Densification of wood – Chemical and structural changes due to ultrasonic and mechanical treatment

This paper presents the state of the art of wood surface densification method by pressing with ultrasound. The properties of ultrasound and its effects on the structure and properties of wood, as well as ultrasound-induced chemical changes in wood material, are described. The following research results were analyzed: the effects of acoustic cavitation in wood material, plasticization of wood lignin by processing with ultrasound, the influence of ultrasound on the wood anatomical structure, the combined effect of ultrasound and wood pressing, and the sterilization of wood using ultrasonic action. Ultrasound causes conversion of lignin from glassy into a quasi-rubbery state, which facilitates compaction of the workpiece surface. Additionally, under ultrasound, growth and collapse of gas bubbles (cavitation phenomena) occur within a liquid medium of wooden substance accompanied by high local temperatures and production of chemically active radicals. This contributes to the destruction of the former and the formation of new bonds in the wood substance, which is important for increasing the stability of the workpiece size after densification. The conclusions made about the ultrasound can be effectively used for the wood plasticization and about prospects of joint use of wood pressing and ultrasound for wood surface densification.

Densification of wood – Chemical and structural changes due to ultrasonic and mechanical treatment

This paper presents the state of the art of wood surface densification method by pressing with ultrasound. The properties of ultrasound and its effects on the structure and properties of wood, as well as ultrasound-induced chemical changes in wood material, are described. The following research results were analyzed: the effects of acoustic cavitation in wood material, plasticization of wood lignin by processing with ultrasound, the influence of ultrasound on the wood anatomical structure, the combined effect of ultrasound and wood pressing, and the sterilization of wood using ultrasonic action. Ultrasound causes conversion of lignin from glassy into a quasi-rubbery state, which facilitates compaction of the workpiece surface. Additionally, under ultrasound, growth and collapse of gas bubbles (cavitation phenomena) occur within a liquid medium of wooden substance accompanied by high local temperatures and production of chemically active radicals. This contributes to the destruction of the former and the formation of new bonds in the wood substance, which is important for increasing the stability of the workpiece size after densification. The conclusions made about the ultrasound can be effectively used for the wood plasticization and about prospects of joint use of wood pressing and ultrasound for wood surface densification.

Nanocellulose from Unbleached Hemp Fibers as a Filler for Biobased Photocured Composites with Epoxidized Cardanol

Biobased composites were successfully prepared using raw materials derived from biomass waste, i.e., an epoxy resin obtained from cardanol and nanocellulose from unbleached hemp fibers. The composites were prepared by solvent exchange and an impregnation of the cellulosic mat with the resin, followed by photocuring. Quantitative conversion was obtained, despite the high amount of fibers (30 wt%) and their absorbance in the UV region of the light spectrum. X-ray diffraction confirmed that the crystalline structure of cellulose did not change during the impregnation and curing process. The cured composites were flexible, hydrophobic, water resistant, transparent with a yellow/brown color, and in the rubbery state at room temperature.

Flotator Oxal as the plasticizer for suspension PVC

The flotator Oxal, mixture of dioxane ethers and alcohols as well as 1, 2 and 3 atomic alcohols, has been studied as a plasticizer for suspension PVC in comparison with the well-known dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DOP). The rheological parameters and gelation ability of plasticizers were determined, the values of the storage modulus and tangent of mechanical loss angle in the glassy and rubbery states were measured by the DMA method, and the glass transition temperatures were determined. The deformation-strength properties and rigidity of polymer films were tested before and after light-thermal aging. Oxal was shown to reveal a fairly low viscosity and high gelation properties in relation to PVC. At the same time, its ability to reduce the glass transition temperature and elasticize the polymer in the glassy and rubbery state is somewhat lower than that of phthalate plasticizers. PVC samples plasticized with DBP have the highest resistance to light-thermal aging.

How dry is dry? Molecular mobility in relation to thallus water content in a lichen

Lichens can withstand extreme desiccation to water contents of ≤ 0.1 g H2O g–1 DW, and in the desiccated state are among the most extremotolerant organisms known. Desiccation-tolerant life-forms such as seeds, mosses and lichens survive ‘vitrification’, that is the transition of their cytoplasm to a ‘glassy’ state, which causes metabolism to cease. However, our understanding of the mechanisms of desiccation tolerance is hindered by poor knowledge of what reactions occur in the desiccated state. Using Flavoparmelia caperata as a model lichen, we determined at what water contents vitrification occurred upon desiccation. Molecular mobility was assessed by dynamic mechanical thermal analysis, and the de- and re-epoxidation of the xanthophyll cycle pigments (measured by HPLC) was used as a proxy to assess enzyme activity. At 20 °C vitrification occurred between 0.12–0.08 g H2O g−1 DW and enzymes were active in a ‘rubbery’ state (0.17 g H2O g−1 DW) but not in a glassy state (0.03 g H2O g−1 DW). Therefore, desiccated tissues may appear to be ‘dry’ in the conventional sense, but subtle differences in water content will have substantial consequences on the types of (bio)chemical reactions that can occur, with downstream effects on longevity in the desiccated state.

Hot Embossing of Micro-Pyramids into Thermoset Thiol-Ene Film

This paper presents the first attempt to texturize a fully crosslinked thermoset shape memory polymer using a hot embossing technique. UV-cured thiol-ene films were successfully embossed with anisotropically-etched Si (100) stamps at a temperature of 100 °C, which is about 50 °C above the glass transition temperature of the polymer. The low storage modulus of the polymer in a rubbery state allowed us to permanently emboss random micro-pyramidal patterns onto the surface of the film with high fidelity by applying 30 MPa pressure for 1 h. Atomic force microscopy (AFM) investigation showed perfect replication of the stamp micropattern with typical height of the largest inverted pyramids close to 0.7 µm and lateral dimensions in the range of 1–2 µm. Changes in surface roughness parameters of the embossed thiol-ene films after annealing them at 100 °C for 1 h or storing for 2 months in air at standard room conditions were negligible. The achieved results open new perspectives for the simple and inexpensive hot embossing technique to be applied for the micropatterning of prepolymerized thermoset shape memory films as an alternative to micropatterning using UV casting.

Dramatic increase in polymer triboelectrification by transition from a glassy to rubbery state

Glassy polymers show an impressive surge in triboelectric surface charge when crossing their respective Tg. In a rubbery state they become softer and more adhesive, therefore heterolysis of polymer bonds and material transfer becomes more probable.

Integrated outstanding precision and mechanical performance of transparent 3D photonic crystal devices employing cross-linked nanospheres via thermoforming in a rubbery state

Transparent photonic crystal devices with preferable optical and mechanical performances fabricated by employing cross-linked photonic crystal nanospheres in a rubbery state.