Melt elongation of a commercial poly(methyl methacrylate) product and a commercial polystyrene

Abstract

Melts of a commercial poly(methy1 methacrylate) product and a commercial polystyrene were elongated homogeneously up to Hencky strains of E > 4 by means of the rotary clamp technique. For this purpose, certain modifications to the rheometer were necessary which are described in detail. Both polymer melts show strain hardening, i. e. the elongational viscosities are higher than the threefold of the linear viscoelastic limiting viscosity measured in shear. The degree of hardening is very different: For the poly(methy1 methacrylate) product the hardening is only small, and so are the recoverable portions of the total strains, whereas for the polystyrene the opposite is true. This different behaviour is connected with a difference of the linear viscoelastic relaxation spectra at long relaxation times. The test results can be described efficiently by the Lodge-Wagner rubberlike liquid constitutive equation.

Novel High‐Speed Elongation Rheometer

“…In other works, the Trouton Factor from Equation ( 6) was validated for PMMA 7N by extensional rheology experiments. [20] 𝜂 E0 = 3𝜂 S0 (6) With the assumption that the elongational viscosity is three times higher than the shear viscosity, shear experiments can be used to determine the viscosity of the PMMA melt based on the temperature (see Figure 6 and Table 1), which are then converted to elongational viscosities. The frequency sweeps were fitted by the Carreau-function using the critical shear rate ̇𝛾c (analogue to εc the critical elongation rate in extension) and the zero-shear viscosity (𝜂 s0 ) as adjustable parameters.…”

“…In other works, the Trouton Factor from Equation () was validated for PMMA 7N by extensional rheology experiments. [ 20 ] $$\begin{equation}{\eta _{{\rm{E}}0}} = 3{\eta _{{\rm{S}}0}}\end{equation}$$With the assumption that the elongational viscosity is three times higher than the shear viscosity, shear experiments can be used to determine the viscosity of the PMMA melt based on the temperature (see Figure and Table 1 ), which are then converted to elongational viscosities.…”

“…PMMA 7N has already been investigated in earlier works with other devices at low elongation rates, demonstrating that the material has at least neglectable strain hardening behavior. [9,20] The granules were dried at 80 °C with vacuum over night for all experiments as the polar groups encourage water absorption, which would badly impact the spinnability.…”

Branching structure and strain hardening of branched metallocene polyethylenes

“…For example, a commercial linear poly(methyl methracrylate) was found to exhibit significant strain hardening [Linster and Meissner (1989)]. For well entangled, linear monodisperse melts, tube models predict that chain stretch and strain hardening will occur when the rate of deformation exceeds the reciprocal of the stretch relaxation time defined as 2s R , where s R is the longest Rouse time.…”