Chemical Composition and Mechanical Properties of Wood after Thermal Modification in Closed Process under Pressure in Nitrogen

In this study, silver birch (Betula pendula) and Scots pine (Pinus sylvestris) wood planks (1000 × 100 × 25 mm) were thermally modified in pilot-scale equipment. Research extended our knowledge of the thermal modification (TM) process in a closed system under nitrogen pressure, as well as how process parameters affect the chemical composition and mechanical strength of wood. Various TM regimes were selected-maximum temperature (150-180 °C), modification time (30-180 min), and initial nitrogen pressure (3-6 bar). Chemical analyses were performed to assess the amount of extractives, lignin, polysaccharides and acetyl group content following the TM process. The mechanical properties of TM wood were characterized using the modulus of rupture (MOR), modulus of elasticity (MOE), and Brinell hardness. The MOR of both studied wood species following TM in nitrogen was reduced, but MOE changes were insignificant. The Brinell hardness of TM birch wood's tangential surface was much higher than that of the radial surface, although Scots pine wood showed the opposite pattern. TM birch and pine wood specimens with the highest mass loss, acetone soluble extractive amount, and the lowest xylan and acetyl group content had the lowest MOR and Brinell hardness.

Research of Potential Catalysts for Two-Component Silyl-Terminated Prepolymer/Epoxy Resin Adhesives

The current research is devoted to the research of potential catalysts for the two-component silyl-terminated prepolymer/epoxy resin system. The catalyst system must catalyze the prepolymer of the opposite component while not curing the prepolymer in the component in which the catalyst is located. Mechanical and rheological characterization of the adhesive was performed. The results of the investigation showed that certain alternative catalyst systems, which are less toxic, may be used instead of traditional catalysts for individual systems. Two-component systems, obtained by using these catalysts systems, cure in an acceptable time scale and demonstrate relatively high tensile strength and deformation values.

Positive and Negative Changes in the Electrical Conductance Related to Hybrid Filler Distribution Gradient in Composite Flexible Thermoelectric Films Subjected to Bending

P-type multiwalled carbon nanotubes (MWCNTs), as well as heterostructures fabricated by direct deposition of inorganic thermoelectric materials as antimony and bismuth chalcogenides on MWCNT networks are known as perspective materials for application in flexible thermoelectric polymer-based composites. In this work, the electrical response of three types of Sb₂Te₃-MWCNT heterostructures-based flexible films-free standing on a flexible substrate, encapsulated in polydimethylsiloxane (PDMS), and mixed in polyvinyl alcohol (PVA) is studied in comparison with the flexible films prepared by the same methods using bare MWCNTs. The electrical conductance of these films when each side of it was subsequently subjected to compressive and tensile stress during the film bending down to a 3 mm radius is investigated in relation to the distribution gradient of Sb₂Te₃-MWCNT heterostructures or bare MWCNTs within the film. It is found that all investigated Sb₂Te₃-MWCNT films exhibit a reversible increase in the conductance in response to the compressive stress of the film side with the highest filler concentration and its decrease in response to the tensile stress. In contrast, free-standing and encapsulated bare MWCNT networks with uniform distribution of nanotubes showed a decrease in the conductance irrelevant to the bending direction. In turn, the samples with the gradient distribution of the MWCNTs, prepared by mixing the MWCNTs with PVA, revealed behavior that is similar to the Sb₂Te₃-MWCNT heterostructures-based films. The analysis of the processes impacting the changes in the conductance of the Sb₂Te₃-MWCNT heterostructures and bare MWCNTs is performed. The proposed in this work bending method can be applied for the control of the uniformity of distribution of components in heterostructures and fillers in polymer-based composites.

Comparison of Two-Component Silyl-Terminated Polyether/Epoxy Resin Model and Complete Systems and Evaluation of Their Mechanical, Rheological and Adhesive Properties

The current research is devoted to the investigation of the influence of a secondary amine compatibilizer and customized additive package on the tensile, rheological and adhesive properties of a Silyl-terminated polyether (SIL)/Epoxy resin (EP) model and completed two-component systems. A SIL/EP model and completed two-component systems were developed over a broad range of the both pre-polymer ratios (90/10-30/70 wt.-to-wt%). Additive packages of the components A and B were designed to prevent premature polycondensation of the respective pre-polymers (including suitable catalysts for each of the pre-polymers, as well as vinyltrimetoxysilane as a drying agent for moisture control), to ensure easy processing and stable performance of the system. Results of the investigation testify that the values of the tensile strength and Shore-A hardness of the compatibilized systems are higher in comparison to unmodified ones. In the presence of the additive package, a further improvement of tensile strength and tensile strain values is observed for SIL-rich compositions (SIL content above 70 wt%), whereas at lower SIL concentrations, the reinforcing effect is considerably reduced. In respects to adhesion properties, the highest values to a broad range of substrates with different surface polarities are observed at the SIL/EP range from 80/20 to 50/50 wt.-to-wt%.

