One-, two- and three-dimensional transient heat transfer finite element models are developed to simulate the resistance welding process of pre-consolidated unidirectional AS4 carbon fibre reinforced Poly-ether-ether-ketone (APC-2/AS4) laminates with a metal mesh heating element, in a lap-shear configuration. The finite element models are used to investigate the effect of process and material parameters on the thermal behaviour of the coupon size welds, yielding to a better understanding of the process. The 1-D model determines: (a) the importance of including the latent heat of PEEK, and (b) the through-thickness temperature gradient away from the edges, for different tooling plate materials. The 2-D model simulates the cross-section of the process, considering the convective and irradiative heat losses from the areas of the heating element exposed to air. The 3-D model includes the heat conduction along the length of the laminates, to fully depict the thermal behaviour of the welds. Finally, the models are compared with experimental data.

Thesis (M.Tech.: Mechanical Engineering)-Dept. of Mechanical Engineering, Durban University of Technology, 2007 xiii, 101 leaves / Polymer nanocomposites may be defined as structures that are formed by infusing layered-silicate clay into a thermosetting orthermoplastic polymer matrix. The nanocomposites are normally particle-filled polymers for which at least one dimension of the dispersed particles is in nanoscale. These clay-polymer nanocomposites have thus attracted great interest in industry and academia due to their exhibition of remarkable enhancements in material properties when compared to the virgin polymer or conventional micro and macro-composites. The present work describes the synthesis, mechanical properties and morphology of nano-phased polypropylene structures. The structures were manufactured by melt- blending low weight percentages of montmorillonite (MMT) nanoclays (0.5, 1, 2, 3, 5 wt. %) and polypropylene (PP) thermoplastic. Both virgin and infused polypropylene structures were then subjected to quasi-static tensile tests, flexural tests, micro-hardness tests, impact testing, compression testing, fracture toughness analysis, dynamic mechanical analysis, tribological testing. Scanning electron microscopy studies were then conducted to analyse the fracture surfaces of pristine PP and PP nanocomposite. X-ray diffraction studies were performed on closite 15A clay and polypropylene composites containing 0.5, 1, 2, 3 and 5 wt. % closite 15A nanoclay to confirm the formation of nanocomposites on the addition of organo clays. Transmission electron miscopy studies were then performed on the PP nanocomposites to determine the formation of intercalated, exfoliated or agglomerated nanoclay structures. Analysis of test data show that the mechanical properties increase with an increase in nanoclay loading up to a threshold of 2 wt. %, thereafter the material properties degrade. At low weight nanoclay loadings the enhancement of properties is attributed to the lower percolation points created by the high aspect ratio nanoclays. The increase in properties may also be attributed to the formation of intercalated and exfoliated nanocomposite structures formed at these loadings of clay. At higher weight loading, degradation in mechanical properties may be attributed to the formation of agglomerated clay tactoids. Results of XRD, transmission electron microscopy studies and scanning electron microscopy studies of the fractured surface of tensile specimens verify these hypotheses.

Publics are facing a great challenge of infections from pathogens. Polyethylene terephthalate (PET) is widely used in health-care settings. It is vital to develop effective and regenerable antimicrobial PET. In this study, effective antibacterial modification of PET was achieved by immobilizing N-halamine biocide poly (N-chloroacrylamide) (PCA) onto PET through the formation of a surface interpenetrating network. The successful and uniform immobilization was confirmed by FTIR and XPS. The immobilization is durable to a 72 hours soxhlet extraction. Surface morphology of the fabrics did not significantly change after modification with IP less than 20%. The modified fabric can bring 100% reduction of 10e6 CFU/ml of several clinical important bacteria in 15 min contact. The regenerability of N-halamine on PAM modified PET was studied by FTIR, titration and N analysis. After 30 regeneration cycles, the PAM-DVB network modified PET was still able to provide 100% reduction of HA-MRSA in 20 min contact.

