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Ecological and technical principles of ARBOFORM®

A new thermoplastic material made exclusively from renewable resources is based on lignin, a natural polymer which is formed by photosynthesis and makes up about 30 % of the substance of every tree and every wood plant. Lignin is second to cellulose as the most abundant natural polymer and, in the tree trunk for instance, forms a three-dimensional supporting structure around the cellulose fibres. Lignin gives natural, as-grown wood the necessary compressive strength, which cellulose cannot provide. The cellulose fibre can only provide tensile strength, which means a compound of natural fibres (cellulose) and lignin makes a material that, just like natural wood, can withstand tensile and compressive loads in combination. By varying the composition of ARBOFORM® both in terms of quality and quantity it is possible to adjust strength, rigidity, dimensional stability with varying temperatures, and other material properties so as to suit specific product requirements.

So this thermoplastic material is 100% from renewable resources and is marketed by TECNARO GmbH under the name of ARBOFORM® (lat.: arbor - the tree).

Lignin of the Spruce
© Peter v. Sengbusch - b-online@botanik.uni-hamburg.de

Lignin is a byproduct of the papermaking industry and about 50 million tonnes are produced in various pulping processes worldwide every year. So far the uses for lignin have been limited, about 95 % being incinerated for thermal energy generation. It is just a small percentage of the lignin that has found material applications, e.g. in the foodstuffs industry.

By mixing specific types of lignin with natural fibres from wood, flax, hemp, sisal or other fibrous plants and natural additives a composition is produced which can be processed at raised temperatures. This material is made into mouldings, sections or panels on conventional plastics processing machines in just the same way as a petrochemical thermoplastic material.

The constantly growing annual output of more than 100 million tonnes of global petrochemical plastics production from crude oil delivers carbonaceous compounds to the surface which, after their useful life as plastics materials, will be disposed in waste incinerators, from where they are emitted, in the form of carbon dioxide (CO2), into the atmosphere. The resulting accumulation of CO2 in the earth's atmosphere is thought to be among the causes of the global greenhouse effect. Even though it is true that the biosphere will fix any increased CO2 content of the air by accelerated plant growth, recent research has found worldwide CO2 emissions to have reached a level that is about seven times higher than the amount the biosphere can fix in the form of organic carbon compounds in any given period of time.

In this context, thermoplastic compounds based on renewable resources offer a more environmentally compatible alternative to synthetic petrochemical plastics. Being made one hundred percent from renewable resources, an ARBOFORM® product, at the end of its useful life, can be disposed in professional refuse incineration plants, like wood, without hesitation. This means that the incineration of the product will emit into the atmosphere just the same amount of CO2 that the plant previously took from the atmosphere while it was growing. So this is a closed CO2 cycle without any accumulation of CO2 in the atmosphere and, hence, no more adding to the greenhouse effect. Moreover, it goes without saying that, given the appropriate surroundings, certain ARBOFORM® formulations are compostable or biodegradable, should local circumstances make incineration appear uneconomic.

In addition to its positive environmental properties from being based on renewable resources ARBOFORM® also has a number of technological advantages over synthetic plastics compounds as a strong engineering material, either on its own or in a composite with natural, as-grown wood. The development of substrate mouldings for fine veneers is a particularly impressive point in case.

Consisting of what constitutes natural wood (lignin and cellulose), ARBOFORM® also has similar mechanical and thermal properties as has natural, grown wood. A material to be used in applications, such as substrates for fine veneers in automobiles, needs to withstand high thermal stress in terms of both temperature variation and negative or positive maximum temperatures. Because of the large differences, by a factor of about 10, that exist between the coefficients of thermal expansion of wood and of plastics it is only with difficulty that fine veneers can be placed on plastic substrates where high thermal standards have to be met. The expansion coefficient of the plastic material being higher than that of the wood veneer, the latter will either split at right angles to the main axis of strain, or there will be localised delamination of the veneer from the substrate moulding at increased temperatures. This is where the technological advantages of the wood-like character of ARBOFORM® come into play. Thanks to the fact that the expansion coefficients of the ARBOFORM® substrate and the covering wood veneer layer are nearly the same, thermal stress is no longer a problem and does not lead to product failure.

ARBOFORM® is a high-quality thermoplastic engineering material for applications that demand high technological standards. It combines the positive properties of natural wood with the processing capabilities of thermoplastic materials. In short:

ARBOFORM® is "liquid wood"