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The primary aim of the study was to evaluate the validity of the elasto-plastic constitutive models implemented in the Finite Element Analysis (FEA) software ANSYS~. This was carried out comparing experimental tensile, bending and puncture or plate penetration test results with the corresponding FEA calculations. The studies were carried out in concern to the slow rate testing and finite element analysis of two thermoplastic materials. The selected materials were a blend of Polycarbonate (PC) and Acrylonitrile-Butadiene-Styrene (ABS), Bavblend" T45 from Bayer Material Science, as an amorphous polymer and a Polypropylene (PP) copolymer, BE677AI from Borealis, as a semi-crystalline polymer. The uniaxial tensile behavior of both materials was used to generate material data input for the simulation software. Due to post yield uncertainties when measuring true values of stress and strain with conventional extensometric devices, an iterative approach was presented here as a solution for measuring large local plastic strains in tensile specimens. The experimental three point bend test and the plate perforation test with hemispherical darts, were used as correlation tests with simulations in order to validate not only the used constitutive elasto-plastic models based on the Von Mises yield criteria, but also to check the influence of different simulation variables. The parameters studied were the element type, mesh density, friction and contact conditions between different parts. Additionally, another yielding criteria, the hydrostatic pressure sensitive Drucker-Prager model, was analysed. It was observed that for both materials, the use of a classical approach for obtaining true values of stress and strain in conjunction with a Von Mises yielding criteria gave acceptable results for the studied testing modes. However, the input curves did not closely correlate with the tensile test results. This was overcome to using an iterative method to correct the input curves to match then to the experimental tensile tests. Being a precise procedure for uniaxial cases, it was observed that for bending or puncture problems this method offered stiffer responses than using the classical approach of stress-strain conversions. Finally, the Drucker-Prager criterion was able to capture in a more precise way bending dominated problems than the usual Von Mises yielding criteria.

This thesis is concerned with the effect of polymer structure on miscibility of the three component blends based on poly(lactic acid) (PLA) with using blending techniques. The examination of novel PLA homologues (pre-synthesised poly(a-esters)), including a range of aliphatic and aromatic poly(a-esters) is an important aspect of the work. Because of their structural simplicity and similarity to PLA, they provide an ideal system to study the effect of polyester structures on the miscibility of PLA polymer blends. The miscibility behaviour of the PLA homologues is compared with other aliphatic polyesters (e.g. poly(e-caprolactone) (PCL), poly(hydroxybutyrate hydroxyvalerate) (P(HB-HV)), together with a series of cellulose-based polymers (e.g. cellulose acetate butyrate (CAB)). The work started with the exploration the technique used for preliminary observation of the miscibility of blends referred to as “a rapid screening method” and then the miscibility of binary blends was observed and characterised by percent transmittance together with the Coleman and Painter miscibility approach. However, it was observed that symmetrical structures (e.g. a1(dimethyl), a2(diethyl)) promote the well-packing which restrict their chains from intermingling into poly(L-lactide) (PLLA) chains and leads the blends to be immiscible, whereas, asymmetrical structures (e.g. a4(cyclohexyl)) behave to the contrary. a6(chloromethyl-methyl) should interact well with PLLA because of the polar group of chloride to form interactions, but it does not. It is difficult to disrupt the helical structure of PLLA. PLA were immiscible with PCL, P(HB-HV), or compatibiliser (e.g. G40, LLA-co-PCL), but miscible with CAB which is a hydrogen-bonded polymer. However, these binary blends provided a useful indication for the exploration the novel three component blends. In summary, the miscibility of the three-component blends are miscible even if only two polymers are miscible. This is the benefit for doing the three components blend in this thesis, which is not an attempt to produce a theoretical explanation for the miscibility of three components blend system.

