Synthesis, Characterization and Properties of Condensation

SYNTHESIS, CHARACTERIZATION AND PROPERTIES OF CONDENSATION

PRODUCT OF MELAMINE WITH AMMONIUM DIHYDROGENPHOSPHATE

TO HASEGAWA a,MIOKO MAEDA a, MAKOTO SAKURAI a, JOSEF NOVOSAD b, HIRO and MAKOTO WATANABE a aDepartment of Applied Chemistry, College of Engineering, Chubu University,

1200 Matsumoto-cho, Kasugai, Aichi 487-8501, JAPAN bDepartment of Inorganic Chemistry, Faculty of Science, Masaryk University, Kotlarska 2,

611 37 Brno, CZECH REPUBLIC

Abstract The reaction of melamine with ammonium dihydrogenphosphate has been investigated by solid-state NMR spectroscopy under different conditions. Synthesized melamine diphosphate (MDP) was characterized by X-ray powder diffraction, solid-state NMR spectroscopy and was also tested for flame retardant ability. The flammability of polypropylene (PP) containing melamine diphosphate, pentaerythritol (PER) or dipentaerythritol (DPER) was characterized by limiting oxygen index (LOI).

INTRODUCTION In recent years, flame retardant (FR) additives have been widely utilized in flame-retarding flammable polymers such as polypropylene due to their advantages such as low smoke, toxicity, no corrosive gas generation, no flame dripping and halogen-free over the halogen- containing compounds [1]. However, the conventional FR additives (e.g. ammonium polyphosphate-pentaerythritol- melamine system) also have some disadvantages [2]. To achieve a certain flame retarding level, a higher loading of FR additive is needed than that of some halogen-containing flame retardants at the expense of the mechanical properties of flame-retarded materials [2]. Consequently, the flame retardancy of FR needs to be improved further. A solution could be addition of synergist [3] such as zeolite (ZEO), silicotungistic acid, etc. to FR additives or adjustment of the relative ratio among three components, i.e. acid source, char former and blowing agent of FRs. For the former, these synergists can improve the flame retardancy, but their polarities adversely influence the mechanical properties of composite. For the latter, increasing the amount of char former relative to the other two components is the method adopted. However, these char formers commonly used in intumescent formulation are often polyol such as pentaerythritol, mannitol or sorbitol. Therefore, the mechanical properties of

30 the flame retardant polymer [polypropylene (PP) etc.]with the concerned FRs are also very poor because of their poor compatibility with the polymeric matrix [2] Several years ago, DSM (Geleen, The Netherlands) and Ciba Specialty Chemicals (Basel , Switzerland) started with the development of halogen-free FRs based on melamine (1,3,5- triazine-2,4,6-triamine). The use of melamine at large scale for fire-retarding applications is however, quite limited. This can be attributed mainly to the lack of fundamental knowledge

on the flame-retarding mechanism of nonhalogen FRs in general, and melamine-based systems in particular.

EXPERIMENTAL

Materials

The following materials were used as received: melamine , ammonium dihydrogen phosphate, pentaerythritol, dipentaerythritol (reactant degree, supplied by Kanto Chemical,

Japan), polypropylene (PP) supplied by Mitsui, Japan . Melamine diphosphate (MDP) was made by ourselves.

X-Ray Diffraction

X-ray powder diffraction patterns of powder samples were collected at room temperature with nickel filtered Cu Ku radiation an Rigaku RAD-1B diffractometer .

Solid-State NMR Spectroscopy

Solid-state 31P NMR spectra were recorded on a JEOL-EX400 FT-NMR spectrometer at

109.25 MHz at room temperature. The excitation pulse and recycle time were 4 .6-4.8 s (4-

6 scans), respectively. 31P shifts is referenced relative to 85 % H3PO4/H2O at O ppm .

Sample Preparation

All samples were prepared by mixing polypropylene and other additives on a two-roll mill

(Test Mixing Roll Machine, type 191-TM) at a temperature range of 180-190 C for 15 min.

Sheets of about 135 •~ 85 •~ 3 mm were obtained by compression moulding on a curing machine for 45 min (the temperature decreased from 150•Ž to 100•Ž) followed by cooling to room temperatures. Standard specimens were cut from the sheets for the limiting oxygen index measurements [7].

