PET interleaving veils for improved fracture toughness of glass fibre/low‐styrene‐emission unsaturated polyester resin composites

The use of interleaved polyethylene terephthalate (PET) veils to increase the interlaminar fracture toughness of glass fiber‐reinforced, low‐styrene emission, unsaturated polyester resin composites, was investigated. PET, being chemically similar to the unsaturated polyester resin, was expected to exhibit good wetting and strong interaction with the matrix. Composite laminates were manufactured by hand lay‐up, with the veil content varying up to 7%. The effects of PET veils on the interlaminar shear strength, flexural strength, flexural modulus, glass transition temperature, damping parameters, and Mode‐I interlaminar fracture toughness of the composite were studied. The veils were found to enhance most of these properties, with only minor negative effects on flexural stiffness and T_g. The PET/resin bonding did indeed prove to be strong, but the enhancement of fracture toughness was not as much as expected, because of the weaker glass/resin interface providing an alternative crack propagation path. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42877.     

Effects of poly(methyl methacrylate)‐based low‐profile additives on the properties of cured unsaturated polyester resins. I. Miscibility,curing behavior,and glass‐transition temperatures

The effects of three series of self‐synthesized poly(methyl methacrylate) (PMMA)‐based low‐profile additives (LPAs), including PMMA, poly(methyl methacrylate‐co‐butyl acrylate), and poly(methyl methacrylate‐co‐butyl acrylate‐co‐maleic anhydride), with different chemical structures and MWs on the miscibility, cured‐sample morphology, curing kinetics, and glass‐transition temperatures for styrene (ST)/unsaturated polyester (UP) resin/LPA ternary systems were investigated by group contribution methods, scanning electron microscopy, differential scanning calorimetry (DSC), and dynamic mechanical analysis, respectively. Before curing at room temperature, the degree of phase separation for the ST/UP/LPA systems was generally explainable by the calculated polarity difference per unit volume between the UP resin and LPA. During curing at 110°C, the compatibility of the ST/UP/LPA systems, as revealed by cured‐sample morphology, was judged from the relative magnitude of the DSC peak reaction rate and the broadness of the peak. On the basis of Takayanagi's mechanical models, the effects of LPA on the final cure conversion and the glass‐transition temperature in the major continuous phase of ST‐crosslinked polyester for the ST/UP/LPA systems was also examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3369–3387, 2004     

Application of azodiisobutyronitrile and azobisisoheptonitrile in low‐density unsaturated polyester resin manufacturing

Low‐density unsaturated polyester resin (LDUPR) is an extended application of unsaturated polyester resin (UPR) material. In this study, azodiisobutyronitrile (AIBN) and azobisisoheptonitrile (ABVN) were presented as composite foaming agents and as initiators in LDUPR manufacturing. On the basis of the kinetics of AIBN and ABVN, their optimum half‐lives (t_1/2's) for LDUPR were both 1.0 h. In this study, the mass ratio of AIBN and ABVN was chosen at 7:3, and the preferred amount of the composite foaming agent was 2 wt % resin. They were treated at a molding temperature of 78.7 ± 1.0°C. The obtained LDUPR had an apparent density of 0.37 ± 0.01 g/cm³ and a specific compression strength of 35.58 ± 1.50 MPa·g^?1·cm^?3; it approached the highest specific compression strength value of rigid polyurethane foam (28–35 MPa g^?1 cm^?3). A dual‐initiation and dual‐foaming mechanism based on the dual‐exothermic decomposition properties of the composite foaming agent was proposed with the support of the differential scanning calorimetry and scanning electron microscopy results. In the first stage, ABVN decomposed, released bubble nuclei, and initiated UPR cross‐polymerization. The bubble nuclei spread in the resin glue and grew. In the second stage, the gas in resin glue was enriched by the AIBN decomposition. The gelation time of the resin glue was influenced by AIBN and delayed. With the curing of resin, more bubbles grew up, took shape, and were retained in the UPR matrix. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40238.     

