Structure-Properties Correlations of PVA-Cellulose Based Nanocomposite Films for Food Packaging Applications

Abstract

Bio-nanocomposites based on poly (vinyl alcohol) (PVA) and cellulosic nanostructures are favorable for active food packaging applications. The current study systematically investigates the mechanical properties, gas permeation, and swelling parameters of PVA composites with cellulose nanocrystals (CNC) or nano lignocellulose (NLC) fibers. Alterations in these macroscopic properties, which are critical for food packaging applications, are correlated with structural information at the molecular level. Strong interactions between the fillers and polymer host matrix were observed, while the PVA crystallinity exhibited a maximum at ~1% loading. Finally, the orientation of the PVA nanocrystals in the uniaxially stretched samples was found to depend non-monotonically on the CNC loading and draw ratio. Concerning the macroscopic properties of the composites, the swelling properties were reduced for the D1 food simulant, while for water, a considerable decrease was observed only when high NLC loadings were involved. Furthermore, although the water vapor transmission rates are roughly similar for all samples, the CO₂, N₂, and O₂ gas permeabilities are low, exhibiting further decrease in the 1% and 1-5% loading for CNC and NLC composites, respectively. The mechanical properties were considerably altered as a consequence of the good dispersion of the filler, increased crystallinity of the polymer matrix, and morphology of the filler. Thus, up to ~50%/~170% enhancement of the Young's modulus and up to ~20%/~50% enhancement of the tensile strength are observed for the CNC/NLC composites. Interestingly, the elongation at break is also increased by ~20% for CNC composites, while it is reduced by ~40% for the NLC composites, signifying the favorable/unfavorable interactions of cellulose/lignin with the matrix.

Keywords: PVA; active food packaging; lignocellulose; nanocellulose; nanocomposites.

Figure 1

SEM images of nano-cellulosic inclusions. (a) CNC and (b) lignocellulose.

Figure 2

Cross-sectional surface SEM images of: (a) PVA pure, (b) 1%, (c) 5% and (d) 10% CNC composite.

Figure 3

Cross-sectional surface SEM images of: (a) 1%, (b) 5%, and (c) 10% PVA lignocellulose composites. (d) 10% composite at a higher magnification; indicative lignocellulose nanofibers are encircled (red circles).

Figure 4

(a) ATR/FTIR spectra of CNC, neat PVA film, and PVA composites with 1, 5, and 10 wt.% CNC % in CNC. (b) ATR/FTIR spectra of NLC, neat PVA film, and PVA composites with 1, 5, and 10 wt.% in lignocellulose.

Figure 5

(a) XRD graph of Pure PVA film, cellulosic inclusion, and PVA composites: 1%, 5%, and 10% CNC. (b) XRD patterns of Pure PVA film, lignocellulose inclusion, and PVA composites with 1%, 5%, and 10% lignocellulose.

Figure 6

(a) DSC thermographs (first heat) of Pure PVA film and PVA composites with 1%, 5%, and 10% CNC. (b) DSC thermographs (first heat) of Pure PVA film and PVA composites with 1%, 5%, and 10% lignocellulose.

Figure 7

Comparative crystallinity index plots vs. inclusion loading, calculated by: (a) ATR/IR, (b) XRD, and (c) DSC. CNC composites (squares) and lignocellulose composites (circles).

Figure 8

(a) Polarized Raman spectra at λ = 1, 2, and 3 of pure PVA, (b) orientation of the PVA crystal phase as a function of draw ratio for neat PVA and its composites, (c) orientation function as a function of loading for two distinct draw ratios.

Figure 9

Mass increase plots of PVA membranes immersed in water (squares) and 50% ETOH/water (circles) for 48 h: (a) CNC composites and (b) lignocellulose composites.

Figure 10

(a) CO₂ permeability (Barrer) bar plot versus cellulose loading. The detection limit was 0.01 Barrer. (b) Sp.WVTR bar plot versus cellulose loading. CNC composites (black), lignocellulose composites (sparse red), and pure PVA (blue).

Figure 11

Stress−strain curves of PVA and PVA-CNC composites (a) and lignocellulose composites (b). Linear region (inlet).