Yes / A methodical 'design of experiment' approach is used to assess the effect of key control parameters on residual wall thickness (RWT) in Gas Assisted Injection Moulding. An empirical model is produced from which the experimental RWT can be determined at any interpolated point. This model includes only those terms with proven statistical significance. The 'true' thermal boundary conditions are determined for a 1-D approximation to the system, this is sufficient to determine the error in a simulation method that enforces coolant temperature as the mould boundary condition for temperature. It is shown that errors in heat-flux and wall temperature are small. A 3-D finite element, pseudo-concentration implementation is presented, with a novel method for simulation of internal gas injection. The simulation is shown to give good agreement with the experimental rate of growth of wall thickness as gas delay is increased; good qualitative agreement is shown for other control parameters.

The gas assisted injection moulding process is an important extension to conventional injection moulding. Gas assist can be applied in a number of ways, but here the penetration of a gas bubble through the polymer melt is of interest. A 3D fi nite element implementation of a pseudo concentration method is employed to simulate the primary penetration of the gas bubble. The wall thickness prediction is an important result since the extent of bubble penetration is sensitive to the remaining melt fraction. A number of methods for experimental measurement are developed to measure characteristics of the gas assisted injection moulding process dynamics and product. Key process variables, on an industrial gas-assist machine, were measured and analysed, leading to an empirical model for wall thickness prediction. Gas delay time and injection velocity are shown to be most influential in controlling residual wall thickness. Simulation results are evaluated against the empirical model. The trends observed, for simulation and experiment, in wall thickness after changes in process variable settings are found to agree qualitatively. The wall thickness prediction is found to be within 10% of the experimentally obtained measurements. / EPSRC

No / The work presented in this paper contributes to a wider research objective aiming at gaining a better understanding of the injection moulding process at microscales. More specifically, it contributes to the development of a new modelling approach combining experimental observation and mathematical modelling to characterise thermal contact resistance that results from the imperfections present on the surfaces when two surfaces are brought in contact. Thus, this paper describes micro and nano structuring technologies (Focus Ion beam and Laser Ablation) used to structure sapphire inserts that are used as ”windows” in the injection moulding process, allowing thermal measurements with a high speed thermal camera whilst sapphire structures are filled with polymer melt. / The Engineering and Physical Sciences Research Council (EPSRC) under the grant EP/I014551/1 and the Interreg IVB project “ECOefficient LASER technology for FACTories of the future”.

A formulation of a subspace identification method for multi-phase processes with applications to rotational moulding and suggestions for improvements and experimental applications. / This thesis focuses on the implementation of subspace identification (SSID) for nonlinear, chemical batch processes by introducing a model identification method for multi-phase processes. In this thesis, a multi-phase process refers to chemical or biological batch-like processes with properties that cause a change in the dynamics during the evolution of the process. This can occur, for example, when a process undergoes a change of state upon reaching a melting point. Existing SSID techniques are not designed to utilize any known, multiphase nature of a process in the model identification stage. The proposed approach, Multiphase Subspace Identification (MPSSID), is conducted by first splitting historical data into phases during the identification step and then building a subspace model for each phase. The phases are then connected via a partial least squares (PLS) model that transforms the states from one phase to the next. This approach makes use of existing SSID techniques that allow for model construction using batches of nonunifrom length. Here, MPSSID is applied to a uniaxial rotational moulding process. In rotational moulding, the dynamics switch as the process undergoes heating, melting, and sintering stages that are visibly distinct and recognizable upon a certain temperature (not time) being reached. Results demonstrate the ability of multiphase models to better predict the temperature trajectories and final product quality of validation batches. As an extension to this rotational moulding analysis, additional MPSSID methods of implementation are proposed and the results are compared. A MPSSID mixed integer linear program is then introduced for implementation within model predictive control. The applications to rotational moulding are presented within the context of plastics manufacturing and the impact of plastic on the global climate crisis, with suggestions for future work. / Thesis / Master of Applied Science (MASc) / The control of chemical processes is an important factor in achieving high quality products. To control a process well, the mathematical model of the system must be accurate. In the past, mathematical models for process control were designed based on engineering approximations. Now, with major advances in computing and sensor technology, it is possible to design a simulation of the entire process. These simulations can be designed using first-principles or black box approaches. First-principles approaches utilize rigorous models that are based on the complex chemical and physical formulas that govern a system. Black box approaches do not look at the first-principles dynamics. They only utilize the measured process inputs and outputs to form a model of the system. They are widely used because of their ease of implementation in comparison to first-principles approaches. In this thesis, a new black box process control model is proposed and is found to yield better theoretical results than existing techniques. This model is tested on data from a plastics manufacturing process called rotational moulding, which involves loading polymer powders into a mould that is simultaneously rotated and heated to yield seamless plastic parts. Lastly, a control framework that is compatible with the new black box model is proposed to be used for future experimental tests.

