Development of novel composites using recovered carbon fibers and resins CFRP wastes

Background:

Epoxy based composites (glass and carbon fiber reinforced) is used in a wide variety of applications from dental structures to aerospace components due to the versatility in the resin chemistry as well as the end-product properties. Among these composites, carbon fiber-reinforced polymer composites (CFRP) are used in specialized applications including aerospace for their very high mechanical strength, low weight, good corrosion and thermal resistance. By 2026, this is expected to increase to 180,400 MT with severe short fall due to demand-supply gap [1]. It is estimated that 30% of carbon fibers produced are discarded as production waste, along with solid waste generated during CFRP manufacturing and at the end-of-life for various CFRP components. Due to the recyclate value, carbon fiber based composite recycling has attracted more attention in comparison to glass based composites.

Various recycling processes such as mechanical, thermal, and chemical processes have been explored in the recent times. Unlike mechanical recycling, thermal and chemical recycling processes recover long continuous fibers with a higher potential for reuse. However, the use of high temperatures (450−550 °C) in thermal processes result in fibers with only 70−75% strength retention and also leads to harmful gas emissions and fiber surface contamination due to char deposition. The past decade has also seen use of supercritical fluids as green approaches for chemical recycling of CFRP waste. However, these processes require high temperatures (400−500 °C) and pressures (10−30 MPa) for the fluids to attain a supercritical state and are thus energy intensive. Chemical recycling methods ensure complete resin removal and recovery of long and continuous fibers with better strength. However, the use of harmful chemicals (e.g., nitric and sulfuric acid) and/or the use of extreme processing conditions (supercritical fluids) limits their scope for large scale application from an environmental and economic viewpointThe latter processes, although comparatively mild, involve the use of catalysts (prone to loss and/or reduced activity after recovery) and high reaction temperatures (220 °C)[2,3]. These methods also do not emphasize the complete recycling/recovery of all the materials involved.

Hence, strategies to recover the fibers as well as the resins or monomers from epoxy based composite wastes without downgrading their properties would be of great environmental and economic benefit. Considering the above mentioned issues, we have reported a sonochemical method for amine cured epoxy based CFRP recycling using a dilute nitric acid/H2O2 mixture [4]. A more efficient and environmentally benign method based on the in situ formation of per acetic acid, was employed in our later studies [5].

Research Gap: Based on these understandings, it is possible to further improve the existing processes or arrive at novel approaches to recycle carbon/epoxy based composites to recover the matrix materials (either as polymers or monomers/oligomers) and fibers and the potential for re-use of these recovered materials is envisaged in the proposed work.

Objectives:

• To recycle carbon/glass fiber reinforced epoxy based composites to recover the fibers as well as the resins using already developed environmentally benign approaches [4,5].

• Evaluation of the properties of the recovered carbon fiber for re-use as short fiber in composites in various matrix materials

• Preparation of short carbon/polymer composites based on the intrefacial properties of the fiber and matrix materials and potentail applications

• Evaluation of the newly developed composites for mechanical and other properties

• Evaluation of the recovered matrix polymer for re-use in potential applications

Outcome:

1. Environmentally benign technologies to recycle carbon/glass fiber reinforced epoxy composites

2. Technologies for the re-use of obtained recycled materials (resins/monomers/fiber)

3. Patents/publications in peer reviewed international journals

References:

1. The outlook for carbon fiber supply and demand, Jeff Sloan, https://www.compositesworld.com/articles/the-outlook-for-carbon-fiber-supply-and-demand (accessed on 2 Feb 2022)

2. M. J. Keith, L. A. Román-Ramı́rez, G. Leeke, A. Ingram, Polym.Degrad. Stab. 2019, 161, 225–234. DOI:https://doi.org/10.1016/j.polymdegradstab.2019.01.015

3. J. Li, P.-L. Xu, Y.-K. Zhu, J.-P. Ding, L.-X. Xue, Y.-Z. Wang, Green Chem. 2012, 14 (12), 3260–3263. DOI: https://doi.org/10.1039/c2gc36294e

4. Mohan Das and Susy Varughese, A Novel Sonochemical Approach for Enhanced Recovery of Carbon Fiber from CFRP Waste Using Mild Acid−Peroxide Mixture, ACS Sustainable Chem. Eng. 2016, 4, 2080−2087, DOI: 10.1021/acssuschemeng.5b01497

5. Mohan Das, Rinu Chacko, and Susy Varughese, An Efficient Method of Recycling of CFRP Waste Using Peracetic Acid, ACS Sustainable Chem. Eng. 2018, 6, 1564−1571