Elastic Yielding after Cold Drawing of Ductile Polymer Glasses

Abstract

This work delineates the molecular mechanism and various characteristics of a remarkable elastic yielding phenomenon observed in cold drawn ductile polymer glasses including poly­(2,6-dimethyl-1,4-phenylene oxide) (PPE), bisphenol A–polycarbonate (PC), poly­(ethylene terephthalate) (PET), and poly­(methyl methacrylate) (PMMA). Elastic yielding occurs when a sizable retractive stress appears from a cold-drawn polymer glass (stored in stress-free state for days after unloading) during annealing above the storage temperature T st that is still well below the glass transition temperature T g. The induction time characterizing the emergence and buildup of the retractive stress to a level of σ* above 10 MPa and the magnitude of σ* both depends on T st and the cold drawing temperature T cd as well as the annealing temperature T el‑yield. It is asserted that there is significant chain tension in the load-bearing strands (LBSs) of the chain network, produced during cold drawing of these ductile polymer glasses. The chain tension is preserved by the vitrification during storage and can drive the glass to undergo localized yielding. Upon “thawing” the segments surrounding LBSs, the chain tension can transmit across the chain network to show up as macroscopic retractive stress.

Deformation and structure evolution of glassy poly(lactic acid) below the glass transition temperature

“…54 Upon stretching, the primary structure, composed of the short-ranged intersegmental van der Waals bonds, requires a high stress to yield and transfer the large load to the load-bearing strands (LBSs) of the chain network. 56 As a consequence, less LBSs can be pulled out from the chain network, producing a smaller amount of cavities and correspondingly a less significant strain softening, even leading to the disappearance of the strain softening at 60°C due to the much weaker primary structure. chain tension, builds up in the LBSs.…”

“…To understand the structure evolution process of glassy PLA below T g , glassy PLA can be perceived as a hybrid structure, which is composed of a primary structure owing to short-ranged van der Waals bonds, and a chain network due to chain interpenetration and uncrossability, as proposed by Wang et al 47,[54][55][56][57] for polymer glasses of high molecular weight under large deformation below T g . Far below T g , glassy PLA is in a deep glassy state, and segmental mobility is much lower due to the strong intersegmental van der Waals forces.…”

“…The lower load is transferred to the LBSs of the chain network, leading to the buildup of lower chain tension. 56 As a consequence, less LBSs can be pulled out from the chain network, producing a smaller amount of cavities and correspondingly a less significant strain softening, even leading to the disappearance of the strain softening at 60 °C due to the much weaker primary structure. Since the segmental mobility is higher at higher drawing temperatures, the segment relaxation occurs more readily during stretching.…”

Aramid Nanofiber Templated In Situ SNAr Polymerization for Maximizing the Performance of All-Organic Nanocomposites

“…During tensile testing, the remarkable yielding behavior and enhanced extensibility of the in situ composite originated from the large-scale elastic-to-plastic transition and stable cold drawing due to stress delocalization (Figure b). Generally, yielding and cold drawing are phenomena that occur at small localized regions because tensile stress is largely concentrated on the tapered region, typically positioned at the center of the specimen . In contrast, the increased ductility and large yielding of the in situ composite were caused by evenly spread external stress throughout the specimen, resulting in delocalized deformation.…”

Lightweight micro-cellular plastics from polylactide/polyolefin hybrids

“…To obtain useful cellular polymers via cold drawing, the matrix should be relatively ductile. 37,38 Stress-strain curves for all the PLA/PBE samples are shown in Figure 2.…”