FIELD OF THE INVENTION

The invention relates to an improved combustible composition, and more particularly, but not exclusively, to a combustible composition suitable for use in igniting primary fuels.

BACKGROUND TO THE INVENTION

Combustible compositions used for igniting primary fuels such as coal, charcoal briquettes and wood, are generally well-known and widely used. Basic solid fire initiating materials such as paper, twigs and sticks have been used universally to start the sustained combustion of the primary fuel. While the aforementioned basic materials are generally safer in use as compared to liquid petroleum and alcohol based materials, these materials have a propensity to burn out before the primary fuel is sufficiently ignited to sustain a fire.

The development of compositions comprising solid hydrocarbon fuels provided a benefit of sustained and intense heat release inherent in liquid petroleum fuel, and at the same time, provided a safer format for storage, handling and use generally associated with a moulded solid composition. The hydrocarbon fuel aforementioned is typically prepared from a liquid hydrocarbon such as paraffin (kerosene), and is used together with a thermosetting material comprising a urea-formaldehyde resin. The combination of paraffin and urea-formaldehyde is cured with or without an acid-based catalyst, the result of which is an aesthetically appealing white solid having improved flame starting and propagation (spread) properties, as compared to the aforementioned basic fire starting materials.

A disadvantage associated with solid hydrocarbon fuel having a formaldehyde-based resin, is that impurities of free formaldehyde are inevitably present in the composition. Also, formaldehyde has been classified as potential human carcinogen and is environmentally unfriendly. Despite typical free formaldehyde levels in the solid fuel composition posing minimal risk to consumers, numerous attempts have been made to offer improved fire initiating materials while promoting environmental friendliness and concomitant elimination of risk to the consumer.

A further disadvantage that may be associated with solid hydrocarbon fuels having a formaldehyde-based resin is that such compositions are prohibited for sale in National Parks in South Africa. Alcohol-based gels have been provided as a solution, however these gels also have limitations in that the efficacy and performance of these gels are significantly lower when compared to the resin-based alternatives. In addition, alcohol gel systems have lower flash points as compared to the liquid hydrocarbon used in a resin based system. The inherent higher volatility of gel systems thus poses an increased risk in storage and usage of the gel product. OBJECT OF THE INVENTION

It is therefore an object of the invention to provide an improved combustible composition wherein the aforesaid disadvantages may be overcome.

It is a further object of the present invention, to provide an alternative environmentally friendly combustible composition to the prior art.

SUMMARY OF THE INVENTION

According to the invention, there is provided a combustible composition including a liquid hydrocarbon in admixture with a carbohydrate. The liquid hydrocarbon may be selected from the list of saturated and unsaturated cyclic hydrocarbons, saturated and unsaturated acyclic hydrocarbons, aromatic hydrocarbons, and/or a combination of these. The liquid hydrocarbon may further be a combustible liquid having a flash point of above 25°C, preferably above 37°C most preferably above 45°C. The combustible liquid may be selected from any one or more of the list of classes of combustible liquids including Class IC, Class II, Class IMA or Class 1MB. Preferably, the combustible liquid is selected from Class MIA, and is most preferably illuminating paraffin. The liquid hydrocarbon may be present in an amount of between 95% to 30% w/w. The liquid hydrocarbon may preferably be present in an amount of 90% to 50% w/w. Most preferably the liquid hydrocarbon may be present in an amount of 80% to 70% w/w. The carbohydrate may be a polysaccharide, such as starch. The polysaccharide may include polyglucosides, alginates, and carginates. The starch may preferably be modified starch or naturally occurring starch.

The modified starch may be a chemically modified starch or a physically modified starch.

The chemically modified starch may be an acid-treated starch, an alkaline-treated starch, a bleached starch, an oxidized starch, an enzyme-treated starch, a monostarch phosphate, a distarch phosphate, a phosphated distarch phosphate, an acetylated distarch phosphate, a starch acetate, an acetylated distarch adipate, a hydroxypropyl starch, a hydroxypropyl distarch phosphate, a hydroxypropyl distarch glycerol, a starch sodium octenyl succinate, an acetylated oxidized starch, cationic starches, hydroxyethyl starch and/or carboxymethylated starches, or a combination thereof.

