Is a clean sheet of paper really that clean? let's find out.
Ok, before anyone says you can make paper from stone, which you can, this study will be about the common type of wood cellulose based paper that you would purchase to put into your photocopier or printer. Yes, that is the type where they use a whole load of energy to chop down trees, mash them up, boil , leach, bleach, lay out and roll.
The specific type is a claimed high quality multi-purpose A4 sized paper from 'motif'.
Paper specifications
you can get the claimed specifications from this link, here is the core data which was established by the Robert Horne Group.
Technical Information
| Substance g/m2 | 80 | 90 | 100 | 120 | 160 |
|---|---|---|---|---|---|
| Caliper um (approx) | 105 | 115 | 135 | 160 | 208 |
| Opacity (ISO) % | 92 | 94 | 96 | 97 | 99 |
| Brightness (ISO) % | 100 | 100 | 100 | 100 | 100 |
| Whiteness CIE D65 | 168 | 168 | 168 | 168 | 168 |
| Smoothness (Bendtsen) TS | 220 | 220 | 220 | 220 | 220 |
| ml/min WS | 220 | 220 | 220 | 220 | 220 |
| Rigidity (Taber) 15ºC MD | 2.4 | 3.0 | 4.3 | 7.2 | 21 |
| Stiffness Units CD | 1.7 | 1.9 | 2.4 | 4.5 | 11 |
| Surface pH | 7.5 | 7.5 | 7.5 | 7.5 | 7.5 |
Environmental Information
| Paper constituent | Description |
|---|---|
| Fibre Source | Virgin wood fibre from sawmill residues, forest thinnings and sustainable forests in Portugal and Finland. |
| Mill Broke | Mill broke is recycled and can be as high as 23% of the Total Fibre Content |
| Filler | approx 19%. |
BLEACHING
Pulps used in the production of the above grade are Elemental Chlorine Free (ECF) giving a resultant AOX level of < 0.09 kg per 1000 kg of pulp.
DISPOSAL OF WASTE BY-PRODUCTS
95% of waste is reused 4% is used as fertilizer and 1% is incinerated.
PAPER MILL EFFLUENT
11.09 m3 /tonnes of water is used during production and is re-used.
ENERGY SOURCE
Gas
TOTAL GROSS PRIMARY ENERGY (Paper Mill)
2297 KwH/tonne
This material is recyclable
Analysis
So, the above is the story you are told, but what really is in it and where? To answer this question, we could not just put a piece of paper on the scanning electron microscope (SEM), because it is an insulator, and whilst some SEMs can look at non-conducting samples, ours couldn't, so, we had to first use a super cool looking plasma machine to coat the paper with 20 nano meters of Gold and Palladium.
With the paper coated in a very thin layer of gold and palladium, the electrons do not build up on the sample 'charging' it and the back scatter electron (BSE) and energy-dispersive X-ray spectroscopy (EDS) can then be used to look for elements in the material.
At 26 times magnification, you can start to see some texture in the coated paper that is sitting on the carbon tape that is sitting on the aluminium SEM sample holder.
Taking a much closer 1000 times magnification, we see that other than the inter-woven cellulose fibres, there is some very obvious grains of some other material there.
With 5000 times magnification, we can see just a few fibres and a close up of rice-particle shaped grains of some other material. Could this be the 'Filler' that constitutes 19% of the paper?
The elements determined by EDS and their distribution is shown below.
From the above data, we can see that C, O, Ca, Cl and Mg was detected in the sample area.
The distribution seems to show carbon and oxygen everywhere, and Calcium and Magnesium in the same location as the 'grains'. This would imply that the 'Filler' in this paper is predominantly CaCO3, better known as Calcium Carbonate which is commonly used for just this purpose.. Interestingly, when you burn wood, 25-45% of the ash is Calcium Carbonate!
The Chlorine is likely a residue from the use of Hydro-Chloric acid, since this is often used to remove or 'leach' the 'ash', or metal ions from the raw paper pulp. It may also be part of a bleaching agent such Magnesium Hypochlorite, though, judging by the distribution of magnesium, where it aligns with the Calcium Carbonate, the magnesium could be a contaminant in the CaCO3. Calcium hypochlorite (Ca(ClO)2) may also have been used for bleaching. Interestingly, Magnesium is found in wood ash, so it could be due to incomplete leaching.
The Cu (Copper) is highlighted in red as it falls below the certainty threshold for the EDS, however, Cu is a component of some wood ashes and if it really is in the sample, it would likely be due to incomplete acid leaching. Common elements contained in wood ash that appear to have been successfully leached are iron, manganese, zinc, potassium and phosphorous.
The cellulose fibres themselves are made from Carbon, Hydrogen and Oxygen with the formula (C6H10O5)n
Conclusion
Paper is a product normally made from wood pulp and will almost always contain some residue of leaching and bleaching agents. In addition, it is very common to add a filler, normally Calcium Carbonate into the mix to both whiten the paper and to make it heavier, glossier and more opaque. Our study of this 'motif premium' brand of A4 paper, follows this formula closely. Some other papers may use other bleaching agents containing Sodium and other fillers/whiteners such as titanium dioxide and talc.
Paper may vary greatly, however, what we can say is that the paper we tested has just C, O, H, Ca, Cl, Mg and maybe a touch of Cu - which makes it a likely a lot 'cleaner' elementally than the wood it started life as.