04 BC purified
When purifying the SCOBY we basically remove residues from the fermentation process like sugar and yeast so that we are left with pure nano cellulose fiber. There are several studies online describing slightly different procedures but most of them are using a combination of aqueous sodium hydroxide, (available in chemist stores) and sodium hypochlorite Which is the main component in standard household bleach.
After the purification process, there is two way that we can turn it into printing ink; either we can simply blend it into a paste or we can dehydrate it and turn it into a nano cellulose powder. During my experiments, I did not see any clear difference in sense of strength and mechanical properties between the two methods however for the lab experiments I mainly used the fresh paste since it is a quicker process. However, the nano cellulose powder method has two advantages one is storage and secondly maybe most importantly since we know exactly how much liquid we add to the powder we can formulate much more precise recipes comparing to the paste method.
possible roadmaps
Experiemnt 1¶
Purification of kombucha pellicle:
Fig 1 Kombucha pellicle was covered with 1.0 M aqueous sodium hydroxide solution thermostated at 90 °C for 1.0 h (recipe for 1.0 M here ) . Then removed from the sodium hydroxide solution and washed with deionized water six times, pat dried with Kleenex tissues.
Fig 2 The pellicle portion was then placed in a second 1.0 M aqueous sodium hydroxide bath thermostated at 90 °C, allowed to stand for 1.0 h washed with deionized water, and dried.
Fig 3 Next the pellicle portion D was covered with aqueous sodium hypochlorite (Bleach 3.5%), and allowed to stand at room temperature (23 °C) for 2.0 h. Then removed from the sodium hypochlorite bath and washed with deionized water (6 times), pat dried with Kleenex tissues.
Fig 4 Finally, the pellicle portion D was transferred to a Petri dish and air-dried for 20 h before being mortared down into a fine powder
Fig 5 The powder was dehydrated with 3 ml of sterilized water and 1 drop of glycerin
Fig 6 air-dried for another 24 hours
Purification process following this study
Fig 1 Purified SCOBY Fig 2. undpurified SCOBY
Conclusion: the purification process was overall succesful however the final bioplastic material was very weak and brittle, more fabrication research needed.
Fig1 dried SCOBY Fig 2&3 BC powder
Experiemnt 2¶
Dried powder:
Process The purified SCOBY was placed in a dehydrator for 20 hours at 20°C. Once the pellicles were dried they were grinded in a coffee grounder for 2 min.
Then strained to divide the bigger pieces from the finer powder using a strainer.
blended SCOBY :
Process Scoby was purified according to above-described protocol after that blended with a household blender for 2 min. Once it reached a slurry consistency it was mixed according to above recipes and extruded (1ml) into individual petridishes and left airdrying for 48 hours.
Conclusion: Sample 55, 56 and 58 still had not dried, for 55 and 56 it could be explained by the hight water percentage but not for 58. An alternative explanation might be the presence of glycerol in all the three samples.
Shrinkage: all the samples was shrinking during drying, naturally Sample 57 had the least amount of shrinkages due to the relatively low water percentage.
Colour: All samples got a more yellowish tone after drying
Tensile strength: no test was conducted however all the samples appears to be to weak for the target application.
fresh BC: S-101 BC powder: S-109
Experiemnt 3¶
Fig1 pellicle during the last Sodium hypochlorite wash Fig 2&3 first and second sodium hydroxide wash Fig4. sodium hypochlorite wash
One of the problems that I encountered during the purification process was that the SCOBY pellicles didn't purify evenly Fig1, they tend to bleach quickly on the surface but required a long time to penetrate all the cellulose layers. Logically this means that for the outer layers of the pellicle was put under more chemical stress than necessary. To avoid that I experimented with blending the scoby into a paste before purifying it. This reduced the last sodium hypochlorite step dramatically from 1+ hour to 5-7 min.
It also made the deionized water wash much more effective since we didn't have the problem of residues of bleach stuck inside the pellicle. Resulting in dried samples without crystallization residues.
Experiemnt 4¶
SCOBY was purified according to previous recipe blended and mixed with polymers and plasticizer on a magnetic stirrer at 60°C for five min.
Then spread out on a Petri dish and left to dry in room temperature with a fan circulating the air.
The two 100% SCOBY samples with 4% and 6% procent glycerin did never fully dry (even after one week) and was very week easily being able to pull apart. The two other samples with sodium alginate or CMC powder as binding polymer were much stronger, flexible and satisfactory.
Conclusion: Both the Sodium alginate and CMC reciepes was satisfactory however I choose to proceed with the Sodium alginate reciepe because of the possibility to cure the print by crosslinking with Calcium chloride which would simplify the printing process significant.
Experiemnt 5¶
SCOBY was purified according to previous recipe blended and mixed with polymers and plasticizer on a magnetic stirrer at 60°C for five min.
Then spread out on a wooden board (to speed up drying) sprayed with calcium chloride before and after molding. The round mold shapes were held in place by a cookie mold.
From left to righ: Fig.1a&b S-87 100% SCOBY 1% Sodium alginate, Fig.2a&b S-89 60% SCOBY 2% Sodium Alginate, Fig.3a&b S-88 100% SCOBY 2% Sodium Alginate, Fig.4a&b S-86 20% SCOBY 2% Sodium alginate. All samples contained 1% w/v Glycerin
The samples were left to dry in room temperature with a fan circulating the air.
Density and grammage of the dried samples was calculated according to bellow method.
Conclusion: Sample 86, 87 and 89 was overall satisfactory, they seemed to be strong and flexible sample 88 was slightly brittle.
All the samples showed some crystallization on the surface this would most likely be because of some residue of hypochlorite from washing the SCOBY.
The samples might also benefit from adding a bit more glycerin to increase flexibility.
The shrinkage was as expected significant less with the 100% SCOBY samples and the extra percent Sodium alginate for sample 86 seemed to also help with “only” 15 times the lost in volume.
From left to righ: Fig.1 s-98a Fig 2 s-98b (with 2% surfactant) s-99 All samples was made from 100% purified SCOBY blended and mixed with 2% Sodium alginate and 2% w/v Glycerin
The samples were left to dry in room temperature with a fan circulating the air.
Conclusion: Sample s-99a was foamed using a icecream stabilizer (surfactant) that gave the sample a softer touch and significant less shrinkage most likely this is because when the water evapourates the air bubbles helps to stabilize the volume and the porous nature of the final sample makes it soft.
Density and grammage seemed to be higher the higher percentage of SCOBY in the sample.
Reflection of the BC purification protocol:¶
We have experimented with several modifications of purification methods as well as studied how different polymers and plasticizers are affecting the nano cellulose fiber.
For the purification process, we have discovered that by blending the SCOBY before purifying it we can get a much faster bleaching process that would suggest a gentler treatment of the fiber.
We have experimented with different drying processes and concluded that airdrying on an absorbing wood surface is the most efficient as that gives a beautiful slightly papery touch, a strong membrane that should be strong and flexible enough to make garments out of.
We have studied how different percentages of plasticizers are affecting the fiber and concluded over 6% w/v inhibits the drying process and concluded that 2% w/v is the optimal concentration for our requirements. We have also studied additions of different polymers like cellulose powder and sodium alginate and concluded that it doesn't have a significant effect on the final material however we have decided to use 2% w/v Sodium alginate blend because it allows us to cure the print (crosslinking with calcium chloride) inside the suspension bath.