John Garner

PLA from PolySciTech used in analysis of mechanical and physical properties for engineering applications

Blog Post created by John Garner on Aug 30, 2019

If you have ever carried groceries in a plastic bag, you are familiar with mechanical deformation of polymers. Notably, for LDPE (material used to make bags), pulling on the polymer causes a series of transitions to occur in which the polymer chains pull out in the direction of the force causing the polymer to grow hard and crystalline in the direction of deformation. This is why when you grab the bag handles they first draw out and grow brighter, narrower, and harder as the polymer elongates under the weight of the stuff inside. At some point the chains have been pulled out as far as they will go and the bag handles become very crystalline and strong enough to be very painful for your hands. All of this is due to polymer transitions under mechanical stress. Recently, researchers at University of Wisconsin used PLA (AP164) from PolySciTech (www.polyscitech.com) to create PLA films for testing of physical and mechanical properties of these polymers. This research holds promise to provide for improved use of these polymers as engineering materials. Read more: Bennin, Trevor, Josh Ricci, and M. D. Ediger. "Enhanced Segmental Dynamics of Poly (lactic acid) Glasses during Constant Strain Rate Deformation." Macromolecules (2019).  https://pubs.acs.org/doi/abs/10.1021/acs.macromol.9b01363

“The combined effects of temperature and deformation on the segmental dynamics of poly(lactic acid) (PLA) glasses were investigated by using probe reorientation measurements. Constant strain rate deformations, with strain rates between 6 × 10–6 and 3 × 10–5 s–1, were performed on PLA glasses at temperatures between Tg – 15 K and Tg – 25 K. Deformation decreases the segmental relaxation time by up to a factor of 30 relative to the undeformed state. The segmental relaxation time in the postyield regime is related to the local strain rate via a power law, with exponents similar to those reported for lightly cross-linked PMMA. The Kohlrausch–Williams–Watts exponent, βKWW, commonly interpreted in terms of the width of the distribution of segmental relaxation times, changes from the undeformed state to the postyield regime, indicating a significant narrowing of the relaxation spectrum. We observe that βKWW is correlated to the deformation-induced increase of segmental mobility for PLA, as was reported for PMMA. The similar responses of PLA and PMMA to deformation suggest that the observed effects are the generic consequences of constant strain rate deformation on the segmental dynamics of polymer glasses.”

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