Discovering 3D printing materials: Plastics

A plastic is a material made up of synthetic or semi-synthetic compounds that has the property of being malleable (able to change shape). Most plastics on the market are entirely synthetic, most often derived from petrochemicals. However, given the growing environmental concerns, plastics derived from renewable materials such as polylactic acid (PLA) are also popular in the market. Due to their low cost, ease of manufacture, versatility and water resistance, plastics are used in a multitude of products and sectors. In the additive manufacturing market, this is no exception: it is the most widely used family of materials.

It must also be said that plastics are compatible with many technologies available today. The most popular and affordable 3D printing process, melt deposition, uses it for example in the form of filaments; stereolithography uses liquid photopolymer resins and laser sintering requires thermoplastic powders. Each plastic will require different 3D printing parameters during the manufacturing process, and will give parts varying properties. In order to better understand the world of plastics in 3D printing, 3Dnatives has prepared a complete guide to help you understand each material, knowing that there are of course others such as metal or organic materials.

Plastics in 3D printing – FDM/FFF

Melten deposition technologies are the best known for using plastic materials. They come in the form of a spool of filament that is placed on the 3D printer. There are many varieties of plastics with different characteristics for each project.

ABS

This is the flagship material for Lego bricks, also widely used in car bodywork, household appliances and in many cowling applications. ABS plastic, i.e. acrylonitrile butadiene styrene, is the most commonly used plastic in the industry. It belongs to the family of thermoplastics or thermal plastics and has an elastomer base based on polybutadiene which makes it more flexible and impact resistant.

ABS has a printing temperature between 230°C and 260°C and can withstand very low (-20°C) and very high (80°C) temperatures. In addition to its good resistance, this material provides a polished surface, is reusable and can be welded by chemical processes (using acetone). However, it is not biodegradable and shrinks on contact with air, which is why the printing bed is heated to prevent parts from peeling off. It is also recommended to use a closed enclosure 3D printer to limit particulate emissions during printing. ABS is used primarily in the Fused Deposition (FDM) technique and as a result is available with most home printers. In addition, a derivative of ABS, in liquid form, is used in the SLA and PolyJet processes.

PLA

Polylactic acid or PLA, unlike ABS, is biodegradable under certain conditions because it is made from renewable materials (corn starch). One of its main characteristics is its low shrinkage in 3D printing, which is why heated plates are not necessary during printing. Printing temperatures should not be very high, between 190°C and 230°C.

PLA is more difficult to handle due to its high cooling and hardening rate. It can also be damaged and rub off on contact with water. However, this generally translucent material is used by most FDM 3D printers and comes in a variety of colors.

ASA

Technically known as Acrylonitrile styrene acrylate, this material has similar properties to ABS with better resistance to UV rays. You can still have some complications during printing, which is why it is recommended to have a heated bed. The printing parameters are very similar to those used with ABS – in the case of ASA, care must be taken to use 3D printers with a closed enclosure or to print in an open space because styrene emissions.

PET

Polyethylene terephthalate, better known as PET, is mainly found in disposable plastic bottles. It is an ideal filament for parts intended for food contact, semi-rigid and offering good resistance. To obtain the best printing results, it is necessary to reach temperatures of 75°C to 90°C. Most often marketed as a translucent filament, there are different variants such as PETG, PETE and PETT. It is a filament that does not emit any odor during printing and is 100% recyclable.

PETG

To stay in the same family, PETG, or glycolized polyester, is a thermoplastic widely used in the additive manufacturing market, combining both the simplicity of 3D printing of PLA and the resistance of ABS . It is an amorphous plastic, which can be 100% recycled. It therefore has the same chemical composition as polyethylene terephthalate (PET). Glycol has been added to reduce its brittleness and therefore its fragility.

PC or Polycarbonate

Polycarbonate (PC) is a very strong material designed for engineering applications. This material is able to withstand high temperatures up to 150°C without deforming. Polycarbonate is susceptible to absorbing moisture from the air, which can affect its performance and print resistance. Therefore, it should be stored in airtight containers. PC is highly valued by the additive manufacturing industry for its strength and transparency. It has a much lower density than glass, which makes it particularly interesting for the design of optical parts, protective screens or decorative objects.

High-performance thermoplastics (PEEK, PEKK, ULTEM)

The evolution of 3D printing technologies has brought with it extensive research work on printing materials, making it possible to develop any a range of high performance filaments that have mechanical characteristics similar to metals. There are several types of high-performance materials such as PEEK, PEKK or ULTEM – they are distinguished by family such as polyaryletherketones (PAEK) or polyetherimides (PEI). These filaments have a very high mechanical and thermal resistance, are very strong while being much lighter than some metals. These properties make them very attractive in the aeronautics, automotive and medical sectors.

Due to their characteristics, high performance thermoplastics cannot be printed on all FDM machines on the market. The 3D printer must have a heating plate capable of reaching at least 230°C, an extrusion at 350°C and a closed enclosure. Today, about 65% of these materials are printed with FDM technology, but they are also found in the form of powders, compatible with SLS technology.

