Abstract
This work presents a study on the uses of tannin-formadehyde derivative into phenolic resins. Eucalyptus tannins (T) were reacted with formaldehyde to form tannin-formaldehyde resin (TF). Then this derivative was used to prepare tannin-formaldehyde/phenol-formaldehyde resins (TFPF) at 20 and 40 %w/w. The kinetic values of thermal curing of Phenol-formaldehyde (PF), tannin-formaldehyde and tannin-formaldehyde/phenol-formaldehyde resins (TFPF) at 20 and 40 wt% from TF were studied by monitoring the weight changes which occurred in the samples weight during thermosetting process at four temperature (160°C, 180°C, 200°C and 220°C). The total evolved condensation products from curing reactions were about 32% - 36% per sample weight, and the rate of curing reaction constants was ranged between 0.163 %wt·min-1 at 160°C and 0.50 %wt·min-1 at 220°C. The path of TFPF curing and kinetic values indicated that these resins could be cured with the behavior and velocity comparable to that of PF. The activation energy of TFPF cross-linking was higher than that of PF. Increasing TF level to 20% and 40% into PF can reduce the amount of PF curing reactions density and weight loss percentage. The global kinetic properties showed that the TF participated in the thermoset network formation with acceptable activity and performance. The general results of this paper show that the TF is a suitable alternative material for partially replacement into PF resin.
Highlights
Phenol-formaldehyde (PF) resins are one of the oldest synthetics thermoset resins
The cross-linking reaction of pure PF, pure tannin-formaldehyde resin (TF) and TF-PF with the mixture of 20% and 40% from TF per PF, were studied by monitoring the weight loss percentage per the weight of sample. This technique is based on the amount of curing reaction products, such as H2O and CH2O, that evolved from the resin during curing reaction [16]
The resins that synthesized from TF and PF were thermally cured
Summary
Phenol-formaldehyde (PF) resins are one of the oldest synthetics thermoset resins. They were derived from the reaction of phenol or mixture of phenols with formaldehyde [1]. There are two types from PF resins: Novolak and Resols, the first one, produced under acidic conditions, while the other manufactured by alkaline catalyzed reactions of phenol with excess amount from formaldehyde. The reaction groups in PF resin are methylol groups (-CH2OH) which are chemically reactive functional groups. They can undergo polymerization and curing reaction with itself or with other compounds under usual conditions [2]. One of the negative and limited factors for uses of PF resin was the high cost of phenols which was dependent on petroleum based raw materials
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