Curable resins based on recycled poly(ethylene terephthalate) for coating applications

Poly(ethylene terephthalate) waste was depolymerised in the presence of diethylene- or tetraethylene glycol and manganese acetate as a catalyst. An epoxy resin was then prepared by the reaction of these oligomers with epichlorohydrin in presence of NaOH as a catalyst. The produced oligomers were condensed with maleic anhydride and ethylene glycol to produce unsaturated polyester. The chemical structures of the resulting epoxy and unsaturated polyester resins were confirmed by ¹HNMR. The vinyl ester resins were used as cross-linking agents for unsaturated polyester resin diluted with styrene, using free radical initiator and accelerator. The 2-amino ethyl piprazine was used as hardener for epoxy resins. The curing behaviour of the unsaturated polyester resin, vinyl ester resins and styrene was evaluated at different temperatures ranged from 25 to 55 °C to calculate the curing activation energy of the system. The cured epoxy and unsaturated polyester resins were evaluated in coating application of steel.     

Microgelation in the curing reaction of unsaturated polyester resins

A series of unsaturated polyesters were synthesized with various chemical structures and molecular weights. These unsaturated polyesters were used to study the curing reaction with styrene by using gel permeation chromatography and differential scanning calorimetry. The variation of the size of microgel particles during the curing reaction in unsaturated polyester–styrene resins was studied by using gel permeation chromatography. The size and structure of the microgels depend strongly on the polymer chain length and the number of vinyl groups on each unsaturated polyester chain. Using the differential scanning calorimetric method, the conversion of styrene and polyester vinyl groups during the reaction was measured. The experimental results of this study revealed that microgel formation has a great effect on the curing reaction of unsaturated polyester resins. © 1994 John Wiley & Sons, Inc.     

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

In 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     

Curing of unsaturated polyester resins: Effects of comonomer composition. II. High-temperature reactions

The effects of comonomer composition of the curing kinetics of unsaturated polyester (UP) resins at 100–120°C were investigated by differential scanning calorimetry (DSC) and infrared spectroscopy (IR) over the entire conversion range. One commercial UP resin, UP2821, with 6.82 unsaturated C?C bonds per polyester molecule, was used. For styrene/UP2821 reactions, experimental results of the initial and maximum reaction rates by DSC at 100–120°C revealed that the styrene content, as well as the reaction temperature, would affect the formation of microgel structures. As the initial molar ratio of styrene to polyester C?C bonds increased, the styrene swelling effect could enhance the intramicrogel crosslinking reactions, while the styrene dilution effect could diminish the intermicrogel crosslinking reactions. The competition between the two reactions would depend on the reaction temperatures. Finally, a microgel-based reaction mechanism was proposed for the high temperature reactions. © 1993 John Wiley & Sons, Inc.     

Compressive Properties and Curing Behaviour of Unsaturated Polyester Resins in the Presence of Vinyl Ester Resins Derived from Recycled Poly(ethylene terephthalate)

Poly(ethylene terephthalate) waste was depolymerised in the presence of tetraethylene glycol and manganese acetate as a catalyst, so as to produce oligomers. An epoxy resin was then prepared by the reaction of these oligomers with epichlorohydrin in presence of NaOH as a catalyst. New diacrylate and dimethacrylate vinylester resins were then synthesized by reaction of the terminal epoxy groups with acrylic and methacrylic acid in the presence of triphenyl phosphite as a catalyst. The chemical structures of the resulting vinyl ester resins were confirmed by ¹HNMR. The vinyl ester resins were used as crosslinking agents for unsaturated polyester resin diluted with styrene, using free radical initiator and accelerator. The curing behaviour of the unsaturated polyester resin, vinyl ester resins and styrene was evaluated at temperatures from 25 to 55 ^○C. The compression properties of the cured resins, having different vinyl ester contents and different cure temperatures, were evaluated. Increasing the cure temperature and the vinyl ester content led to a pronounced improvement in the compression strength and Young’s modulus.     

