Effect of Hot-Pressing Temperature on Characteristics of Straw-Based Binderless Fiberboards with Pulping Effluent

Effect of Hot-Pressing Temperature on the Properties of Eco-Friendly Fiberboard Panels Bonded with Hydrolysis Lignin and Phenol-Formaldehyde Resin

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.

Preparation of Molded Fiber Products from Hydroxylated Lignin Compounded with Lewis Acid-Modified Fibers Its Analysis

In this study, molded fiber products (MFPs) were prepared from lignin compounded with Lewis acid-modified fibers using enzymatic hydrolysis lignin (EHL) as a bio-phenol. The fibers were modified and compounded entirely through hot-pressing. To improve the reactivity of enzymatic lignin, hydroxylated enzymatic hydrolysis lignin (HEHL) was prepared by hydroxylation modification of purified EHL with hydrogen peroxide (H2O2) and ferrous hydroxide (Fe(OH)3). HEHL was mixed uniformly with Lewis acid-modified fibers on a pressure machine and modified during the molding process. The purpose of Lewis acid degradation of hemicellulose-converted furfural with HEHL was to generate a resin structure to improve the mechanical properties of a MFPs. The microstructure of the MFP was shown to be generated by resin structure, and it was demonstrated that HEHL was compounded on Lewis acid-modified fibers during the molding process. The thermal stability of the MFP with composite HEHL did not change significantly owing to the addition of lignin and had higher tensile strength (46.28 MPa) and flexural strength (65.26 MPa) compared to uncompounded and modified MFP. The results of this study are expected to promote the application of high lignin content fibers in molded fibers.

Influence of Lignocellulosic Waste Pre-Treatment on the Characteristics of Bond Rupture

Post-harvest crop residues are an interesting raw material for the production of composite materials. However, their surface often contains waxy and siliceous substances, which can cause adhesion problems. Therefore, various surface pre-treatment methods have been developed to increase the surface tension of these particles and hence to improve adhesive adhesion. The influence of hydrothermal, chemical, plasma and enzymatic treatment was investigated. The aim of the paper is to evaluate the effect of pre-treatments of post-harvest crop residues on the nature of joint failure and adhesive dispersion on the particles. The evaluation is based on microscopic analysis of particles obtained from the rupture area after internal bonding tests. The nature of bond failure and adhesive dispersion on the particle surface is evaluated. The results show a clear influence of material pre-treatment on the failure bond of the bond and, to a large extent, correlate with the mechanical properties of composites published in previous studies. The most suitable treatment appears to be a plasma treatment at a properly adjusted intensity. Conversely, the unsuitable treatment was alkaline, which, although it increased adhesion, deteriorated the overall mechanical properties. Hydrothermal treatment could be also considered as an industrially suitable method.