Low profile additives (LPA) are thermoplastics that are incorporated to unsaturated polyester (UP) resins in order to improve the surface finish of UP/fibreglass composites, widely used in automotive applications. The effect of using LPA on the thermo-mechanical properties of resin transfer moulded UP/fibreglass composites is investigated. The flexural and shear properties are measured by three-point bending tests. The trend of these mechanical properties is identified for 0% to 40% LPA content. All the mechanical properties like flexural strength, flexural modulus and short beam strength reduce upon addition of LPA. The specimens fail by tension in the flexural test and show a mixed shear/tension failure mode in case of short beam tests. From scanning electron microscopy, morphological change of the fractured surface is observed with an LPA-rich phase. Glass transition temperature (Tg) measured by thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA) show reproducible data and compare well with each other. Tg is improved by LPA addition due to the development of a more compatible system compared to neat resin. Differential scanning calorimetry (DSC) is also performed to detect Tg, which gives unreliable results.

In den vergangenen Jahren wurden stetig wachsende Produktionskapazitäten von Biokunststoffen aus nachwachsenden Rohstoffe nverzeichnet. Trotz großer Produktionskapazitäten und einem geeigneten Eigenschaftsprofil findet Stärke nur als hydrophile, mit Weichmachern verarbeitete thermoplastische Stärke (TPS) in Form von Blends mit z. B. Polyestern Anwendung. Gleiches gilt für Kunststoffe auf Proteinbasis. Die vorliegende Arbeit hat die Entwicklung von Biokunststoffen auf Stärkebasis zum Ziel, welche ohne externe Weichmacher thermoplastisch verarbeitbar und hydrophob sind sowie ein mechanisches Eigenschaftsprofil aufweisen, welches ein Potenzial zur Herstellung von Materialien für eine Anwendung als Verpackungsmittel bietet. Um die Rohstoffbasis für Biokunststoffe zu erweitern, soll das erarbeitete Konzept auf zwei industriell verfügbare Proteintypen, Zein und Molkenproteinisolat (WPI), übertragen werden. Als geeignete Materialklasse wurden Fettsäureester der Stärke herausgearbeitet. Zunächst fand ein Vergleich der Säurechlorid-Veresterung und der Umesterung von Fettsäurevinylestern statt, woraus letztere als geeignetere Methode hervorging. Durch Variation der Reaktionsparameter konnte diese optimiert und auf eine Serie der Fettsäurevinylester von Butanoat bis Stearat für DS-Werte bis zu 2,2-2,6 angewandt werden. Möglich war somit eine systematische Studie unter Variation der veresterten Fettsäure sowie des Substitutionsgrades (DS). Sämtliche Produkte mit einem DS ab 1,5 wiesen eine ausgprägte Löslichkeit in organischen Lösungsmitteln auf wodurch sowohl die Aufnahme von NMR-Spektren als auch Molmassenbestimmung mittels Größenausschlusschromatographie mit gekoppelter Mehrwinkel-Laserlichtstreuung (GPC-MALLS) möglich waren. Durch dynamische Lichtstreuung (DLS) wurde das Löslichkeitsverhalten veranschaulicht. Sämtliche Produkte konnten zu Filmen verarbeitet werden, wobei Materialien mit DS 1,5-1,7 hohe Zugfestigkeiten (bis zu 42 MPa) und Elastizitätsmodule (bis 1390 MPa) aufwiesen. Insbesondere Stärkehexanoat mit DS <2 sowie Stärkebutanoat mit DS >2 hatten ein mechanisches Eigenschaftsprofil, welches insbesondere in Bezug auf die Festigkeit/Steifigkeit vergleichbar mit Verpackungsmaterialien wie Polyethylen war (Zugfestigkeit: 15-32 MPa, E-Modul: 300-1300 MPa). Zugfestigkeit und Elastizitätsmodul nahmen mit steigender Kettenlänge der veresterten Fettsäure ab. Ester längerkettiger Fettsäuren (C16-C18) waren spröde. Über Weitwinkel-Röntgenstreuung (WAXS) und Infrarotspektroskopie (ATR-FTIR) konnte der Verlauf der Festigkeiten mit einer zunehmenden Distanz der Stärke im Material begründet werden. Es konnten von DS und Kettenlänge abhängige Glasübergänge detektiert werden, die kristallinen Strukturen der langkettigen Fettsäuren zeigten einen Schmelzpeak. Die Hydrophobie der Filme wurde anhand von Kontaktwinkeln >95° gegen Wasser dargestellt. Blends mit biobasierten Polyterpenen sowie den in der Arbeit hergestellten Zein-Acylderivaten ermöglichten eine weitere Verbesserung der Zugfestigkeit bzw. des Elastizitätsmoduls hochsubstituierter Produkte. Eine thermoplastische Verarbeitung mittels Spritzgießen war sowohl für Produkte mit hohem als auch mittlerem DS-Wert ohne jeglichen Zusatz von Weichmachern möglich. Es entstanden homogene, transparente Prüfstäbe. Untersuchungen der Härte ergaben auch hier für Stärkehexanoat und –butanoat mit Polyethylen vergleichbare Werte. Ausgewählte Produkte wurden zu Fasern nach dem Schmelzspinnverfahren verarbeitet. Hierbei wurden insbesondere für hochsubstituierte Derivate homogenen Fasern erstellt, welche im Vergleich zur Gießfolie signifikant höhere Zugfestigkeiten aufwiesen. Stärkeester mit mittlerem DS ließen sich ebenfalls verarbeiten. Zunächst wurden für eine Übertragung des Konzeptes auf die Proteine Zein und WPI