Polylactic acid, also known as poly(lactic acid) or polylactide (abbreviation PLA) is a thermoplastic polyester with backbone formula (C
n or [–C(CH
n, formally obtained by condensation of lactic acid C(CH
3)(OH)HCOOH with loss of water (hence its name). It can also be prepared by ring-opening polymerization of lactide [–C(CH
2, the cyclic dimer of the basic repeating unit.
CompTox Dashboard (EPA)
|Melting point||150 to 160 °C (302 to 320 °F; 423 to 433 K)|
|0 mg/ml |
|NFPA 704 (fire diamond)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
PLA has become a popular material due to it being economically produced from renewable resources. In 2010, PLA had the second highest consumption volume of any bioplastic of the world, although it is still not a commodity polymer. Its widespread application has been hindered by numerous physical and processing shortcomings. PLA is the most widely used plastic filament material in 3D printing.
Although the name "polylactic acid" is widely used, it does not comply with IUPAC standard nomenclature, which is "poly(lactic acid)". The name "polylactic acid" is potentially ambiguous or confusing, because PLA is not a polyacid (polyelectrolyte), but rather a polyester.
Several industrial routes afford usable (i.e. high molecular weight) PLA. Two main monomers are used: lactic acid, and the cyclic di-ester, lactide. The most common route to PLA is the ring-opening polymerization of lactide with various metal catalysts (typically tin octoate) in solution or as a suspension. The metal-catalyzed reaction tends to cause racemization of the PLA, reducing its stereoregularity compared to the starting material (usually corn starch).
The direct condensation of lactic acid monomers can also be used to produce PLA. This process needs to be carried out at less than 200 °C; above that temperature, the entropically favored lactide monomer is generated. This reaction generates one equivalent of water for every condensation (esterification) step. The condensation reaction is reversible and subject to equilibrium, so removal of water is required to generate high molecular weight species. Water removal by application of a vacuum or by azeotropic distillation is required to drive the reaction toward polycondensation. Molecular weights of 130 kDa can be obtained this way. Even higher molecular weights can be attained by carefully crystallizing the crude polymer from the melt. Carboxylic acid and alcohol end groups are thus concentrated in the amorphous region of the solid polymer, and so they can react. Molecular weights of 128–152 kDa are obtainable thus.
Due to the chiral nature of lactic acid, several distinct forms of polylactide exist: poly-L-lactide (PLLA) is the product resulting from polymerization of L,L-lactide (also known as L-lactide). Progress in biotechnology has resulted in the development of commercial production of the D enantiomer form.
Polymerization of a racemic mixture of L- and D-lactides usually leads to the synthesis of poly-DL-lactide (PDLLA), which is amorphous. Use of stereospecific catalysts can lead to heterotactic PLA which has been found to show crystallinity. The degree of crystallinity, and hence many important properties, is largely controlled by the ratio of D to L enantiomers used, and to a lesser extent on the type of catalyst used. Apart from lactic acid and lactide, lactic acid O-carboxyanhydride ("lac-OCA"), a five-membered cyclic compound has been used academically as well. This compound is more reactive than lactide, because its polymerization is driven by the loss of one equivalent of carbon dioxide per equivalent of lactic acid. Water is not a co-product.
Physical and mechanical propertiesEdit
PLA polymers range from amorphous glassy polymer to semi-crystalline and highly crystalline polymer with a glass transition 60–65 °C, a melting temperature 130-180 °C, and a Young's modulus 2.7–16 GPa. Heat-resistant PLA can withstand temperatures of 110 °C. The basic mechanical properties of PLA are between those of polystyrene and PET. The melting temperature of PLLA can be increased by 40–50 °C and its heat deflection temperature can be increased from approximately 60 °C to up to 190 °C by physically blending the polymer with PDLA (poly-D-lactide). PDLA and PLLA form a highly regular stereocomplex with increased crystallinity. The temperature stability is maximised when a 1:1 blend is used, but even at lower concentrations of 3–10% of PDLA, there is still a substantial improvement. In the latter case, PDLA acts as a nucleating agent, thereby increasing the crystallization rate. Biodegradation of PDLA is slower than for PLA due to the higher crystallinity of PDLA. The flexural modulus of PLA is higher than polystyrene and PLA has good heat sealability.