Control of shrinkage and final conversion of vinyl ester resins cured in low‐temperature molding processes

Vinyl ester resin is a major thermoset polymer used in low‐temperature composite manufacturing processes such as the Seemann composite resin infusion‐molding process (SCRIMP). Volume shrinkage and residual styrene are important concerns for composites produced in such processes. A low‐shrinkage additive (LSA) is a typical agent added to control the volume shrinkage of vinyl ester resins during molding. In this study, the effects of LSA content and the temperature profile (the temperature gradient and peak temperature) on the volume shrinkage control of a vinyl ester resin were investigated. The reaction kinetics of the resin system were also studied. We achieved good volume shrinkage control if we raised the curing temperature slowly to allow sufficient time for phase separation and if the curing temperature reached a high value after phase separation to allow microvoid formation. On the basis of experimental results, we designed an improved SCRIMP to increase resin conversion, reduce resin shrinkage, and produce composites with better properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1486–1496, 2003     

Poly(phenylene ether)/epoxy thermoset blends based on anionic polymerization of epoxy monomer

Low molar mass poly (phenylene ether) (LMW‐PPE) with phenol‐reactive chain ends was used as modifier of epoxy thermoset. The epoxy monomer was diglycidylether of bisphenol A (DGEBA), and several imidazoles were used as initiators of anionic polymerization. The curing and phase separation processes were investigated by different techniques: Differential Scanning Calorimetry, Size Exclusion Chromatography, and Light Transmission measurements. The final morphology of blends was observed by Environmental Scanning Electron Microscopy and Transmission Electron Microscopy. The epoxy network is obtained by imidazole initiated DGEBA homopolymerization. Initial LMW‐PPE/DGEBA mixtures show an UCST behavior with cloud point temperatures between 40 and 90°C. PPE phenol end‐groups can react with epoxy, leading to a better interaction between phases. The curing mechanism and phase separation process are not influenced by the chemical structure of initiators, except when reactive amine groups are present. The phase inversion is observed at 30 wt % of PPE. The mixtures with amine‐substituted imidazole present important differences in the initial miscibility and curing process interpreted in terms of fast room temperature amine‐epoxy reaction during blending. Final domain size is affected by this prereaction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2678–2687, 2004     

Acrylated epoxidized soybean oil as a styrene replacement in a dicyclopentadiene‐modified unsaturated polyester resin

Nonvolatile and nonhazardous acrylated epoxidized soybean oil (AESO) was investigated as a replacement for hazardous styrene in a commercial unsaturated polyester (UPE) resin [a mixture of styrene and a dicyclopentadiene (DCPD)‐modified UPE (DCPD–UPE)]. DCPD–UPE was prepared from ethylene glycol, diethylene glycol, maleic anhydride, and DCPD. Mixtures of AESO and DCPD–UPE [AESO–(DCPD–UPE) resins] were found to be homogeneous, easily pourable solutions at room temperature. The glass‐fiber‐reinforced composites from the AESO–(DCPD–UPE) resins were comparable or even superior to those from the mixture of styrene and DCPD–UPE in terms of the flexural and tensile strengths. The viscoelastic properties of the cured AESO–(DCPD–UPE) resins and the corresponding glass‐fiber‐reinforced composites were characterized by dynamic mechanical analysis. The viscosities and pot lives of the AESO–(DCPD–UPE) resins as a function of the temperature were studied. The curing mechanism of the AESO–(DCPD–UPE) resins is discussed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46212.     

Biodegradable and temperature‐responsive thermoset polyesters with renewable monomers

A series of biodegradable thermoset polyesters, poly(1,8‐octanediol–glycerol–dodecanediaote)s (POGDAs), were synthesized with the polycondensation polymerization method without a catalyst and with different monomer molar ratios. Synthesis was confirmed with structural analysis via Fourier transform infrared spectroscopy. The effect of varying the monomer molar ratio on the material properties was illustrated in the gel content and swelling analysis, ultraviolet–visible spectroscopy, differential scanning calorimetry, X‐ray diffraction, and degradation tests. Degradation tests were performed in phosphate‐buffered solution at 37 °C for 60 days. Temperature‐responsive behavior was revealed with POGDA (0.5 glycerol), and bending tests were performed to study the shape‐memory effect. In vitro cytotoxicity tests and cell proliferation tests suggested that these POGDAs have potential applications in biomedical fields such as tissue engineering. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44007.     

