Orientation of Polylactic Acid–Chitin Nanocomposite Films via Combined Calendering and Uniaxial Drawing: Effect on Structure, Mechanical, and Thermal Properties

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.

Advancements in the biopolymer films for food packaging applications: a short review

“…Thus, to ease out the peeling procedure optimal moisture content must be in the range of 5 and 8% [61]. The suitability of the composite and native biopolymer-based films with other operations such as biaxial orientation (stretching of films using rollers) must also studied [62].…”

“…The most used native hydrophilic biopolymer-based films such as pectin, starch, sodium alginate, gelatin, collagen, chitosan, and many other polysaccharides and proteins have poor water vapor barrier properties because of their hydrophilic nature [62][63][64][65]. However, these polymers have moderate to satisfactory oxygen barrier properties [65,66].…”

Deep Insight into the Effect of Microstructure Evolution on Film-Forming Properties of Polylactide during Uniaxial Hot-Stretching Process

“…As is well-known, the uniaxial hot-stretching above the glass transition temperature ( T g ) is a green and efficient film-forming pathway of PLA, considering the obvious enhancement of mechanical property, transparency, and the like of PLA enabled by hierarchical orientation and crystallization via stretching. − For example, Chen et al conducted the uniaxial prestretching process on PLA near T g and found that the inherent network structure of PLA composed of cohesive entanglement was damaged because of the molecular chain orientation, leading to the brittle–ductile transition . The highly ordered mesophase structure was formed during further stretching, finally endowing PLA with unexpected performance in strength, stiffness, and ductility.…”

Robust Osteoconductive β-Tricalcium Phosphate/L-poly(lactic acid) Membrane via Orientation-Strengthening Technology

“…By treating PLLA chains to induce directional orientation, PLLA can obtain a microstructure similar to the ordered arrangement of woods. Such oriented microstructures can significantly improve the mechanical strength of PLLA-based biomaterials. − Although electrospinning and 3D printing can enable polylactic acid to obtain this orientation structure, their strength is still far from sufficient. For semicrystalline polymers such as PLLA, solid-state stretching is an effective approach to realize the high orientation and regular arrangement of chains through intermolecular friction, with no need to add in other components …”