Meaning
Chemical modification through controlled degradation narrows the molecular weight distribution of base resin to produce controlled rheology polypropylene. This polymer modification happens during extrusion by adding organic peroxides to the melt. Free radicals break long chains into shorter segments, which increases the melt flow rate and lowers melt viscosity.
Higher fluidity allows for faster injection cycles and filling of thin sections in complex moulds.
Molecular Precision
Precise control over chain length distribution reduces internal stress in moulded components. Narrower distributions offer more predictable shrinkage profiles across different geometry thicknesses. Lower viscosity during processing minimizes the motor torque load on screw drives.
Consistent chain length ensures that finished parts maintain structural integrity even when high speed injection settings produce high shear rates at gates.
Production Economics
Virgin material costs for this resin typically sit above standard grades due to the additional peroxide processing step. Regrind handling requires extra caution because previous thermal history already shortened the polymer chains. Adding excessive regrind can shift the flow characteristics away from the target datasheet range.
Production runs often demand virgin material to prevent premature nozzle drooling or gate blistering.
Processing Limits
Higher melt flow rates often decrease the impact resistance of the finished part. Excessive degradation leaves the material prone to environmental stress cracking under heavy mechanical loads. Moulders must balance the processing speed gained through lower viscosity against the loss of ductility in the final product.
Rapid cooling in the mould also influences the final crystallinity levels. Optimal performance depends on keeping the melt temperature within the specified range throughout the production cycle.
