The additives that increase the plasticity of material (the ability of a substance to take the desired shape) or decrease its viscosity are called plasticizers. These substances may be intended to alter physical properties.
They reduce the bond forces between polymer molecule chains to make matter more flexible. Under normal conditions PVC is a hard substance because the distance between molecules is short the intermolecular forces are very strong. If heated, the intermolecular energy is greater than the intermolecular force, which expands the molecular distances and causes the resin to soften. Plasticizers are added to PVC at this stage. Plasticizers move between PVC molecules and prevent the distance between polymer molecules from decreasing. Thus, polymer molecules can be separated even under normal conditions and the softness of the substance is preserved. These processes occur due to the role played by plasticizers, and technically, this process is called plasticization. While PVC molecules have positive and negative polarity in themselves, plasticizers also have polar and apolar parts. PVC molecules and plasticizers are electrically drawn together and the apolar portions open the distance between the polymer molecules to maintain softness. PVCs softened with plasticizers are named as flexible PVC materials. Plasticizers are not just additives. In addition, they are the main components that maintain plasticization efficiency and are well adapted to PVC, as well as demonstrating the physical properties of polymers and have low volatility.
The plasticizer must first be compatible with the resin, the more compatible the two, the better the plasticizer effect. The addition of a plasticizer allows the hard and solid plastics to be soft and elastic, reducing the transition temperature of the plastic glass. In general terms, plasticizers are expected to be of high purity, colorless, neutral, odorless, tasteless and always of the same quality.