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The Conversion of Recycled Carbon Fibre Yarn and Tape Into High Value Fabrics and Materials

Final Report Summary - HVRCFM (The Conversion of Recycled Carbon Fibre Yarn and Tape Into High Value Fabrics and Materials)

Executive Summary:
1.1 Executive Summary

This project was targeted at identifying sources of recycled and/or recovered carbon fibres and developing technologies to convert them into reinforcements by blending them with other suitable raw materials. These reinforcements can eventually be combined with thermoset and/or thermoplastic resins for manufacture of composite parts for a variety of applications. The objectives of the project were successfully achieved in the stipulated time-frame.

The entire project was divided into separate work packages which encompassed all the objectives for the project. The different work packages are described below which summarize the outline of the project –

WP1 - Determine source materials for recovery of waste materials

WP2 - Development of hybrid yarn and tape materials suitable for downstream processing in thermoset composite manufacture.

WP3 - Define suitable weave styles or material structure for the samples to be provided.
Provide perform materials as required for sampling purposes.
Provide a method of fabric conversion suitable for the end user and the yarn properties.

WP4 - Characterisation of materials produced at yarn and fabric stages.

WP5 - Deliver the desired material to support JTI-CS-2011-1-ECO-01-25 call.


Project Context and Objectives:
1.1 Summary description of project context and objectives

The major objectives and context of the project has been described in the above section as part of the different work packages.

A detailed summary of the project objectives is as follows –

WP1 –

Determine source materials for recovery of waste materials

• Characterisation and assessment of suitability of end of life recovered CF and process waste streams (TIL,
SIG)
• Small scale process trials of identified waste streams to confirm suitability (TIL)
• Potential modification of CF waste presentation to optimise processing performance (TIL/SIG)
• Quantification of available and suitable waste streams for commercial processing (TIL/SIG)
• Selection of optimum yarn manufacturing route for main waste streams identified (TIL)
• Identification of all potential thermoset compatible fibres for blending with waste CF (TIL)
• Identification of potential thermoplastic compatible fibres for blending with waste CF (TIL)


WP2 –

Development of hybrid yarn and tape materials suitable for downstream processing in thermoset composite manufacture.


Supply of suitable raw materials for larger scale trials (SIG)
• Hybrid yarn manufacture from end of life discontinuous waste CF and thermoset compatible fibres (TIL)
• Hybrid yarn manufacture from discontinuous process waste CF and thermoset compatible fibres (TIL)
• Commingled yarn manufacture from continuous waste CF and thermoset compatible fibres (TIL)
• Supply of narrow thermoset tape materials for NCF and woven fabric manufacture (TIL)
• Supply and characterisation of wide thermoset NCF materials (TIL/SIG)
• Supply of hybrid thermoplastic yarn and tape materials from discontinuous CF (TIL)

WP3 –

Define suitable weave styles or material structure for the samples to be provided.
Provide perform materials as required for sampling purposes.
Provide a method of fabric conversion suitable for the end user and the yarn properties.


• Input will be required from all partners on the material structure requirement. From the outset each partner will
need to determine the required architecture so that a suitable material can be defined and designed (SIG).
• The machine parameters will need to be programmed to manufacture the samples and loom setup will take place to manufacture required samples (SIG).
• In the case of NCF all samples will undergo evaluation to determine suitable process parameters (SIG).


WP4 –

Characterisation of materials produced at yarn and fabric stages.

This WP will provide the information for subsequent processing and will determine the optimum route for the converted fibres and materials (SIG).


WP5 –

Deliver the desired material to support JTI-CS-2011-1-ECO-01-25 call.

The WP will monitor timescales and deliverables to ensure demonstrator articles and reports are delivered in time to support the call.

Project Results:

1.3 Description of the main S&T Results and Foreground

Materials

15% resin compatible fibres are required in the prepreg system, therefore some other suitable fibres such as Aramid would be added, which will contribute to increase the mechanical performance of the composites.

Therefore, the following materials were sourced:

(i). Epoxy compatible fibres
(ii). Recycled carbon fibres
(iii). Recycle grade aramid fibres


PEI resin fibres

The following two types of PEI fibres were sourced:
(i). PEI 6.7 dtex
(ii). PEI 2.2 dtex

As the finer fibres provide better sliver quality, the 2.2dtex PEI fibre was selected to
blend with CF and Aramid.

