The synergistic effect of borax and chlorinated paraffin as flame – retardants for epoxy and unsaturated polyester resins

: In this investigation , borax (B) (additive I) and chlorinated paraffin (CP.) (additive II) ,were used as flame retardants for each of epoxy and unsaturated polyester resins in the weight ratios of 2,4,6, & 8% by preparing films of (130×130×3) mm dimensions. Also films of these resins with a mixture of [50%(B.)+50%(CP.)] (additive III) in the same weight ratios were prepared in order to study the synergistic effect of these additives on the flammability of the two resins . Three standard test methods were used to measure the flame retardation which are :


Introduction:
The history of all polymer materials were traced by the success of their applications in replacing tradition materials like wood , leather and metals .The rapidly expansion of combustion incourage many researches to use many additives to retard flammability of the polymers [1] .
The chlorinated paraffins (CP) are group of chemicals manufactured by chlorination of liquidparaffin or paraffin wax , containing from 30-70% chlorine , they are largely inert , almost insoluble in water and have extremely low vapor pressure .The most commercialy chlorinated paraffin products are liquids ranged from low to extremely high viscosity .Other types are solids which have longer carbon chains and usually contain 70-72% chlorine [2] .Boric acid and it ' s hydrated salts , in contrast to the anhydrous borates , have low melting point and to a glass at 600 K o but only above 775 K o they become sufficiently fluid to flow .Borax when heated in air dissolves in its own water of hydration and swells to a forty mass , it then loses water [3] .Boric acid and borax are frequently used together , and in the system H3BO-NaB4O7.10H2O, there is a sharp solubility maximum at a temperature depends on the boric acid : borax ratio [4] .The flame-retardation is essentially an interruption of the burning process [5] .There are two distinct types of flameretardant must be recognized : a. Reactive flame retardants are compounds usually containing heteroelements which can also be chemically incorporated in smaller proportions , usually during the polymerization process .b. Additives of flameretardants are incorporated into polymers by physically mixing with the polymer , normally after the polymerization complete [7,8] .

Experimentals:
1 2-Equipments : a. ASTM : D-2863 : The measurement of limiting oxygen Index (LOI) , is widely used for measuring flammability of polymers , The (LOI) is the minimum concentration of oxygen and nitrogen , that supports a candle-like combustion of specimen [9,10] .b. ASTM D-635 : The measurement of rate of burning (R.B) , Extent of burning (E.B) and time of burning (T.B) for self-supporting plastic in a horizontal position [11] .c. ASTM D-3014 : The measurement of maximum flame height (H) [12] .

3-Preparation of samples :
The samples were prepared in the dimensions of (130×130×3)mm, Three sheets of each epoxy and unsatmated polyester resins were prepared for each percentage weight 2,4,6 & 8% with the additives I,II and III .4-Compatibility measurement : Light microscope was used to illustrate the compatibility of polymer with the additives.

Result and Discussion:
1-Measurement of LOI using ASTM : D-2863 : The limiting oxygen index (LOI) for epoxy resin without additives is (19.8) [13], and for unsaturated polyester resin is (20.6).The results obtained from this test are listed in Tables ( 1& 2  The results obtained from these tests showed that the rate of burning (R.B) of the epoxy and the unsaturated polyester resins with the additives has a continuous reduction with increasing the percentage weight of additives , as in (Tables 3 & 4) respectively .(Figs 3 and 4) showed the flame speed curves of flame-retardation for epoxy resin and unsaturated polyester resin .
3-Measurement of flame height (H) using ASTM: D-3014: (Figs. 5&6) showed that the flame height( H )was inversly proportional with increasing the percentage weight of the .additives as mentioned in Tables (5&6) respectively.

4-The compatibility :
The compatibility between polymer and additives is one of the most important factors which effects the flameretardation and means a homogeneous fabric of polymer with additives.Figs.(7  & 8) illustrate the distribution of additives particles and their percentages .

Conclusion:
1-The flame-retardancy efficiency of the additives I,II and III appeared to follow the order : III > II > I 2-Borax (B) and chlorinated paraffin (CP.) together have a good effect to retard the flammability and combustion of both epoxy and unsaturated polyester resins .Their synergistic effect is better in action . .3-The (LOI) increased with increasing the weight percentages of the additives .4-The (R.B) decreased with increasing the weight percentages of the additives .5-The flame height (H) decreased with increasing weight percentages of the additives .6-The good results of limiting oxygen index (LOI), rate of burning (R.B) and flame height (H) mean that the compatibility was of a significant effect on the burning of the two polymers which mean that a good compatibility has taken place during the preparation of the samples .
Finally, the combustion products like; free radicals , (Ċl, OH, chare, ...etc.) will form a layer to prevent burning and oxygen that help continuous burning of polymers to reach the burning front.
), Figs.( 1& 2) represent them.The oxygen concentration required to support a candle-like of epoxy resin and unsaturated polyester resin samples was increased with increasing the weight percentages of additives .The efficiency of I,II and III additives was in the following order : III > II > I 2-Measurement of rate of burning by using ASTM : D-635 :