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Evaluation of Moisture Content in WoodFiber and Recommendation of The Best

Method for Its Determination

Maher Zakaria Ahmed(National Institute for standards (NIS

,B.Sc. physics, Faculty of Science(Ain Shams University (1997

Copyright 2005 © Maher Z. Ahmed NIS

Prof. M. M. El-NeklawyProfessor of physics,

faculty of science, Helwan University

Prof. A. F. Hassan ,Professor of physics

faculty of science, Helwan University

Under supervisionProf. N. I. El-Sayed

Professor of physics,Thermometry Laboratory

National Institute for standards (NIS)

Dr. M. HalawaaAssociate Professor of physics

Thermometry LaboratoryNational Institute for standards (NIS)

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Thermometry DepartmentNational Institute for Standards (NIS)

➢ NIS was established in 1963, the principle function is the maintenance of national primary standards, and giving technical advice in measurements and calibration of high precision measuring devices.

➢ One of functions of Thermometry Department (NIS) is calibration of MC meters.

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Checking calibration

Meter Manufacturing calibration

Property to be measured

Sensitive element

➢determination of the accuracy of an instrument, ➢ascertain necessary correction factors

A comparison between a meter under test and an established standard

➢The comparison of transducer signal outputs against the reference standard to get calibration curve

Output Signal

What & Why Calibration?

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➢ MC is one of important technical specification in wood, because the influence it has on all the major properties that affect the performance of wood in service.

➢ GATT, liberation of international trade, and trade technical barriers.

➢ Quality control in industry and trade.

The Egyptian Need for MC meters calibration

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Moisture Content (MC) basics

Definition of Moisture Content (MC) for a wood

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Moisture content in woodMoisture exists in wood either as1- "bound" water that is held chemically

within the cell walls or as

2- "free" water that is stored in lumen of cell cavities. As freshly cut or "green" wood dries, the free water evaporates first.

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This is a key concept in wood since moisture affects the physical and mechanical properties of wood differently depending on whether the MC% is above or below the FSP.

MC% above FSP: physical and mechanical properties of wood remain constant as MC% changes

MC% below FSP: physical and mechanical properties of wood change as MC% changes The FSP varies for different species of wood, but is typically around 30%.

28.5Spruce, Sitka

27.0Spruce, red

24.0Pine, red

25.5Pine, longleaf

21.0Pine, loblolly

28.0Larch, western

28.0Hemlock, western

26.0Douglas fir

27.0Birch, yellow

24.0Ash, white

FSP(%)Species

Fiber saturation point (FSP): The moisture content at which all of the free water is removed - the cell cavities are empty - but the cell walls are still completely saturated.

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when wood is no longer gaining or losing moisture. it has reached an equilibrium with its environment.

Equilibrium Moisture Content(EMC)

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Moisture Content (MC) measurements methods

➢ Oven dry method➢ Electric Moisture meters (most used

commercially). ➢ Distillation method ➢ Infrared meters

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Realizing NIS calibration system for MC in wood meters and comparing between

Conductance and capacitance-type metersChecking Calibration System for thermometers

Checking Calibration System for MC meters

High Homogenate mediawith different fixed pointes

for comparison Standard Vs. Calibrated meter

,Water bath, Oil bath

For each Wood type Different EMC samples

Standard Meter or method

to compare with

RTD (PT 100) or Standard

Thermometer

Oven-Dry Method

ASTM D4442 & D4444

Client thermometer to

Calibrated

Client Meter to Calibrated

Client MC Meters to Calibrated

Our missing part in NIS

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Oven-Drying MethodThe ovendrying method is generally accepted as a

standard for calibrating other methods (ASTM D4442). This method involves simply weighing the specimen before and after ovendrying to constant weight at 103°C.

Constant weight is defined as no further weight loss when a specimen is weighed to an accuracy of ± 0.2 percent at 3-hour intervals.