The use of continuously reinforced thermoplastics have increased in recent years andoffer some significant advantages over their thermoset counterparts. The utilizationof these materials is however still limited due to the labour intensive processingand manufacturing. In the first part of this thesis, the aim is to investigate howcontinuously reinforced thermoplastics can be used in high volume manufacturingof complex components, specifically when combined with injection moulding. Thesecond part will attempt to develop a conceptual manufacturing process and designof a demonstrator part and perform a structural analysis of the component.To answer the first question, an extensive literature study on continuous fibre materialsand thermoplastics was conducted along with research on established and newlydeveloped manufacturing methods such as automated tape laying and fibre placement,tailored fibre placement and 3D printing combined with injection overmoulding. Theconceptual manufacturing process of the demonstrator part was then based on thisresearch and the design was modeled in using finite element analysis.The results shows that continuously reinforced thermoplastics can be used forhigh volume manufacturing of complex components when combined with injectionmoulding. While some of the processing methods are still in an early developmentstage, the techniques have been tested and implemented. The structural analysis of thedemonstrator part shows that the design can withstand the maximum external loadsthus and provide proof of concept. / Användningen av kontinuerligt fiberarmerade termoplaster har ökat under de senasteåren och erbjuder en del betydande fördelar jämfört med armerade härdplaster.Användningen av dessa material är dock fortfarande begränsad på grund av dearbetsintensiva bearbetnings- och tillverkningsmetoderna. I den första delen av dettaexamensarbete är syftet att undersöka hur kontinuerligt fiberarmerade termoplasterkan användas vid tillverkning med hög volym av komplexa komponenter , speciellti kombination med formsprutning. Den andra delen av arbetet kommer att försökautveckla en konceptuell tillverkningsprocess och design av en exempeldel och utföraen strukturell analys av komponenten.För att besvara den första frågan genomfördes en omfattande litteraturstudie omkontinuerliga fibermaterial och termoplaster samt om etablerade och nyutveckladetillverkningsmetoder som automatiserad tejpläggning och fiberplacering,skräddarsydd fiberplacering och 3D-skrivning kombinerat med formsprutning.Den konceptuella tillverkningsprocessen av exempeldelen baserades sedan pålitteraturstudien och designen modellerades och analyserades med finitaelementmetoden.Resultaten visar att kontinuerligt fiberarmerade termoplaster kan användas förhögvolymtillverkning av komplexa komponenter i kombination med formsprutning.Medan några av bearbetningsmetoderna fortfarande är i ett tidigt utvecklingsskede såhar teknikerna testats och implementerats. Den strukturella analysen av exempeldelenvisar att konstruktionen kan motstå de maximala belastningarna och påvisar på så sättgenomförbarhet.

