What is Polypropylene Fiber?
Polypropylene fiber is a synthetic fiber derived from the polymerization of propylene, a hydrocarbon monomer. The abbreviation for polypropylene is PP. Polypropylene fiber in many ways can be considered the ‘workhorse’ amongst synthetic fibres. Polypropylene is the third most important synthetic chemical fiber in terms of volume after polyester and polyamide, with an annual production. It is produced by polymerization from propylene and is used primarily for technical textiles (e.g. filters) and pack-aging. Despite its low cost, its key properties include its high strength, high toughness and good resistance to chemical attack.
Consequently it finds a wide range of applications – from sacking and large industrial bags to high-tech medical applications. Polypropylene as a fiber was introduced in textile arena in 1970s and now becomes the important member of the fast growing synthetic fibers family.
Polypropylene contains at least 85% propylene. Basic production entails forming a polymer of propylene gases using catalysts to produce polymer chains with few branches. This substance is filtered to remove impurities, and it is then reduced to a powdered resin. Additives are used to stabilize the resin to prevent light and heat degradation. This substance is melted and extruded, often in sheet form, and drawn out to align molecules and increase the materials strength. The sheets are then split into monofilaments (e.g. polytwine and polywrap protuft), multifilament (e.g. Fibriknit™) or staple fibers (e.g. Herculon™) depending upon the end use. Sheets can also be hole-punched and stretched to produce slits, holes or squares which are used in geotextiles. If they are extruded as fibers they are gel spun for added strength. They can also be crimped, looped or produced as flat ribbons. Of the two fibers polypropylene is preferred for textile use because it has a higher melting point.
Properties of Polypropylene Fiber
PP fiber is colorless and has smooth surface. It is circular in cross-section. The common chemicals do not damage the fibers. The most important and useful property is that it shows sustained resistance to insects and micro-organisms. In common with other synthetic fibers, the properties of PP fibers are influenced by a number of factors:
- The grade of PP used in the formation of the fiber
- Fiber-processing conditions
- The additives present
Important properties of polypropylene fiber are point out below:
- Thermoplastic but has a low melting point
- High Strength but the strength depends upon the amount of drawing after it’s extrusion
- Good Abrasion-Resistant and is, therefore, anti-pilling
- Resistant to bleaches, acids, alkalis, perspiration, mildew and insects
- Non-Absorbent at it possesses inbuilt water-repellency
- Crease-Resistant and Shrink-Resistant
- Soft when finely spun
- Excellent Stain–Resistance but still susceptible to oil and grease
- Resilient though increased strength reduces resilience
- It is not very elastic and can become stressed over time
- Oleophilic and hydrophobic
- Good Draping
- Lightweight
- Good wicking properties
PP fibers, for the most part, are highly resistant to chemical attack by acids, alkalis and most organic liquids. The fibers are swollen by some organic liquids at elevated temperatures and may even dissolve in them if the temperature is high enough. The fibers are also susceptible to the action of strong oxidants, such as hydrogen peroxide, which can reduce fiber strength and cause discoloration. In addition, PP fibers are weakened by ultra-violet radiation so that commercial PP fibers contain light stabilizers. The fibers are not degraded by micro-organisms.
Other properties of polypropylene fibers:
| Melting point (°C) | 160–165 |
| Density (g/cm) | 0.90 |
| Moisture regain (%) | 0.04 |
| Tenacity (cN/tex) | 30–80 |
| Elongation at break (%) | 15–35 |
| Abrasion resistance | High |
Besides, polypropylene is highly resistant to strong acids and alkali; oxidising acids may attack it slowly on longer exposure.
Variations of PP Fiber
Polypropylene can be processed into monofilaments, multifilament yarns, staple fibers and spunbonded nonwovens. BCF yarns are produced for carpets and film tapes for packaging.
- Monofilament – includes polytwine, polywrap, and protuft (flat).
- Multifilament – includes Fibriknit™.
- Staple – includes Herculon™.
- Crimped/Looped – can be crimped, depending upon the end use.
- Ribbon – can be produced as a flat, ribbon-like fiber.
- It can be created as a sheet with holes punched out. The sheet is then stretched to produce slits, holes, or squares used in geotextiles.
