Furan resin
Furan resins ( FA resins for short ) are a group of curable, linear resins that are derived from the furan derivatives furfuryl alcohol and furfural . They are ecologically significant as their starting materials are obtained from waste food production. This means that they are completely biogenic and play a special role among thermosets .
The name is derived from furan , since furan rings, among other things, repeatedly appear in the molecular structure of the resins.
Types
The term furan resins is not used consistently in the literature. For example, resins based on furfuryl alcohol and furan are sometimes understood as furan resins and sometimes only those based on furfuryl alcohol. In addition to the homopolymers of the two starting materials, copolymers, for example with formaldehyde , urea or phenol components, are also counted among the furan resins.
Manufacturing and structure
Furan resins based on furfuryl alcohol are produced by polycondensation under the action of weak acids . This creates oligomers of different lengths and linked. The furan rings in it are mainly linked via methylene groups (–CH 2 -), but there are also links via dimethylene ether groups (–CH 2 –O – CH 2 -). However, especially under strongly acidic conditions, formaldehyde is split off from these and methylene groups are formed again.
In order to produce a storable resin, the reaction is stopped by adding caustic soda . The products are brownish in color and have a low to medium viscosity . At 40 ° C they are stable for about 6 months. In a second step, they can either be hardened at room temperature by adding acids (e.g. p -toluenesulfonic acid, phosphoric acid) or at higher temperatures by adding latent hardeners such as ammonium nitrate . The reactions that take place are complex and have been researched for a long time. In 1996 it was found that sections with conjugated double bonds form in the polymers and that these are responsible for the crosslinking .
The cross-connections are formed by reactions of the double bonds outside the furan units with terminal methylol groups or disubstituted furan rings .
properties
Before curing, the properties of furan resins are similar to those of other curable resins. They are capable of binding (ie they can be used as binders ), are reactive towards acids, thermally reactive and crosslinkable. When cured, furan resins are chemically resistant to most chemicals such as strong acids and bases , as well as halogenated hydrocarbons . They are only attacked by oxidizing agents . They are thermally stable, the resistance depending on the duration of the heat exposure. Long-term use is possible at 100–120 ° C without any problems, but the material can also be used up to 150 ° C in individual cases. Some types are characterized by their flame resistance and low smoke development . They also have high strength.
application
Furan resins are mainly used as binders for sand casting molds . There are also numerous other possible uses. They can be used for corrosion-resistant fiber-reinforced plastics or corrosion-resistant inorganic binders (e.g. for refractory bricks). Furan resins can also be used as a thermosetting hard matrix in composite materials . Application examples are natural fiber-reinforced semi-finished products such as interior door panels in cars and MDF panels . The advantages over comparable petrochemical materials are the lower density and extremely low VOC emissions , but the mechanical properties are significantly worse than those of comparable products.
Ecological aspects
The use of furan resins has several advantages over other synthetic resins. Since the starting substances can be produced entirely from renewable raw materials , no scarce fossil raw materials are required. It is also advantageous that residues from agriculture are used, which do not have to be specially grown. No additional space is required and there is no food competition. However, there is a loss of nutrients , which must be compensated for by fertilization . Whether the material use of the raw materials in the form of furan resins is ecologically superior to energy recovery has yet to be assessed.
Individual evidence
- ↑ a b c d e f g Arne Gardziella: Furan resins (FF). In: Wübrand Woebcken (ed.): Kunststoffhandbuch (= Duroplaste. Volume 10). 2nd completely revised edition, Hanser Verlag, Munich, 1988, ISBN 978-3-446-14418-7 , pp. 70–84.
- ↑ a b c Oliver Türk: Material use of renewable raw materials. Springer Vieweg, Wiesbaden, 2014, ISBN 978-3-8348-1763-1 , pp. 443-454.
- ↑ a b c Michael Biron: Thermosets and composites: material selection, applications, manufacturing, and cost analysis. Elsevier, Amsterdam, 2014, ISBN 1-4557-3125-0 , pp. 257-259.
- ↑ JB Barr & SB Wallon: The Chemistry of Furfuryl Alcohol Resins . In: Journal of Applied Polymer Science . tape 15 , 1971, p. 1079-1090 , doi : 10.1002 / app.1971.070150504 .
- ^ RH Kottke: Furan Derivates. In: Encyclopedia of chemical technology. Raymond Eller Kirk & Donald Frederick Othmer, December 4, 2000, accessed August 16, 2019 .
- ↑ a b Alessandro Gandini & Mohamend Naceur Belgacem: Furans . In: Hanna Dodiuk & Sidney H. Goodman (Eds.): Handbook of Thermoset Plastics . Elsevier, Amsterdam 2014, ISBN 978-1-4557-3107-7 , pp. 93-110 .
- ^ A b Alessandro Gandini & Mohamend Naceur Belgacem: Furans in Polymer Chemistry . In: Progress in Polymer Science . tape 22 , no. 6 , 1997, pp. 1203-1379 , doi : 10.1016 / S0079-6700 (97) 00004-X .
- ↑ a b Mekki Choura, Naceur M. Belgacem & Alessandro Gandini: Acid-Catalyzed Polycondensation of Furfuryl Alcohol: Mechanisms of Chromophore Formation and Cross-Linking. In: Macromolecules. 29 (11), 1996, pp. 3839-3850, doi: 10.1021 / ma951522f .
- ↑ a b Michael Biron: Thermosets and composites: material selection, applications, manufacturing, and cost analysis. Elsevier, Amsterdam, 2014, ISBN 1-4557-3125-0 , p. 86.