Enhancement of strength and toughness of bio-nanocomposites with good transparency and heat resistance by reactive processing

Abstract

Growing concerns in addressing environmental challenges are driving the rapid advancement of both bio-based and environmental friendly materials. Biodegradable polymers have been compounded with various nanofillers to fulfill the multiple requirements in real applications. However, current technologies remain to be improved in terms of the intrinsic inferior performance and the lack of interfacial interactions. In this work, we employed a facile route to develop bio-nanocomposites integrating multiple functionalities by reactive processing of polylactide and reactive boehmite nanorods. The grafting of polymer chains onto the surface of the nanorods encourages fully homogeneous dispersion of nanofillers with even 30 wt% loadings. Such nanocomposites exhibit simultaneously enhanced tensile strength, modulus, ductility, and impact strength. Moreover, the bio-based nanocomposites present promising features such as high transparency, improved flame resistance, and heat resistance. This work demonstrates exciting opportunities to produce bio-plastics with diverse functionalities in versatile applications of sustainable packaging industry and engineering plastics.

Keywords: Biomaterials; Materials class; Materials science.

Graphical abstract

Figure 1

Reactive compounding enabled PLLA nanocomposites (A and B) (A) Schematic diagram of the fabrication strategy of PLLA/nanorods’ dispersion, (B) PLLA nanocomposites through reactive compounding process.

Figure 2

Homogeneous dispersion of AG nanorods (A–C) Photographs and corresponding SEM, TEM images of the PLLA nanocomposites containing (A) 5 wt % AlOOH nanorods, (B) 5 wt % and (C) 30 wt % AG nanorods.

Figure 3

Improved mechanical performance (A–E) (A) Photographs of PLLA and the nanocomposites containing 20 wt % nanorods, (B) Representative stress-strain curves, (C) Significant improvement for comparing the mechanical performance of reported PLLA nanocomposites, (D1) Impact strength of PLLA nanocomposites with various concentrations of nanorods, and SEM images of impact sections of PLLA nanocomposites with (D2) 0 wt%, (D3) 5 wt%, (D4) 10 wt%, (D5) 20 wt% and (D6) 30 wt% of modified nanorods, (E) Increase rate (δ) of impact strength comparing with reported PLLA nanocomposites (in the inserted equation, εnanocomposites and ε_PLLA referred to impact strength or impact energy of PLLA-based nanocomposites and pristine PLLA, respectively). Details are given in Tables S2–S4.

Figure 4

Improved optical performance (A–E) Photographs of PLLA nanocomposites containing various contents of nanorods (from 0%, 1%, 3%, 5%, 10%, 20%-30%, weight ratio) with a thickness of 100 μm: (A) before and (B) after annealing at 100°C for 60 min; (C) Light transmittance, and (D) Haze value of PLLA nanocomposites with different content of nanorods before and after annealing (E) Refractive index curves of PLLA nanocomposites with different content of nanorods.

Figure 5

Improved thermal performance (A–K) Dynamic Mechanical Analysis (DMA): (A and B) storage modulus, (I) loss tangent values in dependence of temperature of PLLA nanocomposites; Heat resistance: (C and D) photographs of PLLA nanocomposites after DMA experiments, photographs of (E) PLLA and (F) PLLA nanocomposites with 30 wt % nanorods in boiling water bath (100°C) for 3 min; (G and H) photographs of PLLA and PLLA nanocomposites after dipping in boiling water for 3 min; Crystallization behaviors: POM images of isothermal crystallization of (J) pure PLLA and (K) PLLA nanocomposites with 30 wt% nanorods at 130°C.

Figure 6

Improved flame resistance (A–E) Photographs of PLLA nanocomposites during combustion: (A) 0 wt%, (B) 20 wt%, and (C) 30 wt% nanorods, (D) LOI values of nanocomposites in dependence of nanorods’ loading, (E) SEM images of nanocomposites (30 wt%) after limiting oxygen index testing.

Figure 7

Schematic illustration of simultaneously enhanced tensile strength and impact strength (A–D) (A) Increased free volumes, (B), (C) Forced high elastic deformation of the nanocomposites by nanorods, (D) Radar plot showing the complex correlation among Young’s modulus, strength, elongation at break, impact strength, transmittance after thermal annealing, and LOI values for neat PLLA and the biodegradable nanocomposites containing 20 wt% nanorods.