Wikipedia:Reference desk/Archives/Science/2016 May 30

= May 30 =

Exploding playing cards
Why do the playing cards and die explode in this video? Dismas |(talk) 03:05, 30 May 2016 (UTC)


 * Here is my theory: The paper is not malleable (it can't deform when squeezed). So as the press compresses it, it stores more and more energy, but is unable to dissipate any. Eventually it stores so much pressure that the bonds that makeup the paper can't hold it anymore, and they all release at once, dissipating all the compression energy that it stored. Ariel. (talk) 03:16, 30 May 2016 (UTC)


 * Might nitrocellulose be of interest? Richard Avery (talk) 06:40, 30 May 2016 (UTC)


 * This looks legit to me - the series seems pretty guileless - but unfortunately, even on the high speed the explosion is essentially instantaneous. I feel like the intentional slipperiness of playing cards ought to be involved somehow... but anything I say is, alas, arrant and perhaps errant speculation. Wnt (talk) 11:32, 30 May 2016 (UTC)
 * The deck of playing cards implodes not explodes. The compressive force that triggers the implosion is high enough to deflect the hydraulic press whose structure is not ideally rigid but has a finite spring constant. At the Catastrophic failure of the card structure, the stored force in the press spring remains to accelerate the plunger down to rest at a new equilibrium of lower pressure on the card remnants. With a more rigid press structure and more massive plunger, the implosion process might become visible but in the video it seems instantaneous. AllBestFaith (talk) 16:41, 30 May 2016 (UTC)
 * I think that's a great answer, in that it's approaching the problem in terms of mechanical potential energy.
 * I've been a huge fan of Hydraulic Press Channel - it's pretty great humor mixed with occasional engineering insights.
 * I'm approaching the playing-cards from a sort of pulp and paper kind of angle. I'm guessing that the hydraulic press applies a continuously-increasing bulk pressure on the playing cards, which are comprised of plastic-impregnated paper.  At some point, the bulk pressure from the press exceeds the individual yield-strength of the individual paper fibers (and/or the resin or medium between the paper fibers).  As soon as that critical pressure is reached, that is when the paper structure collapses, and you have a mechanical process that almost resembles a chemical phase-change - an ultra-high-pressure that causes the instantaneous change in the structure.  But this is a physical, not chemical process - it's the pressure at which one component of the playing card's microscopic structure actually yields.
 * This is interesting to me, because resin-impregnated paper-fiber is actually a really sophisticated engineered composite material. For example, phenolic paper is used to line some pretty complex rocket motors because it's less flammable than metal when exposed to the intense, super-high-pressure, super-high-temperature, oxidizer-rich environment inside a rocket motor's combustion chamber.  Compressed paper fiber has also been used to great effect as a low-weight ballistic shield.  Here's a pop-science article from Discover Magazine, Bulletproof Paper Is Stronger Than Kevlar (2009).  We also have an article on nanocellulose, and there are a lot of research papers on making bomb-shields out of wood pulp.
 * So, my feeling is that at first, these paper cards are actually compressing elastically, exactly as User:AllBestFaith described - and the compression is almost impossible to see because the material is very stiff; but as soon as the pressure hits some specific critical level, the internal pulp fiber structure changes, almost like it's squeezing the "air" (or plastic resin) out of the pores between fibers. The result is a new composite material with different macroscopic properties (it becomes brittle and flakey, as seen in the video).  It becomes more dense - the same mass of bulk fiber fits in a significantly smaller volume.  Its flame point probably changes too.  I'm thinking of all of these items in the context of their practical applications to terminal ballistics - if the pressure was applied by a flying piece of metal shrapnel, instead of a smooth application by hydraulic press, would the paper still have such a pressure-resistance?  The Beast has hundreds, or thousands, of pounds of plate-metal armor - which can melt, burn, and spall; but the modern MRAPs - the ones that have been fielded in combat and actually survived real bomb attacks - have fuzzy carpets and cardboard floors.  For example, here's some terrifying promotional literature from the DuPont corporation on their spall-liners made from composite material.  The point is, paper is pretty awesome stuff.  It might even behave better than metal when exposed to extreme pressure and heat.
 * I'd love to see a research paper from a materials-science journal or a pulp-and-paper technology journal about the effects of extremes of pressure on (regular or special-purpose) paper fiber products. There are a handful of good research journals listed in, e.g., our articles on advanced composites, and so on.  Anyone want to help me track down some reading material?  I'm keywording my searches with things like "ultra-high pressure" and "Young's modulus" and "phase transition" and so forth.
 * To get started, here's a great survey paper, from my alma mater: The Dispersion Science of Papermaking (2004). This one reviews a lot of the basic chemistry, intermolecular force theory, and flow dynamics for modern paper-making; it's a good start, and there are some great diagrams of the mechanical interactions of nanoparticulates and fibers as they pertain to bulk material properties... but I don't see anything about extreme pressure.
 * Here's some cool empirical laboratory nano-paper-science: Young’s Modulus of Cellulose Fibrils Measured Using Atomic Force Microscopy (2008). That slide deck gives us a bunch of parameters for the paper fibers in the elastic regime... so that puts a lower bound on the "critical pressure" I described in my hypothesis.  Unfortunately, our Hydraulic Press guy doesn't include the gauge pressure, let alone any measurement of the contact-point pressure, so using his video alone, we can't even estimate what regime the cards "imploded" at.
 * And of course: here's some more paper under extreme pressure...
 * Nimur (talk) 03:13, 31 May 2016 (UTC)


 * Paper is not too bad, unless your playing rock paper scissors. ChemWarfare (talk) 04:01, 31 May 2016 (UTC)