Rheology of unsaturated polyester resins. I. Effects of filler and low-profile additive on the rheological behavior of unsaturated polyester resin

Measurements were taken of the bulk rheological properties of concentrated suspensions of particulates in unsaturated polyester resins, using a cone-and-plate rheometer. The particulates used were clay, calcium carbonate, and milled glass fiber. With clay and milled glass fibers, shear-thinning behavior of suspensions was observed at low shear rates or low shear stresses as the concentration of particulates was increased, whereas concentrated suspensions of calcium carbonate exhibited Newtonian behavior over the range of shear stresses or shear rates investigated. The cone-and-plate rheometer was also used for measurements of the bulk rheological properties of various mixtures of polyester resin and low-profile additives. For low-profile additives, solutions, in styrene, of poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) were used. It was found that the bulk viscosities of all mixtures of polyester resin and PVAc solution lie between those of the individual components, whereas the bulk viscosities of some mixtures of polyester resin and PMMA solution go through a minimum and a maximum, depending on the composition of the mixture. While all mixtures of polyester resin and PVAc solution exhibited negligible normal stress, some mixtures of polyester resin and PMMA solution exhibited noticeable normal stresses. It should be mentioned that polyester resin follows Newtonian behavior. It turned out that all mixtures of polyester resin and PVAc solution exhibited clear, homogeneous solutions, whereas mixtures of polyester resin and PMMA solution exhibited optical heterogeneity, i.e., turbidity. When polyethylene powders were used as low-profile additives, suspensions of polyester resin and polyethylene powders exhibited negative values of normal stress as the concentrations of suspension reached a critical value. When both filler and low-profile additive were put together in polyester resin, the rheological behavior became quite complex, indicating that some interactions exist between the filler and the low-profile additive.     

The effect of the chemical structure of low-profile additives on the curing behavior and chemorheology of unsaturated polyester resin

An experimental study was conducted to investigate the effect of the chemical structure of low-profile additives on the curing behavior and chemorheology of unsaturated polyester resin during isothermal cure. For the study a general-purpose unsaturated polyester resin was cured in the presence of t-butyl perbenzoate as Initiator. The curing behavior of the resin was investigated using differential scanning calorimetry (DSC). Three different thermoplastic low-profile additives were used, namely poly(vinyl acetate) (PVAc), poly(styrene-co-butadiene), which is also known as KRATON DX-1300, and dehydrochlorinated Isobutylene/isoprene copolymer, often referred to as conjugated diene butyl (CDB) rubber. Each of the these additives, about 30 weight percent, was first dissolved in styrene. The solution was then mixed with unsaturated polyester resin and CaCO₃. The CaCO₃ particles helped stabilize the emulsions consisting of resin and KRATCN, and of resin and CDB. For each resin formulation, a series of isothermal DSC runs were made at various levels of cure pressure. It was found that for all three low-profile resins investigated, the final degree of cure went through a maximum as cure pressure was increased from atmospheric to 6.21 MPa (900 psi). We have observed evidence that in the presence of an initiator generating free radicals, the unsaturated double bonds in the KRATON and CDB undergo grafting reactions with the styrene monomers and unsaturated polyester resin, increasing the glass transition temperature of KRATON and CDB, to an extent which varies with the cure conditions employed. Both steady and oscillatory shearing flow properties were determined using a cone-and-plate rheometer. The rheological measurements indicate that the resin/CaCO₃/KRATON and resin/CaCO₃/CDB systems give rise to gel times shorter than the resin/CaCO₃/PVAc system. It is concluded that both KRATON and CDB are more effective, both for enhancing the rate of cure of unsaturated polyester resin and imparting impact properties to the cured composites, than those thermoplastic low-profile additives that contain neither unsaturated double bonds nor a chemical structure that has rubber-like properties in the solid state.     

Thermokinetics of unsaturated polyester and vinyl ester resins

An experimental study was carried out to investigate the isothermal and non-isothermal curing kinetics of unsaturated polyester and vinyl ester resins, using differential scanning calorimetry (DSC). Emphasis was put on investigating the effect of low-profile additives on the curing kinetics of the thermo-setting resins. For the study, a general-purpose polyester resin and a vinyl ester resin were used, together with polyvinyl acetate (PVAc) as low-profile additive, benzoyl peroxide as initiator, and N,N-dimethyl aniline as promoter. It has been found that (1) the addition of the low-profile thermoplastic-additive decreases the rate of cure and, also, the final degree of cure of the resins, (2) the total heat of cure generated by isothermal cure is lower than that generated by non-isothermal cure, and (3) the resin/initiator mixture with promoter exhibits two major exotherm peaks during non-isothermal cure, but only a single exotherm peak during isothermal cure.     

