Effect of surface density and fiber length on the porosity and permeability of nonwoven flax reinforcement

This paper presents an experimental study and modeling of the influence of surface density and fiber length on the permeability of novel nonwoven flax fiber manufactured by the paper making process. Firstly, the relation between surface density, fiber lengths and pore size distribution measured with a porometer capillary instrument is reported in this study. The results show that higher surface density gives a denser fibrous network with a low porosity rate and longer fiber decreases the total number of fibers and increases the pore size for a given surface density. A liquid permeability study was then carried out to identify the impact of surface density, short fiber length and fiber volume fraction on in-plane impregnation of the reinforcement. Permeability was found to be inversely proportional to the reinforcement of surface density. In contrast, an increase of the fiber length increases the in-plane permeability of the reinforcement. Finally, a mathematical modeling is proposed to predict the permeability behavior of these innovative natural fiber webs.