Cellulose nanofiber (CeNF)-reinforced polymer composites have wide potential applications in the manufacturing of optical and mechanical parts owing to their light weight, high mechanical strength, and optical transparency. In this study, CeNF-reinforced homogeneous polypropylene (PP-CeNF) was machined under various conditions by ultraprecision diamond turning, and the results were compared with those of pure PP without CeNF addition. The influence of CeNFs on material removal was investigated by examining the surface topography, chip morphology, cutting forces, and cutting temperature. It was found that the surface defects in pure PP cutting were surface tearing, while the surface defects of PP-CeNF were surface tearing and micro-holes induced by the pulling-outs of CeNFs. Surface tearing increased with cutting speed; pulling-outs of CeNFs were slightly affected by cutting speed but strongly dependent on the tool feed rate. Under a small tool feed rate, the surface roughness could be reduced to ∼10 nm Ra for PP-CeNF. The thermal effect was insignificant in the experiments, whereas the effect of strain rate-induced material hardening was dominant for both workpiece materials at a high cutting speed. This study helps to understand the mechanisms for ultraprecision cutting of CeNF-reinforced polymer composites and provides guidelines for improving the machined surface quality.

1. [1] H. Yano, “Production of Cellulose Nanofiber Reinforced Optically Transparent Film and Its Properties,” J. of the Adhesion Society of Japan, Vol.47, No.5, pp. 210-214, 2011.
2. [2] H. Yano, “Basics and Applications of Cellulose Materials III: Cellulosic Nanocomposites,” J. of the Society of Materials Science, Vol.57, No.3, pp. 310-315, 2008.
3. [3] T. Saito et al., “An Ultrastrong Nanofibrillar Biomaterial: The Strength of Single Cellulose Nanofibrils Revealed via Sonication-Induced Fragmentation,” Biomacromolecules, Vol.14, No.1, pp. 248-253, 2013.
4. [4] T. Nishino, M. Kotera, and M. Kimoto, “Temperature dependence of the elastic modulus of the crystalline regions of cellulose,” Proc. 2nd Int. Cellulose Conf., 2007.
5. [5] T. Nishino, and T. Peijs, “All-cellulose composites,” K. Oksman et al. (Eds.), “Handbook of Green Materials,” pp. 201-216, World Scientific, 2014.
6. [6] A. N. Nakagaito and H. Yano, “The effect of morphological changes from pulp fiber towards nano-scale fibrillated cellulose on the mechanical properties of high-strength plant fiber based composites,” Applied Phisics A, Vol.78, No.4, pp. 547-552, 2004.
7. [7] J. C. Lee, J. A. Lee, D. Y. Lim, and K. Y. Kim, “Fabrication of Cellulose Nanofiber Reinforced Thermoplastic Composites,” Fibers and Polymers, Vol.19, pp. 1753-1759, 2018.
8. [8] M. Nogi et al., “Optically transparent bionanofiber composites with low sensitivity to refractive index of the polymer matrix,” Applied Physics Letters, Vol.87, 243110, 2005.
9. [9] S. Fujisawa et al., “Comparison of mechanical reinforcement effects of surface modified cellulose nanofibrils and carbon nanotubes in PLLA composites,” Composites Science and Technology, No.90, pp. 96-101, 2014.
10. [10] A. Isogai, M. Kawasaki, and H. Yano, “Technical Data of Cellulose Nanofibers,” CMC Publishing Co., Ltd., 2016 (in Japanse).
11. [11] L. Wang, K. Okada, M. Sodenaga, Y. Hikima, M. Ohshima, T. Sekiguchi, and H. Yano, “Effect of surface modification on the dispersion, rheological behavior, crystallization kinetics, and foaming ability of polypropylene/cellulose nanofiber nanocomposites,” Composites Science and Technology, Vol.168, pp. 412-419, 2018.
12. [12] L. Wang, M. Ando, M. Kubota, S. Ishihara, Y. Hikima, M. Ohshima, T. Sekiguchi, A. Sato, and H. Yano, “Effects of hydrophobic-modified cellulose nanofibers (CNFs) on cell morphology and mechanical properties of high void fraction polypropylene nanocomposite foams,” Compos. Part A, Vol.98, No.C, pp. 166-173, 2017.
