Have you ever wondered what makes everyday items so durable and cost-effective? Enter polypropylene (PP), the star among all commodity plastics. This lightweight thermoplastic is tough, rigid, and comes in many forms. With its semi-crystalline structure and low density, PP combines:
- strength,
- flexibility, and
- cost-efficiency
However, picking the right grade from a range of 14K+ commercial polypropylene options available in our master catalog can be a little challenging. In this guide, you will understand how to make the right choice of this indispensable material for your formulation. From production, processing, sustainability, and the real-world applications, let’s explore how PP redefines material innovation.
Polypropylene: Definition, production, & properties
What is polypropylene plastic?
Polypropylene (PP) plastic is a type of polyolefin that is slightly harder than polyethylene. PP is a commodity plastic with low density and high heat resistance. It finds application in packaging, automotive, consumer goods, medical, cast films, etc. Its chemical formula is (C3H6)n.
Molecular structure of PP
How is polypropylene produced?
Polypropylene is made from the polymerization of propene monomer. There are two main syntheses to produce PP:
- Ziegler-Natta polymerization or
- Metallocene catalysis polymerization
Upon polymerization, PP can form three basic chain structures. They depend on the position of the methyl groups:
- Atactic (aPP) – Irregular methyl group (CH3) arrangement
- Isotactic (iPP) – Methyl groups (CH3) arranged on one side of the carbon chain
- Syndiotactic (sPP) – Alternating methyl group (CH3) arrangement
Basic chain structures of PP
Depending on how it is produced and formulated, PP can be:
- hard or soft,
- opaque or transparent,
- light or heavy,
- insulating or conductive,
- neat or reinforced with cheap mineral fillers, short or long glass fibers, natural fibers, or even self-reinforced
What are the properties of PP?
Keeping information about the properties of a thermoplastic beforehand is always beneficial. This helps in selecting the right thermoplastic for an application. It also assists in evaluating if the end-use requirement would be fulfilled or not. Here are some key properties and benefits of polypropylene:
- Melting point: The polypropylene melting range varies depending on the polymer type.
- Homopolymer: 160 – 165°C
- Copolymer: 135 – 159°C
- Density: The polypropylene density is among the lowest of all commodity plastics. This feature makes it a suitable option for lightweight saving applications.
- Homopolymer: 0.904 – 0.908 g/cm3
- Random copolymer: 0.904 – 0.908 g/cm3
- Impact copolymer: 0.898 – 0.900 g/cm3
- Chemical resistance:
- Excellent resistance to dilute and concentrated acids, alcohols, and bases
- Good resistance to aldehydes, esters, aliphatic hydrocarbons, and ketones
- Limited resistance to aromatic and halogenated hydrocarbons and oxidizing agents
- Flammability: PP is a highly flammable material.
- PP retains mechanical & electrical properties at elevated temperatures. This occurs in humid conditions and when submerged in water. It is a water-repellent plastic.
- PP has good resistance to environmental stress cracking.
- It is sensitive to microbial attacks, such as bacteria and mold.
- It exhibits good resistance to steam sterilization.
Key properties of PP
Now that we have covered the basics of PP, including its production and properties, let’s delve into the various types of PP.
PP: Types & their comparisons
What are the types of PP?
The major types of polypropylene available in the market are as follows:
Polypropylene homopolymer
PP homopolymer is the most widely utilized general-purpose grade. It contains only propylene monomer in a semi-crystalline solid form. The main applications of PP homopolymer include packaging, textiles, healthcare, pipes, automotive, and electrical applications.
Polypropylene copolymer
This family is produced by polymerizing propene and ethane. It is further divided into random copolymers and block copolymers.
- PP random copolymer is produced by polymerizing ethene and propene together. It usually features ethene units up to 6% by mass. These units are randomly incorporated into the polypropylene chains. These polymers are flexible and optically clear. This makes them suitable for applications requiring transparency. Also, suitable for products requiring an excellent appearance.
