Plastics,Rubber and Composites: Macromolecular Engineering

Composite materials have gained popularity (despite their generally high cost) in high performance products that need to be lightweight, yet strong enough to take high loads such as aerospace structures (tails, wings and fuselages), boat construction, bicycle frames and racing car bodies. Other uses include storage tanks and fishing rods. Natural composites (wood and fabrics) have found applications in aircraft from the first flight of the Wright Brothers' Flyer 1, in North Carolina on 17 December 1903, to the plethora of uses now enjoyed by engineered materials on both military and civil aircraft, in addition to more exotic applications on unmanned aerial vehicles, space launchers and satellites. Their growing use has arisen from their high specific strength and stiffness, when compared to the more conventional materials, and the ability to tailor their structure to produce more aerodynamically efficient structural configurations. In this paper, it is argued that fibre reinforced polymers, especially carbon fibre reinforced plastics can and will in the near future contribute more than 50% of the structural mass of an aircraft. However, affordability is the key to survival in aerospace, whether civil or military, and therefore efforts should be devoted to analysis and computational simulation of the manufacturing and assembly process as well as the simulation of the performance of the structure, since they are intimately connected.

Delamination damage occurs in carbon fibre reinforced plastic (CFRP) as a result of fire exposure, followed by extensive resin decomposition and charring. The initial delaminations are detectable using portable ultrasonic equipment and appear to coincide with the onset of resin decomposition, as measured by thermogravimetric analysis (TGA). However, further work is needed to determine the exact temperature for permanent damage. The spread of delaminations through the structure correlates with a reduction in compressive strength which can be described using the ‘two-layer' model. Temperature-dependent thermal properties, including anisotropic values of thermal conductivity, enabled the 3-D temperature field to be modelled using a finite element (FE) package. The high in-plane thermal conductivity of CFRP can result in indirect thermal damage in regions adjacent to the zone of fire exposure.

The present research is based on the manufacturing of thick laminates using qualified, aerospace grade prepreg and liquid resin material. After optimising the cure cycle including control over the exothermic reaction, 30 and 50 mm thick laminates were manufactured from both the selected materials and analysed for manufacturability, exothermic reaction and laminate quality. During the curing cycle, temperature was monitored at different sections of the laminate, namely, top, middle and bottom. From the results obtained, it can be confirmed that, curing under the Quickstep processing conditions enables manufacturing thick laminates very rapidly and without the exothermic reaction. This saves tremendous amount of time and avoid wastage of large and costly components.

The aerospace industry is looking for highly efficient and fully automated processes to manufacture large structural components. Placement processes are fulfilling these requirements. Furthermore, they allow to lay up the structure with the highest degree of fibre orientation and well defined fibre position. Already in service are thermoset tape based placement processes. Main disadvantage is the need to have a consolidation process after structure lay-up has finished. Additionally, the required autoclave limits the component size. The thermoplastic tape placement process offers new possibilities. Fully impregnated fibre reinforced thermoplastic tapes are laid onto a mould to build up curved or flat structures step by step. Each tape is melted by a heat source, welded to the layer below, compressed by e.g. a roller, and cooled down below melting temperature. If this is done properly, an in situ consolidation can be achieved, which means no additional consolidation process is needed. The paper is giving an overview about thermoplastic tape placement process and elaborates the requirements to reach in situ consolidation.

Two-dimensional braiding of a generic preform has been undertaken using test, analytical and advanced explicit finite element simulation methods. The generic preform selected incorporates several important features including two cylindrical and one square section, a tapered cone and two dissimilar flanges. The analytical method has been shown to be computationally fast, but has limited accuracy and cannot directly predict braiding imperfections. Conversely, the explicit finite element method does require a complex model description, but has the capability to detect manufacturing imperfections and accurately predict yarn paths and yarn interactions. A detailed evaluation and comparison of the two methods is made against test results from the generic preform, which was deliberately manufactured to have both good and imperfect yarn architecture.

The demand for environmental sustainability has resulted in a great interest in finding new materials that are biodegradable and environmentally friendly. Therefore, materials derived from natural resources are now being extensively studied. Preparation of novel biocomposites based on nanocelluloses has drawn specific attention. It is expected that cellulose nanocomposites will open new areas for applications in medicine, packaging, electronics, the automotive sector, construction and other areas. This article presents a new research field of bionanocomposites where different types of nanocelluloses are used as reinforcements in biopolymers. Isolation of cellulose nanofibres and nanowhiskers from different sources, and processing technologies for the composites, are described and discussed. The main difficulty when producing cellulose based nanocomposites is to disperse the reinforcement in the polymer matrix without degradation of the biopolymer or the reinforcing phase. This can be addressed by improving the interaction (compatibility) between nanofibres and the matrix and by using suitable processing methods. The study of alignment of the nanocelluloses by using magnetic field is discussed and the nanocomposites' mechanical properties, based on the findings from different studies, are presented. Finally, some examples of future nanocomposites are discussed.

This paper discusses the recycling of thermoplastic composite materials in the context of boatbuilding. Work was carried out on the recycling of an experimental thermoplastic composite rigid inflatable boat, originally built by BVT Surface Fleet and tested in service by the Royal National Lifeboat Institution. It was found that a range of useful injection moulding materials could be prepared from the hull material of the craft, demonstrating that structural thermoplastic composites are recyclable in practice as well as in principle, and confirming that they are a sustainable alternative to thermosets.