Polypropylene (PP)

PP is another thermoplastic widely used in the automotive industry, for packaging, disposable professional clothing, and in the manufacture of around a hundred everyday objects. Polypropylene is renowned for its resistance to abrasion and its ability to absorb shocks, in addition to its relative rigidity and flexibility. One of the disadvantages is its low resistance to temperatures and its sensitivity to UV radiation, which is why several printer manufacturers have developed derivatives of this material, imitation polypropylenes, in order to strengthen its physical and mechanical properties.

Flexible materials

Many types of filaments are on the market today and one of the biggest successes is flexible filaments. They are similar to PLA but made from TPE or TPU. The advantage of these filaments is that they make it possible to develop deformable objects, widely used in the fashion industry. In general, they have the same printing characteristics as PLA and can have varying degrees of stiffness. It is recommended to check that the extruder is adequate to avoid jamming the machine.

Composites

Composites are extremely useful for making lightweight yet strong parts. Fibers strengthen a part without adding weight to it, which is why we also call composites fiber reinforced materials. There are two types of reinforcements, short fiber or continuous fiber. In the first case, chopped fibers, i.e. segments less than a millimeter in length, are mixed with traditional 3D printing plastics to increase rigidity and, to a lesser extent, resistance. components. Staple fibers can be mixed with thermoplastics such as nylon, ABS or PLA.

Fibers can also be added to thermoplastics continuously during 3D printing to achieve a stronger part. The main fiber used in the 3D printing sector is carbon fiber, but there are others such as fiberglass or Kevlar.

Hybrid materials

There are different types of materials that mix a base such as PLA with a powder that gives them a different color or finish than the one traditionally obtained; these are filaments generally composed of 70% PLA and 30% of the hybrid material. On the market today, there are filaments made from bamboo, cork, wood, etc. The presence of these materials provides a more organic final texture to the filament. Some hybrid materials incorporate metallic powders, compatible with extrusion technologies, to give parts a metallic finish. They can be based on copper, bronze, silver, etc.

Soluble materials

Soluble plastics can be used to print print media – depending on the complexity and technology used for the desired part – which will subsequently be dissolved. The most widely used soluble plastics today are HIPS (High Impact Polystyrene) and PVA (Polyvinyl Alcohol) which can be dissolved with limonene and water respectively. There are also BVOH filaments or copolymer of butanediol and vinyl alcohol, very popular in dual extrusion 3D printing for being a water-soluble support; according to experts it has better solubility than PVA and is compatible with several materials.

Plastics in 3D printing – SLA

For technologies such as SLA, DLP or even PolyJet, liquid photosensitive resins are used for printing. These can be divided into thermoplastics and thermo-solids. Depending on what we choose, they allow printed objects to have a matte or glossy finish. Among these resins, most are plastics mentioned above, but in liquid form. What differentiates these materials from those of FDM technologies is that it is not possible to mix resins to obtain different results. Also be aware that the use of resins in 3D printing involves a post-processing process: it is necessary to clean the parts with isopropyl alcohol to obtain better results.

Creating parts using resins results in highly detailed objects with a smooth surface; nevertheless, the range of colors is still quite limited with this process. The standard resin has similar properties to ABS: the surface condition of the part will be good given the light-curing process, but the mechanical properties will be moderate. There are more advanced resins for technical applications such as dentistry (which must also be biocompatible) or engineering. Additionally, soft resins that provide greater flexibility and deformation can be used to make jewelry. Over the years, manufacturers have expanded their line of liquid photopolymers to meet the manufacturing needs of various industries. Therefore, you should be able to find resins that are resistant to high temperatures, can withstand heavy impacts, or have high elongation properties.

Plastics in 3D printing – SLS

Selective laser sintering technology uses plastic powders to manufacture parts using a laser that fuses the particles, layer by layer. There are a variety of different materials that allow manufactured objects to have different characteristics in terms of strength, flexibility or texture. These are materials that will also be found in the HP Multi Jet Fusion process.

Polyamides

Polyamide (nylon) objects are usually created from a fine, white, grainy powder using SLS technology. There are, however, a few variations of this material, such as nylon, which are also available as filaments used in fused deposition modeling (FDM). Due to their biocompatibility, polyamides can be used to create parts that come into contact with food (except foods that contain alcohol).

Consisting of semi-crystalline structures, polyamides have a good compromise between mechanical and chemical characteristics, hence their stability, rigidity, flexibility and impact resistance. These advantages mean that this material has many applications in all sectors and offers a high level of detail. Due to their high quality, polyamides are used in the manufacture of gears, parts for the aerospace market, the automotive market, robotics, medical prostheses and injection molds. Among the best-known polyamides are PA12 and PA11, the latter being derived from castor oil and therefore more durable. They are very widely used on HP and EOS machines for example.

Alumide®

Alumide objects are made from a combination of polyamide and powdered aluminum using selective laser sintering technology. With a slightly porous surface and a sandy and grainy appearance, this material offers great solidity, high resistance to temperature (172 ºC max.) and shocks and relative flexibility. However, post-treatments are generally necessary: ​​grinding, polishing, coating and milling for example.

Alumide is used for complex models, design parts or for small series of functional models, requiring significant rigidity and an appearance close to aluminum. The technique used involves weak geometric limits.

And you, what 3D printing plastics do you use? Share your opinion in the comments of the article or with the members of the 3Dnatives forum.