In-situgrown silica/water-borne epoxy shape memory composite foams prepared without blowing agent addition

Thermal Behaviors, Interfacial Microstructure and Molecular Orientation of Shape Memory Polyurethane/SiO2 Based Sealant for Concrete Pavement

Expansion joint failure is one of the main causes that lead to the damages of concrete pavement. The silicon dioxide/shape memory polyurethane (SiO₂/SMPU) is a new kind of sealant which can use its shape memory performance to adapt to the width of the expansion joint with the change of pavement temperature, and it can effectively prolong the service life of the pavement and reduce maintenance costs. In this study, the effects of programming and the addition of SiO₂ particles to the thermodynamic properties of the specimens were detected using differential scanning calorimetry (DSC), the optimal shape memory programming temperature of which is 72.9 °C. Combined with scanning electron microscopy (SEM) and shape memory effect test, the particles are evenly distributed between the two phases, and the shape fixation rate (R_f) of 98.15% and the shape recovery rate (R_r) of 97.31% show that the composite has a good shape memory effect. Fourier transform infrared spectroscopy (FTIR) and dynamic infrared dichroism illustrate the change of the hydrogen bond of soft and hard segments with the SiO₂ particles in the shape memory cycle, revealing the optimal shape memory programming process. This study provides an insight into the reinforcement mechanism of SiO₂ nanoparticles in SMPU matrix and verify whether it can meet the engineering requirements of expansion joints when used as a sealant of concrete pavement.

Effect of Resin and Blocked/Unblocked Hardener Mixture on the Production of Epoxy Foams with CO2 Blocked Hardener in Batch Foaming Process

The present study focuses on the processing and properties of epoxy foams by the use of CO2 blocked hardener N-aminoethylpiperazine (B-AEP) and different resins. Although some studies described the foaming with carbamates, little attention has been given to the interaction of resin properties (such as viscosity) on the foaming performance. Therefore, two resins, diglycidyl ether of bisphenol-A (DGEBA) and epoxy novolac (EN), as well as their 50:50 blend, were foamed with B-AEP and unblocked/blocked AEP hardener mixtures in a batch foaming process. Furthermore, the commercially available chemical blowing agent para-toluenesulfonyl hydrazide (TSH) was used as a benchmark for commonly used chemical blowing agents. The lowest density in this study was reached by the DGEBA+B-AEP system in the range of 215 kg/m3 with the drawback of an inhomogeneous cell structure and high cell size distribution. The best cell morphology and lowest cell size distribution was reached with the EN+15:85% unblocked:blocked hardener mixture, resulting in a density in the range of 394 kg/m3. A syntactic foam was achieved by a DGEBA+50:50% unblocked:blocked hardener mixture with a density of around 496 kg/m3. It was found that a higher viscosity of the resin lead to an increase in the density and a decrease in the cell size distribution range as a result of a closer expansion time window.

Review of Progress in Shape Memory Epoxies and Their Composites

Shape memory polymer (SMP) is capable of memorizing one or more temporary shapes and recovering successively to the permanent shape upon various external stimuli. Beside of the above mentioned one-way variants, also two-way shape memory polymers (SMPs) and shape memory (SM) systems exist which feature a reversible shape change on the basis of "on-off switching" of the external stimulus. The preparation, properties and modelling of shape memory epoxy resins (SMEP), SMEP foams and composites have been surveyed in this exhaustive review article. The underlying mechanisms and characteristics of SM were introduced. Emphasis was put to show new strategies on how to tailor the network architecture and morphology of EPs to improve their SM performance. To produce SMEPs novel preparation techniques, such as electrospinning, ink printing, solid-state foaming, were tried. The potential of SMEPs and related systems as multifunctional materials has been underlined. Added functionality may include, among others, self-healing, sensing, actuation, porosity control, recycling. Recent developments in the modelling of SMEPs were also highlighted. Based on the recent developments some open topics were deduced which are merit of investigations in future works.