The aim of this research is to assess the stability and processability of recycled polypropylene (PP) materials for their suitability for use as matrix material in polymer composite. The work comprises development and characterisation of matrix precursors from recycled PP. The reused PP considered comes from two sources: PP from the self-reinforced PP Pure processing scrap and an automotive grade developed to offer an even material quality. To assess the thermal stability of two PP qualities for subsequent composite manufacturing, oxidation induction time (OIT), melting point T _m, decomposition temperature T _d and viscosity μ were investigated. The results indicate, that Pure processing scrap is very well stabilised and therefore suitable for multiple processing, whereas the automotive grade recycled PP cannot be used for this purpose. Fibres for subsequent composite preforming were spun by melt spinning from the Pure scrap processing and its mechanical properties were characterised.

The present work was devoted to the development of a technique for manufacture of a novel engineering material from carbon fibres and thermoplastic matrix recyclates. Fibre preforms were manufactured employing a papermaking technique for dispersing the carbon fibres. The polypropylene (PP) matrix recyclate was reprocessed into a film. The carbon fibre preforms and PP films were stacked and composite materials were subsequently manufactured by press forming. The mechanical behaviour of carbon fibre preforms was characterised by a compaction test and compared to the results obtained by consolidation test of the carbon fibres reinforced PP composites. The consolidation experiments were found to follow the trend from compaction tests allowing prediction of the amount of polymer material needed, fibre volume fraction as well as composites thickness. The resulting dispersion of fibres and void content were evaluated by microscopy.

The effect of vacuum assistance, mould temperature and ram velocity on the void transport and flow behaviour for sheet moulding compound (SMC) have been investigated with a design of experiment approach of the compression moulding phase. The relative amount of voids has been quantified with a high voltage insulation test and the flow behaviour has been quantified with image analysis of samples moulded with coloured SMC. In conclusion, the setting of high vacuum, low ram velocity and low mould temperature creates a homogeneous flow and minimises the amount of voids.

Creep studies have been carried out under uniaxial tension and uniaxial compression on poly(oxymethylene). Measurements under tension have been modelled using a function with four material parameters. One of these parameters, related to a mean retardation time for the relaxation process responsible for creep, decreases with increasing stress, and this gives rise to non-linear creep behaviour. Measurements of creep under compression indicate that the retardation time parameter is determined by the stress state as well as the stress magnitude. A theoretical extension of the model has been proposed that relates stresses and strains under situations where the stress is not constant but varies with time. This is necessary for the model to be implemented in a finite element system to carry out design calculations that take proper account of the time dependent properties of polymers. The validity of the theory is evaluated through the use of the creep model to predict deformation for a variety of simple stress and strain histories under uniaxial tension. The close agreement between calculation and measurement supports the development of code, in future work, to obtain solutions for multiaxial stresses and strains using a finite element system.

Gas assisted injection moulding (GAIM) is a technique that is successfully used for compensating shrinkage during injection moulding of thick walled but still accurate products with low levels of internal stresses and frozen-in orientation. In this study the authors apply GAIM in moulding 28 mm thick products combining the technique with two component injection moulding: 2C-GAIM. Next, the authors used a movable insert as a local shrinkage compensating device, making the use of gas superfluous: the component, component, compliance, compensating for shrinkage technology is born. It is used for injection moulding robust and accurate transparent polymer products aiming to introduce multifunctionality, to apply hard and soft polymers, and differently coloured polymers, for improved visibility of text or design lines, and moulding text even inside a product for improved aesthetics.

The viscosity, loop tack, peel and shear strength of five different molecular weights of standard Malaysian rubber based pressure sensitive adhesive were studied. Coumarone–indene resin and toluene were used as the tackifier and solvent respectively throughout the experiment. The adhesive was coated on polyethylene terephthalate substrate at a coating thickness of 30, 60, 90 and 120 μm using a Sheen hand coater. Viscosity of the adhesive was determined by a Haake rotary viscometer whereas loop tack, shear and peel strength was measured by a Llyod adhesion tester. Results show that viscosity of adhesive increases with increasing molecular weight of rubber. However, loop tack, shear and peel strength exhibit maximum value at a molecular weight of 8·5 × 10⁴ where maximum wettability of adhesive on the substrate occurs. The adhesion property increases with coating thickness at this optimum molecular weight of rubber.

The effects of three types of carbon blacks, namely, semireinforcing furnace, high abrasion furnace and intermediate super abrasion furnace on the physical properties of poly(ethylene-co-vinyl acetate) have been studied. The properties studied include cure characteristics, mechanical properties, solvent transport behaviour, dielectric properties and the thermal characteristics. The properties were evaluated in terms of the particle size and amount of the fillers used. The mechanical properties of the matrix such as tensile strength, abrasion resistance and hardness were observed to be increasing with filler incorporation. Solvent resistance of the composite has also been observed to be increasing with filler incorporation. The dielectric constant and thermal behaviour of the composite has been studied and explained in terms of the particle size of the filler used.