3.1.2. Morphology Observation

Figure 4 showed the fractured surfaces morphologies of PLA/NPF composites. As can be seen in Figure 4, there was a difference in the adhesion between NPF fiber and PLA matrix. At the lower fiber content, the voids between PLA matrix and NPF fiber were invisible. The composite containing 30% of pulp fiber began to show voids between PLA matrix and NPF fiber. When the fiber content exceeded 30%, the fiber breakages and the voids can be observed more clearly. The NPF fibers were pulled out from the PLA matrix, and the surface of PF fiber was not wrapped by PLA matrix. This suggested a poor adhesion between NPF fiber and PLA matrix.

Figure 5 showed that when treating pulp fiber with epoxidized Tung oil, the bonds between fibers and the PLA improved more significantly, compared to the untreated fibers. Even at 10% of fiber content, it was difficult to distinguish pulp fibers and PLA because the pulp fibers was covered by PLA. At 40 and 50% of fiber content, the gaps and holes between the SPF and PLA matrix can be observed.

50% NPF

**Figure 4.** SEM images of fractured surface of PLA/NPF composites with different NPF contents.

**Figure 5.** SEM images of fractured surface of PLA/SPF composites with different SPF contents.

3.1.3. Fourier Transfer Infrared Spectra

The FTIR spectra of pulp fiber, ETO, PLA, PLA/SPF composites with 10, 30 and 50% SPF were presented in Figure 6.

**Figure 6.** The FTIR spectra of pulp fiber, ETO, PLA, PLA/SPF composites with 10% SPF, 30 SPF and 50% SPF.

In IR spectrum of ETO, the peak at 1642 cm−<sup>1</sup> which was assigned for C=C disappeared. Instead there was appearance of a peak at 824 cm−<sup>1</sup> which was assigned for C-O in epoxy ring [25]. This indicated that epoxidation of Tung oil had occurred. The IR spectrum of the pulp fiber appeared as a peak at 3445 cm−1, which was assigned for O-H stretching vibration. This peak of PLA/SPF composites increased by increasing SPF content. A peak at 1771 cm−1, which was assigned for C=O group in PLA and ETO [16], also increased by increasing SPF content. This might be due to the increase of SPF content means that the ETO content in the composite also increased, so the concentration of C=O group increased.
