Summary description of the project context and the main objectives:

​The development tendency of the replacement of traditional mineral oil-based plastics with innovative bio-based resin systems is nowadays characteristic for many segments of the industry; however, for aeronautical applications (interiors and/or structures) the challenge is much larger than elsewhere. To meet this challenge, in most cases, a flame retarded special thermosetting polymer system has to be prepared using bio-based components. Thermosetting resins have a number of advantages, such as high modulus (stiffness), high heat distortion temperature and excellent solvent resistance, therefore in this project bio-epoxy resin composites with these advantages were planned to develop.

The project aims at providing replacement for petroleum-based plastics, conventionally used for aeronautical applications (internal and external elements as structural materials), through development and synthesis of new and innovative bio-based composites. Because of extreme working conditions in the field of aeronautical applications, the quality and safety requirements are considerably high; therefore researchers face major challenges in fulfilling them.

The new type of epoxy biomaterials to be produced in the frame of this project must meet the high requirements of aviation. In the course of the synthesis different types of carbohydrates are used as starting materials, which are renewable biomaterials and do not compete with the food industry. There is a possibility for producing them economically from sorghum furthermore in the recent decade large oversupply of sugar supports the industrial utilization. Innovative chemical methods are used for manufacturing resin components in order to improve the properties of the resin, including mechanical stability, reduced combustibility, and reduced water uptake. The process of component synthesis is designed considering the principles of green chemistry, energy efficiency, opportunities to scale up, environmental and health protection. Qualification and selection of the right combination of compounds needs to be verified based on complex criteria including the structural, chemical, physical and mechanical properties, flammability, and ageing features. For applying biocomposites as structural materials natural fibre/fabric is planned to be used. These composites need to achieve improved mechanical strength thus their efficiency must be optimized by surface treatment. Resin system selected during the project will be up-scaled using newly developed, Raman spectrometer response governed computer-controlled reactor.

 

Work performed since the beginning of the project and the main results achieved so far:

New epoxy components and flame retardant curing agents were developed and selected. Starting out from glucose (sugar), bifunctional and tetrafunctional epoxy components were synthesized, but due to the difficulties during the synthesis, which would encumber the high-scale production, no larger quantities were produced. Two trifunctional epoxy components, a glucopyranoside and a glucofuranoside-based one were prepared in a more promising way which were chosen for up-scaling due to their higher functionality, and thus high T_g (above 180°C). The former trifunctional product is crystalline, with a melting point of 90 °C; the latter one is a viscous liquid, with easier processability for composite preparation in the next period.

In order to improve the flame retardancy of the bioresins, three types of P-containing amines (an aliphatic and two aromatics) were synthesized, which can act both as reactive flame retardants and crosslinking agents. For their preparation, an environmentally friendly reaction way was established with improved atomic efficiency, starting out from a non-halogenated phosphorylating agent (triethyl phosphate) and producing non-harmful by-product (ethanol).

Four epoxy resin systems were characterized: First, the applicability of the currently mostly used bio-based epoxy resin matrix material, epoxidized soybean oil in DGEBA-based anhydride-cured epoxy resin was studied. After that the effect of epoxidized soybean oil in different aromatic and aliphatic epoxy resins was thoroughly examined, with special emphasis of aliphatic resins which can be potentially synthesized from renewable biomaterials. Characterization of sorbitol-based flame retarded epoxy resin system containing reactive flame retardant synthesized in the frame of T1.4 (Synthesis of flame retardant curing components) was also carried out. Finally, screening of bio-based epoxy resin matrix materials, synthesized in the frame of T1.3 (Synthesis of resin components from bio sources), was performed in order to be able to choose the appropriate bioresin component for up-scaling.

Based on the results, the potential applicability as epoxy resin of the synthesized sugar-based molecules could be determined, and also the glass transition temperature, which is a crucial requirement for materials in aerospace applications. Although GPTE would provide higher T_g (221 °C vs. 189 °C), GFTE was suggested for further up-scaling, because it provides numerous advantages as higher synthesis yield, liquid state, consequently easier processing and composite preparation and lower postcuring temperature. Mechanical properties of the two sugar-based epoxy resin matrices showed no significant difference. Also in order to facilitate the composite preparation the use of liquid curing agents would be preferred e.g. diethyltoluenediamine (DETDA) instead of the solid state diaminodiphenylmethane (DDM) in the next period.

As a first comparison of different natural fabrics, 3 types of hemp, 3 types of jute, 2 types of linen and a hemp/linen, differently woven fabrics were subjected to strip tensile tests. The highest tensile strength values were recorded for the twill woven hemp fabric with the highest areal weight, followed by the hemp/linen plain woven and the linen unidirectional (UD) fabrics.

The flammability of the natural fabrics represents a crucial issue, which can be reduced by surface treatments. The first treatment consisted of filling the capillaries with ammonium phosphate, the second one was a sol-gel with aminosilane and the combination of this two treatments. The flammability of the fabrics, which contained P-atoms in the capillaries decreased significantly. The thermal stability of fabrics subjected to sol-gel treatment was higher than that of the other fabrics. For conclusion, both the thermal stability and the flame retardancy reached the best values when the combined treatment was applied.