Virgin waste CF

T700 types CF in multi-axial waste (MAX 5) were supplied by Sigmatex.

Aramid fibres

The following four types of recycled grade aramid fibres (1.7dtex linear density) were sourced:
(i). Type 1
(ii). Type 1T
(iii). Type 2 and
(iv). Type 55

Depending on the suitable fibre length, only type 55 was selected.

Fibre length distribution of Aramid fibres

The mean length and length distribution of sourced aramid fibres were investigated.
It was found that type 1, 1T and 2 samples contain 40% longer fibres, ranging from 80-
150 mm long, which are considered not to be suitable in our carding process

Type 55 was selected due to shorter fibre length, for better mixing and blending with similar length of CF and PEI fibres.


Initial trials for CF/PEI/Aramid sliver production

As it was decided that 50% CF will be blended with 15% PEI and 35% Aramid fibres, therefore, an initial sliver production was trialled by using this combination.

Pre-opening the aramid fibres
The aramid fibres were pre-opened by pre-carding of the fibres before mixing with CF and PEI.

Pre-opening the PEI
The PEI fibres were also pre-carded to separate the fibres for better blending with CF.

CF/PEI/Aramid sliver production trials
Continuous sliver with 2.5 g/m linear density was produced successfully. It was found that sliver can be made from the above blends that can be used in further processes such as tape and NCF production.

CF length distribution in sliver
CF length distribution was measured in the blended slivers.


Development of carbon fibre and epoxy resin soluble fibre based yarns and fabric for thermoset composite manufacture trials. The following objectives were set out:

(i) Selection of suitable waste carbon fibres
(ii) Selection of epoxy resin soluble/compatible matrix fibres
(iii) Commingled yarn and fabric production


Selection of waste carbon fibres

Chopped/staple carbon fibres (60 mm long) being generated as waste during the multi-axial fabric production process (MAX-5) at Sigmatex, were selected in this work package.


Selection of epoxy resin soluble fibres

To produce yarn from waste CFs, suitable carrier fibres are required to blend with staple CFs during carding process. The crimped carrier fibres will carry the un-crimped CFs during the carding process. Moreover, during the composite fabrication, the epoxy soluble fibres will be dissolved in the matrix system and will work as toughening compounds in the composites.

Therefore, suitable epoxy soluble resin fibres were sourced and selected as carriers in this work package to produce spun yarns using waste carbon fibres. As thermoset (epoxy resin) compatible matrix fibres are limited in availability, therefore, only two fibres have been identified to be used with staple CF fibres as follows:
(i). Poly Ether Sulphone (PES)
(ii). Ultem Polyetherimide ( PEI)

(i). PES fibre: PES fibres supplied by Cytec were characterised. This fibre can be dissolved in epoxy system easily, but the physical properties of the fibres were found very poor to process. Moreover, it was found that the PES fibres were non-crimped, very weak (breaking load only 0.093N) and fell into parts during carding process. Therefore, it was not considered as suitable carrier fibres for staple CFs.


(ii). PEI fibres: Ultem PEI resin fibres (Tg 217o C) were sourced from Fibre Innovation Technology, USA. It was found that PEI fibres were strong, crimped (10-12 crimp/inch) and in staple form (60 mm length) could act as an efficient carriers of staple CFs in carding process. This fibre was also found to dissolve in epoxy system, and therefore, was selected as epoxy compatible fibres.

The following two types of Ultem PEI fibres were sourced:

(i). PEI 6.7 dtex
(ii). PEI 2.2 dtex


Commingled yarn manufacturing

CF/PEI (60/40) blends

The MAX 5 waste carbon fibres and Ultem PEI fibres (2.2dtex) were finally selected to produce yarn. The blends of waste carbon with PEI carrier fibres (60/40 weight ratios) were converted into continuous sliver using a modified carding process. Then the slivers were used to produce spun yarn of 1100 tex by filament wrap spinning process. During the wrap spinning process, PEI filaments were also used as wrapper to produce continuous yarn. The yarns were then delivered to Sigmatex for woven fabric production.

Blending of higher CF% (over 60%) with PEI fibre made the carding process difficult. Moreover, it was found that the yarn contains a significant amount of loose fibres that causes problems in weaving process. Therefore, yarn route was rejected by the partners for further development work.