verschiedene Synthesemethoden verglichen. Die Veresterung mit Säurechloriden ergab hierbei die höchsten Werte. Im Hinblick auf eine gute Löslichkeit in organischen Lösungsmitteln wurde für WPI die Veresterung mit carbonyldiimidazol (CDI)-aktivierten Fettsäuren in DMSO und für Zein die Veresterung mit Säu-rechloriden in Pyridin bevorzugt. Es stellte sich heraus, dass acyliertes WPI zwar hydrophob, jedoch ohne Weichmacher nicht thermoplastisch verarbeitet werden konnte. Die Erstellung von Gießfolien führte zu Sprödbruchverhalten. Unter Zugabe der biobasierten Ölsäure wurde die Anwendung von acyliertem WPI als thermoplastischer Filler z. B. in Blends mit Stärkeestern dargestellt. Im Gegensatz hierzu zeigte acyliertes Zein Glasübergänge <100 °C bei ausreichender Stabilität (150-200 °C). Zeinoleat konnte ohne Weichmacher zu einer transparenten Gießfolie verarbeitet werden. Sämtliche Derivate erwiesen sich als ausgeprägt hydrophob. Zeinoleat konnte über das Schmelzspinnverfahren zu thermoplastischen Fasern verarbeitet werden. / In recent years, a steadily growing production capacity of bioplastic based on renewable resources was noticed. Despite its huge production capacities and an appropriate property profile (ubiquitous occurrence, easy extraction), starch is only applied in addition of plasticizers in a hydrophilic, thermoplastic form in blends with e. g. polyesters. The same applies to bioplastics based on proteins. The actual study has the aim to develop starch-based bioplastics, which are hydrophobic, thermoplastic without the addition of any plasticizer and have mechanical properties to be a suitable alternative material in the area of food packaging. To obtain a variation of the raw materials for bioplastics, the concept shall be applied to two types of industrial available proteins, whey protein isolate (WPI) and Zein. Fatty acid esters of starch came out to be a suitable class of materials. Initially, the methods of esterifying acid chlorides and the transesterification of fatty acid vinyl esters were compared with the latter being more appropriate. Reaction parameters of this method were optimized and it was applied to a complete series of vinyl ester reagents (butanoate to stearate), leading to degree of substitution (DS)-values up to 2.2-2.6. With that, a systematic study of the variation of the fatty acid ester chain as well as the DS became possible. It came out that all products with a DS >1.5 showed a well-marked solubility in organic solvents, whereby solution NMR-studies as well as measurements of the molecular weight distributions by using size exclusion chroma-tography with multi-angle laser light scattering (SEC-MALLS) were possible. The different solution behavior was studied by dynamic light scattering (DLS). All soluble products could be formed into films via casting, where materials with a DS of 1.5-1.7 showed the highest values concerning tensile strength (up to 42 MPa) and Youngs modulus (up to 1390 MPa). Especially starch hexanoate with DS <2 and starch butanoate with a DS >2 revealed mechanical properties which are comparable to usually applied polymers for food packaging, e. g. polyethylene (tensile strength: 15-20 MPa, E-Mod: 300-1300 MPa). Tensile strength and Youngs modulus were reduced with increasing length of the esterified fatty acid. Wide-angle X-Ray scattering (WAXS) and infrared spectroscopy (ATR-FTIR) explained this tendency by an increasing intermolecular distance of the starch in the material. Glassy transitions of the materials were detected and showed a dependency on the type of esterified fatty acid and the DS. The crystalline structures of the esterified long-chain fatty acids revealed a melting peak. All films came out to be hydrophobic with contact angles against water >95°. The tensile strength and the Youngs modulus of the highly substituted products could be further improved by blending them with biobased polyterpenes as well as the acylated Zein. A thermoplastic processing without the use of any plasticizer additives was possible for products with a medium and high DS. Homogeneous, transparent testing specimens were obtained. The specific mechanical values were comparable with the casted films, although the highest values for the tensile strength and the elongation were lower. Investigations of the hardness showed comparable values to polyethylene. Selected samples were further processed to fibers by melt spinning. Especially starch esters with high DS revealed homogeneous fibers with a significant increase in the tensile strength compared to the film or testing specimen. Even fatty acid starch esters with a medium DS were processed by the melt-spinning, but their higher glassy transition lead to a reduced softening behavior. To transfer this concept to the class of proteins, different methods of synthesis were studied in the first step, which differed in their amount of acylation. The acylation using fatty acid chlorides lead to highest values. With regard to a well-marked organic solvent solubility, in the case of