FIBRED MAGNESIUM HYDROXIDE AND

Abstract:　 The fibred mangesiun hydroxide from the bracite was treated with a surface active agent. The modified fibred magesium hydroxide as f lame-retardant,boric acid, barium stearate, polydimethyl siloxane fluid,vinyltr iethoxysilane as synergists of the flame-retardant were added to polyene resin. The flame-resistance polyene material prepared meets the requirements of EWCZ -6287-1.
　　Key words:　fibred Mg(OH)2;　Polyene;　low-smoke;　flame -resistance

1　Introduction
　

　　Polyene is combustible material.In order to make flame-resistant polyene mat erial,non-halogenated flame-retardants are being developed.Magnesium hydroxide is a kind of important flame-retardants developed lately.Magnesium hydroxide h as many advantages, such as good heat-resistance,no toxic gases formed,no corro sion to equipment,good flame-resistance.If common hexagonal granular magne sium hydroxides is used as the flame-resistant, mechanical properties,impact st ren gth and tensile strength of the composites will be reduced by the addition of la rge amounts of the megnesium hydroxide, flowability will get bad when the composite s b eing melt to mould,and silver pattern will appear on the surface of the composit es. A cicular magnesium hydroxidemade by treating the granular magnesium hydroxide wit h brine, lime and surface treating agent can improve these properties. Thi s ma kes synthetic process of the flame-retardant comlpex,also magnesium hydroxide and its composites are relatively expensive.
　　The natural fibred bracite mine mainly containing magesium hydroxide is much cheaper. We analyzed its structure and composition with scanning electron micros cope and electrospectroscopy.The bracite is not of asbestos and cancerogenic mat erial. Its fiber is pure and easily cleavable .It has good flame-resistance an d low corrosivity. It is non-toxic and cl ean inorganic flame-retardant,and good reinforcing agent of the resin.
　　Modified magnesium hydroxide was prepared by treating the fibred magnesium hy droxide［1］from the low cost natural bracite with a solution of sodium ol eate. S urface polarity of the modified fibred magnesium hydroxide is near zero,and it has very large length/diameter ratio, good compatibility with the resin,very go od flame-resistance,mechanical properties,low synthetic cost.It can reinforce t h e resin and ensure the good physical properties of the synthetic flame-resistan c e material.Flame -resistance polyene material was prepared by using the modifie d fibred magnesium hydroxide as flame-retardant.

2　Experimental

　　Melt index was examined with melt index meter XRZ400.Combustion characteristi c UL-94;Tensile strength GB1039-79 and GB1040-79 and Hardness HG2-152-65 w ere followed.Polyene(PE-F-1 8DO12)was supplied by Daqing Petrochemical General Plant,China ,Bracite was from Sichuan Province, China.
2.1　Manufacturing methods
　　Modified Fibred Magnesium Hydroxide was prepared by following steps:The fi bred Mg(OH)2 from natural bracite was added to water, then the mixture was allowed to attain 70℃ and treated with a solution of sodium oleate at 70℃.Sti rring was continued for 1.5h, then the product was filted, dried. Grind afforded the modified fibred magnesium hydroxide aggregate.
2.2　Low-smoke and flame-resistance polyene material
　　Available boric acid, barium stearate, polydimethyl siloxane fluid, vinyltriet hoxysilane and tetrakis ［methyl-β-(3,5-di-t-butyl-4-hydrophenyl)-propi onate］me thane were added to 100 parts of softened polyene.The mixture was blended for 8- 10 min at 130℃,and poured into a mold preheated at 150-155℃.The temperature wa s kept at 150-155℃ for 5 min,then the pressure was raised to 2.5 MPa.After 5 m in,the pr essure was allowed to attain 3 MPa,and the temperature was reduced to 5 0℃ at a rate of 15±2℃/min. After relieving, the low-smoke and flame-resistance polyene material was obtained.

3　Results and Discussion

3.1　Structure and modification of fibred magnesium hydroxide
　　Fibred magnesium hydroxide crystal obtained from the natural bracite by specia l process forms hexagonal system and lamellar structure.In identical lamina, eac h of magnesium ions is surrounded by perfect octahedron composed of atoms of hyd rogen and oxygen, and each atom of oxygen is surrounded by deformed tetrahedron composed of three atoms of magnesium and one atom of hydrogen, the crystal struc ture is schemed in Fig.1(a),above and below magnesium ions are the plane of atom s of oxygen, and the O-H bond is vertical to the plane ,that is shown in Fig.1(b ).There are only ionic bonds in the lamina and molecular actions at interlaminat ion. When laminar crystal of fibred magnesium hydroxide is broken,interlaminar s eparation occurs at interlamination that is combined with weak actions.Mg-OH is ionic bond, O-H is covalent bond. Because of the difference of electronegativity between atoms of oxygen and hydrogen,the pair of shared electrons are partial t o the atom of oxygen,and this makes atom of hydrogen become partially a bare pro ton,so there is strong polar on the surface of fibred Mg(OH)2 crystal.It is hy drophilic.They easily aggregate because of the presence of hydrogen bonds.

