The similar trend was also found
in the flexural strength and impact strength of the composites with
various IPDI content treated, which was shown in Fig. 7B. With an
increase in the isocyanate content, the flexural strength and impact
strength of the composites were improved and then decreased. It
could be explained that the crosslink reaction occurred when the
addition of diisocyanate was at a low concentration. With the
IPDI content increased, the interface adhesion of the composite
was increased. The enhancement of adhesion with the increasing
isocyanate group can be attributed to the enhancement degree of
crosslink reaction at interface. The IPDI content was too high, the
isocyanate group tended to aggregate resulting in the less contract
area with the ramie and the matrix, and lead to a decrease in the
interface between fiber and matrix.