Kevlar-like Aramid Polymers from Mixed PET Waste

Area of Science:

• Polymer Chemistry
• Materials Science
• Sustainable Chemistry

Background:

• Recycling waste polyethylene terephthalate (PET) into valuable materials is crucial for sustainability.
• Aramid polymers are known for their high performance but traditional synthesis can be resource-intensive.

Purpose of the Study:

• To explore sustainable and scalable synthetic routes for aramid polymers from waste PET.
• To characterize the properties of novel aramid polymers derived from PET.

Main Methods:

• Investigated direct depolymerization and polycondensation methods using terephthalic acid (TPA) derived from PET.
• Employed the acid chloride route for highest molecular weight polymer synthesis.
• Utilized size exclusion chromatography, spectroscopy (NMR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) for characterization.

Main Results:

• Direct depolymerization yielded decomposition; polycondensation resulted in low molecular weight aramids.
• The acid chloride method produced novel soluble aramids with molecular weights of 10-35 kDa (Mw) and 28-81 kDa (Mz).
• Polymers exhibited high degradation temperatures (>400 °C) and high char yields, with no detectable glass transition.

Conclusions:

• Novel aramid polymers can be synthesized from waste PET, offering a sustainable alternative.
• Optimized reaction conditions, including pyridine addition and absence of CaCl2, are key for improved synthesis.
• The high thermal stability and potential for gel formation suggest suitability for fiber applications.