Most preferably the starch may be a physically modified starch, such as a pre- gelatinised starch.

The carbohydrate may be present in an amount of between 0.5% and 30% w/w. Preferably, the carbohydrate may be present in an amount of between 1 % and 20% w/w. Most preferably the carbohydrate is present in an amount of between 2% w/w and 10% w/w. There is further provided, according to the invention, for the composition to include a surfactant. Preferably, the surfactant may be an anionic surfactant such as alkyl benzene sulphonic acids and salts thereof.

The invention further provides for the improved combustible composition to include a gelling agent. The gelling agent is preferably water. Optionally, the gelling agent may be ethanol and may further be a combination of ethanol / water.

There is further provided, according to the invention, for a cross-linking agent to be included in the combustible composition. The cross-linking agent may be selected from the list of calcium stearate, calcium oxide, or calcium chloride. Preferably, the cross- linking agent is calcium stearate.

There may be further provided, according to the invention, for one or more solid combustible material to be added to the combustible composition. The solid combustible material may be wood powder or preferably may be wood chips.

Optionally, the combustible composition may include an accelerant. The accelerant may be potassium nitrate.

The invention may further provide for the combustible composition to optionally include a hardening agent. The hardening agent may be a physical hardening agent, such as paraffin wax, or alternatively may be a chemical hardening agent such as hydrochloric acid, hydrogen peroxide, and the like. The composition may be a liquid, gel, a solid block or may preferably be a solid gel. BRIEF DESCRIPTION OF THE INVENTION

The invention will now be described by way of non-limiting example only with reference to the accompanying figures, in which

FIGURE 1 is a graph of average maximum flame height of samples A, B, C and D in an extraction chamber, as set out in Table 3 below according to the invention, at time intervals of 3, 8 and 1 1 minutes, measured against a commercially available prior art solid composition;

FIGURE 2 is a graph of average maximum flame height of samples A, B, C and D of

Figure 1 , however with combustion occurring under conditions having a light draft with samples partially shielded within an extraction chamber, two meters away from a fully opened window;

FIGURE 3 is a graph depicting average burn time of each sample A, B, C and D, as well as samples I, II, II and IV as set out in Table 4 under light draft conditions, from flame propagation to cessation;

FIGURE 4 is a graph showing total average burn times of samples (of light draft conditions and moderate draft conditions) set out in Table 4;

FIGURE 5 is a graph showing changes in performance of combustion of samples listed in Table 4 having regard to combustion under light and moderate draft conditions; FIGURE 6 is a graph showing average burn time of the improved composition in accordance with the invention as against changes in percentage surfactant;

FIGURE 7 is a graph showing total average burn time of the improved composition in accordance with the invention as against changes in percentage surfactant;

FIGURE 8 is a graph showing average burn time of the improved combustible composition in accordance with the invention under light draft conditions as against percentage hydrocarbon (Turpesol); FIGURE 9 is a graph showing total average burn time of the improved combustible composition in accordance with the invention under light draft conditions as against percentage hydrocarbon (Turpesol);

FIGURE 10 is a graph of burn time of each formulation according to the invention as set out in Table 2 (having variations in surfactant:water ratios), as against increasing orders of hydrocarbon:water ratios;

FIGURE 11 is a graph of burn time against hydrogen surfactant ratio of formulations I to IV of Table 2; and

FIGURE 12 is a graph of burn time against hydrogen surfactant ratio of formulations A to D of Table 2; DETAILED DESCRIPTION OF THE INVENTION

