Steam Cracker Co-Processing Mass Balance Basics
Co-processing plastic pyrolysis oil in steam crackers requires yield-based mass balance attribution under ISCC PLUS rules to substantiate circular claims.
Diene Value
Meaning
Chemical titration measures the amount of conjugated double bonds present in an organic material. In polymer sourcing, diene value indicates the concentration of these reactive double bonds within the backbone of elastomers and impact modifiers. Thermoplastic elastomers rely on these unsaturated sites for subsequent functionalization or rubber crosslinking.
Resins with higher values provide more sites for chemical modification.
Polymer Unsaturation
Diels-Alder reaction chemistry underpins the laboratory measurement of this property by reacting the polymer with maleic anhydride. This specific diene value helps compounders characterize the butadiene or diene phase in impact-modified plastics like acrylonitrile butadiene styrene. Raw material specifications must declare this metric to ensure consistent performance during the grafting phase of polymer synthesis.
Variations in the unsaturation level can alter the mechanical performance of the final compounded resin.
Thermal Stability
Double bonds in the polymer structure are highly susceptible to thermal degradation. High diene value accelerates the oxidation of the resin during processing. This oxidation causes yellowing and embrittlement in the finished part.
Compounding Outcome
Moulders face serious process variations when using resins that have inconsistent unsaturation levels. Fluctuations in the diene value alter the viscosity of the molten plastic, leading to common moulding defects like flash or short shots during high-volume production. Sourcing teams use this value as a raw material specification to ensure consistent polymer behavior.
Stable unsaturation profiles prevent the resin from crosslinking prematurely in the extruder barrel, protecting the machinery from pressure spikes.