Sheet Extrusion, Thermoforming Tips for PLA/aPHA Blends

The demand for sustainable packaging solutions is on the rise as consumers and environmentally conscious organizations continue to look for ways to reduce plastic waste and their carbon footprint. Across the plastics packaging supply chain, companies are also facing increasing pressure from both consumers and governments to develop eco-friendly alternatives that minimize waste going to landfills and climate impact. Biopolymers like PLA and PHA are able to meet these sustainability goals while also delivering the performance attributes needed for use as rigid food packaging suitable for commercial-scale adoption.

PLA is an ideal material option for sheet extrusion and thermoforming because of its strength and performance benefits. Produced from annually renewable resources, NatureWorks’ Ingeo PLA appeals to brands and consumers wanting third-party certified safe, compostable, 100% biobased, low-carbon packaging materials that enable the diversion of both food scraps and packaging into the expanding industrial composting infrastructure.

Combining CJ Biomaterials’ PHACT aPHA with Ingeo PLA for thermoformed food packaging enhances mechanical performance (tear resistance and puncture toughness), accelerates the rate of biodegradation and compostability, and maintains transparency, clarity and biobased content. PHACT PHA and Ingeo PLA are also both cleared for food contact use by the U.S. Food & Drug Administration (FDA) via its Food Contact Notifications (FCNs).

This article examines the use of blends of aPHA and PLA, and how they enhance the thermoforming process for packaging. It will also briefly touch on semicrystalline PHA (scPHA), a promising advanced biopolymer that offers greater strength and temperature resistance for more demanding packaging applications.

Putting the PLA/aPHA Blend to the Test

Ingeo PLA has been used commercially in extrusion and thermoforming for over two decades and is valued for its stiffness, formability and transparency. However, early rigid PLA packaging applications relied on non-biobased acrylic modifiers to meet requirements for impact strength. At certain levels, though, these modifiers do not meet the criteria of current third-party compostability certifications, so a new biobased-solution was needed.

In 2023, NatureWorks and CJ Biomaterials announced a joint collaboration designed to accelerate the development of new materials that leverage the unique properties of CJ Biomaterials’ PHACT A1000P PHA technology and NatureWorks’ Ingeo PLA. Through the partnership, the two companies developed new PLA/PHA formulations that could meet the impact resistance benchmarks required by automated food packaging lines while maintaining 100% biobased content, transparency and clarity, and the ability to use reclaimed trim scrap in processing. This new product solution can also meet the increasingly rigorous compostability standards for safety and degradation rates.

Extruding conventional polymers requires higher processing temperatures compared with biopolymers. The PLA/aPHA system provides energy savings from processing at lower temperatures. Typically, PLA temperatures on an extruder require a processing temperature range of 410-430°F, while Ingeo with PHACT will process at 390-410°F, resulting in further energy savings. As a further benefit, throughput is slightly increased by approximately 4% compared with generic PLA.

Combining aPHA with PLA enhances toughness. On its own, PLA is a strong and glassy polymer with excellent stiffness, though it can benefit from enhancements for improved impact strength. PLA has a Tg of approximately 130°F, meaning it remains in a glassy state at room temperature, while aPHA has a Tg of approximately 5°F, which enables it to display rubber-like properties. When aPHA is dispersed as small particles into a matrix of PLA, it acts like a little rubber ball. When impact propagates, it will encounter one of these rubber-like and tough characteristics of PHA, which will effectively stop its propagation. This rubber-like property also improves its durability, enabling the PHA to absorb the force of external pressures.

Adding 10% aPHA to PLA results in a material with 5 in/lb mean failure energy (MFE) as measured with Gardner impact testing on a 0.031-inch thick sheet. This can help prevent damage during transportation or accidental drops of the thermoformed articles and ensure the packaging can endure impacts produced in automated food packaging systems.

The new material was tested for its durability at multiple thicknesses. Subjected to Gardner impact testing (according to ASTM D5420), the PLA/aPHA blend demonstrated improved toughness when tested with 0.020 inch and 0.030 un. sheets compared with a PLA-only solution. For the 0.020-inch sheet, the PLA solution recorded an impact failure of 1.00 inch-pound. The PLA/aPHA blend raised that level to an MFE of 2.85 in-lb. Testing on the 0.030-in. sheet, the MFE of PLA alone at 1.03 in-lb increased to 4.78 in-lb with the PLA/aPHA blend (Figure 1).

The material also exhibited a noticeable reduction in rail chipping, further demonstrating its greater durability (Figure 2).

