30 Juli 2019

Potential of Lignin Use in Plastic Recycling: A Random Match

Value the Random Structure of Lignin by Nature

For utilization of lignin, its random structure designed by nature is considered as a big disadvantage. Would the natural random structure of lignin become an advantage instead? It might be possible in a proposal that utilization of lignin (as compatibilizer) in plastic waste composite because most of post-consumer plastic waste are random in structure due to lack of labelling.

Lignin is the most abundant with rich aromatic components in nature. Its random designed structure by nature is one of main obstacles for lignin utilization in industry. Not surprisingly, much effort was made toward changing the random structure into more regular ones, for example depolymerization of lignin into aromatics (one or a few as major final products) chemically [1] or by biotechnology (synthetic biology) [2]. Such depolymerizations or reconstructure processes usually are costly and few is profitable running as a business. Another important approach is chemically modified lignin as filler/stabilizer/compatilibilizer for composite [3], which is simple in chemistry and less costly. But in composite application, the random structure of lignin is still considered a disadvantage for properties of final composites.
On the other hand, plastic waste composite with two or more components inside (including some known components or unknown ones) will be the most in all recycled plastic waste as foreseen in my last article [4]. Particularly components of composite will be random in the near future considering a fact that labelling of plastic types is not yet compulsory worldwide. Within the random plastic waste composite, in general there are two classes of thermopolymers – aliphatic rich type and aromatic rich type. Both types of polymers prefer to interact with their own kind, which would lead to poor performance of waste composite. Common solution by using a single or several commercial compatilibizers is likely not a good choice because of random components in waste composite. Lignin is prospected to be an ideal compatilibizer due to its random structure by nature.
In summary, a random match of lignin and plastic waste composite may lead to a significant improvement on performance of waste composite. The fact that unmodified lignin waste or simple modified lignin (for example reactive modification [5]) is workable well indicated that this application might be profitable and sustainable.


[1] Formic-acid-induced depolymerization of oxidized lignin to aromatics” Rahimi, A.; Ulbrich, A.; Coon, J. J.; Stahl S. S. Nature 2014, 515, 249–252.
[2] “Funneling Aromatic Products of Chemically Depolymerized Lignin into 2-Pyrone-4-6-dicarboxylic Acid with Novosphingobium aromaticivorans” Perez, J. M.; Kontur, W. S.; Alherech, M.; Coplien, J.; Karlen, S. D.; Stahl, S. S.; Donohue, T. J.; Noguera, D. R. Green Chem. 2019, 21, 1340-1350.
[3] “Lignin as an Additive for Advanced Composites” Polat, Y.; Stojanovska, E.; Negawo, T. A.; Doner E.; and Kilic, A.; Green Biocomposites 71-89.
[4] “An Elephant in Plastic Recycling Room” Gu, L.; https://www.linkedin.com/pulse/elephant-plastic-recycling-room-liuqun-gu/
[5] “Tunable Boc Modification of Lignin and Its Impact on Microbial Degradation Rate” Gu, L.; Wang, M.; Li, H.; Teh, K. N.; Li, Y. and Liu, Y. https://chemrxiv.org/articles/Tunable_Boc_Modification_of_Lignin_and_Its_Impact_on_Microbial_Degradation_Rate/7257212

Source: Liuqun Gu, 2019-07-26.
Author: Liuqun Gu

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