Electric Moisture Meters for Wood

Meters based on the relationships between an electrical property and the moisture on wood below FSP (≈30%), the most commercial used

1- Conductance type metersCapacitance type meters -2

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Experimental Work

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Oven-Dry Method

ASTM D4442 & D4444

Client MC Meters to Calibrated

Calibration System for MC meters

1. Oven (E. Schulz & Co.) 103 ± 2 oC

2. Balance (METTLER TOLEDO) capacity 205 g readability 0.01 mg

3. Desiccators

1- Conductance type meters Testo 606

2- Capacitance type meters Humitest MC-100S

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1. Wood samples (Mosaky, Zan, Aro, and Mogna) The most used in Egyptian market

2. Chambers at 25 oC

3. Saturated Salt Solutions (ASTM D-4933)Magnesium Chloride 33.9 %RH Potassium Acetate 37.7 %RH Potassium Carbonate 43.2 %RHPotassium Sulphate 84.6 %RH

4. humidity and temperature sensors

Testo 625

6.2 7.7 8.5 17.4

EMC

Calibration System for MC meters

Conditioning for 60 days repeated meny times


Our missing part in NIS

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Results And Discussion

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0.61 7.29±0.2 6.68±0.36 36.0908 33.6373 Average

0.98 6.98 6.0 34.9115 32.6349 5

0.06 6.86 6.8 34.8711 32.6337 4

0.33 6.73 6.4 36.5959 34.2878 3

0.92 6.92 6.0 36.6534 34.2809 2

0.75 8.95 8.2 37.4222 34.3492 1

Δ MC%MCS − MCM

MCS %MCM %Wet Wight gm

Dry Wight gmSamples

Comparison between the results of MC% using capacitance meterwith Oven dry method for 5 Mosky samples kept at 43.2% RH and

temperature of 24.8 oC for 60 days

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0.37.3±0.27.0 ±0.6236.090833.6373Average

07734.911532.63495

-0.176.934.871132.63374

0.766.736.595934.28783

-0.176.936.653434.28092

0.988.937.422234.34921

Δ MC%MCS − MCM

MCS %MCM %Wet Wight gm

Dry Wight gm

Samples

Comparison between the results of MC% using conductance meterwith Oven dry method for 5 Mosky samples kept at 43.2% RH and

temperature of 24.8 oC for 60 days

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14.7414.214.4284.6

6.68 7.0 7.29 43.2

6.90 6.8 6.95 37.7

6.32 6.2 5.82 33.9

MCCM%

MCRM%

MCS%

ChamberHumidity

RH%

Average moisture content percent using oven dry method MCS and the results measured by conductance MCRM and capacitance MCCM meters for Mosky wood samples

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Traceability The traceability is: The property of the result of a measurement or the value of astandard whereby it can be related to stated references, usually national or international.standards, through an unbroken chain of comparisons all having stated uncertainties➢The traceability of the instruments used in the measurement is as followingAll the temperatures reading values were measured according to ITS’s-90 whichmean that the reading is traceable to the SI units.

➢hygrmoeters were calibrated by using Testo 650, which are transfer standard traceableto IMGC-Italy.

➢Balance used in weighting process traceable to Mass, Pressure & Density Departmentof NIS

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Sources of Errors and Uncertainties for Electric Moisture Meters

➢ Adequacy of sample ➢ Specimen characteristics

(species, density, moisture distribution, thickness, and temperature)

➢ Electrode contact ➢ Grain direction ➢ Chemicals in the wood ➢ Weather conditions ➢ Skill of operator➢ The maintenance of the meters.

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0.2Assumednormal

Expandeduncertainty

0.1Assumednormal

Combinedstandarduncertainty

0.012Normal0.02BCalibrationof Balance

0.11Normal0.1AStandarduncertainty

StandarduncertaintyDivisorProbability

distributionValueTypeSource ofuncertainty

Uncertainty budget at Confidence level 95% (k=2) for Oven-dry

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0.029√3Rectangular0.05BCalibrationof Balance

0.36Assumednormal

Expandeduncertainty

0.18Assumednormal






Uncertainty budget at Confidence level 95% (k=2) for capacitance

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0.62Assumednormal

Expandeduncertainty

0.31Assumednormal






Uncertainty budget at Confidence level 95% (k=2) for conductance

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References

ASTM D 4442-92, 2002. Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Base Materials, ASTM

ASTM D 4444-92, 2002. Standard Test Methods for Use and Calibration of Hand-Held Moisture Meters, ASTM

ASTM D 4933-99, 2002. Standard Guide for Moisture Conditioning of Wood and Wood-Based Materials

ASTM E 104-85 2002. Standard Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions

Forest Products Laboratory 1999. Wood handbook: Wood as an engineering material. Gen. Tech. Rep. FPLGTR113. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

Ullmann’S Encyclopedia of Industrial Chemistry 6Th Edition 2002. Electronic release, WILEY-VCHWood

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New calibration system to MC conductance meters

Manufacturing Calibration MC meters

Physical Model Equation

Sakuma Eq. from

.Plank Eq

!!!??