There is presently a need for a combustible composition for igniting a primary fuel that not only burns cleanly, but also with a hot, uniform and sustained flame. Further the composition must provide good contact with the primary fuel, be stable during storage, convenient to apply and be clean to handle, while presenting as an environmentally friendly product and as a relatively less hazardous product in use, as an alternative to prior art products. It has now been surprisingly found that a starch-based combustible composition satisfies the aforementioned need in the art, or at the very least, minimizes the disadvantages posed by the prior art. The invention relates to a combustible composition, having a liquid hydrocarbon in admixture with a polysaccharide. The liquid hydrocarbon is preferably illuminating paraffin (or Turpersol). However, the liquid hydrocarbon can alternatively be any hydrocarbon selected from the class of compounds known as combustible materials having a flash point of 37.7°C and higher. The liquid hydrocarbon may further be selected from Class IC, Class II, Class MIA or Class 1MB. The liquid hydrocarbon may be present in an amount of between 95% to 30% w/w, preferably in an amount of 90% to 50% w/w, and most preferably in an amount of 80% to 70% w/w.

The carbohydrate is a pre-gelitinized starch known as Stygel T. However, the carbohydrate may be any suitable polysaccharide, including the various forms of starch. In the context of this invention, the term "starch" should be read to include all forms of naturally occurring starch forms, as well as all forms of modified starch forms. Modified starch forms should be read to include starch forms modified by way of chemical means, or physical means, and includes various forms of substituted starches.

Pure starch is a carbohydrate presented typically in white powder form. It is tasteless and odourless and contains several million amylopectin molecules accompanied by a much larger number of smaller (in size) amylose molecules. A carbohydrate is formed through the linking together of a plurality of monomers, called saccharides. Multiple connected monomers are called polymers. Starch is a carbohydrate polymer of repeating glucose units, which are bonded together through glycosidic bonds. The starch molecule thus formed has concentric rings of alternating amorphous and crystalline regions (or domains).

In the presence of water and heat, intermolecular bonds that define the starch compound break down and allow for bonding sites to engage more water. The general structure of the polymer chain increases in randomness as more water penetrates the aforementioned crystalline regions. Heat allows for these crystalline regions to become more diffused with water and for the chains to begin separating. As the chains separate, an amorphous form of the polysaccharide is created. This process is known as gelatinisation and is responsible for increasing the viscosity of starchy fluids. It is possible to thereafter dehydrate the gel thus formed which ultimately results in a white powder. A pragmatic benefit of pregelitinised starch is that the amorphous form of starch may be recreated without further heating. When treating starch chemically, physically or enzymatically, one can modify or manipulate the glycosidic bonds thereof to give starch new physical and/or chemical properties. The resultant starch is known as a modified starch. In this art, modified starch is used to provide beneficial rheological, heat and compatibility properties to the improved combustible composition according to the invention. Of particular importance to the present invention is the use of pregelitinised starch to facilitate ease of manufacture of the improved combustible composition.

As an additional ingredient to the aforementioned admixture, a foaming agent is added to the combustible composition. In the described embodiment the foaming agent is dodecylbenzene sulphonate, a surfactant. The foaming agent causes the hydrocarbon, water and starch admixture to form a foam, with the concomitant benefit of trapping air molecules within the admixture. This ultimately facilitates combustion of the hydrocarbon within the composition during combustion.

Under intense agitation a pair of immiscible fluids will emulsify. However, this type of emulsion is thermodynamically unstable and the emulsified droplets will combine and form separate phases once again. To prevent the anticipated separation, the surfactant additionally acts as an emulsifying agent. A surfactant typically contains a hydrophilic head that solubilises in water and a lipophilic tail that solubilises in a hydrocarbon. Generally, surfactants aid in emulsification by coating the surface of dispersed droplets, reducing interfacial tension and preventing the droplets from coalescing. Surfactants with longer tail regions have greater solubility in hydrocarbons. The surfactant used in admixture, according to the invention, is any suitable surfactant such as ionic, anionic or amphoteric surfactants. In a preferred embodiment, the surfactant is the anionic surfactant, alkyl benzene sulphonic acids and salts thereof.

