6 th International Technical Textiles Congress, 14-16 October, 2015 İzmir-TÜRKİYE
Abstract: Polypropylene is a commonly used fiber forming polymer, however it burns rapidly. Polypropylene textiles used in transportation vehicles and public areas must be flame retarded in order to ensure safety requirements.
Recently, efforts have been made to improve the fire behavior of polypropylene textiles by flame retardants using various techniques. Considering the major challenges in flame retardant application for textiles those are; the deterioration of mechanical properties due to the high loading of additives and washing durability, melt compounding approach has been employed in this study. An ammonium polyphosphate based intumescent flame retardant was successfully used with Eskişehir sepiolite –a hydrated magnesium silicate with a needle-like structure- to improve the fire resistance of polypropylene. The thermal stability of flame retarded polypropylene has been evaluated by thermal-gravimetric analysis. The flammability of polypropylene has been measured in terms of limit oxygen index and cone calorimeter tests.
Keywords: polypropylene, intumescent, flame retardant, sepiolite, phosphorus
1. INTRODUCTION
Polypropylene (PP) has been widely used in textiles thanks to its high tensile strength and low-cost features, however it burns rapidly, without leaving a char residue due to its wholly aliphatic carbon structure [1]. Flame retardant (FR) materials such as halogenated, phosphorus and metallic compounds have been used to increase flame retardant properties of polypropylene. However due to the environmental and health concerns the use of halogenated flame retardant materials, in particular, is limited [2]. Therefore there is an increasing demand for the development of novel and efficient flame retardant systems. Intumescent flame retardant (IFR) systems have been considered as alternative flame retardants for polyolefins due to their low smoke generation, low release of toxic gases and antidripping properties [3]. However, relatively low flame retardant efficiency of IFR systems require the use of more additives which may further impair the mechanical properties of materials that is a major concern for textile applications in particular. Various clays have been reported to improve flame retardant efficiency and the mechanical properties of IFR-PP formulations [4]. In this study t he effects of Eskişehir sepiolite on fire retardant behavior of various IFR-PP formulations were investigated.
2. MATERIAL AND METHOD
2.1. Preparation of FR polypropylene samples
Ammonium polyphosphate (APP) based IFR (Exolit AP 760, Clariant) and Eskisehir sepiolite were used to increase flame retardant properties of isotactic PP. Eskisehir sepiolite was wet-milled by planetary mill using ethanol as the dispersing medium, then ethanol was removed by evaporation under vacuum.
APP/sepiolite/PP mixtures were compounded by a twin-screw extruder operated with a constant temperature profile of 170°C and molded by injection. A total FR content (APP/sepiolite) of 20 wt% in
PP and various proportions of sepiolite (1 wt%-10 wt%) in FR formulation (APP/sepiolite) were studied
(Table 1). Maleic anhydride grafted polypropylene (MAPP, Sigma Aldrich) was used to improve the compatibility of sepiolite and PP matrix.
Table 1 Sample compositions
SAMPLE ID PP wt % MAPP % Sepiolite wt % APP wt %
Reference
PP/IFR20/SEP1
PP/IFR20/SEP2.5
PP/IFR20/SEP10
100
80
-
-
-
-
-
0.2
0.5
2
PP/IFR20 - -
PP/MAPP/IFR20
75
5 -
PP/MAPP/IFR20/SEP2.5
75
5 0.5
2.2 Characterization of sepiolite and evaluation of fire behavior of PP/FR samples
-
19.8
19.5
18
20
-
19.5
Particle size measurement was performed using a zetasizer (Malvern, NanoZS 3600). Morphologies of the samples were analyzed by SEM (Zeiss Supra 50VP) and the following elemental analysis (EDX
Oxford Instruments Inca Energy) were performed. Flammability was measured according to ASTM
D2863 in terms of limit oxygen index using a LOI test apparatus (Dynsco). Time to ignition (TTI), heat release rate (HRR) and peak heat release rate (pHRR) of the samples were measured by cone

6 th International Technical Textiles Congress, 14-16 October, 2015 İzmir-TÜRKİYE calorimeter (Fire Testing Technology, FTT). Thermogravimetric analysis were performed by TGA/DSC
(TA Instruments Q600) up to 1300°C under N
2
flow, and simultaneous FTIR analysis (Bruker Tensor27) were performed where the principal mass loss was observed.
3. RESULTS AND DISCUSSION
Sepiolite powder with a homogenous size-distribution was successfully produced by wet milling process.
SEM micrographs at various magnifications confirmed the needle-like structure of sepiolite particles.
a) b)
Figure 1 SEM micrographs of sepiolite at different magnifications c)
LOI value of neat PP (19%) increased to 28% by the addition of 20 wt% APP and increased further to
32.2 % when 2.5 wt% APP was replaced by sepiolite in FR formulation.
The degradation of reference
P P sample initiated at about 400°C and the material was almost fully decomposed at 500°C. Even though the onset temperature of decomposition was lower for the sample (PP/IFR20/SEP2.5), a more stable residue was produced at the decomposition temperature of the reference PP. Evolved gases produced where the major mass loss was observed for samples were qualified by FTIR analysis. The major gases produced by the thermal decomposition of PP/IFR20/SEP2.5 are listed in Table 2.
Table 2. Results of the evolved gas analysis by FTIR for sample PP/IFR20/SEP2.5.
Compound Name
2,4-Dimethyl-1-heptene
3-Ethyl-2-methyl-1-pentene
Pentane,3-methylene-
2,3-Dimethyl-1-butene
2,3-Dimethyl-1-hexene
Molecular Formula
C
9
H
18
C
8
H
16
C
6
H
12
C
6
H
12
C
8
H
16
Molecular Weight
126.24
112.22
84.16
84.16
112.22
4. CONCLUSION
Eskişehir sepiolite has been successfully used to improve the fire performance of IFR system as confirmed by the LOI and cone calorimeter measurements. When MAPP was added to replace 5 wt%
PP, the fire resistance was further improved. Such increase was attributed to the formation of ester bonds between hydroxyl groups of sepiolite and anhydride carbonyl groups of MAPP. Therefore MAPP itself has no or little effect of fire retardancy of polypropylene but it enhances the LOI by providing a more homogenous distribution of additives in the polymer [5] .The decomposition behavior of flame retarded polypropylene samples have been investigated by TGA and compared to neat polypropylene.
The PP/IFR/SEP2.5 has been presented as an effective flame retardant for the production of flame retardant polypropylene fibers.
REFERENCES
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