Rheology of unsaturated polyester resins. III. Effects of filler and low-profile additive on the thickening behavior of unsaturated polyester resin

An investigation was made of the rheological behavior of unsaturated polyester resin during thickening in the presence of filler or low-profile additive alone and, also, in the presence of both filler and low-profile additive. For the study, two different types of filler (CaCO₃ and clay) and two different types of low-profile additive (PMMA and PVAc) were evaluated. Compared to the resin/thickener system, the resin/filler/thickener system exhibits shear-thinning behavior as thickening progresses, and gives rise to smaller normal stress effects. On the other hand, the resin/low-profile additive/thickener system exhibits two distinct Newtonian regimes in the viscosity-shear stress curves and gives rise to larger normal stress effects. The viscosity behavior of the resin/filler/low-profile additive/thickener system was found to be very similar to that of the resin/low-profile additive/thickener system. In all cases, when the first normal stress difference was plotted against the shear stress, a correlation was obtained which was independent of thickening period. This behavior was exactly the same as for thickening polyester resin alone, as discussed in Part II of this series.     

Effects of poly(vinyl acetate) and poly(methyl methacrylate) low-profile additives on the curing of unsaturated polyester resins. I. Curing kinetics by DSC and FTIR

The effects of two low-profile additives (LPA), poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) on the curing kinetics during the cure of unsaturated polyester (UP) resins at 110°C were investigated by using a differential scanning calorimeter (DSC) and a Fourier transform infrared spectrometer (FTIR). The effects of temperature, molar ratio of styrene to polyester CC bonds, and LPA content on phase characteristics of the static ternary systems of styrene–UP–PVAc and styrene–UP–PMMA prior to reaction were presented. Depending on the molar ratio of styrene to polyester CC bonds, a small shoulder or a kinetic-controlled plateau in the initial portion of the DSC rate profile was observed for the LPA-containing sample. This was due to the facilitation of intramicrogel crosslinking reactions since LPA could enhance phase separation and thus favor the formation of clearly identified microgel particles. FTIR results showed that adding LPA could enhance the relative conversion of polyester CC bonds to styrene throughout the reaction. Finally, by use of a microgel-based kinetic model and static phase characteristics of styrene–UP–LPA systems at 25°C, the effects of LPA on reaction kinetics regarding intramicrogel and intermicrogel crosslinking reactions, relative conversion of styrene to polyester CC bonds, and the final conversio have been explained. © 1995 John Wiley & Sons, Inc.     

Chemorheology of thermosetting resins. IV. The chemorheology and curing kinetics of vinyl ester resin

The rheological properties and curing kinetics of a vinyl ester resin have been determined during isothermal cure. Both steady and oscillatory shearing flow properties were determined using a cone-and-plate rheometer, and the curing kinetics were determined using a differential scanning calorimeter (DSC). Also determined were the rheological properties and curing kinetics of the resin when it had been thickened using magnesium oxide (MgO), in the presence of calcium carbonate (CaCO₃) as filler and polyvinyl acetate (PVAc) as low-profile additive. The steady shearing flow behavior observed with the vinyl ester resin was found to be very similar to that observed with a general-purpose polyester resin, reported in Paper I of this series [C. D. Han and K. W. Lem, J. Appl. Polym. Sci., 28 , 3155 (1983)]. However, a significant difference in the oscillatory shearing flow behavior was found between the two resins. We have concluded that dynamic measurement is much more sensitive to variations in resin chemistry than steady shearing flow measurement. DSC measurement has permitted us to determine the degree of cure as a function of cure time. By combining the rheological and DSC measurements, we have constructed plots describing how the viscosity increases with the degree of cure, at various isothermal curing temperatures.     

Effects of poly(vinyl acetate) and poly(methyl methacrylate) low-profile additives on the curing of unsaturated polyester resins. II. Morphological changes during cure

The effects of two low-profile additives (LPA), poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA), on the morphological changes during the cure of unsaturated polyester (UP) resins at 110°C were investigated by an approach of integrated reaction kinetics-morphology-phase separation measurements by using a differential scanning calorimeter (DSC), scanning electron microscopy (SEM), optical microscopy (OM), and a low-angle laser light-scattering appartus (LALLS). For the UP resins cured at 110°C, adding LPA could facilitate the phase separation between LPA and crosslinked UP phases early in the reaction, and discrete microgel particles were thus allowed to be identified throughout the reaction. Microvoids and microcracks responsible for the volume shrinkage control could also be observed evidently at the later stage of reaction under SEM. Depending on the types of LPA and the initial molar ratios of styrene to polyester C?C bonds, the morphological changes during the cure varied considerably. The progress of microstructure formation during reaction has been presented. Static ternary phase characteristics for the styrene–UP–LPA system at 25°C have also been employed to elucidate the resulting morphology during the cure in both the continuous and the dispersed phases. © 1995 John Wiley & Sons, Inc.     

