Polyolefin – We explain Polyolefins for you

What are Polyolefin Polymers?

Two juice containers made out of low density polyethylene and one yoghurt container made out of polypropylene, displayed on carpet made from polypropylene

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).

image of principal component analysis to find and identify types of polyolefins like PP polypropylene PE polyethylene high density HDPE. This is part of the XRF data analysis options.
XRF fingerprint principal component analysis can identify different types of polyolefins

 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.

  Polymer Type  SymbolExamples of use
  HDPE  ♴    fuel tanks, bottle caps, plastic bottles,
  LDPE  ♶    liquid containers, tubing, plastic wrap,
  PP  ♷    piping, carpet, roofing, hinges, auto parts,
  EPDM   seals, electrical insulation, roofing,

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 (RG), 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

Further reading

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


View all articles