- While in the PP block copolymer, ethene content is larger. It ranges between 5 and 15%. It has co-monomer units arranged in regular patterns or blocks. The regular pattern makes the thermoplastic tougher and less brittle than the random copolymer. These polymers are suitable for applications requiring high strength, such as industrial usage.
The potential applications of PP homopolymer and PP copolymer are nearly identical. Because of their extensively shared properties, the choice between these two materials is often made based on non-technical criteria. Some of the non-technical criteria are described in the table below.
| PP homopolymer | PP copolymer |
| High strength-to-weight ratio and stiffer & stronger than copolymerGood chemical resistance and weldabilityGood processabilityGood impact resistanceGood stiffnessFood contact acceptableSuitable for corrosion-resistant structures | Bit softer but has better impact strength; tougher and more durable than homopolymerBetter stress crack resistance and low-temperature toughnessHigh processabilityHigh impact resistanceHigh toughnessNot preferable for food contact applications |
Polypropylene, impact copolymer
PP impact copolymer contains a co-mixed PP random copolymer phase. It has an ethylene content of 45-65%. It is useful in parts that require good impact resistance. Impact copolymers are mainly used in packaging, houseware, film, and pipe applications. They are also used in the automotive and electrical segments.
Top 4 types of polypropylene: What to select and when?
Expanded polypropylene
EPP is a closed-cell bead foam with ultra-low density. It produces three-dimensional polymer foam products. EPP bead foam has the following features:
- higher strength-to-weight ratio,
- excellent impact resistance,
- thermal insulation,
- water and chemical resistance
EPP is used in automobiles, packaging, construction products, consumer goods, and more.
Polypropylene terpolymer
PP terpolymer is composed of propylene segments joined by monomers of ethylene and butane (co-monomer). These monomers appear randomly throughout the polymer chain. PP terpolymer has better transparency than PP homopolymer. Also, the incorporation of co-monomers reduces crystalline uniformity in the polymer. This makes it suitable for sealing film applications.
Polypropylene, high melt strength
It is a long-chain-branched material. It combines both high melt strength and extensibility in the melt phase. The key features of PP HMS grades include:
- wide mechanical property range,
- high heat stability, and
- good chemical resistance
HMS PP is widely used to produce soft, low-density foams for food packaging applications. It is also used in the automotive and construction industries.
Bio-based polypropylene
It is a bio-based version of PP. Its monomer propylene is derived from renewable feedstocks. The bio-based content can vary anywhere between 30-100%. Several suppliers are offering pure PP bio-based grades, such as:
- PolyFibra® & Trifilon BioLite®
- PP/PE blend – Terralene® PP 2509 and
- In biocomposite form, like Terratek®, etc.
Comparing the main types of PP
Each type of PP offers unique advantages depending on the required balance of stiffness, impact strength, and processing ease. The following table highlights how their core properties differ to guide your material selection.
| Property | PP, impact copolymer | PP copolymer | PP homopolymer |
| Density, g/cm3 | 0.9 | 0.9 | 0.9 |
| Shore hardness, D | 45-55 | 70-80 | 70-83 |
| Stress at yield, MPa | 11-28 | 20-35 | 35-40 |
| Elongation at break, % | 20-700 | 200-600 | 15-600 |
| Tensile modulus, GPa | 0.4-1 | 1-1.2 | 1.1-1.6 |
| Notched impact strength ASTM D256, J/m | 110-No break | 60-500 | 20-60 |
| HDT A (1.8 MPa), °C | 46-57 | 50-60 | 50-60 |
| Minimum service temperature, °C | -40 to -20 | -20 to -10 | -20 to -10 |
| UL94 fire rating | HB | HB | HB |
Detailed property comparison: PP impact copolymer, PP copolymer, and PP homopolymer
Selecting the right polypropylene type
Finding the perfect PP grade matching your requirements is always critical. But before making the optimal material selection, you should be aware of:
- Material properties that the end product should display
- Manufacturing method as per the intended application, and
- Cost requirements
Get your hands on our advanced Master Catalog, which has new and powerful filters that will make your product selection faster & precise than before. Start your selection journey now!
