Circularity potential
Medium
Strength
Medium
Production energy
High
Stiffness
Low
Embodied CO2
Medium
Density
Low

A lightweight, low cost, widely recycled commodity plastic useful in packaging, textiles, automotive and household goods – it is one of the most widely used plastics. It is impermeable to water, highly resistant to chemicals, very durable, insulating and resistant to fatigue. The homopolymer is available in biocompatible grades suitable for healthcare applications.

PP is one of the least expensive polymers and available in many different grades and formats. Whereas low-grade recycled material can offer cost savings versus virgin, recycled grades of high quality (light colours, no odour and so on) can add up to 50% to the base price. Bio-based materials are up to twice the price, depending on the source and feedstock, but this is likely to come down with time and developments in the technology.

Due to it’s semi-crystalline structure, it has a naturally milky appearance. However, types (such as random copolymer) and additives (clarifiers) have been developed to produce a more transparent appearance in the finished article. Clarifiers are suitable for food application (microwave, dishwasher, freezer and hot-fill safe) and produce a clear, colour-free material. This brings PP into competition with amorphous materials, such as polycarbonate (PC) and even glass, for containers and packaging.

It is combined with various fillers – including mineral (talc), glass fibre, carbon fibre and natural materials (such as wood, hemp and bamboo) – to improve mechanical properties and, in the case of wood-fill, reduce cost and weight. Maleic anhydride grafted polypropylene (PP-g-MAH) is commonly used as the base material, because it improves coupling between the polymer and filler material.

It has low surface energy, which is useful in many cases, but also means it is difficult, but not impossible, to bond with adhesive. It will burn readily when exposed to an open flame (UL 94 HB). It is possible to add flame retardant additives to achieve UL 94 V0, but this has an impact on mechanical properties.


Sustainability concerns
Non-renewable ingredients
Raw material generates polluting by-products
Microplastics


Polypropylene copolymer (PPC) is available as monofilament, used in fused deposition modelling (FDM), as well as selective laser sintering (SLS) powder. It provides a lightweight 3D printing material that is extremely tough (rubber-like durability) and capable of living hinges, clips, latches, water tight containers, food contact applications and translucency. It is not particularly strong, but capable of semi-structural parts if sufficient wall thickness is built up.

PP 3D printing materials tend to be quite expensive. While the raw material is relatively cheap, processing it into a useable format, especially cryogenic powder grinding, adds considerable cost. In addition, they are not used as much as some of the other 3D print materials, like ABS and PETG, and priced accordingly.

It has good chemical resistance, but it prone to degrade in UV light, unless suitable additives are included. It is also very difficult to get anything to stick to it, but can be welded to similar materials. Another significant challenge with PP is that it tends to warp due to the high rate of shrinkage as it cools, because it is semi-crystalline. Therefore, careful heating control is required while printing. Applications span packaging, fashion, apparel, footwear, medical, automotive, product and furniture – it is used for both prototyping and short production runs of functional parts.

Converting pellets into filament ready for printing adds around 6 MJ/kg and 0.5 kgCO2e/kg.


Design properties
Cost usd/kg
20-60
Embodied energy MJ/kg
76-81
Carbon footprint kgCO2e/kg
1.8-4.4
Density kg/m3
900
Tensile modulus GPa
0.23-0.65
Tensile strength MPa
18-35
Flexural modulus GPa
0.25
Flexural strength MPa
9.4
Charpy impact strength kJ/m2
49
Hardness Mohs
1
Rockwell hardness R-scale
80-110
Poissons ratio
0.43
Thermal expansion (µm/m)/ºC
150
Melt temperature ºC
125
Heat deflection temperature ºC
65
Thermal conductivity W/mK
0.12
Temperature min-max °C
-10 to 100
Thermal
insulator
Electrical
insulator