不饱和聚酯树脂微乳液的研究(Ⅰ)不饱和聚酯树脂的微乳化

合成了不同磺酸盐含量的三种不饱和聚酯，通过拟三元相图分析磺酸盐含量、苯乙烯、不同正构醇和水组成的体系对微乳区域的影响。研究结果表明，磺酸盐不饱和聚酯同苯乙烯互溶的前提下，磺酸盐含量越大，其微乳液增溶的水量越大；磺酸盐含量一定时，苯乙烯含量越小，其微乳液增溶的水量越大；正构醇质量分数为在2％～10％范围内，其微乳液增溶的水量最多；三种醇相比较，正丁醇体系的微乳区是W／O型向O／W型过渡的连续区域，正丙醇体系的O／W型微乳液区明显不同于正丁醇体系，正戊醇体系不能形成水包油型的微乳区。     

Urea‐activated 4,4'‐oxibis‐(benzenesulfonyl hydrazide) as foaming agent for low‐density unsaturated polyester resin manufacturing

The activation of foaming agent is critical to its application. In this study, 4,4′‐oxibis‐(benzenesulfonyl hydrazide) (OBSH) activated by urea was used in the manufacture of low‐density unsaturated polyester resin (LDUPR), and the results were compared with that of OBSH activated by zinc oxide and zinc stearate. The experiment results showed that the activation of OBSH by urea was better than by zinc oxide or by zinc stearate. A novel hydrogen bond activation mechanism of urea is presented in this research. Two stages, including the induction stage and the foaming stage, were proposed in the LDUPR manufacture according to the gas evolution curves of activated OBSH. The decomposition temperature and the decomposition time of OBSH activated by urea were determined to match the gelation time of UPR for the manufacture of LDUPR. The disadvantageous chemical behaviors of activated OBSH were eliminated in the induction treatment. The activated OBSH via induction treatment released gas maximally and distributed gas homogeneously in the resin glue, resulting in a better foaming effect than that of the previous foaming agents. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42824.     

Preparation and characterization of a low‐formaldehyde‐emission methylol urea/triethanolamine copolymer composite

A low‐formaldehyde‐emission methylol urea/triethanolamine composite was synthesized through in situ esterification of formaldehyde with triethanolamine and subsequent copolymerization of the synthesized polyester with methylol urea. The effects of the addition of triethanolamine to the polymerization process on some physical properties of the synthesized copolymer were evaluated. The copolymer was characterized with IR spectroscopy and macrophase‐separation techniques. At a given triethanolamine concentration, the composite exhibited macrophase‐separation behavior between that of pure methylol urea and pure polyester. IR spectra showed the presence of the polyester moiety in the composite. The values of the moisture uptake, formaldehyde emission, melting point, and elongation at break of the copolymer were within acceptable levels required in the coating industry. Therefore, the methylol urea/polyester copolymer resin could have potential as a binder in the coating industry. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Improving the heat‐resistance and toughness performance of phenolic resins by adding a rigid aromatic hyperbranched polyester