Getting the above parameters right early in the design process will save time. It will also ensure that the selected PP type meets all the needs of the specific applications. Explore our platform with new features that will enable you to compare grades & search graphically for a seamless sample ordering experience – Select from a range of 14310+ polypropylene grades.
While various types of polypropylene have an impressive array of properties, it also comes with some inherent challenges to consider. It is essential to make you aware of these factors to make informed decisions in selecting the right material for specific needs.
Navigating PP formulation challenges
Embracing some features allows for strategic design choices and fosters a continuous pursuit of advancements in polypropylene technology.
Factors to consider by PP manufacturers
You must consider certain aspects that may be perceived as challenges. Some of them are:
- Poor resistance to UV, impact, and scratches
- Embrittlement below -20°C
- Low upper service temperature, 90 – 120°C
- Attacked by highly oxidizing acids, swell rapidly in chlorinated solvents and aromatics
- Heat-aging stability is adversely affected by contact with metals
- Post-molding dimensional changes due to crystallinity effects. This can be solved with nucleating agents. Watch the video here »
- Poor paint adhesion
However, PP is gradually optimized for its performance by improving its properties using different additives. Let’s understand the role of additives in improving PP properties in detail.
How do additives help improve PP properties?
You can overcome the above-listed challenges by using polymer additives. They can also improve PP’s physical and/or mechanical properties.
For example, PP has poor resistance to UV. The addition of hindered amines to PP provides light stabilization. This enhances the service life as compared to unmodified PP.
Some more additives that are used to improve the properties of PP are mentioned below:
| ClarifiersMinerals | Conductive fillersLubricants | Flame retardantsPigments, and others |
Further, fillers and reinforcers achieve significant properties related to processing and end-use application. Check out filled or reinforced options to choose the grade of your choice:
- Glass-fiber reinforced PP grades
- Mineral-filled PP grades
- Calcium carbonate-filled PP grades
- Carbon-fiber reinforced PP grades
Moreover, self-reinforced polypropylene composites benefit from several general advantages such as:
- mono-material concept,
- low density,
- good mechanical properties,
- high impact resistance, and
- weight savings
Thanks to the combination of low densities and good mechanical properties. It results in up to 50% potential weight savings over glass-reinforced parts. It is easy to recycle.
There have been significant developments seen for self-reinforced PP. These advances bridge the gap between isotropic polymers and glass-reinforced materials. The self-reinforced PP offers a unique combination of processing and performance features. Learn more about the benefits and application scope now »
Natural fiber-reinforced polypropylene options are an interesting step towards cheap, sustainable composites. Low densities lead to noticeable cost savings and weight savings. This is up to 27% over glass fiber or talc-reinforced polypropylene.
The use of new additives, polymerization processes, and blending solutions significantly increases PP performance. Hence, today, PP is less seen as a low-cost solution but much more as a high-performance material. It competes with traditional engineering plastics and metals.
Comparison of PP-based compounds
| Property | Thermoplastic polyolefin | Talc filled PP | Glass filled PP | Long fiber reinforced thermoplastic | Self-reinforced PP |
| Density, g/cm3 | 0.9-1 | 0.97-1.25 | 0.97-1.25 | 1.2 | 0.8-0.9 |
| Shore hardness, D | 10-99 | 75-85 | 70-88 | – | – |
| Rockwell hardness, M | – | 10-45 | – | – | – |
| Stress at yield, MPa | – | 22-28 | 19-70 | – | – |
| Elongation at break, % | 450-850 | 20-30 | 2-30 | 2 | – |
| Tensile modulus, GPa | – | 1.5-3.5 | 1-10 | 4-8 | 4-14 |
| Notched impact strength ASTM D256, J/m | 110-No Break | 30-200 | 38-160 | – | – |
| HDT A (1.8 MPa), °C | – | 56-75 | 50-140 | 160 | – |
| Minimum service temperature, °C | -40 to -20 | -20 to -5 | -30 to -5 | – | – |
| UL94 fire rating | HB | HB | HB | HB | HB |
| Select 14310+ polypropylene grades available in our Master Catalog Request samples and download technical datahseets | |||||
Detailed comparison of polypropylene-based compounds
Now that we have explored how to enhance PP properties, let’s shift focus to its processing methods and the kind of final products they help produce.
