Can waste be turned into bioplastics?

In the 20^th cen­tury, the avail­ab­il­ity of pet­ro­leum led organ­ic chem­ists to focus on a single source. The rise of bio-sourced mater­i­als has widened the scope of research impact­ing the indus­tri­al sec­tor. Syn­thet­ic chem­ists Grégory Noc­ton (Insti­tut poly­tech­nique de Par­is) and Grégory Danoun (CNRS) are turn­ing their atten­tion to waste. 

You are work­ing on new meth­ods of chem­ic­al syn­thes­is using raw mater­i­als such as waste. How do these dif­fer from petroleum? 

Grégory Noc­ton. Industry stake­hold­ers would start by telling you about the avail­ab­il­ity of pet­ro­leum, its homo­gen­eity, vis­cos­ity and that of its deriv­at­ives. But for us chem­ists, the real dif­fer­ence lies in the sim­pli­city of pet­ro­leum products versus the com­plex­ity of raw mater­i­als such as food waste, wood chips and used plastic pack­aging. The molecules in these mater­i­als are rad­ic­ally different. 

Grégory Danoun. In chem­istry, we have a per­fect under­stand­ing of how to man­u­fac­ture poly­mers from pet­ro­chem­ic­als, so basic research in this area presents few chal­lenges. But with raw mater­i­als such as waste, we are using dif­fer­ent chem­ic­al reac­tions and a dif­fer­ent approach – so it is far more exciting! 

You are look­ing for ways to pro­duce poly­mers from waste. What is your approach? 

GN. In prin­ciple, chem­ists can break down any mater­i­al into its basic build­ing blocks, which can then be used as raw mater­i­als. Altern­at­ive resources such as waste help us isol­ate new build­ing blocks, from which we can syn­thes­ize new poly­mers with new and use­ful properties. 

GD. Bio­lo­gists and micro­bi­o­lo­gists have already been explor­ing this using bac­teria and enzymes in pro­cesses such as fer­ment­a­tion, open­ing up aven­ues of research. The role of chem­ists here is key. We need to under­stand how dif­fer­ent molecules in waste gen­er­ate chem­ic­al reac­tions. The fact that there are so many reac­tions just makes things more interesting! 

Wood waste, for example, con­tains a nat­ur­al poly­mer, lignin, which is also found in cer­eal and paper waste. Food waste also con­tains an incred­ible range of molecules, with acids or fatty acids and so on. 

To extract use­ful molecules, we might break down carboxyl­ic acids, leav­ing us with the basic build­ing blocks, plus hydro­gen. This means oppor­tun­it­ies for hydro­gen pro­duc­tion (we recently obtained fund­ing for a stra­tegic hydro­gen pro­ject). The build­ing blocks them­selves can also be used. 

Why not replace pet­ro­leum with some­thing like starch or sug­ar rather than waste? 

GN. Two reas­ons. Firstly, there is already a lot of indus­tri­al R&D into starch and sug­ar, they are now very much main­stream. Hence, if we want to offer some­thing new, we have to look into more com­plex problems. 

Secondly, starch is mainly made from corn and requires a lot of water. If we made poly­ethyl­ene tere­ph­thal­ate (PET) from corn, giv­en glob­al demand for plastic bottles, we would quickly run up against a resource prob­lem – and we’re not even address­ing com­pet­ing demand from the food sec­tor. It makes more sense to work with resources that will remain struc­tur­ally available. 

What can we expect in this area in the future? 

GD. Find­ing new ways of obtain­ing basic build­ing blocks is a fas­cin­at­ing and fast devel­op­ing field. Some of the most inter­est­ing dis­cov­er­ies in the past ten years or so have been made in pho­to­chem­istry, where numer­ous pro­cesses are com­bined using light. We are cre­at­ing reac­tions, try­ing to find new mul­tipur­pose cata­lys­ers or, on the con­trary, highly spe­cif­ic ones aimed at one molecule in a stack of waste (ana­log­ous to highly spe­cif­ic enzymes in biology).

GN. We’re now try­ing to devel­op a wide range of meth­ods, and to break down sci­entif­ic bar­ri­ers. Diverse sources of raw mater­i­als mean more sus­tain­able pro­duc­tion. We want to explore and uncov­er all pos­sib­il­it­ies. If we nar­row our focus, we could end up recre­at­ing the same prob­lems we now have with pet­ro­leum. Had we done this a hun­dred years ago the world would look very dif­fer­ent today!