An in situ Raman spectroscopic method for quantification of polyethylene glycol (PEG) in waterlogged archaeological wood

The weakened microstructure of archaeological wood (AW) objects from waterlogged environments necessitates consolidation to avoid anisotropic shrinkage upon drying. Polymer impregnation through submergence or spraying treatments is commonly applied, and for larger and thicker objects, the impregnation period can stretch over decades. Thus, for efficient treatment, continuous monitoring of the impregnation status is required. Today, such monitoring is often destructive and expensive, requiring segments for extraction and chromatographic quantification. This study proposes an in situ Raman spectroscopic method for quantification of polyethylene glycol (PEG) in waterlogged AW. A calibration model was built on standards of PEG, cellulose powder, and milled wood lignin using orthogonal partial least squares (OPLS). The OPLS model had a strong linear relationship, and the PEG content in wood of varying degrees of degradation could be determined. However, the accuracy of the model was low with a root mean square error of prediction of 11 wt%. The low accuracy was traced to the heterogeneity in the calibration and validation set samples with regard to the small probing volume of the confocal instrumental setup.

Synthesis of Polycarbosilane, Polymer Impregnation Pyrolysis based C SiC Composites and Prototype Development

Due to some extraordinary thermo-mechanical properties, silicon carbide is considered one of the best materials used for high temperature applications in defence and aerospace. Polycarbosilane (PCS) has been widely used as SiC precursor. This paper describes the research and development work undertaken to establish the technologies for synthesis and characterisation of PCS, fabrication process and characterisation of Carbon fibre reinforced SiC matrix (C/SiC) composite laminates and shaped articles. The molecular weight and softening point of the PCS was found to be 1400-1800 Mn and 140-150 °C respectively. Flexural stress of the unidirectional (UD) C/SiC composites and bidirectional (2D) C/SiC composites was found to be 400-450 MPa and 300-350 MPa respectively. Tensile stress of the 2D C/SiC composite was found to be around 200 MPa. Coefficient of thermal expansion and thermal diffusivity of the 2D C/SiC composites at RT- 1000 °C were found to be in range of 0.3-2.2×10-6/ °C and 32-6 mm2/s respectively. The fabrication process developed for the UD and 2D C/SiC composites using the indigenous PCS has been also demonstrated to fabricate typical size divergent rocket nozzle and hot structure. Fabrication process of the SiC fibre has also been described in brief.

Effect of H2O2 Bleaching Treatment on the Properties of Finished Transparent Wood

Transparent wood samples were fabricated from an environmentally-friendly hydrogen peroxide (H2O2) bleached basswood (Tilia) template using polymer impregnation. The wood samples were bleached separately for 30, 60, 90, 120 and 150 min to evaluate the effects on the changes of the chemical composition and properties of finished transparent wood. Experimental results showed decreases in cellulose, hemicellulose, and lignin content with an increasing bleaching time and while decreasing each component to a unique extent. Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) analysis indicated that the wood cell micro-structures were maintained during H2O2 bleaching treatment. This allowed for successful impregnation of polymer into the bleached wood template and strong transparent wood products. The transparent wood possessed a maximum optical transmittance up to 44% at 800 nm with 150 min bleaching time. Moreover, the transparent wood displayed a maximum tensile strength up to 165.1 ± 1.5 MPa with 90 min bleaching time. The elastic modulus (Er) and hardness (H) of the transparent wood samples were lowered along with the increase of H2O2 bleaching treatment time. In addition, the transparent wood with 30 min bleaching time exhibited the highest Er and H values of 20.4 GPa and 0.45 GPa, respectively. This findings may provide one way to choose optimum degrees of H2O2 bleaching treatment for transparent wood fabrication, to fit the physicochemical properties of finished transparent wood.