How to process PP?
Polypropylene can be processed by virtually all processing methods. The most typical processing methods include:
Injection molding with PP
The processing conditions for PP injection molding include:
- Melt temperature: 200-300°C
- Mold temperature: 10-80°C
- Drying is not necessary if stored properly
- High mold temperature will improve the brilliance and appearance of the part
- Mold shrinkage lies between 1.5 and 3%. It depends on:
- processing conditions,
- rheology of the polymer, and
- thickness of the final piece
Watch free video tutorial to improve PP cycle time and limit part shrinkage
Expanded polypropylene (EPP) may be molded in a specialized process. EPP is an ideal material for the injection molding process. It is majorly used for batch and continuous production.
Select 9880+ PP grades suitable for injection molding from our master catalog »
Extrusion with PP
PP can be extruded into tubes, blow and cast films, cables, etc. The processing conditions for PP extrusion include:
- Melt temperature: 200-300°C
- Compression ratio: 3:1
- Cylinder temperatures: 180-205°C
- Pre-drying: No, 3 hours at 105-110°C (221-230°F) for regrind
Select 2480+ commercial PP grades from our platform suitable for extrusion »
Polypropylene film is among the leading materials today. It is used for flexible packaging as well as industrial applications. Depending on the extrusion technique, two main polypropylene film types are produced. These are described below:
Cast polypropylene film (CPP)
CPP is widely known for its versatility.
- Super resistance to tears & puncture
- Greater transparency
- Better heat resistance at high temperatures
- Excellent moisture and atmospheric barriers
- High permeability to water vapor
https://www.youtube.com/embed/xrNETZYtQ-k
General properties of CPP films
(Source: Artsan Packaging1)
Biaxially oriented polypropylene film (BOPP)
BOPP is stretched in both transversal and longitudinal directions, producing molecular chain orientation in two directions.
- Orientation increases tensile strength and stiffness
- Good puncture and flex crack resistance over a wide range of temperatures
- Have excellent gloss, high transparency
- Can be glossy, clear, opaque, matte, or metalized
- Efficient barrier against oxygen and moisture
https://www.youtube.com/embed/NCNK34RY18U
BOPP process
(Source: Innovia Films2)
3D Printing with PP
As a tough, fatigue-resistant, and durable polymer, PP is ideal for low-strength applications. It is currently difficult to use PP for 3D printing processes due to its:
- semi-crystalline structure and
- heavy warping
Several manufacturers have optimized PP properties or even created blends with improved toughness. This makes it suitable for 3D printing applications. Hence, it is recommended to thoroughly refer to the documentation provided by the supplier for printing temperature, printing bed, etc.
Polypropylene is suitable for:
- Complex models
- Prototypes
- Small series of components, and
- Functional models
Select 85+ PP grades available in our master catalog suitable for 3D printing »
Other processing methods for PP
The polypropylene grades can also be processed by blow-molding, thermoforming of sheets, compression-molding, or even rotational molding. This enables hollow parts, thin-wall trays, and large one-piece containers.
Select the perfect PP grade for your processing needs, using the new graphical search option – you can now compare properties, download technical datasheets, and order samples directly from our platform:
Some grades are designed for your specific conversion mode, like blow molding, compression molding, thermoforming, etc. Check out PP grades with various conversion modes here »
TIP: To meet specific requirements, try using the ‘Conversion mode’ facet to narrow down your search.
With its versatile processing options covered, let’s now examine how PP aligns with today’s sustainability goals.
Sustainability aspect of PP
Is PP recyclable?
All plastics have a ‘Resin Identification Code/ Plastic Recycling Code’ based on the type of resin used. PP’s resin identification code is 5. PP is 100% recyclable. Select 95+ recyclable PP grades listed in our master catalog.
PP recycling process and the main challenge
The PP recycling process includes:
- Melting waste plastic to 250°C to get rid of contaminants.
- Removal of residual molecules under vacuum and solidification at approximately 140°C.
