Stoyko Petrin

Lignin is the natural binder in wood and lignocellulosic plants and is regarded as the main natural and renewable source of phenolic compounds. Its incorporation in the composition of fiberboards will enhance both the environmental performance of the panels and the complex use of natural resources. In recent years, the increased valorization of hydrolysis lignin in value-added applications, including adhesives for bonding fiberboard panels, has gained significant research interest. Markedly, a major drawback is the retention of lignin in the pulp until the hot-pressing process. This problem could be overcome by using a small content of phenol–formaldehyde (PF) resin in the adhesive mixture as an auxiliary binder. The aim of this research work was to investigate and evaluate the effect of the hot-pressing temperature, varied from 150 °C to 200 °C, in a modified hot-press cycle on the main physical and mechanical properties of fiberboard panels bonded with unmodified technical hydrolysis lignin (THL) as the main binder and PF resin as an auxiliary one. It was found that panels with very good mechanical properties can be fabricated even at a hot-pressing temperature of 160 °C, while to provide the panels with satisfactory waterproof properties, it is necessary to have a hot-pressing temperature of at least 190 °C.

Background: Bioconjugates are promising alternatives for the multiple targeting of any disease. Pyrrole heterocycle is well known with many activities and is a building block of a lot of medical drugs. On the other hand, peptides are short molecules with many advantages such as small size, ability to penetrate the cell membrane and bond-specific receptors, vectorizing potential, etc. Thus, hybrid molecules between peptide and pyrrole moiety could be a promising alternative as an anti-pain tool. Methods: New bioconjugates with a general formula Pyrrole (α-/β-acid)-FELL-OH (NH2) were synthesized using Fmoc/OtBu peptide synthesis on solid support. HPLC was used to monitor the purity of newly synthesized bioconjugates. Their structures were proven by electrospray ionization mass spectrometry. The Paw Pressure test (Randall–Selitto test) was used to examinate the analgesic activity. Hydrolytic stability of targeted structures was monitored in three model systems with pH 2.0, 7.4 and 9.0, including specific enzymes by means of the HPLC-UV method. Results: The obtained results reveal that all newly synthesized bioconjugates have analgesic activity according to the used test but free pyrrole acids have the best analgesic activity. Conclusions: Although free pyrrole acids showed the best analgesic activity, they are the most unstable for hydrolysis. Combination with peptide structure leads to the hydrolytic stabilization of the bioconjugates, albeit with slightly reduced activity.

Unlike the recycling of particleboards, the recycling of medium-density fiberboards (MDF) is not a widespread industrial practice, and currently, most waste MDF panels are landfilled or incinerated after the end of their life cycle. Therefore, it is of great importance to develop cost-effective methods for MDF recycling. The extraction of resins used for bonding the panels, mostly urea–formaldehyde (UF) resins, is carried out mainly with hydrolysis. Hydrothermal hydrolysis is a more environmentally friendly and cheaper recycling technique compared to acid hydrolysis and allows obtaining a high yield of recycled fibers. The aim of this research work was to investigate and evaluate the effect of hydrolysis regime applied on its efficiency and on the properties of the recycled MDF fibers. For this purpose, thermal hydrolysis was carried out in an autoclave with saturated steam as a heat carrier. The main novelty of the research is the preliminary preparation of the recyclable MDF in samples with dimensions close to those of pulp chips. The effect of hydrolysis regime characteristics, i.e., process time and temperature on the properties of recycled MDF wood fibers, was studied. The hydrolysis temperatures used were 121 °C (saturated steam pressure of 0.2 MPa) and 134 °C (saturated steam pressure of 0.3 MPa); for each temperature, three durations were applied—30, 45, and 60 min. After hydrolysis, the resulting fiber fraction was refined using a hammer mill. The fractional and elemental composition of the recycled fibers obtained were evaluated. The hemicellulose content after each hydrolysis treatment was also determined. The chemical oxygen demand (COD) was defined as an indicator of wastewater contamination and as an indirect indicator of the quantitative yield of the process. The results revealed no significant changes in the elemental composition of the recycled fibers, and the hydrolysis regimes used showed no decrease in pentosan content. The recycled MDF fibers exhibited similar fiber morphology and fractional composition, being shorter than fibers from industrial pulp. The increased temperature and time of hydrolysis resulted in a significant increase in COD values. Based on the obtained results, with a view to the slightest contamination of wastewater (as determined by COD), the most promising hydrolysis regime was at a temperature of 121 °C and a time of 30 min. It should be emphasized that for a confirmation of this statement, the properties of MDF panels fabricated with fibers recycled in different regimes should be subsequently investigated.