An aromatic hyperbranched polyester (AHBP) was synthesized by melt polycondensation from diphenolic acid and characterized by Fourier transform infrared spectrum (FTIR) spectra. The degree of branching (DB) value of AHBP calculated from the ¹³C‐NMR spectroscopy was 0.67. The number‐average molecular weight (M_n) and weight‐average molecular weight (M_w) of AHBP were 1792 and 4480 g/mol, respectively. Novel phenolic resins modified with AHBP (PR/AHBP) were then prepared, in which AHBP was used as toughener of phenolic resins. The effect of AHBP on the thermal properties of phenolic resins was studied by means of differential scanning calorimetry (DSC), thermal gravimetric analyses (TGA), and heat deformation temperature tests. The modified resins presented higher glass transition temperature (T_g) than the unmodified system due to that the rigid backbone structure of AHBP with a great deal of the benzene ring groups restricted the mobility of the chain segments of macromolecules. The DSC, scanning electron microscopy (SEM) analyses showed that AHBP had good compatibility with phenolic resin, and the modified resins showed ductile fracture. The results of mechanical performance measurements exhibited that the impact strength of PR/AHBP containing 15 wt % AHBP was about 130% higher than that of the neat phenolic resin, suggesting that the toughness of PR/AHBP was significantly improved by the addition of AHBP. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42734.     

Peroxide crosslinking of a styrene‐free unsaturated polyester

Thermoset unsaturated polyesters are usually obtained by the crosslinking of unsaturated polyester chains dissolved in an unsaturated, reactive, monomeric diluent, which is usually styrene. This article describes a new approach in which styrene‐free unsaturated polyester chains are intrinsically cured into a crosslinked matrix. The gel time, gel content, swelling degree, glass‐transition temperature, dynamic mechanical properties, tensile properties, and molecular weight between crosslinks (calculated according to both the Flory–Rehner equation and the theory of rubber elasticity) of the crosslinked polymer are studied as a function of the peroxide concentration. All properties change considerably upon the addition of small amounts of peroxide (between 1 and 2 wt %) and change to a lesser extent with higher peroxide concentrations (up to 6 wt %). The thermal properties of the isolated gel fraction are studied as a function of the peroxide concentration. The sol fraction demonstrates a plasticizing effect on the crosslinked network, affecting the glass‐transition temperature and stress–strain behavior of the crosslinked polymer. In light of the crosslink densities derived from swelling experiments, a molecular structure and crosslinking mechanism are suggested for the gel fractions of 1 and 6 wt % peroxide crosslinked unsaturated polyester chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Triethanolamine–azodiisobutyronitrile mixture as a foaming agent for low‐density unsaturated polyester resin manufacturing at a low temperature

A triethanolamine (TEA)–azodiisobutyronitrile (AIBN) mixture was applied to the manufacturing of a low‐density unsaturated polyester resin (LDUPR) at a low temperature ranging from 53 to 66 °C. Hydrogen‐bonding activation in the TEA–AIBN mixture was put forward, and this agreed with the NMR and Fourier transform infrared (FTIR) spectroscopy results. A heat balance in the curing process of a vinyl ester unsaturated polyester resin (UPR) was examined and characterized by differential scanning calorimetry, FTIR spectroscopy, and scanning electron microscopy. The TEA–AIBN mixture decomposed easily because of the hydrogen‐bonding action between TEA and AIBN. The heat release of the activated AIBN decomposition led to the early endothermic polymerization of the vinyl ester UPR. Hydrogen‐bonding activation followed by the heat‐balance process enabled us to manufacture the LDUPR at low temperature. The optimal parameters of LDUPR manufacturing, including a ratio of TEA to AIBN of 0.4 and a dosage of TEA–AIBN mixture of 2.5 phr at a curing temperature of 60 ± 1 °C, were defined by the testing of the apparent density (ρ) and compressive strength of LDUPR. Under these conditions, ρ was 0.39 ± 0.01 g/cm³, and the specific compressive strength was 33.92 ± 1.31 MPa g^?1 cm^?3. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44797.     