A further ingredient that is added to the admixture, according to the invention, is a gelling agent. The gelling agent is preferably water. It will be appreciated that in the case of unmodified or natural starch, the gelling agent, in this instance, water, would need to be pre-heated to a suitable temperature, to enable the starch in combination with the hydrocarbon liquid to bind to each other. The function of water is to create an amorphous aqueous phase within the improved combustible composition. Water is an integral part of the composition as it creates an emulsion with the oil and surfactant. It has also been shown that, other than air flow rate the water content of the improved combustible composition affects the burn rate, burn time, peak flame temperature, heat release rate and flame height. The tests performed in the invention together with literature show that in general, a longer flame height is inversely proportional to the burn time and therefore directly proportional to the burn rate, peak flame temperature and heat release rate. By incrementally increasing the water content it is possible to find a good balance between burn time and the heat released.

The improved combustible composition also contains a binding agent, which serves to bind each of the starch molecules to each other. The binding agent may be any suitable binding agent, including calcium stearate, calcium chloride, and calcium carbonate. The binding agent is preferably calcium stearate. The composition additionally has one or more solid combustible material, for example in the form of wood powder or preferably wood chips. These solid combustible materials function to enhance the aesthetic appeal of the composition. In addition, the solid combustible material acts as a smouldering agent to provide an additional, and in use, flameless heat source.

During manufacture, an accelerant is added to the admixture for purposes of increasing the rate of reaction of combustion. The accelerant may be potassium nitrate.

A hardening agent may optionally be added to the admixture. This may be a physical hardening agent or a chemical hardening agent, and which functions to solidify, to a degree, the composition, as per pre-defined requirements. An end product that tends towards a solid block would include suitable amounts of hardening agents, whereas a more liquid product would include less hardening agent, as is known in the art. Typically, the physical hardening agent is wax such as paraffin wax.

The main role of starch in the present invention is to aid the surfactant in preventing droplets from within the emulsion to combine and separate into their respective phases. The starch thus aids the surfactant in the formulation by further enhancing the stability of the emulsion. The polymer produces a more viscous aqueous phase within the emulsion, making it more difficult for the droplets to coalesce.

The improved combustible composition is manufactured according to the following steps: Having regard to the illustrative examples which follow, add the formula quantities of soft water, surfactant and hydrocarbon together and mix to a moderate vortex. Mix well to allow an emulsion to form. While mixing, slowly add the formula quantity of starch to the admixture. Increase the mixing rate gradually as the starch dissolves in the water and the liquid increases in viscosity. With increasing levels of hydrocarbon the emulsion takes longer to turn into a stable gel. Therefore, continue mixing until gellation occurs and a homogeneous product is observed. This can take up to 10 minutes. Continue mixing until all residual hydrocarbon disappears.

It will be appreciated that variations in the ratio of liquid hydrocarbon:starch (whether natural or modified starch) will increase or decrease the relative viscosity of the combustible composition, in that higher ratios of liquid hydrocarbon as against starch will result in a highly viscous composition. By reducing the amount of hydrocarbon gel and increasing the amount of starch, the viscosity of the composition is reduced in varying stages, which present as (in increasing orders of liquid hydrocarbon and decreasing orders of starch), a gel, a solid gel, and a solid block. Similarly, the physical appearance of the composition can be modified dependant on the ratios of liquid hydrocarbon:surfactant content. With increasing hydrocarbon content, the appearance changes from opaque-white to a translucent grey-white gel, while increasing surfactant content, changes the appearance from translucent gel to translucent gel with air bubble inclusions to white, firm foam. Table 1 below is illustrative of this dynamic in the liquid hydrocarbon:surfactant ratio: Table 1 : Formulations of Compositions

In this specification, references to Gels A to D should be read as gels having a constant surfactan water ratio. In addition, references to Gel I - IV should read as gels containing changes to surfactant:water ratios as appears in Table 1 above.

Experimental

Product development

Each gel batch was produced with a lab scale motorised mixer. Eight batches were manufactured and split into two sets according to the variables that were changed. Batch A to D were produced by maintaining a constant surfactan water ratio (SW ratio) and water:polymer ratio (WP ratio) while increasing the liquid hydrocarbon content. Batch I to IV were produced by maintaining a constant mass concentration of surfactant while increasing the hydrocarbon:water ratio (HW ratio) and SW ratio. The polymer mass concentration for Batch I to IV was limited to range between 4.25 % and 5.75 %. The two sets were formulated in this manner for two reasons:

- To compare the key performance criteria of a gel to the gels in its respective set. - To compare the change in performance of a set with constant SW ratio to the change in performance of a set with increasing SW and HW ratios.

