Factor Affecting Gel Time/Process-Ability of Urea Formaldehyde Resin Based Wood Adhesives

Abstract

Urea-formaldehyde (UF) resin presents the most utilized adhesive system in the manufacture of plywood, particleboard and fiberboard. At the temperatures above 100˚C in the presence of hardener, this resin undergoes crosslinking reaction and the formation of three dimensional cross linked structures takes place and bonding of wood particles in a hot press [1]. UF powder resins show high reactivity and good performance in the production and by their low price; however they lack in water resistance of the hardened resin [2]. Urea-formaldehyde (UF) resins are the most important type of adhesive resins for the production of wood based panels but process-ability and curing behavior of urea formaldehyde resin depended on various factors related to resin properties, types of wood and their properties, amount & type of catalyst, types and amount of polymers addition and environmental conditions [3]. This factor decides the process-ability of UF resin based composite during manufacturing of plywood, particle board and fiberboard. In this review paper, various factors affecting gel time and process-ability of UF resin based wood composite are reviewed.

Chemical composition of Luffa aegyptiaca Mill., Agave durangensis Gentry and Pennisetum sp.

“…Regularly extractives alter the properties of the lignocellulosic material, which in turn modifies its adhesion properties ( Gadhave, Mahanwar & Gadekar, 2017 ; Hse & Kuo, 1988 ). Four of the five materials studied, had low content of non-polar extractives, with the exception of the leaves of Pennisetum sp.…”

The Buffer Effect of Different Wood Species and the Influence of Oak on Panel Composites Binders

“…The formation and strength of glued joints are influenced by numerous wood characteristics. Most of wood species are acidic [ 6 ], and this characteristic affects their wettability [ 5 ], as well as their interaction with the resin [ 7 ].…”

“…The above used term “buffer capacity” refers to the wood’s resistance to a change in pH [ 6 ]. When a high buffer capacity wood is used, a high amount of acid (generally a H 2 SO 4 solution) or alkali (generally a NaOH solution) must be added to change the overall mixture pH.…”

“…The only chance to react to its changes and consequently adapt panels production and performance is through specific measurements. For instance, in order to obtain an optimum bond strength, the press time and temperature must be adjusted depending on the pH environment [ 6 ]. An interesting 2006 laboratory study demonstrated a strong relationship between the buffer capacity of particleboard furnish and its corresponding near-infrared (NIR) spectra via a multivariate analysis (chemometrics) [ 16 ].…”

Comparison of Methodologies for Acid Buffering Capacity Determination—Empirical Verification of Models

“…The chemical properties of wood and wood extractives, such as pH value and buffering capacity, are considered prime factors in bonding [5]. The gel time of a urea-formaldehyde (UF) resin strongly depends on the acidity of the wood substrate which is associated with the content of the wood extractives [6,7]. The buffering capacity of a material is the sum of the buffering capacities of each individual acidic and basic component and the effect of the interactions among them [8].…”