What is Metallocene Polypropylene (mPP) Fiber? Metallocene polypropylene (mPP) fibers modified with copolyamide consisting of 85 wt.% of ε-Caprolactam and 15 wt.% of nylon salt of adipic acid and diethylenetriamine, and isotactic polypropylene grafted with maleineanhydride were prepared and their mechanical properties were evaluated. Blended mPP fibers containing only 4, 8 and 12 wt.% of copolyamide without compatibilizer were not spinnable.
The higher mechanical properties of polypropylene (PP) fibers based on metallocene-catalyzed PP (miPP) in comparison with fibers based on Ziegler Natta-catalyzed PP (zniPP) were presented in periodic literature in the last decade. In comparison with the Ziegler–Natta-catalyzed polypropylene (PP), metallocene polypropylenes are uniform polymers with precisely controlled Mw, end groups, stereoregularity, and narrow PDI. Those characters make metallocene-based iPP a great candidate for producing high-quality industrial fibers by melt spinning.
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. 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.
Advantages of Metallocene Polypropylene (mPP): 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.
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. 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.
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.
Fig: Metallocene based Polypropylene Nonwovens
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.
Table: Comparison of Metallocene PP with Conventional PP
Product Attribute
Metallocene
Conventional PP
Melting Point (°C)
148
162
Flexural Modulus (MPa)
1380
1360
MWD (Mw/Mn)
2.0
3.5 / (2.8) *
Recoverable Compliance
0.4
3.5 / (0.9) *
Applications of Metallocene Polypropylene: 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.
Common applications of metallocene polypropylene fibers are given below:
D. Permentier, C.Y. Cheng and G.A. Stahl, ‘Metallocene Based Propylene Polymer for Nonwoven Applications’, Index 96 Congress Presentations, February 13-16, 1996.
Marcinčin, A., Ujhelyiová, A., Marcinčin, K. et al. Spinning, mechanical and thermal properties of metallocene polypropylene fibers. J Therm Anal Calorim 123, 1329–1341 (2016). https://doi.org/10.1007/s10973-015-4991-4
Renwei Xu, Peng Zhang, Hai Wang, Xu Chen, Jie Xiong, Jinpeng Su, Peng Chen and Zhicheng Zhang “Structure and Properties of a Metallocene Polypropylene Resin with Low Melting Temperature for Melt Spinning Fiber Application”
M. Krištofi, A. Ujhelyiová and J. Ryba “Mechanical Properties of Metallocene Polypropylene Fibres Modified With Copolyamide and Compatibilizer”
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
