Novel co-blended polymer matrix systems for fire resistant structural marine composites

Lead Research Organisation: University of Bolton
Department Name: Centre for Materials Res and Innovation


Fibre-reinforced composites are finding increased usage in load-bearing structures in a variety of applications in marine, automotive and rail transport industries owing to their specific strength and stiffness properties. A serious problem with these composite materials, particularly glass-reinforced polymeric composites, which are the most prevalent in marine and other surface transport applications, is that they support combustion and in fire conditions burn, most often with heavy soot and smoke. Insulation can reduce the fire hazard, but does not eliminate it. Moreover the insulation adds weight and cost to apply.The combustible part of the composite is organic resin matrix. Most common method of fire retarding the resin and hence, the overall composite is the physical and chemical modification of the resin by either adding fire retardant element in the polymer backbone or using fire retardant additives in the resin. For polyester or vinyl ester resins, usually halogenated chemicals are used. While the presence of halogen significantly reduces the flammability of the resin, due to increasing environmental awareness and strict environmental legislations thereof, halogen - containing fire retardants are being strictly scrutinised. When non-halogen flame retardants are used, invariably they are required in large quantities (>30% w/w) to achieve required level of fire retardancy. The high concentrations of additives however, can reduce the mechanical properties of the composite. Moreover, they also affect resin's processability for resin transfer moulding technique, commonly used for these types of composites. We propose here a step change in the resin matrix by reducing the combustibility of vinyl ester and/or polyester resin by co-blending with inherently fire retardant resins, such as phenolic or melamine-formaldehyde resin.This proposal is a joint attempt by 'Fire Materials' group at the University of Bolton and 'Fluid Structure Interactions Research Group (FSIRG) at the University of Southampton to develop, construct, test and model novel, fire-retardant composites, initially for marine applications. The principal focus is to develop a modified polymeric matrix to reduce the combustibility of the vinyl ester or polyester resins by blending with appropriately modified phenolic and melamine resins, which will increase the thermal stability and char-forming capacity of the matrix. The physical and chemical properties of the modified resin will be optimised to enable: (a) the resin to be infusible for moulding leading to good processing ability: (b) low temperature cure capability to maximize compatibility and bonding with glass fibres; and (c) up-scaling to produce large laminates and structures. It is proposed that two different approaches will be taken: the first one 'Material' based, mainly by Bolton, and the other 'Structure' based, to which both Bolton and Southampton will contribute. The specific tasks include resin blending, chemical / physical modification of the resin, process modelling and resin infusion, composite laminate preparation and flammability evaluation. The composite laminates and structures thus produced are expected to comply with the fire performance requirements contained in the International Convention for the Safety of Life at Sea (SOLAS) as `IMO/HSC Code (Code of Safety for High Speed craft of the International Maritime Organisation). Additionally, the structural performance of the composite would be expected to be comparable with current glass/vinyl ester. We also propose to conduct fire performance modelling, mechanical characterisation and progressive damage analysis from a structural design viewpoint.We expect these composites to find applications also in other engineering arenas for which low-weight, thermally resistant and fire-retardant structures are increasingly being sought.

Planned Impact

Who will benefit from this research? The beneficiaries from this work will be the marine industry as a whole from suppliers through manufacturers to end users, including: 1) Boatbuilders of high volume, high value boats (e.g. Sunseeker and Sealine) 2) Shipbuilders of high value, naval ships (e.g. BVT) 3) Boat owners, such as the Royal National Lifeboat Institution (RNLI) 4) Regulatory agencies in marine and composite structure design (e.g. Lloyd's Register) 5) Government and statutory agencies (e.g. Marine and Coastguard Agency, MCA and the Ministry of Defence, MoD) 6) International Maritime Organisation, an organisation of the UN, that ultimately makes recommendations for safe design of ships How will they benefit from this research? 1) Materials suppliers will be able to discern the improved resin chemistry to improve their product range, particularly in applications where fire is an important hazard. 2) Boat and ship designers and builders will be able to generate more efficient and a wider range of designs for the market place offering enhanced safety features from the use of better, fire resistant and lightweight materials. The materials suppliers too would find a better route to world-wide markets for their product ranges thus enabling increased exports. 3) RNLI has the highest specification rescue craft in the world. Their safety design case will be further enhanced through the use of fire retardant materials, supported by structural design approaches. 4) LR will be able to be the first to develop guidelines for ship and boat design based on this work, thereby giving them an edge as compared with their main competitor such as Det Norske Veritas or American Bureau of Shipping 5) The MCA could be seen as driving the safety agenda for the benefit of the UK public at large a significant proportion of whom are into marine sports and yachting where too the product ranges offered could benefit from improved and safer resins. The MCA involvement will also underpin UK inputs into IMO and ISO debates and working groups that ultimately lead to international regulations, standards and statutes. 6) The work is highly relevant to future MoD procurements for next generation surface combatants. What will be done to ensure that they have the opportunity to benefit from this research? Enabling mechanisms and methods of communication to ensure that the industrial and government beneficiaries have the opportunity to benefit from this research are four-fold. 1) The key industrialists and government agencies are collaborators with whom the proposal has been shared before submission. 2) The industrial/government consortium will be part of the Project Management Group (PMG) that will monitor progress and identify strategic directions of work. PMG will include Scott Bader, UK BVT Surface Fleet, British Marine Federation (BMF) Royal National Lifeboat Institution (RNLI), Lloyd's Register, MoD, Maritime Coastguard Agency 3) Dissemination of the findings from the research in the two universities quickly and directly into the concerned organisations, in particular the scientists and engineers most closely associated with the disciplines underpinning this work. The fire group at Bolton have good working relationship with relevant industry, i.e., resin manufacturers, flame retardant manufacturers, commercial fire testing laboratories and composite manufacturers/users, with whom they have been engaged in different research projects over last 10 years or so. The FSIRG group at Southampton also had a track record of collaboration with main players in marine industry. 4) Use specific industrial contexts for defining case study material and test sample design when considering empirical and/or numerical modelling cases for the laboratory studies. That is, laboratory and university based work funded through this grant will be aligned closely with 'real life' scenarios as far as possible.


