Here I will detail my method for improving the adhesive power of simple wheatpaste by including lye during preparation. This method also provides increased durability and spoil resistance. I stumbled across this idea on accident and do not know all of the chemical processes involved. However, I have researched the basic reaction of gluten protiens and alkalis which is described next. Additional information about the chemistry at work here would be helpful and is welcome.
Tools and Materials-
All purpose wheat flour
Lye AKA sodium hydroxide
Corn or tapioca starch
Boiling Pot and stove - A rice cooker will work or a wok like I used here.
Step 1: THEORY
The starch and gluten protiens in wheat flour are natural polymers which provide the adhesive action of wheatpaste. polymer crosslinking and gluten production is increased by including alkali to bring the ph up to about 11. Alkalinity also encourages greater absorption of water in the flour, more starch degradation, and an increase in strength and extensibility. Lye is a strong alkali and is chosen since it is sold economically in ready to use form. Another route could be cooking sodium bicarbonate in the oven to yield semi strong sodium carbonate. plain baking soda is too weak and should not be used. There is a distinct odor created when alkali is added, Which I suspect to be some freebase amine being produced (chemists please help clarify this). Though this recipe doesn't make "freebase wheatpaste" I thought it was funny and semi-true since there's probably some free amines produced in the mix. Lye is dangerous. It can damage pretty much anything it comes in contact with and will react violently with acid and other chemicals. When using the pure powder read and follow all instructions on its packaging and protect yourself from contact. Once cooked into the paste and at ph 11, the base is mostly neutralized. There is a chance you may have some minor irritation from skin contact, but that's about it.
Step 2: Prep
In a large mixing bowl, Combine 4 cups of flour, 1/2 tsp of lye, and 1/4 cup of starch. Mix them together well with the whisk and set aside. Bring about ten cups of water to a boil.
Step 3: Vandal Batter
Put about 3 cups of warm tapwater in a bowl and add about 2 cups of the prepared flour/starch/lye while whisking. whisk until smooth.
Step 4: Cook
The water should be boiling. slowly pour the batter while whisking well. The water will thicken immediately and become harder to whisk.If it becomes too thick add a bit more tapwater to thin. Turn down and simmer for 10-15 minutes. The glue will continue to thicken and develop a translucent appearance when done. Remove from heat.
Step 5: Strain the Glue
Sometimes lumps will develop during the cook. This step eliminates lumps as the liquid is run through a wire mesh into a bucket. Use the whisk against the screen to push as much lumpiness through as possible. Refrigerate the screened glue and discard any stubborn lumps left in the screen.
Step 6: PH Test
Use a PH testing strip to establish safety. It should read between 7 and 11. Paste indicating PH 12 or higher is not safe to use and should be considered caustic. Dilute to lower ph or discard. After standing the ph will even out to around 9 or 10.
Step 7: Additives
Glue can be customised with additives to improve certain qualities.
Some common additives are -
Gelatin - increases flexibility (plasticizer) and adds strength.
Methyl Cellulose - is an adhesive alone which can improve texture and spreadibility.
Dextrin - is the traditional adhesive used on postage stamps. It is prepared by baking corn starch until golden brown and can improve tack and add sheen.
Bleach, alcohol, or peroxide - a splash added to the cooled finished glue will inhibit microorganism growth and extend usable life.