Polypropylene fiber, also known as polypropene or PP, is a synthetic fiber, transformed from 85% propylene, and used in a variety of applications. It is used in many different industries, but one of the most popular is the manufacturing of carpet yarns. For example, most of the economical carpets for light domestic use are made from this fiber. The fiber is thermoplastic, resilient, light weight and resistant to mildew and many different chemicals.
What is Polypropylene?
Polypropylene (PP) is the first stereoregular polymer to have reached industrial importance. It is a thermoplastic, meaning that it becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Polypropylene is processed into film for packaging and into fibres for carpets and clothing.
PP belongs to the group of polyolefins and is partially crystalline and non-polar. It has similar properties as polyethylene, but it is harder and more heat resistant. It is a white rugged material with a high chemical resistance. Poly propylene is the second-most widely produced commodity plastic (after polyethylene) and it is often used for product packaging and labeling.
Polypropylene is manufactured from propylene gas in presence of a catalyst such as titanium chloride. Polypropylene is a by-product of petroleum. You can find some more scientific info here.
PP has the following properties:
- low physical properties
- low heat resistance
- excellent chemical resistance
- translucent to opaque
- low price
- easy to process
Polypropylene chips can be converted to fiber/filament by traditional melt spinning process.
The first fibres from polypropylene were introduced to the textile industry in the 1970s and have become an important member on the synthetic fibres market.
Polypropylene fiber displays good heat insulating properties and is highly resistant to acids, alkalies, and organic solvents. The fiber is sensitive to heat and light, but the resistance to these agents can be influenced by added stabilizers. Filaments and monofilaments are used in the manufacture of cables, nets, filter fabrics and upholstery. In staple form, the fiber is used in carpeting, blankets, outerwear fabrics, knitwear, and filter fabrics. Textured polypropylene fiber is mostly used for carpet manufacturing.
Growth in demand of PP is very high, and it is mainly due to its distinct technical features:
- light weight
- has low thermal conductivity etc.
Because of all this, it is widely used to make undergarments, jackets for outerwear, swimming suits, filters, bags and diapers.
Properties of Polypropylene Fiber
Fiber Structure and Characteristics
PP fibers are composed of crystalline and non-crystalline regions. Each crystal is surrounded by non-crystalline material. Fiber spinning and drawing may influence the orientation of both crystalline and amorphous regions.
The degree of crystallinity of polypropylene fiber is between 50-65% in general, depending on the processing conditions. Crystallization occurs between glass transition temperature and the equilibrium melting point of PP. The crystallization rate is faster at low temperatures.
In general, polypropylene fiber has excellent chemical resistance to acids and alkalis, high abrasion resistance and resistance to insects and pests. PP fiber is also easy to process and inexpensive compared to other synthetic fibers. It also has low moisture absorption.
Some of the main PP fiber characteristics:
- gives good bulk and cover
- resistant to abrasion, deterioriation from chemicals, mildew, perspiration, rot, stain, soil and weather conditions
- resistant to bacteria and micro-organisms
- quick drying
- anti-static behavior
- thermally bondable
- dry hand
- comfortable and lightweight
Because of its low specific gravity, polypropylene yields the greatest volume of fibre for a given weight. This high yield means that polypropylene fibre provides good bulk and cover, while being lighter in weight. Polypropylene is the lightest of all fibers (for example, it is 34% lighter than polyester and 20% lighter than nylon), even lighter than water.
Polypropylene fibers are produced in a variety of types with different tenacities in order to suit varying market requirements. Fibers for general textile uses have tenacities in the range of 4.5-6.0 g/den. High tenacity yarns up to 9.0 g/den are produced for the use in ropes, nets and other similar products. High performance PP fibers have been made with high strength and high modulus.
The techniques include ultra-drawing, solid state extrusion and crystal surface growth. It is possible to make the filaments with tenacities over 13.0 g/den.