31 Limiting Oxygen Index Limiting oxygen index (LOI) of all samples were tested on an oxygenindex instrument

(Oxygen index flammability tester, type No. 214) at room temperature. The limiting oxygen index (LOI) was determined accordingto JIS K 7201 -1,2[5]. LOI is a parameter for evaluating flame retardancy and flammability of polymeric materials in the same conditions. It denotes the lowest volume concentration of oxygen sustaining candle-like burning of materials in mixing gases of nitrogen and oxygen.

RESULTS AND DISCUSSION

Pre a aration and Characterization of Melamine Diphosphate MDP

The reaction of melamine with ammonium dihydrogenphosphate has been investigated by solid-state NMR spectroscopy under different conditions(molar ratio 1 : 1 ,temperatura from 180 to 220•Ž, heating time 1 - 24 hours) . From the experimental results,shownin Table 1 , are the most effective conditions: temperature at 210•Ž and heating time for 2 hours .

TABLE 1 Content of MDP (%) in product of reaction melamine with ammonium dih ydro-genphosph ate under different reaction conditions (temperature, heating time)

Melaminediphosphate [MDP , melaminiumdiphosphate, (C3H7N6+)2.H2P2O72-] is the result of a solid-state reaction of melamine with ammonium dihydrog enphosphate according to Equation (1):

(1)

32 The structure of this compound was established by high-resolution synchrotron powder- diffraction data by Brodski et al. [4]. Synthesized MDP was characterized by X-ray powder diffraction( Fig.1), solid-state NMR spectroscopy and was also tested for flame retardant ability.

Figure 1 XRD diffractogram of MOP

Flame Retardance The combustion characteristics of flame retarded polypropylene containing flame retardant additives, melamine diphosphate (MDP) with pentaerythritol (PER) and dipentaerythritol (DPER) were studied using limiting oxygen index (LOI). Table 2 presents the LOI values results of the flame retarded polypropylene composites. It can be seen that the WI values of the composites increase with the increase in MDP content (PP MDP=9 : 1; 8 : 2; 7 :3). The LOI value of the composite containing 30 % MDP (PP : MDP=7 : 3) is as high as 30. These results illustrate that MDP used alone in PP does not have a very good flame retardancy. When polyols, i.e. pentaerythritol (PER) or dipentaerythritol (DPER) are incorporated into the PP/MDP composites, a remarkable improvement of flame retardation is observed. From the data listed in Table 2, it is clear that at the same additive level, the LOI values of the PP/MDP/PER composites are all higher than that of the PP/MDP composite without PER. For example, the LOI value of the binary composite (PP : MDP=8 : 2) is 28.4, whereas the values of the PP : MDP : PER=8 : 2 : 1 composite is 32.0. In the case of the PP/MDP/DPER composites, the effect of DPER on the flame retardation of the PP/MDP composites is similar to that of PER. The WI value of the PP : MDP DPER =8 : 2 : 2 composite increases compared with the PP/MDP binary composite.

33 TABLE 2 The limiting oxygen index of polypropylene (PP) contaning melamine diphosphat e(MDP) , pentaerythritol (PER) or di-pentaerythritol (DPER). CA - charring agent (PER or DPER), LOI - limiting oxygen index (%)

It has been found that the flame retardation of the PP/MDP/PER(PP/MDP/DPER) t ernary composites is greatly improved compared with that of the PP/MDP bin ary composites, for example an increase in the WI values . The ternary composites on burning form an intumescent protective layer, which helps to further reduce the heat release rat e and smoke emission in comparison with the binary composites .

ACKNOWLEDGEMENTS We would like to thank the Chubu University and the Ministry of Education ,Sports, Culture, Science and Technology (MEXT) Japan for financial supprt .

34 REFERENCES

1. M. Le Bras, M. Bugajny, J. M . Lefebvre and S. Bourbigot, Polym. Int., 49, 1115 (2000). 2. W. Y. Chiang and H. C. H. Hu, J. Appl. Polym. Sci., 82, 2399 (2001). 3. S. Bourbigot, M. Le Bras, P. Breant, J. M. Tremillon and R. Delabel, Fire and Materials, 20, 145 (1996). 4. V. Brodski, R. Peschar, H. Schenk, A. Brinkmann, E. R. H. van Eck, A. P. M. Kentgens, B. Coussens, and A. Braam, J. Phys. Chem. B. 108, 15069 (2004). 5. JIS K 7201-1,2 (ISO 4589-1, 2): Plastics-Determination of burning behaviour by oxygen index-Part 1 & 2 (1999).