A solvent-free method for the direct oxidation of anilines to the corresponding azo and azoxy homocoupling products by using a planetary ball mill was developed. Various oxidants and grinding auxiliaries were tested and a variety of substituted anilines were investigated. It was possible to form chemoselectively either azo, azoxy, or the nitro compounds from reaction of aromatic anilines. The selectivity of the solvent-free reaction is switchable by applying a combination of oxidant and grinding auxiliary. Furthermore, a comparison with other methods of energy input (microwave, classical heating, and ultrasound) highlighted the advantages of the ball mill approach and its high energy efficiency.

Purpose -The purpose of this paper is to describe the development of an eco-friendly tannin-phenol formaldehyde resin (PFT) applicable in the wood composite industry. Design/methodology/approach -The bark of oak (Quercus castaneifolia) contains a large amount of condensed tannin. Condensed tannin, with a large amount of Catechol groups was considered for reducing the formaldehyde emission level on the adhesive system. Physical characteristics of synthesized PFT resin were evaluated. Findings -For optimal extraction, three solvents were used in the extraction process. The results showed that a mixture of water-methanol (1:1 v/v) as extracting solvent is the best solvent and yields about 14 per cent tannin based on dry weight of bark. For producing tannin phenol formaldehyde adhesive, 10 per cent, 20 per cent and 30 per cent (based on PF dry weight) of PF, substituted with natural extracted tannin. For evaluating PFT performance effects of percentage amount of substitution tannin content on the gel time, viscosity, pH, and density of adhesives were evaluated. Based on emission test (JIS A 1460(JIS A -2001 formaldehyde emission of PFT 10 per cent, 20 per cent and 30 per cent were 1.13, 1.12 and 0.4 mg/100 g, which is very low compared with tannin-free PF.Research limitations/implications -Tannin-PF adhesive compared to PF adhesive had lower PH, higher viscosity and shorter gel time. Practical implications -The method developed provides a simple and excellent renewable resource "tannin" which can be used or partially substituted in phenol formaldehyde adhesive. Originality/value -Results showed that replacing PF for tannin reduces modulus of rupture (MOR) and modulus of elasticity (MOE) slightly but has significant effects on IB, water absorption and thickness swelling.

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This work was carried out in collaboration between all authors. JS designed the study, wrote the protocol, and wrote the first draft of the manuscript. CKT managed the literature searches, analyses of the study performed the spectroscopy analysis and MM managed the experimental process and MA identified the species of plant. All authors read and approved the final manuscript.