Thermosetting epoxy resins blended with aromatic thermoplastics are of significant commercial interest in several areas including aerospace, transportation and electronics. These materials offer an excellent combination of mechanical properties ease of processing and overall component cost. A more complete and fundamental understanding of these materials could potentially lead to a new generation of thermoplastic-thermoset blends with enhanced properties that would extend their use into new applications. This thesis studies the reaction induced phase separation behaviour of a thermosetting epoxy resin blended with an aromatic polyethersulphone thermoplastic and explores the link between morphology and physical properties. The phase separation behaviour of the thermoplastic-thermoset blend is studied using a combination of Small Angle Light Scattering (SALS), Differential Scanning Calorimetry (DSC) and Polarised Light Microscopy. A large part of this thesis involved the design and build of specialised SALS equipment that enabled the phase separation of the thermoplastic-thermoset blends to be studied dynamically. The studies show that in this thermoplastic-thermoset blend the mechanism of phase separation appears to be, without exception, spinodal decomposition. There was no evidence of phase separation occurring by nucleation and growth in these blends. The particulate morphologies seen in the thermoplastic-thermoset blends appear to form by the break up of a percolating network that initially forms by spinodal decomposition. This behaviour is termed Percolation to Cluster Transformation (PCT).Cahn-Hilliard theory was used to analyse the SALS data from the reacting thermoplastic-thermoset blends to give kinetic information about the phase separation process. These studies show that this particular blend exhibits Lower Critical Solution Temperature (LCST) behaviour. The work also shows that Cahn-Hilliard theory does not fully describe the spinodal decomposition processes occurring in these thermoplastic-thermoset blends. The effect of blend composition, cure temperature and epoxy functionality on phase separation behaviour are studied. This shows that in certain formulations especially around the critical formulation of the blend both primary and secondary spinodal decompositions occur during cure. This can lead to thermoplastic-thermoset blend formulations that have very unique, and previously unreported, morphologies for these systems. These novel morphologies resemble sub-included or salami morphologies similar to that observed in rubber modified polystyrene (HIPS) but have in fact formed by multiple PCT occurring during cure. This study shows that moisture can significantly influence the properties of epoxy resin based systems. It also appears that a phase inverted morphology consisting of a continuous thermoplastic rich phase with a dispersed thermosetting rich phase appears to offer great advantage in terms of fracture and mechanical properties after both dry and moisture conditioning. The phase-inverted morphology also appears to significantly reduce the moisture ingress of the epoxy blend.

A wide range of thermoplastic composites (TPC) are now being used in automotive applications including vehicle front-end structures, load floors, seat backs, door cassettes and instrument panels. Long fibre thermoplastics (LFT), glass mat thermoplastics (GMT) and fully structural materials such as woven commingled fabric TPCs, e.g. Twintex®, provide a range of properties and mouldability appropriate to specific applications.

A study into the feasibility of thermal welding of an unstable thermoplastic has been undertaken. A heater wire embedded in a diffusion promoting interlayer has been used to accelerate interdiffusion between two poly(vinylchloride) (PVC) plaques. Interlayers consisted of a compatible vinyl resin and a plasticiser. Both normal resistance and an isothermal induction process were used as heat sources, with lap shear testing used to determine the strength of such systems. Vickers hardness testing has been used to ascertain the extent of diffusion and immersion diffusion testing was used to find the activation energy for the process. Micro thermal analysis (MTA) in conjunction with laser induced mass analysis (LIMA), ultra-violet fluorescence microscopy and microscopic infrared techniques were used to study degradation. It has been found that the use of an interlayer allows thermal welding of PVC without deleterious degradation. The concentration and type of plasticiser was found critical in producing a strong weld. Low concentrations of plasticiser did not cause sufficient diffusion and high concentrations of plasticiser in the interlayer produced a weak interface; the optimum amount was dependent on the diffusion coefficient of the plasticiser. Fast fusing plasticisers resulted in higher lap shear strength because they cause a greater extent of diffusion during a constant welding time than slower fusing plasticisers. Degradation products were detected in proximity to the heater wire. Resistance heating was found to cause an exponential increase in degradation closer to the wire while isothermal heating produced a degradation profile with a plateau region next to the heater wire.

The suspension polymerisation of methyl methacrylate (MMA), using polyelectrolyte solutions, sodium polymethacrylate (PMA–Na) and ammonium polymethacrylate (APMA) as suspending agents (stabilisers) was experimentally investigated in this project. The topics examined were: the rheological behaviour of the aqueous polyelectrolyte solutions; the factors that affect drop and particle sizes, dispersion and stabilisation mechanism; and the factors that affect the critical conversion where the onset of the gel effect occurs. The main advantage of using PMA–Na and APMA as stabilisers for the suspension polymerisation is that these stabilisers are not grafted on to the polymer beads' surface, and they are easily washed off and removed after the polymerisation.