Basic Technical Criteria for High Flow Polypropylene Homopolymer Selection
Select high flow polypropylene homopolymers by balancing melt flow rate against impact loss, verifying narrow molecular weight distribution and peroxide residues.
Dialkyl Peroxide
Meaning
Organic compounds containing a peroxy group linked to two alkyl radicals function as high temperature initiators and crosslinking agents in polymer processing. Industry formulations utilize dialkyl peroxide to initiate the polymerization of ethylene or to induce crosslinking in polyethylene and silicone elastomers. The high thermal stability of these chemicals makes them ideal for applications requiring high processing temperatures.
Thermal Decomposition
Free radicals generated by the cleavage of oxygen-oxygen bonds initiate chemical reactions within the polymer melt. A dialkyl peroxide decomposes at a specific rate governed by its half-life temperature, which is the temperature where half of the initiator decomposes in a given time. This chemical behavior allows moulders to control the crosslinking process during injection moulding or extrusion.
When the melt temperature is kept below the activation threshold, premature crosslinking or scorch is prevented.
Rheological Modification
Viscosity reduction in polypropylene resins occurs through controlled degradation during extrusion compounding. Adding a dialkyl peroxide to a polypropylene resin cleaves the polymer chains, narrowing the molecular weight distribution and increasing the melt flow rate. This modification enables the production of high-flow resins suitable for thin-wall injection moulding or melt-blown fiber applications.
Processors depend on this mechanism to balance mechanical properties and processability.
Process Control
Accurate dosing and temperature management prevent the formation of gel particles and inconsistent material properties in the final product. Incorrect concentrations of dialkyl peroxide can lead to incomplete crosslinking or excessive polymer degradation, which decreases the tensile strength of the part. If the peroxide is not fully consumed during the process, residual odor and volatile organic compounds will affect the finished goods.
This requires careful optimization of the residence time inside the compounding extruder. Consistent control of these variables ensures the mechanical properties match the datasheet specifications across the entire production run.