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Syntactic foams (SFs) are characterized by a unique combination of low density, high mechanical properties, and low thermal conductivity. Moreover, these properties can be tuned to specific applications. In contrast to traditional foams, where porosity is formed during the foaming process, porosity in syntactic foams can be obtained simply by incorporating pre-formed bubbles. Because of their high chemical stability and buoyancy, these type of foams found their first application in the marine industry. Nowadays, they are utilized in many other fields, such as in the aerospace and automotive industry. In this work, the multifunctionality of epoxy-based and polypropylene (PP)-based SFs was increased by including a microencapsulated Phase Change Material (PCM), able to impart Thermal Energy Storage (TES) capability at phase transition temperatures of 43 °C and 57 °C. The rheological, morphological, thermal, and mechanical properties of the prepared materials were systematically investigated. A final comparison of the two systems was performed to obtain a better comprehension of their potential in emerging industrial applications.

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Phenolic resins are important components of the composite industry because of their excellent flame retardance and cost effectiveness. However, the common procedure for curing phenolic novolac resins uses hexamethylenetetramine (HMTA) and releases volatiles during the cure, which produce networks with numerous voids. This results in materials that lack the toughness necessary for structural applications. An alternative to curing with HMTA is to crosslink the pendant phenolic groups in the novolac resin with epoxy reagents. This reaction proceeds by nucleophilic addition without the release of any volatiles, thereby creating a void-free network. Flame retardance can be achieved by using an excess of the phenolic component. Network densities can also be controlled to maximize both toughness and stiffness by tailoring the stoichiometry of the reagents. Structure-property relationships of phenolic/epoxy networks have been investigated. Glass transitions decreased, and toughness increased, as the phenolic content in the network was increased. Both results could be correlated to the decrease in network densities along this series, which was investigated by measuring the rubbery moduli well above T_g. Fracture toughness of phenolic/epoxy networks measured by K_1c reached 1.03 MPa-m^1/2, compared with an epoxy control with K^1c = 0.62 MPa-m^1/2 and phenolic control with K_1c = 0.16 MPa-m^1/2. In addition, an increase in novolac content improves flame retardance rather dramatically. The peak heat release rate (PHRR) dropped from 1230 kW/m²⁺ for the epoxy control to 260 kW/m²⁺ for the phenolic/epoxy networks, which approached that of a phenolic resol (PHRR = 116 kW/m²⁺). Phenolic/epoxy composite flame retardance also showed significant improvement when compared to epoxy composites. Melt processability of phenolic/epoxy composites has been achieved through the use of latent nucleophilic initiators. Kinetics of the phenolic/epoxy cure reactions with latent initiators demonstrated that monomeric phosphine initiators yielded faster cure reactions as compared to polymeric initiators. These latent initiators allow composite melt processing, such as prepregging or pultrusion, without premature curing. In addition, cure cycles can be reduced from 4 hours to less than 30 minutes. Composites prepared using these latent initiators had toughness exceeding that of epoxy composites and fatigue limits significantly higher than those of vinyl ester composites. <i>Vita removed, June 10, 2013, per author's request. GMc</i> / Ph. D.

The primary cause of corrosion in transportation structures is due to chlorides which are applied to bridge decks as deicing salts. The direct cost of corrosion damage to the country's infrastructure is approximately $8.3 billion per year. One of the most common corrosion abatement methods in the United States is the barrier protection implemented through the application of fusion bonded epoxy coatings. The purpose of this study was to investigate various coating and exposure parameters to determine their effects on the corrosion of reinforcing steel. The parameters investigated were: chloride content at the bar depth, coated bar corroded area, corrosion product color under the coating, epoxy coating adhesion, coating color, coating damage (holidays and holes), coating thickness, TGA, DSC and EDS analysis and SEM coating cracking investigation. This was accomplished by testing new coated bar specimens as well as specimens extracted from 27 bridge decks located in Virginia. This study demonstrated the following: The extracted ECR coating samples presented extensive cracking compared to the new ECR samples in which the coating cracking was limited to only one sample. The DSC results showed that both the extracted samples as well as new samples are not fully cured during the manufacturing process. The coating degree of curing data also showed that the bars are insufficiently and unevenly heated prior to the application of the powder coating. Additionally, the samples investigated presented significant permanent adhesion loss with little or no epoxy coating residue present on the bar surface, while the EDS analysis showed that once adhesion is lost, corrosion will proceed unimpeded under the coating even in the absence of chlorides. The parameters that presented a direct correlation with the observed corrosion activity were the number of holidays and the number of damaged areas per unit length of bar. This indicates that the passivation of the bare steel exposed to the concrete pore solution at the breaches in the epoxy coating is not the same as a bare bar under similar exposure conditions allowing it instead to corrode at lower concrete chloride concentration levels than bare bars. The results also show a distinct loss of quality control in the handling and possibly storage of new coated bars. The new ECR samples had significantly higher damage density than the samples extracted from concrete even though the coating is damaged during the placement of the concrete, while there was no change in the number of holidays and cure condition. Finally, the data presented further evidence that while limited, the non-destructive corrosion assessment methods available for bare steel reinforced structures may also be used on ECR reinforced structures. In particular, the corrosion rate measurements correlated reasonably well with the chloride concentrations at bar level. This indicates that while the chlorides may not influence the corrosion activity under the coating, they do influence the corrosion activity at breaches in the coating. / Ph. D.

Star-like lignin-poly(propylene oxide) copolymers were prepared by chain-extending steam exploded lignins (tulipifera liriodendron) with propylene oxide and by subsequent endcapping with ethylene oxide. Epoxidation of these copolymers was carried out with epichlorohydrin at room temperature, using KOH as oxyanion forming reagent. The epoxidized compounds were fractionated by solvent precipitation to remove poly(alkylene oxide) homopolymers and to prepare fractions of narrow molecular weight distributions. The epoxides were cross-linked with meta phenylene diamine yielding thermosets which were, depending on lignin content, either low modulus elastomers, or high modulus materials with considerable ductility. The modulus of elasticity was a strong and linear function of lignin content, whereby the highest value was 1100MPa (57% lignin). The curing reaction was of nth-order type, whereby the reaction order changed from close to one at the beginning of the curing reaction to 2, once the reaction becomes diffusion controlled. Curing induced partial demixing of the lignin and poly(propylene oxide) phases which yielded a secondary structure where lignin rich domains in the order of 10 nm were interspersed in a matrix of lignin poor material. However, from TEM and ¹³C solid state cross-polarized NMR analyses it was evident that the domain structure was not that of a classical micro-phase separated copolymer with well defined phase boundaries, but rather had broad interphases. Additionally, the results of multifrequency dynamic mechanical thermal analysis showed that the lignin containing thermosets have very broad glass transition ranges which most likely were due to transitional phase inhomogeneities and provided these materials with good vibrational damping ability. / Ph. D.