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| MOISTURE RESISTANT (MR) PARTICLEBOARD |
Data Sheet 4
May 2004 |
 |
Scope
This Data Sheet covers Particleboard displaying a high degree of resistance to moisture, termed MR Particleboard. Flooring type Particleboard also exhibits high moisture resistance but it is covered in Data Sheet 3.
Board Marking and Identification
Individual sheets of MR Particleboard can usually be identified by a green colouration of the core of the board, visible on board edges. Pack identification is facilitated by a vertical green stripe, approximately 50 mm wide, down the right hand edge of each pack, on the same face as the label.
Manufacture
The manufacturing process of MR Particleboard is as outlined in AWPA Data Sheet 1 - Manufacture. Wood particles are coated with a resin, formed into a mat and pressed to cure the resin and produce the required thickness. It is, however, the resin used that differentiates MR Particleboard from Standard Particleboard. Current MR Particleboard manufactured by AWPA members, uses a melamine-urea formaldehyde (MUF) resin (plus other additives), with a substantial melamine content. Because MUF resin cures to a clear film, similar to UF resin, a green dye is added to the resin mixture for the core flakes, to enable MR Particleboard to be distinguished from Standard Particleboard. MR Particleboard manufactured from other moisture resistant resins (such as phenol formaldehyde, tannin formaldehyde or co-condensates of these with urea formaldehyde) will be dark brown in colour and so readily distinguished from the UF bonded product. The green colouration is only necessary if MUF resin is used.
Wax emulsion is also included in the resin system for MR Particleboard. Wax imparts resistance to the penetration of liquid water by providing water repellant properties to board surfaces.
Mechanical and Physical Properties
Compared with Standard Particleboard, MR Particleboard has higher Bending Strength and Stiffness and higher Internal Bond Strength. Of particular importance are controls on thickness swelling after 24 hours water immersion, and limits on loss of bending and internal bond strength after various simulated durability tests. Typical property values are given in Table 1.
Dimensional Tolerances
Dimensional Tolerances agreed to by AWPA Members are given in the table below. In some cases, these are tighter tolerances than required by the Australian Standard and may not apply to Particleboard from non-member producers.
Product Range
MR Particleboard is manufactured by AWPA Members in the following thicknesses:
| Thin |
9, 12mm |
| Medium |
15, 16, 17, 18 mm |
| Thick |
25, 30, 33 mm |
(NOTE: Not all AWPA Members manufacture all thicknesses).
Table 1
Typical Property Values for MR Particleboard
| Property |
Units |
Thickness Class - mm |
|
|
<=12 |
13-22 |
>23 |
| Density |
kg/m 3 |
670 |
640 - 670 |
600 - 650 |
| Bending Strength (MOR) |
MPa |
19 |
18 |
16 |
| Bending Stiffness (MOE) |
MPa |
3000 |
2800 |
2700 |
| Internal Bond Strength |
MPa |
1.00 |
0.85 |
0.75 |
| Surface Soundness |
MPa |
1.70 |
1.70 |
1.60 |
| Screw Holding |
- Face |
N |
- |
800 |
800 |
|
- Edge |
N |
- |
1100 |
900 |
| Thickness Swell (24hr) |
% |
6 - 7 |
3 - 4 |
3 - 4.5 |
| Cyclic Test |
- Internal Bond |
MPa |
0.50 |
0.41 |
0.26 |
|
- Thickness Swell |
% |
10 - 12 |
9 |
8 - 12 |
| Formaldehyde (Desiccator Method) |
mg/L |
1.0-1.5 |
1.0-1.5 |
1.0-1.5 |
Dimensional Tolerances
| Property |
Units |
All Thicknesses |
| Length & Width |
- Nominal
- cut to size |
mm
mm |
+ 50
+ 1.5 |
+ 50
+ 1.5 |
+ 50
+ 1.5 |
| Thickness |
- variation
- profile |
mm
mm |
+ 0.3
+ 0.3 |
+ 0.3
+ 0.3 |
+ 0.3
+ 0.3 |
| Flatness |
mm/m |
<1.5 |
<1.5 |
<1.5 |
| Squareness |
mm/m |
<1.5 |
<1.5 |
<1.5 |
| Edge Straightness |
mm/m |
<1.5 |
<1.5 |
<1.5 |
MOISTURE PROPERTIES
Moisture Content
Board dimensions are closely related to moisture content and the effect of long exposure to high humidity conditions may give rise to problems where close tolerances are required. Particleboard should be conditioned to reach equilibrium with the humidity level in which it is to be used. Moisture content will normally be in the range of 10-12% when used in air-conditioned buildings.