Study of crosslinking of unsaturated polyester resins by relaxation methods

Radiation and thermal curing of unsaturated polyester resins with styrene were investigated by combining differential thermal analysis with electric and mechanical relaxation techniques. A microprocessor controlled combined relaxation equipment of special construction was used. By radiation initiated curing the reaction was interrupted at different stages and the products were analyzed. Relaxation and simultaneous differential thermal measurements were also made during the course of gamma radiation and peroxide initiated thermal curing. By this way the shift of the characteristic transitions of the resin as a function of conversion could be studied. Also the change of the phase-structure of the resin caused by the reaction was monitored. By deconvolution of the dielectric spectrum band the physical structure was found to become heterogeneous by crosslinking. Besides the shift of the transition temperatures the oscillator strength of the dielectric transition was found to decrease with conversion. Electrical polarization and depolarization studies were also performed. A special intermittent load thermomechanical technique was used for separating elastic from viscous response of the sample subjected to external mechanical force. The transitions exhibited by the thermomechanical curves were found to shift to higher temperatures by crosslinking and the compliance plateaus decreased.     

Effects of low-profile additives on the curing reaction of unsaturated polyester resins

The effect of low-profile additives (LPA), i.e., poly(vinyl acetate) (PVAC) and poly(methyl methacrylate) (PMMA), on the curing reaction of unsaturated polyester (UPE) resins was studied by gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The curing reaction profiles were determined by DSC, while GPC was used to investigate the variation of the sizes of microgel particles during the early stage of curing reaction in UPE–styrene resins. The DSC experimental results indicated that the curing reaction rate decreased as the concentration of LPA increased. At a fixed LPA concentration, the curing reaction rate was slower for resins mixed with LPA possessing worse compatibility with UPE resins. During the early stage of curing reaction, the size and structure of the UPE microgels formation strongly depended on the concentration of LPA and also on the compatibility of the components in the curing system. The experimental results of this study revealed that the concentration of LPA and the compatibility of LPA with UPE resins had a strong influence on the polyester microgel formation and the curing behavior. © 1995 John Wiley & Sons, Inc.     

Polyester resins with carbazole ring

3‐(9‐Carbazolyl)propane‐1,2‐diol was obtained in the reaction of 9‐(2,3‐epoxypropyl)carbazole with water. The obtained diol was further used for modification of unsaturated polyester resin to produce enhanced thermal and heat resistance in comparison with classic resins. The properties of polyesters and polyester resins modified with 3‐(9‐carbazolyl)propane‐1,2‐diol were studied in detail. When 3‐(9‐carbazolyl)propane‐1,2‐diol is used instead of propylene glycol the unsaturated polyester resins possess enhanced thermal stability.© 2013 Society of Chemical Industry     

Control of shrinkage and residual styrene of unsaturated polyester resins cured at low temperatures: I. Effect of curing agents

In low temperature molding processes, control of resin shrinkage and residual monomer is an important concern. The presence of low profile additives (LPAs) can reduce the shrinkage of unsaturated polyester (UP)/styrene (St) resins under proper processing conditions but may increase the residual styrene content. A systematic study was carried out to investigate the effect of the initiator system and reaction temperature on sample morphology, final resin conversion, and resin shrinkage of UP resins with LPA. It was found that the final conversion of the resin system could be improved by using dual initiators. The effect is more obvious at low temperatures. Volume shrinkage measurements of the resin system initiated with dual initiators revealed that good LPA performance was achieved at low (e.g. 35 °C) and high (e.g. 100 °C) temperatures but not at intermediate ones. This can be explained by how temperature affects phase separation, reaction kinetics in the LPA-rich and UP-rich phases, micro-void formation, and thermal expansion.     

