Meaning
Negative changes in the physical or chemical properties of polymer resins occurring during shipping and handling reduce the processability and quality of the material. The process of transit degradation is triggered by environmental exposure, friction, or mechanical stress during transport from the compounding plant to the moulder. This damage can present as moisture absorption, surface abrasion, or the generation of fines in pneumatic convey lines.
The vulnerability of a shipment is determined by the packaging method and the route’s environmental conditions.
Physical Impact
Pneumatic transport and bulk transfer of polymer pellets can cause severe friction between particles and the pipe walls. This friction leads to transit degradation through the creation of angel hair and fine polymer dust. When these fines enter the moulding machine, they melt faster than the pellets, causing burn marks, silver streaks, or clogged filters.
Keeping convey speeds low and using treated pipe walls can minimize this mechanical damage.
Material Damage
Environmental exposure during long-distance shipping can also alter the chemical stability of the polymer. When transit degradation occurs due to heat and humidity, hygroscopic resins like nylon or polycarbonate absorb moisture, which leads to hydrolytic degradation during processing. This chemical breakdown reduces the molecular weight and the impact strength of the molded parts.
Resins must be shipped in moisture-barrier bags or sealed silos to prevent this deterioration.
Preventive Action
Sourcing and logistics strategies must prioritize the protection of resins during transport to maintain consistency. Minimizing the number of transfer points during shipping reduces the risk of transit degradation. Moulders should inspect incoming shipments for torn bags, condensation, and signs of pellet abrasion before accepting the lot.
Testing the moisture content and melt flow rate of incoming resin can catch degradation before the material is loaded into the silos. These preventive steps help to avoid costly moulding defects and ensure that the finished parts meet the performance standards. Choosing direct shipping routes also helps to minimize the exposure to extreme temperature changes.
