 8.7%, which was due to the intramolecular crosslink reaction of the microgel particles. The experimental results revealed that the compatibility between polyesters and the styrene monomer became worse as the intramolecular crosslinking reaction inside the microgel particles caused a tight packing of the micro-gel molecules. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 871–878, 1998

Glycidyl amine adducts as accelerators for the curing of unsaturated polyester resin

The behavior of the adducts of aromatic amines with epoxide compounds as accelerators in curing of an unsaturated polyester resin was studied. To determine their usefulness, the gelation times, peak exotherm temperatures, and chromatographic and gravimetric analyses of the products extracted from the cured resin samples were investigated. The effectiveness of the adducts was compared with that for N,N-dimethylaniline. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:1525–1531, 1997

Glycidyl amine adducts as accelerators for the curing of unsaturated polyester resin

The behavior of the adducts of aromatic amines with epoxide compounds as accelerators in curing of an unsaturated polyester resin was studied. To determine their usefulness, the gelation times, peak exotherm temperatures, and chromatographic and gravimetric analyses of the products extracted from the cured resin samples were investigated. The effectiveness of the adducts was compared with that for N,N-dimethylaniline. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:1525–1531, 1997