 

Description of the expected final results and their potential impacts and use:

By application of non-petrol or fossil-based, natural and renewable sources, new molecules (bioepoxy components and flame retardant curing agents) were synthetized and used in epoxy resins ensuring low VOC emission during in-service life. Patenting of the developed novel technologies and products is considered.

As epoxy component, the newly synthetized glucofuranoside-based structure was selected for further use in the project, as it proved to be effective composite material suitable for industrial applications,because it provides numerous advantages, such as 189 °C T_g, higher synthesis yield, liquid state, consequently easier processing and composite preparation, and lower postcuring temperature. The innovative chemical steps were elaborated considering the principles of green chemistry ensuring the easy up-scaling. By increasing the production rate, the synthesized epoxy component is promising candidate to become a real industrialized composite material.

By application of P-containing flame retardant curing agent and/or surface treated natural fibre, the developed epoxy composites can fulfil the requirements of aircraft interiors FST (Fire, Smoke and Toxicity). No environmental issues are known concerning the used P- and Si-containing flame retardants.

During the preparation of natural fibre reinforced composites 60 mass% fibre content could be achieved by hot pressing, leading to appropriate mechanical properties, consequently the so prepared completely bio-based composites are a possible candidates for the replacement of currently used carbon fibre reinforced synthetic epoxy resin composites in some interior applications areas of the aircraft industry.

 

Participation at conferences:

Oral/poster presentations were/are going to be presented at following conferences:

• 7^th International Conference on Modification, Degradation and Stability, Prague, Czech Republic, September 2012
• International Conference on Bio-based Polymers and Composites, Siófok, Hungary 2012
• Hungarian Academy of Sciences, Meeting of Plastics and Natural Polymers Working Committee, Budapest, Hungary, December 2012
• 4^th International Conference on Smart Materials, Structures and Systems. Montecatini Terme, Italy, June 2012.
• 10^th Conference of George Olah Doctoral School, Budapest, Hungary, February 2013
• XV^th Conference on Heterocycles in Bio-organic Chemistry, Riga, Latvia, May 2013
• 14th European Meeting on Fire Retardant Polymers, FRPM13, Lille, France, July 2013
• BiPoCo 2014 - 2nd International Conference on Bio-Based Polymers and Composites, August 2014, Visegrád, Hungary
• ECCM 15 – 15^th European Conference on Composite Materials, June 2014, Seville, Spain

 

Oral presentations:

1. P. Niedermann, A. Toldy, G. Szebényi, Natural fiber reinforced bio-based epoxy resin composites developed for aeronautical applications, 7^thInternational Conference on Modification, Degradation and Stability, Prague, The Czech Republic, 2012
   
2. B. Szolnoki, K. Madi, A. Toldy, G. Marosi, Development of flame retarded natural-fibre-reinforced epoxy resin composites, 7^th International Conference on Modification, Degradation and Stabilization of Polymers, Prague, Czech Republic, 2012
   
3. Szolnoki B., Rapi Zs., Niedermann P., Toldy A., Bakó P., Marosi Gy.; Égésgátolt epoxigyanta prekurzorok szintézise megújuló nyersanyagforrásból (Synthesis of flame retarded epoxy resin precursors from renewable resources), MTA Műanyag és Természetes Polimerek Munkabizottsági Ülés (Hungarian Academy of Sciences, Meeting of Plastics and Natural Polymers Working Committee), Budapest, 2012. 12. 12.
   
4. B. Szolnoki, B. Bodzay, Zs. Rapi, P. Bakó, A. Toldy, P. Niedermann, Gy. Marosi, Flame Retardant Epoxy Resins From Renewable Sources, 14^thEuropean meeting on Fire Retardancy and Protection of Materials (FRPM13), Lille, France 2013.06.30
   
5. Gy. Marosi, K. Bocz, B. Szolnoki, H. Erdélyi, L. Szabó, E. Zimonyi: Flame retardancy of fully biodegradable composites reinforced with natural fibres, 14^th European meeting on Fire Retardancy and Protection of Materials (FRPM13), Lille, France 2013.06.30
   

 

Poster presentations:

1. B. Szolnoki, B. Bodzay, Zs. Rapi, P. Bakó, A. Toldy, P. Bagi, Gy. Keglevich, Gy. Marosi, Characterization of flame retardant epoxy resins from renewable sources, 10th Conference of George Olah Doctoral School, Budapest, 2013.02.07
   
2. K. Madi, B. Szolnoki, K. Bocz, A. Toldy, Gy. Marosi, K. Bujnowicz, M. Wladyka Przybylak; Flame retardancy of hemp fabric reinforced epoxy resin composites, International Conference on Bio-based Polymers and Composites, Siófok, Hungary, 2012
   
3. E. Bálint, E. Fazekas, M. Kocevar, G. Keglevich           The synthesis of heterocyclic aminophosphonic and aminophosphine derivatives, XVth Conference on Heterocycles in Bio-organic Chemistry, Riga, Latvia 2013.05.26-05.30.
   
