Canadian Forest Service Publications

Pilot mechanical pulping assessment of dry blue-stained and grey-stage wood chips from beetle-killed lodgepole pine. 2009. Hu, T.; Omholt, I.; Johal, S.; Yuen, B.; zhao, M.; Drummond, J.; Miles, K.B.; Stacey, M.; Hellstern, M.; Watson, P.A. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, BC. Mountain Pine Beetle Working Paper 2008-25. 53 p.

Year: 2009

Issued by: Pacific Forestry Centre

Catalog ID: 29243

Language: English

Series: Mountain Pine Beetle Working Paper (PFC - Victoria)

Availability: Order paper copy (free), PDF (download)

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Pilot-plant thermomechanical (TMP) pulping has been performed on green and dry, blue-stained grey-stage lodgepole pine (LPP) chips with different moisture contents. The energy requirements for TMP pulping of the dry, early-grey (kill date approximately 4 years) chips and the dry, late-grey (kill date approximately 6 to 8 years) chips were similar to those for TMP pulping of the green chips, when all the results were taken into consideration. The early-grey and late-grey TMP pulps had lower sheet density and ISO brightness, and higher handsheet surface roughness than the green TMP pulps. No significant difference in long-fibre and fines contents, fibre-length or tensile strength was observed between the green and the early-grey TMP pulps at the same freeness, while indications of a slightly lower tensile index were found for the late-grey TMP. The late-grey TMP also showed a higher light scattering coefficient at a given Canadian Standard Freeness (CSF).

The higher handsheet surface roughness of the late-grey and early-grey TMP pulps was not due to the low moisture content of the late-grey and early-grey chips, but likely due to other changes. The maximum level of the dry, late-grey chips that could be added to the green chips without significantly increasing the surface roughness or lowering the sheet density was 25%.

Low-intensity refining in the post-primary stages of the early-grey and the late-grey TMP improved the fibre length, but did not affect the tensile index at a given CSF significantly. Chip presteaming and water impregnation had a marginal effect on the pulp properties of the late-grey TMP. However, sodium sulfite pretreatment at pH=6 coupled with low-intensity refining of the late-grey chips had a positive effect on the tensile index at a given CSF. Process modifications involving careful sulphite pretreatment could be investigated further if loss of tensile strength due to beetle-killed wood becomes a greater problem in the future. Reducing the refining intensity may be a solution if maintaining the fibre length becomes a critical issue. Both these modifications led to somewhat increased refining energy consumption to reach a given CSF.

Increase of moisture content/water impregnation of the early- and late-grey LPP chips could be achieved by increasing chip presteaming temperature/pressure and/or time, by increasing the water impregnation time, or by controlling the conductivity and pH of the impregnating water at ~200 ?S/cm and ~6.0, respectively. The most economical pretreatment approach to increasing the moisture content of the dry, grey-stage LPP chips prior to TMP pulping appeared to be presteaming at moderate temperature/pressure, followed by 8 to 10 minutes of chip washing with proper control of the conductivity and pH of the chip washing water.

Soaking of the green and the late-grey blocks in a 10% AgNO3 solution, followed by ESEM-EDS analysis of Ag intensity, could provide qualitative information on the movement of water within 10 minutes of water soaking/impregnation. ESEM-EDS results on the green and late-grey blocks are consistent with the water-uptake results obtained using Weyerhaeuser test apparatus. Dry late-grey LPP chips behaved very differently during TMP pulping or water/chemical impregnation than green LPP chips air-dried to the same starting moisture content.