Multilayer plastic films (MLP) represent one of the most difficult segments of global plastic pollution to manage. While they provide excellent food protection, they have proven practically unrecyclable until now. However, a recent study published in the journal Nature Communications has brought a breakthrough: using the STRAP process, different polymer layers can be chemically separated and recovered in nearly their original purity. According to the study’s data, more than 90 percent of the waste can be converted into valuable raw materials, potentially transforming the economics of the packaging industry.
Modern food industry and logistics are inconceivable without multilayer films. These materials—used to store chips, coffee, and ready-made meals, among others—can consist of up to 11 different layers, each serving a specific function (such as oxygen barriers, moisture protection, or printability). The source of the problem is that these layers (typically polyethylene, polypropylene, and polyethylene terephthalate) bond so tightly that they cannot be separated through traditional mechanical recycling, resulting in a low-value mixture with an uncertain structure.
Technological Breakthrough: What is STRAP?
The STRAP (S)olvent-(T)argeted (R)ecovery (A)nd (P)recipitation technology developed by the research team breaks with traditional approaches. The essence of the process is the application of a series of selective solvents that operate according to “solubility parameters” based on thermodynamic calculations.
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Selective Dissolution: During the process, solvents are applied that can only liquefy a specific polymer layer while leaving the other layers intact.
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Extraction and Filtration: The dissolved polymer is separated from the solid residue.
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Precipitation: By adding a so-called antisolvent, the polymer is precipitated from the solution in solid form, thus recovering the pure raw material.
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Solvent Recovery: At the end of the process, the solvents are separated by distillation and cycled back into the system, minimizing chemical waste.
The study emphasizes that the key to STRAP’s success is complex thermodynamic modeling, which allowed for the identification of optimal solvent combinations for the most common polymers, such as PE (polyethylene), PP (polypropylene), and EVOH (ethylene-vinyl alcohol).
Quantifiable Results: Purity and Efficiency
The quantitative data presented in the research highlights the industrial viability of the process. Laboratory and pilot tests yielded the following results:
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Recovery Rate: More than 90% (and in some cases 99%) of the polymers were successfully extracted from the original multilayer structure.
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Purity Indicators: The purity of the recovered resins exceeded 99.5%, meaning their quality is identical to virgin (primary) plastic, making them suitable for food-grade packaging once again.
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Capacity and Volume: Globally, nearly 100 million tons of multilayer film are produced annually, of which less than 1% is currently recycled. The STRAP process could theoretically handle this entire waste stream.
Measurements confirmed that the mechanical properties (tensile strength, melt index) of the recovered polymers did not deteriorate significantly compared to the original raw material, overcoming the greatest limitation of mechanical recycling.
Environmental and Economic Impact Assessment
Researchers also conducted a Life Cycle Assessment (LCA) of the technology, comparing STRAP with the production of new plastic and incineration (energy recovery).
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Energy Consumption: Although solvent recovery (distillation) is energy-intensive, the total cost and energy demand of the process are still lower than producing new polymers from petroleum.
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Carbon Footprint: Calculations show that using STRAP results in 30-50% less $CO_2$ emissions than burning the waste and manufacturing new plastic in its place.
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Economic Viability: The study points out that the economic efficiency of the process depends largely on the efficient (over 99%) recovery of solvents. If industrial-scale plants can maintain laboratory distillation efficiency, the price of recovered polymers will be competitive with market prices.
Conclusion and Future Vision
According to the study published in Nature, recycling multilayer films is not a technological impossibility but a matter of selective chemical processes. In the future, STRAP technology will enable the realization of a “closed-loop” economy in the flexible packaging sector as well. The next step is scaling up the technology and adapting waste collection systems to this new type of chemical recycling.
Official Sources and References:
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Original Article (Nature Communications): Solvent-targeted recovery and precipitation (STRAP) of multilayer plastic films
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Related Research Portal (US Department of Energy): BOTTLE Consortium – Bio-Optimized Technologies to keep Thermoplastics out of Landfills and the Environment
