Carbon Footprint: Water Based vs. Solvent Based Adhesives

Solvent-borne adhesive systems have been key components of engineered rubber components since the 1950s. The efficacy of solvents to assemble the key polymers and resins that form the basis of the primer and adhesive layers provides the flexibility to develop systems to target a variety of performance and processing requirements. Recent breakthroughs in polymer film forming technologies and the development of novel and more effective compositions of matter have enabled new aqueous (water based) systems that surpass the high standards set by solvent systems. It is well known that water based adhesive systems are the best choice to address the need to comply with reduced volatile organic compounds (VOC) limits facing the industry. A comparison of the carbon footprint of water based and solvent systems further highlights the favorable impact that water based systems have for this key sustainability driver.

Performance Comparison of Water and Solvent Based Adhesive Systems

A comparison of LORD Corporation’s proven Chemlok^® 8008/8212 aqueous (water based) adhesive system with high performance solvent adhesives is shown in Table 1.

Meeting the demanding test requirements of the WDK (Wirtschaftsverband der Deutschen Kautschukindustrie e.V.) demonstrates the ability of water based systems to meet the growing need for higher performance demands on engineered rubber components, especially automotive noise, vibration and harshness (NVH) components requiring heat, fluid, and corrosion resistance.

Carbon Footprint Life Cycle Analysis (LCA) for Water and Solvent Based Adhesive Systems

A typical rubber-to-substrate bonding systems consist of a primer to bond to the rigid substrate and the adhesive, which bonds to the flexible rubber substrate to form a cohesive system. Such systems provide high durability and environmental performance expected of engineered rubber components. LORD conducted a LCA study spanning from cradle to gate to determine the carbon footprint of each system. Key elements included in the carbon footprint computations are shown in the process map (Figure 1). We chose to define the carbon footprint for each product as the amount of CO₂ emission associated per m² of coated substrate.

Methodology for Calculating the Carbon Footprint

Our computation methodology was to simulate a 1-shift application on a range of parts that are representative of what is produced in LORD Corporation’s industrial plant in the USA. The metal components shown in the picture (Figure 2) are bonded to rubber as part of our molding operation and are representative of plant production and interchangeable between water and solvent based systems. The adhesive systems, both water and solvent based used at this plant, are representative of widely used commercial systems.

Key elements of the carbon footprint computation were determined as follows:

• Raw materials required for producing the primers and adhesives - based on the similar chemical nature of both systems except for the carrier.
• We computed the carbon footprint utilizing published data on emissions for actual or like materials.
• Primer and adhesive manufacturing - computed from energy consumed for the unit operations during the manufacturing process in LORD Corporation's chemical plant in the USA.
• Application of the primer and adhesive on the substrate - actual data from energy consumed during application in our mechanical plant, as well as the emissions associated with incineration of the waste stream.
• Film thinkness for both adhesive systems as applied on the metal components are identical.
• Coating application times are identical for both systems.
• Water based systems require a higher pre-heat temperature for the substrate than solvent systems; oven temperatures are typically 20° Celsius higher.
• Note: this LCA analysis does not include carbon footprint associated with transportation, useful and end of use service life of the molded components.

Conclusion

Our LCA analysis based on in-house actual production data for RTM devices quantitatively demonstrates that the carbon footprint of aqueous (water based) systems in dramatically lower than their solvent counterparts.

The key differentiating factor is the substantial penalty associated with the production and subsequent oxidation of solvents that comprise solvent systems.