Candles are used universally as a source of light and for pleasant ambience in regular life and at special occasions. A typical candle is made from combustible fuel material that provides structure and stability and contains a wick in the middle. Lighting of the candle ignites the combustible material on the wick which generates heat to melt the solid surrounding the wick, further forming a liquid pool that can flow into the wick by capillary action and burn until all the fuel is consumed. The candle can be used multiple times or all at once.
Candles are made with various raw materials including natural and synthetic materials. The customary base raw materials that are used in candle manufacturing are paraffin wax, bees wax, hardened (hydrogenated) fatty acids (aka stearin), animal waxes like tallow, and hardened fats, oils (hydrogenated fats, aka hydrogenated triacylglycerols or triglycerides). Currently the use of paraffin waxes is most prevalently used due to cost, availability, and different grades of waxes with different melting profiles and physical properties. In addition to the base material, the candle may contain perfumes for aroma, coloring dyes, antioxidants, insect repellents, or other additives to improve the mechanical properties and burning characteristics.
Candle formulations typically contain substantial amounts high melting temperature materials. These materials are liquefied (melted) and processed into candles by adopting various methods that include pouring, molding, dipping, casting, drawing, extrusion or rolling processes. General purpose candles are usually made by molding or pouring processes. Standard commercial candles usually contain 50 to 80 percent petroleum wax, 10 to 35 percent stearic acid (hydrogenated fatty acids), and 0 to 10 percent stabilizers, 0 to 3 percent color and 0 to 10 percent fragrance. Some candles may contain small amounts of candelilla or carnauba waxes to regulate the softening or melting point of the finished wax. Beeswax candles are made of only pure insect wax and paraffin plus a small amount of stiffening wax.
The wick is commonly made of a high grade cotton or linen. The material is woven (or braided) and treated with inorganic materials so that it will burn in one direction and will curl so that its end remains in the candle flame's oxidizing zone for even and intense burning. Often, wire-core wicks are also used. These wicks have a wire center that allows them to burn slightly hotter than cotton and remain erect in the melted wax.
Candles made with petroleum based waxes produce smoke, soot and unpleasant odor due to the presence of branched hydrocarbons, aromatic compounds and sulfur compounds. The soot particles and smoke pose health risk to humans especially when used in closed environments. Also the petroleum raw materials are non renewable, not environmentally friendly and not considered “green”.
The use of partially hydrogenated vegetable oils (triacylglycerols), aka vegetable waxes or fats in candles is advantageous as they are derived from renewable materials. The melting profile of vegetable oils and their suitability to use in candles depends upon the type of oil and unsaturation content and the degree of hydrogenation. However, the hydrogenation process adds significant cost to the material due to the need for a pressure reactor and a metal catalyst. Additionally, transportation, material transfers of solid fats is cumbersome and expensive. Also the use of partially hydrogenated vegetable oils in candles is further complicated by polymorphism, which is the ability to crystallize into different crystal forms that have different melting temperatures and other physical properties. Candles made with predominantly hydrogenated vegetable oils show a white chalky appearance, cracks and specks with time. Most of these defects are a manifestation of polymorphism. The additional disadvantages of using partially hydrogenated vegetable oils include: high volume change or shrinkage during the liquid to solid transition, air pocket formation, textural changes with time, and problems in use such as guttering or brake-outs.
One approach to overcome the disadvantages of using partially hydrogenated vegetable oils involves the use of substantial amounts of liquid oils in the fabrication of a candle. This has number of advantages, including cost and the low volume change or shrinkage while undergoing liquid to solid transition during the manufacturing. Further, the liquid oils (especially polar oils like vegetable oil) have the ability to incorporate higher amounts and uniform distribution of fragrance and coloring materials into the candle, a much desired feature. The use of liquid oils in candles has been reported in the prior art. Wilson S. K. (publication No.: US 20020069580) reported gelled hydrocarbon compositions which were gelled by using low and medium molecular weight triblock polymers. Shinski R. J. (publication No.: US 20030101639) describes a gel candle assembly comprising a gel candle made of three different viscosity mineral oils and a polymer to produce a self supporting structure. Tao et al. (publication No.: US 20040200136) describe a candle composition comprising fatty acid, plant oil and a crystal modifier. Recently Wu et al. (publication No.: US 20080307696) described a candle composition having paraffin, non-hydrogenated oil, and a solidifying amount of congealing reagent comprising petrolatum, oxidized petrolatum, oxidized long chain hydrocarbons, or modified hydrocarbons. These approaches produce functional candles with moderate incorporation of liquid oils, however, there remains a need for improved candle compositions, especially compositions containing natural and renewable materials, to produce high quality candles which incorporate large percentages of liquid oils and/or lower melting, partially hydrogenated vegetable oils.