We investigated the shock initiation of energetic materials with a tabletop apparatus that uses km s−1 laser-driven flyer plates to initiate tiny explosive charges and obtains complete temperature histories with a high dynamic range. By comparing various microstructured formulations, including a pentaerythritol tetranitrate (PETN) based plastic explosive (PBX) denoted XTX-8003, we determined that micron-scale pores were needed to create high hot spot temperatures. In charges where micropores (i.e., micron-sized pores) were present, a hot spot temperature of 6000 K was observed; when the micropores were pre-compressed to nm scale, however, the hot spot temperature dropped to ∼4000 K. By comparing XTX-8003 with an analog that replaced PETN by nonvolatile silica, we showed that the high temperatures require gas in the pores, that the high temperatures were created by adiabatic gas compression, and that the temperatures observed can be controlled by the choice of ambient gases. The hot spots persist in shock-compressed PBXs even in vacuum because the initially empty pores became filled with gas created in-situ by shock-induced chemical decomposition.
Due
to the depletion of fossil fuels, higher oil prices, and greenhouse
gas emissions, the scientific community has been conducting an ongoing
search for viable renewable alternatives to petroleum-based products,
with the anticipation of increased adaptation in the coming years.
New academic and industrial developments have encouraged the utilization
of renewable resources for the development of ecofriendly and sustainable
materials, and here, we focus on those advances that impact polyurethane
(PU) materials. Vegetable oils, algae oils, and polysaccharides are
included among the major renewable resources that have supported the
development of sustainable PU precursors to date. Renewable feedstocks
such as algae have the benefit of requiring only sunshine, carbon
dioxide, and trace minerals to generate a sustainable biomass source,
offering an improved carbon footprint to lessen environmental impacts.
Incorporation of renewable content into commercially viable polymer
materials, particularly PUs, has increasing and realistic potential.
Biobased polyols can currently be purchased, and the potential to
expand into new monomers offers exciting possibilities for new product
development. This Review highlights the latest developments in PU
chemistry from renewable raw materials, as well as the various biological
precursors being employed in the synthesis of thermoset and thermoplastic
PUs. We also provide an overview of literature reports that focus
on biobased polyols and isocyanates, the two major precursors to PUs.
To achieve sustainably-sourced polymers from algae, azelaic acid was prepared from an algae oil waste stream and converted into a flexible polyurethane foam. The heptanoic acid co-product was converted into both a flavoring and a renewable solvent.
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