Influence of processing conditions on shrinkage behavior of low profile unsaturated polyester resins. I: Systems without fillers

Blends of unsaturated polyester resin and polyvinylacetate (PVAc) were molded with a new instrument called the Plastoreactomat (PRM). The shrinkage and exothermic peak of polymerization were recorded during moding, and the influence of the processing conditions (pressure and temperature) on these phenomena and on the morphology was investigated for various PVAc contents. Within the limits of this study, it was found that shrinkage increases as the temperature and pressure increase. These results are discussed in terms of a competition between the phase separation and the reaction rates. In addition, it was verified that a co-continuous two-phase system consisting of the PVAc and the polyester network enhances the low-profile behavior.     

Effects of reactive low‐profile additives on the volume shrinkage and internal pigmentability for low‐temperature cure of unsaturated polyester

The effects of reactive poly(vinyl acetate)‐block‐poly(methyl methacrylate) (PVAc‐b‐PMMA) and poly(vinyl acetate)‐block‐polystyrene (PVAc‐b‐PS) as low‐profile additives (LPA) on the volume shrinkage characteristics and internal pigmentability for low‐shrink unsaturated polyester resins (UP) during the cure at 30°C were investigated. These reactive LPAs, which contained peroxide linkages in their backbones, were synthesized by suspension polymerizations, using polymeric peroxides (PPO) as initiators. Depending on the LPA composition and molecular weight, the reactive LPA could lead to a reduction of cyclization reaction for UP resin during the cure, and would be favorable for the decrease of intrinsic polymerization shrinkage after the cure. The experimental results have been explained by an integrated approach of measurements for the static phase characteristics of the styrene (ST)/UP/LPA system, reaction kinetics, cured sample morphology, and microvoid formation by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), optical microscopy (OM), and image analysis. Based on the Takayanagi mechanical model, factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts have been explored. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 967–979, 2006     

Low‐profile mechanisms in a PVAc/polyester blend

The different steps associated with the curing of a PVAc/polyester blend are identified and correlated to the mechanism of shrinkage control in the presence of a low‐profile additive (LPA). Poly(vinyl acetate) (PVAc) is used as a LPA and is shown to induce a phase separation upon curing that leads to an interconnected globule morphology. This morphology strongly modifies the rheokinetics of the blend compared to that of the neat polyester resin. In particular, the presence of PVAc delays the cure kinetics and the gel time. A comparison between these delays, called shift times, demonstrates an increase in the gel conversion of polyester in the presence of PVAc. This, coupled to the thermal expansion of PVAc at the early stages of curing, contributes to the low‐profile effect. Microvoids in the LPA‐rich phase, which are believed to play a key role in the mechanism of shrinkage control, are efficient at the later stages of curing and during cooling and complete the low‐profile effect. However, it is also shown that the formation of microvoids may indirectly induce macroscopic voids that could be at the origin of pinholes at the surface of the parts molded with this material. POLYM. ENG. SCI. 46:303–313, 2006. © 2006 Society of Plastics Engineers     

Fractal characterization of the fissures occuring during polymerization of low-profile unsaturated polyester resins

Blends of unsaturated polyester resin and polyvinylacetate (PVAc) were cured between two glass slides. In this case, the low-profile effect arises by fissuring with a fractal geometry. This paper shows how the fractal dimension of the fissures depends on the PVAc amount and on the cure temperature. These results are discussed with the present knowledge about the polyester network morphology in two phases more or less co-continuous.     

Characterization of thermoset cure behavior by differential scanning calorimetry. Part II: Effects of low-profile additives

An autocatalyzed second-order kinetic model was adopted to compare the isothermal and dynamic cure behavior of low-profile polyester resins in terms of kinetic parameters such as degree of cure, cure rate, half-life, onset cure temperature, reaction order, and Arrhenius parameters. The reaction orders of low-profile unsaturated polyesters appear to be almost independent of isothermal cure temperatures. The ultimate conversion, conversion at peak maximum, onset cure temperature, and Arrhenius parameters of polyesters are only slightly affected by the concentration and type of low-profile additives in the resins. Low-profile additives, in general, tend to retard the cure rate and suppress the exothermicity of polyester resins because of dilution effects. For low-profile additives such as poly(vinyl acetate) and polyurethane, which are “quite” compatible with polyesters before cure, the overall reaction rates of the resins are substantially enhanced over those of less compatible additives. However, the ultimate conversion of low-profile polyesters is found to be slightly greater than that of neat polyester, in most cases.     