- Delustre – can be made bright
Production of Polypropylene (PP) Fiber
PP is produced by the polymerisation of propene (propylene), itself produced as a by-product in the cracking of oil and from the fractionation of natural gas. Natural gas is a mixture of individual component gases, and fractionation involves their separation and isolation.
The melt spinning processes used to produce polypropylene fibers for the production of multi and monofilament yarns, staple fibers, spun-bonded nonwovens and tapes are essentially the same as those used for other synthetic polymers. In melt spinning process, polymer chips are melted and extruded through a spinneret to form filaments. The specific properties of the material polypropylene have to be taken into account accordingly. Essential parameters of the melt spinning process, and thus important for the property profile of the fibers to be produced, are the molecular weight or melt flow index (MFI) and the molecular weight distribution of the raw material. It should be noted that PP has a relatively high molecular weight (150,000–600,000). With the same molecular weight distribution, the tensile strength of polypropylene filaments increases with increasing molecular weight. For textile applications, mainly polymers in the medium molecular weight range (MFI 230/2.16: approx. 10–25 g/10 min) are used. In the technical field for high-strength cables, polymers with higher viscosity (MFI 230/2.16: approx. 3–5 g/10 min) are selected.
The PP granulate is melted in a single or twin screw extruder. In the process, the polymer is homogenized and uniformly tempered. The melt must be free of impurities such as air bubbles and unmelted portions and fed to the spinnerets at a constant throughput rate. Important parameters of the extrusion process are temperature and viscosity of the polymer, number, diameter and length of the die holes, throughput per die hole, quenching air conditions, draw ratio, draw temperature and fixing conditions. Depending on the application, various additives are often added to the melt in order to achieve certain fiber properties. These include in particular various stabilizers.
Uses of Polypropylene Fiber
Polypropylene fiber is widely used because of its combination of low cost, lightweight, chemical resistance, and decent mechanical performance. But the use of polypropylene is limited in apparel and furnishing; bulk of the fiber produced is used for industrial applications. Filament to filament coefficient of friction of polypropylene (PP) is higher than any other textile fiber. These blend easily and very effectively with other textile fibers. These fibers are the lightest among all fibers known. All these have proved advantageous for development of PP blankets, carpets, apparel fabrics and upholstery.
Polypropylene fiber mainly is used in clothing, jackets, knitwear, coats, base layers for cold weather although it is difficult to remove body odour smells from the fabric, sportswear, sanitary wear (it is treated to make it hydrophilic) and filters. It is also used for soft furnishings, such as lightshades, curtains, seat covers and carpet backing. It is also used in the industrial world to make the following products: absorbers and barriers for oil spills, ropes, tarpaulins, webbing, car seat covers, netting, twine, brush bristles and hernia patches. Polypropylene products make up 93% of the geotextile industry.
Being environmental friendly, artificial grass lawns are made. In the apparel form, it is used as thermal underwear and lining. It is very popular in the automobile industry for making side doors, panels, armsets, interior lining etc. The wardrobe doors of PP are very popular. It is used in drainage pipes and woven/knitted tapes. As it strongly resists microorganism attacks, it is extensively used in ‘Geo-Textile’ (canal linings, soil erosion, as reinforcement in concrete – crack-preventing and road building).
Conclusion
Polypropylene fiber offers an outstanding balance of performance, versatility, and cost-effectiveness. Its lightweight, chemical-resistant, and moisture-wicking properties ensure its continued dominance across various essential sectors, making it a cornerstone of modern material science and industry. Its utility across construction, filtration, textiles, packaging, and other sectors makes it a material of continuing importance.
References
[1] Veit, D. (2023). Fibers: History, Production, Properties, Market. Springer Nature.
[2] Ashford, B. (2016). Fibers to Fabrics.
[3] Sinclair, R. (2014). Textiles and fashion: Materials, Design and Technology. Woodhead Pub Limited.
[4] Khare, A. R. (2024). Principles of spinning: Fibers and Blow Room Cotton Processing in Spinning.
[5] Jindal, A. J. R. (2023). Textile raw materials. Abhishek Publications.
