Influence of functional rubbers on the curing process of unsaturated polyester resins

The influence of an elastomeric second-phase on the kinetics of the curing reaction and the gel-time of a standard unsaturated polyester resin, by using the isothermal and dynamic techniques of differential scanning calorimetry (DSC) and a thermocouple was investigated. In particular we examined two different rubbers (polybutadiene hydroxyl-terminated and polybutadiene isocyanate-terminated), that, in the presence of polyester resins, affect the overall curing reaction kinetics in two ways: the former reduces the rate of reaction whilst the latter increases it.

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Zusammenfassung Der Einfluß einer elastomeren Zweitphase auf die Kinetik der Aushärtung und der Gelierungszeit eines als Standard dienenden ungesättigten Polyesterharzes wurden mittels isothermer und dynamischer DSC untersucht. Insbesondere wurden zwei unterschiedliche Gummis (hydroxylendständiges und isocyanatendständiges Polybutadien) untersucht, die die Kinetik der Aushärtung des Polyasterharzes in unterschiedlicher Weise beeinflussen: hydroxylendständiges Polybutadien verringert, isocyanatendständiges dagegen erhöht die Reaktionsgeschwindigkeit.

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Applications of unsaturated polyester resins

Unsaturated polyester resins containing long chain fatty acids and styrene as cross-linking agents are easily available in Pakistan. I have made use of these resins in the preparation of overprint varnish, ornaments, synthetic marble and other related substances. The octates of manganese, cobalt, calcium and lead along with peroxide were used for jelling and drying of the resins. The effects of metal driers, aluminium stearate, peroxides and unsaturated long chain fatty acids in the composition as mentioned in the experimental section were also studied. The merits and demerits developed in the end products resulting from the variation of these chemicals in the compositions were also noted at their respective places. The article was submitted by the author in English.     

Kinetic study of the cure reaction of unsaturated polyester resins

The kinetics of the cure reaction of standard unsaturated polyester resin was investigated by utilizing the isothermal and dynamic techniques of differential scanning calorimetry (DSC). The kinetic parameters and heat of the copolymerization reaction were determined. A method is proposed for optimization of the curing and postcuring of a polyester resin composite.

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Zusammenfassung Die Kinetik der Aushärtung eines ungesättigten Standardpolyesterharzes wurde mittels isothermer und dynamischer DSC untersucht. Kinetische Parameter und die Reaktionswärmen der Kopolymerisation wurden bestimmt. Eine Methode zur Optimierung der Aushärtung und Nachhärtung von Polyesterharzverbundstoffen wird vorgeschlagen.

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This work was partly supported by the Chimica Fine e Secondaria project of the Italian C.N.R.     

The effect of temperature on the curing of unsaturated polyester resins modified with a liquid polymer

The effect of temperature on the cure kinetics of two different unsaturated polyester resins, Estratil 1.112 and G102, modified with a liquid polymer, has been studied by Fourier transform infrared (FTIR) spectroscopy in the range of 60–80°C and 70–90°C, respectively. The experimental results have been related to the rheological changes during cure.     

Synthesis of unsaturated polyester resins for large sized composites

A series of unsaturated polyesters based on phthalic anhydride (PHA), maleic anhydride (MA), ethylene glycol (EG), diethylene glycol (DG), triethylene glycol (TG), propylene glycol (PG), styrene (Sty) and acrylonitrile (AN) were prepared. The molecular weights of the prepared polyesters were determined by end-group analysis. The effect of the structure of the resin on its curing behavior has been investigated. On the basis of the experimental study, the following were concluded: (1) The maximum curing temperature (T_max) is related to the molecular weight of the glycol incorporated in these castings. In this context the T_max was found to decrease with increasing the molecular weight. Meanwhile the time to peak temperature t_max was increasing. (2) The higher the percentage of AN in the crosslinking monomer system, the slower a resin cures. (3) The values of T_max were found to be influenced to a large extent by the percentage of AN.     

