Recycling Polylactic Acid
Contributors
Summary
We have an ongoing plastic problem. This is not news, but also not the end of the story.
Half of the plastics being produced are single-use plastics, meaning they are only intended to be used once. Compared to how long plastics take to break down, or degrade, there is a large time difference between the time the product is in use versus the time the product degrades.
Plastics are made up of polymers, and the type of polymer can give the plastic different properties. Polyethylene (HDPE/LDPE), polyethylene terephthalate (PET), and polystyrene (PS) are common polymers that make up plastics, but these polymers take about 500 to 1000 years to break down. Currently, composting enzymes and bacteria are unable to break them down any faster. Additionally, traditional plastics are produced from petroleum, which is a nonrenewable resource. Considering the complete life cycle of plastics is crucial and reveals why there is a need for alternatives. Plastics are woven into the fabric of society and examining alternatives to current manufacturing practices is a major concern for green chemists.
Polylactic acid (PLA) is a biodegradable polymer derived from renewable resources. Lactic acid, which is derived from corn, is the monomer used to create this polymer. PLA degrades under compost conditions into CO2, H2O, and humus, all of which are benign. PLA will generally breakdown under industrial composting conditions in approximately 180 days. Because it biodegrades, the volume sent to the landfill can be reduced significantly. Also, the CO2 released during degradation returns the carbon to the atmosphere with no overall net gain. Since the polymer is made from a corn feedstock, the process uses significantly less petroleum than traditional polymers. It is categorized under plastic resin code #7 or #0 (“other plastics”). While it is recyclable, municipal recycling facilities do not generally accept PLA.
Instead of disposing of PLA products in landfills or compost facilities, another option for handling them at the end of their useful life is to reuse them as other products. One thing to do with PLA materials is to convert them into an antimicrobial cleaning solution. Figure 1 shows how PLA is made from raw materials into different products.
Transforming PLA to lactic acid is called a saponification reaction (equation 1). The saponification reaction is an organic hydrolysis reaction that is used to make soap. (Some “green” household cleaners use lactic acid as an active ingredient). Each C–O–C bond that binds two lactic acid monomers together is cleaved to form 2 C–O–H units. Because the reaction occurs in a basic solution, an acidic work-up is needed to convert the deprotonated lactic acid unit (present in the form of a sodium lactate salt) into the desired protonated lactic acid form.
Half of the plastics being produced are single-use plastics, meaning they are only intended to be used once. Compared to how long plastics take to break down, or degrade, there is a large time difference between the time the product is in use versus the time the product degrades.
Plastics are made up of polymers, and the type of polymer can give the plastic different properties. Polyethylene (HDPE/LDPE), polyethylene terephthalate (PET), and polystyrene (PS) are common polymers that make up plastics, but these polymers take about 500 to 1000 years to break down. Currently, composting enzymes and bacteria are unable to break them down any faster. Additionally, traditional plastics are produced from petroleum, which is a nonrenewable resource. Considering the complete life cycle of plastics is crucial and reveals why there is a need for alternatives. Plastics are woven into the fabric of society and examining alternatives to current manufacturing practices is a major concern for green chemists.
Polylactic acid (PLA) is a biodegradable polymer derived from renewable resources. Lactic acid, which is derived from corn, is the monomer used to create this polymer. PLA degrades under compost conditions into CO2, H2O, and humus, all of which are benign. PLA will generally breakdown under industrial composting conditions in approximately 180 days. Because it biodegrades, the volume sent to the landfill can be reduced significantly. Also, the CO2 released during degradation returns the carbon to the atmosphere with no overall net gain. Since the polymer is made from a corn feedstock, the process uses significantly less petroleum than traditional polymers. It is categorized under plastic resin code #7 or #0 (“other plastics”). While it is recyclable, municipal recycling facilities do not generally accept PLA.
Instead of disposing of PLA products in landfills or compost facilities, another option for handling them at the end of their useful life is to reuse them as other products. One thing to do with PLA materials is to convert them into an antimicrobial cleaning solution. Figure 1 shows how PLA is made from raw materials into different products.
Transforming PLA to lactic acid is called a saponification reaction (equation 1). The saponification reaction is an organic hydrolysis reaction that is used to make soap. (Some “green” household cleaners use lactic acid as an active ingredient). Each C–O–C bond that binds two lactic acid monomers together is cleaved to form 2 C–O–H units. Because the reaction occurs in a basic solution, an acidic work-up is needed to convert the deprotonated lactic acid unit (present in the form of a sodium lactate salt) into the desired protonated lactic acid form.
Safety Precautions, Hazards, and Risk Assessment
Safety Information:
- Concentrated base can cause burns. While weighing out the sodium hydroxide (NaOH), wear the proper protective equipment (gloves, goggles, lab coat or apron). If the NaOH touches skin, wash immediately with copious amounts of water. See manufacturer safety data sheet (SDS) for complete handling information.
- Always add acid to water!!
- Concentrated acid can cause burns to skin and can pose a respiratory hazard from the fumes. When measuring, and working with concentrated hydrochloric acid, wear the appropriate protective equipment (gloves, goggles, lab coat or apron) and work in a fume hood to avoid inhalation exposure of the hydrochloric acid fumes. See safety manufacturer safety data sheet (SDS) for complete handling information.
Disposal Information: The final product is safe to use as a cleaner but must be disposed of as laboratory waste because of high ethanol content.
- Concentrated base can cause burns. While weighing out the sodium hydroxide (NaOH), wear the proper protective equipment (gloves, goggles, lab coat or apron). If the NaOH touches skin, wash immediately with copious amounts of water. See manufacturer safety data sheet (SDS) for complete handling information.
- Always add acid to water!!
- Concentrated acid can cause burns to skin and can pose a respiratory hazard from the fumes. When measuring, and working with concentrated hydrochloric acid, wear the appropriate protective equipment (gloves, goggles, lab coat or apron) and work in a fume hood to avoid inhalation exposure of the hydrochloric acid fumes. See safety manufacturer safety data sheet (SDS) for complete handling information.
Disposal Information: The final product is safe to use as a cleaner but must be disposed of as laboratory waste because of high ethanol content.
Digital Object Identifier (DOI)
https://doi.org/10.59877/ZMSM1274
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