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NIRE Annual Report
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 1999

Extraction of Polyflavanoids from Radiata Pine Bark Using Hot Compressed Water

Biomass Division
Global Warming Control Department
Objectives
Radiata pine bark contains significant amounts of polyflavanoids, which react with formaldehyde and are useful for the formation of wood adhesives. The yield of extractives from the bark is one of the critical factors for the commercialization of the radiata pine bark.
In this report, radiata pine bark was extracted using hot compressed water with or without 1% aqueous NaOH (based on the weight of the dried bark) at temperatures of 100°C and higher under different pressures for various holding time.
Results
1. Hot compressed water extraction
The extraction of radiata pine bark using hot compressed water at temperature higher than 100°C gave lower yields of extractives and polyflavanoids than those extracted using the conventional hot water extraction at 100°C under ambient pressure. Furthermore, polyflavanoids are more likely to be polymerised at temperature higher than 100°C.
When a small amount of NaOH was added to the compressed water, the extractives yields from the bark increased remarkably. The extraction of the radiata pine bark at 140°C and 10 atm initial pressure with no holding time at temperature provided the highest yields of extractives as well as polyflavanoids.
2. Energy consumption
The conventional method is based on the extraction with hot water, which is 20 times the bark weight, heated under reflux for 30 min and repeat once. However, the hot compressed water extraction uses water amounting to 4 times the bark weight, heated up to 140°C, cooled immediately, and the extraction is not repeated. Consequently, the hot compressed water extraction requires less than 1/6 the heating energy required for the conventional extraction method.
Fig. 1. Yield of extractives and polyflavanoids obtained from the extraction of radiata pine brek with hot compressed water containing 1% NaOH.
Fig. 1. Yield of extractives and polyflavanoids obtained from the extraction of radiata pine brek with hot compressed water containing 1% NaOH.

*: polyflavnoids content(%)
Selected Publication
1) Extraction of polyflavanoids from radiata pine bark using hot compressed water at temperatures higher than 100°C. Holzforschung 52, 139-145, 1998.
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