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The reaction between unsaturated polyester (UP) resin and styrene (St) is a heterogeneous free-radical chain-growth cross-linking copolymerization. Curing of the UP/St system in the presence of organically-modified nanoclay was studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. A mechanistic kinetic model based on the free radical copolymerization mechanism was developed to simulate the reaction rate and conversion profiles of UP/St resin mixtures with various nanoclay contents cured at low temperatures. The model parameters were determined from several DSC experiments under isothermal conditions. The model, in conjunction with heat transfer analysis, was able to successfully predict the temperature and conversion profiles during curing in two vacuum-infusion liquid composite molding (e.g., the Seemann composite resin infusion molding process [SCRIMP]) experiments. The presence of nanoclay particles enhanced the tensile modulus, but reduced the tensile strength of the UP nanocomposites. The fracture toughness parameter [K.sub.IC] was improved by 30% with the addition of 5 wt% nanoclay. The system with mixed nanoclay and calcium carbonate was found to possess the highest [K.sub.IC] without sacrificing the tensile strength. POLYM. ENG. SCI., 45:496-509, 2005. © 2005 Society of Plastics Engineers, INTRODUCTION Among various thermoset resins, unsaturated polyesters (UP) resins are the most widely used matrix materials in polymeric composites. They represent approximately 75% of the total thermoset composites market by [...]

The toughness of polybenzoxazine can effectively be improved by alloying with isophorone diisocyanate (IPDI)-based urethane prepolymers (PU) or with flexible epoxy (EPO732). The experimental results, i.e., flexural testing and dynamic mechanical analysis, reveal that the toughness of the alloys of the rigid polybenzoxazine and the PU or the EPO732 systematically increases with the amount of either toughener, due to the addition of more flexible molecular segments in the polymer hybrids. The curing temperature of the benzoxazine resin (bisphenol A-aniline type [BA-a]) at about 225[degrees]C shifts to a higher value when the fraction of BA-a in either alloy decreases. Interestingly, the enhancement in the glass transition temperature ([T.sub.g]) of BA-a/PU alloys is clearly observed, i.e., [T.sub.g] of the BA-a/PU alloys are significantly higher ([T.sub.g] beyond 200[degrees]C) than those of the parent resins, i.e., 165[degrees]C for BA-a and -70[degrees]C for PU. However, this characteristic is not observed in the BA-a/EPO732 alloy systems. The enhanced [T.sub.g] of the BA-a/PU alloy at a 70/30 mass ratio is found to be 220[degrees]C, while that of BA-a/EPO732 at the same mass ratio is observed to be only 95[degrees]C, which further decreases as the content of epoxy fraction increases. Furthermore, the degradation temperature based on 5% weight loss in the thermogravimetric analyzer (TGA) thermograms of the BA-a/PU alloys is found to improve with the presence of the PU, though the opposite trend is observed in the BA-a/EPO732 systems. The char yield of both alloy systems is steadily enhanced with the increased benzoxazine content because the char yield of the polybenzoxazine is inherently higher than that of the two tougheners. Therefore, the polybenzoxazine alloys with the IPDI-based urethane prepolymer, e.g., the 70/30 BA-a/PU, are a promising system for a tough, high thermal stability polymeric network, suitable for both bulk and composite matrix applications. POLYM. ENG. SCI., 45:288-296, 2005. [c] 2005 Society of Plastics Engineers, INTRODUCTION The polybenzoxazines, a novel class of thermosetting polymers, possess some intriguing properties such as high thermal stability, easy processing ability, low water absorption, near zero shrinkage upon curing, and [...]

Thermo-setting polymers are widely used as underfill materials to improve the reliability of electronic packages. In the design phase, the influence of underfill applications on reliability is often judged through thermal and mechanical simulations, under assumed operating conditions. Because of lacking insight into the mechanical processes due to polymer curing, the impact of processing induced residual stress fields is often neglected. To investigate the evolution of stress and strain fields during the curing process it is important to assume a more appropriate starting point for subsequent process modeling Furthermore, study of possible damage originating from the fabrication process then comes within reach. To facilitate future analysis of stress and strain fields during the curing process a cure dependent constitutive relation is assumed. An approximate investigation method for the process-dependent mechanical properties, based on Dynamic Mechanic Analysis (DMA), is developed. As an illustration the parameter identification is performed for a selected epoxy resin. [DOI: 10.1115/1.1459471]