This recycled PP can be blended with virgin PP at a rate of 50%.
The main challenge in PP recycling is its low rate of recycling. It is due to the difficulties in collection and sorting of PP. Also the cost of rPP can sometime be higher that virgin polypropylene3.
Uses of recycled polypropylene (rPP) and safety profile
A few applications of rPP include:
| Automobile battery cases, | Signal lights, |
| Battery cables, | Brooms, |
| Brushes, | Ice scrapers, etc. |
The use of PP is considered safe. This is because it does not have any remarkable effect from an occupational health and safety point of view, in terms of chemical toxicity.
Up next, we’ll compare polypropylene with other polymers to highlight their similarities and differences so you can confidently choose the right one from our platform.
Polypropylene vs. other polymers
PP vs. PE – Key differences you should know
Though PP and PE are similar, they also have some unique characteristics. These features can be optimized depending on their manufacturing process and intended application.
Polypropylene is the second most used plastic after polyethylene. Find below what advantages it offers over PE:
- PP has crystal-clear transparency than PE.
- PP has excellent mechanical properties. It has high resistance to fatigue, impact, heat, and freezing.
- PP is harder and can be used for mechanical and structural applications.
- Polypropylene’s density is fixed and only varies when it is filled.
Polyethylene selection is highly dependent on the varying densities of multiple versions.
- PE is available in low, medium, and high-density grades.
- High-density polyethylene is known for its high strength-to-density ratio. It is considered more rigid than PP.
- PE is tough yet light, with good resistance to impact and abrasion.
Quick wrap of their main differences
| Polypropylene | Polyethylene |
| Propylene monomers make PPIt can be produced optically clearPP exhibits high resistance to cracking, acids, organic solvents, and electrolytesIt has a high melting point and good dielectric propertiesPP is more rigid than polyethylene | Ethylene monomers make PEIt can only be made translucent like a milk jugPE stand up better in cold temperaturesIt is a good electrical insulator and offers good tracking resistancePE is sturdy as compared to PP |
| Select commercial grades of polypropylene | Select commercial grades of polyethylene |
Are you still struggling to choose between the two? Let’s have a look at some of their distinct features »
Common features
PP & PE can be designed to be durable and lightweight. These polymers are used in many applications such as bottles and gloves. They are highly malleable and have relatively similar impact resistance. This means strength does not have to be a concern when these plastics are in use.
How does PP challenge polyethylene terephthalate?
In blow-molded bottle applications, PP has emerged as a strong competitor to PET. Compared to PET, the key features of PP include:
- Less expensive,
- Lighter in weight,
- More resistant to the high temperatures of hot filling, and
- Less permeable to moisture
PP bottles can be hot-filled at temperatures up to 100°C. While PET cannot withstand filling temperatures above 76°C.
In its pure state, PP is less clear than PET. Also, the gas barrier properties of PP are not as high as PET, and PP also falls below PET in stiffness. PP has about five times the moisture barrier properties of PET. But PP is about 30 times more permeable than PET to gases such as oxygen and carbon dioxide.
The production cycles of PP bottles have generally been longer than PET bottles. PP also has a narrower range of processing temperatures than PET.
But producers of PP resins and the additives that go into them are making important strides in overcoming these deficits, such as:
- Inserting clarifiers into PP enables it to match PET’s transparency. Clarified grades of PP have a clarity and gloss comparable to PET.
- Nucleators can speed up crystal formation in PP during cooling. This thereby shortens cycle times, and sometimes also improves clarity as well.
- Barrier layers (EVOH sandwich, coatings, etc.) enable PP to compete on a cost basis with both glass and PET containers in many food and beverage applications while offering good barrier properties.
The above steps make PP competitive with PET and can narrow that cost advantage considerably. But PP still comes out as the more economical packaging choice than PET for many applications.
Get a comprehensive review about PET before you make the final decision on the material of your choice »
How is nylon different from PP?
Nylon and polypropylene vary in their chemical structures. Both these polymers offer superior strength to the final parts. There are some significant distinctions you should consider when choosing any of them.