13. [13] B. Yan, Y. Huang, and S. Yeh, “The effect of fiber angles on the machinability of CFRP,” Japan Society for Precision Engineering, Spring 2, pp. 719-720, 1991.
14. [14] T. Kaneeda, “CFRP Cutting Mechanism (3rd Report) – Effects of Tool Edge Roundness and Relief Angle on Cutting Phenomena –,” J. of the Japan Society for Precision Engineering, Vol.57, No.3, pp. 491-496, 1991.
15. [15] W. Huang and J. Yan, “Surface formation mechanism in ultraprecision diamond turning of coarse-grained polycrystalline ZnSe,” Int. J. of Machine Tools and Manufacture, Vol.153, 103554, 2020.
16. [16] M. Heidari, J. Akbari, and J. Yan, “Effects of tool rake angle and tool nose radius on surface quality of ultraprecision diamond-turned porous silicon,” J. of Manufacturing Processes, Vol.37, pp. 321-331, 2019.
17. [17] K. Q. Xiao and L. C. Zhang, “The role of viscous deformation in the machining of polymers,” Int. J. of Mechanical Sciences, Vol.44, No.11, pp. 2317-2336, 2002.
18. [18] Y. C. Jean (Ed.), “Positron and Positronium Chemistry,” World Scientific, 1990.
19. [19] R. F. Boyer, “Transitions and Relaxation,” H. F. Mark and N. M. Bikales (Eds.), “Encyclopedia of Polymer Science and Technology,” Supplement Vol.2, Wiley, 1997.
20. [20] A. Uedono and S. Tanigawa, “Glass Transition and Relaxation Processes of Polymers Studied by Positron Annihilation,” Japanese J. of Polymer Science and Technology, Vol.53, No.10, pp. 563-574, 1996.
21. [21] J. Yan, “Ultraprecision cutting of photoresist/gold composite microstructures,” CIRP Annals, Vol.60, No.1, pp. 133-136, 2011.
22. [22] J. Carr and C. Feger, “Ultraprecision machining of polymers,” Precision Engineering, Vol.15, No.4, pp. 221-237, 1993.
23. [23] H. J. Yoon, B. M. Gil, J. H. Lee et al., “Thermal and Mechanical Properties of Polypropylene/Cellulose Nanofiber Composites,” Polymer-Korea, Vol.44, pp. 255-263, 2020.
24. [24] H. Kurita, R. Ishigami, C. Wu, and F. Narita, “Experimental Evaluation of Tensile Properties of Epoxy Composites with Added Cellulose Nanofiber Slurry,” Strength of Materials, Vol.52, No.5, pp. 798-804, 2020.
25. [25] A. Kobayashi and K. Saito, “On the cutting mechanism of plastics,” CIRP Annals, Vol.11, pp. 82-89, 1962.
26. [26] T. Kaneeda and M. Takahashi, “CFRP cutting mechanism (2nd report) – Analysis of depth of reluctant uncut and deformed part –,” J. of the Japan Society for Precision Engineering, Vol.56, No.6, pp. 1058-1063, 1990.
27. [27] P. S. Sreejith, R. Krishnamurthy, S. K. Malhotra, and K. Narayanasamy, “Evaluation of PCD tool performance during machining of carbon/phenolic ablative composites,” J. of Materials Processing Technology, Vol.104, No.1-2, pp. 53-58, 2000.
28. [28] K. Sakuma and M. Seto, “Tool wear in cutting glass-fiber-reinforced-plastics: The relation between cutting temperature and tool wear,” Bulletin of JSME, Vol.24, No,190, pp. 748-755, 1981.
29. [29] J. Yan, K. Syoji, T. Kuriyagawa, and H. Suzuki, “Ductile regime turning at large tool feed,” J. of Materials Processing Technology, Vol.121, No.2-3, pp. 363-372, 2002.