As the global push for fully biodegradable packaging and barrier materials accelerates, Polyhydroxyalkanoate (PHA) has emerged as a leading sustainable alternative to petroleum-based coatings. Its inherent biodegradability, biocompatibility, and excellent film-forming properties make it an ideal candidate for water-based barrier coating applications — but translating lab-scale potential into commercial-scale, high-performance formulations comes with significant technical hurdles.

Over the past 6+ months, we’ve worked closely with an overseas corporate manufacturing client to address these challenges head-on, as they developed a water-based PHA emulsion for sustainable barrier coatings. In this post, we’re sharing the core technical pain points they encountered during real-world testing, the insights we gained from partnering with PHA material scientists, and the actionable solutions we explored to bring their formulation closer to commercial viability.

Our client’s goal was straightforward but ambitious: develop a water-based PHA emulsion that delivers robust water barrier performance for sustainable packaging applications, with a strict performance target of a 3-minute hot water Cobb value of ~7 gsm. This metric is the gold standard for water barrier performance in coating applications, as it measures the amount of water absorbed by the coated substrate over a set time — the lower the value, the better the water barrier.

They began their testing with two widely available commercial PHA grades, both of which are commonly marketed for coating applications. However, initial lab testing revealed a critical limitation: the inherent hydrophilicity of these grades resulted in a 3-minute hot water Cobb value of ~41 gsm, nearly 6x higher than their target performance threshold.

This gap between expected and actual performance is one we see time and time again with formulators new to PHA. While PHA is widely known for its water resistance in bulk film form, translating that performance into a stable, high-performance water-based emulsion requires a deep understanding of the material’s chemical structure, grade-specific properties, and formulation interactions.

Through our client’s testing and our collaboration with BluePHA’s material science team, we identified four primary technical challenges that formulators must address when working with PHA in water-based barrier coating systems.

The single biggest barrier to achieving target Cobb value performance is the inherent hydrophilicity of many standard PHA grades when processed into water-based emulsions. While the PHA polymer itself is hydrophobic, the emulsification process requires the addition of surfactants and stabilizers that can increase the water sensitivity of the final dried coating.

Through our discussions with material scientists, we confirmed that not all PHA grades are created equal when it comes to hydrophobic performance. Our client’s testing revealed that PHA P330 delivers significantly higher inherent hydrophobicity compared to other standard grades, thanks to its unique polymer chain structure and 1°C glass transition temperature (Tg), which impacts film formation and coalescence in the final coating.

We also learned that the raw material processing methods are directly driven by the end user’s emulsion requirements. For water-based coating applications, the polymerization and post-processing of the PHA powder can be tailored to improve hydrophobicity in emulsion systems — a critical detail that many generic PHA suppliers overlook.

A second, unexpected challenge our client encountered was persistent foaming during the emulsion conversion process. Their optimized PHA emulsion formula (pH 8.31, 23.03% solids content, 1355 cP viscosity at 40°C with a 138°C melting point PHA grade) developed significant foam during high-shear processing, which led to inconsistent coating application, pinhole defects in the dried film, and reduced barrier performance.

This is a common issue with water-based PHA emulsions, as the surfactants required to stabilize the polymer in the aqueous phase also tend to stabilize air bubbles during mixing and processing. Through our technical consultations, we identified that selecting a PHA grade optimized for water-based dispersion (such as BP350, a grade already used by global specialty chemical leaders like Kemira in their barrier coating formulations) can reduce the amount of surfactant required for stable emulsification, in turn minimizing foaming during processing.

Even when a stable emulsion is achieved, many formulators struggle with inconsistent film formation during the drying and curing process. For PHA to deliver its full barrier potential, the polymer particles must fully coalesce into a continuous, defect-free film when applied to a substrate and dried.

The melting temperature (Tm) of the PHA grade is the most critical factor here. Our client’s testing confirmed that lower melting point grades (such as BP350 with a Tm of 138°C) are significantly easier to convert into stable emulsions that form uniform, defect-free films, compared to higher melting point PHA grades. Lower melting temperatures allow for better particle coalescence at standard coating drying temperatures, eliminating pinholes and microcracks that would compromise water barrier performance.

We also found that the physical form of the raw material plays a critical role. PHA powder, rather than granules, is the optimal starting point for water-based emulsion production. Grinding granules into powder in-house adds significant cost and can introduce batch-to-batch variability in particle size, which directly impacts emulsion stability and film formation. Working with a supplier that can provide pre-processed PHA powder optimized for emulsion applications eliminates this variability entirely.

To close the performance gap between their initial test results and their 7 gsm Cobb value target, our client explored chemical modification to improve the hydrophobicity of the PHA emulsion. They asked a critical question: what chemical additives can react with PHA to increase its hydrophobicity in a water-based system?

This is an area of ongoing research and development in the PHA industry, and we learned that while there is significant potential for chemical modification, there is limited commercially validated guidance for formulators. From our consultations with PHA material scientists, we confirmed that while P330 offers higher inherent hydrophobicity, the industry is still refining effective methods to incorporate chemical additives that react with the PHA polymer to enhance water barrier performance without compromising emulsion stability or biodegradability.

For formulators looking to explore this path, our key recommendation is to partner with your PHA supplier early in the development process. Many PHA manufacturers can provide custom copolymer grades with built-in hydrophobic modification, which delivers more consistent and predictable performance than post-polymerization additive modification in your formulation.

1. Start with the right PHA grade for your application: Prioritize grades optimized for water-based emulsion and coating applications, such as BP350 for easy emulsification and film formation, or P330 for enhanced inherent hydrophobicity. Avoid generic industrial PHA grades that are not designed for coating use cases.
2. Source pre-processed PHA powder: Eliminate batch-to-batch variability and reduce production costs by starting with fine, uniform PHA powder, rather than grinding granules in-house. This ensures consistent particle size distribution for stable emulsion production.
3. Optimize emulsion formulation to minimize surfactant use: Work with your PHA supplier to select a grade that disperses easily in water, reducing the amount of surfactant required for stabilization. This will minimize foaming during processing and improve the water resistance of the final dried coating.
4. Align your drying process with the PHA grade’s thermal properties: Ensure your coating line’s drying temperature and dwell time are optimized for the melting temperature of your selected PHA grade, to enable full particle coalescence and a continuous, defect-free barrier film.
5. Partner with your supplier for custom development: If standard grades don’t meet your performance targets, work with your PHA manufacturer to explore custom copolymer grades or pre-modified materials that deliver the hydrophobicity you need, rather than relying on post-formulation additive modification.

While PHA presents unique technical challenges in water-based barrier coating formulations, our client’s testing journey makes it clear that these challenges are not insurmountable. With the right grade selection, optimized raw material processing, and close collaboration with material science experts, formulators can develop PHA-based coatings that meet the strict performance requirements of commercial packaging applications — without compromising on sustainability or biodegradability.

What makes PHA truly unique is that it is one of the only biodegradable polymers that can deliver both the barrier performance and end-of-life biodegradability that brand owners and regulators are demanding. As the industry continues to refine PHA grades specifically for coating applications, and develop more effective hydrophobic modification techniques, we expect to see PHA become the industry standard for sustainable water-based barrier coatings.

If you’re developing a water-based PHA coating formulation and need support selecting the right grade, accessing technical data, or connecting with PHA material scientists, reach out to our team today. For more insights on selecting the right PHA grade for your specific application, check out our full grade comparison guide here.