Can fluorine-free water repellents achieve oil repellency?

Standard fluorine-free water repellents (typically based on hydrocarbons or silicones with short carbon chains) primarily repel water but are not effective in repelling oil.

The following explains why, along with technical solutions that achieve oil repellency.

1. Principle: Why are "waterproof" and "oil repellent" two different things?

The scientific principle behind this is surface tension.

Water: It has a very high surface tension (approximately 72 mN/m). Therefore, if the surface tension of a fabric is lowered below this value, water droplets have difficulty wetting and penetrating it, creating the "lotus effect" where water droplets roll off. This is the fundamental principle of water repellency.

Oil: Oils (such as cooking oil and motor oil) have a very low surface tension (approximately 20-30 mN/m). For a fabric to be oil-repellent, its surface tension must be lower than that of the oil, so that oil droplets cannot wet the surface. This is the principle of oil repellency. Key Point: A surface that is oil-repellent is definitely water-repellent (because its surface tension is lower than that of water); however, a surface that is water-repellent is not necessarily oil-repellent.

2. Chemical Differences: Fluorine-Based vs. Fluorine-Free

Traditional Fluorinated Water- and Oil-Repellents (such as C8/PFOA and the improved C6):

Why do they work? Fluorine atoms are the most electronegative elements in the periodic table and can form extremely stable carbon-fluorine bonds with extremely low surface energy. This chemical structure allows fluorinated finishes to reduce the surface tension of fabrics to very low levels (approximately 10-20 mN/m), far below the surface tension of water and oil. Therefore, they are simultaneously water- and oil-repellent, often referred to as "triple-proof finishes" (water-, oil-, and stain-resistant).

Environmental Issues: Traditional long-chain fluorinated compounds (such as C8) may generate persistent organic pollutants (POPs) such as PFOA/PFOS during production and use. These substances are difficult to degrade in the environment and in the human body, posing potential health risks. Mainstream fluorine-free water repellents (hydrocarbons, silicones, dendrimers, etc.):

How it works: They lower surface tension by forming a hydrophobic film on the fiber surface.

Achievable surface tension: Approximately 25-35 mN/m.

Result: This value is lower than the surface tension of water (72 mN/m), making it effectively water-repellent. However, it is still higher than the surface tension of common oils (20-30 mN/m), so oil droplets can easily wet and penetrate the fabric, rendering it ineffective at repelling oil.

3. Are there any fluorine-free technologies that are "oil-repellent"?

This is a hot research and development topic in the industry, and while some progress has been made, there are limitations:

"Fluorine-like" fluorine-free technologies (e.g., based on long-chain silanes or specialized dendrimers):

Some high-end fluorine-free products attempt to mimic the low surface energy properties of fluorine compounds through complex molecular design. Current Status: They may exhibit some resistance to certain types of oils with high surface tension (e.g., achieving a low rating in olive oil testing), but their broad-spectrum and durability of oil repellency, especially compared to established C6 fluorinated products, are generally not up to par. High oil repellency standards (such as those in AATCC 118 testing) are difficult to achieve.

Physical/Ecological Barrier Technologies:

These technologies form a dense physical film or a "shield" on the fiber surface through cross-linking reactions to block oil penetration. This approach is more of a "fouling-resistant" approach than a true "oil-repellent" approach that reduces surface tension. They may feel harder and have limited protection against low-viscosity oils.