4. M. Fejős, J. Karger-Kocsis, Epoxy Based Shape Memory Polymer Composites with Different Textile Reinforcements. In: Abstracts of 4th International Conference on Smart Materials, Structures and Systems. Montecatini Terme, Italy, 2012.06.10-2012.06.14. Faenza: p. 68. Paper A-15:P80.
   
5. B. Szolnoki, K. Molnar, G. Szebényi, A. Toldy, G. Marosi, Flame Retardancy of Epoxy Resin Composites Reinforced with CNT- Loaded Carbon Nanofibre (FRPM13) Lille, France 2013.06.30
   

  

Articles:

1. P. Niedermann, G. Szebényi, A. Toldy, Natural fiber reinforced bio-based epoxy resin composites developed for aeronautical applications Modification, Degradation and Stabilisation of Polymers 2-6 September 2012 Prague
   
2. A. Toldy, B. Szolnoki, Gy. Marosi; Green chemistry approach for synthesizing phosphorus flame retardant crosslinking agents for epoxy resins, Journal of Applied Polymer Science, 2014, 131 (7) http://dx.doi.org/10.1002/app.40105
   
3. Fejős Márta; Szolnoki Beáta: Szorbit poliglicidil éter alapú bioepoxigyanta és abból készült természetes szöveterősítésű biokompozitok mechanikai és dinamikus mechanikai tulajdonságai (Mechanical and dynamic mechanical characterisation of sorbitol polyglycidyl ether based bioepoxy resin and its natural fibre fabric reinforced biocomposites) Műanyag és Gumi (Plastics and Rubbers) 50, 449-453, 2013.
   
4. M. Fejős, J. Karger-Kocsis, S. Grishchuk; Effects of fibre content and textile structure on dynamic-mechanical and shape-memory properties of ELO/flax biocomposites, Journal of Reinforced Plastics and Composites, 32, 1879-1886 (2013).
   
5. J. Karger-Kocsis, S. Grishchuk, L. Sorochynska; Curing, Gelling, Thermomechanical and Thermal Decomposition Behaviors of Anhydride-Cured Epoxy (DGEBA)/Epoxidized Soybean Oil (ESO) Compositions, Polymer Engineering & Science, under publication, 2013
   
6. P. Niedermann, G. Szebényi, A. Toldy, Effect of epoxidized soybean oil on curing, rheological behaviour, mechanical and thermal properties of aromatic and aliphatic epoxy resins, Journal of Polymers and the Environment (accepted)
   
7. P. Niedermann, G. Szebényi, A. Toldy, Juta erősítés alkáli kezelésének hatása epoxigyanta kompozitok mechanikai tulajdonságaira, (Effect of chemical modification of jute on the mechanical properties of epoxy composites) Műanyag és Gumi (Plastics and Rubbers) (submittedaccepted, will be published in March 2014)
   
8. Zs. Rapi, P. Bakó, Gy. Keglevich, B. Szolnoki, P. Niedermann, A. Toldy, Gy. Marosi, Synthesis and characterization of bio-based epoxy resin components derived from D-glucose, Green Chemistry (submitted)
   
9. B. Szolnoki, K. Bocz, P. Sóti, E. Zimonyi, A. Toldy, B. Morlin, K. Bujnowicz, M. Wladyka-Przybylak, Gy. Marosi, Development of natural fibre reinforced flame retarded epoxy resin composites, European Polymer Journal (submitted)
   

 

Abstracts submitted:

1. B. Szolnoki, Zs. Rapi, P. Bakó, B. Bodzay, A. Toldy, Gy. Marosi, Sugar-based high-tech epoxies: Synthesis and flame retardancy, BiPoCo 2014 - 2nd International Conference on Bio-Based Polymers and Composites, August 2014, Visegrád, Hungary
   
2. P. Niedermann, A. Toldy, Mechanical properties of novel glucose based epoxy resin/jute biocomposites, BiPoCo 2014 - 2nd International Conference on Bio-Based Polymers and Composites, August 2014, Visegrád, Hungary
   

 

Workshops:

• Szolnoki B., Rapi Zs., Niedermann P., Toldy A., Bakó P., Marosi Gy.; Égésgátolt epoxigyanta prekurzorok szintézise megújuló nyersanyagforrásból (Synthesis of flame retarded epoxy resin precursors from renewable resources), MTA Műanyag és Természetes Polimerek Munkabizottsági Ülés (Hungarian Academy of Sciences, Meeting of Plastics and Natural Polymers Working Committee), Budapest, 2012. 12. 12.
• B. Szolnoki, B. Bodzay, Zs. Rapi, P. Bakó, A. Toldy, P. Bagi, Gy. Keglevich, Gy. Marosi, Characterization of flame retardant epoxy resins from renewable sources, 10th Conference of George Olah Doctoral School, Budapest, 2013.02.07