Effect of die temperature on the morphology of microcellular foams

Abstract

A study on the extrusion of microcellular polystyrene foams at different foaming temperatures was carried out using CO, as the foaming agent. The contraction flow in the extrusion die was simulated with FLUENT computational fluid dynamics code at two temperatures (1 50°C and 175°C) to predict pressure and temperature profiles in the die. The location of nucleation onset was determined based on the pressure profile and equilibrium solubility. The relative importance of pressure and temperature in determining the nucleation rate was compared using calculations based on classical homogeneous nucleation theory. Experimentally, the effects of die temperature (i.e., the foaming temperature) on the pressure profile in the die. cell size, cell density, and cell morphology were investigated at different screw rotation speeds (10 -30 rpm). Experimental results were compared with simulations to gain insight into the foaming process. Although the foaming temperature was found to be less significant than the pressure drop or the pressure drop rate in deciding the cell size and cell density, it affects the cell morphology dramatically. Open and closed cell structures can be generated by changing the foaming temperature. Microcellular foams of PS (with cell sizes smaller than 10 +m and cell densities greater than lo9 cells/cm3) are created experimentally when the die temperature is 160°C. the pressure drop through the die is greater than 16 MPa, and the pressure drop rate is higher than lo9 Pa/sec.

Open‐Pore Biodegradable Foams Prepared via Gas Foaming and Microparticulate Templating

“…By increasing the microparticle concentration up to 40 and 50 wt.-% (Figure 3b and c), the pore size decreases as a consequence of the increase in the stiffness of the PCL/NaCl composites (see Figure 1). This restricts the expansion of cells, [11] and is also related to the feasible nucleating effect of the filler. [51] By the further increase of NaCl to 70 wt.-% ( Figure 3d) the foams showed a progressive decrease of the pore size and the pores created by the gas foaming and microparticle leaching became indistinguishable.…”

“…From these points of view, gas foaming with carbon dioxide (CO 2 ) has attracted industrial attention because CO 2 is environmentally friendly, non-flammable, and inexpensive. [11] Moreover, compared to other foaming processes, CO 2 foaming can be…”

Capillary rheometry of a binary mixture polymer/CO2 in a single screw extruder

“…Thus, an evaluation of the exact location of desorption in the die was made. A linear depressurisation was assumed from the entrance to the exit [28]. This linear depressurisation was confirmed by modelling the die flow with Comsol Multiphysics 1 by using Navier Stokes equations for an incompressible fluid.…”

Effects of formulation and processing parameters on the morphology of extruded polypropylene‐(waste ground rubber tire powder) foams

“…The effect of the die temperature on cell size distribution is presented in Figure 4(d), it can be seen that blends prepared by lower die temperature have narrower distribution. The reason is that a low die temperature can causes an increase in die pressure drop, which in turn enlarges the supersaturation, therefore a low die temperature can give a late nucleation and a large nucleation rate simultaneously [37].…”