Plastics,Rubber and Composites: Macromolecular Engineering

A family of random co-poly(amic acid)s containing 4,4′-oxydianiline (ODA) moiety were synthesised in N, N′-dimethylacetamide. The co-poly(amic acid) solutions were used as spinning dope for dry jet wet spinning process into as spun poly(amic acid) (PAA) fibres. The polyimide (PI) fibres were obtained from PAA fibres after being imidised and drawn in furnace. The processability and mechanical properties of the fibres were notably improved by incorporating ODA into 3,3′,4,4′-biphenyltetracarboxylic dianhydride/p-phenylenediamine (BPDA/PPD) backbone. The best strength and modulus of BPDA/PPD/ODA PI fibre (diamine mole ratio of PPD/ODA = 85∶15) attained 2·25 and 96·5 GPa respectively, which were approximately three times the tenacity of the BPDA/PPD PI fibre. The SEM image showed that the cross-section of each stage fibres was round and void free. In addition, ‘skin–core’ and microfibrillar structure were not observed. The thermal properties of PI fibres were also investigated. The results showed that the PI fibres have excellent thermal stability; moreover, the dimensional stability and structural homogeneity of the fibres were significantly improved by heat drawn stage. T_g was found to be ∼290°C by thermomechanical and dynamic mechanical analyses. The X-ray (wide angle X-ray diffraction and small angle X-ray scattering) experiments indicated that the ordering degree of longitudinal and lateral stacks, as well as the molecular orientation of PI fibre, was improved in the preparation process of fibres. Furthermore, the mechanical properties of fibres are profoundly affected by the heat drawn conditions.

The temperature and frequency dependent viscoelasticity of carbon black filled rubber is investigated. Temperature sweep and frequency sweep dynamic mechanical analysis tests are performed to investigate the frequency dependent glass transition temperature and to identify the thermorheological nature of the material. The test results show that master curves of dynamical properties can be constructed by horizontal shifts along the frequency axis alone and cover a frequency range of 21 decades, verifying the material's thermorheological simplicity. This simplicity is confirmed by van Gurp–Palmen and Cole–Cole plots. Moreover, the temperature dependence of the shift factor is modelled well by both the Williams–Landel–Ferry equation and the Arrhenius equation.

This study considers the mechanical properties of a range of thermosetting resin systems, including systems with bioderived content, and associated natural fibre composites. The bioderived resin systems (22 and 40% biocontent) demonstrated similar tensile strength to standard resin systems, indicating their potential to be a substitute for such systems. To optimise the performance of the natural fibre composites, the reinforcement needed to be dried before composite processing. The stiffness and strength of the natural fibre systems improved with degree of alignment, as expected, and with the use of a semiprocessed fibre; in this way, the properties approached those of chopped strand mat E-glass composites. Even the natural fibre composite with the lowest tensile performance still demonstrated a fracture toughness that was halfway in between the E-glass composite and the resin system.

Novel methods for process simulation and cost analysis have been applied during manufacturing process development of a rotor blade pitch horn. The aim is to reduce costs and lead time on the one hand and to enhance part quality on the other hand. Fabric draping has been simulated using the kinematic draping code PAM-QUIKFORM incorporating new processing strategies. Draping strategies were optimised using a genetic algorithm taking into account manufacturing constraints, which led to a fabric shear reduction by up to 10° with the optimised strategy implemented in manufacturing. A novel material generation of prebindered carbon fibre tows has been used to enhance rigidity and dimensional accuracy of the preform and to minimise processing time. State-of-the-art preforming technology has been incorporated in the process significantly increasing the degree of automation. The process had been analysed based on the activity based costs methodology deriving product costs as sum of costs of all activities involved. Development efforts have been concentrated based on the analysis in order to optimise cycle times with a nearly even duration of the subprocesses. In comparison to a manual prepreg manufacturing process, cost savings with the novel, semiautomated preforming process could be quantified to ∼20%.

Electrical, thermal and mechanical properties of conductive polymer composites were investigated in the present work. The composites were polyamide-6 (PA6)/stainless steel fibre (SSF) (PA6 matrix filled by SSFs) and PA6/SSF/CNT (PA6 matrix filled by SSFs and carbon nanotubes) systems. The distribution of fillers in the composites was observed by scanning electron microscopy. The relation between the resistivity of the composites and the mass fraction of fillers was determined, and the conductive percolation threshold value was approximately evaluated according to the sudden dropping of the resistivity. Thermal and mechanical properties of the composites were investigated by means of dynamic mechanical analysis, thermogravimetric analysis and differential scanning calorimeter analysis.

Influence of chain extender (CE) and bonding agent (BA) on the mechanical, interfacial and ballistic properties of AP/Al/HTPB composite is determined and compared. Results indicate a relationship between the two properties. The composite without the additives exhibited extremely poor mechanical properties whereas maximum tensile strength and ultimate elongation is achieved by introducing CE in the conventional composite. Better mechanical properties in this modified composite also contributed in improving the ballistic behaviour. SEM analysis of the condensed combustion residues obtained from the propellant burnt in open atmosphere reveals a considerable decrease in the agglomerate size in the modified composite. This effect is reflected as higher specific impulse in this composite, determined from thrust time profile obtained in static bed test. Pressure time profile for the modified composite manifests a stable and consistent burning at the tail end in tubular geometry as opposed to the conventional system that exhibits a susceptible and unstable tail-off.