We report the synthesis and characterization of lignin-based foams by pyrolyzing cold pressed lignin compacts at 300°C, 500°C, 700°C, and 900°C in an argon (Ar) atmosphere. Detailed thermogravimetric analysis (TGA), thermomechanical analysis (TMA), Fourier transform infrared spectroscopy (FTIR), and microstucture analysis was performed on these samples. Scanning electron microscopy (SEM) and X-ray tomography analysis showed that all the foams had cellular structure, and had a total porosity of 93.3%, 94.5%, 93.9%, and 93.4% after pyrolysis at 300°C, 500°C, 700°C, and 900°C, respectively. Comparatively, the fraction of open porosity of the total porosity increased from 89.7% at 300°C to 97.1% and 98.1% at 500°C and 700°C, respectively, and then decreased to 93.0 % at 900°C. The averaged ultimate compressive strength (UCS) of the foams fabricated at 300°C was ~0.77 MPa. It decreased to ~0.49 MPa at 500°C, after which it increased to ~0.95 MPa at 700°C and then retained similar strength at 900°C. Detailed FTIR analysis showed a decreased in intensity of peaks for all the samples fabricated at higher temperatures, which was further correlated with changes in lignin molecular structure. By analyzing TGA, TMA, FTIR, and microstructure, a novel mechanism for designing lignin-based cellular solids has been proposed in this work. The wettability study by sessile drop test showed that the foams are hydrophobic after pyrolyzing at 300°C and 500°C, after which the compacts became hydrophilic after pyrolyzing at 700°C and 900°C, respectively.

No abstract

We report the synthesis and characterization of PEEK-MAX (Ti 3 SiC 2 , Ti 3 AlC 2 , and Cr 2 AlC), and PEEK-MoAlB composites by hot-pressing. Detailed microstructure analysis by scanning electron microscopy showed that Ti 3 SiC 2 particles are well dispersed in the PEEK matrix after the addition of 5 vol% Ti 3 SiC 2 but at higher concentration (≥10 vol%), the Ti 3 SiC 2 particles segregated at the phase boundaries and formed interpenetrating micro-networks. PEEK-Ti 3 AlC 2 and PEEK-MoAlB composites also showed similar structuring at the microstructural level. PEEK-Cr 2 AlC composites showed a different behavior where Cr 2 AlC particles were well dispersed in the PEEK matrix. All the three PEEK-MAX composites have lower hardness than PEEK-MoAlB composites as MoAlB particulates are appreciably harder than MAX phases but were harder than PEEK. Due to heterogenous nucleation, the addition of MAX phases or MoAlB reduced the crystallization temperature (T c) by a few o C. The formation of imperfect crystals also resulted in the lowering of melting point (T m) of these composites. PEEK reinforced with 10 vol% Ti 3 SiC 2 , Ti 3 AlC 2 and MoAlB showed plastic failure, and had higher strength than PEEK. Comparatively, PEEK reinforced with 10 vol% Cr 2 AlC did not show any enhancement. All the PEEK-MAX and PEEK-MoAlB composites showed triboactive behavior and enhanced wear resistance.

No abstract

In this paper, we report the synthesis and characterization of pyrolyzed lignin compacts reinforced with 50 wt % wheat straw (WS) or sugar beet pulp (SBP) fibers. The compacts were pyrolyzed at 300, 500, 700, and 900 °C in an Ar atmosphere. Detailed thermogravimetric analysis (TGA), thermomechanical analysis (TMA), Fourier transform infrared (FTIR) spectroscopy, and microstructure analysis were performed on these samples. FTIR analysis showed that pyrolysis of lignin–WS and lignin–SBP resulted in aromatic char. Scanning electron microscope (SEM) studies showed that foams obtained by pyrolyzing both lignin–50 wt % SBP and lignin–50 wt % WS composites have a cellular structure. X-ray tomography and energy-dispersive spectrometry (EDS) studies showed that pyrolysis of wheat straw caused the formation of mineral-rich nodules in the pyrolyzed lignin matrix, which was responsible for the denser and uniform microstructure of the lignin–WS composites. Due to this reason, the lignin–WS composites were denser and had a better mechanical strength as compared to the lignin–SBP composites. Both the compositions also showed temperature-dependent wettability behavior.