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Plastics are highly useful economically because of their resistance to diverse types of environmental and chemical agents and their ability to be molded into many types of products. Globally, plastic production is greater than 20 million metric tons per year. However, their widespread use and often their disposable nature results in significant plastic accumulation in the environment. Plastics are made of hydrocarbons, materials that are biodegradable depending on their molecular structure and size. It is hypothesized that pre-treatment of plastic materials could enhance their bioavailability, facilitating their microbial biodegradation. In this dissertation, a process was developed to treat nylon 6,6 polymers by acid hydrolysis to produce a microbial growth medium. The chemical composition of the medium was determined by low pressure liquid chromatography-spectrophotometry and electrospray ionization mass spectrometry and found that the medium was a mixture of molecules with molecular weight > 800 m/z and with similar chemical characteristics to polyamines. There was steady growth of Pseudomonas putida KT2440 in the medium with concomitant substrate biodegradation. Notably, the yeast Yarowia lipolytica grew well in the medium when supplemented with yeast extract. A similar medium derived from nylon 6,6 containing nylon-derived particles supported the growth of Beijerinckia sp. and Streptomyces sp. BAS1. Confocal laser scanning microscopy and flame ionization gas chromatography were used to identify and quantify the production of polyhydroxybutyrate, a type of “bioplastic”. The aforementioned microorganisms were cultivated in a bench-scale bioreactor that was developed as part of this dissertation. The bioreactor had a novel impeller design resulting in enhanced mixing and rotation and also a modular format allowing for diverse configurations. The bioreactor was notable for its durability and low cost. A detailed description of its design is included in the appendices. In summary, plastic materials can potentially be processed into growth media for microorganisms and can be used for production of value-added products. The media described herein can be used in bioconversion processes using a bioreactor.

Natural bone is a composite of collagen based hydrogel and inorganic dahilite crystals. The unusual combination of a hard inorganic material and an underlying elastic hydrogel network endows native bone with unique mechanical properties, such as low stiffness, resistance to tensile and compressive forces and high fracture toughness. Throughout the cavities of the bone, there are bone cells and myriads of soluble and extracellular matrix components that are constantly involved in the bone formation and remodeling process. Among the extra cellular component the acidic matrix proteins that are attached to the collagen scaffold play important templating and inhibitory roles during the mineralization process. It would be interesting to generate such functional scaffolds that mimic a template driven mineralization and which can assist cell adhesion, proliferation, migration and differentiation. Towards this direction, we have chosen one synthetic (Nylon 66 membrane) and one natural (eggshell membrane) scaffold and carried out a template driven mineralization of CaCO₃ as model systems. The surface modifications were carried out by the pre-adsorption of acidic polymers before the deposition of the CaCO₃. The deposition of the crystalline calcium carbonate on these modified templates were archived from a supersaturated solution of Ca(HCO₃)₂. / Singapore-MIT Alliance (SMA)

A fracture mechanics protocol appropriate for small fibers (35 micron diameter) is presented, which allows for the determination of the strength limitations of high performance nylon 6,6 fibers. Specifically, linear elastic fracture mechanics (LEFM) techniques are employed in addition to elastic-plastic fracture mechanics (EPFM) theories to achieve this. We assume that a minute semi-elliptical flaw of an unknown size exists in the specimen, as a result of the detrimental effects of the manufacturing process (melt spinning). Next, we seek to propagate this flaw in a stable manner through an ancillary process such as high cycle or low cycle fatigue (load-unload). After propagation, uniaxial tensile experiments are performed on the fatigued samples, by which the crack growth eventually becomes catastrophic during the process. After performing scanning electron microscopy (SEM) techniques and reviewing fractography, we are able to determine the critical flaw size and ligament length that leads to unstable crack propagation. These results are substituted into the appropriate LEFM equations and are in close agreement with material properties for nylon 6,6. A discussion is provided that draws parallel to the topics discussed in the literature investigation and the experimental results of this study.

