Influence of structural defects on viscoelastic properties of poly(propylene)

Abstract

Straining of annealed isotactic polypropylene beyond yield results in the formation of 0.4-4 vol % of microvoids with sizes of about 5-30 nm. The creep behavior as well as the complex shear and tensile modulus of polypropylene are strongly influenced by the presence of the very small concentration of microvoids, acting as structural defects. The storage modulus in the glassy state may be decreased by 30 % (shear modulus) or 15 % (tensile modulus) relative to the defect-flee state. Possible interpretations are discussed.

Composites of alkaline poly(6-hexanelactam) with solid lubricants: one-step synthesis, structure, and mechanical properties

“…are facilitated. As we have shown in our previous paper 18) , the Nutting equation 1,39,40) e (r,t) = K r m t n describes well the effects of stress r and time t on the creep deformation of PCL composites. The expression for the isothermal dependence of tensile compliance D(r,t) is as follows:…”

Nonlinear tensile creep of linear low density polyethylene/fumed silica nanocomposites: Time-strain superposition and creep prediction

“…Various empirical equations were proposed to fit D ( t, σ) or D v ( t, σ) [18, 42–44]. A relatively simple equation was found suitable for describing isothermal creep of polypropylene and of its blends [3, 18, 40, 45]: where W(σ) is a function of stress, τ rm is the mean retardation time and 0 ≤ n ≤ 1 is the shape parameter reflecting the distribution of retardation times.…”

Composites of alkaline poly(6-caprolactam) and short glass fibers: one-step synthesis, structure and mechanical properties

“…In this paper we have attempted two empirical equations to describe the observed time dependence of tensile compliance D (s, t). The Nutting equation [34][35][36] e (r, t) = K r m t n for creep elongation gives the following expression for tensile compliance D (r, t): log D (r, t) = log K + (m -1) log r + n log t (1) where K, m and n are material parameters (evaluated a posteriori by using experimental data) at a given test temperature. However, in the region of linear stress-strain relationship m = 1 and the isothermal compliance D (t) depends only on time; obviously, K = D (t = 1).…”