WPI the acylation with carbonyldiimidazol (CDI)-activated fatty acid was established. For Zein, the acid chloride acylation in pyridine gave the desired results. It came out the fatty acid acylated soluble WPI could not be thermoplastic processed without additional plasticizers. By using biobased oleic acid as additive, the potential of acylated WPI as a thermoplastic filler in blends with e. g. fatty acid esters of starch was shown. In contrast, fatty acid acyl derivatives of Zein revealed well marked glassy transitions <100 °C with an adequate thermal stability. While Zeinoleate could be formed into transparent films via solvent casting without any plasticizer additives, low amounts of tall oil enabled film-forming in the case of acyl derivatives with shorter fatty acids as well. All derivatives revealed a well-marked hydrophobicity. Finally, Zeinoleate was thermoplastically processed into fibers by melt-spinning without any further additives.

One of the current problems faced by mankind is the problem of safe disposal of waste rubber. Statistics show that the number of waste tires is continuously increasing at a very rapid rate. Since rubber materials do not decompose easily (due to their crosslinked structure), they end up being a serious ???environmental problem???. An intuitive solution to prevent the accumulation of the scrap tires is to continuously reuse them. A new patented reclamation method was discovered in our laboratory, which makes use of a twin screw extruder (TSE) in order to produce reclaimed rubber (referred as devulcanized rubber (DR) from here on) of very high quality. Also, this method has proven to be more economical than other commercial reclaiming methods. Products made solely from a reclaimed material face challenges from those made by virgin materials because of relatively poor properties. However, the striking advantage of using reclaimed rubbers is the cost reduction. Hence, it is important to work on establishing methods by which these reclaimed rubbers could be efficiently used and incorporated into present day products. The deterioration of properties could be minimized by blending them with varying amounts of other materials. A possibility in this direction is manufacturing of thermoplastic vulcanizates (TPVs) using reclaimed rubber and general purpose thermoplastics. In accordance with this idea, the focus of this research is to prepare DR and polypropylene (PP) based TPVs. DR is unique as the rubber itself consists of two phases- one phase consisting of uncrosslinked (including devulcanized rubber molecules), and the other phase consisting of crosslinked (un-devulcanized) rubber. These un-devulcanized crumbs act as stress concentrators because they do not break-up easily, and lead to poor physical properties. Hence, this project tries to find out ways to increase the interfacial adhesion between the rubber and PP by using reactive and non-reactive techniques. Preliminary experiments were carried out in a batch mixer to compare DR and rubber crumb (CR). DR based TPVs showed better properties than CR based TPVs, however, the properties were not useful for commercial applications. Sulphur based dynamic vulcanization was studied in a batch mixer and found to be not effective in improving the properties of DR based blends. On the other hand, DCP/ sulphur based curing system was found to show significant improvement in properties. Therefore, DCP/sulphur based curing package was studied in detail on the blends consisting of DR and PP. The optimum ratio of DCP/sulphur was found to vary depending on the ratio of DR/PP. A hypothesis regarding the mechanism of DCP/sulphur curing has been proposed, which seem to correlate well with the experimental results observed. Additionally, it was determined that DR prepared from tire rubber (DRT) performed better than DR prepared from waste EPDM (DRE) for the curing system used. Accordingly, experiments on a TSE were carried out using DRT and a combination of compatibilizing resins and curatives. This combination showed a drastic improvement in blends properties and once again the optimum ratio of compatibilizing resins seemed to depend on the ratio of DRT/PP. As a result of the work, successful strategies based on reactive compatibilization techniques were developed in order to prepare useful TPVs having up to 70% DR. A series of compatibilization techniques has been evaluated using design of experiments and various characterization techniques such as mechanical tests, scanning electron microscopy, thermal analysis and crosslink density measurements. This led to the development of a formulation, which could improve the blend properties significantly. A tensile strength of around 10 MPa and an elongation-at-break of 150-180 % could be achieved for devulcanized rubber (70%) based TPVs, which has broadened the scope for its commercial applications. In addition to that, the process was established on a TSE that has enabled a continuous and steady production of these TPVs with reasonable throughputs.

