biorubber.md



STARCH-BASED RUBBER

Tactility & sound impression


Description
A rubbery biopolymer based on gelatin and corn starch.

Physical form
Surface
Color without additives: yellow

Fabrication time
Preparation time: 1 Hour
Processing time: 1-7 days
Need attention: None, just leave it to dry while pressed (e.g. on a roster) as long as is feasible with lots of airflow.
Final form achieved after:7 days

Ingredients


Gelatine powder - 50 gr

Functions as polymeer (so it becomes a solid)


Corn starch - 50 gr

Functions as the second polymeer (so it becomes a solid)


Glycerine - 50 gr

Functions as plasticizer that bonds with the gelatine (makes it flexible).


Water - 50 ml/gr and a dash extra

To dissolve and mix the polymeer and plasticizer
To dissolve and mix the corn starch before adding to the other liquid


White vinegar - 15 ml

Vinegar is almost always added to starch-based biopolymers to change the molecular structure of the starch, making it stronger and more workable.


Tools


Cooker or stove (optional: temperature controlled)
Pot
Scale
Sheet of textured plastic for casting
Spoon

Strip of acrylic (or spatula for even spreading)

A press or a stack of heavy books (to keep the slab pressed while drying)


Yield before processing/drying/curing
Approx. 200 ml

Method


Preparation

Weigh your ingredients
Prepare the mold and find a place where you can leave it for a while, ideally near an open window where there's air flow.


Mixing and dissolving the ingredients

bring the water to the boil
optional: add natural dye if you wish to use color
add the glycerine
add the gelatine
keep the temperature below 80 degrees celcius while stirring very very slowly and gently to avoid making bubbles. I prefer a simple spoon to do this, not a whisk.


Cooking the ingredients

dissolve the starch in a separate bowl using a few tablespoons of hot water
when the gelatine is completely dissolved, add the starch mixture and stir for another 5-10 mins at 80 degrees
finish with a thick but still somewhat liquid paste


Casting

The mix is a thick paste that needs to be cast (quickly!) by smearing across a the surface of the mold with a spatula.
It cures quickly at this stage, so be fast
Put the mould away to dry in a cool place with lots of air flow (like near an open window). A warmer place might speed up the drying process but also allow bacteria to grow faster and can result in fungal growth.
The slab will shrink relatively quickly, then take it off the mold and let it air dry
Alternate drying with some periods of keeping it pressed. If you have a roster you can dry and press at the same time.


Drying/curing/growth process

Mold depth:  				N/A
Shrinkage thickness:      5-10 %
Shrinkage width/length:   5-10 %

Shrinkage and deformation control
Letting it dry for a week or so to get to the final form. It will be flexible at first but will slowly harden until its totally rigid. The slab needs some attention during drying as the edges that are thinner will curl up. Trim the piece before it's completely hard. Occassionally press down the slab under a stack of books for a few hours to keep it flat.
Curing agents and release agents
None.
Minimum wait time before releasing from mold
Ready to be released after 1-2 hours.
Post-processing
Store in a dry and ventilated room. Keep pressed until fully dry.
Further research needed on drying/curing/growth?
Not sure.

Process
Getting everything ready, Loes Bogers, 2020
Dissolving the corn starch in some hot water, Loes Bogers, 2020
Dissolve the gelatine until thick, Loes Bogers, 2020
Stirring in the corn starch mixture, Loes Bogers, 2020
Finish with a custard-like thickness, Loes Bogers, 2020
Spread the paste with a spatula (be quick!), Loes Bogers, 2020
The strach-based rubber curing, Loes Bogers, 2020
Trimming the - still flexible - slab for further curing, Loes Bogers, 2020
Drying the slab on a roster (pressed down with books occasionally), Loes Bogers, 2020

Variations on this recipe

Add a natural colorant such as a vegetable dye or water-based ink (e.g. hibiscus, beetroot, madder)
Add less glycerine for a more rigid slab (or try adding more for more flexibility)
Reduce amount of gelatine or leave it out altogether

Stiffeners such as fibres, yarn or natural debris may be added for more structure and reinforcement.


