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.

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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.

In this paper, we report the synthesis and characterization of polylactic acid (PLA)‐MAX (Ti3SiC2, Ti3AlC2, and Cr2AlC) and PLA‐MoAlB composites by fused deposition modeling (FDM). Detailed scanning electron microscopy (SEM) studies showed that the particulate phases are uniformly dispersed in the PLA matrix of 3D‐printed samples. Differential scanning calorimetry (DSC) results showed that the addition of MAX phases promoted crystallization of PLA matrix as compared to MoAlB particulates. The mechanical testing results showed that the PLA matrix is sensitive to the addition of MAX or MoAlB phases, for example, PLA‐5 wt% Ti3SiC2, PLA‐5 wt% Ti3AlC2, and PLA‐5 wt% Cr2AlC had a UTS of ~39 MPa, ~30.5 MPa, and ~38.7 MPa as compared to ~41.5 MPa in pure PLA. Comparatively, PLA‐5 wt% MoAlB had a UTS of ~23.2 MPa which shows that predominantly amorphous PLA‐MoAlB composites have lower strength. The tribological behavior improved after the addition of 1 wt% additives, for example, in PLA‐Cr2AlC, the friction coefficient decreased by 76% to ~0.26 from ~0.34 in pure PLA, and the WR marginally decreased in PLA‐1 wt% Cr2AlC to ~2.2 × 10−5 mm3/Nm as compared to 7.7 × 10−5 mm3/Nm in PLA. SEM investigations of the tribosurfaces showed the tribology is governed by the formation of tribofilms. The wettability study showed that all the 3D‐printed samples are hydrophilic in nature.

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