PP Modification Overview: Filling, Toughening, Reinforcing and Flame Retarding

What each route does

Filling — talc, calcium carbonate, mica: raises stiffness, heat resistance and dimensional stability and lowers cost; costs impact strength and adds density.

Toughening — EPDM, POE, EVA: improves low and room temperature impact; costs stiffness, heat resistance and surface hardness.

Reinforcing — short or long glass fibre: lifts strength and stiffness together and improves creep resistance markedly; costs anisotropy, fibre show and processability.

Flame retarding — brominated, halogen-free phosphorus-nitrogen, intumescent: meets UL94 V-0 or V-2; costs some degradation across all mechanical properties and a clear price increase.

The right order of combination

A common combination is filling plus toughening, as in PP+EPDM-T20: 20% talc carries stiffness while EPDM restores impact. The sequence matters — secure the stiffness gain first, then dose toughener to reach target impact.

Working the other way usually fails to find the same balance: adding the rubber phase first and then filler drives viscosity too high for good dispersion.

Combination limits

Total filler, glass plus mineral, is generally kept under 40%; beyond that melt flow collapses, torque rises, and fibre show and tool wear escalate.

Combining flame retardance with glass requires higher FR loading to counter the candlewick effect, plus an anti-drip agent.

Requests covering all four routes at once usually signal that the design needs revisiting rather than the formulation being pushed harder.