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Description In this collaborative research project between the 'Fire Materials Group' at the University of Bolton and the 'Fluid Structure Interactions Research Group (FSIRG)' at the University of Southampton, a step change in technology to reduce the combustibility of unsaturated polyester (UP) resins by co-blending them with inherently fire retardant and char forming resins has been achieved. Bolton's focus was material based, i.e., identification and/or chemical modification of char-forming resins to render them chemically and physically compatible with unsaturated polyester (and vinyl ester) resins; establishment of curing conditions for these blended resins; casting of them into plaques in order to study their physical, mechanical and fire performances; and preparation of glass-reinforced composite laminates by adjusting curing conditions followed by study of their fire and mechanical performances.

The significant discoveries and developments are listed below:
1. Resole phenolics: Three phenolic resole resins with varying degrees of compatibility with UP resins were sourced from an industrial partner. It was observed that while mechanical properties of the composite laminates from co-blended resins increases with increase in compatibility, the flammability also increases. The resin least compatible with UP conferred the most flame retardance, which however was shown to form interpenetrating network structures with the UP and hence gave acceptable mechanical performance. While flammability of the co-blended resins was significantly reduced over that of the UP, curing temepartures were required to be much higher than that of the latter. Such co-blended resins, although not suitable for bulk marine composites, will be useful for specific applications such as in engine compartments.
2. To further reduce the flammability of UP-resole blends, liquid and reactive types of flame retardants were used. Selected flame retardants were very effective in the UP and also in the least compatible phenolic resole blended system, which is advantageous because of the good mechanical properties of these blends.
3. To further reduce the flammability of UP and UP-resole blends, the styrene was partially replaced with other reactive diluents, without sacrificing the mechanical properties.
4. Novolac phenolic resins were chemically modified and blended with UP resin. These blended resins could be cured at temperatures similar to those used for UP alone and had good mechanical and fire retardant properties.
5. A melamine-formaldehyde resin was also blended with UP. The flammability, and particularly smoke production during burning, were significantly reduced in the blended resins and their composites. However, their mechanical performances were not good, and so further study of these systems was not prioritised.
6. Bio-derived furan resins of varying degree of compatibility with the UP resin were also studied. Compatible resin blends showed good fire performance. However, owing to lack of time, this route was not pursued.

In summary, a number of resin blends were studied in depth. Their chemical natures, mechanisms of thermal degradation and burning have been established and presented in scientific papers. Their processabilities in terms of composite preparation is the main contribution to knowledge. Some of the resin blends developed in Bolton were used by the Southampton team in their studies of resin infusion and process modelling.
Exploitation Route Resin manufacturers can develop and market new resins identified/developed in this project. For example, one of the functionalised novolac resins is self curing, which can be of interest to a phenolic resin manufacturer.
Scott-Bader can market these blended resins.
Composite manufacturers can use these blended resins. Boatbuliders can use these resins in the construction of light-weight flame retardant vessel superstructures.
These systems also have great potential in other transport areas such as in the rail industry.
This work is of interest to DSTL who are able to explore the use of modified resins in military vehicles.
Sectors Aerospace, Defence and Marine,Chemicals,Construction,Education,Manufacturing, including Industrial Biotechology,Transport

