All About PP 3D Printing Filament： Materials, Properties, Definition

3D printing is the process of making a part by subsequently building up a part layer by layer by depositing melted plastic. Polypropylene filament can be used as a raw material for 3D printing. It is gaining acceptance and market share as technical difficulties with printing this thermoplastic is solved. As such PP (polypropylene)  3D printing filament is one of the most popular materials for printing living hinges due to its excellent fatigue resistance and toughness. Polypropylene also has excellent chemical resistance to a wide range of acids, bases, and solvents at room temperature making it widely used in the medical and automotive industries. For more information, see our guide on 3D printing.

Polypropylene is a semicrystalline monomer with the formula (C3H6)n. It is produced via chain-growth polymerization of propene. Polypropylene is available as a homopolymer (general purpose grade), a block copolymer (incorporates between 5 and 15% ethylene), and a random copolymer (incorporates randomly arranged co-monomers along the main polypropylene molecular chain and includes between 1 and 7 % ethylene). Black titanium oxide pigment can be added to color the plastic and improve its UV (Ultraviolet) light resistance. Glass-filled polypropylene filament is available to increase standard polypropylene's heat deflection temperature at the expense of impact resistance.

Some key properties of polypropylene are listed below lists some key mechanical and thermal properties of PP 3D printing filament:

1. Polypropylene has a melting temperature of 130°C and a heat deflection temperature of 64.1°C. 
2. One of the most important properties of PP is its chemical stability. This chemical stability means that it is resistant to many different chemicals, including acids and alkalis. 
3. Polypropylene can resist impact loading with braking or shattering. 
4. Polypropylene can withstand millions of stress cycles without failing.

Comparison of PP Filament Properties

Table 1 lists the properties of PP 3D printing filament in comparison to a range of other high-performance filaments:

Polypropylene (PP) is not commonly used for 3D printing due to the general difficulties involved in the process. The key challenges to using PP 3D printing filament are:

1. It tends to warp during printing if temperatures are not precisely controlled. A heated print volume is therefore needed to limit shrinkage and warping. 
2. Printed PP tends to detach from the print bed if a suitable adhesive is not applied.
3. It will degrade under long exposure to UV light. Although this problem can be mitigated with additives, PP is generally not suited to outdoor applications. 

Listed below are some of the key benefits of printing with polypropylene:

1. It is resistant to a wide range of solvents, bases, and acids at room temperature. However, PP is not resistant to nitric acid with a concentration above 65% or sulphuric acid above 93%.  
2. It has excellent fatigue resistance. PP is widely used for living hinges (i.e. flexible hinges that rely on a material's ability to flex), which can undergo millions of stress reversal cycles without permanent deformation. 
3. PP has excellent impact resistance when compared to more commonly used engineering thermoplastics like nylon or ABS.

Why is PP Used in 3D printing?

PP (Polypropylene) 3D printing filament is not very mechanically strong. However, it does have some unique uses such as living hinges, translucent containers, and wearable device straps. This uses is due to its excellent fatigue strength and chemical resistance. PP is also widely used in the medical and automotive industries. Like most thermoplastics, polypropylene is also recyclable. 

How to Use PP in 3D Printing

PP 3D printing filament is one of the more difficult thermoplastics to print. However, if the correct settings are used there is no reason why excellent results can’t be achieved. Listed below are some tips for printing with polypropylene:

1. PP 3D printing filament does not easily bond to an unprepared build plate. Packaging tape applied to the build plate will create a good bond to the first printed layer, and so will certain specialized glue sticks, such as Magigoo PP.  
2. Polypropylene will easily warp during printing if the print environment is not maintained at a relatively high temperature of 45°C. That being the case, an enclosed print volume is recommended.
3. A “raft” is a printed base on top of which an actual part can be printed. Using a raft will protect the base layer of the part, as sometimes the part will bond too well to a properly prepared build plate, and removing the part can damage its base. A raft can be easily removed by simply pulling it off.

While a heated build volume and proper bed adhesion practices will make printing polypropylene much easier, it is still important to use the optimal settings. Listed below are some key parameters to use as starting points. However, it is always advisable to refer to the specific PP 3D printing filament technical datasheet for your specific printing filament to find the optimal settings. The following data in Table 2 are some of the important printer settings to determine and set before printing with polypropylene filament:

The optimal wall thickness for a polypropylene part depends on the end use of the part being printed. In general, a wall thickness of about 1 mm will be ideal. If a wall doubles as a living hinge, then the ideal print thickness can be as low as 0.4 mm. 

What is a Good Wall Density for 3D Printing PP?

The optimal infill density for a nonfunctional mockup polypropylene 3D printed part is 20%. However, this density must be adjusted depending on the intended application. Load-bearing applications may require 50-80% infill density. The standard grid-type infill will be sufficient for the majority of applications. 

Polypropylene filament for 3D printing is not biodegradable and must be recycled in an industrial facility.  

Like most thermoplastics, polypropylene is recyclable. 

Polypropylene 3D printing filament is not hygroscopic. It does not readily absorb moisture. 

What is the Difference Between PP and PLA in 3D Printing?

PLA (Polylactic Acid) is a rigid and brittle material that has poor fatigue resistance compared to polypropylene. However, PLA is significantly cheaper than PP 3D printing filament and is much easier to print. 

What is the Difference Between PP and ABS in 3D Printing?

ABS (acrylonitrile butadiene styrene) has significantly better mechanical strength than polypropylene 3D printer filament. However, both materials are prone to warping and require heated build volumes during printing. 

What is the Difference Between PP and PET in 3D Printing?

There is considerable overlap in the applications of PP and PET (Polyethylene Terephthalate). For example, both are used to safely store food and liquids. PP and PET also have similar temperature resistances and stiffness properties.

This article presented PP 3D printing filament, explained what it is, and discussed different factors to consider when using it in 3D printing. To learn more about PP 3D printing filament, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities, including 3D printing and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

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