For other buildings, boards may require conditioning to higher or lower moisture contents with the range possibly covering 6-14%. This conditioning is important where close tolerances are required.
Measurement of moisture content may be achieved by weighing and drying or by using an electric moisture meter.
MR Particleboard is intended for use in areas where there is continued high humidity conditions or the occasional risk of wetting. Despite careful attention to performance after exposure to water, MR Particleboard should not be used in circumstances where continued wetting is likely. If the board is continually wet, degradation may occur through glue bond breakdown and through fungal attack.
Absorption and Swelling
MR Particleboard exhibits much slower response to wetting than does Standard Particleboard. While thickness swelling and residual swelling after drying out are also much lower, the slow response rate is a major practical advantage in minimising moisture effects. Residual thickness swell should be unnoticeable unless the board receives a prolonged soaking.
Dimensional Changes
When MR Particleboard is exposed to changing relative humidity conditions -
- Linear dimensions will change about 0.03 - 0.06% for each 1% change in moisture content.
- Thickness change will be about 0.03 - 0.5% for each 1% change in moisture content.
Handling and Storage
Although these boards are defined as moisture resistant, there is a likelihood of some swelling in thickness and change in dimensions if they are exposed to the elements for protracted periods. Care should therefore be taken to ensure that boards are not neglected in storage or on site. Planners should make the same considerations and take the same precautions with MR Particleboard as they would for Standard Particleboard.
Permeability to Moisture Vapour
Moisture vapour will slowly permeate Particleboard; a typical figure for 13 mm MR Particleboard is 4.6 x 10 2 g/m 2 mmHg.
Fire, Thermal, Sound Properties
Behaviour of MR Particleboard is similar to that of Standard Particleboard (see AWPA Data Sheet 2).
Biodeterioration
As with most other wood products, Particleboard is susceptible to attack from wood destroying fungi and termites. However moisture contents of over 18% must be maintained before either form of biodeterioration can occur. Since MR Particleboard is intended for use in applications where there is likely to be moisture, biodeterioration is a higher risk than for Standard Particleboard which must not be used in potentially damp applications.
However the cautionary note discussed under "Moisture Content" must be recalled here. MR Particleboard is intended for use in areas of high humidity or occasional water spillage. The material cannot be expected to perform satisfactorily if continually wet.
Board may be manufactured with fungus resistance. Post treatment with a brush-on preservative will provide surface protection. This will also retard the growth of moulds, which are not wood destroying, but can disfigure the surface appearance under damp conditions.
Finishing and Applications
MR Particleboard is manufactured to the same surface flake specifications as Standard Particleboard. It will thus accept all types of surface finish and decoration in the same way as Standard Particleboard.
| Main finishes are: |
Applications include: |
| ¨ Melamine |
¨ Bathroom Vanities |
| ¨ Wood Veneers |
¨ Kitchen Cupboards and Bench Tops |
| ¨ Vinyl |
¨ Concrete Formwork |
| ¨ Films and Foils |
¨ General use in Tropical Areas |
Health & Safety Information
Normal health and safety precautions should be taken when working with wood panel products. Machine tools should be fitted with dust extraction and work areas should be kept clean. If dust levels exceed The National Occupational Health & Safety Commission's standards, the wearing of a dust mask (AS/NZS 1715 and AS/NZS 1716) and safety glasses is recommended.
Storage and work areas should be adequately ventilated. If large quantities of Particleboard are stored in non-ventilated areas, formaldehyde emissions could accumulate to levels that may irritate some people.
For further information, please contact one of the manufacturers listed below for a Material Safety Data Sheet or download from www.woodpanels.org.au
Whilst the information contained herein is based on data which to the best of our knowledge is reliable and accurate as of the date hereof, no responsibility can be accepted by us for errors or omissions. Since the information contained herein may be applied under conditions beyond our control, no responsibility can be accepted by us for any loss or damage caused by any person acting or refraining from acting as a result of this information.
Published by the Australian Wood Panels Association Incorporated, PO Box 158, Coolangatta Qld 4225, May 2004. |
