Enhancing the Fracture Resistance and Impact Toughness of Mechanically Frothed Epoxy Foams with Hollow Elastomeric Microspheres

Abstract

Nonporous elastomeric particles are often employed to improve the toughness of brittle epoxy foams but this also decreases their compressive strength and stiffness. Herein, a novel strategy utilizing hollow elastomeric microspheres as toughening agent for epoxy foams is presented. The addition of 0.5 wt.% hollow elastomeric microspheres into epoxy foam leads to a 15% increase in critical stress intensity factor (K 1c) to 0.38 MPa m0.5 and 33% increase in Charpy impact strength (acU ) to 1.05 kJ m−2, respectively, compared to unfilled epoxy foam (K 1c = 0.33 MPa m0.5 and acU = 0.79 kJ m−2). However, a further increase in the hollow elastomeric microsphere concentration to 1.0 wt.% leads to microsphere agglomeration, which reduces both K 1c and acU to 0.35 MPa m0.5 and 0.93 kJ m−2, respectively. Nevertheless, the added hollow elastomeric microspheres do not lead to a reduction in the quasi‐static compressive properties of the epoxy foams.

Gas-Generating Polymer Particles: Reducing the Decomposition Temperature of Poly(tert-Butyl Methacrylate) Side Chains Using an Encapsulated Acid Catalyst Approach

“…Many applications for gas-generating particles, including compounding and light-weighting in composite materials, may rely on short processing times at high speeds. − Although t -BMA-based latexes can undergo acid-catalyzed gas generation under heating at a constant rate (see Figure ), we performed a series of experiments to determine how quickly gas generation could occur by manipulating temperature. Figure A shows the results of isothermal TGA experiments on Latex-8 .…”

“…Gas-generating polymer particles have long been used in a wide range of industrial and consumer applications, including drug delivery and controlled release, − and for the design of thermally expandable or hollow microspheres − that can be used to light-weight or thermally insulate paper, plastics, and other composite materials. − Continued interest in this broad class of functional polymer particles has led to recent applications in oil extraction, fragrances, artificial photosynthesis, and biomedical imaging. ,− In these and other emerging applications, − the gas of interest is encapsulated within a polymeric particle and subsequently released or triggered in response to an external stimulus or other controlled conditions. Naturally, the identity and the physicochemical properties of the gas must be selected not only based on the desired application but also by the method of encapsulation and the properties of the polymeric host.…”

“…Fundamental kinetics studies suggest that the gas generation behavior of this system can be further controlled by other variables, including sample pH and the applied heating rate. These additional insights enable a further decrease in decomposition temperature to 120 °C with an onset of gas generation as low as 107 °C in dry particles, temperatures within the range required for myriad applications. − ,− …”

Preparation, Microstructure and Impact Properties of a Novel Stainless Steel Porous Plate

“…A failure criterion describing the failure surface at the onset of plasticity for open-cell, isotropic foams idealized as linearly elastic-perfectly plastic was employed by Gibson et al, 30) and the criterion was applied to the characterization of the impact resistance of honeycomb materials. A novel strategy utilizing hollow elastomeric microspheres as toughening agent for epoxy foams was presented by Song et al 31) The addition of 0.5 wt.% hollow elastomeric microspheres into epoxy foam led to a 15% raise in critical stress intensity factor to 0.38 MPa m 0.5 and 33% increased in impact strength to 1.05 KJ/m 2 . The impact property of 3D printed 15-5 PH stainless steel was investigated by Sagar et al, 32) and the experimentally measured impact energies were 0.01, 6.78 ± 4.07, and 50.84 ± 3.39 J/cm 2 , at low (77 K), room (298 K), and high temperatures (723 K).…”

Cell structures, phase morphologies and impact toughness of phenolphthalein poly(ether ether ketone)/epoxy composite foams

“…However, the further increase in the hollow elastomeric microsphere concentration led to microsphere agglomeration, and then both fracture resistance and impact strength of epoxy foams decreased. [14] Generally, the aggregation of nanoparticles or fibers will happen in the composites with high filler contents, leading to the deterioration of mechanical properties, while the rubber fillers suffers from reduced modulus and thermal stability of epoxy foams. In order to overcome these shortcomings, TP resins are used as toughness modifier for enhancing epoxy foam's mechanical properties.…”