¹³C NMR study of presence of uron structures in amino adhesives and relation with wood‐based panels performance

Abstract

The chemical structure of amino adhesives produced by the strongly acid process was investigated by 13 C Nuclear Magnetic Resonance spectroscopy. This technique allowed the identification of functional groups and its quantitative determination. Concentration of cyclic polymeric structures (urons) was shown to be related with adhesive performance and with particleboard physicomechanical properties and formaldehyde content. Higher urons concentration presented lower viscosity and reactivity. Particleboards produced with resins with lower urons concentration presented lower formaldehyde content, but also lower internal bond strength. Wood-based panels produced fulfilled E1 class requirements for formaldehyde emissions, indicating that strongly acid process is an alternative to the conventional alkaline-acid process.

Decreasing the formaldehyde emission in urea‐formaldehyde using modified starch by strongly acid process

“…For all types of the modified resins, the plywood prepared by method I shows the worst bonding strength than that of blank UF resin, which is labeled as the dash line in Figure . The reason may be because at method I formaldehyde, which was supposed to offer the cross‐link, was consumed by the reaction with glucose as shown in Figure . The plywood made from resins prepared via method II and method III showed comparable bonding strength to that of blank UF resin.…”

“…Emissions have two origins: unreacted formaldehyde and hydrolysis of UF linkages . Costa et al also reported that decomposition of hexamine formed as by‐product during cure also contributes for formaldehyde release during lifetime of board. The formaldehyde emission from the panel used interior application was one of the factors affecting sick buildings syndrome in an indoor environment.…”

Urea formaldehyde resin with low formaldehyde content modified by phenol formaldehyde intermediates and properties of its bamboo particleboards

“…The viscosity of the neat UF resin or not was measured with Brookfield DV‐III programmable rheometer . Free formaldehyde in the prepared adhesives was determined by sodium sulfite method .…”

A New Methodology to Evaluate the Cure of Resin-Impregnated Paper for HPL

“…ABES (Automated Bonding Evaluation System) is a powerful and versatile technique for evaluation the "mechanical cure," allowing the determination of the shear strength as a function of resin type, catalytic system, resin load, cure temperature, time, and substrate [6]. It allows the determination of the isothermal strength development rate of the bond to be characterized at temperatures ranging between ambient and 260°C and may be used to explore many types of bonding systems including those that are thermosetting, as ureaformaldehyde, melamine-urea-formaldehyde and phenol-formaldehyde [7][8][9] and thermoplastic as poly(vinyl acetate) [10]. This instrument may also be used as a platform for a diversity of hybrid experiments related to the characterization of diverse aspects of adhesion [11].…”