The plastics industry is one of the fastest growing major industries in the world. There is an increase in the amount of plastic used for all types of products due to its light weight and ability to reprocess. For this reason, the reprocessing of thermoplastics and the usability of reprocessed materials are gaining significance, and it is important to produce and consume plastic materials in an environmentally friendly way. In addition, rising raw material cost linked to the increased oil prices encouraged for reusing of the plastic materials. The aim of this research was to study and optimize the injection moulding process parameters to achieve a trade-off between the product cost and product quality, measured through mechanical properties and geometry, based on using regrind ratios. The work was underpinned by a comprehensive study of multiple reprocessing effects in order to evaluate the effect of process parameters, material behaviour, reprocessing effects and possible links between the processing parameters and key properties. Experimental investigations were carried out, in particular, focused on the melt preparation phase to identify key process parameters and settings. Multiple reprocessing stages were carried out; using two types of PP material: unfilled and short glass filled. A series of tests were used to examine product quality (mass, colour and shrinkage) and physical properties (density, crystallinity, thermal stability, fibre length, molecular weight, in-line and off-line viscosity, tensile strength, modulus of elasticity, elongation (%) and flexural strength). This investigation showed that the mouldability of the filled and unfilled PP materials, through the successive reprocessing stages (using 100 % regrind), was observed to be relatively consistent. Given the link between the processing parameters and key product and material properties, it is possible to manufacture products with minimal loss to part quality and mechanical properties. The final phase of the work focused on process optimisation study for short glass fibre filled PP material and the identified key process parameters (melt temperature, screw rotational speed, holding pressure, holding time and injection rate). A response surface experiment was planned and carried out for three reprocessing stages (0 %, 25 % and 50 % regrind). The fitted response surface models were utilised to carry out the trade-off analysis between the operating cost (material cost, energy cost and labour cost) and product quality (dimensions and tensile strength) Based on the optimal moulding conditions, the operating cost was reduced (from stage I as a reference), by 24% and 30 % for stage II and stage III respectively. A small, perhaps undetectable, change in product dimensions was noted. In addition, a small reduction in tensile strength was noted (from stage I as a reference), by 0.4% and 0.1 % for stage II and stage III respectively. The same data was applied in other countries (Australia, USA, Brazil, Libya and China) to manufacture the same product; and it was observed that the cost was reduced with increasing of regrind ratio. But the significant reduction of the cost, essentially, depended on those countries which have low wage rates (e.g. Brazil, Libya and China). For example, the cost of moulded product manufactured in China is £ 0.025 (using 50% of regrind), while the cost of the same product produced in Australia is £ 0.12, hence giving a total saving of 79 % and making it a valuable issue to be considered in industry. / Libyan Embassy

Polylactic acid (PLA) is an aliphatic polyester, derived from sustainable natural sources that is biodegradable and can be industrially composted. This material has been in the spotlight recently due to its sustainability and properties. However it has been invented in 1932 by Carothers and then patented by DuPont in 1954 (Standau et al. 2019). The properties of this material though limit its use for applications mainly in the medical sector and in some cases single use packaging. In this research, PLA based blends with improved rheological and thermomechanical properties are investigated. The focus is based in proposing strategies in improving these properties based on commercial methods and processing techniques. In this work, commercial grade PLA has been blended with polycaprolactone (PCL) and polybutylene succinate (PBS) in binary and ternary formulations via twin screw extrusion. PCL has been known to act as an impact modifier for PLA, but to cause a corresponding reduction in strength. Results showed that the binary PLA blends containing PBS and PCL, had reduced viscosity, elastic modulus and strength, but increased strain at break and impact strength. Morphological and thermal analysis showed that the immiscibility of these additives with PLA caused these modifications. Incorporation of a small loading of PBS had a synergistic effect on the PLA-PCL blend properties. Miscibility was improved and enhanced mechanical properties were observed for a ternary blend containing 5wt% of both PBS and PCL compared to binary blends containing 10% of each additive. To increase heat resistance of PLA, the material’s crystallinity has to be increased. However PLA has a relatively slow crystallisation rate making it difficult and expensive to be used in commercial applications where heat resistance is needed. For this reason the chiral nature of PLA has been used to investigate the effect of stereochemistry of PLA in crystallisation. Optically pure PDLA was added to its enantiomer in small amounts (up to 15%) and the properties and crystallisation mechanism of these blends was investigated. Results showed that the addition of PDLA accelerated crystallinity and developed a stucture that increased heat resistance, melt strength and stiffness. Finally, a processing model of developing a fully stereocomplex PLA part based in commercial techniques is proposed. Injection moulded PLA showed even higher heat resistance without the need of further processing the product (increasing crystallinity). / Floreon