Several technologies such as annealing, adding nucleating agents, forming composites with fibers or nano-particles, chain extending and introducing crosslink structures have been used to enhance the mechanical properties of PLA polymers. Polylactic acid can be processed like most thermoplastics into fiber (for example, using conventional melt spinning processes) and film. PLA has similar mechanical properties to PETE polymer, but has a significantly lower maximum continuous use temperature.
Racemic PLA and pure PLLA have low glass transition temperatures, making them undesirable because of low strength and melting point. A stereocomplex of PDLA and PLLA has a higher glass transition temperature, lending it more mechanical strength.
The high surface energy of PLA results in good printability, making it widely used in 3D printing. The tensile strength for 3D printed PLA was previously determined.
PLA is soluble in a range of organic solvents. Ethyl acetate is widely used because of its ease of access and low risk. It is useful in 3D printers for cleaning the extruder heads and for removing PLA supports.
Other safe solvents include propylene carbonate, which is safer than ethyl acetate but is difficult to purchase commercially. Pyridine can be used, but it has a distinct fish odor and is less safe than ethyl acetate. PLA is also soluble in hot benzene, tetrahydrofuran, and dioxane.
PLA is used as a feedstock material in desktop fused filament fabrication by 3D printers, such as RepRap printers. The boiling point of ethyl acetate is low enough to smooth PLA surfaces in a vapor chamber, similar to using acetone vapor to smooth ABS.
PLA-printed solids can be encased in plaster-like moulding materials, then burned out in a furnace, so that the resulting void can be filled with molten metal. This is known as "lost PLA casting", a type of investment casting.
PLA is used in a large variety of consumer products such as disposable tableware, cutlery, housings for kitchen appliances and electronics such as laptops and handheld devices, and microwavable trays. (However, PLA is not suitable for microwavable containers because of its low glass transition temperature.) It is used for compost bags, food packaging and loose-fill packaging material that is cast, injection molded, or spun.  In the form of a film, it shrinks upon heating, allowing it to be used in shrink tunnels. In the form of fibers, it is used for monofilament fishing line and netting. In the form of nonwoven fabrics, it is used for upholstery, disposable garments, awnings, feminine hygiene products, and diapers.
PLA has applications in engineering plastics, where the stereocomplex is blended with a rubber-like polymer such as ABS. Such blends have good form stability and visual transparency, making them useful in low-end packaging applications.
PLA is used for automotive parts such as floor mats, panels, and covers. Its heat resistance and durability are inferior to the widely used polypropylene (PP), but its properties are improved by means such as capping of the end groups to reduce hydrolysis.
In the form of fibers, PLA is used for monofilament fishing line and netting for vegetation and weed prevention. It is used for sandbags, planting pots, binding tape and ropes .
PLA can degrade into innocuous lactic acid, so it is used as medical implants in the form of anchors, screws, plates, pins, rods, and mesh. Depending on the exact type used, it breaks down inside the body within 6 months to 2 years. This gradual degradation is desirable for a support structure, because it gradually transfers the load to the body (e.g. to the bone) as that area heals. The strength characteristics of PLA and PLLA implants are well documented.
Thanks to its bio-compatibility and biodegradability, PLA has also found ample interest as a polymeric scaffold for drug delivery purposes.
PLLA is used to stimulate collagen synthesis in fibroblasts via foreign body reaction in the presence of macrophages. Macrophages act as a stimulant in secretion of cytokines and mediators such as TGF-β, which stimulate the fibroblast to secrete collagen into the surrounding tissue. Therefore, PLLA has potential applications in the dermatological studies  
PLA is degraded abiotically by three mechanisms:
- Hydrolysis: The ester groups of the main chain are cleaved, thus reducing molecular weight.
- Thermal degradation: A complex phenomenon leading to the appearance of different compounds such as lighter molecules and linear and cyclic oligomers with different Mw, and lactide.
- Photodegradation: UV radiation induces degradation. This is a factor mainly where PLA is exposed to sunlight in its applications in plasticulture, packaging containers and films.
The hydrolytic reaction is:
The degradation rate is very slow in ambient temperatures. A 2017 study found that at 25 °C in seawater, PLA showed no loss of mass over a year, but the study did not measure breakdown of the polymer chains or water absorption. As a result, it degrades poorly in landfills and household composts, but is effectively digested in hotter industrial composts, usually degrading best at temperatures of over 60°C.