In recent years, electrical techniques like microdielectrometry have increasingly been utilized for their ability to continuously monitor, in a nondestructive way, the advancement of the reaction of thermoset resins under cure. This paper discusses an extension of this technique for the 'in-situ' monitoring of the crystallization of thermoplastics applied during an injection molding process. Electric sensors were positioned at the walls of the mold cavity so that an analysis of the volume dielectric properties of material during the filling, the post-filling, and the cooling steps could be carried out. Poly(vinylidene fluoride) was chosen for this study. A correlation between the evolution of the dielectric parameters and the succession of the steps in this process was undertaken. The dielectric response was sufficiently sensitive to identify the steps of the closing of the mold, filling, post-filling, cooling, and ejection of the part. In addition, information concerning the crystallization phenomenon near t he wall or in the middle of the sample was collected. The gradual filling of the cavity of the mold was also identified by dielectric measurements. The temperature dependence of dielectric properties of the sample was beneficial in evaluating the increase of the temperature of the mold with the succession of injection cydes. The influence of the packing pressure has been clearly identified and confirms the usefulness of the dielectric method as a probe for detecting the shrinkage of the part during the optimization phase of the machine parameters. The dielectric method detailed herein provides a new non-invasive technique and could be applied to a closed-loop control of the injection molding process., INTRODUCTION Currently, what is considered to be a satisfactory product depends as much on economic factors (minimal waste, minimal cycle time) as on the dimensions and the aspects of the [...]

Two types of polymers with disperse red 19 pendant groups, a thermal-imidization polyimide and a thermal-crosslinking polyurethane, were employed in thermal-assisted optical poling to enhance the photostability of the optically induced polar orientation of molecules. During the seeding process, samples heated in an oven were irradiated simultaneously by the coherent superposition of the 1064 nm fundamental and the 532 nm second-harmonic light of a nanosecond-pulsed Nd:YAG laser. Results showed that the optically aligned azodye molecules were fixed by the thermosetting polymer matrix during the thermal-assisted optical poling process.

Experiments on coated films of waterborne coatings (WBC) under controlled conditions (i.e., 25 ° C, 65% RH) were carried out to study the mechanism of leveling. Data in a companion paper imply that the development of the surface tension gradients plays an important role in promoting leveling. The stress due to surface tension gradients is found to be much greater than the stress introduced by hydrostatic pressure gradients in the film caused by surface tension and the free boundary curvature of the film. This reconfirms that the use of a co-solvent, which evaporates faster than water, greatly accelerates the leveling of a WBC., INTRODUCTION It is important to obtain coatings with a smooth surface for appearance and for the inherent performance properties of the coating film. The quality requirements for the leveling in [...]

The influence of film thickness on the leveling of a thermosetting waterborne coating (WBC) was examined. The theory of Patton has been revised to give the proper force balance and modified to include the changes in surface tension and viscosity during leveling by the evaporation of volatile components. However, the predicted leveling process by a numerical method did not coincide with the observed results. Thus, the driving force in the theory, the hydrostatic pressure gradient in the film, was considered to be insufficient to describe the leveling process of the WBC. The hydrostatic pressure gradient can be a component of the driving force to promote leveling, but the existence of an additional component is suggested., INTRODUCTION Coyle (1) showed that it is impossible to control the formation of surface ripples, called ribs, during the application process by the modification of the rheological properties of the [...]

The simultaneous time-resolved study of structure development and reaction kinetics during polymer processing is an experimental method that has great potential in developing a deeper understanding of the parameters that govern the formation of structure and therefore polymer properties. A combination of synchrotron radiation small-angle x-ray scattering and Fourier-transform infrared spectroscopy experiments have been performed on a series of model segmented block copolyurethanes. These studies confirm that the driving force for structure development in polyurethanes is the thermodynamics of phase separation rather than hydrogen bonding., One significant advantage of using synchrotron radiation small-angle x-ray scattering (SAXS) beam lines for polymer processing studies is that the high x-ray intensity allows time-resolved x-ray scattering experiments on polymers [...]