Mechanical and thermal properties of bio‐based CaCO3/soybean‐based hybrid unsaturated polyester nanocomposites

Bio‐based calcium carbonate nanoparticles (CaCO₃) were synthesized via size reduction of eggshell powder using mechanical attrition followed by high intensity ultrasonic irradiation. The transmission electron microscopic (TEM) and BET surface area measurements show that these particles are less than 10 nm in size and a surface area of ～44 m²/g. Bio‐based nanocomposites were fabricated by infusion of different weight fractions of as‐prepared CaCO₃ nanoparticles into Polylite® 31325‐00 resin system using a non‐contact Thinky® mixing method. As‐prepared bio‐nanocomposites were characterized for their thermal and mechanical properties. TEM studies showed that the particles were well dispersed over the entire volume of the matrix. Thermal analyses indicated that the bio‐nanocomposites are thermally more stable than the corresponding neat systems. Nanocomposite with 2% by weight loading of bio‐CaCO₃ nanoparticles exhibited an 18°C increase in the glass transition temperature over the neat Polylite 31325 system. Mechanical tests have been carried out for both bio‐nanocomposites and neat resin systems. The compression test results of the 2% Bio‐CaCO₃/Polylite 31325 nanocomposite showed an improvement of 14% and 27% in compressive strength and modulus respectively compared with the neat system. Details of the fabrication procedure and thermal and mechanical characterizations are presented in this article. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1442–1452, 2013     

Insolubilization and thermal stabilization of a long‐chain polyester by noncatalyzed melt‐polycondensation synthesis in air

Self‐standing films of poly(ω‐hydroxyl hexadecanoic acid) [poly(ω‐OHC16)] have been prepared by noncatalyzed melt‐polycondensation in air at 150, 175, and 200 °C. Poly(ω‐OHC16)s obtained are characterized as polyesters by infrared spectroscopy (FT‐IR) and solid state magic angle spinning ¹³C nuclear magnetic resonance (¹³C MAS‐NMR). Structurally, poly(ω‐OHC16)s are quite crystalline as revealed by wide angle X‐ray diffraction (WAXD). The presence of oxygen in the reaction atmosphere causes a mild oxidation in the form of peroxyester species, tentatively at the interphase between poly(ω‐OHC16) crystallites, and the structure amorphization. The interfacial peroxyester phase ends up in the encapsulation of the polyester grains and provides a barrier towards the action of solvents. Thermal stabilization and insolubility resulting from the synthesis conditions used are interesting features to prepare solvent and heat resistant poly(ω‐OHC16) coatings. Thus, a few microns thick poly(ω‐OHC16) layer has been fabricated on aluminum foil and its resistivity towards a chloroform:methanol (1:1, v:v) mixture has been confirmed. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44350.     

Effects of reactive low‐profile additives on the properties of cured unsaturated polyester resins. I. Volume shrinkage and internal pigmentability

The effects of reactive poly(methyl methacrylate) (PMMA) and poly(vinyl acetate)‐block‐PMMA as low‐profile additives (LPAs) on the volume shrinkage characteristics and internal pigmentability for low‐shrink unsaturated polyester (UP) resins during curing at 110°C were investigated. These reactive LPAs, which contained peroxide linkages in their backbones, were synthesized by suspension polymerization with polymeric peroxides as initiators. Depending on the LPA composition and molecular weight, the reactive LPAs led to a considerable volume reduction or even to a volume expansion after the curing of styrene (ST)/UP/LPA ternary systems; this was attributed mainly to the expansion effects of the LPAs on the ST‐crosslinked polyester microgel structures caused by the reduction in the cyclization reaction of the UP resin during curing as well as to the repulsive forces between the chain segments of UP and LPAs within the microgel structures. The experimental results were explained by an integrated approach of measurements for the static phase characteristics of the ST/UP/LPA system, reaction kinetics, cured sample morphology, and microvoid formation with differential scanning calorimetry, scanning electron microscopy, optical microscopy, and image analysis. With the aid of the Takayanagi mechanical model, the factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts were also explored. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 264–275, 2005     

Study of the porous network developed during curing of thermoset blends containing low molar weight saturated polyester

Polymerisation of unsaturated polyester/styrene blend added with a thermoplastic additive leads to the formation of a porous biphasic polymer network. In this paper, the porous medium was specifically studied by TEM associated with images analysis by chord length distribution and small angle X-ray scattering (SAXS). When the molar weight and/or the amount of low profile additive (LPA) are sufficient to ensure porosity higher than 2%, chord length distribution can be performed and is characteristic of a Debye random medium and Porod's law was observed in SAXS. The lengths deduced from Porod's law are similar to those observed for Debye random regime and are lower than 50 nm. These characteristics are closely related to the processes happening during curing and especially to the phase separation. For less porous samples, deviation from Porod's law was observed and could be attributed to additional scattering intensity coming from concentration fluctuations within polymer matrix. For nonporous samples, scattering intensity was only due to concentration fluctuations.     