Description 1. Two new types of thermosetting resin, suitable as matrices for fire-retardant composite materials, prepared at Bolton on 10 g scale, were successfully upscaled to 1 kg plus in an industrial laboratory. This showed the potential for producing and exploiting these new resins on a commercial scale. 2. During the tenure of the project, 2 MSc and 7 visiting researchers were trained in the techniques of resin blending, casting, and composite preparation and testing. Short and confidential reports for all the small projects are available. In addition, results from this project have been used in MSc lectures, disseminating knowledge of fire protection of composites to the wider community. 3. All the findings of this research have been published in peer-reviewed journals and presented at national and international conferences, thus informing the scientific community at large of this new technology aimed at producing flame-retardant thermosetting resins. 4. Our overall approach to resin-blending to improve flame retardance has been patented, thus protecting the knowledge for the future benefit of UK plc. 5. Based on the success of this project, another six months research project, ''Development of structural vinyl ester resins with improved flame-retardant properties for marine applications (Bolton/MAST 4)', was funded by Dstl, Ministry of Defence under the MAST scheme (Nov 2014 - May 2015). The aim of this project was to develop a knowledge base and capability with respect to vinyl ester resins that would complement the current knowledge and capability for unsaturated polyester resins. Two commercial vinyl ester resins, one epoxy based and the other novolac based, were blended with two different commercial low molecular weight phenolic resoles, one unmodified and the other containing allyl groups, and the blends cured (crosslinked) to give solids with good flame retardance that in several respects was better than that of the unblended vinyl ester resins. The composites produced from these blended resins, whilst having mechanical properties slightly inferior to those of composites based on vinyl esters alone, nevertheless had better flame retardance, performing especially well in a horizontal UL 94 flame spread test in which they "self-extinguished". Work is in progress through other projects and with industry to explore the commercial viability of these co-blended resins.
First Year Of Impact 2013
Sector Chemicals,Education
Impact Types Societal,Economic

Description Designing carbon fibre -reinforced epoxy composites with improved structural retention on exposure to fire and/or impact
Amount £121,211 (GBP)
Funding ID DSTLX -1000128368 
Organisation Defence Science & Technology Laboratory (DSTL) 
Sector Public
Country United Kingdom
Start 10/2018 
End 09/2021
Description Dstl MAST
Amount £30,000 (GBP)
Funding ID DSTLX1000095120 
Organisation Defence Science & Technology Laboratory (DSTL) 
Sector Public
Country United Kingdom
Start 11/2014 
End 05/2015
Description Effects of impact and fire on aerospace and automotive composite materials containing nano and microparticulate additives
Amount £177,457 (GBP)
Funding ID DSTLX-1000106109 
Organisation Defence Science & Technology Laboratory (DSTL) 
Sector Public
Country United Kingdom
Start 10/2016 
End 03/2020
Description Epoxy-based fire-resistant intumescent protective coatings
Amount £147,717 (GBP)
Funding ID KTP 011026 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 08/2018 
End 07/2020
Description Sensing in carbon fibre composites for early detection of fire
Amount £126,211 (GBP)
Funding ID DSTLX-1000128360 
Organisation Defence Science & Technology Laboratory (DSTL) 
Sector Public
Country United Kingdom
Start 10/2018 
End 09/2021
Title Compatibilised Polymer Blends 
Description The patent relates to polymer blends and particularly, but not exclusively, to fire retardant polymer blends. Polymeric resins used for fibre-reinforced composites, in particular unsaturated polyester and vinyl esters, are flammable and in fire conditions burn, most often with heavy soot and smoke. All available methods of flame retarding them have certain drawbacks. An alternative means of improving flame retardancy is to co-blend these matrix polymer with one having reduced flammability such as a phenolic resin. Unfortunately, matrix polymers like polyesters and vinyl esters are incompatible with phenolic resins. The present invention has been made from a consideration of this by providing a method blending two polymeric materials (a) and (b) as specified herein:- (a) at least one of unsaturated polyester or vinyl ester; and (b) at least one of chemically modified phenolic resin, melamine resin or any other char forming resin, such as polyfurfuryl alcohol or furan resins. The invention may advantageously be used in the production of fire retardant compositions 
IP Reference GB1222468.9 
Protection Patent granted
Year Protection Granted
Licensed No
Impact 1. Two new types of thermosetting resin, suitable as matrices for fire-retardant composite materials, prepared at Bolton on 10 g scale, were successfully upscaled to 1 kg plus in an industrial laboratory. This showed the potential for producing and exploiting these new resins on a commercial scale. 2. All the findings of this research have been published in peer-reviewed journals and presented at national and international conferences, thus informing the scientific community at large of this new technology aimed at producing flame-retardant thermosetting resins.