Glass-fibre reinforced composite materials based on unsaturated polyester resins

The effect of glass-fibre content on the thermal and mechanical properties of cross-linked composites based on unsaturated polyester resins have been investigated by thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical thermal analysis and by measuring the heat distortion temperature (HDT). Two different matrix resins and two different glass mats were used, and the glass-fibre contents varied. Altogether 12 composite systems were tested. The glass- transition temperature of each composite was characteristic to the matrix resin and did not depend on the glass-fibre content, as it was expected. The effect of glass-fibre content on the storage modulus and on HDT has been elucidated. It has been found that up to 12 mass% (6?vol%) glass-fibre content the HDT did not change, above this value it increased with increasing glass-fibre content for each composite, but not at the same extent. This means that matrix-fibre interaction has an important role in the performance of the composites at elevated temperatures. Storage moduli increased with increasing glass-fibre content. The temperatures detected by dynamic mechanical thermal analysis corresponding to the storage modulus of 750?MPa??calculated by Takemori??are above the glass-transition and also increased with higher glass-fibre content in accordance with the real heat-distortion temperature measurements. It may be concluded that the effect of reinforcement on the performance of the composite could be detected more reliably by HDT measurements, since it gives information on the deformation of the composites. Matrix-fibre interaction has an essential role on the performance and on the HDT of the composite materials.     

Using mechanical spectroscopies to study the glass transition dynamics in unsaturated polyester resins cured with different styrene contents

The control of chemical architecture has been one relevant parameter in the study of glass transition dynamics in macromolecular systems. In this study, two polyester resins differing in the styrene content that was added in the curing process were studied using two complementary mechanical spectroscopy techniques: dynamic mechanical analysis (DMA) and thermally stimulated recovery (TSR). Both techniques showed that the -relaxation is shifted to higher temperatures (longer times) with increasing styrene content. Master curves were obtained from the DMA data. The shift factors were used to obtain the temperature dependence of the apparent activation energy, E_a(T). The TSR results also permitted to obtain E_a(T) that also exhibited a maximum around T_g. This behaviour, apparently universally observed in thermally stimulated techniques, was explained by the shift from a Vogel-Fulcher-Tamman-Hesse to an Arrhenius regime. The data also allowed to calculate the fragility index of the two materials, which was found to be higher for the one with higher styrene content. Remarks are made on the dependency of the values of this parameter obtained from different techniques.     

Biobased vinyl levulinate as styrene replacement for unsaturated polyester resins

Vinyl levulinate (VL) is used as a biobased reactive diluent in styrene (St)‐free unsaturated polyester resins (UPR). The reactivity ratios for the radical copolymerization of VL with diethyl fumarate (DEF) are determined by the Jaacks method (r_VL = 0.01 and r_DEF = 0.81 at 60 °C in DMSO‐d₆). The properties of UPRs having a stoichiometric ratio between unsaturated groups from the UPR and either St or VL are compared. Defect‐free, slightly yellow, transparent, and rigid thermosets are obtained after a mild curing cycle. Due to unfavorable reactivity ratios about 5.5 wt % of unpolymerized VL remains inside the network and acts as plasticizer. Consequently, compared with St‐based ones, VL‐based UPRs exhibit lower α relaxation (T_α = 180 and 100 °C, respectively), lower elastic moduli at the rubbery plateau (G′ = 10⁸ and 10⁷ Pa) and lower mechanical properties as measured by three points bending tests. Strain at break (ε_f = 1.8 ± 0.2%) and Charpy impact strength (～2.7 ± 0.3 kJ m^?2) are comparable independently of the RD chemical nature. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3356–3364     

BMD/UP体系非等温固化动力学研究

不饱和聚酯是最常用的一种热固性材料,其力学性能和耐热性是较受关注的两个方面,利用双马来酰亚胺作为第二组分对不饱和聚酯进行耐热改性的工作取得了较好的效果。研究其动力学过程对于固化反应温度、时间等工艺合理优化控制,制备高性能复合材料具有重要意义。考虑到BMD／UP体系中反应的复杂性,本文采用n级动力学模型,进行了非等温动力学研究。     

