Single-component composites made from pure cellulose
- 233 Downloads
Single-component composites made from pure cellulose are sustainable, recyclable, and biodegradable. This enables them to overcome the recycling issues associated with conventional fiber-reinforced composites. The DITF Denkendorf have been looking into the material properties, thepotential and the challenges of this class of alternative materials.
Most fiber-reinforced plastics based on glass, carbon or natural fibers are produced using petroleum-based polymer matrices. With a production volume of 2.3 million tons p.a. in Europe, glass-fiber reinforced plastics (GFRP) used in construction and structural parts account for the largest share . These materials, however, preclude the possibility of proper recycling. Since there is currently no technically viable method of fully recycling GFRP end-of-life waste (currently around 300,000 tons p.a. ), GFRP waste is disposed of through pyrolysis of the polymer matrix, with the residual ash having to go to landfill. In contrast, an alternative process provides for the disposal of GFRP waste as an aggregate material for cement clinker following appropriate preparation and admixture . The demand for recyclable and sustainable composite materials has grown significantly in recent years owing to increased environmental awareness and legal regulations. Cellulose fibers are used extensively in biocomposites and natural-fiber reinforced polymers (NFRP) thanks to their good mechanical properties and widespread availability, information box on page 16. One example is NFRPs with a polyactide matrix that nevertheless only have low thermal resistance. Owing to different polarities in these systems, adhesion at the interface between a hydrophobic polymer matrix and hydrophilic (natural) fibers is frequently very poor. The low mechanical strength, rigidity, and impact resistance of composite materials are the consequence, while the potential of cellulose as a reinforcing component is not fully exploited. High material thicknesses or bonding agents such as maleic anhydride in polypropylene (PP) have to be used in order to achieve the appropriate mechanical characteristics in the composite. However, these composite materials also lack a satisfactory recycling concept.
Single-component polymer composite materials overcome the problems of weak fiber-matrix bonding.
The mechanical properties of the recycled composites were identical to those of the original composite.
On the one hand, single-component polymer composites overcome the issues of weak fiber matrix bonding, allowing the forces acting on the component to be effectively transferred from the matrix to the fibers. On the other hand, as homogeneous composite materials, they offer the prospect of particularly straightforward recycling, as the fibers and matrix do not need to be separated from each other in order to obtain fully discrete materials.
Composite Materials Made from Pure Cellulose
Disposal of End-of-Life Waste
The surface needs to be coated in order to protect the structures from water absorption.
A further possibility of disposal which is not expanded on here, is the softening of the composite in hot steam and then subsequent hot-press molding.
Subsequent Processing of the Composites
Potential Applications and Outlook
Focus is currently directed towards transportation and the automotive industry as one of the largest fields of application for NFRPs and GFRPs. All-cellulose composites constitute an interesting material, in particular for automotive interior trims like door panels, dashboards, or rear window shelves. The major advantages of the new cellulose-based composite material over current state-of-the-art alternatives are deemed to be the thin-walled components that can be realized thanks to good fiber-matrix adhesion with the same or improved spectrum of properties, the disposal strategy for end-of-life waste, and behavior with regard to emissions and fogging that are expected to be judged positively. Furthermore, it may be possible to use the material in other industries in applications with great added value where the sustainability of materials is a special argument in marketing — for example for sports, leisure and lifestyle products such as surfboards, goods for camping and outdoor, hard shell cases, furniture production, or plant containers. Another large-volume example are special products in the construction industry such as cladding panels or in timber construction. Since the technology is so complex, a period of between three and four years must be assumed before it can be implemented on an industrial scale. Technical implementation can be achieved earlier in particular for applications with small production batches where the sustainability of the materials constitutes a key feature. The latest investigations are primarily concentrated on upscaling the manufacture of composite materials. Special attention is being given to improving the washing step to transform it from a static into a dynamic, continuous process.
Cellulose Fibers as Reinforcing Component in Bio-composites
Cellulose fibers are used in natural-fiber reinforced polymers (NFRP) primarily in the form of bast fibers, flax, hemp, kenaf, or recycled cotton. So far, regenerated cellulose fibers, for example from the viscose process, have found little use as a reinforcing component. The matrices are petroleum-based thermosetting plastics or thermoplastics (epoxides, unsaturated polyesters, polyurethanes (PU), acrylates, and polyolefins) . Furthermore, recent years also saw the development of biocomposites with biological matrices such as polylactides, biopolyethylene, biopolyesters and (partly) bio-based epoxides, or PUs as well as resins based on palm or linseed oil. NFRP applications include interior trims in automobile trunks or doors [8, 9].
Producing Single-component Composites from Pure Cellulose
Pure cellulose is infusible and hardly soluble. There are, however, various dissolution methods, of which the relatively new process based on ionic liquids (IL) constitutes an especially environmentally compatible approach that makes sparing use of resources. The ionic liquids used are nontoxic salts that are liquid at room temperature. Unlike conventional processes, they enable cellulose to be dissolved directly with efficient use of materials. What is more, they can be recovered using existing technologies and reused in the process.
The authors would like to thank the Baden-Württemberg Ministry for Economy, Labor and Housing for funding research initiative 7-4332.62-DITF/73, as well as Cordenka and BASF for providing the high-strength viscose fibers and the IL.
- 1]Witten, E.: Der GFK-Markt Europa — Composites-Marktbericht, 2015Google Scholar
- 2]Yazdanbakhsh, A.; Bank, L.: A Critical Review of Research on Reuse of Mechanically Recycled FRP Production and End-of-Life Waste for Construction. In: Polymers (2014), No. 6, 1810Google Scholar
- 4]Spörl, J. M.; Batti, F.; Vocht, M.-P.; Raab, R.; Müller, A.; Hermanutz, F.; Buchmeiser, M. R.: Ionic Liquid Approach Toward Manufacture and Full Recycling of All-Cellulose Composites. In: Macromolecular Materials and Engineering (2018), 1700335Google Scholar
- 5]Hermanutz, F.: Textilverstärkter Formkörper, ein Verfahren zu dessen Herstellung sowie seine Verwendung. DE 102011122560, 2013Google Scholar
- 7]Carus, M. Eder, A.; Scholz, L.: Bioverbundwerkstoffe—Naturfaserversträrkte Kunststoffe (NFK) undHolz-Polymer-Werkstoffe (WPC). F. N. R. e. V. (FNR), Gülzow, 2015, pp. 1–56Google Scholar
- 8]Schweindl, F.; Brand, C.: Himmlisch leicht. Gewichtseinsparungen am Fahrzeugdachhimmel durch naturfaserverstärkte Duroplaste. In: Kunststoffe (2016), No. 7, pp. 76–79Google Scholar
- 9]Carus, M.; Gahle, C.; Pendarovski, C.; Vogt, D.; Ortmann, S.; Grotenhermen, Breuer, F.; Schmidt, T.: Studie zur Markt- und Konkurrenzsituation bei Naturfasern und Naturfaser-Werkstoffen (Deutschland und EU) in Gülzower Fachgespräche. 26, F. N. R. e. V. (FNR), Gülzow, 2008, pp. 1–393Google Scholar