Plasticizer Processing Methods

The suspension PVC process (S-PVC) is the common method of producing PVC.

PVC is obtained in the form of particles with a size of 50 to 200 microns.

These particles are mixed with plasticizers.

Adding an external plasticizer to the PVC polymer increases its flexibility.

 

Adding plasticizers

 

There are five distinct steps in adding plasticizers, which are:

Step 1: The plasticizer is mixed with the resin.

Step 2: The plasticizer penetrates the resin particles and swells them.

Step 3: The polar groups in the PVC resin are separated from each other.

Step 4: The polar groups of the plasticizer interact with the polar groups on the PVC chain.

Step 5: The PVC structure is re-established after cooling, with the plasticizer fully retained

Plasticizer Loss/Bleeding

Incompatibility between the polymer and the plasticizer can cause bleed.

Several factors can lead to migration of plasticizers, including:

• Temperature
• Humidity
• Mechanical stress
• Weathering

This migration can occur from the surface of the plastic, into or onto a substrate with which the plastic is in close contact.

Loss of plasticizer can result in reduced flexibility, brittleness, and cracking.

 

What are the main types of plasticizers?

Plasticizers are classified based on their chemical composition.

It is essential to comprehend the impact of structural elements on the properties of plasticizers and their influence on the base polymers.

For example, the presence of elements such as alcohols in a homologous series of phthalates and adipates.

Different plasticizers affect the physical and chemical properties of materials. Therefore, you require a specific softener or plasticizer to modify the properties and meet the end user's needs.

Several chemical families of plasticizers are used to modify polymers. Among them, the most common models are:

1. Phthalate esters are produced by esterification of phthalic anhydride or phthalic acid.

They are obtained by oxidation of or thoxylene or naphthalene.

The most commonly used phthalate plasticizers are:

• DEHP: low molecular weight or thophthalate. It is still the most widely used PVC plasticizer in the world.
• DINP, DIDP: high molecular weight or thophthalate.

 

Dibasic aliphatic acid esters. These include chemicals such as glutarates, adipates, azelates and sebacates. They are made from dibasic aliphatic acids such as adipic acid and alcohols.

1. Benzoate ester. They are esterification products of benzoic acid and selected alcohols or diols.

 4. Trimellitic esters are produced by esterification of trimellitic anhydride (TMA) and usually C8-C10 alcohols.

1. Polyesters are formed by the reaction of many compounds of dicarboxylic acids and dihydric alcohols.
2. Citrates. They are tetraesters obtained by the reaction of one mole of citric acid with three moles of alcohol. The only hydroxyl group of citric acid is acetylated.
3. Bioplasticizers. These materials are based on epoxidized soybean oil (ESBO), epoxidized linseed oil (ELO), castor oil, palm oil, other vegetable oils, starch, sugar, etc.
4. Others include phosphates, chlorinated paraffins, alkyl sulfonic acid esters, and others.

 

Phthalate Plasticizers

Phthalates are produced by the esterification of phthalic anhydride. Phthalic anhydride is obtained by oxidation of ortho-xylene.

Plasticizer molecule dioctyl terephthalate (DOTP, DEHT)

Phthalates appear as colorless liquids with a mild odor. They have limited solubility in water. However, they are miscible in many organic solvents (mineral oil, etc.). Key advantages and limitations of phthalate plasticizers include:

Advantages:

• They are a popular choice because they resist leaching, evaporation, and migration.
• Phthalates offer durability, flexibility, weather resistance, and can withstand high temperatures.
• Phthalates are cost-effective compared to other plasticizers.

Limitations:

• In polymers such as PVC, phthalates are not chemically bound and leach out of the plastics, resulting in their presence in the environment.
• Some phthalate plasticizers can pose serious health risks because they are carcinogenic and/or developmental toxins.
• Some phthalates can accumulate in the human body at low levels.

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