C.D. Rudd

A fluidised-bed process for the recovery of glass fibres from scrap thermoset composites

A fluidised bed combustion process was developed for the treatment of thermoset composites in the form of process scrap or end-of-life components. The process was shown to be robust, coping with contaminated scrap of variable composition and providing useful outputs in the form of recovered fibres, particulate materials and heat. Comminuted feeds were decomposed at a bed temperature of 450°C and a fluidising velocity of 1.3 m/s. Fibres with mean lengths of up to 5 mm were collected at purities of up to 80% by using a novel rotating sieve separator. Shorter fibres were collected with the particulate mineral fillers. The tensile strength of recovered E-glass fibres was reduced by up to 50% although this depended on the thermal history within the process. Fibre modulus was relatively unaffected by the exposure to high temperatures. Recovered fibres were successfully reused in DMC formulations and veil products. A simple economic model suggests that the process would break even at a throughput of approximately 9000 tonnes scrap composite per year.

A Simulation of Reinforcement Deformation during the Production of Preforms for Liquid Moulding Processes

Composite materials offer an attractive alternative to metals in the automotive and aerospace industries. Of the many possible production methods, liquid moulding processes such as resin transfer moulding (RTM) and structural reaction injection moulding (SRIM) demonstrate potential for high-volume manufacture. It is common to use preformed reinforcements, although this can cause certain problems. Fibre movement during forming can cause adverse effects such as wrinkling and thinning. The high levels of waste generated by subsequent trimming operations are proving unacceptable for medium to high volumes. An accurate modelling capability would allow defects to be predicted at the design stage, and would also allow prediction of the net-shape reinforcement required to form the component with no waste. This paper presents models for both random and directional reinforcement deformation. Random reinforcements are simulated using a modified plasticity theory, while directional reinforcements are modelled using the pin-jointed deformation model.

The characterisation and reuse of glass fibres recycled from scrap composites by the action of a fluidised bed process

This paper describes a new fluidised bed process for recovering reinforcing fibres from scrap thermoset composites. Glass fibres recovered from scrap sheet moulding compound at 450°C using this process have a strength reduced to about half that of virgin fibre. These fibres have been used as partial and full replacement for virgin fibres in a dough moulding compound (DMC). The main physical properties of plaques moulded with the experimental DMCs have been measured. Flexural and Youngs moduli are unaffected by the level of reclaimed fibre used. Flexural and tensile strength are reduced when over 50% of the virgin reinforcement is replaced by fibres recovered at 450°C.

Characterisation of carbon fibres recycled from scrap composites using fluidised bed process

Abstract A carbon fibre recycling process for scrap composites based on fluidised bed technology has been developed. This paper describes the recycling process and the characterisation methods used to analyse the quality of recycled fibre. They include: the measurement of fibre length distribution by image analysis; tensile properties by single fibre testing; and the examination of surface contamination and surface chemistry of fibre by SEM and XPS. Recycled fibres of up to 10 mm mean length were recovered and they retained ~75% of their tensile strength, while the Youngs modulus remained unchanged and the surface condition was similar to the virgin fibre.

Physical and biocompatibility properties of poly-ε-caprolactone produced using in situ polymerisation: a novel manufacturing technique for long-fibre composite materials

Preliminary investigations into a novel process for the production of poly-epsilon-caprolactone (PCL) to be used as a matrix material in a bioabsorbable composite material are detailed. This material is primarily being developed as a bone substitute for use in maxillofacial reconstructive surgery, however, the technique described could be adapted to other areas where bioabsorbable composite materials may be used. The development of a totally bioabsorbable long-fibre composite material would allow a two-stage degradation to occur with the matrix material degrading first leaving a scaffold structure of degradable fibres which would be absorbed at a later stage. Caprolactone monomer was polymerised in situ within a tool cavity to produce a net shape moulding. Inclusion of a fibre preform within the tool cavity which was impregnated by the liquid monomer produces a long-fibre composite material. PCL with a range of molecular weights has been produced using this liquid moulding technique to assess the physical and biocompatibility properties compared to commercially available PCL. Osteoblast-like cells derived from human craniofacial bone (CFC) have been used to assess the in vitro biocompatibility of the PCL. The results show that high-quality PCL with a narrow molecular weight distribution and properties similar to commercially available PCL can be produced using this technique. Polymerisation of the monomer around a woven fibre preform made of a poly(lactic acid) (PLA)/poly(glycolic acid) (PGA) copolymer (vicryl mesh) produced a bioabsorbable long-fibre composite material. Further work is ongoing to develop this system towards a method for improving craniofacial bone reconstruction.

