Lignin boosts properties of starch-based packaging, finds study
Packaging incorporating natural biopolymers can improve the mechanical and barrier properties of starch-based films, according to a study.
Results showed packaging films produced by incorporating isolated lignin improved selected thermo-mechanical and barrier properties with reduction in water vapour permeability, and improved water resistance and seal strength.
Bhat et al said that lignin, a natural biopolymer, was extracted from oil palm black liquor waste (BLW) and sago-starch is produced from sago palm plant in Malaysia.
Preparation method
Food packaging films were prepared by casting method from sago palm starch (as film matrix with 30% w/w glycerol as plasticizer) by adding lignin isolated from oil palm black liquor waste (BLW) as a reinforcing material (1, 2, 3, 4 and 5% v/w).
The sago starch films prepared by incorporating lignin isolated from BLW were found to be comparable with the films incorporated with commercial lignin.
Due to high hydrophilic nature, packaging films produced from starch possesses poor barrier (against gas and moisture) and mechanical properties, said the researchers.
This limits their potential as basic raw materials for developing biodegradable packaging materials.
Biome Bioplastics recently partnered with the University of Warwick’s Centre for Biotechnology and Biorefining in the UK to conduct research into lignin potentially providing the foundation for a new generation of bioplastics.
Exploring the benefits
The film forming solutions were prepared by addition of a percentage of sago-starch with distilled water (4g sago starch/100 ml water) at room temperature and Glycerol was added as plasticizer at a concentration of 30% (30g glycerol/100 g sago starch).
Lignin (isolated lignin and commercial lignin) was dissolved with 90% di-methyl sulfoxide (DMSO) and incorporated into the film solution at different concentrations (1, 2, 3, 4 and 5% v/w of film forming solution.
On comparison with the control, an increase in tensile strength (TS) was recorded in films produced by incorporating isolated lignin from BLW compared to commercial lignin.
“It increased corresponding to increase in the isolated lignin from BLW at 1%, 2% and 3% with a value of 3.48 ± 0.15 megapascals (MPa), 3.76 ± 0.40 MPa and 4.20 ± 0.42 MPa, respectively,” found the researchers.
With regard to elongation at break (EB), a decrease was recorded in films produced by addition of isolated lignin from BLW (at 3, 4 and 5%).
However, no significant differences were recorded in films produced by incorporating 1% and 2% of BLW isolated lignin with the films found to be more stretchable.
Films produced by using 1% and 2% of BLW isolated lignin had higher elastic modulus (EM) values compared to control films.
Those produced by incorporating lignin from BLW at 3% showed highest improvement compared to control and all the other formulations.
Further investigations are underway to evaluate biodegradability of the films for commercial use.
