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.

Accelerated Weathering Testing (AWT) and Bacterial Biodegradation Effects on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/Rapeseed Microfiber Biocomposites Properties.

In the context of sustainable materials, this study explores the effects of accelerated weathering testing and bacterial biodegradation on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/rapeseed microfiber biocomposites. Accelerated weathering, simulating outdoor environmental conditions, and bacterial biodegradation, representing natural degradation processes in soil, were employed to investigate the changes in the mechanical, thermal and morphological properties of these materials during its post-production life cycle. Attention was paid to the assessment of the change of structural, mechanical and calorimetric properties of alkali and N-methylmorpholine N-oxide (NMMO)-treated rapeseed microfiber (RS)-reinforced plasticized PHBV composites before and after accelerated weathering. Results revealed that accelerated weathering led to an increase in stiffness, but a reduction in tensile strength and elongation at break, of the investigated PHBV biocomposites. Additionally, during accelerated weathering, the crystallinity of PHBV biocomposites increased, especially in the presence of RS, due to both the hydrolytic degradation of the polymer matrix and the nucleating effect of the filler. It has been observed that an increase in PHBV crystallinity, determined by DSC measurements, correlates with the intensity ratio I1225/1180 obtained from FTIR-ATR data. The treatment of RS microfibers increased the biodegradation capability of the developed PHBV composites, especially in the case of chemically untreated RS. All the developed PHBV composites demonstrated faster biodegradation in comparison to neat PHBV matrix.

Visco-Elastic and Thermal Properties of Microbiologically Synthesized Polyhydroxyalkanoate Plasticized with Triethyl Citrate.

The current research is devoted to the investigation of the plasticization of polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-hydroxyvalerate (PHBV) with triethyl citrate (TEC). Three different PHB or PHBV-based systems with 10, 20, and 30 wt.% of TEC were prepared by two-roll milling. The effect of TEC on the rheological, thermal, mechanical, and calorimetric properties of the developed compression-molded PHB and PHBV-based systems was determined. It was revealed that the addition of TEC significantly influenced the melting behavior of both polyhydroxyalkanoates (PHA), reducing their melting temperatures and decreasing viscosities. It was also revealed that all the investigated systems demonstrated less than 2% weight loss until 200 °C and rapid degradation did not occur until 240-260 °C in an oxidative environment. Apart from this, a remarkable increase (ca 2.5 times) in ultimate tensile deformation εB was observed by increasing the amount of TEC in either PHB or PHBV. A concomitant, considerable drop in ultimate strength σB and modulus of elasticity E was observed. Comparatively, the plasticization efficiency of TEC was greater in the case of PHBV.

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.

p-Type PVA/MWCNT-Sb2Te3 Composites for Application in Different Types of Flexible Thermoelectric Generators in Combination with n-Type PVA/MWCNT-Bi2Se3 Composites.

This work is devoted to the fabrication of p-type polyvinyl alcohol (PVA)-based flexible thermoelectric composites using multiwall carbon nanotubes-antimony telluride (MWCNT-Sb2Te3) hybrid filler, the study of the thermoelectrical and mechanical properties of these composites, and the application of these composites in two types (planar and radial) of thermoelectric generators (TEG) in combination with the previously reported PVA/MWCNT-Bi2Se3 flexible thermoelectric composites. While the power factors of PVA/MWCNT-Sb2Te3 and PVA/MWCNT-Bi2Se3 composites with 15 wt.% filler were found to be similar, the PVA/MWCNT-Sb2Te3 composite with 25 wt.% filler showed a ~2 times higher power factor in comparison with the PVA/MWCNT-Bi2Se3 composites with 30 wt.% filler, which is attributed to its reduced electrical resistivity. In addition, developed PVA/MWCNT-Sb2Te3 composites showed a superior mechanical, electrical, and thermoelectric stability during 100 consequent bending cycles down to a 3 mm radius, with insignificant fluctuations of the resistance within 0.01% of the initial resistance value of the not bent sample. Demonstrated for the first time, 2-leg TEGs composed from p-type PVA/MWCNT-Sb2Te3 and n-type PVA/MWCNT-Bi2Se3 composites showed a stable performance under different external loads and showed their potential for applications involving low temperature gradients and power requirements in the range of nW.

Characterisation of Nanoclay and Spelt Husk Microfiller-Modified Polypropylene Composites.

Current research is devoted to the investigation of spelt husk (SH) and nanoclay-modified compatibilised polypropylene (PP) binary and ternary composites for injection-moulding applications. PP composites were obtained using twin-screw extrusion. The content of mechanically milled SH microfiller with aspect ratio within 2 and 6 was fixed at 40 wt.%, whereas the amount of nanoclay functional filler in the polypropylene matrix was changed in the range from 0.5 to 5 wt.%. Nanoclay filler was introduced in the polypropylene matrix either in the form of nanoclay powder (C) or as a masterbatch (M). Regular distribution of the clay nanofiller within the polymer matrix has been observed, disregarding its form and concentration. The effects of the individual or combined addition of SH microreinforcement and nanoclay fillers on the rheological, mechanical, calorimetric, and thermal properties of the developed PP composites were investigated. It is revealed that the addition of the nanoclay fillers insignificantly influences the viscosity of both PP nanocomposites and hybrid composites with SH. Additionally, for PP nanocomposites, remarkable increases in tensile and flexural modules and strength are observed by maintaining considerable ultimate deformations, mainly in the case of M-containing systems. Concomitantly, because of the addition of the nanoclay filler, the improvement in thermal stability of PP nanocomposites and PP hybrid composites with SH is observed. As a result of SH addition, considerable increases in tensile and flexural modules are also observed. Results of the research demonstrate the potential of the use of natural materials (agricultural residues and clay minerals) for the development of PP composites with increased stiffness and thermal properties.

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.