Biobased Phenol Formaldehyde Resins Derived from Beetle-Infested Pine Barks—Structure and Composition

Abstract

In this study, two types of biobased bark-derived phenol formaldehyde (PF) resins, namely, liquefied bark-PF and bark extractive-PF, were synthesized from acid-catalyzed phenol-liquefied bark and bark alkaline extractives, respectively. The biobased resins were characterized for their chemical compositions and molecular structures using the liquid-state 13C nuclear magnetic resonance (NMR) technique. The results indicated that the introduction of bark components (either as liquefied bark or as bark extractives) to the phenolic resin synthesis affected resin structures and curing performance. Methylene ether bridges were found in the bark-derived PF resins. Bark components made the formation of para–ortho-methylene linkage more favorable in bark-derived PF resins than in lab PF resins. Molecular structures of the liquefied bark-PF resin differed significantly from those of the bark extractive-PF resins. The liquefied bark-PF resin showed a higher ratio of para–para/ortho–para-methylene link (−CH2−), a higher unsubstituted/substituted hydrogen (−H/–CH2OH) ratio and a higher methylol/methylene (−CH2OH/–CH2−) ratio than the bark extractive-PF resin. The tannin components of the bark extractives accelerated the curing rate of the resulting bark extractive-PF resin. The bark extractives made the ortho position of phenol react more favorably with formaldehyde than the para position. The liquefied bark with phenolated structures had more reactive sites toward formaldehyde than the bark extractives and accelerated the curing rate of the resulting liquefied bark-PF resin.

Modified tannin extracted from black wattle tree as an environmentally friendly antifouling pigment

“…Accordingly, to the free C4 in the A-ring. 57 A displacement in the 97 ppm peak, which corresponds to terminal C6 and C8, is also observed. These modifications in the spectrum corroborate the cleavage of interflavonoid bonds, as expected from the hydrolysis reaction.…”

“…51 The 13 C NMR technique was used to identify the chemical structures of black wattle tannin before and after hydrolysis reaction. Chemical shifts reported for different polyphenols [51][52][53][54][55][56][57][58][59][60][61][62] were used to identify the peaks obtained for black wattle tannin (Figure 2). The peak at 145 ppm corresponds to the C3´ and C4´ of B-ring while and peaks at 156-154 ppm are associated to the C5 and C7 (A-ring) bonded to -OH.…”

“…The peak at 145 ppm corresponds to the C3´ and C4´ of B-ring while and peaks at 156-154 ppm are associated to the C5 and C7 (A-ring) bonded to -OH. 57,58 The chemical shifts at 133 and 118 ppm belongs to the C1´and C5´ atoms, respectively, of B-ring. 57,58 The peak at 115 ppm corresponds to the C4-C8 interflavonoid bond while those at 107-105 to the C4-C6 interflavonoid bond.…”

“…57,58 The chemical shifts at 133 and 118 ppm belongs to the C1´and C5´ atoms, respectively, of B-ring. 57,58 The peak at 115 ppm corresponds to the C4-C8 interflavonoid bond while those at 107-105 to the C4-C6 interflavonoid bond. 57,58 The peak at 97 ppm corresponds to the terminal C6, C8 and C10 of A-ring.…”

“…57,58 The peak at 115 ppm corresponds to the C4-C8 interflavonoid bond while those at 107-105 to the C4-C6 interflavonoid bond. 57,58 The peak at 97 ppm corresponds to the terminal C6, C8 and C10 of A-ring.…”