3.2. Dependence of Young's modulus on GNPs content
Fig. 4 shows the dependence of the Young's modulus on the GNP
weight fraction of the PP/GNPs composites. It can be found that the
values of the Young's modulus of the three composite systems increase
with an increase of the GNPs weight fraction. This indicates
that the stiffening effect of the GNPs on PP is significant. Under the
same GNPs weight fraction, the values of the Young's modulus of
the PP/G1 system are the highest, while the values of the Young's
modulus of the PP/G3 system are the smallest. When inorganic
particles are loaded into polymer materials, they will play a role of
skeleton in the matrix, and the movement of molecular chains will
be limited due to a number of physical crosslinking points between
the GNPs and the matrix, leading to improve the stiffness of the
composite systems. For a crystalline polymer, the inclusions will
play a role of heterogeneous nucleation, leading to increase the
crystalline degree or to change the crystal type structure, and to
improve correspondingly the stiffness of the composite systems in
this case. When the filler particles uniformly disperse in the matrix,
the stiffness of polymer composites will increase with increasing
the number of the inclusions. The smaller the particle size, the
more number of the particles is under the same filler volume
fraction. The lateral dimension of G1 particles is the smallest, while
the lateral dimension of G3 particles is the biggest (see Table 1).
Therefore, the values of the Young's modulus of the PP/G1 system
are the highest, while the values of the Young's modulus of the PP/
G3 system are the smallest.