Wood foam is a new wood-based sustainable thermal insulation material that is recently developed by researchers at Germany’s Fraunhofer Institute for Wood Research WKI. The researchers have developed a both efficient and environmental friendly insulation material which aims at replacing petrochemical plastic insulation materials in the future. As more and more attention is paid to environmental effect, and with a better overall performance than conventional thermal insulation materials, wood foam is the most promising thermal insulation material.
Wood foam offers the same performance as petrochemical plastic insulation materials such as Polyurethane and Expanded polystyrene, while petrochemicals are not environmentally friendly and not renewable. Typically used petrochemical thermal insulation materials are Polyurethane (PU) foam, Expanded Polystyrene (EPS) foam. The thermal conductivity of polyurethane foam and EPS foam is about 0.03 W/m*K which can be said to be good performance compared with mineral wool insulation whose thermal conductivity is 0.04 W/m*K. Although this performance is not as good as silica aerogel 0.02 W/m*K (EngineeringToolBox, 2014) and Vacuum Insulation Panel (VIP) 0.008 W/m*K (EnergySavingTrust.org, 2010), but aerogel is very brittle and fragile, VIP is too expensive and difficult to produce.
Wood foam can be made into rigid foam panel and flexible foam mats, which is also the advantage of PU. The advantage of PU foams is its wide range of characteristics which offers flexibility for application. There are mainly three kinds of polyurethane foams divided by their characteristic and application: 1. Flexible foam used in bedding, furniture and automotive seating. 2. Rigid foam used for thermal insulation panels. 3. Spray foam insulation for building insulation. (Mixture of isocyanate and polyol resin forms expanding foam and are sprayed onto roofs, concrete slabs and into wall cavities.) And wood foam can fulfill all these application requirements. “Our wood foam can be used in exactly the same way as conventional plastic spray foams, but is an entirely natural product made from sustainable raw materials,” said Professor Volker Thole (2014) of Frauhofer WKI.
Comparing with EPS which is easily broken off, wood foam has high flexural stiffness.
There are some other wood-based insulation materials already existed, like mats made from wood fibers and wood wool. But they tend to shed fibers and are less stable in shape than plastic insulation materials. “Over time, the currently used insulation mats made of wood fibers tend to sink in the middle due to temperature fluctuations and damp. This to some extend adversely affects its insulating properties,” said Professor Thole. But the wood foam is as good as conventional plastic foams in this aspect.
People may worry about the risk of fire because wood is a typical inflammable material in people’s mind. This can be solved by adding flame retardant. Many types of insulation are retardant because they contain flame retardant and they are also fire accelerant if not treated. Or it can be treated in the way of EPS fireproofing. EPS foam is coated in a fireproofing chemical called Hexabromocyclododecane (HBCD).
The foam is produced by grinding the wood particles very finely to a slimy mass, then gas is added to expanded it into a frothy foam and then hardened. The substance aiding the hardening process is contained in the wood itself. “It’s a bit like baking, when the dough rises and becomes firm in the oven,” Explained Professor Thole (2014). Finally, the base material is made into rigid foam panels and flexible foam mats.
This process is similar with the production method of EPS foam which is normally produced by two mechanisms: 1. Polystyrene beads are expanded to little balls (pre-expanded polystyrene) with blowing agent like pentane. 2. The little balls are glued together with hot steam.
Comparing with VIP which is the very difficult to produce, the advantage of wood foam production is obvious.
Comparing with fiberglass which is the most commonly used thermal insulation material because of its easy production which is by effectively weaving fine strands of glass into an insulation material. But the main disadvantage of fiberglass is danger of handling because of the glass powder and tiny shards of glass which can harm eyes, lungs and even skin if proper safe protections are not equipped.
Wood foam is claimed to be made from sustainable raw materials by Professor Volker Thole of Frauhofer WKI. So the price won’t keep increasing because of less and less reservations as petroleum.
Figure 1 Brent spot prices of petroleum in dollar as a function of time from 1987 – 2013 monthly average. Sources: Energy Information Administration and Bureau of Labor Statistics.
The price for petroleum keeps increasing since the year 2003 till now, and it has been quadrupled from 40$ to 120$. This is caused by the decreasing amount of petroleum, and the price will be higher and higher. The price of petroleum based thermal insulation materials keeps increasing as the price of petroleum keeps increase. It’s urgent to replace EPS, PU with renewable resources based material – wood foam.