Pure PLA foams are selectively hydrolysed in Dulbecco's modified Eagle's medium (DMEM) supplemented with fetal bovine serum (FBS) (a solution mimicking body fluid). After 30 days of submersion in DMEM+FBS, a PLLA scaffold lost about 20% of its weight.
PLA can also be degraded by some bacteria, such as Amycolatopsis and Saccharothrix. A purified protease from Amycolatopsis sp., PLA depolymerase, can also degrade PLA. Enzymes such as pronase and most effectively proteinase K from Tritirachium album degrade PLA.
End of lifeEdit
Four possible end-of-life scenarios are the most common:
- Recycling: which can be either chemical or mechanical. Currently, the SPI resin identification code 7 ("others") is applicable for PLA. In Belgium, Galactic started the first pilot unit to chemically recycle PLA (Loopla). Unlike mechanical recycling, waste material can hold various contaminants. Polylactic acid can be chemically recycled to monomer by thermal depolymerization or hydrolysis. When purified, the monomer can be used for the manufacturing of virgin PLA with no loss of original properties  (cradle-to-cradle recycling).[dubious ] End-of-life PLA can be chemically recycled to methyl lactate by transesterification.
- Composting: PLA is biodegradable under industrial composting conditions, starting with chemical hydrolysis process, followed by microbial digestion, to ultimately degrade the PLA. Under industrial composting conditions (58 °C), PLA can partly (about half) decompose into water and carbon dioxide in 60 days, after which the remainder decomposes much more slowly, with the rate depending on the material's degree of crystallinity. Environments without the necessary conditions will see very slow decomposition akin to that of non-bioplastics, not fully decomposing for hundreds or thousands of years.
- Incineration: PLA can be incinerated without producing chlorine-containing chemicals or heavy metals because it contains only carbon, oxygen, and hydrogen atoms. Since it does not contain chlorine it does not produce dioxins during incineration.
- Landfill: the least preferable option is landfilling because PLA degrades very slowly in ambient temperatures, often as slowly as other plastics.
- "Material Properties of Polylactic Acid (PLA), Agro Based Polymers". Matbase - Material Properties Database. Archived from the original on 10 February 2012. Retrieved 6 February 2012.
- "Polylactic Acid. Material Safety Data Sheet" (PDF). ampolymer.com. Archived from the original (PDF) on 6 January 2009.
- Ceresana. "Bioplastics - Study: Market, Analysis, Trends - Ceresana". www.ceresana.com. Archived from the original on 4 November 2017. Retrieved 9 May 2018.
- Nagarajan, Vidhya; Mohanty, Amar K.; Misra, Manjusri (2016). "Perspective on Polylactic Acid (PLA) based Sustainable Materials for Durable Applications: Focus on Toughness and Heat Resistance". ACS Sustainable Chemistry & Engineering. 4 (6): 2899–2916. doi:10.1021/acssuschemeng.6b00321.
- Vert, M.; et al. "Nomenclature and Terminology for Linear Lactic Acid-Based Polymers (IUPAC Recommendations 2019)". IUPAC Standards Online. doi:10.1515/iupac.92.0001. Retrieved 26 June 2021.
- Martin, O; Avérous, L (2001). "Poly(lactic acid): plasticization and properties of biodegradable multiphase systems". Polymer. 42 (14): 6209–6219. doi:10.1016/S0032-3861(01)00086-6.
- Södergård, Anders; Mikael Stolt (2010). "3. Industrial Production of High Molecular Weight Poly(Lactic Acid)". In Rafael Auras; Loong-Tak Lim; Susan E. M. Selke; Hideto Tsuji (eds.). Poly(Lactic Acid): Synthesis, Structures, Properties, Processing, and Applications. pp. 27–41. doi:10.1002/9780470649848.ch3. ISBN 9780470649848.
- Drury, Jim (15 February 2016). "Cheaper, greener, route to bioplastic". reuters.com. Archived from the original on 1 December 2017. Retrieved 9 May 2018.
- Dusselier, Michiel; Wouwe, Pieter Van; Dewaele, Annelies; Jacobs, Pierre A.; Sels, Bert F. (3 July 2015). "Shape-selective zeolite catalysis for bioplastics production" (PDF). Science. 349 (6243): 78–80. Bibcode:2015Sci...349...78D. doi:10.1126/science.aaa7169. PMID 26138977. S2CID 206635718.
