Meaning
The initial period during which a polymer absorbs water without undergoing significant molecular weight loss defines the start of moisture-driven degradation. During the hydrolytic induction phase, water molecules diffuse into the amorphous regions of the plastic, but the rate of chain cleavage remains very low. This phase represents a window of safety where the moulded part retains its full mechanical properties despite being exposed to moisture.
Moisture Interaction
Hydrogen bonding between water and polar groups in the polymer chain occurs before chemical reaction begins. In the hydrolytic induction phase, the physical properties of the plastic may change slightly due to plasticization, which increases ductility while slightly reducing stiffness. This reversible phase ends when the water concentration reaches a critical threshold that initiates the cleavage of the ester or amide bonds.
Processing Boundary
Moulding resins that have not been dried adequately can bypass this protective period entirely during high-temperature processing. When a polymer experiences the hydrolytic induction phase at room temperature it is stable, but the heat of injection moulding accelerates the chemical reaction so much that degradation occurs within seconds. This makes pre-drying the resin to specified moisture levels a critical step before start of production.
Material Lifespan
Product designers use the duration of this initial period to estimate the useful life of biodegradable parts in humid environments. Once this period concludes, the material enters a phase of rapid autocatalytic hydrolysis, leading to a swift decline in physical performance.