As it is difficult to increase the CF% in the sliver (reported in D2.1) to >70% due to the limitation of the processing performance of the blends in the carding process, the addition of waste aramid was identified as a possible solution to the problem to act as both a carrier fibre and additional reinforcing fibre. The main objective of this work package was therefore to produce hybrid sliver from CF/ aramid blends. It was also identified that tape from CF/Aramid could be another interesting option for thermoset application. The following targets were identified for the work package:

(i) Production of CF/Aramid and CF/Aramid/PEI hybrid sliver and
(ii) Tape production from CF/Aramid blends

Both sliver and tape can be used in multi-axial fabric production process. For tape, a small % of thermoplastic fibres are required as a binder for the tape production process.


Development of Slivers

Selection of materials

The following materials were selected in this work package:

(i) Waste CFs (Max 5)
(ii) Waste Aramid
(iii) Maleic Anhydride grafted Polypropylene (MAPP) thermoplastic fibres
(iv) PEI




Description the materials

(i). Waste carbon fibres: Waste carbon fibres (60 mm long) generated during the multi-axial fabric production process (MAX-5) at Sigmatex were selected.

(ii). Waste Aramid: Aramid fibres were added as second reinforcement fibre in the blend with CFs.

(iii). Maleic anhydride grafted polypropylene fibres: In the tape making process, a small amount of thermoplastic fibre is required as a binder to hold the CFs and aramid fibres in position and consolidate the tape. Maleic anhydride grafted polypropylene (MAPP) was selected as the binding materials due to the low melt temperature and high melt flow characteristics of this particular material .

Commingled sliver manufacturing

The blending and mixing process of the CFs with carrier fibres reported in D2.2 report was also used in this work package. The following blend ratios were selected through discussion with the project partners:

(i) CF/PEI/Aramid (CF 50%, PEI 15%, Aramid 35%)

(ii) CF/Aramid (70% CF 30% Aramid)
(iii) CF/Aramid/MAPP (50% 30% 20%)

Three different types of materials were produced and delivered to Sigmatex and Cytec for thermoset composite manufacture trials. Waste aramid fibres work as a suitable carrier for staple CFs in the carding process by virtue of the high levels of cohesion exhibited. The slivers and tapes produced were found to offer acceptable levels of strength for multi-axial fabric production process. Depending on the results achieved, further work is possible to reduce the level of MAPP content while still retaining an acceptable level of binding.

Material conversion routes

MAX-5 waste CFs and carrier fibres were converted into suitable textile preforms as part of WP2. Various routes, were investigated to produce suitable composite prepregs from the selected materials.

Conversion of wCFs into continuous slivers


Blending of wCFs with polymer matrix fibres

Prior to composite prepreg production processes, it was necessary to produce continuous slivers from the waste carbon fibres. It is a challenge to produce sliver from chopped waste carbon fibres due to the non-crimped and brittle nature of the CFs. Therefore, carrier fibres are required as a processing aid and the selected carrier fibres were blended with waste CFs in different weight ratios (depending on the thermoplastic or thermoset prepreg production) using a modified fibre opening and blending unit prior to continuous sliver production.

Sliver production

The wCFs/polymer fibre blends were passed through a modified carding process, where the wCFs were further separated by a carding action. During the process of intermingling the CF (55 mm) with matrix fibres (60mm) on the modified card, it was found that the crimped polymer fibres acted as efficient carriers for the non-crimped CFs with minimum fibre breakage and resulted in good intermingling (‘blending’). After carding, the blended CF/matrix fibre sliver was produced.

A continuous sliver with 6-7 g/m linear density was produced successfully from the different blends required for both thermoplastic and thermoset composite prepreg production processes.

Conversion of slivers into tape

It was found that the continuous slivers could not be used directly into new composite fabrication as they were very weak (breaking load 1-1.5N) and broke easily during handling in downstream processes. It was however found that partly stabilised/full stabilised (semi-consolidated /fully consolidated) sliver can be directly used in different prepreg manufacturing processes. As a result, a thermal consolidation process was constructed to stabilise the slivers into a tape. The details of the process was reported in D2.2 deliverable report.