Spirodilactam bisallylether is a new high temperature performance monomer. It melts at 154 degrees C, and is thermally inactive in forming a homopolymer. However, it reacts readily with a bismaleimide via 'ene' reaction. Therefore, it could be used as a comonomer and an effective toughening modifier for bismaleimide. The properties of the blends of spirodilactam bisallylether and 4,4'-bismaleimidodiphenylmethane were studied. The cocured resins have high glass transition temperature, >300 degrees C. By adding 30 to 40 mole % of the bisallylether, the compact tension toughness of the bismaleimide was improved to 0.7 MPa-m(super 1/2). Therefore, the resins have a combination of high glass transition temperature and toughness. They also showed good flexural properties. Despite the high water absorption, 5 to 7%, the resins retained high hot/wet flexural properties because of the high glass transition.

A modified observation system for the leveling process of a coated fluid is proposed, and the observation results are presented and compared with previous results. For the thermosetting waterborne coatings, the theory of Orchard, et al., and ones based on it are not applicable and fail to give even a qualitative description. The theory of Overdiep was found to be reasonable. However, it was insufficient to predict the leveling performances of coatings without experimentation. Qualitatively, the original theory suggests the possibility of the reappearance of surface ripples, in other words, the occurrence of the negative amplitude in the surface ripples during the course of leveling, although little data were presented regarding the phenomenon. It was found here that added co-solvent plays an important role on the leveling rate and also the occurrence and the control of the negative amplitude of the surface ripples. These are thought to relate closely to the volatility of the co-solvent and the composition of the solvent residue in the coated film during the leveling process.

Modifications to the standard spiral flow test commonly used to evaluate the molding capabilities of thermosetting materials can be studied to produce rheological data. Constants in a viscosity model are calculated with a parametr-identification format which maintains at a minimum the difference betwen results of spiral flow tests and simulations of these tests. Applied to an encapsulating epoxy material, the proposed method succeeds in predicting spiral flow experiment results comparable to the simulation results and does not require complex equipment.

The feasibility of using acoustic cure-monitoring sensors to control the manufacturing process is evaluated through an analysis of simultaneous and rheometric measurements involving the epoxy curing process. Results show that the proposed method successfully monitors neat epoxy curing in the curing cycle. The dynamic modulus is tracked using the acoustic modulus defined from the shear velocity which also ranks two epoxy compositions' stiffness. Acoustic and mechanical moduli for fully cured epoxy resins conform well in the case of accounted frequency difference.

V[acute{E}]RONIQUE MICHAUD JAN-ANDERS M[dot{A}]NSON [*] The relative sequence of shrinkage and evolution of modulus of a thermoset resin during cure leads to the build-up of internal stresses, especially if the [...]

The effects of cure temperature and amount of catalyst on the rheokinetical behavior of a melamine-formaldehyde (MF) thermosetting system is investigated using a dynamic mechanical technique similar in nature to Torsion Impregnated Cloth Analysis (TICA) and Torsional Braid Analysis A). The proposed name of the used technique is Torsional Substrate Analysis (TSA). Isothermal cures of the resin are carried out from i 15 ° C to 160 ° C for varying amounts of catalyst. Each TSA measurement exposes several transitions. First, a glass-to-liquid transition during the heatup procedure is seen, indicated by sharp peaks of the loss shear modulus, G″, and loss tangent, tanΔ. Later, vitrification is seen, indicated by a second G″ maximum. Finally, a completion of shift to a diffusion controlled cure reaction occurs, shown as a storage shear modulus, G′, plateau. The rheokinetical data is used to construct Time-Temperature-Transformation (TIT) cure diagrams, for each level of catalyst. High pressure differential scanning calorimetry (HPDSC) measurements are carried out in order to estimate the fractional conversion of samples that have been cured isothermally for times corresponding to a second tanΔ maximum, the second G″ maximum, and the G′ plateau. The fractional conversion is determined by the residual entalphy technique. The HPDSC measurements do not give a clear answer whether the second tanΔ maximum corresponds to gelation or not. It is therefore likely that TSA, like similar techniques, is not capable to detect gelation. A glass transition temperature of 130 ° C and 150 ° C is found to correspond to a fractional conversion of 0.65 and [approximately]0.80, respectively. Preliminary measurements suggest that the maximum glass transition temperature, [T.sub.g∞], of the investigated MF resin is at least 180 ° C., INTRODUCTION The rheokinetical behavior on cure of a melamineformaldehyde (MF) resin with different catalyst levels is investigated in this work. Polymers of melamine (1,3,5-triamino-2,4,6-triazine) and formaldehyde form an important class [...]