358 trillion metric tons of microplastic waste were found in the ocean in 2023. That is a massive quantity. Plus, the presence of plastics in both the environment and humans is detrimental. A recent study reported the 10-fold presence of microplastics in babies and infants. All these are an emergency wake-up call that led scientists to use biopolymers such as polylactic acid (PLA).
Polylactic acid is a biodegradable polymer derived from natural sources; thus, it is an environmentally friendly alternative to traditional plastics derived from fossil fuels. Extrapolate states that the global polylactic acid market is estimated to accrue a valuation of $2,489.3 million by 2030. This blog post explains everything you need to know about this million-dollar polymer.
What is Polylactic Acid?
Polylactic acid (PLA) is a biodegradable thermoplastic polymer made from renewable resources such as corn starch, sugarcane, or other biobased feedstocks. It is a member of the polyester polymer family and is a linear aliphatic polyester.
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PLA and polymers like it have gained popularity as a replacement for traditional petroleum-based plastics because they are biodegradable, biobased, and have a lower environmental footprint than many conventional plastics.
Is PLA Better Than Plastic?
Polylactic acid is regarded as a much more environmentally friendly alternative to the standard plastics that we are used to that originate from fossil fuels.
PLA is a plastic that is sourced from renewable resources like corn, potatoes, and sugarcane, among others, and also has a lower environmental footprint in terms of energy and greenhouse gases during its production process when compared to standard plastics.
Although it can degrade under certain conditions, it does take some time to do so and requires certain composting conditions to fully degrade. PLA is relatively strong and rigid when compared to other plastics, but it can also be a bit brittle.
PLA is one of the most popular plastics for 3D printing due to its low melting temperature and excellent layer-to-layer adhesion, but for more demanding applications where high strength and long-lasting objects are needed, other plastics like PETG and ABS are preferred.
In the end, just like any other technology, PLA and regular plastics have their own pros and cons, and which one is better depends on the requirements and environmental impact of the application that they will be used for.
If an alternative like PLA is available, then it is definitely worth considering its use to contribute to a more sustainable environment.
Advantages of Polylactic Acid
PLA has numerous advantages across diverse applications:
- Sustainability: PLA is sourced from renewable materials like corn, sugarcane, and starch, offering a greener alternative to conventional plastics derived from fossil fuels. This aids in reducing dependence on finite resources and curbing greenhouse gas emissions.
- Biodegradability: Under specific conditions, PLA naturally decomposes over time, making it suitable for applications where environmental impact is a concern.
- Compatibility with Human Tissue: PLA is biocompatible and widely utilized in medical fields for applications like sutures, bone repair screws, and stents. It seamlessly integrates with human tissue and degrades into harmless substances.
- Versatility: PLA boasts versatility, catering to a broad spectrum of products, ranging from cold drink cups and deli containers to fresh produce packaging and 3D printing filaments.
- Superior Gloss and Transparency: PLA showcases excellent gloss and transparency, enhancing its visual appeal across various applications.
Disadvantages of Polylactic Acid
While polylactic acid has its fair share of advantages, there are also a few drawbacks to keep in mind.
- Hydrophobic: PLA is a hydrophobic material, meaning it doesn't get along well with water. While this can be useful in some cases, it can cause issues in living organisms, like localized swelling.
- Low resistance to heat: PLA has a pretty low glass transition temperature of around 55 °C. This means it's not the best choice for applications that require high-temperature resistance. If things get hotter than 50 °C, PLA won't hold up too well.
- Slow to Break Down: PLA may be biodegradable, but it takes time to degrade, especially in certain environments. It needs the right composting conditions to fully break down, and even then, it can take months or even years.
- Brittle: PLA doesn't have the best impact toughness, which can be a downside when it comes to applications that need strong mechanical properties, like bone implants.
- Process limitation: Working with PLA can be a bit challenging. It may require more technical effort and stricter purity standards for the raw materials compared to other plastics.
Is Polylactic Acid Safe For Humans?
Polylactic acid is safe for human consumption in many contexts. A safety evaluation concluded that PLA is "Generally Recognized as Safe" (GRAS) when used as a polymer for the manufacturing of articles intended for holding and/or packaging food. Further studies found that containing PLA residues can be consumed as the substance is toxin-free.
Migration testing has demonstrated that any migrant species from PLA are anticipated to degrade to lactic acid, which is itself a food-grade substance. PLA does migrate a low level of lactic acid; however, this doesn't pose any harmful effects to humans.
How are Polylactic Acids Synthesized?
PLA synthesis involves the polymerization of lactic acid monomers, which can be derived from renewable resources such as corn starch or sugarcane. Here's a detailed synthesis process:
Lactic Acid Production:
Lactic acid can be produced through various methods, including the fermentation of carbohydrates like glucose or chemical synthesis from petrochemicals. However, for PLA synthesis, the preferred route is the fermentation of carbohydrates.
In fermentation, microorganisms such as bacteria (e.g., Lactobacillus species) or fungi (e.g., Rhizopus species) are employed to convert carbohydrates into lactic acid.
Carbohydrate sources can include corn, sugarcane, or other biomass-derived sugars.
Purification of Lactic Acid:
The lactic acid produced in fermentation typically needs purification to remove impurities such as water, salts, and residual microorganisms. Purification methods may include distillation, crystallization, or extraction techniques to obtain high-purity lactic acid.
Polymerization of Lactic Acid:
Lactic acid undergoes polymerization to form PLA. Polymerization can occur through several methods, including direct condensation or ring-opening polymerization.
Ring-opening polymerization (ROP) is the most commonly used method for PLA synthesis. It involves opening the cyclic ester ring of lactide, the cyclic dimer of lactic acid, to form linear PLA chains.
Catalysts are often employed to facilitate the polymerization process. Common catalysts include tin compounds such as stannous octoate or stannous chloride.
The polymerization reaction can be carried out under various conditions, including temperature, pressure, and choice of solvent, to control the molecular weight and properties of the resulting PLA.
Modification and Copolymerization:
PLA properties can be modified by copolymerization with other monomers. For example, lactide can be copolymerized with glycolide to produce poly(lactic-co-glycolic acid) (PLGA), which has different properties compared to PLA.
Copolymerization allows for the tuning of mechanical, thermal, and degradation properties to suit specific applications.
Processing and Formulation:
Once synthesized, PLA can be processed into various forms, such as films, fibers, or molded articles, through techniques like extrusion, injection molding, or solvent casting.
Additives such as plasticizers, stabilizers, or reinforcements may be incorporated into PLA formulations to enhance properties or processing characteristics.
Characterization and Quality Control:
The synthesized PLA undergoes rigorous characterization to ensure it meets the desired specifications and quality standards.
Characterization techniques include molecular weight analysis, thermal analysis (e.g., DSC, TGA), spectroscopic analysis (e.g., FTIR, NMR), and mechanical testing to evaluate properties like strength, modulus, and elongation.
Bottom Line
Polylactic acid is a versatile and sustainable polymer that offers several advantages in different applications. Its overall benefits make it a valuable option for those seeking sustainable and biocompatible materials. As research and development continue in the field of bioplastics, PLA is likely to play an increasingly significant role in promoting a more sustainable and environmentally conscious future.