Effect of non‐reactive solvent on the formation and properties of porous epoxy thermosets formed via reaction‐induced phase separation

BACKGROUND: A reaction‐induced process for producing controlled‐porosity epoxy thermosets with the aid of solvents is presented. The curing reactions were carried out in diglycidyl ether of bisphenol A and 4,4′‐diaminodicyclohexylmethane systems in the presence of appropriate solvents. RESULTS: The phase separation during the polymerization with appropriate solvent was characterized using dynamic light scattering. Supercritical carbon dioxide was used to extract the solvent from the epoxy resin matrix. The morphology and the porosity within the epoxy thermosets were investigated using scanning electron microscopy and atomic force microscopy as a function of solvent content. The results showed that porous epoxy networks with average pore size ranging from 1 to 20 µm were obtained, and the size of pores could be varied by changing the solvent content. Thermal properties were investigated using differential scanning calorimetry and thermogravimetric analysis. The introduction of solvent decreased the glass transition temperature and the thermal stability of the epoxy thermosets but showed no influence on the degradation of the main networks. CONCLUSION: Porous epoxy thermosets have been successfully fabricated through a novel reaction‐induced phase separation process with the aid of appropriate solvents. They should open a wide range of opportunities for new applications. Copyright © 2008 Society of Chemical Industry     

Toughening of thermoset/thermoplastic composites via reaction‐induced phase separation: Epoxy/phenoxy blends

Phase morphology and phase separation behavior of amine‐cured bisphenol‐A diglycidyl ether epoxy and phenoxy mixtures have been investigated by means of time‐resolved small angle light scattering, optical microscopy, and scanning electron microscopy. The starting reactant mixtures composed of epoxy, phenoxy, and curing agents such as diaminodiphenyl sulfone (DDS) and methylene dianiline (MDA) were found to be completely miscible. Upon curing with DDS at 180°C, phase separation took place in various epoxy/phenoxy blends (compositions ranging from 10–40% phenoxy), whereas the MDA curing showed no indication of phase separation. The mechanical and physical properties of single‐phase and two‐phase networks were examined, in that the DDS‐cured epoxy/phenoxy blends having a two‐phase morphology showed improved ductility and toughness without significantly losing other mechanical and thermal properties such as modulus, tensile strength, glass transition and heat deflection temperatures. The energy absorbed to failure during the drop weight impact event was also found to improve relative to those of the single‐phase MDA‐cured blend as well as of the neat epoxy. Such property enhancement of the DDS‐cured blends has been discussed in relation to the two‐phase morphology obtained via scanning electron microscopy micrographs of fractured surfaces. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1257–1268, 2000     

Fire‐retardant hybrid thermosetting resins from unsaturated polyesters and polysilazanes

This introduces an organic–inorganic thermosetting hybrid resin system based on unsaturated polyester and polysilazanes. It shows the chemical modification of unsaturated polyester structures by end capping to enable the combination of both components. In general, halogen‐free unsaturated polyesters are not fire‐retardant and have to be equipped with additives. Fillers and intumescent additives are preponderantly used in today's fire‐retardant formulations. In contrast to these fire‐retardants, polysilazanes act as ceramizing agents. Polysilazanes are suitable fire‐retardants for resin transfer molding due to their low viscosity. Both burning behavior and glass transition temperature (T_g) are investigated as important application properties. In contrast to state‐of‐the‐art fire‐retardant formulations polysilazane‐based thermosetting hybrid resins burn with high intensity and fast extinction. Therefore, total heat and smoke emission is decreased. The formation of ceramic structures during burning results in high residual mechanical properties and a low mass loss. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40375.