- "Bioengineers succeed in producing plastic without the use of fossil fuels". Physorg.com. Archived from the original on 6 June 2011. Retrieved 11 April 2011.
- Kricheldorf, Hans R.; Jonté, J. Michael (1983). "New polymer syntheses". Polymer Bulletin. 9 (6–7). doi:10.1007/BF00262719. S2CID 95429767.
- Jung, Yu Kyung; Kim, Tae Yong (2009). "Metabolic Engineering of Escherichia coli for the production of Polylactic Acid and Its Copolymers". Biotechnology and Bioengineering. 105 (1): 161–71. doi:10.1002/bit.22548. PMID 19937727. S2CID 205499487.
- Lunt, James (3 January 1998). "Large-scale production, properties and commercial applications of polylactic acid polymers". Polymer Degradation and Stability. 59 (1–3): 145–152. doi:10.1016/S0141-3910(97)00148-1. ISSN 0141-3910.
- Södergård, Anders; Mikael Stolt (February 2002). "Properties of lactic acid based polymers and their correlation with composition". Progress in Polymer Science. 27 (6): 1123–1163. doi:10.1016/S0079-6700(02)00012-6.
- Middelton, John C.; Arthur J. Tipton (2000). "Synthetic biodegradable polymers as orthopedic devices". Biomaterial. 21 (23): 2335–2346. doi:10.1016/S0142-9612(00)00101-0. PMID 11055281.
- Gina L. Fiore; Feng Jing; Victor G. Young Jr.; Christopher J. Cramer; Marc A. Hillmyer (2010). "High Tg Aliphatic Polyesters by the Polymerization of Spirolactide Derivatives". Polymer Chemistry. 1 (6): 870–877. doi:10.1039/C0PY00029A.
- Nugroho, Pramono; Mitomo, Hiroshi; Yoshii, Fumio; Kume, Tamikazu (1 May 2001). "Degradation of poly(l-lactic acid) by γ-irradiation". Polymer Degradation and Stability. 72 (2): 337–343. doi:10.1016/S0141-3910(01)00030-1. ISSN 0141-3910.
- Urayama, Hiroshi; Kanamori, Takeshi; Fukushima, Kazuki; Kimura, Yoshiharu (1 September 2003). "Controlled crystal nucleation in the melt-crystallization of poly(l-lactide) and poly(l-lactide)/poly(d-lactide) stereocomplex". Polymer. 44 (19): 5635–5641. doi:10.1016/S0032-3861(03)00583-4. ISSN 0032-3861.
- Tsuji, H. (1 January 1995). "Properties and morphologies of poly(l-lactide): 1. Annealing condition effects on properties and morphologies of poly(l-lactide)". Polymer. 36 (14): 2709–2716. doi:10.1016/0032-3861(95)93647-5. ISSN 0032-3861.
- Urayama, Hiroshi; Ma, Chenghuan; Kimura, Yoshiharu (July 2003). "Mechanical and Thermal Properties of Poly(L-lactide) Incorporating Various Inorganic Fillers with Particle and Whisker Shapes". Macromolecular Materials and Engineering. 288 (7): 562–568. doi:10.1002/mame.200350004. ISSN 1438-7492.
- Trimaille, T.; Pichot, C.; Elaïssari, A.; Fessi, H.; Briançon, S.; Delair, T. (1 November 2003). "Poly(d,l-lactic acid) nanoparticle preparation and colloidal characterization". Colloid and Polymer Science. 281 (12): 1184–1190. doi:10.1007/s00396-003-0894-1. ISSN 0303-402X. S2CID 98078359.
- Hu, Xiao; Xu, Hong-Sheng; Li, Zhong-Ming (4 May 2007). "Morphology and Properties of Poly(L-Lactide) (PLLA) Filled with Hollow Glass Beads". Macromolecular Materials and Engineering. 292 (5): 646–654. doi:10.1002/mame.200600504. ISSN 1438-7492.
- Li, Bo-Hsin; Yang, Ming-Chien (2006). "Improvement of thermal and mechanical properties of poly(L-lactic acid) with 4,4-methylene diphenyl diisocyanate". Polymers for Advanced Technologies. 17 (6): 439–443. doi:10.1002/pat.731. ISSN 1042-7147.