Standard pointes to compare output

signal with measured values

Fixed Points ITS90


measured using Oven-Dry Method

Optical Pyrometer

Obtain all range Calibration

Curve

Conductance MC Meters

Large number of Different EMC samples

needed To cover all range

Manufacturing Calibration thermometers

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Ionic Conduction theory for wood using Anderson-Stuart model for ionic conduction

in amorphous materials

The electric conductance of wood increases as the temperature increases

charge carriers whose number or mobility is increased .by thermal activity

Murphy [39] in an electrolysis experiment proved that conduction in dry cellulose is ionic and probably protonic, and reached the same conclusion.for humidified cellulose

Phenomena such as polarization and the dependence of conductivity onvoltage, the metal used for electrodes and the time of application of voltage

The chemical structure of wood is cellulose 40%, lignin 21%, hemicelluloses.30%, and others materials, which are natural polymers

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Ene

rgy

Distance

No electric field

With electric field… Qeff<Q

Q

Qeff

Assumes q charge per atom

Diffusion:

➢ Electrical Field

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Anderson-Stuart model

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Elliott

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0.420.670.260.260.38

11.2288.612.312.9

126007000003000002090051300

BaldcypressRed PineBigtooth AspenMahoganyBlack Walnut

Resistance M ΩWood Specie25167 MC %

20.89516.422751.917745.093529.8725

0.6924671.91537-3.28605-2.10868-0.266454

-0.50195815.761721.9493-5.3995.41572

BaldcypressRed PineBigtooth AspenMahoganyBlack Walnut

KJIWood Specie

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New calibration system to MC conductance meters

Manufacturing Calibration MC meters

Physical Model EquationStandard pointes to compare output

signal with measured values

Fixed Points ITS90


measured using Oven-Dry Method

e.g. PT thermometer

Optical Pyrometer

Obtain all range Calibration

Curve

Conductance MC Meters

Large number of Different EMC samples

needed To cover all range

Manufacturing Calibration thermometers

NewEquation

Sakuma Eq. from

.Plank Eq

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S.R. Elliott, 2nd ed., Longman Scientific & Technical, 1990 ”Physics of Amorphous Materials"Dekker, SOLID STATE PHYSICS , Chapter 7 Ionic conductivity and diffusion

Kittel, INTRODUCTION TO SOLID STATE PHYSICS Chapter 18

Burns, SOLID STATE PHYSICS

References

The Feynman l e c t u r e s o n p h y s i c s, Volume 1

James, William L, 1988. Electric moisture meters for wood, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

Ullmann’S Encyclopedia of Industrial Chemistry 6Th Edition 2002. Electronic release, WILEY-VCHWood

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➢ NIS has been successful established facilities for calibration of all moisture meters types, by Egyptian market Wood kinds.

➢ The conductance meters having many advantages over capacitance meters. (more cheap, easy to use and maintenance, less

Errors)

➢ capacitance meters desirable where appearance is important.

Conclusion

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➢Anderson-Stuart model explain the D.C. conductance on wood below FSP as a function of MC.

➢Suggesting new calibration method needs only three experimental EMC values.Short time, low cost; comparing the long time and high cost in other method due to large numbers of points needed

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➢ Using of conductance moisture meters for their advantages

➢ The calibration for moisture meters should be checked periodically using standards.

➢ The moisture meters manufactories should the calibration of the meters to wood kinds in Egyptian Market.

➢ Using new calibration method

Recommendations

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One of first Calibration Certificates issued by NIS to Egyptian Co.

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????!!!!!!

Oh., I get it dad

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