- The key benefit of PP is its low melt viscosity, and it offers strength and elasticity. Low melt viscosity enables materials to be easily used in injection molding. It also opens more opportunities and capabilities.
- While nylon is more heat-resistant and malleable than PP. It can offer designers greater design flexibility, i.e., easy bending rather than breaking.
From the end application perspective, both polymers have poor UV stability performance. They require suitable additives to mitigate UV damage risk.
Find out more about nylon, if it is more suitable for your needs »
Having reviewed how PP differs from other polymers, we will now learn its end applications.
Key market applications of polypropylene
Polypropylene is widely used in various applications. However, choosing from a wide range of options can be difficult. Each PP type offers a range of benefits, from good chemical resistance to weldability. Today, it stands at the junction between inexpensive commodity plastics and more or less performing engineering plastics.
Our Master Catalog with over 14310+ PP grades can ease your material selection with its smart comparison and sample ordering features. Some of the popular applications showcasing PP’s versatility are listed below.
Packaging industry
Good barrier properties, high strength, good surface finish, and low cost make polypropylene ideal for several packaging applications. Polypropylene performs well in blow-molded and sheet thermoformed products for food, personal care, health, medical and labware, household chemicals, and beauty aid products.
- Flexible packaging: PP films’ excellent optical clarity and low moisture-vapor transmission make them suitable for use in food packaging. Other markets include shrink-film overwrap, electronic industry films, graphic arts, disposable diaper tabs and closures, etc. PP grades are used to produce oriented, bi-oriented, and cast films and foils.
- Rigid packaging: PP is blow-molded to produce crates, bottles, and pots. PP thin-walled containers are commonly used for food packaging.
Consumer goods
PP is used in several household products and consumer goods applications, like translucent parts, housewares, furniture, appliances, luggage, toys, etc.
Automotive industry
Due to its low cost, outstanding mechanical properties, and moldability, PP is used in automotive parts. Used in battery cases and trays, bumpers, fender liners, interior trim, instrument panels, and door trims. Other features include low coefficient of linear thermal expansion, specific gravity, high chemical resistance, good weatherability, processability, and impact/stiffness balance.
Fibers and fabrics
A large volume of PP is utilized in the market segment known as fibers and fabrics. PP fiber is used in raffia/slit-film, tape, strapping, bulk continuous filament, staple fibers, spun bond, and continuous filament. PP rope and twine are very strong and moisture-resistant, making them suitable for marine uses.
Medical industry
PP is used in various medical applications due to its high chemical and bacterial resistance. The medical-grade PP exhibits good resistance to steam sterilization. Disposable syringes are the most common medical application of PP. Other uses include medical vials, diagnostic devices, petri dishes, intravenous bottles, specimen bottles, food trays, pans, pill containers, etc.
Industrial uses
PP sheets are widely used in the industrial sector to produce acid, chemical tanks, sheets, pipes, Returnable Transport Packaging (RTP), etc. This is enabled by properties, like high tensile strength, resistance to high temperatures, and corrosion resistance.
TIP: Click on the market/application name to access technical data of suitable commercial grades and request a sample of the one best suited to your needs.
- Artsan Packaging. (2023). CPP – Cast Polypropylene Films. YouTube. https://www.youtube.com/watch?v=xrNETZYtQ-k
- Find The Needle. (2022). BOPP Process. YouTube. https://www.youtube.com/watch?v=NCNK34RY18U
- (2024). Polypropylene Recycling Market: Trends, Challenges, and Opportunities for Sutainable Growth. GME Recycling
- https://www.specialchem.com/plastics/guide/polypropylene-pp-plastic?li=141279502&lr=pe181225046&utm_campaign=16820237-Newsletter%20Plastics%20%26%20elastomers&utm_medium=email&_hsenc=p2ANqtz-9l6NIl3WShP-VCVFE115nY5yzK57HbRWlb_u37ZC-T1D4piJBmp5YHFYfW7K-E7pinxbR0m6yMUYw9-aL5pvS34pUTjEYQOczKgjq1zEzayrXUjaY&_hsmi=395065613&utm_content=395065613&utm_source=hs_email