A few years ago, I read a fascinating and lively description of what happens to used T-shirts in our current global trading environment. Pietra Rivoli’s “Travels of a T-Shirt in the Global Economy” details the highly ineffective and wasteful wanderings of a T-shirt from American raw cotton to rags. The route of a single shirt included China and back (twice — once for fabric weaving and once for shirt assembly) and an eventual home for the remains of the shirt in rural Africa, via such organizations as Goodwill.
This brings me to today’s topic: recycling (in the technological sense) of cotton clothing. Anyone who has taken boxes of old clothing to Goodwill — or worse, to the garbage bin — has probably wondered whether there is an effective recycling solution for our worn-out threads.
Now, a research team from the National University of Singapore (NUS) Faculty of Engineering has successfully devised a fast, cheap and green method to convert cotton-based fabric waste, such as unwanted clothing, into highly compressible and ultralight cotton aerogels. The researchers also demonstrated the application of this novel material to keep water bottles cold and to effectively control rapid bleeding.
Aerogels are among the lightest materials in the world and are highly porous with strong absorption capacity and low thermal conductivity. These unique properties make aerogels highly suitable for applications in areas including oil-spill cleaning, personal care products such as diapers, as well as for heat and sound insulation. While aerogels were first created in the 1930s, this advanced material has not been widely adopted by industries due to its high production cost. Leading aerogel scientists around the world are therefore actively looking at ways to improve the manufacturing and consumption of different types of aerogels. Contributing to this global effort, the NUS team has successfully pioneered the development of aerogels using cotton fibres harvested from textile waste.
From Unwanted Clothing to Super Material
Led by Associate Professor Hai Minh Duong and Professor Nhan Phan-Thien from the Department of Mechanical Engineering at NUS Faculty of Engineering, the research team discovered that the novel cotton aerogels can be easily compressed, and they can also very quickly recover up to 97 per cent of their original size when placed in water.
“This new eco-friendly cotton aerogel is a major improvement from the aerogel that our team had previously developed using paper waste. It is highly compressible, hence storage and transportation costs could be greatly reduced. Furthermore, these cotton aerogels can be fabricated within eight hours – this is nine times faster than our earlier invention and about 20 times faster than current commercial fabrication processes. They are also stronger, making them more suitable for mass production. While we have demonstrated novel application of the cotton aerogels for effective hemorrhage control and heat insulation, we will continue to explore new functions for this advanced material,” said Duong.
Effective control of rapid bleeding
Hemorrhage, or the excessive and rapid loss of blood, caused by gunshot wounds or other deeply penetrating wounds can often be life-threatening. Hemorrhage control devices are used to exert internal pressure to stop bleeding and promote blood clotting.
Existing hemorrhage control devices include syringes filled with small capsules of cellulose-based sponge, coated with chitosan, a natural agent derived from the shells of shrimp and other crustaceans that promotes blood clotting. The syringe is inserted into the wound to release the capsule, which expands and applies pressure on the wound to stop the blood flow. However, the expansion and absorption rates of cellulose-based sponges are still relatively slow.
To address these limitations, NUS researchers developed highly compressible hybrid cotton aerogel pellets which are more effective than cellulose-based sponges for treatment of deep hemorrhagic wounds. These pellets – comprising an optimal mix of cotton and cellulose aerogels coated with chitosan – are simple and cost-effective to produce, and they can be easily integrated into a clinical syringe to be used as a hemorrhage control device. The cotton aerogel pellets are also biocompatible, hence they can be safely administered for treatment.
“Each cotton aerogel pellet can expand to 16 times its size in 4.5 seconds – larger and more than three times faster than existing cellulose-based sponges – while retaining their structural integrity. The unique morphology of the cotton aerogels allows for a larger absorption capacity, while the compressible nature enables the material to expand faster to exert pressure on the wound,” said Duong.
The findings for this novel application were published in the scientific journal Colloids and Surfaces A in January 2018.
Soldiers regularly embark on vigorous physical activities in hot and humid conditions. The military canteen is an essential item in a soldier’s survival kit, carrying fluid for rehydration and mitigation of heat injuries. A military canteen can typically hold one litre of water and maintain its cool temperature for about 30 minutes in our tropical climate.
The NUS research team, in collaboration with DSO National Laboratories, developed a light-weight thermal jacket to maintain the temperature of ice slurry – crushed ice and liquid water – at 0.1 to 1.0 degree Celsius for more than four hours. The thermal jacket, which weighs about 200 grams, consists of a cotton aerogel layer embedded within commonly used fabrics to provide heat insulation.
The cotton aerogel-insulated military canteen offers better heat insulation performance compared to commercial insulated water bottles such as FLOE bottles, and is highly comparable to that of vacuum flasks. However, FLOE bottles and vacuum flasks are much heavier and more costly.
“The heat insulation property of the novel cotton aerogels can be applied to various consumer products, such as cooler bags to keep food items fresh. We also foresee tremendous potential for other high value applications, such as pipeline insulation and transportation of liquefied natural gas which needs to be stored at a low temperature,” said Nhan.
The NUS team has filed a patent for the novel cotton aerogels and is exploring opportunities to work with companies to commercialize the technology.