Relating structure and chain dynamics to ballistic performance in transparent epoxy networks exhibiting nanometer scale heterogeneity

Composites Science and Technology

Elder

et al. 2015

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a b s t r a c tBallistic performance, at effective strain rates of (10 4 -10 5 s À1 ), for polymeric dicyclopentadiene (pDCPD)was compared with two epoxy resin/diamine systems with comparable glass transition temperatures. The high rate response was characterized in terms of a projectile penetration kinetic energy, KE 50 , which describes the projectile kinetic energy at a velocity with a 50% probability of sample penetration. pDCPD showed superior penetration resistance, with a 300-400% improvement in ballistic energy dissipation, when compared with the structural epoxy resins. In addition, unlike typical highly crosslinked networks that become brittle at low temperatures, the improved pDCPD performance occurred over a very broad temperature range (À55 to 75°C), despite exhibiting a glass transition temperature characteristic of structural resins ($142°C). In addition to the high T g , pDCPD exhibited a room temperature glassy storage modulus of 1.7 GPa, offering the potential to circumvent the common structural versus energy dissipation trade-off encountered with conventional crosslinked polymers. Quasi-static measurements suggested that the performance of pDCPD is phenomenologically related to higher fracture toughness and lower yield stress relative to typical epoxies, while molecular dynamics simulations suggest the origin is the lack of strong non-covalent interactions and the facile formation of nanoscale voids to accommodate strain in pDCPD.Published by Elsevier Ltd.

Section: Dielectric Spectroscopy Resultsmentioning

confidence: 90%

Section: Thermomechanical Characterizationmentioning

confidence: 99%

Section: Dielectric Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Overcoming the structural versus energy dissipation trade-off in highly crosslinked polymer networks: Ultrahigh strain rate response in polydicyclopentadiene

Knorr

Composites Science and Technology

Elder

et al. 2015

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Dynamic heterogeneity in epoxy networks for protection applications

J of Applied Polymer Sci

Knorr

et al. 2016

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The segmental dynamics and ballistic performance are investigated for a series of thermosetting epoxy networks composed of diglycidyl ether of bisphenol A (DGEBA) cured with mixtures of a rigid cycloaliphatic diamine and a series of flexible propylene oxide diamines. Formulations of DGEBA, cycloaliphatic diamine, and a low molecular weight propylene oxide diamine exhibit miscibility in the fully cured state, resulting in a single glass transition temperature (T g ), described by a Gordon-Taylor relationship. When high molecular weight propylene oxide diamines are used, the monomers are partially miscible, and the resulting cured epoxy exhibits dynamic heterogeneity, as evidenced by dual T g 's. These dynamically heterogeneous systems composed of rigid and flexible domains can exhibit enhanced ballistic impact response when the length scale of the phase separation is small, and the composition is near a phase inversion point. The dynamic heterogeneity also broadens the temperature window for impact performance, which is important for practical applications in military systems.

Transparent, methacrylate‐based polymer networks with controlled crosslinker ductility

J of Applied Polymer Sci

Orlicki

Napadensky

et al. 2020

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A series of transparent methacrylate-based crosslinked polymer networks are prepared in which the crosslinker length is controlled as a means to investigate the effects of network ductility on mechanical and ballistic properties. In each network the optical clarity of pure poly(methyl methacrylate) (PMMA) is retained, as well as a low value of haze. Both the glass transition temperature (T g) and the tensile modulus of the networks are highly tunable, with network values both above and well below that of pure PMMA or the pure crosslinker network. The ballistic performance is likewise affected, with performance values of up to 400% greater than neat PMMA. We examine the effects of the crosslinker molecular weight on the impact performance, finding that, in these systems, the molecular weight between crosslinks is not a driving factor for the impact performance, and this may broadly translate to polymer networks in general. We find that improvements in ballistic performance can be realized at low molecular weight between crosslinks, provided the crosslinking agent is of sufficient ductility.