EPOXIDIZED SOYABEAN OIL (SECONDARY PLASTICIZER) USED IN PVC COMPOUND

Epoxidized soybean Oil (ESO) is an additive to flexible Polyvinyl Chloride (PVC) that gains its name from the reaction that occurs with the unsaturated soybean oil. The epoxidation reaction takes place at a carbon to carbon double bond site. The oxygen atom (usually in the form of a peroxide or a peracid) comes in and attaches itself between the two carbons to create a single bonded triangular ring between the three molecules called an oxirane. This oxirane can be used as a way of separate well formed ESO molecules from those that will be less effective. Those ESO molecules with higher oxirane percentages will product better results than those with low oxirane percentages.

Because epoxidized soybean oil is synthesized from the bio-based, renewable resource of soybean crops, the level of saturation of the soybean oil and ultimately the oxirane value of the ESO created from it, is dependent on the growing conditions of the soybeans. Very hot, dry weather is known to inhibit the formation of the unsaturated C18-3 and C18-2 double bonds in the soybean oil and will therefore lead to lower oxirane values in the ESO produced from it.

The climate of American Midwest is very well suited to producing high oxirane value ESO. The United States is responsible for about 32% of the total soybeans grown worldwide, with Brazil and Argentina also significant producers of the oilseed.

Although ESO was first introduced into the plastics market over thirty years ago as a bio based plasticizer that could be a drop-in replacement to Dioctyl phthalate (DOP), it has found a strong niche as a secondary plasticizer due to its heat and light stabilization effects in PVC compounds. The epoxide group is more reactive than a double bond, thus providing a more energetically favorable site for reaction and making it a good hydrochloric acid scavenger and plasticizer.

Epoxidized soybean oil, better known by its acronym, ESBO, is a plasticizer used in polyvinyl chloride (PVC) plastics. It serves as a plasticizer and as a scavenger for hydrochloric acid liberated from PVC when the PVC undergoes heat treatment.

A few EU surveys have shown fairly high levels of ESBO in foods, in which about 4% were above the current specific migration limit (SML) for ESBO of 60 mg/kg and about 15% of the samples were above 30 mg ESBO/kg food. High migration levels might lead to an intake that exceeds the existing Tolerable Daily Intake of 1 mg/kg body weight/day.

Epoxidized linolein a major component of ESBO

ESBO is manufactured from soybean oil through the process of epoxidation. The reason why vegetable oils are widely used as plasticizers is because the high numbers of carbon-carbon double bonds present in vegetable oils make them a good target for manipulation into some other useful products like in this case – from soybean oil into epoxidized soybean oil. The epoxide group is more reactive than double bond, thus providing a more energetically favorable site for reaction and making the oil a good hydrochloric acid scavenger and plasticizer. Usually a peroxide or a peracid is used to add an atom of oxygen and convert the -C=C- bond to an epoxide group.

Metal closures incorporate a ring-shaped gasket formed from a bead of liquid plastisol containing up to 40% ESBO which is moulded into the correct profile in the closure shell using a hot punch, then fused by passing through an oven at 200°C for 90 seconds. PVC starts to break down at this high temperature and releases hydrogen chloride. ESBO functions as a stabilizer to scavenge this hydrogen chloride to prevent the autocatalytic breakdown of the polymer. It also functions as a plasticizer.
Vegetable oil finds sustainable and renewable source of raw material. The unsaturation present in vegetable oils can be chemically modified to a value added product by a complicated reaction called ‘epoxidation’. Due to the high reactivity of the oxirane ring epoxides can also act as a raw material for synthesis of variety of chemicals such as alcohols (polyols), glycols, olefinic compounds, lubricants, plasticizer and stabilizer for polymers and their demand is increasing day by day. Vegetable oil represents one of the cheapest and most abundant biological feedstock available in large quantities and its use as starting material offers numerous advantages such as low toxicity and inherent biodegradability. Thus the economic value of the vegetable oil could be increased by converting the vegetable oil into epoxidized vegetable oil. The double bonds in the vegetable oil are used as reactive sites in the coatings and they can also be functionalized by epoxidation. Thus the high molecular weight products can be obtained by increasing the cross linking. Now due to the increasing levels of awareness regarding environment is driving the development of sustainable green materials.

Petrochemical based resin such as epoxy, polyester and vinyl ester find more engineering application because of their advantageous material properties such as high stiffness and strength. However these resins have serious drawbacks in terms of biodegradability, initial processing cost, energy consumption and health hazards. Consequently there is a requirement to develop novel biobased product from renewable feedstock. Therefore a number of researchers have been studied vegetable oils as alternative feedstock to substitute for petroleum. Hence it needs to be explored for the various applications in chemical industry.

The double bonds in the vegetable oils are used as reactive sites in coatings and they can also be functionalized by epoxidation. The utilization of epoxidized vegetable oil has become more common in the past few years. Moreover, plasticizers and additives for polymer PVC derived from vegetable oil based have been shown to have improved performance in terms of high resistance to heat and light.
As energy demands increase and fossil fuel reserves are limited, there has been a growing interest in the utilization of renewable resources as an alternative to petroleum-based polymers. Consequently, much attention has been focused on the development of polymeric materials from vegetable oils, a ustainable resource. Vegetable oil, which is readily available and is a comparatively inexpensive material, can be used to synthesize various types of polymers. Today, one of the most important epoxidized vegetable oils is epoxidized soybean oil (ESO), and its worldwide production is about 200,000 t/year. Several derivatives of vegetable oils are used as polymerizable monomers in a radiation curable system due to their environmentally friendly character and low cost when compared to products from petroleum. Moreover, the long fatty acid chains of vegetable oils impart desirable flexibility and toughness to some brittle resin systems such as epoxy, urethane and polyester resins. Triglyceride oils are one of the most important sources for biopolymers. Triglycerides from plants, such as soy bean, palm, rapeseed or sun flower, can be utilized. Triglycerides are composed of three fatty acid chains joined by a glycerol center, with a typical structure.