How to tell if the surface of TPE material is bleeding?
Time of issue:2026-07-16 20:02
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How to tell if the surface of TPE material is bleeding?
The exudation during the processing of TPE materials and products operates on a principle similar to precipitation in chemistry. The only difference is that the solution is replaced by the overall TPE compounding system, and the solute is replaced by low-molecular-weight substances. Exudation in TPE products refers to the gradual migration of these low-molecular-weight substances to the surface over time. Because TPE is a solid-state dispersion and dissolution system, this exudation is relatively slow, typically taking anywhere from 3 to 30 days. In chemistry, the exudation of substances in a solid-state dispersion system is also referred to as migration. So, how can we tell if the surface of a TPE material is bleeding?
There are three main types of surface exudation in TPE materials: blooming, wax exudation, and oil bleeding.
1. Blooming
Blooming is the most common type. The primary cause of blooming in TPE-S thermoplastic elastomers is the exudation of antioxidants (anti-aging agents). In severe cases, a distinct white layer is visible on the material's surface. However, under normal circumstances, the whitening is not visible to the naked eye but becomes obvious upon touch, presenting as a powdery residue.
Blooming is the most common type. The primary cause of blooming in TPE-S thermoplastic elastomers is the exudation of antioxidants (anti-aging agents). In severe cases, a distinct white layer is visible on the material's surface. However, under normal circumstances, the whitening is not visible to the naked eye but becomes obvious upon touch, presenting as a powdery residue.
In some cases, touching the TPE material does not cause whitening; instead, it requires vigorous scratching to reveal a white mark, commonly known as "scratch whitening." This is usually caused by excessive filler addition and inadequate surface treatment of the fillers.
Common solutions include:
2. Oil Bleeding
Oil bleeding is mainly caused by excessive oil filling in the material. At low temperatures, the material's crystallinity increases, causing some of the oil originally distributed in the amorphous regions to migrate to the surface. Conversely, at high temperatures, the molecular movement of materials like SBS/SEBS increases, reducing their oil-retention capacity and also leading to oil migration to the surface.
Oil bleeding is mainly caused by excessive oil filling in the material. At low temperatures, the material's crystallinity increases, causing some of the oil originally distributed in the amorphous regions to migrate to the surface. Conversely, at high temperatures, the molecular movement of materials like SBS/SEBS increases, reducing their oil-retention capacity and also leading to oil migration to the surface.
To improve oil bleeding, it is crucial to ensure the filling oil is as compatible as possible with the SEBS/SBS base resin. Never overfill oils in low-molecular-weight styrenic elastomers. Relatively speaking, paraffinic oils provide a drier hand feel, but naphthenic oils actually offer better compatibility with SEBS/SBS.
3. Wax Exudation
Wax exudation is typically caused by an excess of lubricants, such as polyethylene wax, stearic acid, stearates, and erucamide. It is worth noting that additives like silicone masterbatch (polysiloxane) naturally tend to exude to the material's surface to interact with the mold; therefore, their dosage should be kept to a minimum. While some waxes have a synergistic effect, others are more prone to causing exudation.
Wax exudation is typically caused by an excess of lubricants, such as polyethylene wax, stearic acid, stearates, and erucamide. It is worth noting that additives like silicone masterbatch (polysiloxane) naturally tend to exude to the material's surface to interact with the mold; therefore, their dosage should be kept to a minimum. While some waxes have a synergistic effect, others are more prone to causing exudation.
Wax exudation generally does not result in "scratch whitening." Instead, it manifests as shiny scratch marks. In severe cases, the surface may feel sticky. If the material also exhibits blooming, the surface will feel both sticky and appear whitened.
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