showed the effects of various IPDI content treated on ramie/PLA
composites. Compared to the ramie/PLA composites without treatment
(shown in Fig. 4A(a)), the composites with various IPDI content
treated all showed an increased interfacial adhesion (shown
in Figs 4A(c) and 8(a)–(c)). With the IPDI content increased, the gaps
existed at the fiber–matrix interface became no distinct, and the
surface of fiber became coarse. Furthermore, it can be found that
ramie appeared to be coated with PLA matrix. This was considered
to be further evidence in support of the conclusion that the
increased isocyanate group content results in an increase in the
interfacial adhesion between ramie and the PLA matrix. However,
for the composite with 2% IPDI treated, the interfacial adhesion
was not improved further, and some gaps between ramie and matrix
became relatively wide. These morphological findings supported
the trend of tensile properties with the increased IPDI content