A critical aspect of reducing costs and increasing the circularity of materials in extrusion and thermoforming is the ability to reintroduce trim scrap back into the extruder in the form of reclaim while still meeting performance targets for the final packaging. Unused material left over from cutting parts out of extruded sheet is ground into flake, recrystallized and dried, then reintroduced into the extruder feed.

When testing how the PLA/aPHA blend performed using regrind, the material held up well. Instead of regrinding sheet to feed the extruder, pellets were prepared that had undergone one to five passes, or heat histories, through a W-P twin-screw extruder and were blended to simulate 50% and 70% regrind content. The goal was to have clarity of 90% or greater, and haze less than 10%. When the PLA/aPHA material was approximated at a 50% and 70% regrind level, it met the performance goals, recording clarity of 94% and total haze of 10% (Figure 3).

By blending aPHA with PLA, processors can create a more workable material that both enhances processing and improves the overall performance of the final packaging solution. In the last year, CJ Biomaterials also developed the general-purpose masterbatch PHACT MA1250P-2, which enables the addition of a PHA/PLA masterbatch into a PLA system on a single screw extruder with no twin screw needed. Both NatureWorks and CJ Biomaterials offer resins that are packaged pre-dried and sealed in barrier packaging so they can be tested prior to the capital investment of a drying system, as Ingeo and PHACT must be dried prior to use at commercial scale.

Positive Environmental Impact of PLA/aPHA blends

In the thermoforming space, PLA/aPHA blends stand out as a sustainable solution for rigid food packaging. Using these two certified-biobased polymers increases the use of annually renewable feedstocks, reduces the carbon impact of materials and decreases the use of fossil-fuel feedstocks.

As certified compostable materials, Ingeo PLA and PHACT PHA can create packaging that does not create persistent microplastics in the environment and helps enable the diversion of food scraps away from landfills and into compost. Food degrading in landfills is the third largest source of methane emissions in the US. In contrast, creating and using compost improves soil health and biodiversity. These cumulative benefits for our climate are why the composting and compostable products industry are adopting science-based certifications that ensure compostable products are nontoxic and properly degrade in industrial compost environments.

In the U.S., the Biodegradable Products Institute (BPI) is the leading third-party certifier of compostable products. BPI’s certification is based on ASTM standards D6400 and D6868 that set pass/fail criteria for the disintegration, biodegradation and ecotoxicity of compostable materials. These standards were modeled after compost conditions, documented in the U.S. Composting Council’s (USCC) composting handbook, needed to safely compost food waste and produce stable, high-quality compost. In addition to standards-based testing, BPI requires that submitted products are free of PFAS and other fluorinated chemicals. Both Ingeo PLA and PHACT PHA have passed this testing and carry BPI certification.

Recent legislation in the state of California has significantly increased the amount of food scraps being sent to industrial composters in the state. In response, composters in California have accelerated their composting processes outside best practices to accommodate the increased volumes of food scraps. In turn, this has created demand for faster degrading compostable products.

Completed biodegradation testing shows that the new PLA/aPHA formulation can biodegrade within 60 days at industrial composting temperatures (Figure 4). Early results from a field disintegration study in an industrial aerated static pile show that the Ingeo with PHACT solution has a high probability to degrade within the 60-day time frame under field conditions.

About the Authors

John Licata is the director of applications at CJ Biomaterials, a leading manufacturer of PHA biopolymers under the brand name PHACT. He has over 20 years of experience working with PHA in a variety of functions. He started his PHA career as a process engineer at Metabolix where he helped develop the novel process for purifying PHA from fermentation. Currently, his role is to help CJ Biomaterials customers find solutions to their end-of-life needs for their products. 339-999-2693; john.licata@cj.net;  cjbiomaterials.com.

Eunhye Lee is the group manager of polymers application R&D at CJ Biomaterials. She received her Ph.D. in polymer engineering from Osaka University and has more than 10 years of experience in conducting research on biopolymers. In particular, she has led application studies on biopolymers such as PLA, PHA and PGA. Recently, she published several papers on the behavior of polymer properties and the use of biopolymers. Eunhye is now conducting research on improving the physical properties of PHA biopolymers and compounds, including tuning rates of biodegradability. 339-999-2693; grace.lee@cj.net .

Andrea Auchter is the technical lead for rigid packaging applications in the food service sector for NatureWorks, a global leader that invents and manufactures Ingeo, a portfolio of high-performing biopolymers. During her time at NatureWorks, Auchter launched a newly developed extrusion coating grade and created solutions for faster composting of packaging. 952-562-3400; andrea_auchter@natureworksllc.com; natureworksllc.com.