Margaret J. Sobkowicz

Processing and properties of a solid energy fuel from municipal solid waste (MSW) and recycled plastics

Diversion of waste streams such as plastics, woods, papers and other solid trash from municipal landfills and extraction of useful materials from landfills is an area of increasing interest especially in densely populated areas. One promising technology for recycling municipal solid waste (MSW) is to burn the high-energy-content components in standard coal power plant. This research aims to reform wastes into briquettes that are compatible with typical coal combustion processes. In order to comply with the standards of coal-fired power plants, the feedstock must be mechanically robust, free of hazardous contaminants, and moisture resistant, while retaining high fuel value. This study aims to investigate the effects of processing conditions and added recyclable plastics on the properties of MSW solid fuels. A well-sorted waste stream high in paper and fiber content was combined with controlled levels of recyclable plastics PE, PP, PET and PS and formed into briquettes using a compression molding technique. The effect of added plastics and moisture content on binding attraction and energy efficiency were investigated. The stability of the briquettes to moisture exposure, the fuel composition by proximate analysis, briquette mechanical strength, and burning efficiency were evaluated. It was found that high processing temperature ensures better properties of the product addition of milled mixed plastic waste leads to better encapsulation as well as to greater calorific value. Also some moisture removal (but not complete) improves the compacting process and results in higher heating value. Analysis of the post-processing water uptake and compressive strength showed a correlation between density and stability to both mechanical stress and humid environment. Proximate analysis indicated heating values comparable to coal. The results showed that mechanical and moisture uptake stability were improved when the moisture and air contents were optimized. Moreover, the briquette sample composition was similar to biomass fuels but had significant advantages due to addition of waste plastics that have high energy content compared to other waste types. Addition of PP and HDPE presented better benefits than addition of PET due to lower softening temperature and lower oxygen content. It should be noted that while harmful emissions such as dioxins, furans and mercury can result from burning plastics, WTE facilities have been able to control these emissions to meet US EPA standards. This research provides a drop-in coal replacement that reduces demand on landfill space and replaces a significant fraction of fossil-derived fuel with a renewable alternative.

Supramolecular BioNanocomposites: Grafting of Biobased Polylactide to Carbon Nanoparticle Surfaces

Novel carbon nanostructures are attracting increasing interest and the combination of graphitic substrates with grafted biodegradable polymers may ultimately be of interest in a variety of biomedical and sensing applications. Here, a novel graphitic nanosubstrate, carbon nanospheres derived from cellulose, is functionalized with polylactides (PLA) using an established thionyl chloride intermediate scheme; the resulting supramolecular bionanocomposite is 97% from renewable resources. In addition, a direct ‘grafting from’ approach is utilized to grow polylactide chains on multi-walled carbon nanotubes (MWCNT). In the latter case, unlike previous approaches, the ring-opening polymerization is initiated directly from a hydroxyl bearing surface. Verification of the covalent attachment and characterization of the grafted layer are accomplished via a variety of techniques and methods. Even after repeated washing, thermal gravimetric analysis clearly shows the presence of a grafted layer, which decomposes at approximately 300°C, a value characteristic of PLA; it is found that 20 mg m–2 of PLA is grafted to the MWCNT and 3.9 mg m–2 of PLA is grafted to the carbon nanospheres. Solubility tests clearly show the graphitic structures have been fundamentally altered in their physiochemical properties; they become highly soluble in chloroform after the grafting reaction is complete. Transmission electron microscopy provides evidence of a 2–3 nm thick polymer layer. Finally, Fourier transform infrared spectroscopy shows several characteristic peaks of PLA including the ester group at 1760 cm–1.

Tuning oxygen permeability in azobenzene-containing side-chain liquid crystalline polymers

A series of poly[4-(4-cyanoazobenzene-4′-oxy)alkyl methacrylate]s, side-chain liquid crystalline polymers (azoLCPs) were synthesized with methylene groups as spacers varying from 5 to 12. The thermal properties and phase transition temperatures of the polymers were characterized with differential scanning calorimetry and polarized optical microscopy and a relationship between spacer lengths, glass transition (Tg) and clearing temperatures (Tc) of the polymers was established. The Tg decreased with increasing spacer length, while the Tc exibited an odd–even effect with varying spacer length. X-ray diffraction was used to determine the degree crystallinity above and below Tc. The azoLCPs exhibited smectic ↔ nematic ↔ isotropic phases. Increasing crystallinity correlated linearly with decreasing gas permeability as measured using an oxygen permeation analyzer, which was used to measure the films’ permeability to oxygen (O2) gas. Switching of the azoLCPs from a liquid crystalline to an isotropic state was accomplished by heating the films above their Tc, which resulted in at least a 10-fold increase in the O2 permeability coefficient (PO2). Increasing the methylene spacer length of the azoLCP had little or no effect on gas permeability however it did decrease the Tc, allowing fine control of the temperature at which the switch in PO2 takes place by tuning the mesophase between nematic and isotropic states.