Über die Netzwerkstruktur mit Elektronenstrahlen gehärteter ungesättigter Polyester

On crosslinking of some unsaturated polyesters by electron beams more than 60% of the unsaturated basic units react. A dimerisation is by far the dominating reaction. Oligomers are formed only in very small amounts. The modulus of elasticity, the tensile strength and the elongation at break of films obtained from unsaturated polyesters by electron beam curing were higher than those of unsaturated polyester resins containing styrene, either cured by peroxide or by electron beams.     

Modification of unsaturated polyester resin with bismaleimide

The modification of a commercially available unsaturated polyester resin with 4,4′‐bismaleimidodiphenylmethane is presented. The properties of the modified resins were compared with those of the nonmodified resin, and the resins were characterized in the noncured state and after curing. The results indicate that the addition of bismaleimide to unsaturated polyester resin not only improves its properties but also accelerates the curing reactions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2003–2007, 2001     

氢氧化铝用作不饱和聚酯树脂阻燃剂的研究

本文研究了氢氧化铝作为不饱和聚酯树脂阻燃性添加剂的阻燃性能,测定了加入氢氧化铝后树脂粘度、固化特性、力学性能和热性能的变化.     

封端不饱和聚酯树脂的制备与表征

以顺丁烯二酸酐与邻苯二甲酸酐的摩尔比为7：3,制备了一种以环己醇封端的不饱和聚酯树脂,固化剂和促进剂用量分别为1%和2%,凝胶时间和固化时间分别为4 min和13 min。用聚合放热峰温、红外光谱和热重-差热对不饱和聚酯树脂进行了表征。     

The effect of pressure on the curing behavior of unsaturated polyester resins

The effect of pressure on the curing behavior of unsaturated polyester resin was investigated, both experimentally and theoretically. The resin used was a general-purpose unsaturated polyester resin and the initiator used was t-butyl perbenzoate. A series of isothermal runs with differential scanning calorimetry (DSC) were made at various levels of cure pressure. It was found that the rate of cure was retarded under pressure, and that the ultimate degree of cure went through a maximum at a certain pressure as the cure pressure was increased from atmospheric pressure to 6.21 MPa (900 psi). It was interpreted that pressure has two competing effects on the curing behavior of unsaturated polyester resin; one is a free volume effect that hinders the curing reaction and the other is a thermodynamic effect that favors it. Therefore, when the pressure is higher than a certain level, the free volume effect becomes predominant over the thermodynamic effect, the ultimate degree of cure diminishing as the cure pressure is increased beyond that level. Theoretical interpretation of the experimental results is given, using a mechanistic kinetic model developed in our previous publication.     

利用废聚酯薄膜制备不饱和聚酯树脂工艺研究

以废聚酯薄膜(PET)为原料制得了不饱和聚酯树脂(UPR),通过产物酸值测定研究了反应温度、催化剂种类对聚酯薄膜降解反应的影响,通过固化性能测试及其浇注体和玻璃钢制品的力学和热性能测试确定了废聚酯薄膜的用量,并将制品的性能与邻苯型196#不饱和聚酯树脂作了比较。结果表明:采用有机锡类和醋酸锌的复合催化剂,反应温度210～225℃,废聚酯薄膜与顺丁烯二酸酐物质的量比1:2.7时UPR产品性能最优,其力学性能、耐热性和耐腐蚀性均优于196#UPR。     

Curing of unsaturated polyester resins—effects of pressure

The effects of pressure ranging from 0.1 to 6.21 MPa (0–900 psig) on the curing of unsaturated polyester resins at 110°c were investigated by an approach of integrated reaction kinetics-rheology-morphology measurements using a pressure differential scanning calorimeter (DSC), an infrared spectrophotometer (IR), a Haake rheometer, and by using scanning electron microscopy (SEM). Increasing pressure was found to delay the gel effect, and a previously unknown plateau of kinetic-controlled region in the initial portion of the DSC rate profile was observed. The plateau region was mainly attributed to the crosslinking of C ? C double bonds inside the microgel particles, as revealed by the conversions of styrene and polyester C ? C bonds measured by IR, gel conversion data and SEM micrographs. The mechanisms of reaction kinetics both at atmospheric pressure and under pressures have also been elucidated by the progress of buildup of microgel structures.     