PA 66 nanocomposites and PA 66 blends were prepared using Cloisite 15A, Cloisite 25A and Cloisite 30B as organoclays and Lotader 2210 (E-BA-MAH), Lotader AX8840 (E-GMA) and Lotader AX8900 (E-MA-GMA) as impact modifiers. The effects of the composition, types of the components and the addition order of the nanocomposites on the morphology, mechanical, flow and thermal properties were investigated. Melt compounding step was carried out twice in a co-rotating twin-screw extruder. This was called as All-S mixing sequence when all the components were melt mixed, simultaneously. The concentration of the elastomer was determined as 5 wt% and the organoclay as 2 wt% to minimize agglomeration of the organoclay and decrease in the mechanical properties. The components which exhibited the best mechanical results and organoclay delamination in All-S mixing sequences were compounded by using different addition orders. Substantial increases were not observed in the tensile, impact, flexural and hardness test results of the nanocomposites compared to the polymer matrix that was twice extruded. Addition order of the components affected the properties of the nanocomposites and dispersion of the elastomeric domains and the organoclay. The best mechanical test results were obtained for All-S mixing sequence of (PA 66-15A-2210). The degree of organoclay dispersion is better in Cloisite 15A and Cloisite 25A containing nanocomposites than the ones which have Cloisite 30B. Low melt flow index values aided dispersion of the organoclay whereas the slight changes in the crystallinity did not significantly contribute to the changes in the mechanical properties of the nanocomposites or the blends.

Cellulose fiber was used to reinforce higher melting temperature engineering thermoplastics, such as nylon 6 and nylon 66. The continuous extrusion - direct compression molding processing and extrusion-injection molding were chosen to make cellulose fiber/nylon 6 or 66 composites. Tensile, flexural and Izod impact tests were used to demonstrate the mechanical properties of the composites. The continuous extrusion-compression molding processing can decrease the thermal degradation of cellulose fiber, but fiber doesn't disperse well with this procedure. Injection molding gave samples with better fiber dispersion and less void content, and thus gave better mechanical properties than compression molding. Low temperature compounding was used to extrude cellulose fiber/nylon composites. Plasticizer and a ceramic powder were used to decrease the processing temperature. Low temperature extrusion gave better mechanical properties than high temperature extrusion. The tensile modulus of nylon 6 composite with 30 % fiber can reach 5GPa; with a tensile strength of 68MPa; a flexural modulus of 4GPa, and a flexural strength of 100MPa. The tensile modulus of nylon 66 composites with 30 %fiber can reach 5GPa;with a flexural modulus of 5GPa; a tensile strength of 70MPa; and a flexural strength of 147MPa. The effect of thermal degradation on fiber properties was estimated. The Halpin-Tsai model and the Cox model were used to estimate the composite modulus. The Kelly-Tyson model was used to estimate the composite strength. The result indicates that the change of fiber properties determines the final properties of composites. Fiber length has a minor affect on both modulus and strength as long as the fiber length is above the critical length.