Publics are facing a great challenge of infections from pathogens. Polyethylene terephthalate (PET) is widely used in health-care settings. It is vital to develop effective and regenerable antimicrobial PET. In this study, effective antibacterial modification of PET was achieved by immobilizing N-halamine biocide poly (N-chloroacrylamide) (PCA) onto PET through the formation of a surface interpenetrating network. The successful and uniform immobilization was confirmed by FTIR and XPS. The immobilization is durable to a 72 hours soxhlet extraction. Surface morphology of the fabrics did not significantly change after modification with IP less than 20%. The modified fabric can bring 100% reduction of 10e6 CFU/ml of several clinical important bacteria in 15 min contact. The regenerability of N-halamine on PAM modified PET was studied by FTIR, titration and N analysis. After 30 regeneration cycles, the PAM-DVB network modified PET was still able to provide 100% reduction of HA-MRSA in 20 min contact.

Injection molding technology is utilized for a wide range of applications from mobile phone covers to bumper fascia of automotive vehicles. Foam injection molding (FIM) is a branched manufacturing process of conventional injection molding, but it was designed to take advantage of existing foaming technology, including material cost saving and weight reduction, and to provide additional benefits such as improvement in dimensional stability, faster cycle time, and so on. Gas-assisted injection molding (GAIM) is another supplemental technology of injection molding and offers several advantages as well. This thesis study takes the next step and develops innovative gas-assisted foam injection molding (GAFIM) technology, which is the result of a synergistic combination of two existing manufacturing technologies, FIM and GAIM, in order to produce a unique thermoplastic foam structure with proficient acoustic properties. The foam structure manufactured by GAFIM consists of a solid skin layer, a foam layer, and a hollow core; and its 6.4-mm thick sample outperformed the conventional 22-mm thick polyurethane foam in terms of the acoustic absorption coefficient. With respect to foaming technology, GAFIM was able to achieve a highly uniform foam morphology by completely decoupling the filling and foaming phases. Moreover, the additional shear and extensional energies from GAFIM promoted a more cell nucleation-dominant foaming behavior, which resulted in higher cell density and smaller cell sizes with both CO2 and N2 as physical blowing agents. Lastly, it provided more direct control of the degree of foaming because the pressure drop and pressure drop rate was controlled by a single parameter, that being the gas injection pressure. In summary, innovative, gas-assisted foam injection molding technology offers not only a new strategy to produce acoustically functioning thermoplastic foam products, but also technological advantages over the conventional foam injection molding process. Gas-assisted foam injection molding can become the bedrock for more innovative future applications.

