PLA (Polylactide)

General Information about PLA Filament

Polylactic Acid (PLA) is one of the most popular and widely used 3D printer filaments, especially favored by beginners due to its ease of use and versatility. It is an eco-friendly thermoplastic polyester derived from renewable organic resources such as corn starch, sugarcane, or cassava. PLA is biodegradable under industrial composting conditions and its production consumes less energy and generates fewer greenhouse gases compared to traditional plastics. It generally does not emit toxic fumes or strong odors during printing, making it suitable for use in various environments like classrooms and offices.

PLA filament can be produced through direct condensation polymerization or ring-opening polymerization. It is also often blended with other materials like wood, metal, or carbon fiber to achieve different aesthetics or enhanced properties. While PLA is known for its good detail and low warping, it has limitations in heat resistance and can be brittle.

Physical Properties

PLA possesses several key physical characteristics that make it suitable for 3D printing:
Density: Typically ranges from 1.21 to 1.43 g/cm³, with many sources citing around 1.24 – 1.25 g/cm³.
Color and Transparency: It is naturally colorless and transparent, but can be easily colored.
Melting Temperature: Generally between 170°C and 230°C, with some sources listing ranges like 150°C to 160°C or 175°C.
Glass Transition Temperature (Tg): Typically around 50°C to 65°C, often cited as approximately 53°C or 57°C.
Heat Deflection Temperature (HDT): Around 49°C to 80°C (at 0.455 MPa), depending on the specific PLA type and additives. Heat-resistant PLA can withstand higher temperatures, up to 110°C, and its HDT can be increased significantly by blending with PDLA (poly-D-lactide).
Moisture Absorption: PLA is hygroscopic, meaning it tends to absorb moisture from the air, which can affect print quality. Proper storage in a dry environment is recommended.
Flammability: Polymers made of lactic acid are flammable.

Printing Settings

Optimal printing settings for PLA can vary slightly between filament brands and 3D printer models, but here are general recommendations:
Nozzle Temperature (Extruder Temperature): Most commonly recommended between 190°C and 220°C. Some manufacturers suggest a slightly higher temperature for the first layer (e.g., 215°C) to improve bed adhesion. Temperatures on the lower end can result in cleaner prints, while higher temperatures can improve layer adhesion and flow.
Bed Temperature (Build Platform Temperature): A heated bed is not always strictly required for PLA, but it is highly recommended for better adhesion and to prevent warping. Recommended temperatures typically range from 35°C to 60°C, with 40°C to 60°C being common suggestions. For the first two layers, some recommend slightly higher temperatures (e.g., 65°C) to ensure good adhesion.
Print Speed: An ideal speed is often cited between 50 mm/s and 100 mm/s. Slower speeds (e.g., 50-80 mm/s) are better for detailed models, while faster speeds (e.g., 100-120 mm/s or higher with specific nozzles) can be used for less intricate parts.
Cooling Fan: High cooling fan speed (100% after the first few layers) is generally recommended for PLA to ensure clean, crisp layers and prevent issues like “elephant’s foot” or poor overhangs. It’s often suggested to turn off cooling for the first layer or two to aid bed adhesion.
Layer Height: Typical layer heights range from 0.12 mm to 0.3 mm. A thicker first layer (e.g., 0.25 mm or greater) can help with bed adhesion.
Retraction: Increasing retraction speed (30-80 mm/s) and distance (2-5 mm for Bowden setups, 1-2 mm for direct drive) helps to minimize stringing and oozing.
Build Plate Adhesion: Various surfaces can be used, including tempered glass, PEI sheets (smooth or satin), or carbon fiber board. Adhesives like glue stick or hairspray can also be applied.
Enclosure: Not strictly necessary, as PLA is less sensitive to ambient temperature changes compared to other materials like ABS. However, a controlled environment can still be beneficial.

Mechanical Properties

While PLA is easy to print, its mechanical properties have certain limitations, particularly in terms of brittleness and heat resistance:
Tensile Strength: Ranges from 38 to 70 MPa, with some sources reporting values around 45-49 MPa or 7080 psi (approximately 48.8 MPa).
Tensile Modulus (Young’s Modulus): Typically around 2.7 to 4.2 GPa, with some data sheets showing 1000-1100 MPa or 3120 MPa.
Elongation at Break: Often reported as less than 10%, highlighting its brittle nature. Some sources indicate higher ranges (e.g., 13.5-15.5% or 41.3-63.8%), which might be for tougher PLA variants.
Elongation at Yield: Approximately 2%.
Flexural Strength: Around 69-85 MPa.
Flexural Modulus: Approximately 3280 MPa.
Impact Strength (Notched Izod): Generally low, with values like 16-19 KJ/m² or 0.3 ft·lb/in (approx. 16 J/m). This indicates its brittleness and susceptibility to fracture under impact.
Hardness: Around 95D (Shore D) or 66 (Shore D).
Stiffness: PLA is a stiff material that maintains its form until its breaking point.
PLA’s mechanical properties can be influenced by printing parameters (like infill density, layer height, and printing speed) and can be enhanced by incorporating additives like carbon fibers or other fillers.

History of PLA

When and By Whom was PLA First Found?

The initial discovery of Polylactic Acid (PLA) is attributed to Wallace Carothers, a scientist working at DuPont. He first synthesized a low molecular weight PLA in 1932 by heating lactic acid under a vacuum. Carothers is also famously known for inventing nylon. His early work on PLA was part of an effort to find environmentally friendly plastics.

Why Was PLA Produced in the First Place?

While Carothers made the initial discovery, the widespread production and commercialization of PLA took many decades. Here’s a breakdown of the motivations behind its development and eventual widespread use:

Search for Environmentally Friendly Alternatives: From its early days, there was an interest in developing plastics from renewable resources as an alternative to petroleum-based plastics. Carothers’ initial work was driven by this desire. The realization that fossil fuel resources are finite and that traditional plastics pose significant environmental challenges (like pollution and slow degradation) has always been a strong motivator for bioplastic research.
Biomedical Applications: In the mid-20th century, particularly after studies by Kulkarni et al. in the 1960s on the biodegradation and non-toxicity of PLA, its potential in the biomedical field became apparent. Its biocompatibility and bioabsorbable nature made it suitable for applications like dissolvable sutures, drug delivery systems, and medical implants. This was a significant early driver for developing higher molecular weight PLA with more stable properties.
Cost and Industrial Feasibility: For many years, the commercial production of PLA on a large scale was too costly. Advances in biotechnology and fermentation processes in the late 20th century, particularly in the 1980s and 1990s, significantly reduced the cost of producing lactic acid from renewable sources like corn starch and sugarcane. Companies like Cargill (which later formed Cargill Dow Polymers LLC, now NatureWorks) played a pivotal role in developing commercially viable methods for mass-producing high molecular weight PLA. The formal launch of NatureWorks™ PLA technology in 2001 marked a major turning point for industrial-scale production.
Rise of 3D Printing: In the early 2000s, with the emergence of desktop 3D printers and open-source initiatives like the RepRap project, there was a need for accessible and easy-to-use filament materials. PLA quickly became a preferred choice due to its low melting point, minimal warping, and ease of printing, especially for beginners. It gained significant popularity in the 3D printing community around 2010-2012 and remains one of the most widely used filaments in additive manufacturing today.