TABLE OF CONTENTS Plasticisers are added to PVC to achieve flexibility and workability. The flexibility or softness is determined by the type of plasticiser and level used in relation to the PVC (phr). They also operate as an internal lubricant between the PVC molecules. Based on high-boiling organic esters, e.g., phthalates, adipates, trimellitates, phosphates, and so on, addition levels can be as low as 20 phr for semi-rigid to 100 phr for very flexible applications.
Plasticisers act to reduce the glass transition temperature ( T g) of PVC. For many uses a reduction of T g to ambient temperature is required. When PVC is heated in the presence of a plasticiser, the plasticiser penetrates and swells the resin particles. This results in the polar groups in the PVC resin being freed from each other and plasticiser polar groups interacting with the resin polar groups. As long as there is sufficient compatibility between polymer and plasticiser, the plasticiser will be retained in the flexible product that results. There is no chemical reaction between the plasticiser and the PVC and so it can be considered as a two-phase blend. The action of these materials is known as external plasticisation.
The ability of PVC to accept high plasticiser levels is attributed to regions of order (microcrystallites) within a predominantly amorphous polymer structure, being reduced but not eliminated by incorporation of the plasticiser. Plasticisers are held in solution by dipolar attraction within the amorphous regions whilst inter-chain association, through the microcrystallites, provides elastic...
