3.1. LOPA characterization
The FTIR spectra of raw OPA particles and LENR-coated
OPA particles are shown in Fig. 1. The characteristic vibration
bands for the raw OPA have already been noted in a
previous report [10] where the existence of Si–O, Al–O or
Si–O–Al and also calcite was confirmed. However, with the
LENR coating, the FTIR analysis in the 450–4000 cm1
indicated that the OPA functional group was changing. The
new peak observed within 2800–3000 cm1 was assigned
to the stretching vibration of CH2 and CH3 modes
from the isoprene unit of ENR itself. Also, the bands from
850–1300 cm1 tended to broaden compared to the FTIR
spectra of raw OPA. It is suggested that there was a combination
or physical interactions between the functional
group (Si–O) of OPA with the oxirane groups from the LENR
during the coating process.
The surface morphologies of raw OPA and LENR-coated
OPA were studied and are compared in Fig. 2. The raw OPA
typically showed irregular shapes with a rough surface and
a porous structure. The surface of the ash is capable of
absorption, and thus the LENR would penetrate into the
porous structure of the OPA during the coating process and
form a coating layer. This LENR layer was believed to form
an interphase within OPA and NR, thereby improving the
compatibility between OPA and NR matrices. Unfortunately,
the LENR coating method used may lead to an
agglomeration of OPA (as shown in Fig. 2b), which may
cause difficulties in the compounding process.
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