[Fatima (OP)]

Hi,

Could you please share with me all you know about wood material pH.

What are the factors that can affect wood material pH, and how to measure it? I have thin veneers 1 mm and want to find surface pH measurement.

[Bored chemist]

pH isn't defined for a surface.

What are you trying to achieve?

[Fatima (OP)]

then what does it mean when literature says pH value of oak wood is 5?
i want to see if pH is different for different wood types (is pH of birch wood different from pH of alder), and if pH of rough surface of veneer is greater than pH of smooth surface, or what else do you think could contribute to significant difference in pH of hardwood species?

[Bored chemist]

If you shake up oak sawdust with water, filter it, and measure the pH of the solution it will be near 5.

I doubt there is a big difference between different trees.

You will need a good pH meter because the solution will be poorly buffered.


This isn't an easy experiment to do properly and I don't see the point.

[Fatima (OP)]

I am doing it with SevenCompact™ S210 pH meter.
It measures the pH of the surface.
I put a droplet of water on surface of veneer and place the electrod over to take the reading. It takes a few minutes to stabilize and give me pH readings. However the time pH metre takes to stabilize varies a lot.
I also want to work on my experimental technique, how to improve it to give more accurate results.
And when the electrod comes in contact with surface of my sample, what exactly is it giving me pH of? is it giving me pH of only the surface, or a certain area under and over the surface? Is it giving pH of the whole sample or only pH of the point it is directly in contact with (please find attached photo of the equipment)

pH measurement of wood is important, because different woods can cause rust when come in contact with metal especially if wood species are very acidic. Similarly the curing process of adhesives in preparation of wood composites is affected by wood material pH. I just want to figure out what kind of variables will affect pH of my wood veneer

[Bored chemist]

It's hard to know what you are really measuring.
For a start the carbon dioxide in that air will produce a solution with a pH of about 5.
If the wood is "trying" to produce a different pH you will get a meaningless answer, depending on how much each influences the meter.
And also, the addition of the pH electrode itself will change the pH.

A major part of the discolouration and corrosion of iron is due to tannins in the wood rater than "acidity" as such. You can probably look up which ones are high in tannin. (Oak certainly is; most softwoods aren't).

There are lots of issues about how well glues stick to wood, including which direction the knife was travelling when the veneer was cut.

It would generally be easier to check by direct measurement of the strength of a glued joint.

[Fatima (OP)]

why do you think carbondioxide in air will affect the reading
and how does introduction of electrod change the pH

i agree there are other factors at play too like you mentioned strength of glued joint, but some other people in my group are measuring it. my area of research is wood material pH. I want to understand concept of pH better, and why certain method of measurement could be appropriate for my experimental design and how to try to improve my experimental design

many thanks for engaging

[CliffordK]

Some trees like acidic soils, some like basic soils.  And, I've hard that different leaves will break down either acidic or basic.

I hadn't heard of this applying to wood, but it isn't surprising.

As @Bored chemist mentions, measurements would have to be carefully controlled.  So, for example, repeat your experiment with just water and no wood.  Distilled, deionized water?

I'd probably run my experiment with fine sawdust from a file or such. Let it seep, then filter out with a metallic or ceramic filter and test the water.

You are probably reading relatively soluble salts or organic compounds in the wood including carboxylic acids.

Keep in mind that some metals like iron based alloys are quite happy in a basic solution.

[Bored chemist]

why do you think carbondioxide in air will affect the reading

Because it dissolves in water to form carbonic acid.

and how does introduction of electrod change the pH

because (unless you have special electrodes, designed not to do this) materials are leached from the electrode into the water.

[Petrochemicals]

Get some saw dust and stick it in some distilled water give it a swirl, leave it for a couple of minutes and then measure it.

https://www.thespruce.com/do-it-yourself-soil-ph-test-4125833

[Bored chemist]

Get some saw dust and stick it in some distilled water give it a swirl, leave it for a couple of minutes and then measure it.

https://www.thespruce.com/do-it-yourself-soil-ph-test-4125833

Other random number generators are available.

[Colin2B]

I am doing it with SevenCompact™ S210 pH meter.
It measures the pH of the surface.
I put a droplet of water on surface of veneer and place the electrod over to take the reading. It takes a few minutes to stabilize and give me pH readings. However the time pH metre takes to stabilize varies a lot.

The direct contact meter is most accurate with fibre saturation and your veneer samples will be very dry so they will vary on the amount of water they absorb (even with samples of the same wood), this is probably why you are getting varying stabilisation times.

With the sawdust method @Bored chemist mentions, the ratio of wood to water will affect the pH. These figures are for Beech
Wood/Water          pH
Ratio
1:1                      4.73
1:2                      4.91
1:3                      5.07
1:4                      5.30

Might be worth talking to a fibre board manufacturer, pH affects the cure of the resins they use so they know a bit about measuring it.

 

[Bored chemist]

Probably worth talking to the pH meter manufacturers as well.