Effect of co-promoter and secondary monomer on shrinkage control of unsaturated polyester (UP)/styrene (St)/low-profile additive (LPA) systems cured at low temperatures

The shrinkage of unsaturated polyester (UP)/styrene (St) resins cured at low temperatures can be reduced by the presence of low-profile additives (LPAs). It is believed that the reaction-induced phase separation and the polymerization shrinkage in both the LPA-rich and UP-rich phases result in the formation of microvoids, which partially compensates the resin shrinkage. The relative reaction rate in the two phases plays an important role in shrinkage control. In this study, secondary monomers [such as divinylbenzene (DVB) and trimethylopropane trimethacrylate (TMPTMA)] and a co-promoter, 2,4-pentandione (2,4-P), were added into the UP/St/LPA resin systems to investigate their effect on the shrinkage control of resins cured at low temperatures. Dilatometery results showed that the addition of both TMPTMA and 2,4-P resulted in an earlier volume expansion during curing and better shrinkage control. The phase separation, reaction kinetics, and viscosity changes in the LPA-rich and UP-rich phases during curing were also investigated. The results confirmed that the increased reaction rate in the LPA-rich phase led to an earlier formation of microvoids and, consequently, less volume shrinkage of the cured resin. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 738–749, 2001     

DSC法研究不饱和聚酯树脂的固化反应动力学及其固化过程

采用示差扫描量热法（DSC）分别研究了Ashland UP（R36）以及DSMUP（972B）这两种不饱和聚酯树脂（UP）的固化过程,并利用了KiSSinger方程、Crane经验方程等分析了这两种树脂的固化反应,得到了其固化反应的表观活化能、Arrhenius指前因子（频率因子）、反应级数等动力学参数,最后利用Y—B外推法确定了这两种不同树脂的凝胶温度、固化温度和后固化温度等固化工艺温度。     

Unsaturated Polyester Resins Obtained from Glycolysis Products of Waste PET

Abstract

Waste polyethylene terephthalate (PET) flakes were depolymerized by using ethylene glycol (EG), propylene glycol (PG), diethylene glycol (DEG), and triethylene glycol (TEG) in the presence of zinc acetate as catalyst. All glycolysis products were reacted with maleic anhydride and mixed with styrene monomer to get unsaturated polyester (UP) resins. Molecular weights of all synthesized UP resins were determined by end-group analysis. The curing characteristics such as gel time and maximum curing temperatures, and mechanical properties such as hardness, tensile strength, and elastic module of these resins were investigated. The waste PET resins were compared with the reference resins prepared with the same glycols and the properties of the resins were found to be compatible with the properties of the reference resins.     

Comparison of unsaturated polyester and vinylester resins in low temperature polymerization

Many composite products are produced at low temperatures in processes such as resin transfer molding (RTM), vacuum infusion molding (e.g., Seemann Composite Resin Infusion Molding Process—SCRIMP), and hand lay‐up. These processes are widely used for marine, civil infrastructure, transportation and defense applications. Unsaturated polyester and vinylester resins are two major resins used in these processes due to their low cost, good performance, and processibility. In this study, the reaction kinetics and rheological changes of these two resins cured at low temperatures were studied. Effects of resin type, initiator, promoter, inhibitor and retarder on the reaction kinetics and rheological behaviors were examined using a Differential Scanning Calorimeter (DSC) and a Rheometrics Dynamic Analyzer (RDA). A model was developed to quantify the effects of resin type, temperature, and different curing agents on the gel time for both polyester and vinylester resins cured at low temperatures. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1230–1242, 2001