The hygroscopic properties of EPS Particles in different humidity environments have a significant impact on their mechanical properties.
1. Hygroscopic process and initial impact
When EPS Particles are exposed to a humid environment, due to the molecular structure of polystyrene, it will absorb moisture in the environment. In the early stages of moisture absorption, moisture molecules will gather on the surface of EPS Particles and at the entrance of the microporous structure. This will increase the apparent weight of EPS Particles and form a thin water film on the surface of the particles due to the intervention of water molecules. This water film will weaken the original intermolecular force on the particle surface. When subjected to a small external force, the friction and bonding force between particles will decrease. For example, in some application scenarios that require high particle accumulation stability, such as loose-fill packaging materials, EPS Particles are more likely to slide and shift after absorbing moisture, thus affecting the stability of the overall structure.
2. Continuous moisture absorption and structural damage
As the humidity increases and the moisture absorption time prolongs, moisture will gradually penetrate into the internal microporous structure of EPS Particles. The microporous structure inside EPS Particles is a key factor in maintaining certain mechanical properties. The intrusion of moisture will destroy this structure. On the one hand, moisture will swell the micropore walls, change the shape and size of the micropores, and make the originally regular micropore structure irregular. On the other hand, the presence of moisture can trigger some physical and chemical changes, such as hydrolysis reactions (although the degree of this reaction is relatively small), leading to the breakage of polystyrene molecular chains. This series of changes significantly reduces the compressive strength and impact strength of EPS Particles. For example, in the field of building insulation, moisture-absorbed EPS insulation materials are more likely to be deformed and damaged when subjected to external pressure (such as the weight of the building, wind load, etc.), thus reducing the insulation effect.
3. Humidity changes and fatigue damage
Changes in the humidity environment, such as alternating dry and wet conditions, are a test for the mechanical properties of EPS Particles. When EPS Particles undergo a drying process after absorbing moisture, stress changes will occur inside the particles due to the evaporation of water. This stress change will repeatedly act on the destroyed micropore structure and molecular chains, causing fatigue damage. Just like repeatedly bending a metal wire will cause it to eventually break, the mechanical properties of EPS Particles will accelerate deterioration in this environment of repeated changes in humidity, and may eventually fail to meet their basic requirements in various applications.
