Natural rubber (NR), obtained from Hevea brasiliensis, has been
regarded as a good toughening agent for PLA [18e22] and it can
avoid disrupting the renewability of PLA. But, whether the other
characteristics of PLA, i.e. biodegradability, will be affected greatly
by the introduction of NR? The problem keeps unsolved. In general,
the incorporation of additives will accelerate or retard the hydrolysis
by affecting the crystallinity, water permeability and some
other things, and hence affect the biodegradation. In the study of the
hydrolytic degradation of Polylactide/montmorillonite nanocomposites,
Paul et al. has found that the relative hydrophilicity of
the clay plays determining roles in the hydrolytic degradation process
and accelerates the hydrolysis [23]. Similar results have been
reported by Zhou [12]. Moreover, because of the water segregation
of modified montmorillonite and Sepiolite, PLA hydrolysis has been
delayed [24]. Haynes and his coworkers have found a significant
retard of the hydrolysis of PLA by adding 5e20 wt% fluoroPLA copolymers
because of the hydrophobicity of the copolymers [25].
Natural rubber contains more than 90 wt% polyisoprene which is
also a hydrophobic material. Although natural rubber has been used
as toughening agent of PLA, no conclusion has been made regarding
on the effect of NR on the hydrolysis of PLA, which should be solved
in the development of NR toughening PLA materials