Simulation of the curing process of an unsaturated polyester resin in adiabatic conditions

The exothermal process of curing of thermoset resins in adiabatic conditions cannot be monitored by differential thermal analysis techniques such as DSC. Starting from the specific reaction rate, heat capacity as function of the temperature and the heat of reaction at some reference temperature, it is possible to design any adiabatic operation. In this paper we apply the energy balance to the curing process in adiabatic conditions and solve the basic rate law for the two empirical kinetic functionsf(α) usually used:n ^th-order kinetics [f(α)=(1?α)ⁿ], and autocatalytic kinetics [f(α)=α^m(1?α)ⁿ], where α is the degree of conversion andn andm the reaction orders, in order to obtain the heat generation curve (dH/dt) as a function of time, as well as the change of temperature with time, the explosion time, the maximum adiabatic temperature and the rate of reaction as a function of the degree of conversion.     

Intercrosslinked polymer networks by simultaneous curing of unsaturated polyesters and bismaleimide resins

The modification of an unsaturated polyester resin by incorporating a second co-reactive monomer as a thermosetting bismaleimide is described The bismaleimide was readily dissolved in the uncured polyester matrix up to a concentration of about 20% wt. FTIR isothermal measurements indicated that the kinetics and the mechanism of the curing process were strongly affected by the presence of the bismaleimide. The resulting inter-crosslinked network showed a gradual enhancement of the elastic modulus in a wide range of temperatures by increasing the bimaleimide amount in the system. This enhancement was obtained without altering the intrinsic toughness of the matrix.     

Effect of the initiator content and temperature on the curing of an unsaturated polyester resin

The influence of temperature and the initiator concentration on the curing of an unsaturated polyester resin was studied by means of differential scanning calorimetry (DSC) and Fourier‐transform infrared spectroscopy (FTIR). It was established that there is an isoconversional relationship of the type lnt = a − bln[I]₀ between the curing time, t, and the initial initiator concentration, [I]₀, at a given temperature. This relationship indicates that the degree of conversion curves vs. the logarithm of the curing time at different [I]₀ may be superposed by displacement relative to a reference curve. It was confirmed that the reaction mechanism varies throughout the whole curing process, although it does not vary with the temperature and the [I]₀ at each degree of conversion. It was established that there is a universal isoconversional relationship of the type lnt = d − bln[I]₀ + E/RT that expresses the dependency of the curing time on the temperature, T, and the [I]₀. The parameters a, b, and d depend on the reaction mechanism, and can be calculated on the basis of isothermal experiments at different temperatures and with different [I]₀. The adjustment lnt = d − bln[I]₀ + E/RT shows that there is an equivalence between the effect on the curing kinetics of the temperature and the initiator concentration. The same curing process can be achieved by using different combinations of curing temperatures and the [I]₀. In the two adjustments established, it is not necessary to know the reaction mechanism, and the only assumption made is that for a given conversion the reaction mechanism is invariant with respect to the [I]₀ and the temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 751–768, 1999     

Structure of unsaturated polyester resins crosslinked with styrene as studied by raman spectroscopy

An unsaturated polyester resin and the styrene-crosslinked polyester were studied with laser Raman spectroscopy. Following the polyesterification reaction, Raman measurements showed that the polyester contained 55% fumarate and 45% maleate unsaturation. Additionally, the glycol fragment was indicated to exist as the gauche isomer. The 1213 cm^?1 line is assigned to the glycol-ester linkage and can be measured to follow the conversion to polymer. After the crosslinking reaction, styrene was found to copolymerize preferentially with the fumarate unsaturation. There was no evidence of forming long-chain polystyrene crosslinks. Our results indicate that, after crosslinking, 41% of the fumarates have reacted with styrene and there is an average of two styrene molecules in each link.     

