How to Maximize the Performance of PDMS in Textile and Construction Industries?

The construction sequence of polydimethylsiloxane (PDMS) confers special abilities to the material, permitting both water and oil resistance to an extraordinary degree. Incorporating polymers of mixed Siloxane and PDMS into the construction results in seamless integration through the fabric, with the Siloxane component creating an adhesion to fabric fibers, while the PDMS component contributes to the surface of the fabric. These polymerized PDMS components create an unprecedented hydrophobic surface through molecular expression and additionally repels common oils, creating both hydrophobic and oleophobic characteristics that last for the life of the fabric. The results of the process create surface contact angles of greater than 150° with water and around 130° with oils. The most unique attribute of PDMS is that is unlike fluorinated abrasion resistant coatings that will crack with flexing and bending, the PDMS coating retains its oleophobic and hydrophobic properties through an extended life of abrasion resistance.

Performance Benchmarking: PDMS vs. Fluorinated Coatings Under AATCC 118 and ISO 14419 Testing

While fluorinated systems provide slightly better oil resistance, PDMS still fulfill functional criteria for most garments, workwear, and technical textiles, even those with OEKO-TEX® Standard 100 and bluesign® specifications. Without carbon- fluorine, PDMS avoids the risk of bioaccumulation, as well as the persistent environmental harm and regulatory risks associated with PFAS.

The adoption of PDMS and possible emerging marketing opportunities are due to the EU’s new restrictions on PFAS and other new regulations from the EPA.

Legislation requiring the search for alternatives to PFAS has been rapidly evolving. Examples include the EU’s recent REACH 2023 additions and the US EPA 2021-2024 strategic plan. This has been noticed by manufacturers of textiles, and many of them are switching to silicone-based repellents. Since 2022, the adoption of these materials has increased by close to 60% as indicated by reports within the industry. Manufacturers are making the case of the GRAS status of PDMS and how easily it is integrated into existing production processes. While other potential options (such as bio-based solutions and hybrid chemistries) are still being evaluated, PDMS is the preferred option due to it being a tried and tested solution, being fully compliant with regulations, and being easily integrated into existing production processes. This makes it the top candidate to fit the needs of being PFAS-free while providing oil and water repellency to textiles.

The functionality of PDMS can be manipulated by altering its molecular weight and degree of crosslinking. Shorter chain PDMS, like F-3600, forms a more dense surface layer, resulting in water contact angles exceeding 140° while achieving a very low (and undesirable) level of transpiration (< 15 g/m²/24h). Such PDMS variants can be employed for medical and sport garments, for which comfort is a critical factor. In contrast, longer chain PDMS like F-12000, forms more extensive molecular entanglements resulting in stronger interlayer bonds and better wash durability >20 cycles in accordance with ISO 6330 (for crosslinking reduced air permeability). Degree of crosslinking dictates much of the described balance of performance attributes.

For protective apparel for industrial workers where abrasion resistance is of utmost importance, a well-balanced use of F-12000 type materials provides the best overall combination of durability and abrasion resistance (ISO 12947-2) standards. Meanwhile, F-3600 based products tend to focus on use cases that require higher levels of comfort. What is truly remarkable from industry testing is the ability of certain intermediate chain lengths (with appropriate crosslinking) to maintain contact angles of above 130 degrees after 50 cycles of the Martindale abrasion test. This is about 35% more than what is seen with conventional siloxane formulations in terms of durability and comfort balance. These results were published in 2023 in the journal Textile Chemistry, an international, peer-reviewed journal.

Assessing Long Term Durability of PDMS Coating on Real Life Textiles

When it comes to durability of PDMS coatings, they offer excellent laundering resilience and water repellency retention even after 20 plus industrial laundering cycles
(ISO 6330/12945-2 data). PDMS coatings lose only 15% of their water repelling ability while wax and acrylic alternatives lose more than 50% of their waterproofing ability after only 10 cycles of washing. Why do PDMS coatings perform the best? During the curing stage of PDMS coatings their strong chemical bonds form with the fabric fibers that fight the most aggressive washing detergents and cleaning agents and withstands fabric abrasion from repeated washes. Some of these special proprietary formulations still show stiffness contact angle greater than 140 degrees after 50 washes. This means they are perfect for use in critical technical safety applications for firefighter uniforms and outdoor apparel that require water repellent coatings to withstand industrial laundering cycles.

High-Friction Applications: Abrasion Resistance & Mechanical Wear Performance

Possibly one of the most surprising and extraordinary applications of PDMS is its superior wear resistance in extreme environment such as automotive interiors, military grade fabrics and industrial work wear. PDMS coated fabrics have been tested by ISO 12947-2 and have been shown to exhibit < 5% weight loss and no loss of coating integrity after 50,000 (fifty thousand) cycles. In contrast, uncoated fabrics without crosslinking exhibit 20% weight loss and severe coating failure with the same equivalent cycles. PDMS crosslinking is extremely beneficial as its elastomeric nature distributes stress evenly across the surface of the coating. This is ideal to ensure that microfractures do not develop or propagate as the coating is repeatedly flexed and compressed. Most importantly though, all of this protection is offered without sacrificing ventilation. Protective fabrics with PDMS coating ensure the wearer is protected from all of the hazards without compromising their comfort. This is a key feature for long-duration shifts.

Improving the Structural Functionality of PDMS Within Construction Materials

Reinforcement techniques: Silica, cellulose nano-crystals, and POSS fillers for tensile strength and elasticity (ASTM D412)

The base PDMS material is just too soft for construction applications, so we need the most robust modifications. Silica nanoparticles create dense crosslinking networks in the PDMS which provides better load distribution. This is shown through PDMS/silica tensile strength testing, which can yield 3 times the strength of unfilled PDMS at ASTM D412 standards (3). Another component is cellulose nanocrystals (CNC) which can aid the functionality of the silica nanoparticles. This is because the CNCs are long and have numerous hydroxyl groups which means they have strong adhesion to the PDMS base. This adhesion helps to maintain the flexibility of the PDMS while also making it waterproof. Another option is the use of polyhedral oligomeric silsesquioxane (POSS) fillers. These filler's cage structures integrate nicely with the siloxane network at the nano level. When added at 10 to 15% the POSS fillers can increase tear strength by roughly 40% while also retaining elasticity to the material after multiple cycles of extension. When we use all three, we achieve the optimal tensile strength, which is usually greater than 5 MPa, and a permanent stretch of less than 15% after numerous cycles of stretch and recovery.

This makes the composite ideal for sealing joints in concrete, waterproof coatings, and those seismic dampers that must endure weathering and physical changes, including temperature changes, ultraviolet radiation, and flexing.

FAQ

What is PDMS and why is it used in textiles?

PDMS, or polydimethylsiloxane, is a silicone-based, water and oil repellent material. Since PDMS effectively adheres to the fibers of the fabric, it creates a permanent, protective coating that does not use any chemical treatments.

How does PDMS compare with fluorinated coatings?

PDMS provides the same level of repellence as fluorinated coatings but is free of the health and environmental dangers of PFAS. PDMS coatings continue to be repellent and flexible, while fluorinated coatings lose their repellent properties and become brittle.

Is PDMS safe and environmentally friendly?

PDMS is environmentally safe and friendly. PDMS is OEKO-TEX® Standard 100 and bluesign® certified. Since PDMS is not made with harmful carbon-fluorine bonds, the health and environmental risks are significantly less.

Can PDMS coatings withstand industrial laundering?

PDMS coatings are more effective than wax and acrylic coatings and have been shown to retain 85% of their water repellency after 20 cycles of industrial laundering.