Molecular origin of aging and yielding of polymer glasses

Citation for published version (APA):Grigoriadi, K., van Breemen, L. C. A., Hütter, M., & Anderson, P. D. (2016). Molecular origin of aging andyielding of polymer glasses.

Document status and date:Published: 16/12/2016

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Download date: 21. Nov. 2020

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Introduction and objectivesGlasses usually exist in a non-equilibrium state and their

relaxation toward equilibrium is commonly referred to as

physical aging. All polymers age over time. While aging,

polymers embrittle, which is a severe limitation for applications.

The physical aging and deformation kinetics depend on

molecular structure. The goal of this project is, therefore

twofold, to provide, for glassy polymers, connections between:

a) Molecular architecture and yielding kinetics and

b) Molecular architecture and physical-aging kinetics

OR

Results and discussion

The changes of yielding with physical aging is captured

from the nanoindentation experiments.

The thermally rejuvenated and at 70oC aged specimens

age faster than the ones aged at 25oC, see Fig. 2.

The mechanically-rejuvenated specimens have a

different thermodynamical state than the thermally-

rejuvenated specimens at room temperature due to their

different proccessing. In conclusion they show different

aging speed.

The overestimation of yield stresses is probably due to

inhomogeneous deformation (stress concentrations) and

a potential increase of contact area during indentation,

which is influenced by the absolute age/yield-stress value

of the sample.

References[1] XP Handbook User Manual, http://www.msm.cam.ac.uk

[2] van Melick H.G.H. et al., Polymer, 44:1171-1179 (2003)

Future WorkPerform simultaneous mechanical and dielectric spectro-

scopy/FTIR experiments.

Goal: Link the kinetics of aging with that of yielding

through the respective relaxation processes.

Experimental approach

water at 0oC

polymer film

rolling mill stand

incoming

filmrejuv.

film

x-axis

rolling cylinders

110oC

polystyrene pellets

upper mould

lower mould

175oC

age up to one week at 25oC or 70oC

flat tip indenter,

10 μm top diameterpolystyrene film,

100 μm thick

mechanical rejuvenation thermal rejuvenation

Thin samples are a requirement for dielectric measurements,

(see future work). As a result the yielding of the samples is

assessed by nanoindentation tests. The samples are prepared

according to two protocols prior to testing, see Fig. 1, b-c.

annealing for 30 min quenching

sample preparation

Molecular Origin of Aging and

Yielding of Polymer Glasses

K. Grigoriadi (1,2), L.C.A. van Breemen (1), M. Hütter (1), P.D. Anderson (1)

(1) TU Eindhoven, Mechanical Engineering, Polymer Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

(2) Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, the Netherlands.

Contact information: K.Grigoriadi@tue.nl /www.tue.nl/pt

This research forms part of the research programme of the Dutch

Polymer Insitute (DPI), project #745

nanoindentation tests

Fig. 1: (a) Sample preperation, (b) mechanical (c) thermal rejuvenation and (d) schematic

of the Nanoindenter XP for micromechanical testing[1].

(a)

(b)

(d)

/department of mechanical engineering

(c)

Fig. 2: Thermally rejuvenated (aged at 25oC), thermally rejuvenated (aged at

70oC), mechanically rejuvenated (aged at 25oC), mechanically rejuvenated

(aged at 25oC) literature data[2]. Yield stress is measured by compression tests[2].

Apparent yield stress is the stress calculated from the nanoindentation tests.