Why is it necessary to analyze the dry mass of textiles?

Are the costs to buy textile raw fibers equivalent to the quantity of material purchased?

Several types of textile fiber have the characteristic of being hygroscopic, that is, to tend to absorb or to release some quantities of water content in relation to the humidity and temperature conditions of the environment we they are stored; wool fibers, for example, can retain up to 30% of moisture without being detectable by human touch, even if they are compared to similar fibers under standard humidity conditions.

The official regains (%) are associated with the fiber material type and are listed below:

FIBER MATERIAL REGAIN (%)
Combed wool 18.25
Carded wool 17
Cotton 8.50
Silk 11
Kapok 10.90
Linen 12
Hemp 12
Jute 17
Ramie 8,50
Acetate 9
Viscose 13
Acrylic 2
Polyamide nylon continuos yarn 5.75
Polyamide nylon discontinuous fiber 6.25
Polyester continuous yarn 1.50
Polyester discountinuous fiber 1.5
Mixed fibers

Moisture content (MC%) is a property of fiber material and it becomes significant in the commercial transactions due to the frequent disputes, and has determined the need to establish the correct percentage of water (expressed on the dry weight) that a textile product must contain.

absorption-desorption-curves

absorption-curves-for-various-materials

For this purpose, the “commercial or legal mass” has been defined as the net weight of the textile materials containing a acceptable quantity of water expressed in percentage (%) that has to be compared to the fiber official regain (%) and this one has to be considered in the evaluation of the commercial regain value established conventionally for each textile fiber material as indicated on Directive 96/74/CE.

The commercial weight is obtained through a conditioning process to determining the dry mass of the textile fibers and the subsequent application of the conventional regain value to determine the final correction to add or to subtract to the total gross weight of the fiber bales; this conditioning process is called “oven-drying method” and it is of direct type, therefore through the use of rapid drying ovens or alternatively are used analytical measuring devices for the indirect methods.

Public institutes and other certification bodies exclusively use the method of drying with ovens with the issue of a conditioning process certification of the analyzes done in compliance with national and international industry standards UNI, IWTO, BISFA, etc..


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