PLASTICS FROM SEAWEED
Workshop by Norman Friedrich, 2.4.2017
Extracting alginate, agar and carrageen from macro algae – a biochemistry workshop with Norman Friedrich from Martin Luther University Halle.
We spent the first part of the day with a presentation which introduced us to the chemical characteristics and possible applications of three substances extracted from algae. Alginate, agar and carrageen are mainly used as thickening agents, which are all water-soluble.
The second part of the workshop showed us experiments how to extract these substances. We were divided into groups, each one dealing with another type of algae and extraction.
Intructions from the biochemistry workshop
The principles of operation were quite similar in all groups, mostly the substances which we worked with varied. All groups used distilled water and a magnetic stirring unit.
extraction of carrageen from red algae Chondrus crispus
This is probably the easiest experiment. 10g of the Algae are cooked in 200ml water for 10min. The solution quickly shows thickening qualities. The resulting substance is then separated from the algae biomass by filtering and the carrageen is finally precipitated in 400ml ethanol (C2H5OH).
extraction of agar from red algae Gracilaria vermiculophylla
8g of the dried algae are cut into pieces and heated at 85°C for 3.5h in 200ml of 3% sodium hydroxide solution (NaOH). The liquid is removed by filtering and the residual algae material is washed and boiled in 200ml of 0.5% acetic acid solution (CH3COOH). After 1 h the solution is discarded once again. In the next step the algae are heated at 85°C for 2h in 200ml water. The mass is being processed to a homogenous mixture, which is then filtered. The solid residues are discarded and the liquid filtrate is concentrated to 50 ml by evaporating water at 60 °C. This solution is then mixed with 200ml ethanol (C2H5OH). The mixture is left under constant stirring for 24h, filtrated off and the solid residue is dried on air.
extraction of alginate from brown algae Fucus visiculosus
First 12g of the dried, crushed algae are boiled in 150ml water for 30min. In the following step the water is removed by filtering and 150ml of 0.5% calcium chloride solution (CaCl2) are added to the algae. The solution is boiled for another 30min after which the calcium chloride solution is poured off. After washing the algae material with water, 150ml of 0.5% sodium chloride solution (NaCl) are added. The mixture is set to boil for 1h. Then the liquid is discarded again while the biomass is set to boil for 30 min in 100ml of 3% sodium carbonate solution (Na2CO3). This step degrades the plant material. Later 100ml water are added before the solution is filtered off. Subsequently, the sodium alginate is precipitaH5OH). The mixture is then left under constant stirring for 24h and can either be stored in ethanol or filtrated and dried to obtain a powder.
extraction of alginate from brown algae from Sargassum muticum
As a start 8g of the shredded algae are moderately heated (60 °C) in 100ml of 2% hydrochloric acid solution for 3h. The acid solution is then poured off and the remaining algae are washed with water. 100ml of 3% sodium carbonate solution (Na2CO3) are added to the biomass and heated for 3,5h at 85 °C. The product is precipitated by adding 200ml ethanol (C2H5OH), after which it can be filtrated and left to dry.