Understanding Polyethylene Specific Gravity Testing and Plaque Preparation
Polyethylene specific gravity testing requires standardized 15 K/min plaque cooling and 24-hour conditioning to prevent thermal history errors exceeding 0.003 g/cm³.
Wetting Agent
Meaning
Reduction of the surface tension of a liquid is achieved by adding a chemical surfactant that allows the liquid to spread more easily across a solid polymer surface. This additive, known as a wetting agent, is used in aqueous molding release agents, coatings and cleaning solutions. It enhances the contact between the liquid phase and the high-surface-energy polymer or mold metal.
The additive is effective only in concentrations up to its critical micelle concentration, beyond which no further reduction in surface tension occurs.
Chemical Action
Molecules of the surfactant arrange themselves at the interface between the liquid and the solid. When a wetting agent is added, it reduces the contact angle of the droplet on the plastic surface. This allows the liquid to form a continuous thin film rather than beads.
It improves the uniformity of the applied coating.
Injection Molding Role
Mold release sprays rely on these surfactants to coat the intricate details of a mold cavity. A wetting agent helps the release spray cover the metal surface evenly without leaving dry spots. This ensures consistent ejection of the molded parts and prevents sticking.
It reduces cycle times by minimizing part ejection problems.
Surface Quality
Paint adhesion is improved by removing these residues. Proper washing steps prevent painting defects.