Crystallisation is gaining a lot of interest in pharmaceutical industry to help designing active ingredients with tailored physicochemical properties. Many factors have been found to affect the crystallisation process, including process parameters and material attributes. Several studies in the literature have discussed the role of these parameters in the crystallisation process. A comprehensive study is still missing in this field where all the significant terms are taken into consideration, including the square effect and the interaction terms between different parameters. In this study, a thorough investigation into the main factors affecting crystallisation of a polymeric system, processed via injection moulding, was presented and a sample of response optimisation was introduced which can be mimicked to suite a specific need. Three grades of pure polyethylene oxide; 20K, 200K and 2M, were first characterised using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) and shear rheometry. The onset of degradation and the rate varied according to molecular weight of polyethylene oxide (PEO). The peak melting temperature and the difference in enthalpy between melting and crystallisation were both in a direct proportion with PEO molecular weight. PEO200K and PEO2M struggle to recrystallise to the same extent of the original state at the tested cooling rates, while PEO20K can retain up to a similar crystallinity degree when cooled at 1 °C/min. Onset of crystallisation temperature (Tc1) was high for PEO2M and the difference between the 20K and 200K were pronounced at low cooling rate (20K is higher than 200K). The rheometer study showed that PEO2M has a solid-like structure around melting point which explains the difficulty in processing this grade at a low temperature via IM. PEO20K was almost stable within the strain values studied (Newtonian behaviour). For higher grades, PEO showed a shear thinning behaviour. The complex viscosity for PEO2M is characterised by a steeper slope compared to PEO200K, which indicates higher shear thinning sensitivity due to higher entanglement of the longer chains. For binary blends of PEO, the enthalpy of crystallisation studied by DSC was in direct proportion to the lowest molecular weight PEO content (PEOL %) in PEO20K/200K and PEO20K/2M blends. The effect of PEOL% on Tc1 became slightly pronounced for PEO20K-2M blends where Tc1 exhibited slight inverse proportionality to PEOL% and it became more significant for PEO200K-2M blends. It was interesting to find that Tc1 for the blends did not necessarily lie between the values of the homopolymers. In all binary blends, Tc1 was inversely proportional to cooling rate for the set of cooling rates tested. Thermal analysis using hot stage polarised light microscopy yields different behaviours of various PEO grades against the first detection of crystals especially where the lowest grade showed highest detection temperature. Visual observation of PEO binary blends caplets processed at various conditions via injection moulding (IM) showed the low-quality caplets processed at mould temperature above Tc1 of the sample. The factors affecting crystallisation of injection moulded caplets were studied using response surface methodology for two responses; peak melting temperature (Tm) and relative change in crystallinity (∆Xc%) compared to an unprocessed sample. Mould temperature (Tmould) was the most significant factor in all binary blend models. The relationship between Tmould and the two responses was positive non-linear at the Tmould ˂ Tc1. Injection speed was also a significant factor for both responses in PEO20K-200K blends. For Tm, the injection speed had a positive linear relationship while the opposite trend was found for ∆Xc%. The interaction term found in the RSM study for all models was only between the injection speed and the PEOL % which shows the couple effect between these two factors. Molecular effect was considered a significant factor in all ∆Xc% models across the three binary blends. The order of ∆Xc% sensitivity to the change in PEOL% was 3, 5 and 7 % for 20K-200K, 200K-2M and 20K-2M.

