Interfacial Adhesion Characteristics of Kenaf Fibres Subjected to Different Polymer Matrices and Fibre Treatments

Table 6

Main fibre pullout mechanisms and their brief remarks for the different types of fibre treatments used subjected to polyurethane matrix at dry loading conditions.

Polyurethane
Corresponding SEM figure	Fibre treatment	Brief remark/explanation	Main fibre pullout mechanism
Figure 8(a)	Untreated	(i) Fibre was detached from matrix which caused several fibre strands still embedded in the matrix; (ii) Sign of impurities on fibre surfaces which could have caused severe crack at the resinous region during the pullout (i.e., the impurities on the fibre surfaces were forced out from the matrix)	Fibre breakage with slight pullout
Figure 8(b)	4% HCl	(i) Sign of low fibre contraction and deformed fibre surfaces due to the treatment; (ii) Many tiny hollow spots on fibre surfaces which caused several weak points (i.e., stress concentrations) during the pullout	Brittle-like fracture at end of fibre was observed because of the acidic treatment
Figure 8(c)	6% HCl	(i) Massive debonding associated with high amount of fibre split from the main core fibre; (ii) Fibre could easily get detached as it was brittle after the treatment; (iii) However, the signs of fibre splits also showed that the fibre resisted the pullout force when it was embedded in PU as the matrix	Torn fibre and slight fibre pullout
Figure 8(d)	4% NaOH	Slight debonding of fibre was seen at the resinous region	Pure fibre breakage
Figure 8(e)	6% NaOH	(i) A rough fibre surface was observed after the treatment which resisted the fibre from pulling out from the matrix; (ii) End of fibre breakage was still in good shape indicating that the fibre could withstand the high pullout force (more than 3 N), thus increasing the IAS of the fibre and matrix	Pure fibre breakage