Tape production process

A thermal bonding technology was developed and constructed to produce semi-consolidated continuous tape from the carded sliver assembly. The whole unit contains three separate regions; fibre feeding, spreading and a heating zone. On leaving the drafting stage, the thin web of fibre is heated above the melting point of the PA66 polymer fibres and tension applied to produce further alignment of the carbon fibres. A pressure of 2 bar was then applied by a pair of pressurised rollers, ‘melting’ the matrix fibres to the carbon fibres to produce a 0.6 mm thickness semi-consolidated tape.



During the tape making process, the contact dwell time (CDT) in second for pressure rollers and heating dwell time (HDT) were calculated.

Different types of tapes with different areal densities were produced for both thermoplastic and thermoset composite applications using different CF%.

Thermoplastic tapes

The semi-consolidated thermoplastic tapes manufactured as thermoplastic composite prepreg contain 50-55% CF and 50-45% thermoplastic matrix fibres. During composite moulding, the thermoplastic fibres melt and act as matrix. These type of prepregs are found as attractive option for thermoplastic route as the tape/sheets are very flexible and light in weight. Those tapes can be used directly as unidirectional prepregs and also can be slit into narrow widths for tape woven fabric production.


Thermoset tapes

Slivers produced from wCFs and aramid blends (70% 30%) and mixing with epoxy compatible carrier fibres (50% wCFs, 35% AR and 15% PEI) or 60% CF 40% PEI were converted to stabilised tapes (see Figure 8). The subsequent tapes were used in NCF production line to make biaxial (+45o/-45o) fabrics.


Conversion of the tapes/slivers into Non-crimped fabric (NCF)

NCF production process

The wider tapes produced using the tape-making unit were used directly for NCF production. Another alternative route was also established to use the sliver directly into NCF production, where the slivers were partly stabilized using a binder and produce a wider sheet.


Biaxial non-crimped fabrics (NCFs) were produced by the continuous placement of the stabilized sliver sheets in a +45o/-45o lay-up protocol and stitch-bonded with a polymer filament yarn of 55dtex. The nominal weight of the NCF prepreg produced was 200±10g/m2. Figure 10 also shows the top and bottom surfaces of the NCF with plain and zigzag stitch patterns, respectively. The stitch density was 640/m2.

Conversion of waste CFs into continuous slivers by mixing with different carrier fibres has been developed. Different routes for prepreg manufacturing using the carded slivers have also been successfully developed for both thermoplastic and thermoset composite applications.

From initial work carried out by Tilsatec, the route for material supply for 2D fabrics is Tape. 60/40 CF/PET were provided by Tilsatec and used as weft on a standard Dornier loom. The use of tape for warp is not feasible at this time due to the amount of tape needed and the requirement for an alternative warp delivery system.
Woven 10mm tapes laminated (4layers only). Consolidation was successful although warp and weft required for further research. Sigmatex are currently trialling a new development machine which will be more suited to the manufacture of tape fabrics and will assess the recycled material when available.


With Plain, Twill and satin weaves making up the majority of fabrics in the composites industry, tape woven demonstrators were manufactured to show the appearance of the fabrics using the recycle Cf/PET tape. Initial findings showed that the fibre was quite stiff and difficult to pick up by the standard rapier mechanism. Given the width and the stiffness of the materials it was concluded that warp delivery would need to be updated and an alternative method of weft insertion would need to be realised to make the fabric a success. Sigmatex has now purchased a new machine that is suitable for characterising and weaving the tape materials and will continue to develop these materials.

Manufacture NCF Material

The sliver produced by Tilsatec did not have enough strength to be used directly on the NCF machine and needed pre-processing to allow transfer across the bed. The method of consolidation used a belt press to form a sheet of material which can then be placed on the bed of the machine at different angles. In this instance a 60:40 consolidated material was manufactured on the NCF to provide +/-45 degree material. This initial sample was then further processed to understand the processing parameters required for sample production. The University of Manchester provided the facility of a hot press capable of achieving the pressure and temperature expected to process the fabric.

The material was layered in 6 separate layers of 150 gsm per layer slivers to make a total Fabric weight of 900gsm. The materials were pressed at a temperature of 260°C for 1 hour at a pressure of 10 Bar. The resultant materials, although consolidated had significant dry spots and the through thickness bonding was poor.

