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Introduction

The word plastic is derived from the Greek plastikos meaning capable of being shaped, or from plastos, capable of being moulded. Plastic

refers to malleability or plasticity during manufacture, allowing the material to be cast, pressed, or extruded into a variety of shapes and sizes (Weil and Levchik, 2008). Most polymers are not used in the “pure” state, but contain additives that enhance their performance in the intended end-use applications. Fillers are relatively inert

Abstract

The plastics industry has been challenged by restrictions on or complete ban placed on the use of halogenated flame retardants because of their adverse health, safety and environment effects and requirement of higher loading for inefficient aluminium and magnesium hydroxides. Recently, there is renewed interest in using safe, readily available, cheap and efficient inorganic flame retardants, most especially ammonium salts as flame retardants for the commodity polyhydrocarbon thermoplastics. In order to produce a flame retardant GPPS, 220ìm-thick pure (additive-free) polystyrene film was prepared by compression moulding technique in this work. Varying amounts of calcium trioxocarbonate (IV) (CaCO ) and ammonium tetraoxophosphate (V) [(NH ) PO ] were added, singly and in combination, to 3 4 3 4

the pure polystyrene pellets to prepare 9 films of the same thickness by the same technique. Flammability tests (vertical burn, limiting oxygen index and horizontal burn) and mechanical properties (tensile strength and elongation-at-break) were investigated according to UL 94 and ASTM standards to evaluate the efficacy of the two fillers on all the 10 prepared sample films. The experimental results showed that flammability properties of the untreated polystyrene sample have been enhanced by both fillers, alone or in combination. In addition to enhancement of ?ame retardance, dripping resistance of the treated samples was also imparted in direct proportion to the loading of the two fillers. The synergistic effect of the two fillers resulted to attainment of V-0 rating and an increase in both the limiting oxygen index and horizoncal burn time of the filled samples. The synergism in flame retardance efficacy of the two fillers are attributed to the release of the two inert gases of ammonia (NH ) by ammonium tetraoxophosphate (V) [(NH ) PO ] and carbon (IV) oxide (CO ) by calcium 3 4 3 4 2

trioxocarbonate (IV) (CaCO ) when the treated general-purpose polystyrene sample films burn. The 3

mechanical properties (tensile strength and elongation-at-break) of the CaCO and (NH ) PO -filled 3 4 3 4

GPPS samples were improved when the two fillers were used singly or in combination in comparison to the pure (control, untreated) GSPS film. The slight improvement in the mechanical properties of the treated samples indicated the compatibility of the two fillers and the pure GPPS resin.

Effect of Calcium Carbonate and Ammonium Phosphate on the Flammability and Mechanical Properties of

General-Purpose Polystyrene (GPPS)

1 2 1* H. ABBA, E.T. MUSA AND A. MUSA

1Department of Chemistry, Ahmadu Bello University, P.M.B.1045, Zaria, Nigeria. 2Department of Chemical Sciences, Federal University, P.M.B. 0182,

Kashere, Gombe State, Nigeria.* Corresponding Author

E-mail: habba@abu.edu.ng, hamzaabbah@yahoo.com

Keywords: Ammonia, combustion, flame retardant, limiting oxygen index, polystyrene

50

materials added to a plastic to modify its strength, performance, working properties, or other qualities, or to reduce the cost of production. Flame retardants are a key component in reducing the devastating impact of fires on people, property and the environment. They are added to potentially flammable materials, including plastics, to prevent fire from starting, limit its spread or stop the burning process, and they are economically viable and have no deleterious effects on other desired properties (Chen and Wang, 2010; Wilkie and Morgan, 2010). Since flame retardance refers to a function and not a family of chemical compounds, a variety of chemicals with different properties and structures act as flame retardants and are often combined for effectiveness (Morgan, 2006; Deodhar et al., 2011) Although halogenated flame retardants are cheap, readily available and efficient, they are being increasingly scrutinized in recent years. Their tendency to accumulate in living organisms, persist in the environment, and concerns raised about their potential decomposition products in case of fire, coupled with stricter fire safety standards and environmental regulations, call for production and use of safer alternative flame retardants (Betts, 2008; 2009; van der Veen and de Boer, 2012). It has recently been reported(Yen-Thi-Hai et al., 2013) that inert inorganic materials such as CaCO and (NH ) PO that 3 4 3 4

