(6) Sustainability

Although melamine sponge(MF) itself is not toxic to the environment, but it is not biodegradable which means it can’t be broken down by microorganism or natural abiotic factors^[1]. So we need to design some ways to dispose it. However, if melamine sponge can’t be disposed properly, it may cause pollution. For example, if we forced to break down the melamine sponge at a very high temperature, the process will cause much poisonous oxycarbide and oxynitride like CO, NO and NO₂ which is bad for the environment. In order to maintain the sustainability of the environment, many scientists have design many methods to recycle melamine sponge. There are two general ways:

The one is to design a better method to break down this material. For example, Shaodi Wu and co-workers has developed a method to hydrolyze melamine sponge by NaOH-H₂O system. They disposed melamine sponge in NaOH-H₂O system in mild conditions (160°C), finding that the degradation ratio of melamine sponge is 97wt%. The main production of this reaction is ammelide and ammeline which can be used to make other materials like melamine urea-formaldehyde resin(MUF), and this process is very eco-friendly^[2].

The other way is to reuse melamine sponge by adding it to other materials directly. For example, Xiaotong Wang and co-workers tried to pulverize the waste melamine sponge into powder and add it into polyurethane foam (PUF) as a flame-retardant filler. The following test shows melamine sponge powder decrease the heat release rate(HRR) and the flammability of PUF a lot, when a small amount of guanidine phosphate(GP) is added, the performance of PUF is better^[3].

Fig1.Images of (a) PUF, (b)PUF-MF/30 and (c) PUF-MF/30-GP in flame test^[4]

Fig2.HRR curves of MF, PUF, PUF-MF/30 and PUF-MF/30-GP^[5]

These two ways gives us the directions when we need to dispose melamine sponge in a sustainable way.  

References

[1]“Are Melamine Sponges Eco-Friendly? Ethically Engineered,” 05, 2022. https://www.ethicallyengineered.com/are-melamine-sponges-eco-friendly/.

[2]Wu et al., “An efficient and mild recycling of waste melamine formaldehyde foams by alkaline hydrolysis,” Green Energy & Environment, vol. 29, Oct. 2022, doi: https://doi.org/10.1016/j.gee.2022.10.008.

[3][4][5]X. Wang, Y. Shi, Y. Liu, and Q. Wang, “Recycling of waste melamine formaldehyde foam as flame-retardant filler for polyurethane foam,” Journal of Polymer Research, vol. 26, no. 3, Mar. 2019, doi: https://doi.org/10.1007/s10965-019-1717-5.