CA2994131A1

CA2994131A1 - High performance wood

Info

Publication number: CA2994131A1
Application number: CA2994131A
Authority: CA
Inventors: Larry A. Smith; Pascal Beaudoin
Original assignee: Topten Railway Ties Inc
Current assignee: Topten Railway Ties Inc
Priority date: 2018-02-16
Filing date: 2018-02-16
Publication date: 2019-08-16

Abstract

A process to improve the performance of wood for use in such products as railway ties, posts and fence staves and the like, by first thermal-vacuum drying in a special kiln that preserves the wood's natural porosity. The dried wood is then loaded into an autoclave where it is submerged in- and impregnated with- a solution of resin dissolved in super critical carbon dioxide (hereinafter SCCD). The resulting solution has extremely low viscosity and is therefore able to penetrate deeply into the wood.
Multiple timed pressure changes in the autoclave maximizes saturation by the solution.
The surplus solution is then drained and the resin allowed to cure thereby bonding the woods xylem/fibre structures together for strength and to seal against weathering and against microbial and insect infestation that leads to rot.

Description

FIELD OF THE INVENTION
The present invention is in the field of protecting and preserving the wood of products such as railway ties, posts, fence staves and the like, that must resist long term strain stress, and exposure to weathering, and below ground attack by insects, fungi, bacteria that lead to rot and eventual destruction.
BACKGROUND OF THE INVENTION
The long-term resistance of wood to rot, splitting, splintering and pulverizing is a long sought after goal especially in long-term contact with the ground. In the case of railway ties such rot and splitting can lead to deadly derailment and so constant inspection and replacement of ties is required, at considerable expense. To date creosote, copper compounds and other poisonous chemicals are used to preserve such outdoor structures.
Is widely known that they leach into the environment causing public health issues such as contamination of ground water. Because of leaching, protection also drops off.
Such chemicals do not add strength to the wood nor do they enhance its electrical properties.
A better way to improve wood is clearly needed and the instant invention offers a method of achieving same.

DETAILED DESCRIPTION OF THE INVENTION

Strength and weather resistance of wood is achieved by impregnating/saturating it with a solution of polymerizable/curable resin dissolved in SCCD. SCCD occurs when carbon dioxide is at a temperature of 32.1 C and at a pressure of 73.8 bar (1,070 psi).
At those critical conditions carbon dioxide becomes a liquid-gas with unique properties including very high solvency and very low viscosity, both of which are advantageous to the instant invention. Other chemicals including, but not limited to, fungicides, insecticides, and fire retardants, alone or in combination, may be added to the impregnation solution.
The present process begins in a proprietary wood drying kiln as taught in US
patent 8,291,611, which dries the wood in a highly controlled manner that lessens damage to the wood's fibre/xylem structures and maintains the wood porosity. The dried wood is then loaded into an autoclave wherein it is submerged in the resin solution.
Next the wood is subjected to timed cycles of pressure changes. Lastly the remaining solution is drained, and the resin cured.
The processing steps can be listed follows:
1. Determine the density and/or species of the wood, and moisture content.
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2. Load wood into vacuum-heat kiln for controlled drying.

3. Transfer wood to autoclave.

4. Pump resin solution into autoclave to submerge the wood.

5. Pressure and decompress to predetermined values and intervals

6. Drain autoclave.

7. Allow resin to cure.

8. Unload high performance wood.

Item 1. Determining the density will establish a rate of decompression that will prevent burst damage to less dense woods.
Item 5 may follow pressurizing cycles such as:
Cycle 1 Pressure increased at the rate of 100 pounds per square inch (psi) per minute to 250 psi, held for 2 minutes then reduced to atmospheric pressure at 50 psi per minute.
Cycle 2 Pressure increased at the rate of 50 psi per minute to 250 psi, held for 3 minutes then reduced to atmospheric pressure at 20 psi per minute.
Cycle 3 Pressure increased at the rate of 80 psi per minute to 250 psi, held for 4 minutes then reduced to atmospheric pressure at 20 psi per minute 4 of 6 Testing has shown that seven such cycles achieves the requisite saturation.
the repeated cycling of pressure in the autoclave is believed to cause the minute tubular xylem tubes/fibres of the wood to expand and contract (change volumetrically) whereby they effectively pump the solution through the wood to maximize penetration/saturation than is not possible in traditional single-pressure impregnation processes.
Upon curing, the resin has bonded and sealed all the wood fibre together to make a high performance wood with increased strength and resistance to splintering, and sealed against weathering, rot, infestation, and resistant to electric phenomena both dielectric and conductive.
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