Analysis of bubble nucleation and growth in the pultrusion process of phenolic foam composites

A study was carried out to analyze the foaming characteristics in the pultrusion process of phenolic foam composites. For the experimental study, a lab-scale pultrusion apparatus was constructed. Glass fiber roving and a resol type phenolic resin were used as reinforcement and matrix, respectively. Methylene chloride (CH2Cl2) was employed as a physical blowing agent. The number and the average size of bubbles were measured using a scanning electron microscope and an image analyzer. For the theoretical analysis, a model that combines classical heterogeneous nucleation with bubble growth in a gradually hardening resin was considered. The process variables considered were the pulling speed, the die wall temperature and the mass fraction of blowing agent. A computer code was written to solve a system of equations from the model. Numerical results were compared with the experimental data for different process variables. Close agreement was observed.