Subsequently further trials were carried using 8 layers at +/-45 degrees out at higher pressure of 50 Bar and at a higher temperature of 290°C. The cycle time was reduced from 1 hour to 15 minutes and the resultant material had good consolidation. Testing showed that although there appeared to be good consolidation, under testing the material had high porosity.

Prepeg analysis
Analysis of CF/matrix fibre blends
It was observed that the PA66 matrix fibres had acted as a carrier of the non-crimped carbon fibres during carding process thereby giving cohesion to the commingled mass, which enabled the production of the waste carbon fibre/PA66 (wCF/PA66) continuous sliver with linear density 6-7g/m. SEM images of sliver specimens showed that the CF fibres were uniformly commingled/blended with the matrix fibres and reasonably well aligned with the sliver axial length.

Analysis of Non-crimped fabric (NCF) prepregs
Biaxial non-crimped fabrics (NCF) were produced from the slivers and tapes for both thermoplastic and thermoset composite applications. It was mentioned in D2.4 report that the NCF prepregs were produced by the continuous placement of the stabilized sliver sheets in a +45o/-45o lay-up protocol and stitch-bonded with a PA66 filament yarn of 55dtex. The nominal weight of the NCF prepreg produced was 400±10g/m2.

Two types of NCF prepregs were produced as follows:

i. NCF thermoplastic composite prepreg. This prepreg contains 50% CF and 50% PA66 thermoplastic polymer fibres. The PA66 polymer fibres will melt and form the polymer matrix.
ii. NCF thermoset composite prepreg containing up to 70% CF or mixture of CFs with Aramid fibres. Additional resin is required to make composite parts

It can be mentioned here that the NCF was found to be highly formable and could be used in many complex composite shapes.

Conversion of thermoplastic fabric prepregs into composites

A 3 mm thick laminate was fabricated using an 8-ply stack of the biaxial (+45o/-45o) noncrimped fabric prepreg, where the fabric plies were cross-laid in a manner which re-orientated the +45/-45o fibre inclination and produced a [0/90o] layup. Hot compaction, 280oC temperature and 50bar pressure for 15min was used to consolidate the NCF assembly. The high pressure (50bar) was used to compress the bulky stack of the dry NCF plies to obtain full consolidation.

Fabrication of thermoset composite using noncrimped fabrics

Three types of thermoset laminates were fabricated using two types of epoxy resins: LTM217 and MTM57. Semi-cured epoxy resin films were used in both cases. The resin films were applied to the fabric to produce laminates containing 55% resin (by vol.) in final laminates. The bi-axial (-45 /+45) NCF fabrics were cut for a 0/90 lay up and 6 plies of fabric were used to obtain 3 mm thick laminates. The CF-AF-MAPP tape prepreg (discussed in D2.4 report) was laid up 0/90 to obtain a balanced structure.


Total reinforcement wt. fraction and volume fractions were calculated from the density of the fibres and resin in individual laminate. CF weight fraction and CF volume fraction were also calculated in the composite laminates using the following formula:
Vc = 1/ [1+ pf/ pm (1/Wc –1)]

Where, Vc is total carbon fibre volume fraction in laminate. Wc is CF weight fraction. Pf and Pm are the densities of the CF and resin, respectively.


Mechanical testing of composites

Tensile testing
The tensile properties of the specimen were tested according to ASTM D3039-08 standard. A tabbed rectangular specimen (see Fig. 30) was mounted in the grips of the test machine (gauge length 138 mm) and load was applied to the specimen at a constant rate of speed until the specimen failed. The ultimate tensile strength of the specimen was calculated from the failure load.

Flexural testing
Flexural properties of the laminates were tested according to the BS EN ISO 14125 standard. A rectangular specimen was cut into 80 mm length and a span to thickness ratio of 16:1 mm was used. Loading was applied at a constant crosshead rate of 5mm/min at the centre of the span length. The load applied to the specimen and the deflection were measured during the test. The flexural strength and flexural modulus were calculated.

Compressive strength
Compressive strength of the laminates was calculated according to the ASTM D695-89 (Boeing Modification) standard. A tabbed rectangular specimen with a 4.8mm gauge length was mounted in cruciform anti-buckling jig. Load was applied through the end of the specimen at a constant rate (1.3mm/min) of crosshead speed until the specimen failed. The ultimate load at which catastrophic failure occurred was used to calculate the compressive strength.

