Conversion of Food Waste into Polylactic acid Fibre

Scientific concepts, discoveries, and nature/phenomena presented

Food waste → sustainable materials

• Food loss and waste at scale: ~1/3 of global food produced for human consumption is lost or wasted annually (FAO estimate).
• Environmental motivation: disposing food waste in landfills is described as unsustainable due to landfill space depletion and environmental burden.

Bioconversion using fungi (solid-state fermentation)

• Solid-state fermentation (SSF): specific fungi are added to food waste.
• In situ enzyme production: fungi actively secrete enzymes while growing on the solid substrate.
• Hydrolysis in a bioreactor: the enzyme-rich fungal biomass is blended with food waste and hydrolyzed to produce a nutrient-rich fermentation feedstock.
• Microbial fermentation to lactic acid: bacteria consume nutrients from the hydrolysate to produce lactic acid.

Recovery and purification of lactic acid

• Cell biomass removal:
  • Filtration
  • Centrifugation
• Removal of colored impurities:
  • Activated carbon adsorption after mixing to absorb impurities.
• Concentration:
  • Rotary evaporation to concentrate the solution.
• Liquid–liquid extraction:
  • Continuous extraction using ethyl acetate with sonication.
  • Separation of organic phase using a separatory funnel.
• Isolation of lactic acid:
  • Distillation (reported: ~40 °C for ~30 minutes) to obtain lactic acid.

Polymer chemistry: PLA from lactic acid

• Polymer production pathway: lactic acid is transformed into PLA (polylactic acid) via a route involving:
  • Dehydration
  • Oligomerization
  • Depolymerization to synthesize lactide as an intermediate
• Catalysis (novel catalytic method):
  • Zinc oxide (ZnO) nanoparticle dispersion as the catalyst during lactide synthesis
• Purification of lactide:
  • Recrystallization using ethyl acetate
  • Vacuum filtration to separate the precipitate
  • Vacuum oven drying
• PLA synthesis:
  • Ring-opening polymerization (ROP) of lactide:
    • Heating to ~200 °C for ~25 minutes under a nitrogen atmosphere
• PLA purification and final isolation:
  • Precipitation in cold methanol
  • Vacuum filtration and vacuum drying
• Material property outcome:
  • Produced PLA is described as high purity with relatively heavy molecular weight

PLA fiber manufacture and biodegradability (environmental end-of-life)

• Melt spinning converts PLA into textile fibers.
• Biodegradation: PLA fibers can ultimately degrade in nature into H₂O and CO₂, enabling a sustainable PLA lifecycle.

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Methodology (process steps as a workflow)

1. 1) Enzymatic breakdown (SSF)

   • Add specific fungi to food waste.
   • Let fungi secrete enzymes in situ via solid-state fermentation.
   • Blend enzyme-rich fungal biomass with food waste.
   • Hydrolyze in a bioreactor to form a nutrient-rich feedstock.

2. 2) Lactic acid fermentation

   • Bacteria ferment the feedstock to produce lactic acid.

3. 3) Lactic acid recovery

   • Filter and centrifuge to remove cell biomass.
   • Use activated carbon to remove colored impurities.
   • Concentrate via rotary evaporation.
   • Extract using ethyl acetate with sonication.
   • Separate phases with a separatory funnel.
   • Distill (reported conditions) to isolate lactic acid.

4. 4) Convert lactic acid → PLA

   • Form lactide through dehydration/oligomerization/depoylmerization.
   • Use ZnO nanoparticle catalyst for lactide synthesis.
   • Purify lactide by recrystallization (ethyl acetate), then vacuum filtration and drying.
   • Perform ring-opening polymerization of lactide to make PLA (heated under nitrogen).
   • Purify PLA by methanol precipitation, then vacuum filtration and drying.

5. 5) Fiber production and end-of-life

   • Produce fibers via melt spinning.
   • Rely on biodegradation to H₂O and CO₂.

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Researchers or sources featured

• Food and Agriculture Organization of the United Nations (FAO) (source of the food loss/waste estimate)