**4. Conclusions**

This research suggested that pulp fiber could be successfully used as a reinforcement in PLA-based composites. The tensile properties of PLA/PF composites firstly increased after adding the fiber, and then decreased when the content of fiber was over 30%. With the addition of PF fiber, the flexural modulus of PLA-based composites increased, but the flexural strength of them experienced no change. An improvement in the mechanical properties was possibly caused by PF reinforcement, as well as the efficient stress transfer between the PLA matrix and fiber. The PLA-based composite with 30% SPF fiber had the optimal mechanical properties; the tensile strength, tensile modulus, flexural strength and flexural modulus of this composite increased by 45.86%, 39.12%, 20.74%, and 70.79%, respectively, when compared with those of the neat PLA. In addition, the thermal stability of the PLA/PF composites decreased by the increase of the PF fiber.

The interaction between pulp fibers and PLA matrix improved, as the ETO content increased. The tensile and flexural strength of the composite increased by adding ETO with the percentage of 5–10% content. The mechanical properties of composites reduced when the ETO content was high (in amount of 15% of fiber) because ETO acted as a plasticizer for PLA.

**Author Contributions:** Conceptualization: T.T.N. and T.H.P.T.; data curation: T.T.P.; formal analysis: T.T.N. and T.T.P.; investigation: T.T.N. and T.T.P.; methodology: T.T.N. and T.H.P.T.; project administration: V.K.N.; software: T.H.P.T. and T.T.P.; writing—original draft: T.H.P.T. and T.T.P.; writing—review and editing: V.K.N. and T.T.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