Experimental characterisation of the consolidation of a commingled glass/polypropylene composite

Commingled fabrics offer a cost-effective solution to the manufacture of thermoplastic composites with aligned reinforcements. Consolidation and subsequent void reduction would appear to be the rate-determining stage during processing. Models for consolidation have concentrated on transverse flow of matrix into the reinforcement tows. Experimental studies for other materials have suggested alternative mechanisms, in particular dissolution of entrapped air into the polymer matrix under continued application of pressure. In this study a series of experiments were used to determine the effects of rate, temperature and holding pressure on the consolidation of a glass/polyproplyene commingled fabric. Results are presented in terms of consolidation pressure, void content and micrographs to illustrate the evolution of the microstructure. Increasing rate resulted in increased consolidation pressure as expected, although significant shear thinning occurred even at modest mould closure speeds. Increased rate also led to an increase in void content at the end of the consolidation phase (prior to dissolution into the matrix). The application of pressure during cooling resulted in a dramatic decrease in void content, with levels of less than 1% observed for 3 MPa (regardless of the rate of consolidation). Experiments where the material was heated to 200°C and then cooled to the required temperature prior to consolidation indicated a significant effect of supercooling. This resulted in almost no change in the required consolidation pressure with increasing material temperature above 150°C. Observations of the microstructure at various stages during consolidation suggested that pre-heating of the material resulted in pools of coalesced matrix both within and between the tows. At the end of consolidation the remaining voids were predominantly in the matrix rich regions between tows.

The effect of shear deformation on the processing and mechanical properties of aligned reinforcements

Abstract The growth of liquid moulding processes for the production of structural and semi-structural components has been eased by the development of computer-aided engineering tools for structural analysis and process modelling. However, the accuracy of these tools is dependent on the available material property data. These are usually obtained from experimental or theoretical analysis of flat plaques. These methods do not take into account reinforcement deformation during the preforming process. Deformation, caused by forming two-dimensional reinforcements over threedimensional surfaces, can result in local fibre reorientations and volume fraction changes within the preform. In this study the major deformation mode, simple shear, is isolated. The effects of simple shear deformation on permeability and elastic properties of engineered and woven glass fabrics are investigated. Predictions of elastic properties are made by using established methods and compared with experimental data for a range of fabric architectures. A semiempirical method is applied to characterise the effects of shear on reinforcement permeability.

Mechanical properties of weft knit glass fibre/polyester laminates

Abstract Weft knitting is a well-established process for fibre conversion. It is of particular interest to the manufacturer of fibre composites because of its potential for the net shape manufacture of preforms. The garment industry is capable of producing complex shapes in high volumes using existing CAD/ CAM techniques which have direct application to preform production. This paper describes an investigation of the fibre configuration produced in weft knitting and the mechanical properties which are found in laminates using glass fibres in this form of reinforcement. The mechanical properties of the laminate are examined on the basis of both experimental results and predictions made by the application of a simple elastic model. Results are presented for both the basic plain weft knit construction and those which arise from modified versions of this stitch. A comparison with the properties of laminates produced by conventional preform technology is made.

Weight loss, ion release and initial mechanical properties of a binary calcium phosphate glass fibre/PCL composite

Composites comprising a biodegradable polymeric matrix and a bioactive filler show considerable promise in the field of regenerative medicine, and could potentially serve as degradable bone fracture fixation devices, depending on the properties obtained. Therefore, glass fibres from a binary calcium phosphate (50P(2)O(5)+50CaO) glass were used to reinforce polycaprolactone, at two different volume fractions (V(f)). As-drawn, non-treated and heat-treated fibres were assessed. Weight loss, ion release and the initial mechanical properties of the fibres and composites produced have been investigated. Single fibre tensile testing revealed a fibre strength of 474MPa and a tensile modulus of 44GPa. Weibull analysis suggested a scale value of 524. The composites yielded flexural strength and modulus of up to 30MPa and 2.5GPa, respectively. These values are comparable with human trabecular bone. An 8% mass loss was seen for the lower V(f) composite, whereas for the two higher V(f) composites an approximate 20% mass loss was observed over the course of the 5week study. A plateau in the degradation profile at 350h indicated that fibre dissolution was complete at this interval. This assertion was further supported via ion release studies. The leaching of fibres from the composite created a porous structure, including continuous channels within the polymer matrix. This offers further scope for tailoring scaffold development, as cells from the surrounding tissue may be induced to migrate into the resulting porous matrix.

Use of Resin Transfer Molding Simulation to Predict Flow, Saturation, and Compaction in the VARTM Process

Vacuum Assisted Resin Transfer Molding (VARTM) and Resin Transfer Molding (RTM) are among the most significant and widely used Liquid Composite manufacturing processes. In RTM preformed-reinforcement materials are placed in a mold cavity, which is subsequently closed and infused with resin. RTM numerical simulations have been developed and used for a number of years for gate assessment and optimization purposes. Available simulation packages are capable of describing/predicting flow patterns and fill times in geometrically complex parts manufactured by the resin transfer molding process. Unlike RTM, the VARTM process uses only one sided molds (tool surfaces) where performs are placed and enclosed by a sealed vacuum bag. To improve the delivery of the resin, a distribution media is sometimes used to cover the preform during the injection process. Attempts to extend the usability of the existing RTM algorithms and software packages to the VARTM domain have been made but there are some fundamental differences between the two processes. Most significant of these are 1) the thickness variations in VARTM due to changes in compaction force during resin flow 2) fiber tow saturation, which may be significant in the VARTM process. This paper presents examples on how existing RTM filling simulation codes can be adapted and used to predict flow, thickness of the preform during the filling stage and permeability changes during the VARTM filling process. The results are compared with results obtained from an analytic model as well as with limited experimental results. The similarities and differences between the modeling of RTM and VARTM process are highlighted.Copyright