Inter-laminar shear properties
Inter-laminar shear strength (ILSS) was according to the ASTM D2344-84 standard by using short beam method. The beam size was 20 mm.


The rectangular specimen was centrally loaded at 1.3mm/min in a three-point bend fixture until the failure occurred. The test support span to specimen thickness ratio was 5:1. The ILSS was calculated.

Results and discussions

CF/PA66 thermoplastic composites

The fabrication procedure of CF/PA66 thermoplastic laminates and methodology of different tests were described in section 3 and 5. The NCF composite fabricated contains 4 layers of prepreg in the 0o direction and further 4 plies in 90o direction on [0/90]o lay up. The mechanical tests of the NCF composites were conducted in 0o direction.

The average tensile and flexural strengths were found to be 255.9MPa and 192.5MPa respectively. The average tensile and flexural moduli were 22.14GPa and 18.01GPa respectively. As the NCF composite contains 4 layers of prepreg in the 0o direction and further 4 plies in 90o direction, 50% (i.e. 4 plies) of the fibres in 0o contributed to both tensile and flexural properties.


The average compressive strength and modulus were found to be 122.68MPa and 23.6 GPa, respectively. The ILSS was found to be 15.11 MPa of the NCF laminates.


It was found that the composite panels made from the NCF, showed no traces of the stitching threads used in the making of the NCF prepreg. Both the constituent PA66 staple fibres in the slivers and the PA66 filament stitching threads on the fabric surface, that held together the fabric structure, had melted and had diffused during consolidation of the composite panels. However, the SEM image (50 x magnifications) obtained from the cross-section of the laminate showed the laminate contains a significant number of voids.


Due to the large void%, the density of composite made from the NCF was measured to be 1.19g/cm3: significantly lower than the calculated value (1.39g/cm3); the low value indicates a relatively high void content calculated to be ~14%. The high void content is most likely due to an insufficient level of matrix fibres to impregnate the CF presents. The density and hence the porosity and mechanical properties of NCF composite could be potentially enhanced by:
- optimisation of matrix fibres %
- use of finer matrix fibres
- improved uniformity in fibre mixing


Comparing the results of bi-axial NCF composite sample (fabricated in this project) with a commercially available (Tenax, Germany, CF/PA12 yarn) composite made of stretch broken CF/PA12 commingle UD yarn laminates in not applicable as the available material was made from longer CF (70-90 mm long) commingled yarns. It is reported that the flexural modulus of Tenax CF/PA12 UD composite (50% CF by vol.) were 60 GPa, which effectively equivalent to 30 GPa in bi-axial format. Flexural modulus obtained for the bi-axial NCF composite was 18.5 GPa for 36% CF by volume which is equivalent to 26GPa for 50% CF by volume. So, it is found that the modulus of NCF composite is only 13% lower than equivalent virgin Tenax CF/PA12 composite with same CF volume fraction in similar format. This is due to the short/discontinuous wCF used in NCF prepreg in this project and the high porosity (10%) found in the laminates also has reduced the mechanical properties of NCF composite.


Thermoset composites

The fabrication procedure of epoxy thermoset laminates and methodology of different tests were described in previous sections. The NCF epoxy composite fabricated contains 6 layers of prepreg in the 0o direction and further 6 plies in 90o direction on [0/90o] layup. The mechanical tests of the epoxy composites were conducted in 0o direction. The results obtained from different test are discussed here.

By analysing the test results it was found that all three NCF/epoxy composites have similar tensile strength ranges from 225 MPa–240 MPa. The flexural strengths were found to be from 362-386 MPa, the compression strengths were found to be from 228-255 MPa and ILSS were also found to be from 32-43MPa. The strengths were found very similar in all samples.

