The quality of the wood bonding depending on the method of applying the selected thermoplastic biopolymers

The quality of the wood bonding depending on the method of applying the selected thermoplastic biopolymers. The aim of the research was to determine the effect of the method of applying the biopolymer on the surface of bonding solid wood elements on the quality of the obtained adhesive connection. The results of conducted mechanical research show that the highest average value of shear strength was observed for birch lamellas bonded with PLA, both with the first and second method of application. In case of estimating the quality of the bonding of wooden elements, better results were achieved for PLA and the second method of application the "green" adhesive.

OVERVIEW OF GLUED WOOD BUILDING MATERIALS

Currently, environmental friendliness is one of the main requirements for products of any kind all over the world. The use of wood as a building material fully meets this requirement. Every year the share of wooden housing construction increases, and not only in the segment of low-rise, but also multi-storey wooden houses and structures. When working with a tree, it is necessary to take into account its features and disadvantages. When the humidity changes, the wood changes its size, is affected by fungi and insects, and has a high fire hazard class. In order to improve the performance properties of wood, its modification is widely used, through the use of various processing methods: drying, heat treatment, impregnation with various compositions, gluing. Recently, a large number of innovative construction materials based on wood bonding have appeared on the market: LVL-beams, CLT-panels, glued beams, wooden I-beams. The use of these materials from glued wood in construction allows the use of renewable, eco-friendly raw materials. And despite the higher cost of these materials compared to traditional building materials, they are competitive in their properties: light weight, less load on the foundation, are not subject to corrosion, are easily installed even in areas with difficult engineering and geological conditions, when exposed to fire, they retain their structural strength longer, are easily transported and disposed of.

Application of Myrcia splendens tannins in the composition of urea-formaldehyde adhesive for sustainable wood bonding

Tannins from Myrcia splendens from the Amazon rainforest were used for the first time in the formulation of a urea-tannin-formaldehyde (UTF) resin. The objective was to evaluate the effect of different tannin proportions on the glue line performance in Pinus sp. woods, glued with UTF adhesive. The tannins were extracted in a water bath, using 1500 mL of water and 100g of dry bark (liquor/bark 15:1), with addition of 3% Na2SO3, at a temperature of 70 °C for three hours. The adhesives formulations were based on the gradual replacement of mass of the urea-formaldehyde (UF) adhesive by tannin powder, totalizing four compositions and one control treatment. UTF adhesives were evaluated for their physicochemical properties, shear bond strength (wet and dry) and wood failure. The addition of M. splendens tannins to the urea formaldehyde adhesive promoted an increase in glue line strength. The proportion of 5.0% of tannins proved to be ideal in the formulation of the UTF adhesive, considering all the parameters evaluated. Thus, this study proves the potential use of Amazonian tannins from Myrcia splendens in the partial composition of more sustainable UTF adhesives.

Wood Adhesives Based on Natural Resources: A Critical Review: Part IV. Special Topics

Various naturally-based chemicals can be used directly as wood adhesives or are precursors for the synthesis of adhesive resins. Liquefaction and pyrolysis of wood yield various smaller chemicals derived from the different wood components, which then are used in the preparation of adhesives by replacing mainly phenol as raw material. The possible replacement of formaldehyde in aminoplastic and phenolic resins would solve the question of the subsequent formaldehyde emission.<br/> The multiple unsaturations of the triglycerides in vegetable oils enable polymerization for the direct synthesis of thermosets, as well as bases for polyfunctionalization and crosslinking.<br/> Natural polymers, such as poly(lactic acid)s (PLAs), natural rubber, or poly(hyhydroxyalkanoate)s (PHAs) are thermoplastics and can be used for various special applications in wood bonding, in case they can also be crosslinked. For other thermoplastic wood adhesives, such as PUR or PA, chemicals based on natural resources can at least replace a part or even all synthetic raw materials (monomers); these monomers derive from targeted decomposition of the wood material in biorefineries.<br/> Cellulose nanofibrils (CNFs) can be used as as sole adhesives or as components of adhesives. Hydrogen bonding has a key function in binder applications related to adhesion between cellulose nanoparticles and other materials. CNFs are able to establish strong bonding between wood particles/fibres through flexible and strong films by a simple drying process.<br/> Cashew nut shell liquid (CNSL) is a by-product of the cashew nut processing with cardanol (CD) as main component. CD-formaldehyde resins show improved flexibility compared to phenol-formaldehyde (PF) resins; CD can replace up to 40% of the phenol.