Trans crystallization behavior and strong reinforcement effect of cellulose nanocrystals on reinforced poly(butylene succinate) nanocomposites

Abstract

Biodegradable poly(butylene succinate) (PBS) nanocomposites are polymerized via in situ polymerization of succinic acid (SA) with cellulose nanocrystal (CNC)-loaded 1,4-butanediol (1,4-BD) mixtures. As reinforcement fillers, whisker-like CNCs are first dispersed in alcohol and sequentially spray-dried, before adding them to 1,4-BD. During the polymerization, the remains of sodium sulfonate in the CNC surfaces retard the polycondensation reaction, which is carefully controlled for the CNC-loaded systems. For the 0.1-1.0 wt% CNC-loaded PBS nanocomposites, it is found the nano-fillers are sufficiently dispersed to induce different crystallization behavior of the matrix polymer. The CNCs may initially act as heterogeneous nucleation sites of the molten PBS chains, during melt crystallization. In this case, most of them tend to be pushed out from the growing crystallites, which develop different nanocomposite morphologies with increasing CNC content. Among the resulting nanocomposites, the 0.1 wt% CNC-loaded system shows the highest tensile strength of 65.9 MPa, similar to that of nylon 6, as a representative engineering polymer as well as 2 fold elongation at break compared with Homo PBS. The in situ polymerized CNC-loaded PBS nanocomposites are expected to be a 100% biomass material for a virtuous cycle of biorefinery. Moreover, they demonstrate that the CNC-loaded PBS nanocomposite with a low CNC loading content can be used in various commercial applications for pollution abatement.

Scheme 1. The preparation method of CNC using sulfuric acid.

Fig. 1. Morphology of CNCs: (a and b) TEM, (c) AFM images.

Fig. 2. The image of three different types of 1.0 wt% CNC solutions dispersed in 1,4-BD after sonication for 5 min.

Fig. 3. DSC thermograms of Homo PBS and PCN samples: (a) heating and (b) cooling curves with a constant rate of 10 °C min⁻¹.

Fig. 4. TGA curves of Homo-PBS and PCN samples with different CNC loadings.

Fig. 5. Schematic diagram of mechanical properties of the 0.1 wt% CNC-loaded nanocomposites compared with biodegradable polymer, their nanocomposites and petrochemical polymer.

Fig. 6. (a) WAXD patterns of CNCs and the PCN samples. TEM micrographs of (b) PCN03 and (c) PCN10.

Fig. 7. Polarizing optical microscope images of (a) Homo-PBS and (b) PCN03 during isothermal crystallization at 90 °C.

Fig. 8. High-resolution AFM topographies of spherulites containing different CNC loadings: (a) Homo-PBS; (b) PCN03; (c) PCN 05 (at a high resolution images).

Fig. 9. (a) Master curves of dynamic melt viscosity and (b) Cole–Cole plots of the PCN series; the values in parentheses are the slopes of the Cole–Cole plots.

Fig. 10. Schematic diagram of the effect of CNCs on the change in interaction of the PBS backbone.