Fibre/matrix adhesion of cellulose fibres in PLA, PP and MAPP: A critical review of pull-out test, microbond test and single fibre fragmentation test results

The present work deals with the practical fibre/matrix adhesion of regenerated cellulose fibres (lyocell) and bast fibre bundles (flax, kenaf) in different matrices (polylactide-PLA, polypropylene-PP, maleic-anhydride-grafted polypropylene-MAPP). The influence of different testing procedures (pull-out test, microbond test, fragmentation test) on the fibre/matrix characteristics is discussed. The results of the different tests showed the same trends, but the absolute values differ. Clearly higher interfacial shear strength (IFSS) for cellulose fibres was found in PLA and MAPP in comparison to PP due to higher polarity. In addition, bast fibres displayed higher apparent IFSS values compared to lyocell because of their rougher surface and their chemical composition. The apparent IFSS of the pull-out test resulted in higher values compared to results obtained from the fragmentation test. This phenomenon is explained by different stress distributions due to variable specimen geometry, different behaviour of failure and the friction which occurs between fibre and matrix during fibre pull-out in the pull-out test.