Response surface optimization for improving the processing behavior of melamine formaldehyde impregnation resins

Abstract

Melamine‐formaldehyde resins are widely used for decorative paper impregnation. Resin properties relevant for impregnation are mainly determined already at the stage of resin synthesis by the applied reaction conditions. Thus, understanding the relationship between reaction conditions and technological properties is important. Response surface methodology based on orthogonal parameter level variations is the most suitable tool to identify and quantify factor effects and deduce causal correlation patterns. Here, two major process factors of MF resin synthesis were systematically varied using such a statistical experimental design. To arrive at resins having a broad range of technological properties, initial pH and M:F ratio were varied in a wide range (pH: 7.9–12.1; M:F ratio: 1:1.5–1:4.5). The impregnation behavior of the resins was modeled using viscosity, penetration rate and residual curing capacity as technological responses. Based on the response surface models, nonlinear and synergistic action of process factors was quantified and a suitable process window for preparing resins with favorable impregnation performance was defined. It was found that low M:F ratios (~1:2–1:2.5) and comparatively high starting pHs (~pH 11) yield impregnation resins with rapid impregnation behavior and good residual curing capacity.

Prediction of Residual Curing Capacity of Melamine-Formaldehyde Resins at an Early Stage of Synthesis by In-Line FTIR Spectroscopy

“…A lower degree of pre-condensation leads to a higher residual curing capacity and vice versa. This confirms earlier findings [ 23 ] and can be explained by the fact that resins with lower M:F ratios need to form less bridges during the synthesis to reach the same water tolerance as resins with high M:F ratio. MF resins with high formaldehyde content (M:F 1:4) show high content of methylol moieties (potential cross-linker), but due to the already rather advanced cross-linking state the rigidity of the network suppresses further bridge formation [ 21 ].…”

“…Melamine-formaldehyde resins were synthesized basically according to the process described by Pizzi [ 5 , 23 ]. The general approach was as follows.…”

“…Laminate properties can be tuned by applying appropriate hardening schemes to one and the same liquid resin [20][21][22]. However, this is only possible within certain limits and both the processing behavior and the performance in solid state of a resin are mainly determined by the applied synthesis conditions and, in particular, by the melamine-to-formaldehyde ratio [23]. Resins produced within an initial pH range of 7.9 and 12.1, and a range of melamine-to-formaldehyde M:F ratio from 1:1.5 to 1:4.5, show very different property profiles in terms of viscosity, penetration into paper, and residual curing capacity, although these resins all displayed the same water tolerance (as determined by titration with water) and have the same polarity (as determined by contact angle measurements) [23].…”

Unravelling the Phases of Melamine Formaldehyde Resin Cure by Infrared Spectroscopy (FTIR) and Multivariate Curve Resolution (MCR)

“…Decisive factors determining the particular proportions between the three spectroscopic components in this initial stage are, among others, the molar ratio F/M with which the pre-polymer was synthesized, the reaction conditions used (pH, temperature, reaction time, etc.) [10] and whether, as in the present case, spray drying or other further treatments have been applied.…”

“…Such decorative laminates are used in a wide variety of products. These range from furniture [3,4], highly abrasion-resistant flooring [5], chemical-resistant laboratory tables, and steam-resistant working surfaces to antibacterial surfaces [6], durable exterior cladding and special applications such as anti-fingerprint surfaces [7], custom design surfaces [8,9], white boards for office use [7], drilling entry boards for the electronics industry or even self-healing surfaces [10].…”