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     

Heat-resistant glass-reinforced plastics based on unsaturated polyester resins modified with divinyl aromatic compounds

The effects exerted by elevated temperatures and thermal oxidative isothermal aging in air at 150, 200, 250, and 300°C on the thermal and physicomechanical properties of glass-reinforced plastics based on copolymers of unsaturated polyester resins with divinyl aromatic compounds and formulations was studied.     

Analysis and aging of unsaturated polyester resins in contemporary art installations by NMR spectroscopy

Two original art installations constructed from unsaturated polyester resins (UPR) and four different reference UPR products (before and after UVB aging) were analyzed by high-resolution 1D and 2D nuclear magnetic resonance (NMR) spectroscopy. Breaking strain studies were also conducted for the four UPR model products before and after different aging procedures (moisture, UVB exposure, melt/freeze). NMR analysis of the chemical composition of the UPR resin extracts showed they contain several low MW organic compounds and oligomers rich in polar -OH groups that play a significant role in the degradation behavior of the composite UPR materials. Statistical analysis of the NMR compositional data showed that styrene and benzaldehyde contents can be used to differentiate between fresh and aged UPR samples. The phthalate and propylene glycol unit speciation (esterified, primary or secondary -OH) of the extracts provided evidence that UPR resin C was used in the construction of the two art installations, and direct comparison of (1)H and (13)C NMR spectra verified this compositional similarity. UPR resin C was shown by both NMR and breaking strain studies to be the reference UPR most susceptible to degradation by different aging procedures, a characteristic attributed to the lower styrene content of resin C.     

Application of ftir spectroscopy to the study of curing of glass reinforced polyester composites

The effect of glass fiber reinforcements on the curing behavior of unsaturated polyester commercial resins was investigated by Fourier transform infrared spectroscopy. Two different E-glass fibers and two commercial resins were employed. The results indicate that both the glass fiber content and the fiber size have a pronounced effect on the ultimate values of the styrene conversion. Some complications found in the infrared analysis of commercial resins are also presented.     

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.     

Reaction kinetics and microgel particle size characterization of ultraviolet‐curing unsaturated polyester acrylates

The free‐radical reaction kinetics and microgel formation of UV‐curing unsaturated polyester acrylates were studied in terms of the effects of internal maleic and terminal acrylate unsaturations. A triacrylate‐functional monomer, trimethylolpropane triacrylate, was used as the reactive diluent. A time‐resolved Fourier transform infrared technique was used to evaluate the consumption of double bonds and showed that internal (maleic) double bonds were involved in microgel formation at a rate similar to that of the more reactive terminal (acrylic) double bonds. Dynamic light scattering was used to measure the microgel particle size. The introduction of internal unsaturations caused smaller microgels, whereas terminal acrylate unsaturations resulted in larger particle sizes. These results were attributed to the higher tendency of the internal maleic double bonds toward intramolecular cyclization reactions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6544–6557, 2006     

Study of the thermal decomposition of flame-retarded unsaturated polyester resins by thermogravimetric analysis and Py-GC/MS

The thermal degradation behaviours of flame-retarded unsaturated polyester resin formulations containing ammonium polyphosphate (APP), Cloisite 25A nanoclay and zinc based smoke suppressants have been studied using thermogravimetric analysis (TGA) combined with infrared analysis of the evolved gases (EGA) and pyrolysis/gas chromatography-mass spectrometry (GC/MS). In TGA-EGA experiments, the mass loss as a function of temperature has been correlated with the evolution of carbon monoxide (CO) and carbon dioxide (CO₂) and oxygen (O₂) consumption as measured by an oxygen analyser. The effect of APP, Cloisite 25A and the smoke suppressants on the evolution of CO and CO₂ has been examined. The decomposition behaviour of flame-retarded polyester resins under isothermal pyrolytic conditions was investigated and the evolved gaseous products were collected and qualitatively and semi-quantitatively analysed via GC/MS. The addition of APP does not yield many new gaseous products relative to the unmodified polyester resin neither does the presence of zinc borate (ZB) and zinc stannate (ZS) together with APP. Possible chemical interactions are discussed in an attempt to explain the observed results.