All About Polypropylene (PP): Production, Price, Market & its Properties
What is Polypropylene (PP)?
Polypropylene (PP) also termed as “polypropene” is thermoplastics in nature. It is a linear hydrocarbon polymer expressed as (CnH2n). PP polymer is one of the most versatile polymers and is used as both plastic and as fiber.
The polymer has tough characteristics like it is mechanically rugged and resistant to many chemical solvents like bases and acids. This makes polypropylene plastic ideal for various end-use industries. The main application of PP plastic is in packaging and labeling, textiles, plastic parts and reusable containers of various types.
The PP plastic is also preferred by manufactures for molding household goods, automotive products, marine and RV products. It is also safe to use PP plastics as a food container because it avoids leaching of chemicals into food products.
The polymer can be used in different processing technologies such as Injection Molding, Blow Molding, sheet extrusion and thermoforming.
Polypropylene Resin Price and Trends
PP resin is made from propylene and propylene is the second most produced building block in the petrochemical industry. The price of propylene is susceptible to the pricing of the petrochemical industry. The trends that effect petrochemical industry pricing are the growth of economies around the world along with discoveries on new oil & gas fields.
Propylene is produced by ethylene steam crackers. The propylene is co-product of steam cracking and the quantity produced depends on the nature of feedstock. If the feedstock is light like ethane then very less propylene is produced but when the feedstock becomes heavier to propane to butane and then naphtha the quantity of propylene co-produce is more.
Now the United States has seen low-cost ethane since 2008, as a result, there a shift in propylene production. The two major shifts are:
- The existing crackers are now are working with a very light feedstock which in turn leaves with lesser and lesser propylene production.
- As therein increase in availability of lightweight feedstock the production of steam cracker designed to crack only lightweight feedstock producing less propylene.
The availability of low-cost ethane along with the production of ethylene steam cracker with the only cracking ability of lightweight feedstock has reduced the production of propylene. These factors are impacting the pricing of PP resin.
But as and when the oil price decline sharply the advantage of cracking low weight feedstock diminish and cracking trend shift towards heavier feedstock. This leads to more production of propylene which in times lowers the prices of pp resin.
History of PP Polymer
The history of PP polymer is very interesting. In 1951 two researchers from Phillips Petroleum Company, J. Paul Hogan, and Robert L. Banks while working to convert propylene to gaseous form discovered this polymer. Later it was polymerized by two German scientists Giulio Natta and Karl Rehn. Natta used Ziegler-Natta catalyst during the polymerization process.
With ideal properties for molding, this plastic is now days used from household hoods to make the medical device.
Production Process & Technology Used for PP Polymer
How is PP Polymer made?
PP polymer is a made polymerization of monomer propylene with the help of the catalyst. Propylene is the base monomer and is gaseous at room temperature which is used for PP production.
There are many commercial technologies that are used for making pp polymer. Depending upon the technology the pp polymer produced has a unique set of properties. All the technology has similar basic steps. Steps in production of PP polymer
- First, the feedstock material and additives must be purified. The catalyst material should be prepared. The feedstock that is used is propylene.
- Then the polymerization takes place either in the gas phase with fluidized bed / stirred reactor or a liquid phase in with slurry/solution
- After that, the polymer particles are separated from existing monomers and diluents. The monomer and diluents are recovered and fed again in the process.
What Technology is used to manufacture the Polymer?
The two main commercial technology used in production PP resin is UNIPOL PP Technology and LyondellBasell Spheripol Technology.
The UNIPOL PP technology is gas phase technology with lesser moving part and equipment. It is supposed to be less complex with simple processes leading to lower CapEx cost with lower operating cost. Being simple in design has low maintenance cost also.
The LyondellBasell Spheripol Technology the process is based on high specificity controlled morphology catalyst and is highly efficient along with less polluting. This technology is more common globally and has a market share of around 39% in producing PP resin.
The Unipol PP technology accounted for 16% share for production of the polymer. The other technologies used in production are Novolen (11%), Innovene PP (7%), Hypol (4%), Borstar PP (3%), Chisso (3%), Sumitomo (3%) and others.
