Expanded polystyrene made using D-limonene as a plasticizer

A process of forming expanded polystyrene beads having internal cells of a size typically generated by including a larger amount of pentane in the formulation, comprising:

• heating a mixture of styrene, demineralized water, brominated flame retardant chemicals, a peroxide first polymerization initiator, paraffin, tricalcium phosphate (TCP), a surfactant, an extender and D-limonene to a first polymerization temperature;
• adding 3-8% by weight pentane and a second polymerization initiator to the mixture and heating to a second polymerization temperature to form EPS beads having cells as large as if about 25% more pentane was used than the amount of pentane which actually was used.