Comparing with VIP which is of the most expensive thermal insulations, VIPS use membrane walls to prevent the air from entering the panel. The membrane is supported by a rigid, highly-porous material, such as aerogel and fumed silica against atmosphere pressure and chemicals are needed to collect gas leaked through the membrane. All the components above: membrane wall, aerogel, fumed silica and gas collection chemicals are all expensive subject, besides the vacuum forming is another costing part.
Wood foam is claimed to be an entirely natural product, which means it doesn’t include any synthetic chemicals, even the substance aiding the hardening process is contained in the wood itself. Also the raw material wood is claimed to be sustainable and the wood is biodegradable, which means the whole production chain from raw material to final product is green.
Cellulose may be the most eco-friendly conventional thermal insulation material, because it is made from recycled cardboard, paper, and other similar materials. But skilled individuals are needed to install it and the newspaper dust can cause allergies that some people may have. (2011)
Comparing with petrochemical based materials, wood foam is much more eco-friendly. Firstly, the petrochemical based thermal insulation materials are mostly non-biodegradable, and chemical additives are added into the product and aid the production process. Besides, there are also specific influences of specific kinds. PU foam is said to have health risk such as skin and respiratory harm present in spray polyurethane foams. But fully reacted polyurethane polymer is chemically inert. Extruded polystyrene (XPS) uses hydro-fluorocarbons (HFC) as blowing agent which has very high global warming potential. EPS is non-biodegradable and there will be rough panel edges and dust when cut.
The main application of wood foam is aimed at building insulations, because buildings are major demand for thermal insulation to keep indoor climate stable. Conventional construction insulation material are petrochemical based rigid boards or expandable foams, although they have good insulation performance, but they are not eco-friendly. Nowadays, countries and unions are setting goals to become green and sustainable society, wood foam offers a good choice. Spray foam (PU) insulation is a commonly used building insulation. Mixture of isocyanate and polyol resin forms expanding foam and are sprayed onto roofs, concrete slabs and into wall cavities. But it is said to have health risk like skin and respiratory harm present in spray polyurethane foams when installed incorrectly. But by correct installation, fully reacted polyurethane polymer is chemically inert. One interesting thing is PU foams made using aromatic isocyanates discolor exposed to visible light. It turns from off-white to yellow to reddish brown. But visible light has little effect on foam properties. And these drawbacks of spray foam don’t exist in wood foam insulation. Wood foam can also be produced in sheets as the expandable polystyrene sheet used in building insulation. The only drawback is that it needs additional chemicals to make the foam rise and set, but it is still more sustainable and green than petrochemical foams, as explained by Andrew Liszewski (2014).
Wood foam is also aimed at packaging industry. EPS is often used as packaging because it can prevent damage and its thermal insulation required for food and medical transportation. Although EPS is rigid and tough but it has a low sheer strength which makes it easily break off. Wood foam not only can offer all the advantages of damping, light and thermal insulation, but also can prevent the disadvantage of low shear strength, so wood foam is a promising alternative to replace EPS packaging.
The researchers of Fraunhofer is now trying to find the best choice of tree species to be the raw material. And they are also developing industrial scale production process for the wood foam.
As wood foam has good performance, easy production, low cost, eco-friendliness and flexible applications, it can be forecasted that wood foam is the most promising new thermal insulation material especially in replacing conventional petrochemical based foams.
Andrew Liszewski. (2014, March). Insulating Foam Made From Wood Makes Your Log Cabin Warm and Authentic. Retrieved from http://gizmodo.com/insulating-foam-made-from-wood-makes-your-log-cabin-war-1548168076
EnergySavingTrust.org. (2010). Insulation materials chart: Thermal properties and environmental ratings. Retrieved from http://www.energysavingtrust.org.uk/content/download/2640/62057/version/1/file/CE71+-+Insulation+materials+chart%E2%80%93+thermal+properties+and+environmental+ratings.pdf
EngineeringToolBox. (2014). Thermal conductivity of some common materials and gases. Retrieved from http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html
Thermaxxjackets.com. (2011, June). 5 most common thermal insulation materials. Retieved from http://www.thermaxxjackets.com/5-most-common-thermal-insulation-materials/
Volker Thole. (2014a, March). Effective thermal insulation with wood foam. Retrieved from http://www.fraunhofer.de/en/press/research-news/2014/march/effective-thermal-insulation.html
Volker Thole. (2014b, March). Effective thermal insulation with wood foam. Retrieved from http://www.fraunhofer.de/en/press/research-news/2014/march/effective-thermal-insulation.html