Peter Stewart Allan

The occurrence of the γ-phase in injection moulded polypropylene in relation to the processing conditions

Abstract Wide-angle X-ray diffraction has been used to characterize different grades of conventionally injection moulded and shear-controlled-orientation injection moulded isotactic polypropylene. The occurrence of the γ-phase in injection mouldings was discussed in particular. A newly defined γ-phase index is used as a criterion for the characterization of mouldings. The γ-phase was shown to be associated with pronounced molecular orientation while the β-phase is indicative of low modulus. Shear-controlled-orientation injection moulding (SCORIM) provided for a good control on the final properties of the mouldings.

Mechanical behavior of injection-molded starch-based polymers

This work evaluates the mechanical performance of injection-molded starch-based copolymers, 60/40 (mol/mol) starch/poly(ethylene vinyl alcohol), and the possibility of improving material properties through deliberately induced anisotropy during processing. Different types of samples were produced by conventional and shear-controlled injection molding (Scorim) and tested under tensile and impact loading. The behavior of three distinct grades is discussed in terms of the respective fracture morphology (evaluated by scanning electron microscopy). A comparison is made between the behavior of conventional and Scorim samples. The results show that the mechanical properties of the materials used were significantly improved by the employment of the Scorim process. The stiffness values of the conventional moldings were doubled, without reducing the ductility of the polymer. The impact data showed a material sensitivity, and consequent loss of properties, to the localized shear imposed to the melt during processing. This situation is attributed to very narrow mold gates (in the case of pingated systems) and leads to much reduced impact performance.

γ Phase in injection moulded isotactic polypropylene

Abstract Wide angle X-ray diffraction has been used to investigate polymorphism in isotactic polypropylene (IPP) mouldings produced by conventional injection moulding and by shear controlled orientation injection moulding (SCORIM). γ Phase was found to form in highly oriented IPP produced by SCORIM, with a marked enhancement of the preferred orientation of the α phase and percentage crystallinity when compared with conventionally moulded IPP.

Optimisation of continuous and pulsed cooling in injection moulding processes

Abstract The concept of pulsed cooling in injection moulding involves cycling the flow of coolant in order that cooling only takes place as and when it is required, as opposed to continuous cooling, where the coolant in run through the channels throughout the entire process. It is claimed that using the pulsed cooling method, with reduced temperature coolants, may reduce cycle times and overall energy consumption for the injection moulding process, when compared with continuous cooling. It is also suggested that this is not at the expense of component integrity since common defects such as warpage, which could come about due to non-uniform cooling of the component, or impedance of flow of the polymer into the mould cavity during injection, do not normally appear. The present study uses a previously validated numerical model in order to optimise the cooling phase of the injection moulding process, for both continuous and pulsed cooling, in order to assess the advantages and disadvantages of each method, with respect to cycle times. In addition, the optimisations were carried out with a view to improve cycle times experimentally, taking into consideration the findings of the study.

Shear controlled orientation technology for the management of reinforcing fibres in moulded and extruded composite materials

Abstract The controlled application of macroscopic shears to solidifying melts containing alignable constituents provides for the management of fibres in, and the production of components to close tolerances. Shear controlled orientation technology (SCORTEC) may be applied to the thermoplastic and thermoset matrix composites, and to ceramic and metal matrix composites processed with the aid of sacrificial polymer binders. The principles of SCORTEC as applied to moulding and extrusion processes will be described, together with examples of typical property enhancement possible, and potential fields of application.