Metallocene Polypropylene | Advantages of Metallocene Polypropylene | Metallocene Based Polypropylene Nonwoven | Application of Metallocene Polypropylene

In past decades, the use of polypropylene, has dominated in the production of melt blown and spunbonded nonwovens. The main reasons for the growing use of PP in polymer-laid nonwovens are that the raw materials are relatively inexpensive and available throughout the world, and PP resins can offer a relatively attractive cost combined with good value and ease of use when compared to conventional resins, such as polyester and polyamides. Continuing advances in PP fiber grade resins are strengthening the olefins price / properties ratio, which make them more suitable for polymer-laid nonwovens applications.

Polypropylene resins have been produced from Ziegler-Natta catalysts for over 30 years. The drive for technology evolution has been the industry's desire to continuously improve control of the molecular architecture that leads to improved polymer performance.

In 1990's, the introduction of single site catalyst for making superior polyolefin resins set another technological trend, marked with Metallocene Catalysts having a precise control over molecular architecture for highly tailored polymers; improved processing; and properties for all polyolefins. This technology has been developed and designed for nonwoven applications [1]. The manufacturer may be able to take properties and very low extractables. Advantage of the higher barrier properties is to reduce basis weight or increase line speed. Because this material is so clean, the nonwoven manufacturer may be able to extend the intervals between die changes and process clean-ups. The absence of peroxide in this product leads to reduced viscosity variations and more consistent extrusion performance. Reduced process air rates are possible with this material, which can reduce energy costs. Due to these advantages, this innovative new melt blown material is expected to gain rapid acceptance in the nonwovens industry.

2. Advantages of Metallocene Polypropylene (PP)
Metallocene catalysts offer unique advantages versus conventional catalysts. They allow producing consistent, controllable molecular structures that can be designed to:
  • Improve toughness
  • Provide excellent impact resistance
  • Reduce haze
  • Provide excellent organoleptics (low off-taste and odor)
  • Allow tailoring of processing characteristics to fit the conversion process
  • It allows control the molecular structure of polyolefines.
  • It enables to virtually eliminate non-targeted molecular weight species in resins
  • It allows incorporation of co-monomers and ter-monomers with precision.
  • It offers a greater control of molecular weight distribution (MWD).
  • It leaves a small amount of catalyst residue in the finished product.
2.1 Specialty of metallocene catalyst
In PP manufacturing, the monomers are reacted using a catalyst. All catalysts have reactive sites enabling them to perform their function, i.e. linking individual molecules of monomers to form a polymeric chain. Conventional catalysts have many reactive sites located randomly on the surface of the catalysts. This produces different and varying polymers (See fig-1 below). The new catalyst system, which is known as single site catalyst, also has many reactive sites, but all sites are identical. This in turn gives identical polymers and does away variability of polymers.
Fig. 1: Comparison of two types of catalysts [2]
3. Metallocene based PP Nonwowens
Metallocene based PP resins for nonwovens and fiber applications can help to produce polymers with very low catalyst residues and very high purity. The polymer modification process, called controlled rheology, enables us to tailor the resin for the specific need of nonwovens applications. Advantages of the fiber grade metallocene based PP resin in spunbonding and melt blowing over the conventional resin:
  • It produces finer denier fibers than conventional resins.
  • The optimum bonding temperatures are lower because of the lower melting point
  • Excellent spinning continuity or fewer breaks in spinning.
  • Spinning can be carried out at higher draw force.
  • Substantial reduction in volatile deposits.
  • Available in broader MFR range, especially helpful for melt blowing.
  • Key features of Metallocene Polymers
The primary feature that makes metallocene-catalyzed polymers preferable to conventional polymers is structural uniformity, which eliminates very low and high molecular weight polymer components present with conventional catalysts (Fig.2).
Table -1 Comparison of Metallocene PP with Conventional PP

Product Attribute
Conventional PP
Melting Point (°C)
Flexural Modulus (MPa)
MWD (Mw/Mn)
3.5 / (2.8) *
Recoverable Compliance
3.5 / (0.9) *

Fig. 3: Thermo mechanical analysis (TMA) of filaments from different PP [4]
Fig. 4: Tensile strength comparison of filaments from different PP [4]
4. Applications
Presently, the metallocene based polyolefin polymers are produced by many companies in the world, but among those, BASF, Germany, and ExxonMobile Chemical Co., USA are the main producers of metallocene based PP. Exxon began development of Escorene Polypropylene grades used for nonwovens in 1960, and introduced AchieveTM propylene polymers based on Exxpol catalyst technology in 1995. This brought in overall property improvements versus conventional polypropylene yielding finer and stronger fibers at a lower production cost. 

Applications of Metallocene Polypropylene:
  • Hygiene: diapers, disposals
  • Medical: operation gowns and covers
  • Filtration: air purification systems
  • Household: mattress covers, upholstery, disposable products
  • Wipes: wet wipes.
  • Geotextiles
  1. D. Permentier, C.Y. Cheng and G.A. Stahl, 'Metallocene Based Propylene Polymer for Nonwoven Applications', Index 96 Congress Presentations, February 13-16, 1996.
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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