Development of eco-friendly modified cellulose nanofiber reinforced polystyrene nanocomposites: thermal, mechanical, and optical properties

Abstract

The fiber extracted from pineapple leaf was treated by 2,2,6,6-tetramethylpiperidine (TEMPO) to prepare the cellulose nanofiber (CNF). Subsequently, it was eco-friendly modified by suspension polymerization and the sol-gel method, respectively, in order to improve its affinity with the polymer matrix. The obtained CNFs was reinforced into a polystyrene (PS) substrate to acquire nanocomposites. The FTIR results showed that after alkali and acid neutralization treatment, lignin and impurities of PLF can be effectively removed. In addition, the nano-scale fibers were obtained by TEMPO oxidation reaction (OF), suspension polymerization (SF) and sol-gel modification (GF). The results of contact angle revealed the improved hydrophobicity of CNFs after modification. Especially the SF, resulted in hydrophobicity (55.84o) as compared with that of the OF (12.02 o). The XRD results showed that the crystallinities of OF, SF and GF are 80.78, 78.48 and 67.16%, respectively. The TGA analysis revealed that the degradation temperature and char yield of the GF (14.14%) were higher than those of OF (6.02%) and SF (8.44%). Tensile studies of the nanocomposites indicated improved mechanical properties by the addition of modified CNFs compared to the TEMPO-reacted ones. The tensile strengths of nanocomposite PSCNF (31.1 MPa) and PSGPH (28.1 MPa) are better than those of POCNF (26.7 MPa). The heat distortion temperature (HDT) of the nanocomposites increased with increasing different kinds of CNFs content. Among all of the nanocomposites, the 3 wt% GF containing one showed the best value (93.8 °C), and the increment was 3.5 °C as compared with pristine PS (90.3 °C). The optical properties of the materials revealed that TEMPO oxidized CNFs without modification has poor light transparency due to its poor compatibility and fiber aggregation.