- Di, Yingwei; Iannace, Salvatore; Di Maio, Ernesto; Nicolais, Luigi (4 November 2005). "Reactively Modified Poly(lactic acid): Properties and Foam Processing". Macromolecular Materials and Engineering. 290 (11): 1083–1090. doi:10.1002/mame.200500115. ISSN 1438-7492.
- "Compare Materials: PLA and PETE". Makeitfrom.com. Archived from the original on 1 May 2011. Retrieved 11 April 2011.
- Luo, Fuhong; Fortenberry, Alexander; Ren, Jie; Qiang, Zhe (20 August 2020). "Recent Progress in Enhancing Poly(Lactic Acid) Stereocomplex Formation for Material Property Improvement". Frontiers in Chemistry. 8: 688. Bibcode:2020FrCh....8..688L. doi:10.3389/fchem.2020.00688. PMC 7468453. PMID 32974273.
- Giordano, R.A.; Wu, B.M.; Borland, S.W.; Cima, L.G.; Sachs, E.M.; Cima, M.J. (1997). "Mechanical properties of dense polylactic acid structures fabricated by three dimensional printing". Journal of Biomaterials Science, Polymer Edition. 8 (1): 63–75. doi:10.1163/156856297x00588. PMID 8933291.
- Sato, Shuichi; Gondo, Daiki; Wada, Takayuki; Nagai, Kazukiy (2013). "Effects of Various Liquid Organic Solvents on Solvent-Induced Crystallization of AMorphous Poly(lactic acid) Film". Journal of Applied Polymer Science. 129 (3): 1607–1617. doi:10.1002/app.38833.
- Garlotta, Donald (2001). "A Literature Review of Poly(Lactic Acid)". Journal of Polymers and the Environment. 9 (2): 63–84. doi:10.1023/A:1020200822435. S2CID 8630569. Archived from the original on 26 May 2013.
- "PLA". Reprap Wiki. 4 April 2011. Archived from the original on 16 July 2011. Retrieved 11 April 2011.
- "PLA". MakerBot Industries. Archived from the original on 23 April 2011. Retrieved 11 April 2011.
- Coysh, Adrian (12 April 2013). "Dichloromethane Vapor Treating PLA parts". Thingiverse.com. Archived from the original on 1 December 2017. Retrieved 9 May 2018.
- Sanladerer, Thomas (9 December 2016). "Does Acetone also work for welding and smoothing PLA 3D printed parts?". youtube.com. Retrieved 9 January 2021.
- "Metal Casting with Your 3D Printer". Make: DIY Projects and Ideas for Makers. Retrieved 30 November 2018.
- Rafael Auras; Loong-Tak Lim; Susan E. M. Selke; Hideto Tsuji, eds. (2010). Poly(Lactic Acid): Synthesis, Structures, Properties, Processing, and Applications. doi:10.1002/9780470649848. ISBN 9780470293669.
- Nazre, A.; Lin, S. (1994). Harvey, J. Paul; Games, Robert F. (eds.). Theoretical Strength Comparison of Bioabsorbable (PLLA) Plates and Conventional Stainless Steel and Titanium Plates Used in Internal Fracture Fixation. p. 53. ISBN 978-0-8031-1897-3.
- Lam, C. X. F.; Olkowski, R.; Swieszkowski, W.; Tan, K. C.; Gibson, I.; Hutmacher, D. W. (2008). "Mechanical and in vitro evaluations of composite PLDLLA/TCP scaffolds for bone engineering". Virtual and Physical Prototyping. 3 (4): 193–197. doi:10.1080/17452750802551298. S2CID 135582844.
- Bose, S.; Vahabzadeh, S.; Bandyopadhyay, A. (2013). "Bone tissue engineering using 3D printing". Materials Today. 16 (12): 496–504. doi:10.1016/j.mattod.2013.11.017.
- Ray, S., Adelnia, H., & Ta, H. T. (2021). Collagen and the Effect of Poly-L-lactic Acid based Materials on its Synthesis. Biomaterials Science
- Ray, S.; Ta, H.T. Investigating the Effect of Biomaterials Such as Poly-(l-Lactic Acid) Particles on Collagen Synthesis In Vitro: Method Is Matter. J. Funct. Biomater. 2020, 11, 51. https://doi.org/10.3390/jfb11030051
- Guo, Shuang-Zhuang; Yang, Xuelu; Heuzey, Marie-Claude; Therriault, Daniel (2015). "3D printing of a multifunctional nanocomposite helical liquid sensor". Nanoscale. 7 (15): 6451–6. Bibcode:2015Nanos...7.6451G. doi:10.1039/C5NR00278H. PMID 25793923.
