In nature, foamed structures largely made up of air-scattered light create an optical phenomenon known as structural whiteness, note scientists at Kyoto University, Japan. Inspired by this natural phenomenon, the research team developed a foam-based technology to give packaging polymers a white color.
The technology, referred to as Deep Foam Photolithography (DFP), uses light and a mild solvent to color polymers. The light breaks the polymer into smaller molecular fragments, which interact with the solvent. This causes the material to swell and form an open, porous structure.
The porous structure scatters light, resulting in what researchers refer to as “intense whiteness.” Additionally, the foam becomes a rough structure with strong water-repellent properties, “similar to those found on a lotus leaf.”
“DFP could be used to make polymer packaging white and water-repellent through the structure of the polymer itself, rather than by adding white pigments or fluorinated coatings,” Easan Sivaniah, professor at the Institute for Integrated Cell-Material Sciences (ICEMS), Kyoto University, tells Packaging Insights.
“For packaging, this could be particularly interesting for films and other thin polymer materials, where we can control the optical and surface properties very precisely.”
Sivaniah is a lead author of the study, conducted at ICEMS, alongside textile researchers of Donghua University, China, and published in Nature.
Packaging applications
In addition to flexible films, the scientist says that labels and surface coatings have potential for the technology. “We are also interested in whether the technology can eventually be applied to molded packaging,” he adds.
Biomimetic structures can transform light into color, the research team highlights (Image compositing: Blender 3D and Photoshop).“We have demonstrated DFP in several polymers, including PET, polystyrene, polycarbonate, cellulose triacetate, polysulfone, and polymethyl methacrylate.”
Sivaniah explains that DFP for PET is particularly interesting for packaging because it is already widely used commercially. “We would also like to investigate polymers such as PE and PP, although we have not yet demonstrated the process in those materials.”
He says that the research team does not yet know what the potential effects of DFP are on packaging recyclability. “This is something we need to test properly.”
“One attractive aspect is that the whiteness and water repellency come from the polymer structure rather than from adding a separate pigment or PFAS coating. But we need to test how DFP-treated materials behave in real recycling processes before making any claims about recyclability,” he details.
“An associated concern is whether this technology can lead to microplastic proliferation. However, we have some evidence that the process can be applied to plastics with good biosorbability.”
Packaging Insights explored how plastic recycling can exacerbate microplastic pollution with Dr. Valiyaveetil Shamsudheen Semeena of the UK Centre for Ecology & Hydrology.
Avoiding titanium dioxide
The most common white colorant currently used in packaging, films, and coatings is titanium dioxide. It provides brightness and opacity in creating white materials. However, there are safety concerns surrounding the inorganic compound, according to the research team. In 2022, the EU banned its use as a food additive.
ICEMS posits that their DFP could potentially replace the use of titanium dioxide by the packaging industry. However, Sivaniah adds that titanium dioxide is a “very effective white pigment.”
“I would not describe DFP as simply a one-to-one replacement at this stage.”
“What we have shown is that we can produce very strong whiteness through the physical structure of the polymer, without using titanium dioxide. The next step is to make direct comparisons under realistic packaging conditions.”
He also highlights that there are questions increasingly raised about the health implications of titanium dioxide. Questions, he says, that were not raised a decade ago, adding there is “no definite ruling on the matter” thus far.
DFP can remove the need for PFAS by impacting the physical structure of the material, explain researchers.Earlier this year, Inter IKEA Group backed a €13.4 million (US$15.6 million) Series A round investment to scale a cellulose-based alternative to titanium dioxide for coatings, cosmetics, and food applications, developed by the Swiss biomaterials company Seprify.
Sivaniah continues: “Another factor is that titanium dioxide formulations often suffer from sedimentation, due to the difference in density of the titanium dioxide additives. So this can potentially be avoided.”
Additionally, a spokesperson for Sidel previously told Packaging Insights that there are technical complexities that come with blowing PET preforms that contain titanium dioxide colorant. The process requires longer and more controlled heating to achieve consistent material distribution.
In related developments, scientists at Shanghai Jiao Tong University, China, used titanium dioxide nanoparticles in a composite polymer matrix to create a film to extend the shelf life of kiwifruit.
Benefits and upcoming development
The research team points to DFP’s water-resistant properties, further highlighting the safety benefits of using the technology to achieve a white color in packaging.
While PFAS are widely used to provide water and oil repellency, there are also growing concerns about their impacts on environmental and human health, with authorities across India, the US, and the EU taking steps to ban their use in food packaging.
DFP removes the need for PFAS usage for surface functionality by impacting the physical structure of the material itself, the researchers add. They say this offers a “fundamentally different approach” to engineering packaging materials.
“The next step is to move from laboratory samples to commercially relevant polymer films and packaging structures,” says Sivaniah.
“We want to test optical performance, durability, processing, and recycling, and also understand how DFP could be incorporated into existing manufacturing processes. Ultimately, we would like to test the technology with packaging companies on real products.”
AloJapan.com