Flexible N-Type Thermoelectric Composites Based on Non-Conductive Polymer with Innovative Bi2Se3-CNT Hybrid Nanostructured Filler

This research is devoted to the fabrication of polyvinyl alcohol (PVOH) based n-type thermoelectric composites with innovative hybrid bismuth selenide-multiwalled carbon nanotube (Bi₂Se₃-MWCNT) fillers for application in flexible thermoelectric devices. Hybrid fillers were synthesized by direct deposition of Bi₂Se₃ on multiwalled carbon nanotubes using a physical vapor deposition method, thus ensuring direct electrical contact between the carbon nanotubes and Bi₂Se₃. The Seebeck coefficient of prepared PVOH/Bi₂Se₃-MWCNT composites was found to be comparable with that for the Bi₂Se₃ thin films, reaching -100 µV·K^-1 for the composite with 30 wt.% filler, and fluctuations of the resistance of these composites did not exceed 1% during 100 repetitive bending cycles down to 10 mm radius, indicating the good mechanical durability of these composites and proving their high potential for application in flexible thermoelectrics. In addition, other properties of the fabricated composites that are important for the use of polymer-based materials such as thermal stability, storage modulus and linear coefficient of thermal expansion were found to be improved in comparison with the neat PVOH.

The relationship of structure, thermal and water vapor permeability barrier properties of poly(butylene succinate)/organomodified beidellite clay bionanocomposites prepared by in situ polycondensation

The exploitation of beidellite clay (BDT), used as a nanofiller in the preparation of poly(butylene succinate) (PBS)/organoclay biodegradable nanocomposites, was investigated. A series of bionanocomposites with various loadings of the organoclay (3CTA-BDT) were prepared by in situ polycondensation reaction between succinic anhydride (SuAh) and 1,4-butanediol (1,4-BD) at atmospheric pressure in refluxing decalin with azeotropic removal of water, and the reaction was catalyzed by non-toxic bismuth chloride (BiCl₃). X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that 3CTA-BDT was likely exfoliated and well dispersed in PBS matrix. Thermal properties (TGA, DSC and thermal conductivity), contact angle measurements and water vapor sorption behavior of the corresponding nanocomposites were also discussed. Compared to pure PBS, a significant reduction of the diffusion coefficient and the water vapor permeability (WVP) by 44 and 37%, respectively, was observed by adding only 5 wt% of 3CTA-BDT. These results could make these bionanocomposites suitable materials for food packaging application.

The exploitation of beidellite clay (BDT), used as a nanofiller in the preparation of poly(butylene succinate) (PBS)/organoclay biodegradable nanocomposites, was investigated. Their thermal and water vapor barrier properties were also studied.

Radiation-chemically modified PP/CNT composites

In this work, the authors studied the effects of electron beam (EB)-induced changes in stress-strain characteristics, heat shrinkage stresses, and structure characteristics on polypropylene (PP) composites containing bisphenol-A-dimethacrylate (BPDMA) as the radiation sensitizer and different contents of multi-walled carbon nanotube (CNT) filler (0–2 wt.%). The effect of stearic acid (SA) as the surface modifier on the improvement of CNT dispersion in the PP matrix was also studied. Initially, PP blends with different contents (up to 10 wt.%) of BPDMA were prepared to determine the effective concentration of the sensitizer for the modification of the PP matrix. PP/BPDMA composites and blends filled with CNTs were irradiated up to 25–50 kGy of radiation doses. The properties of unirradiated compositions and those modified by EB, were compared. Radiation-induced changes were confirmed by gel fraction and by the changes in Fourier transform infrared spectroscopy spectra. The results showed an increase in Young’s modulus, yield strength, and thermal-relaxation stresses for the irradiated PP/CNT compositions grafted with 3 wt.% of BPDMA and compatibilized with SA.