The results of the foregoing adjustments in HW and SW ratios are shown in Tables 3 and 4 below. Formula quantities of water, surfactant and liquid hydrocarbon were added to a mixing vessel and the mixer was then switched on to form a vortex. Care was taken to eliminate splashing and a speed of 400 rpm was achieved. After 5 minutes, the formula quantity of starch was added and the speed gradually increased to 1000 rpm. The emulsion was then monitored closely to observe the gel point. After gelling was initiated, the motor speed was increased to 2000 rpm to trap air in the gel, to further enhance the rate of gelling, and to ensure the complete absorption of liquid hydrocarbon.

Burn time and flame height

The apparatus used in each test included a standard instrument for weighing samples, a stopwatch, ceramic tiles for bearing samples during combustion and an extraction chamber. The burn time and flame height of each batch were each recorded for comparison and as a function of batch composition. A 30 g sample of gel was placed on a ceramic tile and shaped into a rectangular shape block; the shape and sample weight are representative of a typical piece of a prior art solid hydrocarbon based fuel. This was repeated for a total of three times per batch. The sample was ignited and the timer started once flame propagation was observed. The maximum flame height was then recorded at 3, 8 and 1 1 minutes. This was accomplished by measuring the three maximum peak flame heights observed within a period of 30 seconds. Upon complete flame cessation the timer was stopped and the burn time was recorded.

The following Tables 2 and 3 represent flame height and burn time of the improved combustible composition according to the invention as compared to a commercially available prior art embodiment sold under the trade name "Blitz® Firelighters", taken at specified time intervals. In all other instances herein, Blitz® is used as a control.

Table 2: Values for Average Flame Heights under varying Conditions

Sample (mass 30 g)

Time

(min) Blitz Control A B C D 1 II III IV

Flame 3 min 32 26 30 31 33 32 33 32 32

Height (cm)

Light Draft 8 min 18 19 20 20 23 23 23 24 20

1 11 min 12 15 13 16 16 16 16 16 14

Flame 3 min 30 26 30 30 33 32 32 32 34

Height (cm)

Light Draft 8 min 20 18 19 20 21 22 23 24 20

2 11 min 12 15 14 16 15 16 15 17 14

Flame 3 min 29 25 27 31 29 31 32 31 32

Height (cm)

Moderate 8 min 21 16 17 19 21 20 21 22 19

Draft 3 11 min 15 11 13 16 15 16 14 13 12

3 min 31.0 26.0 30.0 30.5 33.0 32.0 32.5 32.0 33.0

Light Draft

Averages 8 min 19.0 18.5 19.5 20.0 22.0 22.5 23.0 24.0 20.0

11 min 12.0 15.0 13.5 16.0 15.5 16.0 15.5 16.5 14.0

3 min 30.3 25.7 29.0 30.7 31.7 31.7 32.3 31.7 32.7

Total

Averages 8 min 19.7 17.7 18.7 19.7 21.7 21.7 22.3 23.3 19.7

11 min 13.0 13.7 13.3 16.0 15.3 16.0 15.0 15.3 13.3 Table 3: Burn Time of the Invention in comparison to Blitz®

Table 4: Compositions Having Varying Hydrocarbon:Surfactant Ratios

The following are examples of the invention each displaying the characteristics relating to viscosity and appearance as hereinbefore described.

Example 1

Ingredients Batch I Batch II

% w/w % w/w

Turpesol Illuminating Paraffin C10-C14 59.62 65

Stygel T Premodified Starch 8.64 7.48

Nansa 30 Dodecylbenzene sulphonate 30 % 5.01 4.34

Soft Water H2O 26.73 23.14 Example 2

It will be appreciated that a number of variations in detail are possible in respect of the invention, and without departing from the scope or spirit of the invention. For instance, the invention may also be achieved by cross-linking the starch with a starch-based cross-linking agent. The aforementioned variations are considered to fall within the scope of the present disclosure.