Studies on High-Performance Sustainable Blends from Lignin, a Low- Cost Renewable Feedstock

Demand for plant-derived materials has increased in recent years not only to boost the economics in US Agricultural and Forestry sectors, but also to address environmental concerns. Lignin, an aromatic polymer, extracted from biomass has the potential to be used for preparing innovative materials. Developing high-performance polymers from lignin is attractive, but often requires additional lignin modification and cost-intensive functionalization that creates chemical wastes. The overarching goal of this study was the development of sustainable high-performance alloys from thermoplastic and lignin without chemical modification using melt-blending technique, which is technically the most convenient and inexpensive method. Thus, the approach aimed to find value for lignin, a low-cost byproduct of modern biorefineries and woody biomass pulping industry. More specifically, we conducted comprehensive study on thermal, rheological, morphological, and structural properties of the thermoplastic-lignin blends together with lignin’s chemistry and thermal behavior to understand and improve the materials’ performance.The first part of the study involved exploiting lignin’s miscibility with polyethylene oxide (PEO) to enhance the compatibility between lignin and acrylonitrile-butadiene-styrene (ABS) polymer under reactive mixing conditions and develop a recyclable renewable matrix for sustainable composite applications.The second part consisted on manipulating the melt behavior of polyethylene terephthalate (PET) polyester from pre-consumer wastes using a renewable plasticizer tall oil fatty acid (TOFA). To avoid lignin degradation and devolatilization during amalgamation with plasticized PET we devised thermal treatment of lignin that not only improved the stability but also reduced dispersed lignin domains in the matrix.The last part was based on understanding the effect of source-dependent lignin chemistry on its compatibility with a renewable polyester. Organosolv lignin from oak, methanol fractionated Kraft pine lignin, and methanol fractionated acetic acid extracted wheat straw lignin give equivalent melt processability. Blends of these lignins with polylactic acid (PLA) were studied to understand the relationship between the lignin chemistry and resulting blends’ thermal stability, mechanical properties, and melt-rheology.This study answered questions on the role of lignin chemistry that affects the properties of thermoplastic/lignin blends and developed methods to modify melting behavior of both thermoplastic matrices and lignin without thermal degradation

Pretreatment and Pyrolysis of Rayon-based Precursor for Carbon Fibers

In this work, two rayon fibers were investigated as carbon fiber precursors. A detailed consideration has been applied to a domestically produced cellulose fiber to carbon fiber (CF) transition. This transition of precursor to carbon fiber can be subdivided into two stages: pyrolysis (thermal decomposition) of cellulose in air and high temperature treatment in an inert atmosphere. The specific objectives were to investigate the stabilization stage of the produced rayon with respect to changes taking place during thermal decomposition, and to evaluate the effects on the properties of the carbonized fiber. Changes taking place during the conversion process of the domestic precursor are compared with respect to the commercial rayon fiber. Phosphoric acid was used as a catalyst and a flame retardant during stabilization. It was observed that the acid plays a multirole of heat absorption, catalytic dehydration by lowering the required temperatures, and acts as a protection during carbonization. The effects of time and temperature during stabilization were studied systematically. The temperature affects the structural changes taking place, and the time required for completion of stabilization reactions. The thermal behaviors of rayon fibers were analysed by Thermogravimetry Analysis (TGA) and Differential Scanning Calorimetry (DSC). The results showed that the phosphoric acid treated fibers underwent pyrolysis under lower temperatures and over a wider temperature range. Wide Angle X-ray Diffraction (WAXD) was used to analyse the degree of cristallinity of the precursor and the subsquent carbon fibers. The highly ordered and oriented precursor becomes totally amorphous after pyrolysis. The crystallite order was reinduced during carbonization under tension. Fourier Transform Infrared Spectroscopy (FTRI) was utilized to investigate the chemical transition during the heat treatment. The intensity of peaks corresponding to chemical groups present in the precursor decreased by the end of low temperature pyrolysis and disapeared during carbonization indicating the fibers were mostly carbon. The mechanical properties, morphology and structure of the precursor and the obtained carbon fibers were studied by Scanning Electron Microscopy (SEM). An increase in applied tension during carbonization increased the carbon content slightly leading to better quality fibers

Recycling Waste Polyester via Modification with a Renewable Fatty Acid for Enhanced Processability

Polyethylene terephthalate (PET) waste often contains a large amount of thermally unstable contaminants and additives that negatively impacts processing. A reduced processing temperature is desired. In this work, we report using a renewably sourced tall oil fatty acid (TOFA) as a modifier for recycled PET. To that end, PET was compounded with TOFA at different concentrations and extruded at 240 °C. Phase transition behaviors characterized by thermal and dynamic mechanical analyses exhibit shifts in the melting and recrystallization temperatures of PET to lower temperatures and depression of glass transition temperature from 91 to 65 °C. Addition of TOFA also creates crystal-phase imperfection that slows recrystallization, an important processing parameter. Changes in the morphology of plasticized PET reduces and stabilizes the melt viscosity at 240 and 250 °C. Melt-spun, undrawn continuous filaments of diameter 36–46 μm made from these low-melting PET exhibit 29–38 MPa tensile strength, 2.7–2.8 GPa tensile modulus, and 20–36% elongation. These results suggest a potential path for reusing waste PET as high-performance polymeric fibers

Sustainable Waste Tire Derived Carbon Material as a Potential Anode for Lithium-Ion Batteries

The rapidly growing automobile industry increases the accumulation of end-of-life tires each year throughout the world. Waste tires lead to increased environmental issues and lasting resource problems. Recycling hazardous wastes to produce value-added products is becoming essential for the sustainable progress of society. A patented sulfonation process followed by pyrolysis at 1100 °C in a nitrogen atmosphere was used to produce carbon material from these tires and utilized as an anode in lithium-ion batteries. The combustion of the volatiles released in waste tire pyrolysis produces lower fossil CO2 emissions per unit of energy (136.51 gCO2/kW·h) compared to other conventional fossil fuels such as coal or fuel–oil, usually used in power generation. The strategy used in this research may be applied to other rechargeable batteries, supercapacitors, catalysts, and other electrochemical devices. The Raman vibrational spectra observed on these carbons show a graphitic carbon with significant disorder structure. Further, structural studies reveal a unique disordered carbon nanostructure with a higher interlayer distance of 4.5 Å compared to 3.43 Å in the commercial graphite. The carbon material derived from tires was used as an anode in lithium-ion batteries exhibited a reversible capacity of 360 mAh/g at C/3. However, the reversible capacity increased to 432 mAh/g at C/10 when this carbon particle was coated with a thin layer of carbon. A novel strategy of prelithiation applied for improving the first cycle efficiency to 94% is also presented