Polymer foaming with chemical blowing agents: Experiment and modeling

Abstract

International audienceAn experimental and theoretical analysis of the polypropylene foaming process using three different chemical blowing agents (CBA) was performed. A simple experiment was designed to analyze the foaming process of polypropylene (PP)/CO2 system under two different pressure conditions. The expansion ratio and final foam structure was measured both by direct observation and from optical measurements and image analysis, showing a good agreement. A single bubble simulation based on relevant differential scanning calorimetry and thermo-gravimetrical analysis experiments, assuming each CBA particles as a nucleation site and accounting for gas diffusion in the surrounding polymer matrix has been built. The sensitivity of the model to physical and processing parameters has been tested. The calculation results are compared to the experiments and open the route to a simplified method for evaluating the efficiency of CBA

Thermoplastic Foams: Processing, Manufacturing, and Characterization

“…Azodicarbonamide (AC) is the most known exothermic foaming agent high gas yield. It has decomposition temperatures between 170 and 200°C [13]. Sodium bicarbonate and zinc bicarbonate are the most common endothermic blowing agents.…”

“…The pressure must be high enough in order to keep the dissolved gas in the polymer before it exits the die. If the pressure and temperature are not set correctly, foaming agent will not be decomposed and can induce left particles or agglomerations of foaming agent, which can lead to poor cell morphology and poor surface quality [13]. The most known chemical foaming agent is azodicarbonamide (ADC), an exothermic chemical foaming agent.…”

“…On the other hand, chemical foaming is less complicated and can liberate gases under certain processing conditions either due to chemical reaction or thermal decomposition [13]. Chemical foaming agents are added to polymer either prior to or during plasticization, similar to foam extrusion by chemical foaming agents.…”

“…It releases high-amount of N 2 gas together with CO 2 in lower amount into the polymer. However, due to the toxic byproducts of ACD, endothermic type commercial foaming agents are being used, such as Clariant's Hydrocerol [13,14].…”

“…In last few years, a commercial foaming agent, Hydrocerol, has been extensively employed as endothermic foaming agent. Hydrocerol has decomposition temperatures between 160 and 210°C and can be added directly into the hopper of an injection-molding machine in the form of pellets in proportions from 1% to 4 wt.% [13].…”