World Production and Market Forecast of PP Resin
Production of PP Resin
The production of pp resin has been growing year on year basis. The growing demand from end-segment has led to expansion and new capacity being added regularly.
China remains the leading producer of PP polymer. The global production of PP was around 73.7 million tons in 2016. China produced 20.2 million tons with a share of 27% in the total global production. New capacities have been added in China. Since 2008 to 2016, China has increased its global market share of producing PP by 11%. It accounts for 16% of world’s total production in 2008.
The Asia region produced 18.7 million tons excluding China with a share of 25% in the entire production. The other region was Europe 11 million tons, North America 8.6 million tons, the Middle East 7.6 million tons etc.
Production of the PP resin is dominated by few players globally. Lyondell Basell is the world largest pp manufacturer in 2016. It produced around 6.5 million tons of the resin. The second largest pp manufacturer was Sinopec Group with the production of 6.4 million tons followed by PetroChina Group (4.6 million tons), Braskem Group (4 million tons) and others. The top 10 producers account for almost 55% of the total production of pp globally.
Market forecast of PP Resin
The market is forecasted to grow more than US$ 110 bn by 2020. The market was around 56 million tons in 2016 and will cross 75 million tons by 2022 as per industry. The polymer has many advantageous properties which make it preferred polymer for the end segment industries such as packaging, automotive, consumer goods, electrical & electronics etc.
The packaging industry occupied the largest share of PP plastics in 2016. The market driver in the coming year will be the packaging industry and automotive industry because of light-weighting of the vehicle. The PP polymer finds it increasing use in packaging industry because of its twist retention property and toughness. Besides this, it does not contain Bisphenol A (BPA) so makes a good option for food and drink packaging.
The demands of PP plastic products are increasing but volatility in the price of the pp resin is inhibiting the growth of the market. The growing environmental issues and availability of feedstock are putting pressure on manufacturers to explore bio-based pp polymer.
Properties of PP Resin
PP is tough and very robust plastics. The properties of this polymer depend on the molecular weight and distribution of monomer. PP resin characteristics can be classified into Physical, Chemical, Mechanical and Thermal aspects on the basis of their varied properties.
PP resin does not face stress- cracking problems as they have good heat resistant. It offers other physical properties which expand their usage segments such as they are translucent, have good fatigue resistance and are tough along with being semi-rigid. They have excellent aesthetic properties so are used in a lot in automotive sectors where shine and gloss are required on parts such as the bumper.
PP resin is resistant to acid, bases, water or detergents. PP plastics can be a good choice for containers because of it being resistant to acid and bases. They have low density, high softening point and offer higher rigidity and hardness. At room temperature, it is resistant to organic solvents.
Polypropylene density remains between 0.895 g/ cm3 for amorphous and 0.92 g/ cm3 crystalline. However, this density may change with fillers. It is usually found tough and flexible and primarily when copolymerized with ethylene. It is reasonably economical and has good resistance to fatigue.
The PP plastics because of its properties are easy to weld using thermoplastic welding equipment. This leads to its use fabricating storage tanks for chemical, water, and other liquid materials.
Polypropylene melting point is 160°C. The range of commercial pp varies from 160 to 166°C depending on the PP material and its crystallinity.It offers large thermal expansion but still, it’s less than that of polyethylene.
What are different Polypropylene Grades?
Three types of PP grade are available. Choice of the grade for an application depends on following points:
- Homopolymer: This grade is considered as general grade and can be used for a variety of general purpose. It is stronger and stiffer than copolymer with high distortion temperature (HDT).They are durable, rigid plastics available in translucent white color and other colors.
- Block Copolymer: They are tougher and durable than homopolymer. Their composition consists of 5% to 15% of ethylene with enhanced impact resistance.
- Random Copolymer: Random copolymer chemical composition consists of 1% &% of ethylene. They have better flexibility; lower melting points and their structure consist of co-monomer units arranged randomly across pp molecule chain.
