The mechanical behaviour and physical ageing of semicrystalline polymers: 2

doi:10.1016/0032-3861(87)90354-5

Polymer

Volume 28, Issue 9, August 1987, Pages 1534-1542

https://doi.org/10.1016/0032-3861(87)90354-5 Get rights and content

Abstract

The model of an extended glass transition in semicrystalline polymers (see Part 1¹) has been further evaluated. It is shown that the model can explain the effect of ageing on the dynamic mechanical properties and also the effect of the quenching temperature on volume relaxation. It is further shown that, for semicrystalline and amorphous polymers, the ageing after complicated thermal histories is strikingly similar. It is finally demonstrated that, above T_g, filled rubbers show the same (physical) ageing effects as semicrystalline polymers.

References (8)

L.C.E. Struik
Polymer
(1987)
L.C.E. Struik
Polymer
(1980)
P.P.A. Smit
Rheol. Acta
(1966)
F.R. Schwarzl
Rheol. Acta
(1966)

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Citation Excerpt :
A broadened glass transition concept was used by Struik to explain the aging effect below Tg on the mechanical properties of semi-crystalline polymers [22,23]. It was believed that compared to amorphous polymers, the segmental mobility of amorphous phase can be reduced by the crystalline phase in semi-crystalline polymers and the closer to the crystal surface, the more restrictions on the molecular mobility [22,23]. Therefore, the Tg of the amorphous phase is usually broad due to the different levels of segmental mobility of amorphous phase in terms of their relative distance to the crystal surface [22].
Annealing is widely utilized in industry to manipulate the mechanical properties of semi-crystalline polymers. In this work, poly(ether-ether-ketone) (PEEK) was annealed at different temperatures above its glass transition temperature (T_g) to investigate its influences on the viscoelastic behavior of PEEK. A set of master curves on long-term creep and stress relaxation behaviors of PEEK were obtained via time-temperature superposition and showed that a higher annealing temperature leads to more retardation. The underlying molecular mechanism is related to a higher activation energy of β-relaxation (E_β) associated with the molecular motions below T_g. A physics-based Ngai's Coupling model was chosen for the analysis, suggesting a higher degree of restriction on molecular mobility due to annealing, which is mainly attributed to the increases in the density of the amorphous phase and the crystallinity. Usefulness of the Ngai's Coupling model for the prediction of long-term viscoelastic behavior of semi-crystalline polymers is discussed.

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Polymer paperThe mechanical behaviour and physical ageing of semicrystalline polymers: 2

Abstract

Polymer

Polymer

Rheol. Acta

Rheol. Acta

Polymer paper
The mechanical behaviour and physical ageing of semicrystalline polymers: 2