Estimation and calculation of cotton fabric shrinkage and wrinkle phenomenon

Introduction: Cellulose cotton fabrics consist of a group of fibers made up of chains dispersed between parallel regular regions called crystalline regions and other random and irregular regions called amorphous regions.

While cellulosic chains are generally parallel in crystal fields, we find them intersecting in random fields, and therefore the effect of tension in random regions is to try to organize them somehow so that they will return by removing the tension on them. they return to their basic positions and thus expand elastically, as in the crystalline regions. When the ropes are stretched, they are subjected to a little slip on each other, after which it is difficult for them to return to their original position and therefore their elasticity stretched, causing wrinkling. Therefore, the more crystalline the cotton, the greater its wrinkling ability.

In the dry state, textile fibers resist wrinkling more than in the wet state, and this is because the chains in the dry state are linked by hydrogen bridges and these bridges disappear when wet, so we find a trend. Wrinkle the tissue when the weather is humid or the body is more sweaty:

Cellulosic structure and hydrogen bonds between chains

Most flexible lycra fabrics, especially knitted circular fabrics, need thermal fixation to improve their appearance and stabilize their size for a certain weight and provide a smooth surface. We can tighten raw fabrics and then thermally fix the new width without the width. job requirements (usually when the width of the fabric comes out. More weave than necessary), so we start with the relax phase to follow the riveting process.

Thermal fixing requires strict control and thorough work to ensure the uniformity of thermal distribution over the entire surface of the fabric through hot air currents driven by the engineering designs of the thermal fixing chambers, and the installation is 185-190 m for a period of 45 seconds, and the operating conditions are the quality of the lycra fibers and determined by the respective fibers and required properties Equally, namely:

Required weight for a given length and width depending on the knitting.
The type of clothing from which the fabric will be separated.
Required properties for the finished fabric, such as whiteness and color, stability and tensile strength.
The type, origin, content, composition and number of fibers associated with lycra
Quality and precision of lubricants used in weaving and knitting machines.
Finishing stages, ram features, geometry and air movement in it.

Table (1) shows the effect of temperature and time on some lycra fabric properties.

Table 1The cloth may have a slight rate of shrinkage after processing; this requires a stretch ratio of 5-15% in addition to the width required to compensate for the percentage of shrinkage that can be applied to the fabric as a result of further processing. The actual width to be considered when dyeing and finishing and thermal fixation relate to the accumulated technical expertise and test results. The fabric must be thoroughly cooled when exiting the installation rooms to ensure the stability of the properties.

For some light lycra types such as “socks and ready-made parts”, we can facilitate the steam fixing conditions for 30-60 seconds to 110-120 m degrees, but for this method a vacuum air in pressurized machines does not give us a constant fabric width, which does not create dependence on it. .

HSE heat treatment efficiency: heat treatment is evaluated according to the efficiency, called HSE heat treatment efficiency, and the measurement process takes place after treatment at a certain temperature and time on the ram as follows:

We prove an example of a raw canvas and we are 160 cm wide, ie HSW = 160 cm and boiled for 10 minutes, drying at the comfort “relaxation stage” and after drying we measure its final width and make it 144 cm. When FW = 144 cm, the percentage return is calculated as follows:

Yield = Width after drying / Raw screen

Or: Raw width = Width after drying / yield, i.e .:


So efficiency = 144/160 = 0.9, so 90%

Therefore, if we want to get a 152 cm wide fabric after heat treatment and at the same cost-effective:


So the required raw width = 152 / 0.9 = 169 cm

We can find a difference between the theoretical and practical HSW values ​​due to some minor operating differences regarding the model of the machines, liquor ratio and humidity after spinning and before entering RAM, so it is recommended. To estimate the value of the correction factor, first do real practical experiments.

Bleaching “stripping”: operating conditions sometimes require discoloring or stripping of lycra-containing rubber fabric for one reason or another; this may be spotting, chromatic aberration, or lack of leveling. As we can see in Table (2), chlorine oxidants that negatively affect the durability of lycra:

Table 2: Color stripping application using hypochlorite: If the stripping process does not respond to sodium hydrosulfite, we can refer to a process using hypochlorite. It should be noted that sodium hypochlorite releases oxygen in an alkaline environment that oxidizes components and impurities. As a result, while the acidic environment releases toxic and oxidizing chlorine gas, it strongly damages the fibers and corrodes the machine. For this reason, it is strictly forbidden to apply the stripping bath with an acidic environment to cellulose fibers with an acidic environment. ventilation of the production hall.

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