Table of Mechanical Properties of PP Fibres
|Tensile strength (gf/den)||3.5 to 5.5|
|Elongation (%)||40 to 100|
|Moisture absorption (%)||0 to 0.05|
|Softening point (ºC)||140|
|Melting point (ºC)||165|
|Chemical resistance||generally excellent|
|Thermal conductivity||6.0 (with air as 1.0)|
|Resistance to mildew and moth||excellent|
The degree of orientation achieved by drawing has influence on the mechanical properties of polypropylene filaments. The higher the degree of stretch, the higher the tensile strength and the lower the elongation. Commercial monofilaments have an elongation at break in the region of 12-25%. Multifilaments and staple fibers are in the range of 20-30% and 20-35%.
Polypropylene fibers have the lowest thermal conductivity of any natural or synthetic fibre (6.0 compared to 7.3 for wool, 11.2 for viscose and 17.5 for cotton). PP fibres retain more heat for a longer period of time, have excellent insulative properties in apparel, and, combined with its hydrophobic nature, keep wearer dry and warm.
Polypropylene fibers have a softening point around 150°C and a melting point at 160-170°C. At low temperatures of -70°C or lower, PP fibers keep their excellent flexibility. At high temperature (but below 120°C), PP fibers nearly keep all of their normal mechanical properties. PP fibers have the lowest thermal conductivity of all commercial fibers, and in this respect they are the warmest fibers of all, even warmer than wool.
When it comes to the effect of extreme cold, they remain flexible at temperatures in the region of -55°C.
The dyeability of fibers is controlled by both their chemical and physical properties. Fibers that have polar functional groups in their molecular repeat units can more easily be dyed. These polar groups may serve as active sites for combination with dye molecules by chemical bonds.
Since polypropylene molecular chains have no polar functional groups (active sites for chemical bonds or dyesites) and relatively high crystallinity (50-65%), dye molecules cannot be chemically attracted to the fibers. The dye molecules cannot even be strongly adsorbed by the fiber surfaces because of their hydrophobic properties.
Because of these reasons, making PP dyeable has remained a very important challenge to polymer and textile chemists for many decades. Approaches to dye polypropylene using polyblends, copolymers, plasma treatment, and specially designed dyes have been all thoroughly explored.
Current technology for the manufacturing of dyeable polypropylene relies mainly on polyblending, copolymerization, and grafting technologies. Dyeable PP can be produced via nanotechnology. In the modern industry, polypropylene fibre can be dope-dyed (spun-dyed) by the manufacturer in virtually unlimited color choices.
How Is Polypropylene Fiber Made?
Polypropylene chips can be converted to fiber/filament by standard melt spinning process, though the operating parameters can be adjusted depending on the final products.
The production of polypropylene fiber varies among the manufacturers. The manufacturing process differs, so that desirous properties can be achieved including dyeability, light stability, heat sensitivity etc.
The basic production procedure includes polymerizing propylene gas with the help of a metal compound like titanium chloride. The polymer formed from propylene is slurried in the diluent to decompose the catalyst, then it is filtered, purified and finally reduced to polypropylene resin.
The resin so formed is melted and extruded through a spinneret in a filament form. These filaments are then treated in order to get the desired properties.
Main phases of the production process:
- Metering: One or more spinning gear pumps receives the molten polymer and sends it through the spinning pack to homogenize the product, feed the spinning pack at a constant rate, and prevent fluctuation due to screw extruder. Polymer, in the form of pellets or granules, is fed into an extruder, where it is melted and pumped via a positive displacement pump to the melt spin pack.
- Spinning: The spin pack consists of filters and channels that supply molten polymer to a multifilament spinneret. The distributor distributes the molten polymer over to die surface. The diameter of the die varies from 0.5 to 1.5 mm, depending on the denier required.
- Quenching: Newly extruded molten filaments that exit the spinneret are cooled, usually by cool air, without damaging the filaments, and solidified. The cooling zone can be as simple as a region in which quenching air is blown across the filaments, or it may be an elaborate chamber constructed so the cooling environment can be strictly controlled.
- Finishing: In order to improve antistatic and reduce abrasion.
- Hot Stretching: Process of enhancement of the physico-mechanical properties.
- Crimping: Improving the bulk.
- Thermosetting: Treatment in hot air or steam that removes the internal stresses and relaxes fibers. The resultant fibers are heat-set with increased denier.