- Castro-Aguirre, E.; Iñiguez-Franco, F.; Samsudin, H.; Fang, X.; Auras, R. (December 2016). "Poly(lactic acid)—Mass production, processing, industrial applications, and end of life". Advanced Drug Delivery Reviews. 107: 333–366. doi:10.1016/j.addr.2016.03.010. PMID 27046295.
- Bagheri, Amir Reza; Laforsch, Christian; Greiner, Andreas; Agarwal, Seema (July 2017). "Fate of So-Called Biodegradable Polymers in Seawater and Freshwater". Global Challenges. 1 (4): 1700048. doi:10.1002/gch2.201700048. PMC 6607129. PMID 31565274.
- "Is PLA Biodegradable? – The Truth". All3DP. 10 December 2019. Retrieved 26 June 2021.
- Pavia FC; La Carrubba V; Piccarolo S; Brucato V (August 2008). "Polymeric scaffolds prepared via thermally induced phase separation: tuning of structure and morphology". Journal of Biomedical Materials Research Part A. 86 (2): 459–466. doi:10.1002/jbm.a.31621. PMID 17975822.
- Román-Ramírez, Luis A.; Mckeown, Paul; Jones, Matthew D.; Wood, Joseph (4 January 2019). "Poly(lactic acid) Degradation into Methyl Lactate Catalyzed by a Well-Defined Zn(II) Complex". ACS Catalysis. 9 (1): 409–416. doi:10.1021/acscatal.8b04863.
- McKeown, Paul; Román‐Ramírez, Luis A.; Bates, Samuel; Wood, Joseph; Jones, Matthew D. (2019). "Zinc Complexes for PLA Formation and Chemical Recycling: Towards a Circular Economy" (PDF). ChemSusChem. 12 (24): 5233–5238. doi:10.1002/cssc.201902755. ISSN 1864-564X. PMID 31714680. S2CID 207941305.
- Román-Ramírez, Luis A.; McKeown, Paul; Shah, Chanak; Abraham, Joshua; Jones, Matthew D.; Wood, Joseph (20 May 2020). "Chemical Degradation of End-of-Life Poly(lactic acid) into Methyl Lactate by a Zn(II) Complex". Industrial & Engineering Chemistry Research. 59 (24): 11149–11156. doi:10.1021/acs.iecr.0c01122. ISSN 0888-5885. PMC 7304880. PMID 32581423.
- Yutaka Tokiwa; Buenaventurada P. Calabia; Charles U. Ugwu; Seiichi Aiba (September 2009). "Biodegradability of Plastics". International Journal of Molecular Sciences. 10 (9): 3722–3742. doi:10.3390/ijms10093722. PMC 2769161. PMID 19865515.
- "Chemical recycling closes the LOOPLA for cradle-to-cradle PLA". 20 November 2015.
- Gorrasi, Giuliana; Pantani, Roberto (2017), Di Lorenzo, Maria Laura; Androsch, René (eds.), "Hydrolysis and Biodegradation of Poly(lactic acid)", Synthesis, Structure and Properties of Poly(lactic acid), Cham: Springer International Publishing, 279, pp. 119–151, doi:10.1007/12_2016_12, ISBN 978-3-319-64229-1, retrieved 4 December 2020
- Iovino, R.; et al. (2008). "Biodegradation of poly(lactic acid)/starch/coir biocompositesunder controlled composting conditions". Polymer Degradation and Stabilit. 93: 147. doi:10.1016/j.polymdegradstab.2007.10.011.
- Pantani, R.; Sorrentino, A. (2013). "Influence of crystallinity on the biodegradation rate of injection-moulded poly(lactic acid) samples in controlled composting conditions". Polymer Degradation and Stability. 98 (5): 1089. doi:10.1016/j.polymdegradstab.2013.01.005.
- "How long does it take for plastics to biodegrade?". HowStuffWorks. 15 December 2010. Retrieved 9 March 2021.
- "End of Life Options for Bioplastics – Recycling, Energy, Composting, Landfill - Bioplastics Guide | Bioplastics Guide". Retrieved 9 March 2021.
|Wikimedia Commons has media related to Polylactides.|