A honeycomb of bamboo rings at the heart of COMBOO

Making Innovative Use of Renewable Materials

Steinbeis experts provide help with two ZIM projects looking at bamboo

Given what’s said about the damage caused to the environment by carbon emissions, just like industry, researchers are interested in reducing carbon footprints. Guidelines laid down by the government are also intended to bring about steady reductions in emissions, in all areas of life. Forschungsnetz Berlin, the research network in Berlin and a Steinbeis Innovation Center (SIC), has been participating in two projects looking at the application and processing of renewable materials, as well as related possibilities to cut carbon emissions.

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As an expert in publicly funded research, Forschungsnetz Berlin has been involved in a long series of innovative sustainability projects revolving around future developments. Two such projects – both funded by the AiF (the German association of industrial research alliances) as part of ZIM (the Central Innovation Program for SMEs sponsored by the Federal Ministry of Education and Research) – offer insights into research being carried out by industrial enterprises in Berlin and Brandenburg. The focus of these projects lies in reducing the carbon emissions of furnishings found in mobile homes, as well as bonding and joining technology.

Benefiting from synergies

Many components used in mobile homes and RVs (recreational vehicle), such as exterior walls and a variety of fittings, are made of composite materials, often formed as sandwich-structure composites. These are made from a lightweight core between so-called skins. Whereas the skins absorb tensile and compressive forces, the role of the core is to absorb shear stress and keep the skins separate.

In 2019, AlexDesign-PolyGlas GmbH, a company based in Berlin with extensive expertise in the design and processing of fiberglass composites, was inspired by a large number of customer requests to come up with the idea of offering a range of flexible components for retrofitting and converting motorhomes. To make better use of synergies, it decided to look for business partners, which it found in the form of the company “Fenster und Türen Wittstock GmbH”, the Research Network Berlin Steinbeis Innovation Center and Berliner Hochschule für Technik (BHT), which has links to the Steinbeis Enterprise through a collaboration agreement.

The partners were convinced that the ambitious aims of the project could be met by using renewable materials, not just for outer layers but also for the core materials. Initial discussions and subsequent research played to the synergies offered by the experience and know-how of the different project partners, which revolved around a number of alternative or complementary fiber materials such as rice straw, banana leaves, coconut, sisal and bamboo fibers. As natural materials, none are available yet in a form that can enter immediate processing, and until now there is no evidence of official approvals for components made from such materials. As part of the project, a number of in-house experiments are underway to identify any new materials offering potential, although in some cases processing is proving problematic.

Bamboo – a material of many talents

The project partners see bamboo as an alternative to the inner layers usually found in sandwich-structure composites. Not only does it grows extremely quickly, but it is also indigenous to all continents except Europe and the Antarctic. There are well over 1,000 species of bamboo, and with growth rates of up to 100 centimeters per day, it can grow to heights of up to 30 meters. Its long, slender culms (stems) consist of hollow cylindrical sections divided by so-called nodes, which prevent the bamboo from collapsing on itself. Bamboo is ready to harvest after only five to seven years, compared to 70 years for native conifers. As a material, the structure of bamboo also differs from that of timber. For example, it is much denser around the edges than in the interior. Until now, bamboo for industrial applications has been cut, sanded, and glued together, most often for use in parquet floors or as serving tablets, although it can also be found in use as beams, rotary cut veneer, or even clothing, although production is extremely cost-intensive / or laborious.

The bamboo being looked at by the project partners is undergoing as little processing as possible, initially on a test basis in structural elements used to make mobile home components. It is also being used as core layers of a new kind of door and door panel in living and entrance areas. This was made possible by the development of COMBOO (a portmanteau of “honeyCOMB” and “bambOO”), which was created by cutting bamboo canes into rings and arranging them into a honeycomb pattern, before adding covering layers to form sandwich elements. In addition to its low density, another feature of this component is the beneficial properties of bamboo as a source material: Its hollow cavities offer strong insulation benefits, and if necessary this can even be improved on by adding environmentally friendly insulation.

An innovative construction

The second project, which is being conducted by the Steinbeis experts from Berlin with the support of their partners at BHT, involves the “friction welding of wood and bamboo.” The focus of this project lies in innovative connections and joining techniques for the newly developed materials. There are already a number of resins and adhesives on the market, with a linseed oil content of up to 56%. These are used to process fibers into fiber composites. Innovative ideas are also needed for connecting the components. One could be a kind of friction welding process that offers a novel approach to joining beams or poles and allows different types of indigenous wooden materials to be effectively and efficiently connected to one another, as well as bamboo. From an economic and ecological standpoint, friction-welding wood and bamboo, or combining them in different ways, is a highly interesting process for using these materials together. It offers a variety of advantages over conventional methods, such as using less glue and wood, since residues can also be re-used. In addition, there is no need for welding materials, material losses , and it is also possible to produce bamboo tubes with almost uniform diameters. A particular feature of friction welding wood is that above certain friction levels, some of its constituents soften and even dissolve or evaporate.

Another unique property of wood is that timber elements (lignin, cellulose, and hemicellulose) pass through tightly intertwined wood fiber composites between the pieces of wood being joined, transforming them into a matrix of molten intercellular wood material. These same elements are found in bamboo, meaning it can also be joined using friction welding. This was also confirmed through experiments conducted for the ZIM-funded project, which involved using a friction welding device developed by tool manufacturer Christian Dunkel GmbH, Berlin, on wood and bamboo. The parameters required for the process, such as friction speed, connection times, joining pressure, connection force, and holding times, were investigated by the project partners by looking at different materials and numerous combinations of materials (wood with wood, wood with bamboo, bamboo with bamboo).


Prof. Dr. Andreas Loth (author)
Professor for Design and Implementation of Mechatronic Systems
Berliner Hochschule für Technik (Berlin)

Dr. Ansgar Keller
Steinbeis Entrepreneur
Steinbeis Innovation Center Forschungsnetz Berlin (SIC) (Berlin)

Christian Schrembs
Steinbeis Innovation Center Forschungsnetz Berlin (SIC) (Berlin)

Prof. Dr.-Ing. Ralf Förster
Production Engineering Laboratory Manager
Berliner Hochschule für Technik (Berlin)

Heiko Kirchner
Managing Director
AlexDesign-PolyGlas GmbH (Berlin)

Matthias Krause
Managing Director
Fenster und Türen Wittstock GmbH (Wittstock-Dosse)

Christian Dunkel
Werkzeugbau Christian Dunkel GmbH (Berlin)