# Breaking down cellulose using impact force

#### yahastu

Generic biomass such as leaves contain a large amount of total carbohydrates, mostly in the form of cellulose.

Some animals such as apes and can digest cellulose and that is how they can survive on leaves.

Humans cannot digest cellulose because we lack the enzymes necessary to decompose cellulose. In addition, some leaves may contain toxins that we need to avoid.

Because leaves are plentiful and contain large amounts of energy, I'm curious to explore the question of what it would take to make leaves digestable by humans. I'm particularly interested in how this could be accomplished without super advanced tools, for example in a survival situation or primitive society.

I can think of three possible ways off the top of my head that seem like they might be plausible.

1) Breed animals that do have the necessary enzymes, such as sloths. You could then feed the sloth leaves, let the sloths convert the biomass into meat, and then you can eat the meat.

2) Would it be possible to cultivate the enzymes that break down cellulose directly, thereby cutting the sloth out of the picture?

3) In a survival situation, the first two would not be an option. However, it is known that the crystalline structure of cellulose can be destroyed and turned into amorphous form when subjected to high pressure (25 MPa).

Questions:

1) If you subjected a bunch of leaves to pressures over 25 MPa, would you then be able to digest the resulting leaf paste, assuming that these particular leaves do not contain toxins?

2) If the leaves do contain toxins, such as tannins, perhaps you could first grind up the leaves, then leech out the tannins by leaving them in a stream, and then finally subject them to higher pressures in order to break down the remaining cellulose and make it edible?

3) Would it be possible to achieve the necessary 25 MPa (megapascal) using primitive tools?

25 MPa is equivalent to 3,625.94 pounds per square inch (psi).

A 20 lb sledgehammer, lifted to a height of about 9 ft and let fall by the force of gravity, will be traveling at about 8 m/s when it strikes.

Now we need to know how fast the sledgehammer comes to a stop. Not sure, maybe 0.1 seconds?

F = m*(v/t) = 9 kg * 8 m/s / 0.1 s = 720 Newton

Suppose we hit an area the size of a nail head (0.01 sq inch = 6.4516e-6 m^2 ) by fashioning a pointy tip onto the sledgehammer. Then we get:

720 Newton / 6.4516e-6 m^2 = 111.6 megapascals. Wow, we destroyed that cellulose!

I'm guessing that the amount of calories we get from the 0.01 sq inch bit of cellulose is probably less than what it takes to swing the sledgehammer....but we did it, we can successfully digest the cellulose, right?

Last edited:

#### jim mcnamara

Mentor
Couple of points:
1. Humans already consume a variety of green leafy vegetables - spinach, chard, cabbage.

2. Through the selection of better tasting plants that are more digestible those plants are very edible. This took many generations, thousands of years. Romaine lettuce (or cos) was first domesticated by the Romans

3. Plants humans do not eat are often toxic, so we would have to deal with that problem for new plants we wanted to smash up.

Xylem tissue has most of the cellulose tissue in plants, large plants also have lignin - ex: trees. For a greater return, you may want to consider some other plant tissues, not leaves or wood. Lignin is hard to remove, usually requires a soak in lye $$NaOH$$ . Plus leaves of many trees have some nasty compounds in them - example: cyanogenic glycosides in cherry leaves and bark. Which creates cyanide on exposure to air. So that leaves us to consider tissues like the less edible parts of fruits, roots, underground stems (rhizomes) - peels and skins, for example.

I'm not at all sure that mechanical breakdown is doing any more then smacking up the lignin as I mentioned above (with lye). Slow cooking with acid (like lemon juice) for really long periods can hydrolyze some kinds of sugar polymers. Possibly to the point of making some simple sugars - i.e., digestible.

You can experiment with cheap cotton balls - nearly 100% cellulose. Take them to an anvil see what you get.

"Breaking down cellulose using impact force"

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving