Plastics,Rubber and Composites: Macromolecular Engineering

It has long been a desire for both the polymer academic and industrial (production and process) communities to gain a true understanding of the effects of molecular architecture variables upon polymer properties and the implications for polymer process engineering. It has also long been realised that the greatest chance of gaining this insight is not to work with industrial grade materials, which are usually polydisperse both in terms of molecular weight and architecture, but to study model polymers, synthesised in the laboratory, usually by technically challenging methods such as anionic polymerisation. It is only by using polymers in which the molecular variables such as molecular weight, polydispersity and long chain branching are controlled with a high degree of precision, that we can hope to correlate these variables with key physical properties such as melt rheology, crystallinity and solid state properties. As polymer theoreticians develop ever more sophisticated models to predict the relationships between molecular structure and physical properties the challenge to the synthetic polymer chemist is to design and build (engineer) ever more complex yet well defined molecular structures to allow experimental validation (or otherwise) of the models. Here the author discusses how the synthetic chemist has risen to meet that challenge over the years.

The present work presents a possibility to produce a rubber elastic and electrically conductive polymer material on the basis of dynamic vulcanisates. Thanks to the specific morphology of dynamic vulcanisates and the non-uniform carbon black distribution, carbon black filled dynamic vulcanisates can exhibit a very low percolation threshold of ∼4 wt-%. Keeping the carbon black content low, a broad spectrum of resistivity properties can be achieved by variation of material factors like type and content of rubber phase and filler, concentration of cross-linking agent and compatibiliser and technological factors like mixing time respectively. In comparison with thermoplastic elastomers on the basis of block copolymers dynamic vulcanisates show a distinct lower percolation threshold. Up to a carbon black content of ∼10 wt-% the mechanical properties of carbon black filled dynamic vulcanisates are not negative influenced essentially. To characterise the development of the carbon black dispersion and distribution processes and the conductivity properties in an internal mixer, the method of online measured electrical conductivity is suited very well for carbon black containing rubber mixtures. It could be shown in pre-investigations that this method promises to be a very useful tool for monitoring the mixing processes of carbon black filled dynamic vulcanisates in continuous mixing processes by means of extruders too.

Simulations of the isothermal and non-isothermal filling of a rectangular cavity were carried out for polystyrene using a Giesekus viscoelastic constitutive equation, whereby in the non-isothermal case the thermal resistance at the mould wall was modelled with different heat transfer coefficients to investigate the effect of the thermal resistance on the development of the molecular orientation. Results for stress development along the flow front and the cold wall were compared showing that the principal stress differences in the middle of the flow front are lower than those at the mould wall. In case of the non-isothermal filling, the latter one will increase further while the melt is gradually cooling down, which is especially true if the thermal resistance at the mould wall has been properly considered. Consequently, the high molecular orientation at the wall seems to be rather a result of the non-isothermal shear flow than of the extension at the advancing front as usually assumed.

In water assisted injection moulded parts, structural ribs are usually designed to reinforce the parts as well as to serve as water channels. Water penetration in the channels results in improved mouldability and minimises sinkmarks. However, water leaves a rib core void, which reduces part rigidity. The present study examines the core out shapes of channels in water assisted injection moulded parts. The effects of channel geometry as well as processing conditions such as water injection delay time, water temperature, water pressure, etc., on the core out shapes were investigated. For the parameters selected, melt temperature, short shot size and water injection delay time were found to be the principal factors affecting the core out shapes of moulded parts. The core out geometries in water assisted injection moulded parts were compared with those in gas assisted injection moulded products. Water penetrated the parts with higher core out ratios, which are the ratios of the cross-sectional area of the water (gas) channel to the area of the water (gas) bubble in moulded parts, than gas. The core out geometry of water assisted injection moulded parts mainly resembles that of the water channel, while the void shape of gas assisted injection moulded parts tends to be more round shaped. Channels with ribs on top exhibited the highest bending strengths. Furthermore, a numerical simulation of the temperature distribution in the channels was completed to better interpret the water core out behaviour in water assisted injection moulded products.

A novel inline measuring system can be applied to polymer extrusion to achieve real time data on melt quality. Disturbing particles such as gels, unmolten resins, black spots or gas bubbles can be detected within flowing transparent polymer melts continuously without any lag of time directly during extrusion processing. In the first part of the present paper the state of the art related to particle monitoring in polymer melts in terms of ‘process analytical technology (PAT)' will be presented briefly. After this the microphotometric measuring principle of the used inline process sensors from polymer melt particle (PMP) type will be described as well as various kinds of sensor adaptation to extruder machines. First experiments were realised on labscale extruders applying model particle systems to achieve detailed information on sensor performance characteristics. As a next step industrial polymer systems have been examined on pilot plant extruders. Finally results of these experiments contributed to the transfer of inline particle measurements to production line extruders.

Real time information on process parameters such as residence time distribution (RTD) is essential for diagnosis and control of continuous processes. In the present paper, an improved apparatus for inline measurement of RTD of thermomechanically complex systems was developed. The apparatus possessed many important advantages over those reported in the literatures. A reference detector was added to the system to improve the resistance of the latter to both external and internal disturbances, and it had two light paths instead of one. Meanwhile, a special optical fibre probe with pressure and heat resistance was designed to obtain operating data under high pressure and high temperature circumstance. As an important use of the improved apparatus, the local residence volume distributions of turbine mixing elements were investigated under various operating conditions such as feedrate and screw speed, on the basis of inline measurement of partial RTDs. The working principle of this apparatus is expected to be suitable for various types of process equipments and chemical systems including thermomechanically complex systems.

The Leeds die drawing process has been used to produce biaxially oriented polypropylene pipes with significant enhancement of hoop mechanical properties in terms of tensile modulus and tensile strength owing to a unique orientation of the α crystallites throughout their cross-section. Pendulum impact tests on these pipes show major improvements in impact resistance. Hydrostatic pressure tests were undertaken at room temperature 95 and 110°C. Major improvements in behaviour were found including more than an order of magnitude increase in lifetime at 95°C. Furthermore, the toughness was improved enormously leading to a brittle tough transition temperature below −70°C.