Meaning
Chemical degradation of functionalised polyolefin resins occurs when water molecules cleave the ester or anhydride bonds that facilitate adhesion between dissimilar material layers. Adhesive tie layer hydrolysis primarily affects multilayer structures where a maleic anhydride grafted tie resin joins a polar barrier like ethylene vinyl alcohol to a non-polar substrate.
Structural Failure
Delamination of film or rigid packaging components results from the loss of chemical bonding at the interface. While the bulk properties of the polymer often remain stable, adhesive tie layer hydrolysis reduces peel strength until the layers separate under mechanical stress.
Extrusion Influence
Processing temperatures in the die head can accelerate the rate of bond cleavage if the resin has not been dried to the specified dew point. Excessive heat combined with residual moisture triggers adhesive tie layer hydrolysis during the melt phase, leading to immediate optical defects or bubbles. Moulders monitor torque and pressure for signs of viscosity changes that indicate polymer chain scission.
This chemical breakdown is irreversible and renders the resin unsuitable for high-barrier applications.
Moisture Sensitivity
Environmental storage conditions for hygroscopic tie resins dictate the shelf life of the raw material before conversion. High humidity in the warehouse allows ambient moisture to penetrate resin bags, which initiates adhesive tie layer hydrolysis before the pellet enters the extruder throat. This process compromises the integrity of the final bond.
