Polylactide from PolySciTech used in analysis of temperature and humidity effects on polymer mechanical behavior.

Polymers can be visualized as long chains. The chains can be in a random jumble (amorphous) or neatly lined up and stacked tightly together (crystalline) or various combinations in between. The degree of organization of the polymers plays a dramatic role in the mechanical stiffness and strength of the materials made from the polymer. A classic example for this is polyvinylchloride which is both used for generation of garden-hoses (flexible) and credit-cards (stiff). Based on the processing and additives used, PVC can either be extremely flexible or extremely stiff. Recently, researchers at University of Wisconsin−Madison used PLA (AP164) to perform mechanical analysis under different conditions for determining humidity and temperature effects on polymer behavior. This research holds promise in furthering understanding about polymer behavior in solid state. Read more: Ricci, Josh, Trevor Bennin, Enran Xing, and M. D. Ediger. "Linear Stress Relaxation and Probe Reorientation: Comparison of the Segmental Dynamics of Two Glassy Polymers during Physical Aging." Macromolecules (2019). https://pubs.acs.org/doi/abs/10.1021/acs.macromol.9b01625

“Segmental dynamics of glassy poly(methyl methacrylate) (PMMA) and poly(lactic acid) (PLA) have been measured over 8 h of aging via both optical probe reorientation and mechanical stress relaxation experiments performed in the linear response regime, in a temperature range between 6 and 30 K below the glass transition temperature (Tg). A clear power law relationship between relaxation times and aging times is observed in all experiments. For both PLA and PMMA glasses, the probe reorientation times are strongly correlated with stress relaxation times over the observed range of aging times and aging temperatures, with the two relaxation times related by a power law with an exponent of ∼1. Comparisons of these data sets with previously published work indicate that the relationship between the two relaxation times is not influenced by secondary relaxation processes, low levels of crosslinking, or the presence of a plasticizer. These results support the view that the probe reorientation technique is a good reporter of segmental dynamics in the glassy state.”