Rheo-Cooling applied to Plastics. J.P. Ibar New School Polymer Physics As the primary use of a mold is shape material into an object, not cool it, conventional molds are designed apply specific cooling treatments materials, although they implicitly used as heat transfer agents solidify material. When development aimed at implementing and cooled plastic in mold, this implementation has been called “Rheomolding”. Rheomolding based processes rheology principles vary value physical transitions (Tg, Tm) temperature decreases cross them any given speed. Take rubber, for instance: its modulus depends on T-Tg) where T Tg glass transition temperature. itself function pressure frequency amplitude vibration if such mechanical force exerted it shear or vibration). The figure below shows dependence Polystyrene. varies by 32 oC/Kbar. This means that one applies variation 1 Kbar per sec, instance, obtains rate i.e. 1920 min!. achievable conduction, especially bulk material, yet gives you possibilities see previous blog: l water less than 5 sec)!. Fig. 1 shows that the rate of cooling influences state glass once Tg is crossed. We can measure specific volume at different temperatures while material cools: break and change slope corresponds to Tg; if quenched, its higher produced in a of non-equilibrium which is more pronounced. In fact one can demonstrate that the material cooled faster in a different state by studying DSC trace obtained heating piece it after has to room temperature. This shown following figure (“Figure 8”). One sees “fast cooling”, at 80 oC/min produces on characteristic quenched glasses: there only drop baseline occurring Tg, no peak visible. For 2oC/cooling rate, visible, indicating an overshoot heat capacity before liquid reached. pronounced for even smaller rate 0.5 min. OK, we have in hand a nice way to know if the glass was slowly cooled or “quenched” during its solidification: can run DSC scan on it and determine size of peak at Tg. This be very useful characterize glasses formed by Rheo-Cooling. What other physical parameter think alter value phase transitions, besides pressure? Frequency maps were popular 70s which provided variation transitions with frequency (T , etc.). An example is shown figure below for transition Polystyrene. The mechanical representation this says that Tg dependent when material oscillated, like pressure. The Frequency map shows that the value of Tg varies by 49 oC when frequency from 10-1.5 Hz (point corresponding to 1000/T = 2.725) 105 2.4). In other words, one can sweep increase or decrease at a given rate and this will correspond Rheo-Cooling Heating effects. For instance, choose vary linearly logarithmic simulate cooling rates produce various types non-equilibrium states for glass formed under such conditions. CLICK ON THE VIDEO LINK BELOW: Apparatus induce in polymer glasses video shown above I present an equipment which was built apply variable ramps high amplitude hydrostatic oscillations during plastic order implement kinds treatments across plastic. is swept low as temperature decreases, raising any chosen rate. oscillation also increasing same time. These are continued until material reduced level where effects no longer required maintain product integrity (~ 20 below Tg). we hear 1 3000 Hz. sample Polystyrene disk confined mold room temperature, heated initial it viscoelastic rubber, pressurized pressure between 500 10,000 PSI, being capable 0 100% excursion. apparatus has channels heating cartridges disposed control passage refrigerant fluids, water, mix glycerol compressed air. lower half is attached to a vibrating table which imposes the pressure excursion plastic disk through an accelerometer. The upper mold fixed and connected cell. A pneumatic air piston, shaped like flat inflatable disk, transmits average hydrostatic force while electromagnetic shaking exerts excursion. We see in video different elements composing Rheomolding apparatus set up: watch technician take machine apart, once Rheo-cooling experiment done, order separate two halves extract treated polystyrene disk. This sample submitted series of tests determine difference properties between references ( purely static runs) “Rheomolded” conditions. characterized thermal, mechanical dielectric these materials. run DSC for samples reveal what type non-equilibrium states were achieved by or heating glass was being cooled conduction. figure below (“Fig. 7”) tells story treatments are, each time, compared reference obtained under same conditions , except without any frequency sweep no vibration”). Treated sample 1: The REFERENCE curve for treated 1 is the 2nd from top. It shows a typical drop off of Heat Flow baseline at Tg, characteristic fast cooled (80 oC/min). top DSC trace, however, corresponding to TREATED sample, very strange: trace displays strong peak slowly specimen, but, noticeably, baselines melt and glass are same, unlike samples see above). This as if there was no longer difference in Capacity below above Tg: Cp(@Tg)=0! 2 lower two traces): is, again, sample: Tg. different reference identically but with vibration during cooling. endothermal characteristics Tg more complex than untreated sample. In particular, endotherm broader extending over 40 oC range Then, seems be shifted upward by an exothermic wave, way similar what happened 2. At end, up high melting region, heat capacity extrapolate solid similarly seen treatment 1. conclusion, it appears that which has been Rheo-Cooled had thermal room temperature after treatment) could extrapolated liquid region where known polymer equilibrium. would mean treated sample behaved below Tg like a which had reached equilibrium, i.e. specimen has been extensively annealed. The other possibility that comes to mind is challenge the fact liquid region, above Tg, at equilibrium; in words, Rheo-Cooling can create non-equilibrium states. It took me build another machine, Fluidizer, subject of recent publications, prove state could, indeed, be brought out with respect its entanglement. This brings us Split-Dual-Phase model entanglement, I have discussed already previous blogs and lectures. Something clear this author: melt manipulation such as and/or Fluidification, any combination thereof, gives formidable new tools prepare plastics. And, for change, not based on what chemists do: synthesize zillions molecules blends; but rather it because understanding physics interactions between macromolecules opens wide door way they processed: welcome age smart processing! PS will provide separate seminar processing details experiments described blog.