The birch residues for obtaining advanced composite packaging

Eco-friendly, biodegradable, and recyclable materials for food packaging are a priority worldwide. Among packaging materials, the use of plastics accounts for about 38-40%, and this trend of using plastics for packaging is expected to remain unchanged. Thus, the main challenge is minimising the negative effect of plastic packaging on the environment is the creation of plastic packaging consisting of biobased materials with a high content.

Birch wood (Betula pendula) is utilised in the production of pulp, plywood, and furniture. During this process, sawdust and bark are generated as by-products, which are often used as fuel. However, sawdust and bark can be utilised more effectively in the formulation of recycled polypropylene/polylactic acid (rPP/PLA) composite packaging, specifically designed for creating food containers through extrusion and injection moulding. The birch outer bark is rich in extractives, which can be isolated in good yields with organic solvents. After the extraction, birch outer bark contains suberin and, by its depolymerisation, suberinic acids are obtained. Thus, the remaining biomass can be used as a valuable ingredient for composite packaging.

The research conducted showed that the alkali-treated sawdust and microparticles from the residue obtained after extracting betulin (a non-aromatic diol) from the outer bark were used as a lignocellulosic filler in the developed composite packaging. Additionally, suberinic acids obtained from the outer bark were used as a lubricant, enhancing the processing parameters of the composite packaging by reducing energy consumption. The obtained composite packaging samples, filled with the lignocellulosic fillers and containing the biolubricant, exhibited good mechanical properties, decreased water uptake and dimensional swelling, as well as lower energy consumption compared to the formulation without suberinic acids.