Effect of Medium-Chain-Length Alkyl Silane Modified Nanocellulose in Poly(3-hydroxybutyrate) Nanocomposites

Abstract

Poly (3-hydroxybutyrate) (PHB) is a valuable biopolymer that is produced in industrial quantity but is not widely used in applications due to some drawbacks. The addition of cellulose nanofibers (CNF) as a biofiller in PHB/CNF nanocomposites may improve PHB properties and enlarge its application field. In this work, n-octyltriethoxy silane (OTES), a medium-chain-length alkyl silane, was used to surface chemically modify the CNF (CNF_OTES) to enhance their hydrophobicity and improve their compatibility with PHB. The surface functionalization of CNF and nanodimension were emphasized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, atomic force microscopy, dynamic light scattering, and water contact angle (CA). Surface modification of CNF with OTES led to an increase in thermal stability by 25 °C and more than the doubling of CA. As a result of the higher surface hydrophobicity, the CNF_OTES were more homogeneously dispersed in PHB than unmodified CNF, leading to a PHB nanocomposite with better thermal and mechanical properties. Thus, an increase by 122% of the storage modulus at 25 °C, a slight increase in crystallinity, a better melting processability, and good thermal stability were obtained after reinforcing PHB with CNF_OTES, paving the way for increasing PHB applicability.

Keywords: AFM; alkyl silane; cellulose nanofibers; nanodimension; polyhydroxyalkanoates.

Figure 1

Chemical functionalization of CNF with OTES.

Figure 2

FTIR spectra of CNF and CNF_OTES (A); 3000–2800 cm⁻¹ (B); and 1400–600 cm⁻¹ regions (C).

Figure 3

XPS survey spectra of CNF and CNF_OTES.

Figure 4

Images of water droplets on the surface of CNF and CNF_OTES during water contact angle measurement.

Figure 5

TG (A) and DTG (B) diagrams of CNF and CNF_OTES.

Figure 6

Topographic and PFE images of CNF and CNF_OTES (scanning areas 5 µm × 5 µm and 3 µm × 3 µm) (A); topographic and PFE images of CNF_OTES (1 µm× 1 µm) (B).

Figure 6

Topographic and PFE images of CNF and CNF_OTES (scanning areas 5 µm × 5 µm and 3 µm × 3 µm) (A); topographic and PFE images of CNF_OTES (1 µm× 1 µm) (B).

Figure 7

Distribution of cellulose nanofibers’ width resulted from AFM-QNM analysis (A); particle size distribution by DLS for CNF and CNF_OTES (B).

Figure 8

Brabender torque (A) and molten material’s temperature (B) variation with time for PHB, PHB/CNF, and PHB/CNF_OTES nanocomposites.

Figure 9

Storage modulus values for PHB and nanocomposites at different temperatures.

Figure 10

SEM images of the fractured surface of neat PHB (A), PHB/CNF (B), and PHB/CNF_OTES (C) nanocomposites; nanofiber agglomerations were marked with red circles, while well-dispersed nanofibers had blue arrows.

Figure 11

DSC curves of nanocomposites: first heating (A), second heating (B), and cooling (C).

Figure 12

TGA (A) and DTG (B) curves of PHB nanocomposites.