Cultural origins of this recipe
Biopolymer production is older than petrol-based plastics. In 1500 BC, people in Egypt were already using glues based on gelatin, casein and albumin for furniture constructions. Gelatin casting as a technique has also been used in production of jelly-based foods such as aspic, jelly desserts and candy.
Needs further research?   Not sure

References this recipe draws from


Bioresin (gelatin) Recipe by Cecilia Raspanti (Textile Lab, Waag), Fabricademy Class "Biofabricating", 2019, link.

The Bioplastics Cookbook: A Catalogue of Bioplastics Recipes by Margaret Dunne for Fabtextiles, 2018, link


Known concerns and contestations*
Needs further research
Gelatin is an animal-based ingredient. Some might find it problematic to use resources that requires killing an animal because of religious or animal welfare beliefs. Arguments are also made that as long as there's a meat industry, it is better to use product from the entire animal, including skin and bones. Some might consider gelatin to be a product that comes from a waste stream, but this is considered controversial by others.
Acrylic (for the mold) is a petrol based plastic but results in very shiny foils and sheets and can be reused endlessly for casting high quality bioplastic sheets.
Using renewable ingredients is not by definition petrol-free. Imagine they have to travel long distances by plane, boat or truck: it takes fuel. Also, the effects of GMO technologies and pesticides can be harmful to the environment and it's worth using knowing the source and production standards involved. If you can afford it, buying organic ingredients is a good starting point.

Sustainability tags

Renewable ingredients: yes
Vegan: no
Made of by-products or waste:  no
Biocompostable final product:  yes
Reuse: further research needed

Needs further research?:  not sure
Recycling biopolymers with PET plastics contaminates the waste stream. Compost bioplastics in a warm environment with sufficient airflow.

Material properties

Comparative qualities
This slab feels a bit like a rubber car tyre. It's tough but resilient. It has a storng sour smell from the vinegar (this slowly fades).

Technical and sensory properties


Strength: strong

Hardness: resilient

Transparency: translucent

Glossiness: satin

Weight: medium

Structure: closed

Texture: smooth

Temperature: cool

Shape memory: high

Odor: strong

Stickiness: medium

Weather resistance: needs further research

Acoustic properties: needs further research

Anti-bacterial: needs further research

Non-allergenic: needs further research

Electrical properties: needs further research

Heat resistance: low

Water resistance: needs further research

Chemical resistance: needs further research

Scratch resistance: moderate

Surface friction: medium

Color modifiers: none


About this entry

Maker(s) of this sample

Name: Loes Bogers
Affiliation: Fabricademy student at Waag Textile Lab Amsterdam
Location:  Rotterdam, the Netherlands
Date: 16-03-2020 – 22-03-2020


Environmental conditions

Outside temp:  5-11 degrees Celcius
Room temp:  18 – 22 degrees Celcius
PH tap water:  7-8


Recipe validation
Has recipe been validated? Yes
By Cecilia Raspanti, Textile Lab, Waag Amsterdam, 16 March 2020

Estimated cost (consumables) in local currency
2,26 Euros for a yield of approx 250 ml

Local supplier/sourcing info
Gelatin powder - Jacob Hooy (online retailers)
Glycerine 1.23 - Orphi/Chempropack (online retailers)
White vinegar - supermarket
Corn starch (organic, non-GMO) - supermarket
Molds - Textured plastic, old packaging material, textile shop, homeware shops

Copyright information

This recipe is in the public domain (CC0)
Yes

This recipe was previously published by someone else
Yes, in: ADDD HERE
##References


The Secrets of Bioplastic by Clara Davis (Fabtex, IAAC, Fab Lab Barcelona), 2017, link.

The Bioplastics Cookbook: A Catalogue of Bioplastics Recipes by Margaret Dunne for Fabtextiles, 2018, link

Material archive sample Maria Viftrup
"Make it and Break it: Bioplastics from Plant Starch with
incorporation of Engineering Practices", by Richard Harris, Carla Ahrenstorff
Gracye Theryo, Aaron Johnson, Jane Wissinger. Center for Sustainable Polymers at the University of Minnesota, 2017: https://csp.umn.edu/wp-content/uploads/2017/03/Make-it-and-Break-it.pdf


Images of final product
Starch-based rubber, Loes Bogers, 2020
Starch-based rubber, Loes Bogers, 2020
Starch-based rubber, Loes Bogers, 2020
Starch-based rubber, Loes Bogers, 2020
Starch-based rubber, Loes Bogers, 2020