Abstract
The orientation of polymer composites is one way to increase the mechanical properties of the material in a desired direction. In this study, the aim was to orient chitin nanocrystal (ChNC)-reinforced poly(lactic acid) (PLA) nanocomposites by combining two techniques: calendering and solid-state drawing. The effect of orientation on thermal properties, crystallinity, degree of orientation, mechanical properties and microstructure was studied. The orientation affected the thermal and structural behavior of the nanocomposites. The degree of crystallinity increased from 8% for the isotropic compression-molded films to 53% for the nanocomposites drawn with the highest draw ratio. The wide-angle X-ray scattering results confirmed an orientation factor of 0.9 for the solid-state drawn nanocomposites. The mechanical properties of the oriented nanocomposite films were significantly improved by the orientation, and the pre-orientation achieved by film calendering showed very positive effects on solid-state drawn nanocomposites: The highest mechanical properties were achieved for pre-oriented nanocomposites. The stiffness increased from 2.3 to 4 GPa, the strength from 37 to 170 MPa, the elongation at break from 3 to 75%, and the work of fracture from 1 to 96 MJ/m3. This study demonstrates that the pre-orientation has positive effect on the orientation of the nanocomposites structure and that it is an extremely efficient means to produce films with high strength and toughness.
Highlights
There is a growing worldwide interest in developing bio-based materials for sustainable development to mitigate the waste disposal problems created by petroleum-based polymeric materials
Very small peaks at 9.4◦, 12.5◦, and 25.1◦ appeared in this pattern that could be attributed to the 5 wt% of chitin nanocrystal (ChNC) in the nanocomposite; they were assigned to the (020), (021), and
After solid-state drawing (SSD), the compression molded film (CM)-SSD-4 sample showed a much more intense but slightly broadened diffraction peak at 16.4◦ in Figure 2b, which can be attributed to the strain-induced crystallization behavior and decreased size of the poly(lactic acid) (PLA) crystallites in the nanocomposite resulting from the drawing process [26]
Summary
There is a growing worldwide interest in developing bio-based materials for sustainable development to mitigate the waste disposal problems created by petroleum-based polymeric materials. PLA is brittle for the following reasons: (1) low glass transition temperature (Tg ≈ 55 ◦ C), which makes the polymer chain rigid and inflexible, and (2) slow crystal nucleation, which leads to a large spherulite size [4]. To overcome these limitations, researchers have used plasticizers [5], copolymers [6], and nucleating agents [7] to improve PLA crystallization behavior. By adding plasticizers to the PLA matrix, the elongation at break increases but the tensile strength and modulus decrease [8]
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