In this study, a carbon fiber/vinyl ester‐polyurethane interpenetrating polymer network (IPN) laminate composite was fabricated and characterized for the first time. The IPN matrix, consisting of a commercially available vinyl ester and polyurethane, was synthesized via a sequential method with vinyl ester as the rigid phase and polyurethane as the flexible phase. Good compatibility between the two phases in the matrix was achieved and confirmed via differential scanning calorimetry and dynamic mechanical analysis. The thermomechanical response of the IPN matrix was compared with that of an unmodified vinyl ester resin. The presence of the more ductile polyurethane in the IPN matrix depressed the glass transition temperature (from 94 to 84°C), but also served to improve damping response at all frequencies studied. Tensile and flexural tests were performed on the carbon fiber/IPN and carbon fiber/vinyl ester composites to determine their mechanical response. The IPN composite exhibited lower tensile properties than the vinyl ester composite. However, its flexural properties were on par with those of the vinyl ester composite.
Graft semi-interpenetrating polymer networks (IPNs) out of poly(ethylene glycol), PEG8000-based polyurethane, and acrylic copolymers were synthesized for phase change applications. The chemical structure of the IPN samples was checked with Fourier transform infrared spectroscopy. Thermal properties of the IPNs were studied using differential scanning calorimetry and thermogravimetric analysis. A scanning electron microscope was used to study the surface morphology of the IPN samples. Moreover, polarized optical microscopy and X-ray diffraction were utilized to examine the crystallization properties of the IPNs. The cycling stability of the IPNs was studied as well. Overall, graft-IPN samples show high thermal and cycling stability with excellent shape solidity and no change in crystallization properties compared to the pristine PEG8000. The results confirm the enormous potential of IPNs in a wide variety of phase change applications.
The stress relaxation behavior of acrylic-polyurethane (PU)-based graftinterpenetrating polymer networks (IPNs) was characterized via dynamic mechanical analysis (DMA) and modeled using finite element method (FEM) analysis. Stress relaxation of glassy IPN specimens was experimentally studied under flexural testing, while rubbery IPN specimens were tested in tension. The effects of varying the styrene content in the acrylic copolymer phase, compatibility of the two phases in IPNs, and changing the concentration of acrylic copolymer and PU were studied. A higher percentage of styrene content resulted in higher homogeneity of IPN specimens, and decrease in initial modulus for acrylic copolymer specimens. Additionally, glassy IPN specimens with 90% styrene shows resistance to relaxation as high as acrylic copolymer samples. Experimental results were used to develop a numerical model to study stress relaxation response of specimens. While polymer systems have been
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