Modeling confinement in polymer nanocomposites from linear viscoelasticity data

The ability of the time-dependent diffusion–double-reptation (TDD-DR) theory to predict the molecular structure and dynamics of polymer nanocomposites is investigated for poly(butylene succinate) blended with fumed silica particles with contrasting surface treatments (unmodified and modified with silanes). Structural and dynamic parameters such as confined polymer fraction (ϕs) and relaxation time are extracted from fitting the experimental curves for relaxation modulus G(t) by the TDD-DR model with fluctuation effects included. A good fit of experimental data over seven time decades is obtained after modification of the TDD-DR model to account for Rouse relaxation on the short time scale. The fraction of confined polymer extracted from model fitting is in quantitative agreement with the value obtained from the specific reversing heat capacity for poly(butylene succinate) (PBS)/fumed silica nanocomposites. Based on parameters deduced from rheological data, we study the influence of surface functionality on the microstructure of polymer matrix. We conclude that increasing the polymer–particle compatibility through introduction of a hydrophobic functionality on the surface of the particles results in increased amount of confined PBS chains and strong immobilization of the PBS molecules. These interface effects are discussed for the first time in terms of TDD-DR model that takes into account the dynamics of bound polymer chains, allowing prediction of the universal nature of the confinement effect and its role in polymer nanocomposite processing and bulk physical properties.

Analysis of Models Predicting Morphology Transitions in Reactive Twin-Screw Extrusion of Bio-Based Polyester/Polyamide Blends

Abstract Immiscible PLA/PA11 of 80/20 and 50/50 wt% were compatibilized through addition of p-toluenesulfonic acid (TsOH) catalyst in reactive ultra-high speed twin-screw extrusion. Two mixing screw designs were compared for their ability to disperse the PA11 droplets in the PLA matrix as a function of screw speed up to 2000 rpm. The size and polydispersity of droplets of dispersed PA11 decreased when a high shear (HS) screw was used, whereas broad droplet size distribution was produced in the low shear (LS) screw. Two models predicting the droplet size dependence on shear rate, viscosity ratio and interfacial tension were fit to the experimental data. The Serpe model including volume fraction effects produced a better fit compared to the Wu model, which does not include volume fraction effects. Mechanical testing indicated that the compatibility of PLA/PA11 blends was improved through addition of TsOH catalyst for 50/50 wt% blends due to ester – amide exchange reactions at the interfaces in the immiscible PLA and PA11 phases. The enhancement of ductility was greater after processing with the LS screw configuration than the HS screw configuration. The inferior properties after high shear mixing were likely due to molecular weight degradation during processing. While the aggressive shear in the HS screw design resulted in fine dispersion, care should be taken to minimize degradation, especially for shear sensitive polymers.

Experimental Study of Drag Reduction on Superhydrophobic Surfaces Using Quartz Crystal Microbalance (QCM)

A durable superhydrophobic coating formulation with epoxy binder thermoset was used to coat on surfaces, which provide high quality for corrosion protection, reduced biofouling and improved hydrodynamic behavior. The single and double layers coating of these nanostructured epoxy were fabricated and coated on a novel quartz crystal microbalance (QCM) technique to investigate their hydrophobic properties. Different static and dynamic wettability were obtained and characterized by evaluating the electrical impedance of QCM coated with nanostructured epoxy in air and DI water. It was found that QCM is able to quantitatively characterize the hydrophobicity of these nanostructured polymer surfaces. For double layer coating, the frequency shift in DI water was smaller in comparison to the single layer one. The reduction in mechanical impedance of QCM clearly demonstrates the effect of enhanced hydrophobicity for both single and double layers. The experimental results show that the hydrophobic surface resulted in smaller mechanical impedance loading, while the hydrophilic surface exerted much larger mechanical impedance. The outcome of this research will build a solid foundation for the further improvement of vehicles coated with superhydrophobic surfaces operating in water and increased equipment life.Copyright