Statistical screening analysis of the chemical composition and kinetic study of phenol-formaldehyde resins synthesized in the presence of polyamines as co-catalysts.

Magdalena Cygan,Stanisław Krompiec,Mariusz Szemień,Lakshminarayana Polavarapu

doi:10.1371/journal.pone.0195069

Abstract

The physico-chemical and application properties of phenol-formaldehyde resins used in the production of laminated plastics depend on such factors as: type and amount of catalyst, formaldehyde-to-phenol mole ratio, temperature and time of the synthesis process. The special impact on the reaction mechanism and kinetics, e.g. on the formation of mono-, di- and trihydroxymethyl derivatives of phenol (PhOH) is a consequence of the type and amount of the catalyst. This paper presents the results of optimisation research of resol resin synthesis catalysed by trimethylamine (TEA) carried out according to 32 experimental design. The aim of the research was to determine the synthesis conditions under which it is possible to achieve products with reduced content of unconverted formaldehyde (CH2O), phenol and its hydroxymetyl derivatives, while maintaining the required physico-chemical properties. The process employing selected polyamines as well as TEA together with polyamine co-catalysts i.e. diethylenetriamine (DETA) and triethylenetetraamine (TETA) was also studied. The results were compared with those of the resins which were synthesised with the use of classic catalysts–ammonia (NH3) and triethylamine for which the content of CH2O, PhOH and its hydroxymethyl derivatives was respectively: NH3—5.13% and 46.27%, TEA—0.33% and 52.41%. In the case DETA was added, the content of phenol and its hydroxymethyl derivatives could be reduced by 52.49% in relation to the resin obtained with the use of TEA and by 46.19% in relation to the resin obtained with the use of ammonia. The formaldehyde content was reduced by 78.79% and 98.64%, respectively. When TETA was added as a co-catalyst, the content of phenol and its derivatives was reduced by 48.04% versus triethylamine-catalysed resin and by 41.15% versus ammonia-catalysed material. The reduction in formaldehyde content reached 84.85% and 99.03%, respectively. The results of kinetic study were also presented, the prediction accuracy of the proposed kinetic model is more than 98% for all the catalysts in the state variable space. Polyamine co-catalysts gave much higher rate constants (0.50 and 0.45 for TETA and DETA, respectively).

Highlights

The resol resins are produced in the phenol-formaldehyde condensation process, in the presence of basic catalysts, under various temperature and time regimes
The findings presented in this report showed that the use of triethylamine in the synthesis of resins made it possible to reduce the formaldehyde content down to the required level 0.5%
Statistical screening analysis and kinetic study of phenol-formaldehyde resins to increase the amount of triethylamine, since higher nitrogen contents in resins would adversely impact their performance properties

Summary

Introduction

The resol resins are produced in the phenol-formaldehyde condensation process, in the presence of basic catalysts, under various temperature and time regimes. They were synthesised for the first time over 100 years ago, the present-day products of that type are still considered an important sector in the polymer chemistry. The production process of those plastics is based on applying a resin to a substrate material, i.e. usually paper or textiles, and on drying that composite in drying chambers [7,8,9,10]. Unwanted emissions and deposition of some resin components and/or substrate particulates in drying chambers and in ventilation ducts take place during that process. The high-temperature process can discharge unreacted formaldehyde which, pursuant to the new EU Directive, was classified as carcinogenic (cat. 1B) and mutagenic (cat. 2) from 2016

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