Task 6

What is the problem? 

• Plastic pollution is one of the biggest problems to tackle in the 21^st century since plastic production has increased from 2.3 million tons in 1950 to 448 million tons in 2015 and is expected to double that by 2050.
• It is estimated that one ton of recycled plastic saves 5.7MWh of electricity, 685 gallons of oil, and 30 cubic yards of landfill space, but only 8.7% plastics are recycled on a global scale.
• Although using recycled plastics offer many economic and business opportunities, cross-contamination by other plastics reduces the quality of the recovered plastics significantly and diminishes their economic advantages over virgin plastic.
• Furthermore, plastics contribute to about 4.5% of global greenhouse gas emissions, therefore implementing a circular economy approach, via efficient recycling, is crucial in protecting the climate. Hence, efficiency of plastic recycling also dictates climate change.

What are the currently used technologies for plastic sorting?

• Plastic recycling, in a community level, is done in a Material Recycling Facility (MRF) where plastics along with other wastes such as aluminum, cardboard, paper and etc. are sorted simultaneously.
• However, plastic sorting in an MRF is predominantly done manually which creates higher chances of false identification, results in poor quality of sorted bales and exposes the workers to toxic additives coming from the waste.
• Secondary plastic sorting facilities take in the unsorted plastics from MRFs and use a more mechanized approach of sorting plastics which makes it more efficient than the MRFs. Various machines using different techniques are used in secondary sorting facilities which make the sorting process in secondary sorting facilities more efficient than MRF sorting but transportation of unsorted plastic bales create more carbon footprint and increase costs due to transportation. So, efficient sorting process that can be implemented in an MRF itself is of utmost importance.
• At present, the most effective methods like NIR, LIBS, Raman spectroscopy or AI robotic arms have poor sensitivity, subpar selectivity, increased risk of false identification and inability to detect black plastics.

Hence, we have developed a novel, simple and cost-effective technique named Transient Thermal Barcode (TTB) that can increase the sensitivity, molecular selectivity, and speed of plastic sorting while having the potential of being easily implemented in an MRF itself.

• The science behind the Transient Thermal Barcode (TTB) technique is
• Shining the mid-Infrared region onto the plastic sample at their respective unique wavelength. The scientific reason behind choosing mid-IR for TTB is that the mid-Infrared part of the electromagnetic spectrum is called the ‘fingerprint regime’ due to the absence of overtones hence each peak obtained is unique to each different plastic.
• Infrared (IR) region of the electromagnetic waves excite vibrational states in molecules they are incident in i.e., when IR is incident on a material, the material absorbs that wavelength and goes into higher vibrational states.
• When the vibrational relaxation happens through thermal radiative pathways, it gives rise to a temperature increase. Measuring temperature change in a sample upon IR incidence, which is a direct result of photon absorption, can give us complementary information to transmittance/reflectance studies performed in the same sample.
• If the samples are illuminated with the wavelength corresponding to their unique spectral peaks, the sample will have an increased temperature rise at that specific wavelength.
• The increased local temperature can be imaged with a temperature sensitive camera i.e., IR camera. Superimposition of the IR camera image and a visible light camera image should provide us a unique thermal barcode pattern for each plastic, which in turn might enable high throughput sorting.
• This high sensitivity, high selectivity technique has the potential to sort black plastics rapidly, which is a major challenge for any other currently used technique as black plastic absorb all wavelengths. The technique also has the potential to be implemented for real time plastic detection at Material Recovery Facilities (MRFs) for increased efficiency and reduced false identification.

• Provisional Patent filed: - Transient Thermal Barcode

• Future work will focus on making TTB full-fledged technology that can be translated to an MRF like setting.