Thermoplasticized Bread Waste and Poly(butylene adipate-co-terephthalate) Blends: A Sustainable Alternative to Starch in Eco-Friendly Packaging

Bread and derived products are among the most wasted food in the developed world, with more than 30% of unsold and subsequently thrown away daily goods, causing significant environmental harm (disposal, transportation, etc.) and substantial economic losses. The main constituent of these products is starch-rich flour, which is mixed with water and minor components such as salt and lipids before baking. Valorizing this bread waste (BW) by taking advantage of its high polysaccharide content would be highly desirable. In the present work, BW was used as an inexpensive source of starchy material and a replacement of native starch that does not compete with food crops. Biodegradable plastics were produced by plasticizing BW with glycerol in a ratio from 85/15 to 80/20 (w/w) to produce thermoplasticized BW (TPB), which was then mixed with poly(butylene adipate-co-terephthalate) (PBAT) in a weight ratio varying from 70/30 to 50/50 in the presence of a compatibilizing agent using a melt-processing route to produce pellets and thin films. The morphology of the resulting materials, their mechanical and thermal properties, and their moisture sorption as a function of the TPB content and compatibilization were investigated. Satisfactory mechanical and moisture resistance was achieved with a TPB content of up to 40 wt % in the presence of a small amount of added PBAT-grafted maleic anhydride as a compatibilizing agent. A pilot extrusion-blowing test was run with a 60/40 (w/w) PBAT/TPB blend, resulting in uniform ∼30 μm-thick films free of defects. This proof of concept demonstrates the possible replacement of edible starch with BW to reduce food waste for the production of biodegradable plastic packaging, with potential applications as consumer bags, packaging, and agricultural mulch films, among others.