Polylactide ( PLA ) is a biodegradable, biocompatible , thermoplastic , aliphatic polyester , the monomer of which is lactic acid . Annually renewable resources such as corn and sugarcane serve as raw materials for production. It is used for the production of products with a short service life (food packaging, disposable tableware, bags, various containers), as well as in medicine, for the production of surgical sutures and pins.
Polylactide | |
|---|---|
 | |
Are common | |
| Systematic name | poly (3,6-dimethyl-1,4-dioxane-2,5-dione |
| Abbreviations | PLA |
| Chem. formula | (C 3 H 4 O 2 ) n |
Physical properties | |
| Molar mass | (72) n |
| Density | 1.290 \ 1.248 g / cm³ (crystalline \ amorphous) [1] |
Thermal properties | |
| T. melt. | 170-180 ℃ (100% L-PLA) |
| T. glass. | 54-58 \ 50-53 ℃ (L-PLA \ L, D-PLA) |
| Specific heat of fusion | 93 J / g (100% L-PLA) |
Classification | |
| CAS Number | |
| Data is provided for standard conditions (25 ℃, 100 kPa) , unless otherwise indicated. | |
Content
Synthesis
There are two methods for the synthesis of polylactide: polycondensation of lactic acid and polymerization of lactide. A combination of these is used in industry. By polycondensation of lactic acid, only low molecular weight polylactide can be obtained, since in the process a by-product is released - water, which is difficult to divert from the reaction, and therefore the growing polymer chain is destroyed. The resulting low molecular weight polylactide is depolymerized to a lactic acid dimer , lactide. The resulting lactide is polymerized at high temperature with the addition of a tin octanoate catalyst, to obtain a high molecular weight polylactide.
Properties and structure
Both lactic acid and lactide exhibit optical activity , that is, they exist in the form of two L- and D- stereoisomers , which are mirror images of each other. By varying the relative content of these forms in polylactide, one can set the properties of the obtained polymer, as well as obtain various classes of polylactide materials. Polylactide from 100% L-lactide ( L-PLA ) has a high degree of stereoregularity, which gives it crystallinity . Glass transition temperature of L-PLA: 54–58 ° C [2] , melting point 170–180 ° C, heat capacity jump of 100% amorphous PLA 0.54 J / (g · K). Using a mixture of D- and L-forms of lactide during polymerization, an amorphous polylactide ( L, D-PLA ) is obtained, the glass transition temperature of which is 50–53 ° C [3] , there is no melting, since there is no crystalline phase .
The highest melting point of the stereo complex, consisting of pure L-PLA and pure D-PLA. The two chains are intertwined, and the additional interactions formed between them lead to an increase in the melting temperature (up to 220 ° C).
Physical Properties
| Value | Value |
|---|---|
| Melting temperature | 173-178 ° C |
| Softening point | 50 ° C |
| Hardness (Rockwell) | R70-R90 |
| Elongation at break | 3.8% |
| Bending strength | 55.3 MPa |
| Tensile strength | 57.8 MPa |
| Tensile modulus | 3.3 GPa |
| Flexural modulus | 2.3 GPa |
| Glass transition temperature | 60-65 ° C |
| Density | 1.23-1.25 g / cm³ |
| Minimum wall thickness | 1 mm |
| Print accuracy | ± 0.1% |
| The smallest detail size | 0.3 mm |
| Shrinkage in the manufacture of products | not |
| Moisture absorption | 0.5-50% |
Applications
Polylactide is used for the production of environmentally friendly biodegradable packaging, disposable tableware, and personal care products. Biodegradable polylactide bags are used in major retail chains such as Wal-Mart Stores and Kmart . Due to its biocompatibility, polylactide is widely used in medicine, for the production of surgical sutures and pins, as well as in drug delivery systems.
Polylactide meets the concept of sustainable development , since annually renewable natural resources are used for its synthesis. Polylactide packaging products are an environmentally friendly alternative to traditional biodegradable packaging based on chemically resistant polymers.
Polylactide is also used in 3D printers as a starting material for printing. [four]
Production
The largest producer of L-PLA is the American company Nature Works (140,000 tons / year). PLA is also produced by Toyota ( Japan ), Hitachi (Japan), DuPont ( USA ), Galactic ( Belgium ), Hisun Biomaterials ( China ), and the main manufacturer of L, D-PLA is PURAC and Total Corbion ( Netherlands ). In Russia, PLA plastic is manufactured by FD Plast, Best Filament, and over time (for 2019) more and more manufacturers / suppliers of this material appear in the Russian Federation, however, biodegradable dishes and packaging are imported from different countries by JC and Geovita .
A typical PLA manufacturing process assumes that metal-containing catalysts that are hazardous to health and the environment are used in the polymerization of lactones. [five]
Since 2015, Russia has launched the production of medical high-purity PLA at the facilities of VNIISV JSC
Since 2018, GDC, the first company in the CIS, has launched a new line in its own production of biodegradable packaging using polylactide film under its own DoECO brand name.
See also
- Polymerization
- Polycondensation
Notes
- ↑ Polymer Data Handbook, Oxford University Press 1999.
- ↑ T. Maharanaa, B. Mohantyb, YS Negi. Melt-solid polycondensation of lactic acid and its biodegradability; Progress in Polymer Science 34 (2009) 99—124
- ↑ Garlotta D. A literature review of poly (lactic acid). J Polym Environ 2001; 9: 63-84.
- ↑ Where do the pens grow from. Lenta.ru tested the world's first hand-held 3D printer
- ↑ InnoREX - Ultrasound-Improved Polylactide Extrusion Technology