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Drying Technique of Improved-preservative Treated Rubberwood. ITTO/CFC Project ( PD 103/01 REV.4 (I) ). GAO Ruiqing Teng Tonglian LI Xiaoling CRIWI, Chinese Academy of Forestry. Haikou China, 2008. Main Content. 1 Introduction 2 Test Material and method 2.1 Test material

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Drying Technique of Improved-preservative Treated Rubberwood

ITTO/CFC Project(PD 103/01 REV.4 (I) )

GAO Ruiqing Teng Tonglian LI Xiaoling

CRIWI, Chinese Academy of Forestry

Haikou China, 2008

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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Main Content

1 Introduction

2 Test Material and method

2.1 Test material

2.2 Drying characteristics test

2.3 Rubberwood drying schedule test

3 Drying schedule testing results analysis Visible drying defects

3.1 Drying quality

3.1.1 Visible drying defects

3.1.2 Final Moisture contents (Wf)

3.1.3 Moisture content gradient along the thickness direction (Wg)

3.1.4 Drying stress index (Y)

3.2 Deformation

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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Main Content

3.2 Deformation

3.3 Drying speed

3.4 Rubberwood color after drying

4. Conclusion

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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1Introduction

  • Wood drying is one of the most important steps in wood processing. Before use, wood must be reasonable dried, avoiding drying defects, improving strength and stability, so as to make value-added solid wood products.
  • Rubberwood is a very important tropical wood resource in China
  • Need chemical preservation and reasonable drying
  • The key problem to be solved of this project is to determine the best rubberwood drying technique after they are treated by new preservatives with containing none NaPCP.

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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2 Test Material and method

  • 2 Test method
    • 2.1 Test material
  • Species: rubberwood(Hevea brasilie)
  • Tree age:25-33 years
  • producing area:(1)Xilian Farm, Hainan Province
  • (2)Nanmao Farm, Hainan Province
  • Log diameter:220-450mm
  • Log length:2,000-2,200mm

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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2.2 Drying characteristics test

electricity heated oven

constant temperature at 103℃.

test sample size of 200×100×20 mm

test stops when the MC below 1%

visible drying defects

inner checks

cross-section deformation value

drying rate (MC 30 to 5%)

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

tab 1 status of initial checks
Tab. 1 Status of initial checks

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

tab 2 status of internal checks and cross section deformation after drying
Tab.2 status of internal checks and cross-section deformation after drying

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

tab 3 moisture content changing during the 100 drying test
Tab.3 Moisture content changing during the 100℃ drying test (%)

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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2.3 Rubberwood drying schedule test

Rubberwood drying schedules for test were made out according to the results of 100℃ drying characteristics testing. and all the drying schedules tests were carried out in one of the rubberwood processing mill located in Hainan Province. The test sample size of rubberwood was 800-1,200mm long , 80mm wide and 30mm thick. After preservatives treatment, the test samples were deposited in the air-drying shelter for a short term. And then the kiln drying tests were executed in this mill. After a series of testing, 3 drying schedules were finally selected (see table 4 –6).

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

table 4 drying schedule a thickness 25 30mm
Table 4 Drying schedule A (Thickness:25-30mm)

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

table 5 drying schedule b thickness 25 30mm
Table 5 Drying schedule B (Thickness:25-30mm)

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

table 6 drying schedule c thickness 25 30mm
Table 6 Drying schedule C (Thickness:25-30mm)

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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3. Drying schedule testing results analysis

3.1 Drying quality

3.1.1 Visible drying defects

slight end checks, in which, some of them were developed into end-surface checks.

small surface checks

Schedule C to dry rubberwood timber with pith, severe checks, splits and deformations occurred

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

table 7 inspected drying indices unit
Table 7 Inspected Drying Indices unit: %

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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3.1.2 Final Moisture contents (Wf)

The desired final moisture content of this test was 10%.

The results showed the final moisture contents of rubberwood were around 10%, and the difference of moisture content between different samples was very small.

The drying quality meets the need of grade one or grade two of national drying standard sawn timber.

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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3.1.3 Moisture content gradient along the thickness direction (Wg)

The results of moisture content gradient along the thickness direction showed that the moisture content difference between different layers was small

meets grade 1 requirement national drying standard of sawn timber.

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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3.1.4 Drying stress index (Y)

To reduce drying stress, following methods adopted:

Preheating

mid-conditioning

final equilibrium treatment

The results showed that, the drying stress index was in order of grade one of national drying standard of sawn timber.

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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3.2 Deformation

  • Different deformations, including bowing, cupping, warping and twisting.
  • the rubberwood deformation on the upside of the stack was bigger than the lower side
  • the spacing stickers kept in straight lines
  • some heavy load were put on the top of stack
  • the proper middle term treatment

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3.4 Rubberwood color after drying

The results showed the color of dried rubberwood had a close relationship with the drying temperature and humidity.

The higher the drying temperature was, the bigger the humidity was and the longer the drying time was, the darker the color was.

The rubberwood color became darker and brown when they were dried according to schedule C, while the color almost kept the original natural color when they were dried according to schedule A.

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

conclusions
The drying characteristic grade of rubberwood with new preservatives treated was grade 2 of initial check, grade 2 of internal check and grade 1 of deformation.

According to the result of drying characteristic test and a series of the drying schedules tests, 3 optimum drying schedules were made.

Rubberwood with or without pith should be dried separately. Pith free rubberwood could be dried according to the high temperature drying schedule C with good drying quality which the drying checks, deformation and moisture contents of dried rubberwood were all fit the national drying standard of grade 1.

Conclusions

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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4 Conclusions (cont)

  • Uniform spacing stickers and heavy load on top of stack was recommended to reduce deformation. When drying rubberwood with pith, the drying temperature should be lower and middle term treatment time should be increase.
  • The color of dried rubberwood has a close relationship with the drying temperature and humidity. In order to keep the original color of rubberwood, the rubberwood should be dried according to drying schedule

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

conclusions cont
Drying time had a close relationship with the drying schedule. When drying rubberwood according to the 3 different schedules, their drying time were 11, 8 and 45 days respectively.

Drying time greatly affected the drying costing. Improving the drying speed or shortening drying time will reduce the drying costing.

Above all, in order to improve the drying efficient and reduce the drying costing, the rubberwood should be dried according to schedule C; In the other hand, in order to keep the original color of rubberwood, they should be dried according to schedule A; Schedule B can also be adopted according to the requirement of final products of the rubberwood by the manufactory.

Conclusions (cont)

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008

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Thank you

for your attention!

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International Workshop CRIWI, Chinese Academy of Forestry Haikou 2008