Metrohm has revealed how its 842 Titrando, 800 Dosino and Tiamo software are assisting with depolymerisation studies at the University of Stuttgart.
Biogas and biodiesel have been well known to the general public for several years.
But what are bioplastics and how are they formed? For many millions of years, bacteria have been using carbon compounds as storage substances.
Among other things, microorganisms require nitrogen and phosphorus for growth and cell division.
If one of these two elements is missing, cell division stops.
At the same time, the cells switch their internal program to storage by taking up carbon, mainly from sugars, fatty acids and other compounds.
This carbon is then stored inside the cells in the form of granula that are made up of poly(3-hydroxyalkanoate) (PHA), a group of polyesters of which poly(3-hydroxybutyric acid) (PHB) is particularly widespread.
As soon as the bacteria have everything they require for cell division again, the stored carbon is consumed.
PHA compounds have material properties that very closely resemble those of conventional plastics such as PET.
Additionally, they are biodegradable and can be obtained from self-regenerating raw materials.
Other types of bioplastic have been developed as well, for example on the basis of corn starch or polylactic acid (PLA).
Up to now, PHA products have only been used for tests purposes; PHA isolation and processing is still much more expensive than the manufacturing of plastic from crude.
In Prof Dr Jendrossek's workgroup in the institute for Microbiology at the University of Stuttgart, the focus of interest is the degradation of the polymer in the cell itself (depolymerisation).
It is chiefly the enzymes (so-called PHA depolymerises) that are responsible for this and they are therefore being studied in detail in order to learn more about their exact role within the cell system.
Part of this enzyme is located on the granula surface and, if needed, splits the long polyester molecules into shorter ones that serve as building blocks for cell metabolism.
The enzyme activity can be measured by the acid that is released by the hydrolysis of each ester bond.
For the activity test, the granula are isolated from the bacteria and placed in the reaction vessel of the 842 Titrando together with several millilitres of a weak buffer.
Using this pH-stat titrator allows to detect the weak acid release at the small PHB spheres.
A precise and robust pH micro-electrode transmits any variation from the set pH value via the Tiamo software (v1.1) to the dosing unit of the 800 Dosino.
To again obtain the set pH, NaOH (for example, c(NaOH) = 0.01 mol/L) is added by the Dosino with a variable dosing rate ranging theoretically from 0.01 uL/min up to 60 mL/min.
By continuously recording and plotting the amount of base consumed versus time, the acid release rate can easily be monitored in real time on the computer display.
This procedure is ideally suitable for studying the influence of various substances on the hydrolysis rate of the PHB granula.
A thermostatted reaction vessel equipped with a temperature sensor also allows the effects of temperature changes on the release rate of acid to be investigated.
As two pH-stat titrations can be carried out in parallel with Tiamo, the acid release can be recorded simultaneously at two different temperatures.
Two measuring cells and two electrodes connected to the 842 Titrando are required to do this.
At the end of the measurement, the data and the graphs can be entered in a prestructured report data sheet and printed out; they can also be exported into other programs (Excel, Powerpoint) for further processing.
With Tiamo the graphs can be compared, reports optimised, comments inserted, and there are virtually no limits to result presentation.
