Introduction: Transparent Wood
Make strong and CLEAR composite materials with natural wood! Get all the strength of wood without all that darn opacity getting in your way! I figured out a quick and simple recipe with some cheap ingredients you can do right at home! Build wooden windows, or clear, wood cell-phone cases!
This video gives a quick overview of the whole thing, and shows some examples of the material in motion!
This is based off the paper by Zhu et al, called "Highly Anisotropic, Highly Transparent Wood Composites" http://onlinelibrary.wiley.com.sci-hub.cc/doi/10.1...
The basic idea is that wood can be thought of as two parts:
Cellulose: Strong structural strings which are naturally clear
Lignin: a sort of opaque glue that holds all those strong cellulose fibers together
If you can strip away the opaque (and non-structural) parts of the wood (the lignin) and replace it with clear epoxy, then you will have all the strength of the Cellulose fibers, but also be able to see through it!
In this way, you are making a composite material, much like fiberglass! One of the extra cool things about this, though, is that you are able to retain the existing structures formed by the way the wood grew, to theoretically make it extra strong and lightweight!
I saw lots of articles discussing this clever idea when this scientific paper first came out, and I wanted to see how do-able it would be as a simple process people can do at home. Turns out even with my basic, modified recipe, you can get some great results!
It's a pretty simple recipe that would be a fun experiment to do with kids to share ideas about chemicals and materials properties of wood. It can also as part of a design process
Note: This involves using some caustic chemicals. This is a first for me, so it was a bit out of my comfort zone, but I came through unscathed, and you can too! just use safety glasses and gloves!
Step 1: Materials and Recipe
- Thin pieces of wood (mine ranged fro .75mm-3mm - thicker takes more dissolving time)
- Large pyrex container (chemicals won't corrode it or react with it) (I used a glass brownie pan)
- Small scale (for weighing chemicals)
- Hot Plate
- Mixing Cups
- Popsicle Sticks
- Safety Glasses
- Safety Gloves
- Smock / Chemical Resistant Apron
- Sodium Hydroxide (NaOH) ($14)
- Sodium Sulfite (Na2SO3) ($6)
- Hydrogen Peroxide (H2O2) ($18)
The official recipe in the calls for about 8% H2O2, which you can make from 35% H2O2
available here: https://www.amazon.com/Hydrogen-Peroxide-Filled-Dr...
or I just used a whole bottle of regular cheap 3% H2O2 that you can get at the grocery store! It didn't bleach it that much, but it got it pretty transparent.
- Rubbing Alchohol ($2) (buy it at any store)
Aeromarine 300/21 -The official type they used in the paper: https://www.amazon.com/AeroMarine-300-Epoxy-Resin-... ($63)
Smooth-on (similar kind) (20$) https://www.amazon.com/Smooth--Smooth-Cast-Liquid-...
Table-top (kinda flexible) ($43) https://www.amazon.com/gp/product/B00V2GKMWW/ref=o...
This recipe is a modified basic version of comes from a paper by Zhu et al-
Highly Anisotropic, Highly Transparent Wood Composites
Mingwei Zhu, Jianwei Song, Tian Li, Amy Gong, Yanbin Wang, Jiaqi Dai, Yonggang Yao, Wei Luo, Doug Henderson, and Liangbing Hu*
http://onlinelibrary.wiley.com/doi/10.1002/adma.20... or Sci-Hub to get more Open Access: http://onlinelibrary.wiley.com.sci-hub.cc/doi/10.1...
- Make a bath from 1 liter water, 100 grams of NaOH, 50 grams of Na2SO3.
- Put in wood and heat at a low temparature for 10 hours
- Drain bath, rinse wood with water
- Create new bath from 1 bottle of H2O2 and heat for 2 hours
- Rinse and preserve in Rubbing Alcohol
- Take wood from alcohol and place in epoxy
- Vacuum the epoxy through the wood 3 times over 30 minutes
- Let cure
From their paper, here is their full recipe-
"Materials and Chemicals: Basswood from Walnut Hollow Company
was used in this study. The chemicals used in removing lignin contents
from wood were sodium hydroxide (>98%, Sigma-Aldrich), sodium sulphite (>98%, Sigma-Aldrich), and hydrogen peroxide (30% solution, EMD Millipore Corporation). The polymer used for infiltration was
epoxy resin (#300 resin and #21 nonblushing cycloaliphatic hardener,
AeroMarine Products, Inc.). The solvents used were ethanol alcohol
(190 proof, Pharmco-Aaper) and deionized (DI) water.
Lignin Removal from Wood: The lignin removal solution was prepared
by dissolving NaOH (2.5 mol L−1
The wood slices were immersed in the lignin removal solution and kept
boiling for 12 h, followed by rinsing in hot distilled water three times to
remove most of the chemicals. The wood blocks were then placed in
the bleaching solution (H2O2, 2.5 mol L−1
without stirring. When the yellow color of the sample disappeared, the
samples were removed and rinsed with cold water. The lignin-removed
samples were preserved in ethanol.
