Condensed tannins from grape pomace: Characterization by FTIR and MALDI TOF and production of environment friendly wood adhesive

Condensed tannins were extracted from grape pomace using a water medium in presence of three different bases as catalyst (NaOH, Na2CO3 or NaHCO3) and were characterized by FT-IR and MALDI-TOF spectrometry. It was demonstrated that the tannin extracts contained oligomers up to 6 repeating flavonoid units, with dominant procyanidin with a minor amount of prodelphinidin units. The structure of grape pomace tannin extracted did not present noticeable discrepancy exception of the ratio of the opening pyran ring which was different as a function of the catalyst used. Two different formulations (nonfortified tannin adhesive and fortified with addition of 20% of polymeric 4,4′-diphenyl methane diisocyanate (pMDI)) were used to press one layer particle board. It has been proved that the extraction processes largely affect the adhesive properties of the extracts obtained from the same raw material. Especially the particleboards prepared from tannins extracted using Na2CO3 as catalyst and without pMDI, give a high internal bonding value (IB = 0.45 MPa), which was good enough to pass relevant international standard specifications for interior grade panels. Formaldehyde emission of these panels is very low, well under the European Norm requirements (≤6.5 mg/100 g panel).

► Condensed tannins were extracted from grape pomace using a water medium. ► Extracts were characterized by FT-IR, thermomechanical analysis and MALDI-TOF spectrometry. ► Different formulations were used to press one layer particle board. ► It has been shown that the extraction processes largely affect the structure and the adhesive properties of the extracts.