What is moisture content and moisture regain?

Moisture Regain: Moisture regain is defined as the amount of water (or moisture) expressed as the percentage of oven-dry weight.

Moisture regain, MR = (W / D) × 100%,  where W = weight of moisture; D = Oven dry weight of the sample

Moisture Content: Moisture content is defined as the amount of water expressed as the percentage of the original weight of the sample. 

Moisture content, MC = [W / (W+D)] × 100% 
                                     = MR / [1 + (MR/100)], where W = weight of moisture; D = oven dry weight of sample, W + D = original weight of sample.

Oven-dry weight: It is the weight of the sample after removing all water or moisture by heating in an oven at 105℃ to constant weight. The weight of the water is the difference in the weight of the sample before and after drying. 
Moisture Content & Moisture Regain of fibres

Factors affecting the regain of textile material: 
1. Time: When a textile material is placed in a given atmosphere it takes a certain amount of time to reach equilibrium. This rate of conditioning depends on factors such as the size and form of material and the nature of the material, external conditions, etc. 

2. Relative humidity: The regain of textile material depends on the relative humidity of the atmosphere. Regain is higher at higher relative humidity (RH).

3. Temperature: It has a negligible effect on regain. For example, a change of 10°C may bring a change of 0.3 per cent in the regain of cotton. 

4. The previous history of the sample: Regain is affected by the nature of the material and the atmospheric condition in which the material has been stored or processed. For example, bleached or scoured cotton will absorb more moisture than untreated material because the removal of impurities helps in more absorption of moisture.

Textile Fibre
Moisture Regain (MR%)
Moisture Content (MC%)
Cotton
8.5
7.34
Jute
13.75
12.1
Silk 
11.0
9.91
Wool  
16.0
13.8
Flax
12.4
10.4
Hemp
12.4
10.4

Reference: A Practical Guide to Textile Testing by K. Amutha (Woodhead Publishing)

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