What does the contact angle of hydrophilic masterbatch mean? How does it affect the hydrophilic effect?

The meaning of contact angle

The contact angle is an indicator used to measure the wetting ability of a material's surface. When a liquid is dropped on a solid surface, the angle formed between the edge of the liquid droplet and the material surface is the contact angle. This value reflects whether the liquid can spread out on the material surface: a larger contact angle means the droplet gathers into a droplet shape, indicating that the material is hydrophobic; a smaller contact angle means the liquid droplet spreads easily and wets the surface, representing better hydrophilic effect.

When hydrophilic masterbatch is added to plastics or fiber substrates, essentially it is changing the surface energy of the finished material and adjusting the size of the contact angle, thereby achieving hydrophilic and moisture-wicking functions. It does not change the main structure of the substrate itself; rather, it relies on the internal hydrophilic components migrating to the surface to change the surface wetting characteristics.

How does the contact angle affect the hydrophilic effect

The contact angle directly determines the interaction mode between water vapor, liquid water and the material. When the contact angle falls within an appropriate range, water can spread along the fiber surface, and liquid water can quickly spread and conduct, making the fabric capable of conducting and transmitting moisture, suitable for quick-drying fabrics and filtering materials.

If the contact angle is too large, even if a hydrophilic masterbatch is added, the surface wetting is insufficient, and water droplets still remain on the surface, resulting in an unsatisfactory hydrophilic effect. However, the contact angle is not necessarily the smaller the better; excessive wetting can cause the hydrophilic additive to precipitate, resulting in a sticky surface, color shift, and may also reduce the durability of water resistance. After multiple washes, the hydrophilic performance quickly declines.

During the production process, the masterbatch formula, addition ratio, and processing temperature all affect the contact angle of the final molded product. If the processing temperature is inappropriate, the hydrophilic components are prone to premature decomposition or unbalanced migration, resulting in initial hydrophilic compliance but rapid decline later. Additionally, the type of substrate also has an impact. With the same hydrophilic masterbatch, when added to different fiber systems, the measured contact angle will vary.

When selecting, one should not only rely on the contact angle reference indicated by the masterbatch but also test on the finished sample. Balance the wetting ability and durability performance, consider the initial hydrophilic effect and stability after water washing and aging, and avoid only pursuing a low contact angle while ignoring side effects such as precipitation and yellowing.

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