Role of the Intercrystalline Tie Chains Network in the Mechanical Response of Semicrystalline Polymers

We examine the microscopic origin of the tensile response in semicrystalline polymers by performing large-scale molecular dynamics simulations of various chain lengths. We investigate the microscopic rearrangements of the polymers during tensile deformation and show that the intercrystalline chain connections known as tie chains contribute significantly to the elastic and plastic response. These results suggest that the mechanical behavior of semicrystalline polymers is controlled by two interpenetrated networks of entanglements and tie chains.

Figure 1

An example of CG-PVA semicrystalline configurations with $N=1000$ monomers that consists of chain-folded crystallites (red) connected by an amorphous network.

Figure 2

Stress versus strain from uniaxial tensile deformation of semicrystalline (solid lines) and amorphous (dotted lines) polymers of different lengths at (a) $T=0.7$ and (b) $T=0.2$.

Figure 3

Effective microscopic stretch ${\lambda }_{\mathrm{eff}}\equiv R_y/R_y^0$ versus macroscopic stretch $\lambda \equiv L_y/L_y^0$ for semicrystalline (solid lines) and amorphous (dashed lines) polymers at (a) $T=0.7$ and (b) $T=0.2$.

Figure 4

Chain length dependence of (a) Young’s modulus $E$, (b) yield stress ${\sigma }_y$, and (c) strain-hardening modulus $G_H$ for amorphous and semicrystalline polymers obtained by continuous cooling and by cutting the chains of semicrystalline samples into half. For cut chains, $N$ refers to their length after cutting (see text).

Figure 5

(a) Degree of crystallinity ${\mathrm{\Phi }}_c$ at $T=0.2$ and $T=0.7$ as a function of polymer length $N$; the inset shows the average volume of the crystalline domains. (b) Fraction of tie bonds $f_{\mathrm{tie}}$ and (c) the average length of tie strands $⟨N_{\mathrm{tie}}⟩$ versus $N$.

Figure 6

(a),(b) Stress versus strain and (c),(d) effective microscopic stretch versus macroscopic stretch for semicrystalline polymers of various lengths obtained from continuous cooling (solid lines) and from cutting of polymers into half (dashed lines) at $T=0.7$ and $T=0.2$, respectively.