The environmental sustainability matter is getting a milestone to develop a new economy, where the CO2 reduction due to the human footprint will be mandatory. It will take a short time to result in practical actions the latest goals promised by the COP, and bamboo is considered a natural resource for the sustainable industrial future.
Bamboo is a unique natural product, further than a reliable partner to sustainable economic development. Its physical and mechanical properties represent an appropriate mix between lightness and strength, which give it a fundamental role as a structural material for industrial purposes.
Features
There are more than 1600 bamboo species, some of which have never been studied. Most people believe that bamboo is a tree, but it’s grass and belongs to the Gramineae family.
It’s highly efficient to fix the CO2, 30% more than the other trees, and it contributes to lowering the greenhouse effect and global warming, absorbing something like 50 CO2 tons/hectare every year.
Bamboo cultivation is eco-friendly, and it doesn’t need chemicals, or pesticides. It creates healthy fields, and the rhizome’s density keeps a compact soil, preventing erosion. It is one of the less used and more abundant natural resources available on the planet, growing up in the tropical, subtropical, and temperate areas of all the world continents. There are bamboo native species in Asia and Oceania, further than America and Africa. The Antarctic and Europe haven’t native bamboo species, but Europe has a friendly climate for its cultivation. Both grassy and wooden bamboo species exist, but only the wooden ones can be used for structural purposes. Studying bamboo microstructure is essential to understand how and why this extraordinary natural resource can be employed as an industrial material.
Structure
Bamboo is a natural composite material. Looking at the culm cross-section, you can find the denser fibres close to the external layer, which acts as reinforcement, surrounded by a matrix mainly composed of vessels and parenchyma tissue. Other smaller elementary fibres make threads join each other by the cell wall. Each elemental fibre has a poly lamellae structure, characterized by a primary barrier, transition lamellae that aren’t always present in all the bamboo species, and a secondary wall composed by thick lamellae where the cellulose fibrils are quite entirely aligned with the axis fibre, and thin lamellae, where the cellulose fibrils are quite wholly orthogonal to the axis fibre.
Sustainability isn’t only a matter of raw material, but it also involves its conversion process. An advantage of the conversion of the renewable resource is the lower process temperature compared to the not renewable one. Bamboo, thanks to the high silica content in the external layer, which acts as delayed combustion, and the internal diaphragms, which act as a fire barrier, is a fire-resistance material, much more than other wooden material.
Utilizations
There are several ways to use bamboo as a construction material. One possibility is about the fibre extraction through mechanical treatment, chemical treatment, or their mix with a specific process temperature. The fibre extraction is tricky, with the risk of damaging it, making it unusable.
Researchers have achieved remarkable results, extracting fibres with good mechanical properties, with Young modulus from 20 to 50GPa, traction strength from 600 to 1000MPa, and strain to failure from 1,7 to 6%.
The main issue is understanding how to transfer the fibre mechanical properties to the composite material. Several experiments and papers are available in the literature, but regardless of the matrix, thermoplastic, or thermoset, an effective solution has not been fully achieved yet, neither with a fibre, post-treatment to improve the interface with the matrix.
Bamboo fibres used as reinforcement material in composites are more accessible than other natural fibres. The lower bamboo fibre’s relative moisture content gives higher composite stability and higher adhesion fibre-matrix. Another significant advantage is the microfibrils angle that directly affects the stress-strain curve. Bamboo microfibrils angle belongs to 10 – 12°, and it is responsible for a linear stress-strain curve up to failure.
Thermoplastic composites are favoured because of the end-of-life recycling, but their main issue is the process temperature, limiting the possible matrix to PP or MAPP. A temperature higher than 200°C should be needed to improve the fibre-matrix adhesion, but there would be fibre degradation by increasing the temperature. That’s the reason why researchers are looking for a new matrix, trying to realize (produce) eco composite materials with a biodegradable matrix.
Another possible bamboo field of application is semi-finished products as a scriber, recycling most of the wooden technology and the thermal treatment for outdoor use.
The final product is still a composite material based on bamboo fibres and phenolic resin, with a percentage fibre volume higher than thermoplastic or epoxy thermoset composites, improving mechanical properties and sizing stability. The hot pressing is a fundamental part of their production process because a proper setup of its parameters allows manufacturing high-density composite, building a suitable solid for structural purposes.
Bamboo, thanks to its physical and mechanical properties and the positive benefit of its cultivation on the environment, is the best candidate to lead society on the way to sustainable development. Bamboo has been creating excitement in the world of research, which has been studying it to understand better its microstructure and its extraordinary properties, which have given it the name of “green gold” and “natural steel.”
The way for the green economy is still long but well defined, and we know that bamboo is a natural resource for the sustainable industrial future. So we trust that the Japanese fable about bamboo will get real soon, promising a prosperous future for everybody.
Article by Stefano Dominoni for Prosperity Bamboo