This thesis was made in cooperation with Roxtec. Roxtec specialises in cable sealingsolutions and are world leading in their area. In many of Roxtec’s products steel isused in the frame holding the sealing rubber. To lower Roxtec’s environmental foot-print plastic would be used instead in the frames if possible, more specific polyamide6.6 with 25% glass fiber reinforcement (PA66GF25). Polyamide is affected to agreater extent by temperature and humidity than steel and therefore poses a greaterrisk when considering the sealing capability in harsh conditions. The purpose of thisthesis is therefore to investigate the effects on the Young’s modulus by temperatureand relative humidity, which both correlate to moisture content in the plastic. Theintended temperature and moisture saturation interval are -40◦C to 80◦C and 0% to100% moisture saturation respectively. Tensile test samples were made through machining samples from existing productsand conditioning them to desired moisture content. With the use of tensile testingthe Young’s modulus could be determined for a number of combinations of temper-ature and moisture content. From this data an approximated polynomial surfaceof the Young’s modulus could be produced. The conditioning of the test piecescould be accelerated by submersion in heated water, decreasing conditioning timeto less than two days. The approximation of the Young’s modulus function couldbe done using polynomial approximation. The resulting polynomial for the positivetemperatures was of the third order dependant of the two variables moisture con-tent and temperature. For the negative temperatures a single variable polynomialwas approximated due to only one moisture content being tested for. To ensure thevalidity of the model each test combination consisted of three individual tensile testof which an average was calculated. The approximated function was then comparedto a data sheet value for a certain moisture content and temperature. From theresulting surface approximation of the Young’s modulus in positive temperatures itcan be deduced that PA66GF25 is more greatly affected by moisture content thantemperature. Especially at low levels of moisture content where the rise in Young’smodulus is exponential while more linear at higher moisture contents. The maximumand minimum Young’s modulus was found to be 8 GPa and 2.7 GPa respectively.The negative temperature approximation was restricted to one moisture content andtherefore resulted in a graph. The behaviour of this graph was likely a result of icein the material as similarities to a study regarding the mechanical properties of icewas found. / Detta examensarbete gjordes i sammarbete med Roxtec. Roxtec specialialiserar sig ikabeltätningslösningar och är världsledande i området. I många av Roxtecs produk-ter så används stål till att försegla gummi. För att minska Roxtecs miljöpåverkan såskulle plast användas till tätningarnas ramar om möjligt, speficikt polyamid 6.6 med25% glasfiberförstärkning (PA66GF25). Polyamid påverkas till större andel av tem-peratur och luftfuktighet än stål och utsätts därmed för en större risk med avseendepå tätnings kapabiliteten i tuffa miljöer. Syftet med detta arbete är därmed attundersöka effekterna på Elasticitetsmodul från temperatur och luftfuktighet, vilkakorrelerar mot fuktmättnadsgraden i plasten. Det avsedda temperaturintervallet är-40◦C till 80◦C och 0% till 100% fuktmättnadsgrad. Dragprovstesterna gjordes genom bearbetning av existerande produkter följt av kon-ditionering till önskad fuktmättnadsgrad. Genom genomförandet av dragprov, såkunde Youngs modul bestämmas för ett antal kombinationer av temperaturer ochfukterhalter. Från denna data så kunde en polynomyta för Youngs modul approx-imeras. Konditioneringen av dragprovsbitarna kunde accelereras genom nedsänkningi upphettat vatten, vilket minskade konditioneringstiden till mindre än två dygn. Ap-proximeringen av funktionen för Youngs modul kunde göras genom polynomapprox-imering, vilket resulterade i en tredje ordnings polynom beroende på två variablernafuktmättnadsgrad och temperatur. En annan approximation gjordes för de nega-tiva temperaturerna, då enbart temperaturberoende beteende undersöktes med enkonstant fuktmättnadsgrad. För att säkerställa validiteten av modellen så gjordestre mätningar på varje testkombination ifrån vilket ett medel kalkylerades. Den ap-proximerade funktionen jämfördes sedan med värdena från datablad för en viss fukt-mättnadsgrad och temperatur. Från den resulterande ytapproximationen av Youngsmodul för de positiva temperaturerna, så kan slutsatsen att PA66GF25 är avsevärtmycket mer påverkad av fukt än temperatur dras. Detta är tydligare för de testernamed låga fuktmättnadsgrader då ökningen av Youngs modul är exponentiell medanden är mer linjär för högre fuktmättnadsgrad. Den maximala och minimala Youngsmodul visade sig vara 8 GPa och 2.7 GPa respektive. De negativa temperaturernasapproximation var begränsad till en fuktmättnadsgrad och därmed resulterade i engraf kring 5 GPa. Beteendet hos denna graf var troligtvis ett resultat från isen imaterialet vars beteende är snarlikt en studie på isens mekaniska egenskaper visadepå.

The catalytic depolymerization/pyrolysis of nylon 6 and 66 were investigated with the prospect of helping to curb the amount of carpet landfilled. Thermogravimetric analysis was used to determine which catalysts (and their nylon/catalyst ratio) were most suited for the depolymerization. By adding bases, the onset of degradation for some bases was 100 aC lower than that of the pure nylons. Potassium hydroxide and sodium hydroxide were found to be the most effective catalysts at a catalyst ratio of 100:1 of nylon 6 and nylon 66 to catalyst, respectively. After determining the most efficient catalyst, kinetic models/parameters from the TGA data were determined. These parameters were used in a reactive extrusion model for depolymerizing nylon 6 in carpet. Data from the model was then used to do cost analysis for the process. It was found that to get a Present Value Ratio greater than 1, the flow rate has to be greater than or equal to 500 lb/hr. At even higher flow rates up to the model¡¦s limit (1500 lb/hr), the Net Present Value shows that this process is economically viable. Extrusion of a 100:1 ratio of pure N6 and KOH was done in a 30 mm counter-rotating non-intermeshing twin screw extruder. The material collected from the vents of the extruder was tested with a gas chromatograph- mass spectrum (GC-MS) in tandem. There was only one significant peak from the GC and the primary molecular weight on the MS was 113, the molecular weight of caprolactam. This shows that the process could be profitable and require little purification if done industrially.