Effects of poly(methyl methacrylate)‐based low‐profile additives on the properties of cured unsaturated polyester resins. II. Volume shrinkage characteristics and internal pigmentability

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 volume shrinkage characteristics and internal pigmentability for low‐shrink unsaturated polyester (UP) resins during curing were investigated by an integrated approach of static phase characteristics of the ternary styrene (ST)/UP/LPA system, reaction kinetics, cured‐sample morphology, microvoid formation, and property measurements. The relative volume fraction of microvoids generated during the cure was controlled by the stiffness of the UP resin used, the compatibility of the uncured ST/UP/LPA systems, and the glass‐transition temperature of the LPAs used. On the basis of the Takayanagi mechanical model, the LPA mechanism on volume shrinkage control, which accounted for phase separation and microvoid formation, and factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts are discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3388–3397, 2004     

Phase separation of unsaturated polyester resin blended with poly(vinyl acetate)

The behavior of phase separation during the curing reaction of unsaturated polyester (UPE) resin in the presence of low profile additive, that is, poly(vinyl acetate) (PVAc), was studied by low-angle laser light scattering (LALS) and scanning electron microscopy (SEM). The experimental results revealed that the PVAc-rich phase was regularly dispersed in the cured styrene–UPE matrix for styrene–UPE resin blended with 5 wt % of PVAc. As the PVAc content was increased higher than 10 wt %, a cocontinuous PVAc and cured styrene–UPE phase was observed for the cured systems. The LALS observations were carried out in situ at a curing temperature of 100°C; thus, the effect of the rate of exothermic heat released from curing reaction on the morphology of curing system was investigated and reported in this work. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2413–2428, 1999     

Effect of nanoclay on shrinkage control of low profile unsaturated polyester (UP) resin cured at room temperature

The addition of a small amount of nanoclay (1-3 wt%) can provide excellent volume shrinkage control of unsaturated polyester (UP)/styrene (St)/poly(vinyl acetate) (PVAc) systems cured at room temperature. PVAc serves as the low profile additive (LPA). In this study, both temperature-induced phase separation of the uncured resin mixture and transmission electron microscopy (TEM) of the cured sample revealed that nanoclay resided in the LPA-rich phase, leading to a higher reaction rate and earlier onset of micro-cracking in the LPA-rich phase or at the interface of the LPA-rich and UP-rich phases. Consequently, an earlier volume expansion during curing was observed in reactive dilatometry, resulting in better shrinkage control. On-line measurement of the composite thickness change during vacuum-infusion liquid composite molding [e.g. the Seemann Composite Resin Infusion Molding Process (SCRIMP)] further proved excellent volume shrinkage control of nanoclay filled systems, leading to a smoother composite surface.     

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.     

不饱和聚酯树脂改性研究进展

综述了不饱和聚酯树脂(UPR)改性的研究进展。介绍了收缩率控制机理,低收缩研究发展的4个阶段,低收缩剂LSA的典型代表——聚苯乙烯(PS),聚甲基丙烯酸甲酯(PMMA),聚醋酸乙烯(PVAc),PVAc-PS共聚物。讨论了UPR增韧改性方法,提高分子主链对称性,在分子结构中引入长链醇与长链酸,长链醇包括一缩二乙二醇、二缩三乙二醇及聚乙二醇;长链二元酸如己二酸等。此外还可加入热塑性弹性体,如液体橡胶、液体聚氨酯等以形成互穿网络结构增韧UPR。论述了提高UPR阻燃性的2种途径,即选用本质阻燃性树脂和向UPR中添加阻燃剂。介绍了含卤有机阻燃剂、无机阻燃剂、主链或主链与侧链均含磷的阻燃剂和赋予阻燃性的影响因素。介绍了部分采用可降解的植物纤维——竹纤维制备的UP复合材料和木粉改善UPR的性能。这些方法使不饱和聚酯树脂在低收缩性能、力学性能、阻燃性能等方面得到了改善,扩展了其应用范围。     

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     

低收缩添加剂对聚酯树脂固化的影响

本文采用SPI法测定加入不同含量低收缩添加剂（LPA）的不饱和聚酯树脂的固化放热曲线。研究了低收缩添加剂的用量，以及中低温固化体系对不饱和聚酯树脂的凝胶时间，固化时间，放热峰温度，固化放热量的影响。     

低收缩型不饱和聚酯树脂的研究进展

综述了目前不饱和聚酯树脂低收缩性的研究进展,探讨了包括聚醋酸乙烯酯、聚苯乙烯、聚氨酯和嵌段共聚等在内的添加低收缩添加剂和改变原料或工艺对收缩率的影响。论述了新型低收缩不饱和聚酯的合成和工艺方法等。参考文献13篇。