Test Name : Moisture Content
Summary : Presence of excess moisture is paper based packaging has a multifold effect. The standard moisture in Paper or paper based packaging should be between 6-8%. Studies suggest that in case of Shipper Cartons, for every 1% increase in this moisture %, the compression strength of the cartons will fall by 6.5%. So when the moisture goes up to 12% (very common in monsoon season), the compression strength will take a dip of 26%. This needs to be accounted for while preparing specifications for packaging to be used in high humidity/moisture conditions.
Another major issue which specifically is of interest to the Food & Pharma industry is the formation of mildew (mold / fungus). Moisture and porosity in paper when combined with dark and cold climate of a warehouse, provide the perfect conditions for bacteria and fungus to develop and grow rapidly, which is a cause of serious concern.
Moisture should be kept under control to avoid rapid growth of such organisms.
Test Method :
There are 2 types of Tests :
- Samples are weighed and then kept in an Oven @ 105 ± 2ºC for 2 hours. The loss in weight is found out and moisture % calculated as :
Moisture % = (Loss in Weight / Original Weight) x 100
This test works on the principle called “Loss On Drying” (or LOD in short) and is the most scientific way to testing moisture content or average moisture.
- Samples are penetrated with an electronic device which measure the electrical resistance between 2 penetration points. Since electrical resistance is related to the moisture in the substrate, the correlation can be established.
These devices are known as the Instant Moisture Meters. They are the quickest way to detect moisture %, but it is to be noted that presence of any contaminant in the paper (usually in recycled paper) will have an effect on the electrical resistance. Also paper from different wood types will have slightly different properties and hence the moisture meter will not be a very accurate test method.
Further when testing corrugated boards, the moisture meter will tend to give you the peak moisture (because it measures the least electrical resistance) from amongst all the layers / plies of the board.
Eg. If we test a 5 ply corrugated board which as 12-10-10-10-10 moisture % in its layers, the Instant Moisture Meter will show a reading of 12%, whereas the Oven (LOD method) will give you a result of 10.4%
Oven method is the most authentic method but takes a lot of time. Test reports should be based on this method only.
Instant Moisture Meters are not the most correct method but offer quick results which may be good enough for in-process decisions and quick checks.