Development of halogen-free flame retardant polypropylene compounds for pipe application

Hannelore Mattausch

Research output: ThesisDoctoral Thesis


Burning protection is a necessary precaution for various applications such as conduit systems, transport or building industry, as fire causes human victims and major economic damage. Polymer compounds are conventionally filled with halogenated flame retardant additives. In case of fire, toxic substances such as hydrogen chloride or dioxine are formed. This is the main reason for the general requirement to reduce the halogen content to zero. Furthermore, halogenated flame retardants have also a negative impact on environment and wildlife. Most commercial available halogen-free flame retardants for polypropylene (PP) have to be used with high filler loading (> 20 wt%) which leads to difficulties in processability, poor mechanical properties and unfavorable cost performance. Therefore, the aim of this research work was to develop a halogen-free flame retardant for polypropylene conduits with a filler content below 10 wt%, adequate mechanical properties, colorable and processable with standard compounding and extrusion equipment. In this research work, 15 hypotheses were established whereat just four hypotheses were corroborated and 11 hypotheses were rejected. In theory, with the help of the statistical analysis logistic regression, the prediction of the probability of burning respectively dripping behavior can be determined. In this work, it was shown that the conducted logistic regression could only give information about trends in the mode of actions of the flame retardant PP compounds due to high and thus unreliable standard errors of the regression coefficients. Furthermore, no single PP compound sample showed non-burning and non-dripping behavior at the same time during UL94 test. A combination of different characterization methods was applied in order to understand the mechanisms between the FR additives and the polymer matrix. Thermogravimetric analysis (TGA) measurements were used to investigate the thermal decomposition and thermal stability of PP compounds. With cone calorimeter tests the polymer compound behavior under the controlled influence of heat radiation was characterized. The morphology of a burned surface gave information about the FR efficiency of the specimen and was observed via scanning electron microscope (SEM). Pyrolysis-gas chromatography/mass spectrometer analysis provided information about the chemical fragments during pyrolysis process. The product pipe was characterized by the pipe flame test, compression test for pipes and by the low temperature impact strength test. PP pipes filled with expandable graphite (EG) passed only the pipes flame test. The mechanical tests for these compounds failed due to the too early foaming of the EG particles. All material product tests were passed with phosphorous-based FR additive combination with low filler content (<7 wt%). A systematic concept for the development of halogen-free FR polyolefin product was proposed to save time and costs for development works. This concept combines the industrial and academic course of development to offer an even more efficient and effective generic and synergistic approach.
Translated title of the contributionEntwicklung von halogenfreien flammhemmenden Polypropylen-Compounds für die Rohranwendung
Original languageEnglish
  • Holzer, Clemens, Assessor A (internal)
  • Flachberger, Helmut, Assessor B (internal)
Publication statusPublished - 2015

Bibliographical note

no embargo


  • polypropylene
  • flame retardant
  • pipe extrusion
  • polyolefine
  • halogen-free
  • Py-GC/MS
  • Cone Calorimeter

Cite this