Where is my 3D printed polypropylene?

Where is my 3D printed polypropylene?

Ms Rachel Gordon
Where is my 3D printed polypropylene?
The new IDTechEx Research report 3D Printing Materials 2016-2016 has highlighted the growing market for professionals using desktop thermoplastic extrusion 3D printers. Many types of businesses are increasingly making prototypes, models and final products for sale. A large proportion of desktop machines are not used by hobbyists, but are owned and operated within companies or schools. This means the users tend to be more persistent, and the machines need to be more reliable and have higher usage rates. Businesses get through more filament than the standard home user. 73% of 3D printing filament by mass is sold to professionals with desktop machines.
Figure: Market share of end-user of thermoplastic 3D printing filament by mass. Source: 3D Printing Materials 2016-2026 (www.IDTechEx.com/3dmats)

Professionals demand better filaments

This growing market of professionals is demanding better quality filaments. There are thousands of engineering thermoplastics and only a few are available in filament form. Engineers are searching to print prototypes in the same material as the final product will be made in. Product designers want to 3D print objects in materials they are used to using.
Polypropylene is used in a wide variety of applications including packaging, textiles, ropes, carpets, stationery, containers (including most plastic living hinges), laboratory equipment, loudspeakers, automotive components and polymer banknotes.
PP is the commodity plastic with the lowest density. Polypropylene is normally tough and flexible, and has good resistance to fatigue. It is often chosen for its resistance to corrosion and chemical leaching, and its resilience against most forms of physical damage, including impact and freezing. Polypropylene is also highly colorfast, which is useful in carpets and textiles.

Technical challenges limit materials availability

Until recently, PP was not available for 3D printing. There are a number of factors that make PP difficult to 3D print. Melt viscosity is very low, so it is difficult to extrude. The pseudoplastic nature of polypropylene is strongly dependant on the molecular weight, molecular weight distribution, and crystallinity. It is very difficult to get PP to stick to the print bed.
PP has a high coefficient of thermal expansion. Shrinkage of polypropylene is typically around 1%, but prediction of the actual value is difficult due to the strong influence of processing conditions. This means PP warps badly, and attempts to allow for the shrinkage in the design are rarely successful.
German RepRap do sell a PP filament, a spool of 3mm diameter food-grade PP plastic in black retails for €55 for 0.85kg. The filament is being produced exclusively for German RepRap according to US FDA regulations and the relevant EU standards. Users report that it is difficult to use reliably.

Competition from the free market

IDTechEx predict a wider range of thermoplastic filaments will become available over the next couple of years, mostly due to pressure from professional and industrial users. This will open new applications and easier certification in a number of industries. Progress has been slow, but increasing availability and quality of competing filaments on the open market are putting pressure onto 3D printer manufacturers who supply their own filaments.
There is strong demand for PP because it is currently impossible to print snap fit parts or living hinges reliably. However, the technical challenges will not be easily overcome. A close analogy is more likely in the short time.
3D Printing Materials 2016-2026 contains comprehensive coverage of the key materials available for 3D printing including thermoplastic filaments, photopolymers, thermoplastic powders and metal powders, as well as alternative ways to print metals, biomaterials, ceramics and conductive materials. 29 materials suppliers have been interviewed and profiled. The report contains comprehensive market data including forecasts to 2026 by mass and revenue.