Surface preparation: Advanced technologies for improved adhesion
Last update on May 29, 2026
This article was originally published in 2008 and revised in 2026.
Are you working on adhesive bonding formulations or evaluating substrate compatibility? Several surface treatment technologies have emerged in recent years as alternatives to conventional processes. These developments are relevant across both metal and polymer substrates.
They address recurring constraints in formulation work, including performance requirements, environmental compliance, and processing efficiency.
The primary drivers behind these newer methods include:
- The need to bond new substrate materials that conventional treatments handle poorly
- Stricter environmental and occupational health regulations
- Cost and productivity pressures across manufacturing workflows
Many of these processes are safer and more environmentally friendly. In addition, they also offer relevant advantages for formulators, like faster processing, reduced rework, and lower operational costs. The cost impact can be observed across equipment, implementation, operation, rework, and waste removal.
Let's now turn our attention towards modern surface treatment processes and understand how they contribute to enhancing bonding for substrates.
Metal surface preparation - What has changed?
The need to provide a fast, safe, and environmentally friendly process is dominant in metal surface treatments. Much of the recent development work in metal surface treatment has focused on aluminum. It is widely used across industry segments as it is an ideal substrate for adhesive bonding.
Aluminum is frequently chosen as a reference substrate for adhesive testing and research. This happens particularly because of the stable aluminum oxide layer present on its surface. Manufacturers use aluminum to demonstrate the properties of their products. Find out aluminum oxide grades in the Master Catalog - Compare options and read technical data.
Current work is focused on moving away from chromium-based treatments. This is because they are subject to increasing regulatory restrictions due to carcinogenicity concerns.
If you are formulating for metal substrates, the following alternatives to chromic acid anodizing and FPL etching are available.
Chromate-free etching process (PT2)
The carcinogenic property of chromium has led to alterations in surface treatment processes. A chromate-free etching process designated PT2 has been developed for bonding metals, particularly aluminum. It addresses occupational health and safety requirements while maintaining bonding performance. This is relevant if your process currently uses chromic acid anodizing or conventional FPL etching and you are looking to transition to a compliant alternative.1
Sulfuric acid/sulfuric boric acid anodizing
Sulfuric acid and sulfuric boric acid anodizing of aluminum are currently in development.2 For automotive applications, a non-toxic aluminum coil pretreatment has been developed. This is non-toxic and compatible with weld bonding. The proprietary treatment is reported to perform comparably to chromium-based pretreatments under salt spray exposure conditions.3
Sol-gel process
Sol-gel processes enhance the bondability and corrosion resistance of aluminum, titanium, and other metal substrates. The process uses a ceramic inorganic coating to establish an oxide base layer. For the pretreatment of aluminum, the formulation includes alumina and organosilane. In addition to ensuring environmental compliance, the process is also reported to reduce costs and energy consumption.4
Sol-gel surface treatment process
Ion beam etching
Bond strengths of some materials can be improved if the mating surfaces are etched or textured before joining. Ion beam etching has been applied to stainless steel, graphite, and fluorocarbon surfaces.5 The process introduces surface texture in the form of needles or spikes, which improves mechanical bonding. Bond strength in both tension and shear is reported to exceed that of chemically etched plastics. A notable characteristic is that the surface treatment effect does not diminish over time, which is a limitation of conventional chemical etching.
The challenge does not end with metals; polymers are some of the most difficult substrates to bond. Let's take a closer look at the emerging treatments to address them.
Polymeric surface preparation
Additional active chemical treating processes
- Wilson I. et al. (1997). Pretreatment for Bonded Aluminum Structures. Advanced Materials and Processes.
- Brown J. (1993). Aerospace Adhesives in the 90s. International SAMPE Symposium.
- Wilson I. et. al. (1997). Pretreatment for Bonded Aluminum Structures. Advanced Materials and Processes.
- Zheng, H. et. al. (1996). An Environmentally Benign Aluminum Alloy Surface Pretreatment Process of Adhesive Bonding. International SAMPE Technical Conference.
- (1980). Ion-Beam Etching for Strong Adhesive Bonds. NASA Lewis Research Center
- Tetra-Etch and Fluoro-Etch. Action Technologies Inc.
- Uddin M. N. et. al. (1997). Laser Surface Engineering of Automotive Components. Plastics Engineering.
- Doyle, D. J. (1992). Structural Adhesives Engineering III - Conference Proceedings. PRI Adhesives Group.
- Novak I. and Poliak V. (n.d.). Modification of Adhesive Properties of Isotactic Polypropylene. International Polymer Science Technology.
- Institute for Environmental Physics. (n.d.). Johannes Kepler University.
- Atomoflo. (n.d.). Surfix Technologies, LLC.
- Plasma3. (n.d.). Enercon Industries Corporation.
- Plasma3. (n.d.). Enercon Industries Corporation.
- Sicor. (n.d.). CSIRO Manufacturing and Infrastructure Technology.
- Hibbard D. (2001). Sticky Science. Adhesives Age.
- Long T. et al. (2000). Central Functionalized Tri-Block Copolymer for Surface Modification with Switchable Surface Properties. American Chemical Society.
- (n.d.). Florotec Inc.
- Bliefert C. (1994). Fluoridation of Plastic Surfaces. Metalloberflaeche.
- Kranz G. et al. (n.d.). Int. J. Adhesion and Adhesives.
- Lin C. (1993). Modification of Polypropylene by Peroxide Catalyst Grafting of Maleic Anhydride for Adhesive Bonding.
- Brenman M. and Lerchenthal H. (1976). Increase of Adhesive Bond Strength Through the Mechanochemical Creation of Free Radicals. Polymer Engineering and Science.
- The Loctite Design Guide for Bonding Plastics. (n.d.). Loctite Corporation.
- Davim, Gupta K. (2021). Advanced Welding and Deforming. ScienceDirect.