Fraunhofer Institute for Kelicaince Research ISC pursues future-looking material development by designing inorganic biological hybrid polymer coatings (Ormocer®) for surfaces that do not contain PFAS.
PFAS (one and polyfluoroalkyl substances) are frequently used in many industrial and commercial products and applications due to their excellent properties, based on the unique strength of the fluorine carbon bonds that are hardly affected by chemical attacks. They have very fire-resistant, chemically stable water, dirt, and fat leaves, very low coefficient of friction, low surface energy, and low permeability to gases and liquids. Furthermore, they are particularly durable and considered to be relatively low in production costs, making them essential in the fields of chemistry, electricity, automotive industry, mechanical engineering, medical technology, textile industry, and packaging and renewable energy systems.
Its mobility, particularly high stability, allows PFA to enter the environment and pause with the problem of environmental pollution. At the same time, it has been proven to accumulate in living things. In reputable research, they are also associated with negative effects.
Prohibiting important substances: Where to find alternatives
To address environmental issues and replace PFA in a sustainable and regulatory compliant way, we need to find replacement materials that meet the very high requirements of the aforementioned processes and products. In addition to basic chemical, physical, and technical features and performance, alternatives should ideally cover the similar versatility of applications at competitive manufacturing costs, making them suitable for use in a variety of application areas and compatible with existing manufacturing processes and materials.
Given the long list of requirements and wide range of applications, it is clear that, based on current knowledge, PFAS material alternatives are not a direct 1:1 replacement. This highlights the need to accurately define material specifications and the required property portfolio, and, where possible, compromise material selection in terms of maintenance cycles, durability, and more.
Design of TaylorMade Multifunctional Coating Materials as the Key to PFAS-Free Coatings
The Chemical Coating Technology Division of Fraunhofer ISC develops customized multifunctional coating materials for a variety of materials, including glass, metal, plastic, fiber-based materials such as paper and (technical) textiles. Coating as a finish provides improved or additional surface properties to the substrate. This sustainable material design extends the service life of the substrate by applying a very thin coating, and simultaneously expands the selection of basic materials that can be used for a wide range of applications.
The designed coating material is based on inorganic organic hybrid polymers (Ormocer® – Organic Modified Ceramics and Bioorimocer®, Figure 1). These hybrid materials combine the characteristic structures of inorganic, glass-like materials with organic structural units and have been continuously developed at Fraunhofer ISC for decades. The formation of covalent bonds between inorganic and organic domains combines the properties of both materials at the molecular level in homogeneous composites. This molecular design toolbox allows you to individually adapt the properties of the final layer to your desired specifications and applications.
In addition to the inherent thermal stability of up to 250°C under continuous loads, acids, detergents, solvents or oils (even at high temperatures for long periods), and materials platforms allow for a diverse portfolio of properties with only one functional coating layer. In this way, many of the properties known from PFAS materials can be achieved and promote their replacement. Applications range from packaging, textiles, automotive and mechanical engineering to medical technology and aerospace.
In particular, Ormocer® coating materials are based on oligomers with inorganic silicon backbones formed during synthesis. The formation of organic networks is primarily carried out during adaptive drying processes and thermal or UV light-induced curing reactions. Through molecular links of inorganic and organic building blocks, highly stable materials are created, allowing new combinations of properties.
The use of functional silanes specifically designed for the intended application allows modulation of layer polarity and enhances additional surface properties. These properties include hydrophobicity, surface energy below 20 mn/m, dirt repellency, ease of cleaning (resistance to substances such as toothpaste, coffee, red wine, and certain oils), and the effects of antibiotics. Furthermore, Ormocer® coating solutions are processed in medium conditions, easy to scale up, exhibit very good adhesion to almost any type of substrate, and can be applied using all standard industrial coating processes, making this material platform a simple yet versatile tool for making the surfaces of various substrate materials work.
Fluorine-free coatings for textiles and food packaging
Based on Ormocer® technology, a coating formulation for repellent was developed, resulting in the ZEROF project. The goal of this EU project is to develop fluorine-free coatings for fabrics and food packaging based on renewable raw materials and non-toxic compounds. Fraunhofer ISC is committed to safe and sustainable PFAS free coating solutions with comparable performance, particularly in terms of water and oil repellency.
The entire material research and development follows the SSBD (safe and sustainable by design) framework. Therefore, all material alternatives developed are evaluated in terms of safety and performance, while all process steps are evaluated against ecological and economic standards. From this iterative process, material design guidelines are developed and directly incorporated into material optimization. Furthermore, consumer acceptance is valued and exploitation strategies are developed through stakeholder engagement.
Fraunhofer ISC focuses on the design and development of Omniphobic Ormocer® coating formulations for functional textile applications such as upholstery, contributing to a safer, PFAS-free world.
Either the desired water or oil repellent itself can be easily addressed in a purely chemical sense, but the combination of both properties remains difficult. The first results in water repellency have been achieved in water-based functional coating formulations. Grease resistance is addressed by the introduction of surface patterning through nano and microstructures by optimizing Ormocer®-based coating materials through tailored chemical compositions and integrating particulate and chemical performance additives. This is an iterative process that works closely with VTT (Finland) partners on optimizing synthetic procedures and Leitat (Spain) on coating formulations of fiber substrates. Figure 2 shows zero-zero repellency coated with Ormocer®, while Figure 3 below shows the cleaning properties of the coated dough against grease, coffee and synthetic soil.
Raw materials for further development of PFAS-free coatings
Through the implementation of the Zerof project, we have learned a lot about developing alternatives to PFAS-free coatings. We acquire basic knowledge of various strategies that can be applied, and use the knowledge we have gathered to further develop PFAS-free coatings for other applications. Specifically, Fraunhofer ISC is working on a variety of Ormocer®-based PFAS alternatives for technical applications, including simple clean surfaces for furniture (see Figure 4), anti-stick coatings in mechanical engineering. It has high kit values, grease stability, and wet-chemical functionalization of fabrics. In the latter application, the adaptability of the Ormocer® matrix is utilized by increasing the organic content and adding silicone to achieve additional oil repellency. Other potential facilities include coatings for medical applications such as paints and anti-stick coatings, and personal care products and surgical instruments.
Another publicly funded project at Fraunhofer ISC at Fnr-Biocoattex will draw these developments into a new level of sustainability. Here, although oil-replenished surfaces do not play a role, bio-based coatings are developed for bio-based textile applications (hemp fibers and bio-based synthetic leather) that allow surfaces to be easily cleaned with repeated water. In this project, biopolymers such as cellulose will be incorporated into the hybrid layer matrix to provide greater flexibility and biodegradability. Suberin (a plant-based hydrophobic biopolymer), sugar fatty acids, or chitosan are used to address hydrophobic properties. The formulations are applied to highly flexible substrates using industrially relevant methods. The goal is a construction module reinforced with sustainable seat covers and hemp fibers, and Ormocer® aims to improve the adhesion of the fiber matrix and increase water resistance.
This article will also be featured in the 23rd edition of Quarterly Publication.
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