Pulp It! - 3D Printable Recycled Cardboard Molds

Tired of throwing cardboard boxes away? Want to recycle at home with a 3D printer? I've got the perfect project for you.

Pulp It! offers new ways to reshape recycled cardboard at home with just a 3D printer. Download different molds and start making recycled products today.

Supplies

Only basic tools are needed to make incredible cardboard products:

FDM 3D Printer: Any 3D printer works as the molds are made with PLA plastic
Blender: Used to pulp the cardboard. Similar tools may also work.
Cloth: To remove excess water from the pulp.
Clamps: To press the parts together and form the cardboard product.
Scissors: to cut the cardboard into smaller pieces.

And some supplies too:

PLA plastic: To 3D print the molds.
Cardboard: Or any other pulp-based material such as paper or packing material.
Glue: PVA glue or rice paste works best.
Water

Step 1: Pulp It Mold Set

The Pulp It! mold set includes four different designs: Pencil Holder, Box, Tray and Coaster.

Also, an Autodesk Fusion 360 parametric design is also available. With it, you can easily change the dimensions of the mold and customize it with your own text and logo.

Step 2: 3D Printing the Molds

Choose one or more of the mold designs and 3D print them. Keep in mind that these parts will need to withstand pressure, so they need to be resistant.

Recommended print settings:

Layer Height: 0.2-0.3mm
Wall thickness: 1.6mm
Top/Bottom thickness: 1.5mm
Infill Density: 20%

Tip: The mold designs are compatible with larger nozzles. Use a 0.6mm or 0.8mm nozzle to print the molds faster. That will also make them more resistant!

Each mold has at least four parts:

Walls: Vertical walls that form the side shape.
Wall Clip: This clip keeps the wall mold closed and withstands some pressure.
Bottom lid: It forms the bottom part of the mold and it's flat. It could also be curved.
Top lid: It forms the interior shape and determines the object's thickness.

There are some molds such as the ones from the Box design that include two different Top lid parts. That's because the same mold set makes two different objects just by changing the Top lid: one makes the cardboard container and the other one the cardboard lid.

Don't know which one to start with?

If it's the first time you'll make objects with recycled cardboard and 3D printed molds, I personally recommend trying the Box design.

Step 3: Making the Pulp

Now the fun part begins!

Preparing the cardboard

Almost any type of pulp-based materials work. If you're using cardboard boxes make sure any tape or coatings are removed before making the pulp.

Make sure you cut the cardboard into smaller pieces so you can easily blend them. For example, 1x3" (25x75mm) cardboard pieces work great for standard-size blenders.

Choosing the binder

A water-soluble binder is required to improve the strength of the final product and it also helps keep its shape when drying.

There are two main binders that I recommend: PVA glue and rice paste (AKA rice glue). I personally recommend using PVA glue if it's your first time working with paper pulp as it's easier to use.

Tip: If you have access to soluble PVA filament for FDM 3D printers, you can dissolve some of it and use it as glue.

Mixing the ingredients

This isn't an exact science. It's recommended to start with the water and binder and slowly add the cardboard until the mix is dense enough.

Warning: Never add too much cardboard as you can damage the blender.

Here's the amount of material I start with:

Water: 500g
Cardboard: 150g
Binder: 30g

Mix all the ingredients until the pulp has a homogeneous consistency. If you can still see pieces of cardboard, you need to blend them more. You can always remove some cardboard bits from the pulp if they had a non-soluble material such as tape or staples that you didn't see during the cutting process.

When making pulp it's difficult to estimate the right amount to make as the density of the mix can vary. However, it's always better to prepare too much than to run out of it in the middle of a project.

In one of the images, we can see the before and after of paper pulp. Both amounts of pulp have a similar volume, but the wet pulp on the left will reduce its size by 80% if pressed as the one on the right.

Removing the excess water

Don't worry if the pulp has too much water as you're going to remove it using the cloth.

Wrap some pulp in a cloth and squeeze it until the consistency is similar to wet clay. If the pulp has too much water, the part will break when you demold it, and if it's too solid, you may have trouble shaping the part.

Tip: Don't immediately discard the water you remove from the pulp, as it still contains some glue and you can reuse it to make more pulp.

Step 4: Making the Object

Now that the pulp is ready, let's make the object.

Assemble the mold

Put all the mold parts together except the top pressing part. Make sure the wall clip is in place or the pulp will escape from that side.

Fill it with pulp

Fill the mold with enough pulp so it almost reaches the top. Leave approximately 3mm so you can easily insert the top pressing part and align it with the vertical walls.

If you're using the Pencil Holder or Box molds you may prefer to use them upside down. This way you can manually add the pulp to form the walls of the object. This way that part will look cleaner and it'll probably be stronger.

Press it

Push the top pressing part with your hand to remove all the water you can. Depending on how much water you already removed, you will notice how the pulp volume reduces when you press it. You can always add more pulp while you remove water.

Tip: If you want to add more pulp to the mold, do it before you remove all the water or use watery pulp. This way all the pulp will have a similar density and the appearance of the object will be homogeneous.

But, how important it is to press the pulp and mold?

In the picture below you can see two objects made with the same Pencil Holder mold. The one on the left wasn't pressed enough, which meant the object had too much water, deforming the object when dried. The example on the right was filled upside down and the pulp was hand-pressed to make sure the walls of the object were filled with dense pulp.

Press it more

After pressing with your hand you need to start pressing with an adjustable clamp or a vise. You need to remove all the water.

Tighten the clamp until the mold is completely closed. If there's too much material inside the mold, you can leave it that way or remove the excess material.

Drying

Once there's no more water coming out of the mold, the drying process begins. You can start removing mold parts in the following order:

Clamp/vise: 6 hours after molding
Bottom part: 12 hours after molding
Wall: 24 hours after molding
Top pressing part: 48 hours after molding

What if you're impatient?

If your pulp didn't have much water, you may be able to remove the clamps and wall and bottom parts of the mold after 4-6 hours. This is only recommended for basic shapes such as the ones I share, as the mold may still deform.

Note: The object will shrink as it dries, so the final dimensions of the object may slightly change. The shrinkage % varies depending on the pulp density.

Demolding

Even though the demolding process takes place as the object dries, there are some things you must consider.

Open the wall part when removing it

The reason why the wall mold is open is to allow you to open it when removing it to reduce friction between the object and the mold. This is especially useful if you're an impatient maker as wet pulp sticks to the mold.

Add more pulp if there are holes

Sometimes when the pulp has too much water, it won't be evenly distributed inside the mold and you'll find some holes on the mold surface.

If you notice this while the mold isn't fully dried, you can add some pulp in the holes and press it again.

Step 5: Post-processing

Once the object is completely dry, you can post-process it in many different ways.

Compressed cardboard objects have similar properties as MDF wood. This means you can easily sand the object, cut any excess material or drill it.

After post-processing them, your products may end up looking like this. If they don't, don't worry. They were made with recycled cardboard and no one expects them to look perfect.

Step 6: Parametric Design

A parametric 3D model made with Autodesk Fusion 360 is available for download. With it, you can easily modify the size of your mold and customize the text and logos.

Besides modifying the mold appearance, you can also create stamps to customize the final object, adding text, logos or drawings. Simply extrude a mirrored version of your design on the stamp, print it and place it inside the mold.