What is PLA Plastic?
Polylactide, also known as PLA, is one of the most popular thermoplastics derived from lactic monomers extracted from natural sources like sugarcane or corn. It is a versatile biodegradable plastic with good applicability to several products. Polylactide is the second most widely used bioplastic (the most used bioplastic is thermoplastic starch) worldwide. The PLA characteristic is similar to Polypropylene(PP) and Polyethylene(PE). It is relatively inexpensive to produce as it can be done in the existing manufacturing machine, originally designed for traditional thermoplastics derived from petroleum.
These are the largest producers of PLA plastic worldwide:
- RPT company
- Total Corbion PLA
The wide range of applications with PLA material makes it a go-to bioplastic for manufacturers looking for strength and appearance in the thermoplastic. The most common applications are found in medical devices and food packaging.
Different Types of Polylactic Resins –
There are multiple variations of PLA resins available in the market, mainly due to their high demand for several applications. The main variations are – Regular PLLA (Poly-L-lactic Acid), PDLA (Poly-D-lactic Acid), and PDLLA (Poly-DL-lactic Acid).
They have slight changes in their fundamental properties; however, they are derived from a single source – Lactic acid: C3H6O3.
How is PLA Made?
Before getting to how PLA is made, let’s first understand its basic ingredient – lactic acid.
Lactic acid(hydroxy propionic acid) is the most widely materializing hydroxycarboxylic optical active acid. The molecule is present with two enantiomers – L- and D-lactic Acid.
PLA material is formed from the lactic monomers extracted by fermentation of sugarcane, beet-sugar, etc.
PLA contains stereoisomers such as:
- Poly(L-lactide) (PLLA)
- poly(D-lactide) (PDLA),
- and Poly(DL-lactide) (PDLLA)
Polylactide is produced using three methods. Here are they:
Source - Royal Society of Medicine
Once PLA plastic is produced by using lactide monomer and then formed lactide is followed up by ROP using metal alkoxides a catalyst, the creation of a high molecular weight polyester – PLA.
Direct polycondensation reaction:
Here, the key role is played by the coupling agents. They act by low molecular weight polymer – to higher molecular weight polymers.
Azeotropic dehydrative condensation:
High molecular weight products can be obtained if the organic solvents are blended with the reaction mixture to remove the water.
Out of the three methods, ROP is the most sought after for industrial PLA material production thanks to its low cost and time consumption and final product with high molecular weight.
Recently two new methods have been adopted by manufacturers – microwave irradiation and ultrasonic sonochemistry. They are also fast and cost-effective.
Fundamental Properties of PLA Plastic –
PLA has a high glass transition temperature in the range of 55-60°C. Almost all the PLA’s commercial products are semi-crystalline in nature and have a high melting point of 180°C.
- PLA material boasts high strength and stiffness, comparable to polystyrene(PS) at room temperature.
- It is a high modulus thermoplastic with an attractive appearance.
- Energy consumption by PLA while production is less than other plastics and greater thermal processing capabilities.
- It is a thermoplastic which means it can be reheated several times without any significant change in the mechanical properties.
- Almost carbon-neutral, making it safe for mother nature; on the contrary, its renewable sources absorb carbon.
Below are the typical PLA material properties:
Polylactic Acid (PLA)
PLLA: 61 – 66 MPa (8840 – 9500 PSI) ***
PLLA: 157 – 170 °C (315 – 338 °F) **
PLLA: 178 – 240 °C (353 – 464 °F) **
|Specific Gravity||PLLA: 1.24 *****|
PLLA: 48 – 110 MPa (6,950 – 16,000 PSI) ***
|Heat Deflection Temperature (HDT)||
49 – 52 °C (121 – 126 °F) at 0.46 MPa (66 PSI) ****
PLLA: 0.37 – 0.41% (0.0037 – 0.0041 in/in)******
Disadvantages of Polylactide –
Although the advantages completely overweight the disadvantages, it is still important to discuss them. Here are they:
- Polylactide has a low crystallization rate, and processing results in amorphous products.
- Poor ductility and low impact strength limit its applications compared to other thermoplastics.
- Thermal instability and meager gas barrier performance can also become an issue for some manufacturers.
- It has a slow degradation rate.
Can PLA Material Properties Improve?
Some various blends and additives can improve, modify, or change properties in PLA. Let’s have a look at some of them:
CaCO3 is one of the fillers used to improve PLA’s impact toughness. Load it at 30%, and by doing that, a significant increase in toughness can be witnessed.
Using plasticizers other than lactide monomers, Citrate esters & low-Mw PEG have shown decent improvement in PLA’s toughness but can lead to a substantial loss in tensile stress at break and tensile modulus.
Oher plasticizers for PLA are promoted because lactide monomers are excellent for PLA but tend to move to the surface.
Blending PLA with PCL(Polycaprolactone) can also create a rubbery degradable polyester with supremely high( almost 5 times) elongation at break. The blend is ideal for increasing the toughness in PLA.
Certain modifiers can also be used to improve properties in PLA. But modifier content must be limited, or it can decrease the PLA’s composability.
PLA and PHA:
Blending PLA and PHA has resulted in a tremendous increase in toughness but can moderately decrease modulus and strength, although it wouldn’t be something to worry about. Another benefit is that it won’t compromise the biodegradability and compostability of PLA.
Nanocomposites are one of the latest techniques used as an alternative to traditional composites. Nanoscale fillets are the main components of nanocomposites. An improvement in several aspects like matrix adhesion, high surface area, and better aspect ratio make these nanofillers very advantageous compared to traditional additives.
A good example is PLA-clay nanocomposites – Which show good growth in mechanical and thermal properties.
Engaging read – What is Polystyrene? | The Definitive Guide
Applications of PLA Plastic –
- Food packaging
- Structural Applications
- Medical & Healthcare
- Fibres & Fabric
#1 Food Packaging:
PLA material is extensively used as a food packaging material for mostly short-shelf-life products like fruits, vegetables, meat, and seafood. The FDA approval from the US government body makes it even more encouraging.
The main packaging applications include blister packaging, salad and ice-cream cups, containers, drinking cups, etc.
#2 Structural Applications:
There is a growing need for lighter and more fuel-efficient automobiles, becoming a boon for PLA and PLA-based composites. In addition, PLA plastic shows good impact properties and tensile strength and can be useful in making automobile interior parts.
PLA’s constantly improving properties also apply for ceiling materials, front panels, Pillow cover, floor mats, etc. In addition, PLA composites are recommended to be used in hybrid vehicle rooftops.
#3 Medical & Healthcare:
PLA boasts great biodegradability and bio compostability, making it an ideal choice for manufacturing medical implants. It is used in delivery system materials, tissue engineering scaffolds, bioabsorbable implants, and covering membranes.
There is a lot of research output to support PLA’s use in artificial tissue re-creation and dermatological treatments.
#4 Fibres & Fabric:
Thanks to suitable fibers and fabric manufacturing properties like low moisture absorption, UV resistance, and low smoke generation, PLA Plastic is compatible with producing shirts, sportswear, carpets, beddings, insulation materials, proactive foams, etc.
Processing Methods for PLA –
Processing Conditions for Injection Molding:
Before processing, PLA material must be dried using traditional drying systems. Recommended conditions for drying is as follows:
- Moisture must be lower than 250 ppm to keep the melt viscosity in check over higher temperatures.
- Drying before processing for 2-3 hours at 45°C up to 90°C is advisable.
- Usually, anhydrous dryer temperature will be more than the melting point of PLA plastic.
- To tackle or prevent issues like sticking and bridging, the drying system should be checked for ideal temperature during operations, as valve leakage is one of the major problems in this process.
Although this is optional, adding colorants in the masterbatch at 10-15% weightage in the resing by the dry blender. Adding it by the injection molder. The addition is primarily done using liquid injection technology.
Below are the typical conditions for injection molding with PLA:
|Dew Point||(-)40 – (-)35°C|
|Adapter Temperature||185 – 200°C|
|Drying Temperature||45 – 100°C|
|Mold Temperature||10 – 105°C|
55.16 – 137.9 MPa
|Melt Temperature||155°C – 245°C|
|Feed Temperature||165 – 185°C|
|Moisture Content||0.01 – 0.025%|
|Screw Speed||20 – 180 rpm|
|Die Temperature||50 – 100°C|
|Drying Air Flow Rate||14.16 l/pm|
Plating out to lactide is a common phenomenon if the injection speed is too low or mold temperature is too cold.
