Although paper is a more environmentally friendly packaging material than plastic, it’s often contaminated with additives, such as adhesives used to create a secure seal. That complicates the recycling process and reduces the quality of recycled paper. Now, German researchers at four Fraunhofer institutes have developed an alternative process that can seal paper packaging without glue or plastic using a carbon monoxide laser.
The new system, currently called the Papure project, leverages the expertise of the Fraunhofer institutes, each of which focuses on areas such as polymer research, engineering and packaging, and laser beam technologies. The first step of the new sealing process involves analyzing the chemical composition and morphology of various paper types using techniques such as scanning electron microscopy and X-ray photoelectron spectroscopy to determine if they can be sealed without an additive. The amounts of ingredients such as hemicellulose, cellulose, lignin, talc, and calcium carbonate in the paper can affect the strength of the final packaging’s seals.
Once a paper type is approved, it’s irradiated with a CO laser in a controlled process that rapidly heats its surface, converting the lignin, hemicellulose, and cellulose into short-chain compounds. From there, what researchers call “fusible cleavage products” remain on the paper’s surface and act like a natural glue, creating a tight seal when heat and pressure are applied. The researchers are still fine-tuning the various parameters of the Papure project, including laser intensity and paper seam design, to maximize bond strength. But in current testing, they’ve found that a 2cm seal that’s just 3mm wide is strong enough to support a 44-pound load.
The researchers have already built a “laboratory-scale modular paper processing manufacturing unit” capable of producing a flat, four-sided paper bag design that’s commonly used today by companies like Lego. They’re also working to streamline and shrink the design of the laser and sealing modules and to integrate measurement systems that can assess the quality of the seals being produced and automatically adjust various settings to ensure they’re meeting a specific bond strength target. By the end of September, their goal is for the pilot machine to produce 10 packages per minute.