Polylactic Acid (PLA), abbreviated as PLA, is the most commonly used material in FDM(Fused Deposition Modeling) as it’s affordable, stable and easy to print. The bio-based characteristic that PLA commonly uses crops like corn, sugarcane, and cassava as its raw material makes it eco-friendly and bio-degradable. To achieve better 3D printing results, many companies work to improve the properties of PLA. They have developed various modified PLAs based on the original PLA filament. These PLAs include PLA+, PLA Meta, Silk PLA, Rainbow PLA, Marble PLA, Twinkling PLA, and wood PLA composites. PLA filament is the most basic 3D printer filament and forms the main component of most specialty 3D printer filaments. PLA is so important that we must have an in-depth understanding of it.
1.The history of PLA
In 1857, Marcellin Berthelot, a French chemist, discovered lactic acid, an organic acid, by hydrolyzing ammonium lactate. Ten years later, he successfully fermented glucose into lactic acid for the first time, laying the foundation for the industrial production of lactic acid.
In the early 20th century, ICI( Imperial Chemical Industries) developed a technology to ferment starch raw materials to produce lactic acid, and built the world's first large-scale lactic acid fermentation production device in 1930. Since then, low-cost lactic acid production by fermentation method has become possible, creating conditions for the development and application of PLA.
In 1932, Chemist Carothers of DuPont first synthesized high molecular weight polylactic acid(PLA) by direct polymerization of lactic acid, which marks the birth of PLA polymers.
In 1954, British chemist Darby synthesized the first biodegradable polymer, Poly-Hydroxyalkanoates (PHAs), from PLA. Subsequent studies showed that PHA and PLA both have biological activity and good bio-compatibility, making them a trend of research in the biomedical field.
Entering the 21st century, with the development of polyester chemistry and polymer chemistry, research on lactic acid and PLA made great progress. Preparation methods, polymerization mechanisms, and performance control were well understood. PLA, meanwhile, has become the well-suited and main material for 3D printing, promoting the widespread application of 3D printing technology in family education and industrial design. This makes 3D printing a powerful tool for customized production and customization.
2.How to produce PLA
Step 1: Raw Material Selection
PLA, a biodegradable polymer, is typically synthesized from plant-based sources such as corn starch or sugarcane and other grains. These materials are suitable for PLA with their high yield and low cost. Mostly composed of glucose units with large molecular weights, these starches require further processing to convert into lactic acid, the raw material for Poly-lactic acid(PLA)。
Step 2: Starch Gelatinization
Mix the starch granules with water and apply heat under pressure until the starch is completely dissolved to constitute a starch slurry. Generally the process will be under 130-170°C and 0.5-2 MPa for 30-60 minutes, and mandates precise control of duration, temperature and pressure to prevent starch degradation and quality defects. The starch gelatinization rate commonly attains 85% or higher.
Step 3: Saccharification and Fermentation
Apply a composite saccharifying enzyme at 55-65°C and pH 5.5-6.5 to transform the starch slurry into glucose. Then inoculate lactobacillus in an anaerobic environment to ferment for 24-36 hours, transforming glucose into lactic acid, with a concentration of 10-15%. This process necessitates sterility and rigorous control of conditions to maximize yield which is commonly 80% or better.
Step 4: PLA Polymerization
This process require two procedures - Low Polymerization and High Polymerization. With the aid of catalyst, the low Polymerization takes place lasting 1-3h, subsequently followed by the high Polymerization lasting 3-5h at higher temperature. These two reactions duration and temperature require stringent control to accomplish the target product.
Step 5: Purification
Undesirable components, such as impurities, unreacted substances, low polymerization, and unconverted monomers, need to be removed from the fermentation liquid. This step culminates in the acquisition of purified, highly polymerized PLA, 99.5% or higher. This step is crucial for product performance.
Step 6: Processing
High-purity PLA can be attained through the above sequence of procedures. Then PLA is processed into fibers, pellets and films through extrusion or injection molding at 190-220°C. Subsequently, the PLA undergoes a winding machine process, transforming it into filaments you most commonly use.
In summary, PLA production requires precise control of complex biochemical processes and a high degree of technical expertise. Each step has specific parameters and conditions that must be carefully regulated to achieve the desired product. Maintaining high standards of quality and purity throughout the process is essential. With its sustainability and biodegradability, PLA has become an important material for 3D printing.
For those concerned about food shortages, producing PLA could reduce the grain supply. In fact, the current production of PLA is a very small percentage of food consumption.
While PLA is both fundamental and crucial, its mechanical properties are average. PLA printed parts have relatively poor impact resistance and lower dimensional precision. The surfaces of PLA 3D printed objects are relatively rough and require post-processing to achieve a shiny finish. The characteristics of PLA can be further observed by comparing it with other 3d printer filaments.
- PLA and PLA+. The toughness and impact, temp-resistance of PLA+ is not as good as PLA+. In some occasions with high requirements, PLA+ is more suitable for its improved toughness and impact, temp-resistance. That’s why we regard is as “PLA PLUS”.
- PLA and TPU. When it comes to the elasticity, toughness, and high impact strength, TPU is undoubtedly the winner, making it an ideal material for shock-absorbing and buffering because it has an elongation at break of up to more than 800% and its tensile strength can reach be 35MPa.
- PLA and PETG. PETG is more chemically stable than PLA. Plus, PETF is tougher and also has higher impact strength than PLA. The IZOD Impact Strength of PETG is nearly 1.5 times of PLA. But the 3d printing surface finish is not good as PLA.
- PLA and ABS. ABS has relatively high hardness, toughness and impact strength. The IZOD Impact Strengthof ABS can reach be 29KJ/㎡, nearly 5 times of PLA. ABS is also more resistant to high temperatures.
However, PLA is the most commonly used material in 3D printing. It has advantages such as easy printing, bio-compatibility and low cost. Despite some limitations, PLA is easy to handle with high success rates yet low costs for beginners. Thus PLA holds an important position in 3D printing and often represents the first choice for users to get started in the 3D printing world. Additionally, through adding heterogeneous functional additives, the properties and features of PLA can undergo a drastic change, engendering manifold vivid 3D printing materials. For example, By adding silk powder, silk-like smoothness and soft texture can be imparted to PLA; By adding lignin, wood flour and flavonoid compounds, PLA can have the texture of wood; By adding marble powder and other mineral fillers, PLA can be given the aesthetic texture of stone; By adding pigments with photo-sensitivity and thermal-sensitivity, the color change effect of PLA can be achieved; By adding fluorescent powder, PLA can glow at night absorbing ultraviolet light. These materials not only expand the application scope of PLA, but also vastly enrich people's lives and consumption options. With technological progress, the novel capacities obtained by PLA's ductility will progressively increase, and ingenious products for 3D printing will become ever more profuse.