1. Influence of Selected Additives on Flammability
of Flame Retarded, Halogen-Free Polyolefinic Composites
Stanisław Kudłaa, Krzysztof Bujnowiczb, Katarzyna Szpilskaa
aInstitute of Heavy Organic Synthesis, Energetyków 9, Kędzierzyn-Koźle, Poland
bInstitute of Natural Fibres & Medicinal Plants, Wojska Polskiego 71B, Poznań, Poland
Introduction
Nowadays, the problem of flame retardation is of great interest, especially in the field of plastics’ industry since RoHS directive was issued. There is a possibility to get flame-retarded plastics with the use of inorganic fillers like aluminum or magnesium hydroxide. However, in such cases the mechanical properties, especially elongation at break of highly filled plastics suffered greatly.
As far as ethylene (co)polymers are concerned, the problem of nanocomposites synthesis is especially challenging because of the hydrophobic character of the polymer matrix and processing difficulties associated with complex viscoelasticity of the systems.
One of the promising, perspective ways for obtaining new generation of halogen-free, flame-retarded plastic materials, including polyolefinic ones, is the usage of nanotechnology. Basing on theoretical assumption and on experimental results obtained up to date, nanocomposites seem to be very promising.
The aim
The main object of our work is to obtain new kinds of flame-retarded, halogen-free materials based on ethylene (co)polymers, filled with metal hydroxide and nanoclays, with improved properties.
Materials
Polymers: low density polyethylene LDPE, Malen E FGNX, 23D022; d = 0,92 g/cm3, MFI = 2,0 g/10 min. – Basell Orlen Polyolefins,
ethylene-vinyl acetate copolymer EVA, Escorene UL 00328; d = 0,95 g/cm3, MFI = 3,0 g/10 min. – ExxonMobil Chemical,
Flame retardant: aluminium hydroxie ATH, surface treated, precipitated, Martinal OL-107C – Albemarle
Nanoclays: Nanofil 5 & Nanofil SE3000 – Rockwood Additives, ZK1-T & ZK7-T – home-made experimental products, Halloysite PJF – Intermark, Poland
Dicumyl peroxide as cross-linking agent (c = 2 wt.%).
All samples were prepared by two-roll milling and forming in a laboratory press.
Fire hazard testing (EN :2002+A1)
Limiting oxygen index, LOI (ISO 4589, part 1 and 2)
Detailed results of flammability tests for LDPE/ATH-based composites.
All multi-components composites consist of 50 wt.% of ATH.
Results of LOI determination for LDPE composites flame-retarded with:
ATH: 40%, 50% or 60% (white bars), and
ATH (50% always) + nanoclays at different concentration (blue bars).
* only one specimen from a set of five specimens does not comply; otherwise V-1.
Cone calorimetry (ISO )
The cone calorimeter is the most advanced apparatus among all bench-scale reaction-to-fire test instruments. The main property determined during the tests is the heat release rate (HRR). The rate of heat release is determined by measuring oxygen consumption derived from oxygen concentration and flow rate in the combustion product stream. This test method is based on the observation that, generally, the net heat of combustion is proportional to the amount of oxygen required for combustion, namely heat energy of approximately 13.1 MJ is released per kilogram of oxygen consumed, irrespectively to the type of organic material tested.
The test samples had dimensions of 100x100x4 mm, and were held in horizontal position in a retaining frame of Atlas Cone 2A apparatus. Heat flux was set at
35 kW/m2. A spark igniter was used.
LDPE/ATH composites
EVA/ATH composites
Conclusions
Nanoclays investigated are efficient auxiliary materials which usage in flame-retarded, halogen-free polyolefins seems fully reasonable. It is important to underline that the composites were prepared in a very simple manner, without any compatibilizer, so they can’t be consider as nanocomposites. Exfoliation process could probably improve flame retardation effect of the nanoclays. The research is continuing in our laboratory.
According to LOI results, nanoclays can replace ATH at slightly higher than 1:1 wt. ratio to get the same degree of flame-retardation. Judging by HRR peaks value clays are 2-times more effective than ATH. For LDPE composites more efficient were both Nanofils whilst for EVA composites halloysite clay was the best. Cross-linking further somewhat improves flame-retardation.
Project number ZPB/31/72427/IT2/10 by Polish National Centre for Research and Development