PLA Plastic filaments for 3D Printing –
3D printing is a rapidly growing processing method adopted by molders worldwide due to its ability to manufacture complex parts with demanding geometries. Polylactide is mostly utilized by the FDM 3D printing method. PLA is also environment friendly making it more compatible with 3D printing than other materials like ABS and PEEK
Talking about its suitability with polylactide can manufacture biomedical devices with complex shapes using computer-made designs and algorithms. Patient-specific devices can also be made using the same technology, which can really help bring a revolution to the medical industry.
Is PLA Toxic?
Shortly, no. It is not toxic, at least in solid form. As we earlier discussed, polylactide is biodegradable and used in food packaging and medical applications. However, similar to other non-toxic plastics, inhaling or absorbing your skin in air or liquid form can be dangerous.
One must be extremely careful to prevent inhaling or absorbing the resin during the manufacturing process.
The Future of Polylactide –
Polylactide market, By Volume(%) by end-user insutry, 2018
Source: Mordor Intelligence
According to a study conducted by Mordor Intelligence, polylactide will register a CAGR of 20% until 2026. The growth is fueled by major government policies supporting bio-plastics, demand for cellulose in the textile industry, and the food packaging industry.
Obviously, things can change drastically because of the Covid-19 pandemic shutting off the world’s economy and manufacturing, let alone plastic processing. But when writing this post, a Covid-19 has been rolled out, people are coming out, and various government stimulus is also on the cards.
Food packaging is the largest consumer of PLA plastic right now, and the trend will continue for some time. Asia is the largest consumer of polylactide (thanks to china), followed by North America and Europe.
1. Is PLA safe to drink from?
Ans. As PLA is a bioplastic, it is generally considered safe for food and water safe. However, things are not that simple. Manufacturers often add different additives to improve upon certain features of PLA like color, strength, and other features. These filaments make PLA unsafe to digest.
2. Can I microwave PLA?
Ans. No, polylactide acid is not safe for microwaving or any other situation or scenario with excess heat as it is not made to be used in heated conditions. Microwaves heat their insides by agitating water molecules which can be harmful to PLA material.
3. Is PETG stronger than PLA?
Ans. Both PETG and PLA are user-friendly materials and can be used in 3D printing. However, PLA is a better candidate for 3D printing as it is more forgiving when it comes to settings. On the other hand, PETG is stronger, more durable, and more impact-resistant than PLA. Interestingly, you don’t have a heated bed to print with materials.
4. At what temperature does PLA warp?
Ans. PLA has a relatively low melting point, and any temperature beyond 180 °C will cause warping. Therefore, keeping the temperature between 160° C to 170°C will yield the best results from a production standpoint. The best way to prevent warping is using an adequately heated and level build plate.
5. Can you 3D print PLA without a cooling fan?
Ans. 3D printing without PLA will be disastrous. Without a cooling fan, the material is more likely to cure at the corners. That process can hamper the production quality adversely because the curled-up layer might touch the nozzle on the next and become even hotter. For good quality and smooth production, cooling is necessary.
Suggested Read –
- What is Hardness in Plastics? An In-Depth Guide
- Food Grade Plastic: The Best Plastics for Food Applications
- Which is the Best Acrylic Glue? | The Best Plexiglass Glue
- Plastics Vs. Polymers | What are the Differences?
- LDPE Vs HDPE: What are the Differences and Similarities
- How to Keep Your Plastic Workshop in Best Shape?
- Antistatic vs. Static Dissipative Plastics | Which One to Choose?
- Step Growth vs Chain Growth Polymerization
The Takeaway –
So that the thoughts and views I had about PLA plastic and resin. It’s rapidly growing bio-plastic, which can help you preserve the environment as well as boost your profits. En though PLA is a bioplastic, it has a lot to offer for both a manufacturer and consumer to choose it over other plastic materials derived from petroleum.
Kindly share your reviews in the comment box.