Wood-polymer materials or wood-plastic composites (WPC) are composite materials made from a lignocellulose-containing component and thermoplastically processable polymer.As a material of great use, WCP still has a difficult time as a secondary raw material.In general, WPC consists of 30 to 85 percent wood fibers or wood flour, 15 to 70 percent plastic and 0.2 to four percent additives, the proportions of which vary depending on the area of ​​application.Extruded WPC is most often used for floor boards in outdoor areas, i.e. for verandas, terraces or swimming pools;According to the specialist agency for renewable raw materials, their share was 79 percent in 2012.There are also products for harbor docks, jetties and promenades.Other applications in construction and gardening add up to around seven percent.Shelf systems made of WPC are common in everyday life, but together with technical profiles and other consumer goods, they only make up one percent.The proportion of wood in these so-called decking applications is between 50 and 80 percent.The automotive sector plays an important role with 13 percent.Here, WPC is mainly used in the extrusion and thermoforming of interior parts, but also for compression molding of thermoset.In 2012, around 15,000 tons of wood granulate with a fiber content of around 40 percent were used for injection molded parts.According to a market study by the Nova Institute, the share of decking production was 67 percent in 2012, followed by interior fittings for automobiles at 23 percent, cladding and fences at six percent and technical applications, furniture cladding and consumer goods at four percent.Significant growth rates A total of around 260,000 tons of wood and polymer-containing materials were processed across Europe in 2012, 210,000 tons of which were extruded.Around half of this production took place in Germany, otherwise mainly in France and the Benelux countries.In the future, we can expect significant growth rates for extruded WPC in the construction and furniture industry, but also in the automotive sector.Growth to over 300,000 tons by 2020 is assumed.The specialist agency for renewable raw materials expects the highest increases in the injection molding process of consumer goods, furniture and technical parts: Their production is expected to increase from 15,000 tons in 2012 to over 100,000 tons in 2020.According to experts, around 60,000 tons of wood-polymer composites are currently being put on the market in Germany every year.A relevant return in the waste disposal market is expected in around five to ten years.Wood-polymer materials are mostly marketed as recyclable products.However, WPC has not yet been specifically assigned under waste law.The recycling centers are confronted with increasing amounts of WPC that cannot be allocated.Nevertheless, various recycling processes are open for the treatment of these materials.Undamaged production residues on extruded WPC can be reused in "internal recycling".Used WCP profiles can either be disposed of in the bulky waste and energetically recycled or sent to "end-of-life recycling".There are three alternatives available: downcycling the plastic into park benches, flower pots and the like;the manufacture of chipboard by adding recycled material;and the co-extrusion of WPC, whereby the core made of recycled material is coated with special new polymer material.However, it is also possible to feed the material back into the production process as recycled material.In principle more ecologically sensible In 2014, scientists from the Thünen Institute for Wood Research and the Center for Wood Management at the University of Hamburg investigated to what extent the recycling and disposal of wood-plastic composites is worthwhile.The authors of the report considered the recycling of materials such as decking for new products in principle more ecologically sensible than incineration, as it avoids emissions of greenhouse gases or halogen compounds.But incineration is still the predominant practice, and as long as there is no need for secondary WPC, the separate sorting and processing of this raw material will not take place.As far as the "product design of WPC from an ecological point of view" - so the title of the study - is concerned, attention must be paid to the relationship between old WPC and fresh wood and plastic: It is decisive for whether recycling can be classified as environmentally friendly or not.No systematic withdrawal This was also underlined by one of the authors of the study, Philipp F. Sommerhuber, in his dissertation in 2016.In his opinion, there is partly a market for used plastics and wood, but none for used WPC.Some manufacturers claim to offer take-backs for deckings;However, most recommend disposal of smaller WPC quantities to be disposed of with household waste and, in the case of larger quantities, either treatment as recyclable waste wood or thermal use.Overall, there is no comprehensive, systematic return of WPC, so that the predominant disposal route in Germany is incineration and in other EU countries it is probably landfill, where on average almost 50 percent of post-consumer plastic is thermally disposed of.In Sommerhuber's view, life cycle analyzes show that the recycling of WPC is the preferable alternative to incineration with energy recovery in order to obtain secondary raw materials.At the Wood-Plastic Composites (WPC) and Natural Fiber Composites (NFC) trade fair in December 2015, Peter Kotiadis made it clear that recycling strategies can at least help to increase