Evaluating Rosin Esters as a Bio-Based Tackifier for Hygiene Adhesives

Sustainability. Recyclability. Disposability.

All manufacturers of consumer products are no strangers to these terms and their growing importance in the industry. For some industries, the switch is easy. For others, the challenges can range from material safety and supply chain reliability, to performance requirements and quality concerns.

For disposable hygiene products, like diapers, sanitary napkins, or adult incontinence products, safety is nonnegotiable. Every component, including the adhesives that help hold a diaper together, must be evaluated carefully to understand how it performs in its intended application.

As hygiene products continue to evolve, adhesive formulations must balance multiple requirements, including adhesive strength, compatibility with polymer systems, low-temperature viscosity, color stability, odor, and sustainability considerations. Rosin esters are widely valued because they can deliver strong performance across many of these attributes.

Rosin esters provide a great solution to sustainability and performance; however, cytotoxicity testing can trigger concerns. But what does cytotoxic potential mean in this context? And does it really give us a complete picture of biocompatibility?

Experts, standards organizations, and regulatory authorities consistently recognize that cytotoxicity results should not be used in isolation to determine product safety. In the case of hygiene adhesives, additional testing, including skin irritation and skin sensitization assessments, is necessary to understand whether a material presents a meaningful concern in real-world use.

For formulators looking for high-performing sustainable raw materials, this distinction matters.

What cytotoxicity testing does, and does not, tell us

Cytotoxicity testing has been used for decades as an in vitro screening tool to evaluate how materials interact with cells under laboratory conditions. The test can help identify materials that warrant further investigation. However, experts caution against treating cytotoxicity as a final determination of product safety.

ISO 10993-5:2009 states that a material should not be assessed for its intended use based solely on cytotoxicity data. Laboratory testing conditions often differ significantly from real-world exposure scenarios. Cytotoxicity tests are intentionally sensitive and may evaluate materials under exaggerated conditions that do not reflect how a finished product is actually used. As a result, cytotoxicity findings alone provide only part of the picture.

The importance of follow-up testing

For products that may involve skin contact, follow-up investigations typically focus on skin irritation and skin sensitization. These tests are designed to determine whether a material has the potential to cause irritation or trigger an allergic skin response. According to ISO 10993-5:2009 guidance and industry practice, these endpoints are highly relevant when evaluating materials used in hygiene applications.

This broader evaluation approach is also reflected in findings from the European Commission’s CASP 2022 program. The program evaluated multiple hygiene products, including diapers, and concluded that cytotoxicity results should be interpreted alongside other biocompatibility data rather than used as a standalone indicator of safety. Out of 11 diapers tested, seven did not meet cytotoxicity requirements, but were ultimately determined by market surveillance authorities to present low risk in relation to cytotoxicity.

Evaluating Rosin Esters in Hygiene Adhesives

To better understand the biocompatibility profile of rosin ester-containing hygiene adhesive formulations, additional evaluations were conducted beyond cytotoxicity testing.

The tested diaper construction adhesive formulation contained an SBS polymer, a rosin ester tackifier, naphthenic oil, and antioxidant additives. Follow-up studies through independent laboratories evaluated both skin irritation and skin sensitization potential using established in vitro methods.

The results showed:

• Cytotoxicity potential under specific in vitro test conditions.
• Classification as not skin-irritant in a skin irritation assessment.
• Classification as not skin-sensitizing in the GARDskin Medical Device assay.

The skin sensitization and skin irritation studies concluded that the diaper construction adhesive was classified as a non-sensitizer, with negative results observed in both polar and nonpolar extraction vehicles.

In this case, a cytotoxicity result did not correspond with skin safety testing.

The Complete Picture

Actual product use is a critical component in safety assessments. For hygiene adhesives, this means considering the material, the finished formulation, the intended exposure scenario, and the full set of relevant biocompatibility data.

The available testing on rosin ester-containing hygiene adhesive formulations reinforces an important principle. A positive cytotoxicity result should not automatically be interpreted as a product safety concern. Rather, it should be viewed as part of a broader investigation that includes skin irritation and skin sensitization testing, along with consideration of real-world product exposure.

When evaluated using this more complete approach, testing has shown that the studied diaper construction adhesive formulation was classified as not skin-irritant and not skin-sensitizing under the conditions tested.

Safety, Performance, and Sustainability

As the hygiene industry continues to increase the use of sustainable raw materials, informed, science-based evaluation becomes increasingly important. Rosin esters offer a combination of performance, high bio-based content, and encouraging biocompatibility data when assessed through a comprehensive testing approach.

The available data reinforce the importance of evaluating safety in context and considering the full body of evidence when assessing materials for hygiene adhesive applications. The benefits of rosin esters as a tackifier in hygiene adhesive formulations are numerous, warranting consideration as a sustainable alternative to traditional fossil-based tackifiers.

Continue the conversation by exploring the science behind rosin esters in hygiene adhesives. Access additional resources or request a sample to evaluate their performance in your own formulations.