- Cutting: The fibers are cut into 20 to 120 mm length, depending on whether they are intended for cotton or woolen system.
How Is Polypropylene Fibre Used?
Polypropylene fibre can be used in a wide range of applications. These are only some examples:
- automotive industry
- fiber, filament, film, pipes
- upholstery fabrics and bed covers
- toys, bottle caps, disposables
- technical filters
- woven bags
- ropes and twins
- construction fabrics
- absorbent products (diapers)
- furniture industry
Because of its superior performance characteristics and comparatively low-cost, PP fiber finds extensive use in the nonwovens industry, and it dominates in many nonwoven markets. The main application areas include: nonwoven fabrics, absorbent product coverstock markets, home furnishings and automotive markets.
Textile Applications of Polypropylene Fibers
Textile flooring was the first and largest scope of the polypropylene fibre usage: The high abrasion resistance, the non-absorption of dirt, liquids and stains, the ease of washing, the color resistance and the absence of fire spread made it preferred even to natural fibres.
This application of polypropylene has been extended to outdoor carpets, highly stabilized to radiation and heat: golf and tennis courts, edges of swimming pools and car interiors. In the later years, a method was developed for the production of yarns with thin count, making it possible to compose a fabric that was particularly suitable for sports knitwear, where the positive factor was the non-absorption of sweat and its transport outside, thus leaving the body dry.
The polypropylene underwear and sportswear shows excellent thermal insulation, great abrasion resistance, transfer of sweat from the body to the adjacent absorbent fabric (cotton, for example) etc.
Some of the main uses of polypropylene fibres in the textile industry are:
- Food labels and packaging
Polypropylene Staple Fiber
Polypropylene staple fiber is used in the manufacture of needle carpets, sanitary and household articles, etc. Some of the main applications include: nonwoven fabrics, absorbent product markets (diapers), home furnishings and automotive industry. It is also used for woven carpets, non woven carpets, upholstery, spinning yarns, filer fabrics, thermal bonded fabrics, insulations, felts, building constructions…
Polypropylene BCF Yarn
PP BCF yarn is used in textile floor industry and the production of packaging fabrics (big bags) and trimmings. We produce BCF with a wide range of decitex and color palettes, with our without UV stabilizer, as per customer requirement.
Polypropylene CF Yarn
PP CF yarn is used in rope industry and trimmings.
Continuous Multifilament Yarns (CF Yarns) have medium tenacity. They are suitable for weaving, knitting and a wide range of applications. Some of them include: mattress ticking, upholstery, window blinds, performance clothing, fashion textiles and variuous technical applications.
Polypropylene Fiber Reinforced Concrete
Although concrete offers many advantages when it comes to mechanical characteristics and economic aspects of the construction, the brittle behavior of the material remains a large handicap for the seismic and other applications where flexible behavior is essentially required. However, the development of polypropylene fiber-reinforced concrete (PFRC) has provided a technical basis for improving these deficiencies.
Lately, the use of PP fibers has increased greatly in construction of structures, because the addition of fibers in concrete improves the toughness, flexural strength, tensile strength and impact strength, as well as failure mode of concrete. Polypropylene twine is cheap, abundantly available, and like all manmade fibers of a consistent quality. (More technical info can be found here.)
Frequently Asked Questions about PP Fiber
1. Q: How Much Does Polypropylene Fabric Cost?
A: Since polypropylene is one of the most widely produced types of plastic, it is generally quite inexpensive in bulk. A large number of factories compete with each other for their place on the world’s plastics market, and this competition drives prices low.
However, the polypropylene fabric may be relatively expensive, but that mostly depends on the end use. For example, the polypropylene fabric that is designed to be made into apparel has higher cost than the PP fabric for other uses, which generally has relatively low prices.
2. Q: Polyester vs Polypropilene: Main Points of Difference
A: Both polypropylene (PP) and polyester (PES) are the two major fibres mainly used in traditional spinning and weaving, nonwovens industry, yarns and composites. Both fibres are available as virgin and bottle grade (from regenerated material). Virgin fibre is used for apparel purposes and regenerated fibre is used in nonwovens for making carpets, floor coverings, blankets and filters.