The feasibility of the injection moulding (IM) was explored for the development of novel drug delivery systems. Controlled release formulations were developed using a substituted cellulose derivative, hydroxypropyl methyl cellulose acetate succinate (HPMCAS) and a graft co-polymer (Soluplus®). BCS class II drugs ibuprofen and the felodipine were selected based on their physicochemical properties. In the present work, a homogenous dispersion of drugs in the polymer matrices was achieved using Hot Melt Extrusion (HME) and extruded pellets obtained were used for the development of the injection moulded systems. Four systems were developed using the IM consisting of ibuprofen-HPMCAS, ibuprofen-Soluplus®, felodipine-PEO-HPMCAS and felodipine-Soluplus®. The ibuprofen acts as a good plasticiser compared to felodipine therefore, felodipine containing IM systems required a plasticiser (PEO) when processed with HPMCAS. The analysis of extruded pellets and injection moulded systems using modulated DSC (MDSC) and Raman spectroscopy confirmed the formation of an amorphous molecular dispersion (i.e solid solution) in the case of all four systems. The phase separation behaviour and the amorphous stability of the systems was studied at various stress conditions. This revealed the “surface crystallisation” behaviour of the ibuprofen-HPMCAS systems. Temperature-composition phase diagram constructed based on the melting point depression and the Flory-Huggins lattice solution theory provided the explanation for the phase separation and crystallisation behaviour of ibuprofen-HPMCAS systems. The advanced characterisation techniques like DMA, 2D XRD and 3D laser microscopy provided the detailed understanding of crystal habits, phase seperation and surface crystallisation. The significant effect of the stress conditions on the rate of shrinkage was observed where, higher shrinkage tendency of a HPMCAS IM system was observed compared to Soluplus® IM systems. The extruded pellets provided the faster drug release compared to the moulded tablets suggests the effect of particle size as well as the densification during IM on the dissolution rate of the dosage form. The nature of the polymer and processing history were the contributing factors for the dissolution of the dosage forms. / The thesis is hardbound in two volumes. Volume II starts at Chapter 5, page 135.

The emergence of microneedle (MN) technologies offers a route for a pain free, straightforward and efficient way of transdermal drug delivery, but technological barriers still exist which pose significant challenges for manufacture of MN systems with high volume outputs at low cost. The main aim of this research was to develop new ways for MN manufacture primarily using micro-injection moulding processes with high performance engineering thermoplastics. During the moulding process these polymeric melts will be subjected to extreme stress and temperature gradients and detailed material characterisation combined with in-line monitoring is desirable to optimise the moulding parameters and will help in achieving sharp microneedles with acceptable quality. Hence high shear rheology of these selected materials was performed at wall shear rates carried out in excess of 107 s-1 over a range of temperatures to predict the flow behaviour of polymer melts at such high shear strain rates. This information was fed into injection moulding simulation software tools (Moldflow) to assist the MN production process design. The optimal design was then used to produce a full 3D solid model of the injection mould and mould insert. Furthermore various design of experiments were conducted considering input parameters such as injection pressure, injection speed, melt temperature, filling time and mould cavity temperature. Response variables including product quality and data acquired from the cavity pressure and temperature transducers were used to optimise the manufacturing process. The moulded MNs were geometrically assessed using a range of characterisation techniques such as atomic force microscopy, confocal microscopy and scanning electron microscopy. An attempt to make hollow MNs was performed and encountered many challenges like partial cavity filling and part ejection during processing. Studies were carried out to understand the problem and identified the major problem was in tool design and improvements to the moulding tool design were recommended. Plasma treatment and mechanical abrasion were employed to increase the surface energy of the moulded polymer surfaces with the aim of enhancing protein adsorption. Sample surface structures before and after treatment were studied using AFM and surface energies have been obtained using contact angle measurement and calculated using Owens-Wendt theory. Adsorption performance of bovine serum albumin and release kinetics for each sample set was assessed using a Franz diffusion cell. Results indicate that plasma treatment significantly increases the surface energy and roughness resulting in better adsorption and release of BSA. To assist design-optimisation and to assess performance, a greater understanding of MN penetration behaviour is required. Contact stiffness, failure strength and creep behaviour were measured during compression tests of MN against a steel surface, and in-vitro penetration of MNs into porcine skin. The MN penetration process into porcine skin was imaged using optical coherence tomography. Finally, a finite element model of skin was established to understand the effect of tip geometry on penetration. The output of findings from this research will provide proof of concept level development and understanding of mechanisms of MN penetration and failure, facilitating design improvements for micro-injection moulded polymeric MNs.