produce non-combustible gases can be used to dilute the fuel in the solid and gaseous phases. Bellayer et al. (2011), Deodhar et al. (2011) and Hull et al. (2011) have also reported on the use of CaCO and (NH ) PO as flame retardant for 3 4 3 4

polypropylene and action of mineral fillers in fire retardant plastics. Use of calcium carbonate as fire retardant for plastics has been reported by several workers (Hermanson et al., 2003; Bellayer et al., 2009; Isitman et al., 2011). Similarly, the use of ammonium phosphate as fire retardant for plastics and its mechanism of action has also been severally reported (Giraud et al., 2005; Saihi et al., 2006; Samyn et al., 2007; Vroman et al., 2010; Hassan et al., 2013; Mabey and Kish, 2013).

Polystyrene (PS), the fourth largest thermoplastic by production volume, is a synthetic aromatic polymer, made from the styrene monomer, and is

.

either classified as general-purpose polystyrene (GPPS) or as high-impact polystyrene (HIPS)Allcock et al., 2003; et al., 20 :

( Mahdavian 04)

H. Abba et al.: Effect of Calcium Carbonate & Ammonium Phosphate on the Flammability & Mechanical Properties of GPPS

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52

Table 1: Effect of concentration (%) of CaCO and (NH ) PO (singly and in combination) on the 3 4 3 4

UL 94 vertical burn rating of the GPPS films

Sample number Sample composition (%) Vertical burn rating PS (NH4)3PO4 CaCO3 (NH4)3PO4 + CaCO3

1 100 0.0 0.0 0.0 V-2 2 97.5 2.5 0.0 0.0 V-2 3 97.5 0.0 2.5 0.0 V-1 4 97.5 0.0 0.0 2.5 V-2 5 95.0 5.0 0.0 0.0 V-2 6 95.0 0.0 5.0 0.0 V-1 7 95.0 0.0 0.0 5.0 V-0 8 92.5 7.5 0.0 0.0 V-2 9 92.5 0.0 7.5 0.0 V-1 10 92.5 0.0 0.0 7.5 V-0

PS = Polystyrene

H. Abba et al.: Effect of Calcium Carbonate & Ammonium Phosphate on the Flammability & Mechanical Properties of GPPS

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Nigerian Journal of Science Vol 49 (2015): 49-55

0

20

40

60

80

100

120

1 2 3 4 5 6 7 8 9 10

LO

I (%

)/H

ori

zonta

l burn

tim

e (s

)

Sample composition (phr)

Horizoncal burn time

LOI )

Figure 1: Effect of concentration of CaCO and 3

(NH ) PO on the limiting oxygen index 4 3 4

and UL 94 horizontal burn time of the GPPS films

0

10

20

30

40

50

60

70

80

1 2 3 4 5 6 7 8 9 10

Ten

sile

str

ength

(M

Pa)

/Elo

ngat

ion a

t bre

ak (

%)

Sample composition (phr)

Elongation at break

Tensile strength

Figure 2: Effect of concentration of CaCO and 3

(NH ) PO on the tensile strength and 4 3 4

elongation at break of the GPPS films

Conclusion

Combination of (NH ) PO and CaCO4 3 4 3

NH and CO3 2

produced a

synergistic effect on the flame resistance due to production of two inert gases ( ) on

their thermal decompositions. The two gases form

54

a gaseous protective layer that excludes oxygen and dilute the fuel in its gaseous phase and shield the polymer (GPPS) from being burnt when exposed to flame.

GPPS

The two inorganic compounds used were found to effectively increase the limiting oxygen index and horizontal burn time, as well as improved the vertical burn rating without compromising the mechanical properties studied (tensile strength and elongation at break). Since combination of the two inorganic compounds used are effective flame retardants, they are recommended for inclusion into

as alternatives to the toxic and environment hostile conventional halogenated and inefficient metal hydroxide flame retardants.

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*H. Abba, E.T. Musa and A. MusaNigerian Journal of Science Vol. 49 (2015): 49-55ISSN 0029 0114