How is Polypropylene (PP) vs Polyethylene (PE) different?
PP is different from polyethylene in the following ways:
- It can be used as plastics and fiber both.
- The polymer higher melting point than polyethylene
- And it is less stable than polyethylene
- It has better fatigue resistance than PE and is used as hinges.
- PE has less static charge so attract less dust than PP
How is Polypropylene Molding done?
Plastic molding is a technique used for shaping the plastics using rigid frames and molds. The molding is commonly used for manufacturing car parts, containers, signs and other high volume items. Plastic molding involves filling liquid polymer in the hollow mold so that it can take its shape. This process involves a high range of pressure and immense heat. There are different techniques used in plastic molding including Injection molding, blow molding, rotational molding, and compression molding.
For processing of the polymer, the melt flow rate is an important determinant. Melt Flow Rate (MFR) or Melt Flow Index (MFI) defines the molecular weight of the PP. It is an indicator of how easily the molten polymer will flow during the molding process. It has high melt flow rate. With high MFR the filling of the mold is done easily.
Two commonly used techniques in PP molding are- PP Injection Molding and PP Blow Molding.
Polypropylene Injection Molding
Injection molding is a process where materials are injected into molds to produce parts. PP polymer use in plastic injection molding is increasing because of favorable properties.
PP injection molding is used in various industries to manufacture goods for different segments because of its basic properties like good chemical and moisture resistance, flexibility in molding and is economical.
When the PP resin has moderate flow rate injection molding process is used a wide range of products such as medical products, construction products, consumer products (containers, sporting goods, toys etc.) and in hardware.
Polypropylene Blow Molding
Blow molding technique is used for the production of large quantities of hollow objects of plastics. Primarily Plastics blow molding technique is used for manufacturing plastic bottles, jars, and containers (both narrow and wide-mouthed containers).
PP Blow Molding technique is commonly used for huge containers, plastic bottles etc. PP material is used in blow molding technique due to its properties which offer ease in manufacturing process such as good moisture barrier, chemical resistance, and stability at high temperatures (up to 200° F)
In blow molding process the preferred characteristics of PP resin are high molecular weight and low flow grades.
PP Blow Molding Technique is applicable for various products made up of PP material such as food containers, plastic bottles, milk jugs, Ice chests and on large-scale PP Blow molding is used for duct work, water tanks, fuel tanks, recycle bins and overflow bottles.
What is Polypropylene Uses?
The PP polymer can be processed by extrusion blow molding, injection molding, and general purpose extrusion. Expanded PP (EPP) may be molded in a specialist process. Properties of polymer make them applicable to a variety of end-use segments of the plastic market. Some of the prominent segments making use of PP plastics are:
PP material is leading in film extrusion market. The film market can be divided into three major sectors-Food and confectioneries, clothing and tobacco. It is used in films which are widely used in flexible packaging for products being manufactured under these categories.
It is used in rigid packaging in different forms such as in reusable crates which provide ease of transport, safe and efficient storage of products. PP material is used in the manufacturing of caps and closures which pamper the growth of Pet bottle market. PP is also blow molded for producing bottles used for packaging products like detergents and toiletries etc.
Polypropylene Sheet & Tubing
It has a good chemical resistance. PP plastics can be easily welded and machined. It possesses a good strength to weight ratio and due to its hard, high gloss surface, polypropylene tubing is ideally suited to environments where there is a concern for bacteria build up that can interfere with flow. PP sheets can be heat formed, shaped and welded to fabricate ducts, hoods and much more. The sheets have excellent corrosion resistance to a wide range of items. It cannot be cemented but is easily welded with a plastic welder.
The polymer is not UV stabilized but is USDA approved and meets FDA standards makes it preferred polymer. The pp polymer has a 0.9 density, rigid with fair impact resistance and very good abrasion resistance.
PP material is prominently used for sheet and tubing purpose due to it suitable properties for sheets and tubes.
In the automotive sector, PP plastics are used for automotive interiors as it provides low coefficient for linear thermal expansion and specific gravity, high chemical resistance, and stiffness. PP material is commonly used for dashboard, bumper, cladding and cushioning in vehicles.