Similar trends were also seen on their stiffness values, where the tensile moduli were from 15.5 to 19.5 Gpa, flexural moduli were from 15.5 to 18.5 GPa and the compression modulus were from 14 to 17.3 GPa, respectively.It was also found that using of small % of PEI with CF has little effect on the composite’s properties

According to a Cytec materials property archive, continuous carbon fiber 2x2 twill fabric/epoxy composites (55% CF volume fraction) can reach tensile and flexural modulus of 64.6 GPa and 61.36 GPa, respectively, which are much higher than the 19.5GPa tensile stiffness and 18.5GPa flexural stiffness values of the NCF epoxy composites. The lower stiffness values of NCF/ epoxy laminates were due to shorter CF’s length and lower CF volume fraction in the laminates. The average CF length was found to be 40mm and the CF volume fractions were found to be 28% in CF/AR/epoxy laminates and 20% in other NCF/epoxy laminates. Moreover, all the epoxy laminates were fabricates using a film stacking process, therefore, resin infusion inside the bulky fabric layers may not have been sufficient to fully wet the CFs resulting in poor mechanical performance. Resin infusion process has been recommended instead of film stacking process to achieve better mechanical properties from the NCF fabrics in future work.


Conclusion

Based on the results and discussion above, key points may be concluded as follows:
- A novel process for producing cost effective rCF/PA66 thermoplastic non-crimped bi-axial fabric has been developed to provide a dry-prepreg. The NCF thermoplastic prepreg (400g/m2) may be considered as a promising material for lightweight composite applications. It was found that the rCFs are relatively aligned and well distributed/blended with matrix fibres. Therefore, good mechanical properties of NCF thermoplastic composites were achieved. However, the properties may be improved by using finer resin fibres, better mixing of the fibres and improved composite fabrication technique.
- A novel cost effective rCF thermoset non-crimped bi-axial fabric has been developed from waste carbon fibres but the NCF thermoset fabric prepregs contain very lower % of CFs. The fabric prepregs were found to be very light in weight (300g/m2) and suitable for any complex composite shapes. The mechanical properties of the rCF/epoxy composites were also found to be good on the basis of the CF% in the laminates but can be further improved by increasing CF% in the prepregs. It was also found that the NCF is more suitable for resin infusion process instead of resin film stacking and likely to provide improved mechanical properties.

Finally, it can be concluded that the both NCFs for both thermoplastic and thermoset composite applications can be attractive materials for composite end users in many applications as a potential replacement for virgin CF and heavy weight glass fibre composites. The NCF production process from waste /recycled CFs can be one of the suitable processes to re-use the waste fibres into higher value composite manufactures than those currently commonly employed for waste materials.

Potential Impact:
With growth of the use of Carbon Fibres increasing significantly within Aerospace and Automotive sectors, waste levels will also increase. By having a method and supply chain to create new materials from virgin waste the impact for future manufacturing is much improved. As the cost of fibre reduces even further, more widespread use of Carbon Fibre is anticipated in wider markets. Through the course of this project the ability to manufacture a thermoplastic carbon with the matrix already integrated in the material has been demonstrated. The opportunity to create a structure by just pressing the material reduces processing time and also reduces the need to use other thermoplastic matrix materials.
With cycle times for processing of materials into automotive being a primary driving force, it is expected that the materials developed through this process will find uses where stiffness is required and thermoforming is an option. The high dry fabric waste levels that are currently being demonstrated in the automotive sector at approximately 40%, could be incorporated into the materials developed in this project.
By optimising the use of dry fibre waste into the materials developed in this project, the carbon Fibre properties can be exploited better that crushing or milling the fibres. This creates an intermediate use of the Carbon and improves the product lifecycle, getting more from the high cost fibre. The energy used in the manufacture of Carbon Fibre is high and by having this additional process, overall lifetime and therefore energy costs are used more effectively.
The dissemination activity surrounds the promotion of the materials openly at conferences, including JEC Europe, JEC USA and JEC Asia. A paper and abstract is planned to be presented at Composites Innovation 2014.

List of Websites:
Chris McHugh
Technical Manager
Sigmatex (UK) Ltd
Manor Farm Road
Norton
Runcorn
WA7 1TE
Tel No: 01928 570050
Fax No: 01928 570051

Email: chris.mchugh@sigmatex.co.uk
Web: www.sigmatex.com


Simon Havis
Tilsatec
A Division of Sirdar Spinning Ltd
Flanshaw Lane
Wakefield
West Yorkshire
WF2 9ND

Direct: + 44 1924 231668
Mobile: + 44 7951 587203
E-Mail: simon.havis@tilsatec.com
Visit our web site www.tilsatec.com