Active biodegradable packaging films modified with grape seeds lignin

Abstract

Biodegradable packaging materials represent one possible solution for how to reduce the negative environmental impact of plastics. The main idea of this work was to investigate the possibility of utilizing grape seed lignin for the modification of polyhydroxyalkanoates with the use of its antioxidant capacity in packaging films. For this purpose, polymeric films based on the blend of high crystalline poly(3-hydroxybutyrate) (PHB) and amorphous polyhydroxyalkanoate (PHA) were prepared. PHB/PHA films displayed Young modulus of 240 MPa, tensile strength at a maximum of 6.6 MPa and elongation at break of 95.2%. The physical properties of PHB/PHA films were modified by the addition of 1-10 wt% of grape seeds lignin (GS-L). GS-L lignin showed a high antioxidant capacity: 238 milligrams of Trolox equivalents were equal to one gram of grape seeds lignin. The incorporation of grape seeds lignin into PHB/PHA films positively influenced their gas barrier properties, antioxidant activity and biodegradability. The values of oxygen and carbon dioxide transition rate of PHB/PHA with 1 wt% of GS-L were 7.3 and 36.3 cm³ m^-2 24 h 0.1 MPa, respectively. The inhibition percentage of the ABTS radical determined in PHB/PHA/GS-L was in the range of 29.2% to 100% depending on the lignin concentration. The biodegradability test carried out under controlled composting environment for 90 days showed that the PHB/PHA film with 50 w/w% of amorphous PHA reached the degradability degree of 68.8% being about 26.6% higher decomposition than in the case of neat high crystalline PHB film. The degradability degree of PHA films in compost within the tested period reflected the modification of the semi-crystalline character and varied with the incorporated lignin. From the toxicological point of view, the composts obtained after biodegradation of PHA films proved the non-toxicity of PHB/PHA/GS-L materials and its degradation products showed a positive effect on white mustard (Sinapis alba L.) seeds germination.

Fig. 1. The used approach to extract lignin from grape seeds.

Fig. 2. PHB, PHB/PHA, PHB/PHA_1_GS-L, PHB/PHA_5_GS-L, and PHB/PHA_10_GS-L films at the beginning of composting.

Fig. 3. ATR-IR spectrum of the grape seeds lignin (GS-L).

Fig. 4. ATR-FTIR spectra of neat PHB and PHB/PHA blends with or without grape seeds lignin (GS-L), (a) spectral range of 4000–400 cm⁻¹ and (b) spectral range of 3100–1400 cm⁻¹.

Fig. 5. DSC (a) first heating scans and (b) cooling scans for PHA, PHB, PHB/PHA, PHB/PHA_1_GS-L, PHB/PHA_5_GS-L, and PHB/PHA_10_GS-L.

Fig. 6. Weight of the samples as a function of temperature obtained by TGA for PHB and PHB/PHA films.

Fig. 7. Antioxidant activity of GS-L lignin in PHB/PHA blend films expressed as inhibition percentage of ABTS radicals. Bars marked by different letters are significantly different (p < 0.01).

Fig. 8. SEM morphology of neat PHB, PHB/PHA, PHB/PHA_1-GS-L and PHB/PHA_10-GS-L.

Fig. 9. Seed germination inhibition test of PHB, PHB/PHA, PHB/PHA_1_GS-L, PHB/PHA_5_GS-L, and PHB/PHA_10_GS-L films.