Polyolefin – We explain Polyolefins for you

What are Polyolefin Polymers?

Polyolefins are macromolecules formed by the polymerization of olefin monomer units. The IUPAC nomenclature term for polyolefins is poly(alkene). The most common polyolefins are polypropylene (PP) and polyethylene (PE), for instance. In other words, these polymers are prevalent in a wide array of applications depending on the material characteristics of the polymer, most notably consumer plastic. Thus, molecular properties like molecular weight (MW) distribution and branching are fundamental and related to parameters such as material fatigue, impact strength, and resistance to degradation. For example, fingerprint principal component analysis can identify different polyolefin types easily. As a result, these properties routinely inform research and development (R&D) as well as for quality control and assurance (QC, QA).

 Analysis of fillers and additives in polymers like polyolefins

Another established and non-destructive technique is X-ray Fluorescence of XRF for short. Here, we can quantify the concentration of additives and fillers. For example the elements F, Na, Mg, Al, Si, P, S, Ca, Ti, and Zn may require control and specification to ppm level. To clarify, including many kinds of PP and PE like iPP, HDPE, LDPE, mPE, ULMWPE. And you can even get a set of calibration standards for these elements on our webstore: ADPOL basic standards. The ADPOL module works with a range of XRF systems like the Zetium, Axios and Epsilon. As a result you can deploy it with existing system running superQ or Epsilon software.

 Common types of polyolefin polymers

Polyolefins polymers are some of the most prevalent plastics used today and come in various types

• Polyethylene (PE) with subgroups
  • high-density HDPE
  • low-density LDPE
  • linear low-density LLDPE
• Polypropylene (PP)
• Ehylene propylene diene monomer (EPDM) rubber

The table below gives a glimpse of the wide-scale distribution of these materials, ranging from everyday household use to specialized industrial applications. Here, most take advantage of the resistance to heat and an array of common solvents. This then makes the materials economical for many tough high wear applications.

Polyolefin melting point

Polyolefins are typically dissolved in high-boiling solvents, such as 1,2,4-trichlorobenzene (TCB), 1,2-dichlorobenzene (ODCB) or decahydronaphthalene (decalin), at temperatures from 130 – 160 °C. However, Molecular Weight characterization needs can sometimes be met with simple Ubbelohde intrinsic viscosity data or melt flow index determinations. On the other hand, for advanced characterization, high-temperature Gel Permeation Chromatography is used to compare different branching agents, to predict performance and to correlate with rheology results. 

In other words, Molecular Weight (MW), a radius of gyration (R_G), and Mark-Houwink constants are often of interest. Similarly, some low molecular weight or oligomeric polyolefins may be (partially) soluble in xylenes and other organic solvents which allows for analysis of % monomer or % xylene-soluble fraction. In summary, these characteristics have a direct correlation to the physical properties, like flexibility & strength, of the final material.

Previously

• Center of GPC Excellence is one year old.

Further reading

• Firstly an example Scientific poster: Use of LALS in High-temperature GPC.
• In addition, there is an application note on Rapid and Easy ID of Polyolefin types.
• Application note: Analysis of Carbon-Filled Polyethylene By Advanced Triple Detection High-Temperature Gel Permeation Chromatography (HT-GPC).
• Application Communication: FIPA of EPDM elastomers.
• Finally, an application note on sub ppm level titanium in polyolefins.

Have any questions? Please email me ulf.nobbmann@malvern.com – Thanks! Opinions are those of the author. Our editorial team modifies them occasionally.