Polymer Infiltration: Epoxy resin was prepared by mixing the two liquid
components (#300 resin and #21 nonblushing cycloaliphatic hardener)
at a ratio of 2 to 1. Then the lignin-removed wood was placed at the
bottom of a dish and immersed in the liquid resin. The solution was
then degased under 200 Pa to remove the gas and ethanol solvent in
wood. Approximately 5 min later, the vacuum was released to let the
resin filling into wood structure by atmosphere pressure. The process
was repeated for three times. All the above processes were finished
within 30 min to avoid the polymer solidification. Finally, the dish
containing the wood sample and resin was kept static at 30 °C for 12 h.
The resin-infiltrated wood sample was peeled off from the dish after the
resin was completely solidified.
) and Na2SO3 (0.4 mol L−1)"
Step 2: Prep the Bath
First, fill a bath with 1 liter of water. Remember to use a chemical-resistant container that you can heat up (like a nice pyrex glass).
Put the container on your heat source (like the hot-plate). Rig up a ventilation system (there aren't really many fumes, I was just worried there might be, but it is nice to turn on a fan).
Get all your safety glasses and gloves on (these are like the burny chemicals that they scar their hands with in "Fight Club".)
Measure out 100 grams of Sodium Hydroxide (NaOH - Lye). Be careful to not drip water into the powdered chemical.
Slowly pour the chemical into the bath while stirring to prevent the lye from clumping up.
After it has all dissolved clear, measure out 50 grams of the Na2SO3. Again, slowly pour into the liquid while stirring.
Gently set your wood into the bath. Don't fill it up too much as the liquid will evaporate, and wood that dries out will start curling in an annoying way.
Step 3: Dissolve the Lignin
Bring your mixture to a boil. The scientific recipe calls for boiling the wood in this mixture for 12 hours. With my simple setup, that made the water evaporate too quickly. Instead I just set the hotplate to its lowest setting (around 250 F). I kept it warm like this for 10 hours. Longer would have probably helped even more! Im not sure what will happen if you leave it for too long.
The biggest problem you can encounter in this step is if the water evaporates. This will make your wood curl and get all wavy-which is annoying. If you lose too much liquid, just add more in.
In my initial tests, my basin almost dried up twice, and I added 500ml of water each time.
After the time is over, and your liquid has turned nice and brown, rinse out your wood with water.
You can take a look at your wood, it should have become much more translucent (but probably not that transparent yet).
Step 4: Bleach the Color
Next soak your wood in a bottle of Hydrogen Peroxide! This is fun and satisfying. Again keep the heat on. This is the process that will really bleach out lots of that final color and leave your wood as nice diaphonous films.
Let cook for 2 hours minimum. Add more Hydrogen Peroxide if your wood stops bubbling.
Rinse it all off in water.
Step 5: Preserve the Wood
After you took all that lignin, "glue," out of the wood, you need to keep it from falling apart. If it dries out now, all the little cellulose fibers will just curl and peel away from each other.
- Rinse all the chemicals off.
- Lay them all in a container.
- Pour rubbing alcohol over them.
- Store them in the alcohol until ready for epoxy.
Step 6: Set in Epoxy
Prepare surfaces that you can mold you wood into the epoxy. I lined buckets with some silicone (since the epoxy won't stick to the silicone), but you could also grease your containers with some oil (like Pam Cooking Spray).
- Drip off excess alcohol
- Pour a thin layer of epoxy
- lay down your chunk of wood
- pour a little bit more epoxy on top
Step 7: Vacuum the Epoxy
Your vacuum times will have to depend on your epoxy (in case its pot-life is too short), but the basic workflow I did was this:
- Bring to a Vacuum
- Let sit with the alcohol and epoxy bubbling through for 10 minutes
- Release Vacuum
- Repeat 2 more times
Towards the last time, you will notice far fewer bubbles going through the epoxy!
Step 8: Let Cure
The time depends on your epoxy, but generally leave it alone for a couple of hours. Heat will help it cure quicker!
Step 9: Results
From my first try at figuring out this recipe, I was quite pleased with the results!
Step 10: Improvements
My first examples here surprised me with how well they worked (for not really knowing what I was doing). Here's some tips on how to potentially improve this basic recipe to get even better results:
- Don't use wood laminates (like plywood)
- The layers just dissolve in the bath, and start curling up
- Use some kind of lid on the bath
- This will help your solution evaporate less, and prevent the wood from curling more
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Please be positive and constructive.
Is the wood after bleaching very soft, is it like a paper ? I was thinking I could use a transparent wood to my project but I don't want to use epoxy and prefer flexible material.
I haven't done it, but thinking about how and why this works.. The initial chemical bath is there to remove the lignin from the wood, basically leaving the cellulose. Lignins are polymers and are what lends the strength and rigidity to the cellulose fibres. Without it, I'm thinking the wood would become almost like a fabric - though as the cellulose fibres are laid out like a mat and not interwoven, it would be pretty delicate and pull apart easily. Think of it like Fibreglass.. the cellulose is the fibre, the lignin is the resin you impregnate it with to add the stiffness and bind it together. In this process - that is then replaced with the epoxy.... so in reality, this really isn't "wood" any more - think of it as a composite like fibreglass or carbon fibre, but made with a substrate of cellulose that has been processed from wood.
As to getting a flexible material... You might be able to substitute in a different polymer. Rather than the epoxy that's used here, you could perhaps try something like a two-part silicone compound with a softer shore rating.. bear in mind though that this compound is what now provides most of the strength to the new material, particularly in the 'cross grain' direction. If you need something uniformly strong, I'd suggest starting with a thin plywood.