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(a)

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(b)
Fig.1　Crystal structure of bra cite

　　In order to prevent aggregate formation,reinforce its compatibility with res in,and improve the mechanic properties of the composite,the fibred magnesium hyd roxide was treated with coupling agents. Titanate, aluminate and aluminium-tita nium composite may be used as the coupling agents［2］.
　　Several factors influence the selection of coupling agents:(1)surface config uration of the agents;(2)electronegativity of atoms of the coupling agents;(3)mo lecular geometry;(4)steric hindrance.
　　The amounts of coupling agents can be determined by the method of double tangen t through some macrographic performance curve showing the lubricating property o f the filler.
　　Stearic acid ,stearate and sodium oleate are also good modifiers.
3.2　The Mechanics of flame-retardation of fibred magnesium hydroxide
　　The thermal decomposition of fibred magnesium hydroxide is expressed as follows :

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It is an endothermic reaction,a lot of heat can be absorbed during the decomp osition.This makes the surface temperature of the resin lower and the water stea m formed during the decomposition is a kind of noninflammable gas that can dilu te the concentration of surrounding oxygen of the resin.In addition,the magnesiu n oxide can form a covered layer on the surface of the resin;the layer prevents t he resin from further combustion.It is found that the effect of flame-resistanc e of fibred magnesium hydroxide was related to the amount of fibred magnesium hyd roxide.The result of various parts of fibred magnesium hydroxide for 100 parts o f polyene resin is shown in Table 1.

Table 1　Effect of Fibred Mg(OH)2 on the Properties of Polyene Resin
Location Mg Si Fe Cu Zn Ca Mn Ni
1 43.39 21.53 23.98 8.90 2.21 - - -
2 24.95 14.37 4.81 9.48 4.04 1.35 0.62 0.39
Average 34.17 17.95 34.36 9.17 3.12 　 　 　

　　The data presented in Table1 illustrate that quite large variations in combust ion length of polyene resin correspond to extremely small differences in the am ount of fibred magnesium hydroxide.Combustion property of the resin correspondin g to 120 parts of fibred magnesium hydroxide was twice as large as the property corresponding to 80 parts of fibred magnesium hydroxide. That also increases the hardness. A larger amount of fibred magnesium hydroxide results in slightly im pro ved tensile and breaking strength,but largely decreased toughness and antistatic improved property.The melt index greatly decreases when the amount of fibred ma gnesium hydroxide is over 100 parts.

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　　Substances as synergists of flame-retardant can be added to resin.The presence of synergists of flame-retardant could improve the amount of fibred magnesium hydroxide and effectiveness of flame-resistanced of fibred magnesium hydroxide, a nd protect the composites from melt dropping during burning.They also decreased the side effects produced by the addition of large amount of fibred magnesium h ydroxide.Different kinds and amounts of synergists of flame-resistance led to different effects.We have used boric acid, barium stearate and polydimethyl siloxa ne fluid as synergists of flame-retardant and determined their optimum amounts i n cross-over experiments.The composition of flame-resistance material using th e fibred magnesium hydroxide as flame-retardant is listed in Table 2 .Table 3 sho ws the properties of the composite.

Table 2　Composition of Flame-resistance Polyene Material
Composition polyene
resin Fibred
Mg(OH)2 Boric
acid Barium
stearate P olydimethyl
siloxane fluid Vinyltri-
ethoxy-
silane Antioxidant
Portion 100 100 5 5 3.5 0.5 0.5

*tetrakis［methyl-β-(3,5-di-t-butyl-4-hydrophenyl)-propionate］methane

Table 3　Properties of Flame-resistance Polyene Material
Properties Test value
Hardness /HRR ≥85
Tensile strength /Mpa 12
Breaking elongation /% 100-300
Softening point /℃ 110
Change in size 2.5
By heat treatment /% 　
Oxygen index 35
Surface resistance /Ωcm 109

　　From Table 3, it is found that the above formulations have good compatibi lity with polyene resin.Fibred magnesium hydroxide taking large length/diameter rati o also has performance of reinforcement and antistatic property. In addition to the aformentioned performance for polyene ,fibred magnesium hyd roxide also plays an important role in eliminating smoke.Horizontal combustion t ests performed with the samples of flame-resistance polyene material led us to f ind that no identical smoke was produced though the flame was very small and dar k.Only little smoke was produced during non-flame combustion or when the fire d ied.
　　In conclusion, fibred magnesium hydroxide from natural bracite mine has large l ength/diameter ratio, and good properties and excellent reinforcing and fire-re tarding effect by incorporating fibred magnesium hydroxide to polyene .The flame -resistance polyene material can meet the requirements of EWCZ-6287-1.

　　ZHANG Jin′an(张金安)：Born in 1964;Lecturer;Dept of Chemical Engineering ,S tuff and Works University of Daqing ,Daqing 163255, China.




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