Strong Polyamide-6 Nanocomposites with Cellulose Nanofibers Mediated by Green Solvent Mixtures

Abstract

Cellulose nanofiber (CNF) as a bio-based reinforcement has attracted tremendous interests in engineering polymer composites. This study developed a sustainable approach to reinforce polyamide-6 or nylon-6 (PA6) with CNFs through solvent casting in formic acid/water mixtures. The methodology provides an energy-efficient pathway towards well-dispersed high-CNF content PA6 biocomposites. Nanocomposite formulations up to 50 wt.% of CNFs were prepared, and excellent improvements in the tensile properties were observed, with an increase in the elastic modulus from 1.5 to 4.2 GPa, and in the tensile strength from 46.3 to 124 MPa. The experimental tensile values were compared with the analytical values obtained by micromechanical models. Fractured surfaces were observed using scanning electron microscopy to examine the interface morphology. FTIR revealed strong hydrogen bonding at the interface, and the thermal parameters were determined using TGA and DSC, where the nanocomposites’ crystallinity tended to reduce with the increase in the CNF content. In addition, nanocomposites showed good thermomechanical stability for all formulations. Overall, this work provides a facile fabrication pathway for high-CNF content nanocomposites of PA6 for high-performance and advanced material applications.

Valorization of nylon and viscose-rayon textile yarn wastes for fabricating nanocomposite films

“…With the addition of nanocellulose, the structuring of the surface (Figure 6b-6d) was observed when compared to neat nylon. This surface structuring could be due to the reorientation of hydrogen bonds in nylon polymeric chains due to the formation of new hydrogen bonds between nylon and nanocellulose (as seen previously) [51]. In the FESEM of cryo-fractured cross-section images, the thickness of all the films was around 50 μm (Figure 6e-6h).…”

“…As the concentration of nanocellulose in the films was very low (≤1%) and the limitations of FTIR to sense the material up to a few microns deep inside the film [53], the prominent characteristic peak of nanocellulose (1200 to 900 cm -1 ) was not visible in the nano composite films (data not shown). From Figure 3b, with the addition of nanocellulose in the nylon films, a continuous increase of broad peak at 3460 cm -1 was observed, attributed to the formation of new hydrogen bonds with the OH groups of cellulose and amide groups of nylon [51]. At the maximum concentration of nanocellulose in the film (1%), the peak intensity at 3460 cm -1 increased abruptly, possibly due to the increased hydrogen bonding between the nanocellulose and the nylon that reoriented the original hydrogen bonding in the nylon polymeric chain [51].…”

“…From Figure 3b, with the addition of nanocellulose in the nylon films, a continuous increase of broad peak at 3460 cm -1 was observed, attributed to the formation of new hydrogen bonds with the OH groups of cellulose and amide groups of nylon [51]. At the maximum concentration of nanocellulose in the film (1%), the peak intensity at 3460 cm -1 increased abruptly, possibly due to the increased hydrogen bonding between the nanocellulose and the nylon that reoriented the original hydrogen bonding in the nylon polymeric chain [51].…”

“…To compare the chemical composition of nylon yarn waste and nylon films, the spectra were normalized at 1168 cm -1 [49,50]. From Figure 3a, a broad peak around 3460 cm -1 (-OH stretching) was observed in nylon yarn waste, which is usually absent or very weak in the spectrum of industrial-grade nylon pellets [51]. It indicates the presence of additives like talc powder (as a nucleating agent) or phenols (antioxidant) in the nylon yarn that is usually added to enhance the mechanical properties and thermal stability, respectively, during the manufacturing process of nylon fibers for textile application [52].…”

“…In contrast, a reduction in the peak intensity at 695, 1198, 1367, 1418, 2925, and 2850 cm -1 for neat nylon film was evident compared to the nylon yarn waste. This observation is attributed to the conversion of α-crystalline form (stable) of nylon to γ-crystalline form (metastable) that was mediated through solvent processing [51].…”