- PES is available in higher tenacity grades compared to polypropylene, which is suitable for industrial fabrics with higher stipulated strength.
- Polypropylene is not normally used for sewing threads because of its low melting point.
- Elongation is much higher in PP. This gives better elasticity for material and improved moulding.
- Density of polypropylene (0.91g/cc) is much lower than that of polyester (1.38 g/cc). As a result, Diameter of polypropylene fibre is proportionately higher than polyester fibre of the same denier. Polypropylene is dope dyed and is available in an extensive range of colors and shades. On the other hand, dope dyed polyester is available only in a limited number of colors.
- Melting point of polypropylene (165 C) is much lower than that of polyester (260 C). Material made from this fibre is therefore not suitable in fire fighting and similar clothing where temperatures are high.
- Resistance to UV light is inferior with PP compared to PES, but an UV stabilizer can be added during the manufacturing process.
- PP is highly inert to chemicals and is suitable as fishing nets and geotextiles in alkaline and acidic soils.
3. Q: What Different Types of Polypropylene Fabric Are There?
A: There are many different additives that can be added to polypropylene in its liquid state to alter the attributes of the material. In addition, there are two major types of this plastic:
- Homopolymer polypropylene: Polypro plastic is considered to be homopolymer when it is in its original state without any additives. This type of polypro plastic is not generally considered to be a good material for fabric.
- Copolymer polypropylene: Most types of polypropylene fabrics are copolymer. This type of polypro plastic is further split into block copolymer polypropylene and random copolymer polypropylene. The co-monomer units in the block form of this plastic are arranged in regular square patterns, but the co-monomer units in the random form are arranged in relatively random patterns. Either block or random polypropylene is suited for fabric applications, but block polypro plastic is more commonly used.
4. Q: Is polypropylene toxic to humans?
A: Poly propilene is one of the few types of plastic that are approved for use in food and pharmaceutical industries because they are considered to be mostly harmless to human health. In many studies, polypropylene is considered to be among the safest types of all plastics. It is robust and heat resistant, so it is unlikely to leach even when exposed to warm or hot water.
Why You Should Use Polypropylene Fiber – Main Advantages and Disadvantages
Although polypropylene fibers have some drawbacks, mainly the low melting temperature which prevents PP from being ironed like cotton, wool or nylons, limited texturizability, poor adhesion to glues and latex etc., there are many benefits of PP fibers.
Because of its specific characteristics, it is perfect for some kinds of industries (manufacturing of carpet yarns and absorbent products, for example). The fiber is thermoplastic, resilient, light weight and resistant to mildew and many different chemicals.
These are only some of the advantages that you should consider:
- PP is a light fiber: its density (.91 gm/cm³) is the lowest of all synthetic fibers.
- It does not absorb moisture. This means the wet and dry polypropylene fibre properties are identical. Low moisture regain is not considered a disadvantage because it helps in quick transport of moisture as is required in special applications like babies’ ever-dry diapers.
- It has excellent chemical resistance. PP fibres are very resistant to most acids and alkalis.
- The thermal conductivity of PP fibre is lower than that of other fibres and may be used in applications as thermal wear.
To conclude: polypropylene fabric is a nonwoven textile, which means that it is made directly from a material without any need for spinning of weaving. The main benefit of PP as a fabric is its moisture transfer abilities; this textile cannot absorb any moisture, and moisture passes through PP fabric entirely. This attribute allows moisture that is exuded while wearing a polypropylene garment to evaporate much more quickly than it would with a moisture-retaining garment. Therefore, this fabric is popular in textiles that are worn close to the skin.
Also, keep in mind that polypropylene fabric is one of the lightest synthetic fibers in existence and it is incredibly resistant to most acids and alkalis. In addition, the thermal conductivity of this substance is lower than that of most synthetic fibers, which means that it is ideally suited for cold weather wear.
Furthermore, this fabric is highly resistant to abrasion, and it also resists insects and other pests. Due to its notable thermoplastic qualities, it’s easy to mold polypro plastic into various shapes and forms, and it can be reformed through melting.
All of these features make it ideal for some specific industries and uses. If yours is one of those or if you have any questions or concerns, please do not hesitate to contact us.