There are about 6.3 billion metric tons of plastic waste in the world. It exists in the water, air and soil where the fish and vegetables we eat grow. In fact, only 2 1% of plastic products are recycled or burned. Therefore, it is very important to find new ways to reuse it. With the increasing demand for new buildings around the world, it is a good idea to use it to make building materials.

In buildings, the main function of walls is to support the roof and floor and provide protection from the weather. In order to build a wall, we must stack several materials-just like making sandwiches or hamburgers.

The outer wall of a building is usually made of brick (moisture-proof), and the inner wall is made of concrete mortar and gypsum board, decorated with paint or wallpaper. In modern buildings, there is usually a gap between them (so that moisture can escape or prevent it from coming in), which is a sponge-like heat insulation material used for heat preservation. Especially in cold countries, walls need to store as much heat as possible to improve energy efficiency.

Nest brick

20 19, a researcher developed a 3D printing brick made of household plastic waste. The idea of this brick comes from an unexpected place-the nest of Baya weaver bird in Southeast Asia.

The residents of this beautiful yellow grassland are famous for their carefully woven houses. Male birds weave soft grass stems and palm leaves into hats with claws and beaks. The upper part is relatively large and will lay eggs, and the lower part is a slender entrance similar to a tunnel. The woven structure of the nest can protect the eggs from wind, rain and sun exposure during hatching.

The researchers tried to make bricks in a similar way. Instead of plant fibers, they weave with plastic yarns. First, they tore up plastic sheets with discarded plastic water bottles to make yarns. Then we put the yarn into a 3D printer. The printer melts the yarn, and then uses a conical nozzle to deposit the melted plastic exactly where they want it. Think of it as icing on the cake with your best decorating skills. They programmed the printer so that the melted plastics crossed to form a grid or mesh pattern. Then we wrap the grid with a solid outer layer to trap the air in the cavity to better insulate the heat.

This kind of brick is very strong. The research shows that the strength of the wall of a five-story building is equivalent to that of ordinary cement mortar bricks. The performance of the partition wall of clay brick with the same size is ten times that of traditional clay brick.

Life-size Lego toys

Bricks inspired by weaving birds are considered to be the first choice of building materials. But this is not the only kind of brick made of household plastic waste.

Another model is to chop up the plastic and then grind it into powder. Fine-grained plastic can be easily poured into brick molds (just like you fill an ice box with water). Then transfer the mold to a melting furnace to melt the plastic powder, and finally press it into solid plastic bricks. This reminds us of Lego that children play with.

The advantage of making plastic bricks in this way is that we can combine different types of plastics-from water bottles and milk cartons to food packaging and bottle caps-because they all melt between 200 and 250 degrees Celsius.

In addition, they can be easily assembled and linked, and a wall is like a life-size Lego project. Once the wall is built, you can cover it with clay or cement on both sides, inside and outside, which will make the surface smoother.

Bottle house wall

The cheapest and most ingenious way is to combine traditional building materials with agricultural waste by using plastic waste.

Researchers from De Montfort University collaborated with local entrepreneurs in Nigeria to develop a prototype of a bottle house. The waste water bottle is filled with sand or water to form a bottle brick that is strong enough, and then it is glued together with clay.

One disadvantage of this method is that it can't keep warm. Instead, it reduces the building temperature by absorbing sunlight to prevent the indoor temperature from rising. Although this is exactly what tropical countries need, the weather in Britain needs more warmth.

In addition to adjusting the materials according to the specific location and weather of the building, we also need to use plastics carefully, because some plastics will release toxic substances under ultraviolet light and high temperature. In other words, there is still much research and work to be done in this field.