Preparations Of Phenolated Larch-bark Formaldehyde Adhesive And The Characterizations

Bark, one of residues in forestry processing, are composed of cellulose, hemicellulose, lignin and some extractives (e.g., tannin). With the petrol resource reducing gradually, the utilization of biomass materials such as bark has being obtained more and more attentions.The larch (larix pinus) bark contains more tannin than other regular bark and it is rich in larch foreast in northeast China. The adhesive preparation with phenolated larch bark for wood processing was well studied in current paper by means of the traditional chemical analysis techniques combined with different scanning calorimetry (DSC), nuclear magnetic resonance (¹H-NMR, ¹³C-NMR) and gel permeation chromatography (GPC). It focused on the cooking process of phenolated larch-bark formaldehyde (BPF) and stressed on the effects of BPF with multiple additions of sodium hydroxide, various sodium hydroxide contents and various phenolating catalysts. Meanwhile, the chemical structures of the phenolated larch-bark prepared by various catalysts were also probed. It found that:1) The BPF adhesives prepared with more than two NaOH additions had the advantage of fast thermosetting but also had some disadvantages, such as higher free formaldehyde content in the adhesive, higher free formaldehyde release from the bonded panels and poor wet strength. However, the BPF adhesive prepared with two NaOH additions had the lowest free formaldehyde content, the lowest free formaldehyde release, and an acceptable thermosetting rate and wet shear strength.2) The NaOH content (the third NaOH addition 0%, 2%, 4% and 6%) had obvious effects on properties of BPF adhesives. When the third NaOH addition was 0% NaOH (i.e., only water introduced) the BPF adhesive (J-2) performed better than the other adhesives (J-3, J-4, and J-5), in terms of long storage life (40 days), which meets the demands for commercial applications, and the best wet strength, which were comparable to the commercial PF adhesive. In addition, adhesive J-2 had a faster curing rate than the PF adhesive (in terms of gel time) and an acceptable free formaldehyde release, a release that was far lower than the Grade E₀ and Grade FC₀ requirements for plywood.3) The phenolating catalyst had obvious effects on the properties of bark adhesives. The storage time of BPF adhesive increased with the proportion of the phosphor acid in the combiantion catalyst. The BPF prepared by the phenolated larch-bark with combination catalyst has the better performance than that with sulfuric acid by oneself. The BPF adhesive prepared by the phenolated larch-bark with the catalyst S: P: T=1: 1: 1 has the longest storage time and can be used to produce plywood with high quality, which indicated it can be commcerialized. 4) The phenolating catalyst had obvious effects on the liquefaction and the properties of phenolated bark. The liquefied capability of sulforic acid (98%) is better than toluene-p-sulfonic acid that is better than phosphoric acid. The better catylst can be obtained by combanating with a certain proportion. The liquefied bark can react with formaldehyde, the bark liquefied with catalyst of S: P=1: 1 can consume the most formaldehyde, 0.7052g HCHO per gram of liquefied bark. The stronger the acidity of the combiantion catalyzer resulted in the more bonded phenol, i.e., the more phenol can be reacted with the bark.In sum, the study found a synthetic prcoess to utilize bark to prepare wood adhesive. The liquefiction degree could be up to 95%. The phenolate larch-bark could be used as the stuff for adhesive preparation without further treatment, during which approximate 30wt% of the phenol could be replaced.