PP plastics are produced in various consumer end-use segments like households, furniture, appliances, Luggage, Toys, Battery cases and other durables used for leisure purpose. Injection Molding is used in manufacturing process of PP material for rigid packaging.
The polymer material is resistant to corrosion and chemical leaching which protects from physical damage so they are also used in the manufacturing of sheet, pipe. Compounding and returnable transport packaging also use pp material. Injection molding again dominates the conversion process of PP in the industrial sector.
Clothing, Fiber & Fabrics
It is also used on large scale for clothing. PP material is majorly used in nonwovens, having maximum utilization in diapers and sanitary products as it is treated to absorb water instead of repelling. PP is used in warm weather clothing, jewelry, and some other wearable accessories
PP fiber is used in manufacturing tape, staple fibers, spun bound, strapping and filaments. The polymer finds vast application in textile industry. Polypropylene fabric is used where it is required that a material provides stain resistance, durability, and high abrasion resistance.
PP is commonly used in medical for organ prolapsed repairs, in operations and surgeries such as used in a hernia. The main uses of PP polymer are as suture and mesh in the medical industry.
Polypropylene Suture and its Uses
PP material finds its high use in the medical suture. PP suture is used for skin closure for human and veterinary purposes.
The properties of PP Suture are:
- The pp suture are synthetic and non-absorbable
- They have uniform diameter with high tensile strength
- Smooth texture with high plasticity
- They are less reactive, durable and long lasting
- The suture is sterile and hinder bacterial growth
Polypropylene Mesh and its Uses
The polymer is also used as a mesh. The PP mesh is used for the surgical purpose.
The properties of PP Mesh are:
- The mesh is very strong with uniform strength
- They are very smooth with less friction so provide excellent use in laparoscopic placement of mesh on the required spot.
- The pp mesh is sterile and does not provide bacterial growth.
- They have a thin thickness with less mesh so provide less discomfort to the patient than other material. Also, leave a minimal scar on the wound.
Advantages and Disadvantages of PP Material
It offers a wide range of uses in various sectors comprising of both manufacturing and end-user consumer products.
Advantages of PP Polymer
- PP material is easily available and is inexpensive.
- Their semi-crystalline nature offers high flexural strength.
- It has good chemical resistance for different bases and acids and is also very resistant to absorbing moisture.
- It is a good electric insulator along with good fatigue resistance which is required for manufacturing of various products.
- They have good impact resistance with strong resistance to fatigue
- The polymer is also tough and heat resistant
- On processing, they tend to be smooth with excellent aesthetic properties
- They have a high melting point which makes the vastly used for microwave food containers.
Disadvantages of PP Polymer
- High thermal expansion coefficient limits the high-temperature applications of PP material.
- PP is highly flammable and is difficult to paint as it has poor bonding properties.
- They are prone to oxidation and UV degradation.
- PP polymer has poor resistance to chlorinated solvents and aromatics which affect the usage of pp in manufacturing processes.
Is Polypropylene Safe to Use?
The pp plastics is generally considered safer than most their other counterparts plastic material. They do not leach harmful chemical when used as food containers. The PP plastics are flexible, tough, heat resistant and provide a barrier to moisture. These properties along with microwave-safe make them an obvious choice as food containers.
They are used as a plastic cup, baby bottles, food containers and other kitchenware items. As material identification to the consumer, the products are marked as “PP”
Recycling and Sustainability of PP Polymer
PP polymer identification code is “5” for recycling. The PP polymer has the ability to be recycled many times. After, continuous recycling the polymer the PP plastic gets thermally degraded. As it is thermally degraded so its bonding becomes weak because of which it needs to be disposed of by other means.
Recycling of PP polymer is very high because there is a market for various recycling products. In the United States, almost 95% battery is made of PP polymer are recycled.
PP consumes less energy and produces less solid waste than other plastics. During its production process, less carbon dioxide is produced therefore making these plastics more environmentally friendly than others.