Injection molding technology is utilized for a wide range of applications from mobile phone covers to bumper fascia of automotive vehicles. Foam injection molding (FIM) is a branched manufacturing process of conventional injection molding, but it was designed to take advantage of existing foaming technology, including material cost saving and weight reduction, and to provide additional benefits such as improvement in dimensional stability, faster cycle time, and so on. Gas-assisted injection molding (GAIM) is another supplemental technology of injection molding and offers several advantages as well. This thesis study takes the next step and develops innovative gas-assisted foam injection molding (GAFIM) technology, which is the result of a synergistic combination of two existing manufacturing technologies, FIM and GAIM, in order to produce a unique thermoplastic foam structure with proficient acoustic properties. The foam structure manufactured by GAFIM consists of a solid skin layer, a foam layer, and a hollow core; and its 6.4-mm thick sample outperformed the conventional 22-mm thick polyurethane foam in terms of the acoustic absorption coefficient. With respect to foaming technology, GAFIM was able to achieve a highly uniform foam morphology by completely decoupling the filling and foaming phases. Moreover, the additional shear and extensional energies from GAFIM promoted a more cell nucleation-dominant foaming behavior, which resulted in higher cell density and smaller cell sizes with both CO2 and N2 as physical blowing agents. Lastly, it provided more direct control of the degree of foaming because the pressure drop and pressure drop rate was controlled by a single parameter, that being the gas injection pressure. In summary, innovative, gas-assisted foam injection molding technology offers not only a new strategy to produce acoustically functioning thermoplastic foam products, but also technological advantages over the conventional foam injection molding process. Gas-assisted foam injection molding can become the bedrock for more innovative future applications.

Thermoplastic composites using natural fibres are studied intensively and widely used in applications including automotive, packaging, consumer goods and construction. Good balance of mechanical properties, processability and low cost are great advantages of these materials on top of the environmental benefits. Recently, there have been various efforts to amplify the positive effects on the environment by replacing the conventional polymers by bio-derived renewable polymers in the composites. Recent studies conducted from our research group showed competitiveness of plant fibre-thermoplastic composites. Implementing the promising results and experience, a new composite design using renewable polyethylene as the matrix material was studied. This polyethylene is a renewable thermoplastic that was derived from sugar cane ethanol. The objectives of this study were to employ renewable high density polyethylene (HDPE) into composites using wheat straw and flax fibre to extend the range of properties of the HDPE while keeping the amount of renewable content to nearly 100%. The chemical resistance of these materials has not been reported before and it was investigated here by measuring and comparing the properties before and after accelerated chemical ageing. Both wheat straw and flax fibre had two different grades in size. Each of them was compounded with HDPE and additives (antioxidant and coupling agent) in a co-rotating twin screw extruder. The concentrations of fibres were varied from 0 to 30 wt-%. Then, injection molded samples were prepared for measurement of properties: tensile, flexural, impact tests. The effects of reinforcing fibre size were studied first. Both length and aspect ratio were considered. For both types of fibre composites, a general trend was observed. There was no clear evidence of improvements in flexural (strength and modulus) and tensile (strength, percentage elongation at break) properties with respect to the change in fibre size. However, impact (IZOD impact strength, Gardner impact failure energy) properties showed some improvements. This result was due to no substantial difference in size and aspect ratios in post-processed fibres that were actually residing in the matrix. There were remarkable improvements in flexural strength and modulus when the fibre content increased. However, minor decreases in tensile properties were observed. Furthermore, the impact properties were very sensitive to the concentration of fibres. As the fibre concentration went up, there were significant decreases in both IZOD impact strength and Gardner impact failure energy. Chemical resistance of these composites was studied by exposing them in six different chemical solutions (hydrochloric acid, acetic acid, sodium hydroxide, ethyl alcohol, industrial detergent, water) for up to thirty days. The increase in weight and leaching behaviour was observed. As the fibre content increased within the composites, the weight gain was more rapid during chemical ageing. Because there were more fibres exposed on the surface after chemical ageing, it is likely that they contributed to the higher flux of liquids (used for chemical ageing) inside the sample. Among the physical properties, tensile properties were most susceptible to the chemical ageing. One possible reason could be due to the exposed surface area to volume ratio, which was the highest in tensile bars and therefore faster mass transfer taking place into the matrix per volume. Finally, morphological study using scanned electron spectroscopy (SEM) revealed the damage on the surface when exposed to the chemicals. The fibres on the surface had been leached out in the sodium hydroxide solution leaving empty spaces. The fractured surface was also monitored via SEM. Though there was not enough evidence of strong interfacial interactions between the fibre and the polymer, good dispersions were observed.