the recycling rate of plastics.As the head of research at the WPC manufacturer Fiberon reported, his company uses 50,000 tons of recycled plastic and wood by-products for the manufacture of building materials every year: The resulting WPC boards contain 93 percent recycled material, while new material is only used to coat the decking comes.Material costs reduced significantly As a result, the use of recyclates saves material and money.This was the conclusion reached in 2016 by five companies in Austria whose project examined the recyclate flows for wood residues, plastics and WPC boards for quality, quantity, costs and availability.Some results of the one and a half year work of Transfercenter für Kunststofftechnik GmbH, Rehau Polymer Industrie GmbH, Thermoplastkreislauf GmbH, Theurl Leimholzbau GmbH and Erema Engineering und Recycling Maschinen und Anlagen GmbH: When post-consumer recycling of laid boards, the mechanical properties were themselves after four years of weathering with 100 percent recycled material still comparable with those of the basic recipe.And the material costs for WPC boards could be reduced by 37 percent by using half of the return material and the new material.However, the return from deckings was assessed as (too) low.Research into material WPC recycling The research of the Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut (WKI) on “Material WPC recycling of wood-polymer composites using the example of Decking ".The investigations led to the following conclusion: “The pre-aged WPC terrace decking used in the project from industrial production on the basis of PE, PP and PVC could be easily refurbished and re-extruded into profiles according to type, using mixtures of fresh and used WPC . "The materials were largely able to meet the DIN EN 15534-4 requirements for flexural properties, water absorption and swelling, resistance to impact stress and color stability.A closer look was also taken to see whether mixtures of used WPC based on polyolefins and PVC can also be processed.The tests revealed the miscibility of the WPC recyclates and thus the compatibility of the pure plastics, with the polymers in the WPC getting along a little better than the pure plastics.When using suitable additives for stabilization - according to the results of the investigation - it can be assumed that WPC recyclates can also be used in mixtures.With DSD material The use of WPC regranulates in downcycling products, which are usually made of materials from the Dual System Germany, was also classified as technically feasible.The purchase price for material from the Dual System Germany was around 0.26 euros per kilogram in 2016 (as of 2016), which means that a competitive price for the WPC recyclate could have been calculated.The Association of the German Wood-Based Panels Industry interpreted the results of the study to mean “that WPC regranulates can be processed into downcycling products such as site fence feet without any problems.Wood-polymer materials can be used in several material ways before they are finally burned to generate energy. "An independent material In terms of waste legislation, however, the classification of WPC is by no means "problem-free".As the study from 2014 found, discarded composites are not initially collected separately based on their material composition, but with the help of other product categories in which WPC in general and decking in particular do not appear.In addition - as the Federal Environment Agency argues - according to the current waste wood ordinance, WPC with wood proportions over 50 percent fall under the term waste wood, while those with wood proportions below 50 percent do not.However, since the processes for energetic recovery of waste wood are not designed for high plastic proportions and waste wood WPC mixtures are not suitable for use in the wood-based materials industry, the Federal Environment Agency recommends that WPC be explicitly excluded from the term waste wood or from the scope of the regulation when amending the waste wood ordinance .Instead, wood-polymer composites should be viewed as an independent material with specific properties, which can be recycled back into WPC if a separate recycling loop is set up.From a technical point of view, the material-specific sorting of the composites would not present any difficulty: the investigation of the material recycling of decking showed without a doubt that, with the help of near-infrared spectrometry, WPC material can in principle be recognized, classified and automatically sorted between other types of plastic.WPC business: loss-making Regardless of this, the disposal market for WPC will only reach an economically relevant level in a number of years, according to estimates.Until then, what Philipp F. Sommerhuber wrote in 2016 should apply: “In practice, however, wood-plastic composites are - due to the non-existent demand for secondary WPC raw materials - as admixtures in waste wood or bulky waste recycling and therefore end up as Residual waste in incineration plants. "So it comes as no surprise that in February 2018 Rafael Daum, CEO of the plastics specialist Rehau Austria, stated in an interview that with Relazzo terrace profiles "a product has been developed, a mixture of wood and plastics that does not weather".However, the fact that in January 2019 a regional newspaper reported that Rehau was “withdrawing from the loss-making WPC business”, stopped producing and selling profiles and decking made of wood-polymer composite material and had to lay off 64 employees.